Tag Archives: Geophysics

Low coherency of wind induced seismic noise: Implications for gravitational wave detection [CL]

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http://arxiv.org/abs/2205.04079


Seismic noise poses challenges for gravitational wave detection. Effective vibration isolation and methods to subtract unsheildable Newtonian Noise are examples. Seismic arrays offer one way to deal with these issues assuming seismic coherency. In this paper we find that wind induced seismic noise is incoherent and will dramatically reduce the projected low frequency sensitivity of future gravitational wave detectors. To quantify this, we measure the coherence length of wind induced seismic noise from 0.06–20~Hz in three distinct locations: close to a building, among tall trees and in shrubs. We show that wind induced seismic noise is ubiquitous and reduces the coherence lengths form several hundred meters to 2–40~m for 0.06–0.1~Hz, from $>$60~m to 3–16~m for 1.5–2.5~Hz and from $>$35~m to 1–16~m around 16.6 Hz frequency bands in the study area. This leads to significant loss of velocity and angular resolution of the array for primary microseism, 5 times worse Newtonian Noise cancellation by wiener filtering at 2~Hz, while it does not pose additional challenge for Newtonian Noise cancellation between 10–20~Hz.

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H. Satari, C. Blair, L. Ju, et. al.
Tue, 10 May 22
20/70

Comments: 15 pages, 8 figures

On Sea-Level Change in Coastal Areas [CL]

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http://arxiv.org/abs/2205.03895


Variations in sea-level, based on tide gauge data (GSLTG) and on combining tide gauges and satellite data (GSLl) are subjected to singular spectrum analysis (SSA), to determine their trends and periodic or quasi-periodic components. GLSTG increases by 90 mm from 1860 to 2020, a contribution of 0.56 mm/yr to the mean rise rate. Annual to multi-decadal periods of ~90/80, 60, 30, 20, 10/11, and 4/5 years are found in both GSLTG and GSLl. These periods are commensurable periods of the Jovian planets, combinations of the periods of Neptune (165 yr), Uranus (84 yr), Saturn (29 yr) and Jupiter (12 yr). These same periods are encountered in sea-level changes, motion of the rotation pole RP and evolution of global pressure GP, suggesting physical links. The first SSA components comprise most of the signal variance: 95% for GSLTG, 89% for GSLI, 98% for GP, 75% for RP. Laplace derived the Liouville-Euler equations that govern the rotation and translation of the rotation axis of any celestial body. He emphasized that one must consider the orbital kinetic moments of all planets in addition to gravitational attractions and concluded that the Earth’s rotation axis should undergo motions that carry the combinations of periods of the Sun, Moon and planets. Almost all the periods found in the SSA components of sea-level (GSLl and GSLTG), global pressure (GP) and polar motion (RP), of their modulations and their derivatives can be associated with the Jovian planets. It would be of interest to search for data series with longer time spans, that could allow one to test whether the trends themselves could be segments of components with still longer periodicities (e.g. 175 yr Jose cycle).

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V. Courtillot, J. Mouël and F. Lopes
Tue, 10 May 22
48/70

Comments: N/A

TEM analyses of in situ presolar grains from unequilibrated ordinary chondrite LL3.0 Semarkona [EPA]

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http://arxiv.org/abs/2205.04372


We investigated six presolar grains from very primitive regions of the matrix in the unequilibrated ordinary chondrite Semarkona with TEM. These grains include one SiC, one oxide (Mg-Al spinel), and four silicates. Structural and elemental compositional studies of presolar grains located within their meteorite hosts have the potential to provide information on conditions and processes throughout the grains’ histories. Our analyses show that the SiC and spinel grains are stoichiometric and well crystallized. In contrast, the majority of the silicate grains are non-stoichiometric and poorly crystallized. These findings are consistent with previous TEM studies of presolar grains from interplanetary dust particles and chondritic meteorites. We interpret the poorly crystalline nature, non-stoichiometry, more Fe- rather than Mg-rich compositions, and/or compositional heterogeneities as features of the formation by condensation under non-equilibrium conditions. Evidence for parent body alteration includes rims with mobile elements (S or Fe) on the SiC grain and one silicate grain. Other features characteristic of secondary processing in the interstellar medium, the solar nebula, and/or on parent bodies, were not observed or are better explained by processes operating in circumstellar envelopes. In general, there was very little overprinting of primary features of the presolar grains by secondary processes (e.g., ion irradiation, grain-grain collisions, thermal metamorphism, aqueous alteration). This finding underlines the need for additional TEM studies of presolar grains located in the primitive matrix regions of Semarkona, to address gaps in our knowledge of presolar grain populations accreted to ordinary chondrites.

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S. Singerling, L. Nittler, J. Barosch, et. al.
Tue, 10 May 22
54/70

Comments: 50 pages including supplementary materials

Deep two-phase, hemispherical magma oceans on lava planets [EPA]

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http://arxiv.org/abs/2205.02864


Astronomers have discovered a handful of exoplanets with rocky bulk compositions but orbiting so close to their host star that the surface of the planet must be at least partially molten. It is expected that the dayside of such “lava planets” harbors a rock vapor atmosphere that flows quickly towards the airless nightside — this partial atmosphere is critical to the interpretation of lava planet observations, but transports negligible heat towards the nightside. As a result, the surface temperature of the magma ocean may range from 3000~K near the sub-stellar point down to 1500~K near the day-night terminator. We use simple models incorporating the thermodynamics and geochemistry of partial melt to predict the physical and chemical properties of the magma ocean as a function of the distance from the sub-stellar point. Our two principal findings are that 1) the dayside magma ocean is much deeper than previously thought, probably extending down to the core-mantle boundary in some locations, and 2) much of the dayside is only partially molten, leading to gradients in the surface chemistry of the magma ocean. These findings have important implications for the dynamics of the magma ocean as well as the composition and dynamics of the atmosphere.

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C. Boukaré, N. Cowan and J. Badro
Mon, 9 May 22
47/63

Comments: 16 pages, 5 figures. Resubmitted to ApJ after revision

Free Core Nutation and its relation to the Spin-Over Mode [EPA]

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http://arxiv.org/abs/2205.02799


The time-varying response of the Earth’s and other planets’ rotation to external gravitational torques depends strongly on their internal structure. In particular, the existence of the mode known as the Free Core Nutation in the fluid core, is known to amplify the forced nutations in the near-diurnal retrograde frequency band (as measured in the planetary frame of reference). Due to their proximity in shape and frequency, this mode is sometimes equated with the so-called Spin-Over Mode which denotes the free oscillation of a steadily rotating ellipsoidal fluid core. Through a careful study of the freely rotating two-layer planetary model with a rigid mantle and an inviscid fluid core, we show that the Spin-Over Mode frequency corresponds to that where the sum of the external and internal torques on the mantle are balanced, causing it to rotate steadily. The presence of dissipation at the Core-Mantle Boundary causes the Free Core Nutation to become damped and slightly offset its resonance frequency. We show that this offset, which is $\approx-1$ day for the Earth, can be interpreted as the result of the proximity of the Free Core Nutation frequency to that of the Spin-Over Mode, which now corresponds to a minimum in the magnitude of the transfer function for nutations. We also show how this proximity leads to a slightly lower Quality factor for the resonance than that compute from the usual formula. We conclude by discussing possible implications of this mechanism for Mars, the Moon, and the long-term evolution of the Earth.

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J. Rekier
Fri, 6 May 22
20/55

Comments: 26 pages, 6 figures, accepted for publication in AAS PSJ

Fingering convection in the stably-stratified layers of planetary cores [EPA]

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http://arxiv.org/abs/2205.01761


Stably-stratified layers may be present at the top of the electrically-conducting fluid layers of many planets either because the temperature gradient is locally subadiabatic or because a stable composition gradient is maintained by the segregation of chemical elements. Here we study the double-diffusive processes taking place in such a stable layer, considering the case of Mercury’s core where the temperature gradient is stable but the composition gradient is unstable over a 800km-thick layer. The large difference in the molecular diffusivities leads to the development of buoyancy-driven instabilities that drive radial flows known as fingering convection. We model fingering convection using hydrodynamical simulations in a rotating spherical shell and varying the rotation rate and the stratification strength. For small Rayleigh numbers (i.e. weak background temperature and composition gradients), fingering convection takes the form of columnar flows aligned with the rotation axis and with an azimuthal size comparable with the layer thickness. For larger Rayleigh numbers, the flows retain a columnar structure but the azimuthal size is drastically reduced leading to thin sheet-like structures that are elongated in the meridional direction. The azimuthal length decreases when the thermal stratification increases, following closely the scaling law expected from the linear non-rotating planar theory (Stern, 1960). We find that the radial flows always remain laminar with local Reynolds number of order 1-10. Equatorially-symmetric zonal flows form due to latitudinal variations of the axisymmetric composition. The zonal velocity exceeds the non-axisymmetric velocities at the largest Rayleigh numbers. We discuss plausible implications for planetary magnetic fields.

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C. Guervilly
Thu, 5 May 22
44/51

Comments: submitted for publication to JGR: Planets

Geologic context of the bright MARSIS reflectors in Ultimi Scopuli, South Polar Layered Deposits, Mars [EPA]

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http://arxiv.org/abs/2205.00091


Radar-bright basal reflectors have been detected below the South Polar Layered Deposits (SPLD), Mars using Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) data and have an exciting but controversial interpretation: liquid water from subglacial lakes. We mapped the surface of the SPLD immediately above and surrounding the putative lakes (1:2M map scale) in order to provide geologic context for interpretation of the bright basal reflectors. We use THEMIS daytime IR (100 m/pixel), CTX (6 m/pixel), and HiRISE (25 cm/pixel) data to characterize geologic units and typical surface roughness. We find evidence for multiple geologic units with features due to CO2 and aeolian-related processes. We do not find evidence for surface modification linked to the postulated lake locations. This is not consistent with the interpretation of the MARSIS basal radar reflector as subglacial lakes.

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M. Landis and J. Whitten
Tue, 3 May 22
50/82

Comments: 29 pages, 2 figures (main paper), 4 (supplement), accepted 4/29/2022 at Geophysical Research Letters

Hydrogen emission from meteors and meteorites: mapping traces of H$_{2}$O molecules and organic compounds in small Solar system bodies [EPA]

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http://arxiv.org/abs/2205.00813


The hydrogen emission from meteors is assumed to originate mainly from the meteoroid composition, making it a potential tracer of H$_{2}$O molecules and organic compounds. H$\alpha$ line was previously detected in individual fireballs, but its variation in a larger meteor dataset and dependency on the dynamical origin and physical properties have not yet been studied. Here we investigate the relative intensity of H$\alpha$ within 304 meteor spectra observed by the AMOS network. We demonstrate that H$\alpha$ emission is favored in faster meteors ($v_i >>$ 30 km s$^{-1}$) which form the high-temperature spectral component. H$\alpha$ was found to be a characteristic spectral feature of cometary meteoroids with $\sim$ 92\% of all meteoroids with detected H$\alpha$ originating from Halley-type and long-period orbits. Our results suggest that hydrogen is being depleted from meteoroids with lower perihelion distances (q $<$ 0.4 au). No asteroidal meteoroids with detected H emission were found. However, using spectral data from simulated ablation of different meteorite types, we show that H emission from asteroidal materials can occur, and apparently correlates with their water and organic matter content. Strongest H emission was detected from carbonaceous chondrites (CM and CV) and achondrites (ureilite and aubrite), while it was lacking in most ordinary chondrites. The detection of H$\alpha$ in asteroidal meteoroids could be used to identify meteoroids of carbonaceous or achondritic composition. Overall, our results suggest that H$\alpha$ emission correlates with the emission of other volatiles (Na and CN) and presents a suitable tracer of water and organic matter in meteoroids.

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P. Matlovič, A. Pisarčíková, J. Tóth, et. al.
Tue, 3 May 22
82/82

Comments: N/A

The origin of Earth's mantle nitrogen: primordial or early biogeochemical cycling? [CL]

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http://arxiv.org/abs/2204.14002


Earth’s mantle nitrogen (N) content is comparable to that found in its N-rich atmosphere. Mantle N has been proposed to be primordial or sourced by later subduction, yet its origin has not been elucidated. Here we model N partitioning during the magma ocean stage following planet formation and the subsequent cycling between the surface and mantle over Earth history using argon (Ar) and N isotopes as tracers. The partitioning model, constrained by Ar, shows that only about 10% of the total N content can be trapped in the solidified mantle due to N’s low solubility in magma and low partitioning coefficients in minerals in oxidized conditions supported from geophysical and geochemical studies. A possible solution for the primordial origin is that Earth had about 10 times more N at the time of magma ocean solidification. We show that the excess N could be removed by impact erosion during late accretion. The cycling model, constrained by N isotopes, shows that mantle N can originate from efficient N subduction, if the sedimentary N burial rate on early Earth is comparable to that of modern Earth. Such a high N burial rate requires biotic processing. Finally, our model provides a methodology to distinguish the two possible origins with future analysis of the surface and mantle N isotope record.

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H. Kurokawa, M. Laneuville, Y. Li, et. al.
Mon, 2 May 22
13/52

Comments: 43 pages, 14 figures, accepted for publication in Geochemistry, Geophysics, Geosystems

Isotope velocimetry: Experimental and theoretical demonstration of the potential importance of gas flow for isotope fractionation during evaporation of protoplanetary material [EPA]

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http://arxiv.org/abs/2204.13020


We use new experiments and a theoretical analysis of the results to show that the isotopic fractionation associated with laser-heating aerodynamic levitation experiments is consistent with the velocity of flowing gas as the primary control on the fractionation. The new Fe and Mg isotope data are well explained where the gas is treated as a low-viscosity fluid that flows around the molten spheres with high Reynolds numbers and minimal drag. A relationship between the ratio of headwind velocity to thermal velocity and saturation is obtained on the basis of this analysis. The recognition that it is the ratio of flow velocity to thermal velocity that controls fractionation allows for extrapolation to other environments in which molten rock encounters gas with appreciable headwinds. In this way, in some circumstances, the degree of isotope fractionation attending evaporation is as much a velocimeter as it is a barometer.

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E. Young, C. Macris, H. Tang, et. al.
Thu, 28 Apr 22
12/70

Comments: Accepted for publication in Earth and Planetary Science Letters

Alfvén waves: To the 80th anniversary of discovery [CL]

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http://arxiv.org/abs/2204.12700


The paper is dedicated to the anniversary of the discovery of Alfv\’en waves. The concept of Alfv\’en waves has played an outstanding role in the formation and development of cosmical electrodynamics. A distinctive feature of Alfv\’en waves is that at each point in space the group velocity vector and the external magnetic field vector are collinear to each other. As a result, Alfv\’en waves can carry momentum, energy, and information over long distances. We briefly describe two Alfv\’en resonators, one of which is formed in the ionosphere, and the second presumably exists in the Earth’s radiation belt. The existence of an ionospheric resonator is justified theoretically and confirmed by numerous observations. The second resonator is located between reflection points located high above the Earth symmetrically with respect to the plane of the geomagnetic equator. Keywords: Alfv\’en velocity, dispersion law, group velocity, geometric optics, heavy ions.

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A. Guglielmi, B. Klain and A. Potapov
Thu, 28 Apr 22
70/70

Comments: 5 pages, 1 figure

Large-scale Volcanism and the Heat Death of Terrestrial Worlds [EPA]

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http://arxiv.org/abs/2204.12475


Large-scale volcanism has played a critical role in the long-term habitability of Earth. Contrary to widely held belief, volcanism, rather than impactors, has had the greatest influence on and bears most of the responsibility for large-scale mass extinction events throughout Earth’s history. We examine the timing of large igneous provinces (LIPs) throughout Earth’s history to estimate the likelihood of nearly simultaneous events that could drive a planet into an extreme moist or runaway greenhouse, leading to the end of volatile cycling and causing the heat death of formerly temperate terrestrial worlds. In one approach, we make a conservative estimate of the rate at which sets of near-simultaneous LIPs (pairs, triplets, and quartets) occur in a random history statistically the same as Earth’s. We find that LIPs closer in time than 0.1-1 million yr are likely; significantly, this is less than the time over which terrestrial LIP environmental effects are known to persist. In another approach, we assess the cumulative effects with simulated time series consisting of randomly occurring LIP events with realistic time profiles. Both approaches support the conjecture that environmental impacts of LIPs, while narrowly avoiding grave effects on the climate history of Earth, could have been responsible for the heat death of our sister world Venus.

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M. Way, R. Ernst and J. Scargle
Wed, 27 Apr 22
28/68

Comments: 11 pages, 7 figures, published in The Planetary Science Journal

Observation of large scale precursor correlations between cosmic rays and earthquakes [CL]

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http://arxiv.org/abs/2204.12310


The search for correlations between secondary cosmic ray detection rates and seismic effects has long been a subject of investigation motivated by the hope of identifying a new precursor type that could feed a global early warning system against earthquakes. Here we show for the first time that the average variation of the cosmic ray detection rates correlates with the global seismic activity to be observed with a time lag of approximately two weeks, and that the significance of the effect varies with a periodicity resembling the undecenal solar cycle, with a shift in phase of around three years, exceeding 6 sigma at local maxima. The precursor characteristics of the observed correlations point to a pioneer perspective of an early warning system against earthquakes.

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P. Homola, V. Marchenko, A. Napolitano, et. al.
Wed, 27 Apr 22
41/68

Comments: 16 pages, 4 figures in the main article and 11 pages and 4 figures in the Suplementary Material

Experimental Simulations of Shock Textures in BCC Iron: Implications for Iron Meteorites [EPA]

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http://arxiv.org/abs/2204.09195


Neumann band in iron meteorites, which is deformation twins in kamacite (Fe-Ni alloy), has been known to be a characteristic texture indicating ancient collisions on parent bodies of meteorites. We conducted a series of shock recovery experiments on bcc iron with the projectile velocity at 1.5 km/sec at various initial temperatures, room temperature, 670 K, and 1100 K, and conducted an annealing experiment on the shocked iron. We also conducted numerical simulations with the iSALE-2D code to investigate peak pressure and temperature distributions in the nontransparent targets. The effects of pressure and temperature on the formation and disappearance of the twins (Neumann band) were explored based on laboratory and numerical experiments. The twin was formed in the run products of the experiments conducted at room temperature and 670 K, whereas it was not observed in the run product formed by the impact at 1100 K. The present experiments combined with the numerical simulations revealed that the twin was formed by impacts with various shock pressures from 1.5-2 GPa to around 13 GPa. The twin in iron almost disappeared by annealing at 1070 K. The iron meteorites with Neumann bands were shocked at this pressure range and temperatures at least up to 670 K, and were not heated to the temperatures above 1070 K after the Neumann band formation.

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E. Ohtani, T. Sakurabayashi and K. Kurosawa
Thu, 21 Apr 22
8/73

Comments: Accepted for publication in Progress in Earth and Planetary Science

The long-term evolution of the atmosphere of Venus: processes and feedback mechanisms [EPA]

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http://arxiv.org/abs/2204.08540


In this chapter, we focus on the long-term evolution of the atmosphere of Venus, and how it has been affected by interior/exterior cycles. The formation and evolution of Venus’s atmosphere, leading to the present-day surface conditions, remain hotly debated and involve questions that tie into many disciplines. Here, we explore the mechanisms that shaped the evolution of the atmosphere, starting with the volatile sources and sinks. Going from the deep interior to the top of the atmosphere, we describe fundamental processes such as volcanic outgassing, surface-atmosphere interactions, and atmosphere escape. Furthermore, we address more complex aspects of the history of Venus, including the role of meteoritic impacts, how magnetic field generation is tied into long-term evolution, and the implications of feedback cycles for atmospheric evolution. Finally, we highlight three plausible end-member evolutionary pathways that Venus might have followed, from the accretion to its present-day state, based on current modeling and observations. In a first scenario, the planet was desiccated early-on, during the magma ocean phase, by atmospheric escape. In a second scenario, Venus could have harbored surface liquid water for long periods of time, until its temperate climate was destabilized and it entered a runaway greenhouse phase. In a third scenario, Venus’s inefficient outgassing could have kept water inside the planet, where hydrogen was trapped in the core and the mantle was oxidized. We discuss existing evidence and future observations/missions needed to refine our understanding of the planet’s history and of the complex feedback cycles between the interior, surface, and atmosphere that operate in the past, present or future of Venus.

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C. Gillmann, M. Way, G. Avice, et. al.
Wed, 20 Apr 22
25/62

Comments: N/A

Aeolian sediment transport on Io from lava-frost interactions [EPA]

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http://arxiv.org/abs/2204.08595


Surface modification on Jupiter’s volcanically active moon, Io, has to date been attributed almost exclusively to lava emplacement and volcanic plume deposits. Here we demonstrate that wind-blown transport of sediment may also be altering the Ionian surface. Specifically, shallow subsurface interactions between lava and Io’s widespread sulfur dioxide (SO$_2$) frost can produce localized sublimation vapor flows with sufficient gas densities to enable particle saltation. We calculate anticipated outgassing velocities from lava-SO$_2$ frost interactions, and compare these to the saltation thresholds predicted when accounting for the tenuous nature of the sublimated vapor. We find that saltation may occur if frost temperatures surpass 155 K. Finally we make the first measurements of the dimensions of linear features in images from the Galileo probe, previously termed “ridges”, which demonstrate certain similarities to dunes on other planetary bodies. Io joins a growing list of bodies with tenuous and transient atmospheres where aeolian sediment transport may be an important control on the landscape.

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G. McDonald, J. Harper, L. Ojha, et. al.
Wed, 20 Apr 22
32/62

Comments: 17 pages, 6 figures. Published in Nature Communications

$δ^{44/40}$Ca-$δ^{88/86}$Sr multi-proxy constrains primary origin of Marinoan cap carbonates [CL]

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http://arxiv.org/abs/2204.02563


The Neoproterozoic Earth experienced at least two global-scale glaciations termed Snowball Earth events. ‘Cap carbonates’ were widely deposited after the events, but controversy surrounds their origin. Here, we apply the novel $\delta^{44/40}$Ca-$\delta^{88/86}$Sr multi-proxy to two Marinoan (ca. 635 Ma) cap carbonate sequences from Namibia and show that the rocks archive primary environmental signals deriving from a combination of seawater-glacial meltwater mixing and kinetic isotope effects. In an outer platform section, dolostone $\delta^{44/40}$Ca and $\delta^{88/86}$Sr values define a line predicted for kinetic mass-dependent isotope fractionation. This dolostone mostly precipitated from meltwater. Moreover, stratigraphically higher samples exhibiting the fastest precipitation rates correlate with elevated 87Sr/86Sr ratios, consistent with long-held expectations that a rapid deglacial weathering pulse forced cap carbonate formation. An inner-platform dolostone shows greater effects from water-mass mixing but still reveals that precipitation rates increased up-section. Overlying limestones show the greatest Ca and Sr contributions from seawater. Amplification of local coastal processes during global ice sheet collapse offers a simple but sufficient proposition to explain the Ca isotope heterogeneity of cap carbonates. Detection of kinetic isotope effects in the rock record provides a basis for developing the $\delta^{44/40}$Ca-$\delta^{88/86}$Sr multi-proxy as an indicator of saturation state and $p$CO$_2$.

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J. Wang, A. Jacobson, B. Sageman, et. al.
Thu, 7 Apr 22
26/45

Comments: N/A

Deviation of Mercury's spin axis from an exact Cassini state induced by dissipation [EPA]

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http://arxiv.org/abs/2204.01526


We compute predictions of the deviation of Mercury’s spin axis from an exact Cassini state caused by tidal dissipation, and viscous and electromagnetic (EM) friction at the core-mantle boundary (CMB) and inner core boundary (ICB). Viscous friction at the CMB generates a phase lead, viscous and EM friction at the ICB produce a phase lag; the magnitude of the deviation depends on the inner core size, kinematic viscosity and magnetic field strength, but cannot exceed an upper bound. For a small inner core, viscous friction at the CMB results in a maximum phase lead of 0.027 arcsec. For a large inner core (radius $>1000$ km), EM friction at the ICB generates the largest phase lag, but it does not exceed 0.1 arcsec. Elastic deformations induced by the misaligned fluid and solid cores play a first order role in the phase lead/lag caused by viscous and EM coupling, and contribute to a perturbation in mantle obliquity on par with that caused by tidal deformations. Tidal dissipation results in a phase lag and its magnitude (in units of arcsec) is given by the empirical relation (80/Q), where Q is the quality factor; Q=80 results in a phase lag of ~1 arcsec. A large inner core with a low viscosity of the order of 10^{17} Pa s or lower can significantly affect $Q$ and thus the resulting phase lag. The limited mantle phase lag suggested by observations (<10 arcsec) implies a lower limit on the bulk mantle viscosity of approximately 10^{17} Pa s.

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I. MacPherson and M. Dumberry
Tue, 5 Apr 22
33/83

Comments: 40 pages, 11 figures

Evidence of changes in the low-latitude plasma drift under IMF $B_z$ coupling: a TIEGCM simulation approach [CL]

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http://arxiv.org/abs/2204.01282


Study of the dynamic nature of low-latitude ionosphere during geomagnetically disturbed conditions, especially in the EIA and the magnetic equatorial regions are vital for understanding the underlying physics as well as for mitigating space weather hazards on the sophisticated technological systems essential for human civilization. An important aspect of the space weather studies is the thorough understanding of coupling between the solar wind and the terrestrial magnetosphere-ionosphere system and subsequent influence on the low-latitude ionosphere. This paper presents an effort to understand the influence of actual values of the north-south component of Interplanetary Magnetic Field (IMF, $B_z$) on the vertical plasma drifts at a location near the EIA and the geomagnetic equator. The strong storm event of October 13, 2016, falling in the descending phase of solar cycle 24, has been taken up as a case study. Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) simulation runs have been performed under two scenarios: first when no coupling is present (IMF $B_z$ = 0 nT) and second when actual observations of the values of IMF $B_z$ is given as inputs to the model. Observations show when actual data is fed to the model, there is significant shift of the vertical drift towards westward, while there is an increase in the peak value of the westward drift after the pre-reversal enhancement. This study is an initial effort to understand the variations in low-latitude plasma motions during the main phase of strong geomagnetic storms. This initial work will be followed up with understanding the global plasma drift variations under the influence of other components of the IMF near the EIA and the dip equatorial regions.

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S. Chakraborty
Tue, 5 Apr 22
79/83

Comments: 4 pages, 2 figures, accepted for publication as a Young Scientist Award (YSA) Paper at the 3rd URSI Atlantic-Asia-Pacific Radio Science Conference (URSI-AT-AP-RASC 2022), Gran Canaria, Spain

COWS all tHE way Down (COWSHED) I: Could cow based planetoids support methane atmospheres? [EPA]

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http://arxiv.org/abs/2203.16609


More often than not a lunch time conversation will veer off into bizarre and uncharted territories. In rare instances these frontiers of conversation can lead to deep insights about the Universe we inhabit. This paper details the fruits of one such conversation. In this paper we will answer the question: How many cows do you need to form a planetoid entirely comprised of cows, which will support a methane atmoosphere produced by the planetary herd? We will not only present the necessary assumptions and theory underpinning the cow-culations, but also present a thorough (and rather robust) discussion of the viability of, and implications for accomplishing, such a feat.

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W. Roper, T. Cook, V. Korbina, et. al.
Fri, 1 Apr 22
6/85

Comments: N/A

Time-Varying Magnetopause Reconnection during Sudden Commencement: Global MHD Simulations [CL]

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http://arxiv.org/abs/2203.14056


In response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). Whilst such compressions have also been associated with a contraction of the ionospheric polar cap due to the triggering of reconnection in the magnetotail, the effect of any changes in dayside reconnection is less clear and is a key component in fully understanding the system response. In this study we explore the time-dependent nature of dayside coupling during SC by performing global simulations using the Gorgon MHD code, and impact the magnetosphere with a series of interplanetary shocks with different parameters. We identify the location and evolution of the reconnection region in each case as the shock propagates through the magnetosphere, finding strong enhancement in the dayside reconnection rate and prompt expansion of the dayside polar cap prior to the eventual triggering of tail reconnection. This effect pervades for a variety of IMF orientations, and the reconnection rate is most enhanced for events with higher dynamic pressure. We explain this by repeating the simulations with a large explicit resistivity, showing that compression of the magnetosheath plasma near the propagating shock front allows for reconnection of much greater intensity and at different locations on the dayside magnetopause than during typical solar wind conditions. The results indicate that the dynamic behaviour of dayside coupling may render steady models of reconnection inaccurate during the onset of a severe space weather event.

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J. Eggington, R. Desai, L. Mejnertsen, et. al.
Tue, 29 Mar 22
8/73

Comments: N/A

3D Adapted Random Forest Vision (3DARFV) for Untangling Heterogeneous-Fabric Exceeding Deep Learning Semantic Segmentation Efficiency at the Utmost Accuracy [CL]

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http://arxiv.org/abs/2203.12469


Planetary exploration depends heavily on 3D image data to characterize the static and dynamic properties of the rock and environment. Analyzing 3D images requires many computations, causing efficiency to suffer lengthy processing time alongside large energy consumption. High-Performance Computing (HPC) provides apparent efficiency at the expense of energy consumption. However, for remote explorations, the conveyed surveillance and the robotized sensing need faster data analysis with ultimate accuracy to make real-time decisions. In such environments, access to HPC and energy is limited. Therefore, we realize that reducing the number of computations to optimal and maintaining the desired accuracy leads to higher efficiency. This paper demonstrates the semantic segmentation capability of a probabilistic decision tree algorithm, 3D Adapted Random Forest Vision (3DARFV), exceeding deep learning algorithm efficiency at the utmost accuracy.

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O. Alfarisi, Z. Aung, Q. Huang, et. al.
Thu, 24 Mar 22
37/56

Comments: N/A

Short-Lived Radionuclides in Meteorites and the Sun's Birth Environment [EPA]

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http://arxiv.org/abs/2203.11169


The solar nebula contained a number of short-lived radionuclides (SLRs) with half-lives of tens of Myr or less, comparable to the timescales for formation of protostars and protoplanetary disks. Therefore, determining the origins of SLRs would provide insights into star formation and the Sun’s astrophysical birth environment. In this chapter, we review how isotopic studies of meteorites reveal the existence and abundances of these now-extinct radionuclides; and the evidence that the SLR ${}^{10}{\rm Be}$, which uniquely among the SLRs is not produced during typical stellar nucleosynthesis, was distributed homogeneously in the solar nebula. We review the evidence that the SLRs ${}^{26}{\rm Al}$, ${}^{53}{\rm Mn}$, and ${}^{182}{\rm Hf}$, and other radionuclides, were also homogeneously distributed and can be used to date events during the Solar System’s planet-forming epoch. The homogeneity of the SLRs, especially ${}^{10}{\rm Be}$, strongly suggests they were all inherited from the Sun’s molecular cloud, and that production by irradiation within the solar nebula was very limited, except for ${}^{36}{\rm Cl}$. We review astrophysical models for the origin of ${}^{10}{\rm Be}$, showing that it requires that the Sun formed in a spiral arm of the Galaxy with higher star formation rate than the Galaxy-wide average. Likewise, we review the astrophysical models for the origins of the other SLRs and show that they likely arose from contamination of the Sun’s molecular cloud by massive stars over tens of Myr, most likely dominated by ejecta from Wolf-Rayet stars. The other SLRs also demand formation of the Sun in a spiral arm of the Galaxy with a star formation rate as high as demanded by the Solar System initial ${}^{10}{\rm Be}$ abundance. We discuss the astrophysical implications, and suggest further tests of these models and future directions for the field.

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S. Desch, E. Young, E. Dunham, et. al.
Tue, 22 Mar 22
19/82

Comments: 37 pages, 8 figures. Submitted as a chapter to Protostars and Planets VII

Geophysical Evolution During Rocky Planet Formation [EPA]

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http://arxiv.org/abs/2203.10023


Progressive astronomical characterization of planet-forming disks and rocky exoplanets highlight the need for increasing interdisciplinary efforts to understand the birth and life cycle of terrestrial worlds in a unified picture. Here, we review major geophysical and geochemical processes that shape the evolution of rocky planets and their precursor planetesimals during planetary formation and early evolution, and how these map onto the astrophysical timeline and varying accretion environments of planetary growth. The evolution of the coupled core-mantle-atmosphere system of growing protoplanets diverges in thermal, compositional, and structural states to first order, and ultimately shapes key planetary characteristics that can discern planets harboring clement surface conditions from those that do not. Astronomical campaigns seeking to investigate rocky exoplanets will require significant advances in laboratory characterization of planetary materials and time- and spatially-resolved theoretical models of planetary evolution, to extend planetary science beyond the Solar System and constrain the origins and frequency of habitable worlds like our own.

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T. Lichtenberg, L. Schaefer, M. Nakajima, et. al.
Mon, 21 Mar 22
1/60

Comments: 37 pages, 10 figures; under review for publication as a chapter in Protostars and Planets VII, University of Arizona Press; comments welcome; figures available at this https URL

Martian meteorites reflectance and implications for rover missions [EPA]

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http://arxiv.org/abs/2203.10051


In the next decade, two rovers will characterize in situ the mineralogy of rocks on Mars, using for the first time near-infrared reflectance spectrometers: SuperCam onboard the Mars 2020 rover and MicrOmega onboard the ExoMars rover, although this technique is predominantly used in orbit for mineralogical investigations. Until successful completion of sample-return missions from Mars, Martian meteorites are currently the only samples of the red planet available for study in terrestrial laboratories and comparison with in situ data. However, the current spectral database available for these samples does not represent their diversity and consists primarily of spectra acquired on finely crushed samples, albeit grain size is known to greatly affect spectral features. We measured the reflected light of a broad Martian meteorite suite as a means to catalogue and characterize their spectra between 0.4 and 3 microns. These measurements are achieved using a point spectrometer acquiring data comparable to SuperCam, and an imaging spectrometer producing hyperspectral cubes similarly to MicrOmega. Our results indicate that point spectrometry is sufficient to discriminate the different Martian meteorites families, to identify their primary petrology based on band parameters, and to detect their low content in alteration minerals. However, significant spectral mixing occurs in the point measurements, even at spot sizes down to a few millimeters, and imaging spectroscopy is needed to correctly identify the various mineral phases in the meteorites. Bidirectional spectral measurements confirm their non-Lambertian behavior, with backward and suspected forward scattering peaks. With changing observation geometry, the main absorption strengths show variations up to 10-15 percents. All the spectra presented are provided in the supplementary data for further comparison with in situ and orbital measurements.

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L. Mandon, P. Beck, C. Quantin-Nataf, et. al.
Mon, 21 Mar 22
23/60

Comments: N/A

Electrical Conductivity of Iron in Earth's Core from Microscopic Ohm's Law [CL]

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http://arxiv.org/abs/2203.06025


Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties under Earth-core conditions calls for sophisticated theoretical methods that can support diagnostics. We present results of the electrical conductivity within the pressure and temperature ranges found in Earth’s core from simulating microscopic Ohm’s law using time-dependent density functional theory. Our predictions provide a new perspective on resolving discrepancies in recent experiments.

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K. Ramakrishna, M. Lokamani, A. Baczewski, et. al.
Mon, 14 Mar 22
22/67

Comments: N/A

Global Gravity Field Model from Taiji-1 Observations [CL]

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http://arxiv.org/abs/2203.05876


Taiji-1 is the first technology demonstration satellite of the Taiji program of China’s space-borne gravitational wave antenna. After the demonstration of the key individual technologies, Taiji-1 continues collecting the data of the precision orbit determinations, the satellite attitudes, and the non-conservative forces exerted on the S/C. Therefore, during its free-fall, Taiji-1 can be viewed as operating in the high-low satellite-to-satellite tracking mode of a gravity recovery mission. In this work, one month data from Taiji-1’s observations have been selected and the techniques are developed to resolve the long term interruptions and disturbances in the measurement data due to the scheduled technology demonstration experiments. The first global gravity model TJGM-r1911, that independently derived from China’s own satellite mission, is successfully built from Taiji-1’s observations. Compared with gravity models from CHAMP and other satellite gravity missions, accuracy discrepancies exist, which is mainly caused by the data discontinuity problem. As the approved extended free-falling phase with minimal disruptions and disturbances, Taiji-1 will serve as the first satellite gravity mission for China since 2022 and will provide us the independent measurement of both the static and the monthly time-variable global gravity field.

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L. Wu, P. Xu, S. Zhao, et. al.
Mon, 14 Mar 22
23/67

Comments: 12 pages, 17 figures

Dielectric properties and stratigraphy of regolith in the lunar South Pole-Aitken basin: Observations from the Lunar Penetrating Radar [EPA]

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http://arxiv.org/abs/2203.02840


We examine data obtained by the Lunar Penetrating Radar (LPR) onboard the Chang’E-4 (CE-4) mission to study the dielectric properties and stratigraphy of lunar regolith on the far side of the Moon. The data collected from January 2019 to September 2020 were processed to generate a 540 m radargram. The travel velocity of the radar signal and the permittivity of the regolith were deduced from hyperbolas in the radargram. As CE-4 LPR detected distinct planar reflectors, we evaluated the dielectric loss from the maximum penetration depth based on the radar equation. The derived dielectric properties are compared with the measurements of Apollo samples and Chang’E-2 microwave radiometer observations. The results suggest that regolith at the landing site has a permittivity of 2.64-3.85 and a loss tangent of 0.0032-0.0044, indicating that the local regolith is composed of a fine-grained, low-loss material that is much more homogeneous than that found at the Chang’E-3 landing site. The total thickness of weathered material is 40 m, with several regolith layers and a buried craternidentified in the reconstructed subsurface structure. These layers clearly record a series of impact events from the adjacent regions. We suggest that the top layer is primarily made up of the ejecta from a large crater 140 km away. In contrast, the material source of other thinner layers comes from nearby smaller craters.

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J. Feng, M. Siegler and M. White
Tue, 8 Mar 22
61/100

Comments: 9 pages, 9 figures

A dynamo simulation generating Saturn-like small magnetic dipole tilts [EPA]

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http://arxiv.org/abs/2203.03520


Among planetary dynamos, the magnetic field of Saturn stands out in its exceptional level of axisymmetry. One of its peculiar features is that the magnetic dipole mode is tilted with respect to the planetary rotation axis by only $\approx 0.007^{\circ}$ or less. Numerical dynamo simulations performed in this context have had great difficulty in producing such small dipole tilt angles without introducing ad hoc ingredients such as a latitudinally varying heat flux pattern in the outer layers or stably stratified layers (SSL). Here we present a numerical dynamo simulation that generates a highly axisymmetric dynamo with a dipole tilt of about $\approx 0.0008^{\circ}$ on average. The model consists of a deep dynamo layer and an overlying low-conductivity layer but without any SSL. We highlight a novel mechanism where strong differential rotation generated in the atmospheric layer penetrates into the dynamo region, helping to maintain a very small magnetic dipole tilt.

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R. Yadav, H. Cao and J. Bloxham
Tue, 8 Mar 22
86/100

Comments: To appear in Geophysical Research Letters; 11 pages, double columns

First results of Low-latitude Ionospheric Irregularities measured by NavIC and GPS near the Anomaly Crest and the Magnetic Equator [CL]

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http://arxiv.org/abs/2203.02218


Ionospheric irregularity studies are important aspects for understanding ionospheric physics and related processes, especially near the low-latitude regions. However, simultaneous measurements (utilizing the L-band signals of NavIC and GPS) of irregularity scale sizes over the Indian longitude sector, has not been addressed extensively. To address this problem, the paper presents simultaneous characterization of low-latitude ionospheric irregularities over a location near the northern EIA crest (Indore: 22.52$^\circ$N, 75.92$^\circ$E geographic and magnetic dip of 32.23$^\circ$N) and a location (Hyderabad: 17.41$^\circ$N, 78.55$^\circ$E geographic and magnetic dip of 21.69$^\circ$N) between the crest and the magnetic equator, utilizing the Indian navigation system, NavIC and GPS L5 signal C/N$_o$ variations to determine the range of the ionospheric irregularity scale sizes using Power Spectral Density (PSD) analysis. The study period spans from September 2017- September 2019, covering both disturbed and quiet-time conditions in the declining phase of solar cycle 24. Observations show that the irregularity scale size ranges from about 500 m to 6 km. This study for the first time, shows the nature of the temporal PSD for ionospheric scintillation during varying solar and geophysical conditions, by measuring the irregularity scale sizes utilizing simultaneous observations from NavIC and GPS from locations near the northern crest of the EIA and in between crest and the magnetic equator, ensuring proper characterization of ionosphere over the geosensitive Indian subcontinent.

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S. Chakraborty, A. Datta and D. Ayyagari
Mon, 7 Mar 22
12/64

Comments: Under Review in JGR: Space Physics

Successful Recovery of an Observed Meteorite Fall Using Drones and Machine Learning [EPA]

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http://arxiv.org/abs/2203.01466


We report the first-time recovery of a fresh meteorite fall using a drone and a machine learning algorithm. A fireball on the 1st April 2021 was observed over Western Australia by the Desert Fireball Network, for which a fall area was calculated for the predicted surviving mass. A search team arrived on site and surveyed 5.1 km2 area over a 4-day period. A convolutional neural network, trained on previously-recovered meteorites with fusion crusts, processed the images on our field computer after each flight. meteorite candidates identified by the algorithm were sorted by team members using two user interfaces to eliminate false positives. Surviving candidates were revisited with a smaller drone, and imaged in higher resolution, before being eliminated or finally being visited in-person. The 70 g meteorite was recovered within 50 m of the calculated fall line using, demonstrating the effectiveness of this methodology which will facilitate the efficient collection of many more observed meteorite falls.

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S. Anderson, M. Towner, J. Fairweather, et. al.
Fri, 4 Mar 22
45/63

Comments: 4 Figures, 1 Table, 10 pages

Scaling and phase diagrams of planetary sediment transport [EPA]

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http://arxiv.org/abs/2203.00562


Sediment transport by atmospheric winds shapes the surface and affects the climates of planetary bodies. Reliably predicting the occurrence and rate of sediment transport in the Solar System has been notoriously difficult because fluid density, grain size and soil cohesiveness vary across many orders of magnitude. Here, we use recent advances in analytical and numerical sediment transport modeling to derive general scaling relations for planetary transport. In particular, we show that the equations of motion of rebounding grains predict that the minimum threshold fluid shear velocity needed to sustain transport (transport cessation threshold) scales with the particle-fluid-density ratio ($s$) as $s^{1/3}$, in contrast to the $s^{1/2}$-scaling exhibited by the threshold for transport initiation. The grain size corresponding to this minimum is in the range $80{-}290~\mu\mathrm{m}$ for Solar System bodies. Our results, summarized in phase diagrams for the cessation threshold, mean transport rate and dust emission potential, explain the observed eastward propagation of Titan’s dunes, in spite of a predominantly westward wind circulation, indicate active dust cycles on Earth, Mars and Titan, and suggest marginal but active atmospheric transport on Venus, Triton and Pluto.

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T. Pähtz, O. Duŕan and F. Comola
Wed, 2 Mar 22
36/54

Comments: N/A

Performance of NavIC for studying the ionosphere at an EIA region in India [CL]

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http://arxiv.org/abs/2001.02964


This paper emphasizes on NavIC’s performance in ionospheric studies over the Indian subcontinent region. The study is performed using data of one year (2017-18) at IIT Indore, a location near the northern crest of Equatorial Ionization Anomaly (EIA). It has been observed that even without the individual error corrections, the results are within $\pm20\%$ of NavIC VTEC estimates observed over the 1\ensuremath{^{\circ}} x 1\ensuremath{^{\circ}} grid of IPP surrounding the GPS VTEC estimates for most of the time. Additionally, ionospheric response during two distinct geomagnetic storms (September 08 and 28, 2017) at the same location and other IGS stations covering the Indian subcontinent using both GPS and NavIC has also been presented. This analysis revealed similar variations in TEC during the geomagnetic storms of September 2017, indicating the suitability of NavIC to study space weather events along with the ionospheric studies over the Indian subcontinent.

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D. Ayyagari, S. Chakraborty, S. Das, et. al.
Tue, 1 Mar 22
11/80

Comments: 38 Pages, 16 Figures, Accepted for publication in Advances in Space Research

Connecting Asteroids and Meteorites with visible and near-infrared spectroscopy [EPA]

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http://arxiv.org/abs/2202.13797


We identify spectral similarities between asteroids and meteorites. We identify spectral matches between 500 asteroid spectra and over 1,000 samples of RELAB meteorite spectra over 0.45-2.5 microns. We reproduce many major and previously known meteorite-asteroid connections and find possible new, more rare or less-established connections. Well-established connections include: ordinary chondrites (OC) with S-complex asteroids; pristine CM carbonaceous chondrites with Ch-type asteroids and heated CMs with C-type asteroids; HED meteorites with V-types; enstatite chondrites with Xc-type asteroids; CV meteorites with K-type asteroids; Brachinites, Pallasites and R chondrites with olivine-dominated A-type asteroids.
We find a trend from Q, Sq, S, Sr to Sv correlates with LL to H, with Q-types matching predominately to L and LL ordinary chondrites, and Sr and Sv matching predominantly with L and H ordinary chondrites. Ordinary chondrite samples that match to the X-complex, all measurements of slabs and many labeled as dark or black (shocked) OCs. We find carbonaceous chondrite samples having spectral slopes large enough to match D-type asteroid spectra.
In many cases the asteroid type to meteorite type links are not unique. While there are well established matches between an asteroid class and meteorite class, there are less common but still spectrally compatible matches between many asteroid types and meteorite types. This result emphasizes the diversity of asteroid and meteorite compositions and highlights the degeneracy of classification by spectral features alone. Recent and upcoming spacecraft missions will shed light on the compositions of many of the asteroid classes, particularly those without diagnostic features, (C-, B-, X-, and D-types), with measurements of Ceres, Ryugu, Bennu, Psyche, and C-, P-, and D-types as part of the Lucy mission.

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F. DeMeo, B. Burt, M. Marsset, et. al.
Tue, 1 Mar 22
42/80

Comments: Accepted for publication in Icarus. 38 pages, 8 figures

Effects of Mercury surface temperature on the sodium abundance in its exosphere [EPA]

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http://arxiv.org/abs/2202.11467


The link between the surface temperature of Mercury and the exosphere sodium content has been investigated. Observations show that, along the orbit of Mercury, two maxima of total Na content are present: one at aphelion and one at perihelion. Previous models, based on a simple thermal map, were not able to reproduce the aphelion peak. Here we introduce a new thermophysical model giving soil temperatures as an input for the IAPS exospheric model already used in the past with the input of a simple thermal map. By comparing the reference model output with the new one, we show that such improved surface temperature map is crucial to explain the temporal variability of Sodium along the orbit.

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E. Rognini, A. Mura, M. Capria, et. al.
Thu, 24 Feb 22
19/52

Comments: N/A

The role of slow magnetostrophic waves in the formation of the axial dipole in planetary dynamos [CL]

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http://arxiv.org/abs/2202.08784


The preference for the axial dipole in planetary dynamos is investigated through the analysis of wave motions in spherical dynamo models. Our study focuses on the role of slow magnetostrophic waves, which are generated from localized balances between the Lorentz, Coriolis and buoyancy (MAC) forces. Since the slow waves are known to intensify with increasing field strength, simulations in which the field grows from a small seed towards saturation are useful in understanding the role of these waves in dynamo action. Axial group velocity measurements in the energy-containing scales show that fast inertial waves slightly modified by the magnetic field and buoyancy are dominant under weak fields. However, the dominance of the slow waves is evident for strong fields satisfying $|\omega_M/\omega_C| \sim $ 0.1, where $\omega_M$ and $\omega_C$ are the frequencies of the Alfv\’en and inertial waves respectively. A MAC wave window of azimuthal wavenumbers is identified wherein helicity generation by the slow waves strongly correlates with dipole generation. Analysis of the magnetic induction equation suggests a poloidal–poloidal field conversion in the formation of the dipole. Finally, the attenuation of slow waves may result in polarity reversals in a strongly driven Earth’s core.

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A. Varma and B. Sreenivasan
Fri, 18 Feb 22
47/63

Comments: 26 pages, 14 figures

Arpu Kuilpu: An H5 from the Outer Main Belt [EPA]

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http://arxiv.org/abs/2202.07185


On 1 June 2019, just before 7:30 PM local time, the Desert Fireball Network detected a -9.3 magnitude fireball over South Australia near the Western Australia border. The event was observed by six fireball observatories, and lasted for five seconds. One station was nearly directly underneath the trajectory, greatly constraining the trajectory solution. This trajectory’s backward numerical integrations indicate that the object originated from the outer main belt with a semi-major axis of 2.75 au. A light curve was also extracted and showed that the body experienced very little fragmentation during its atmospheric passage. A search campaign was conducted with several Desert Fireball Network team members and other volunteers. One 42 g fragment was recovered within the predicted fall area based on the dark flight model. Based on measurements of short-lived radionuclides, the fragment was confirmed to be a fresh fall. The meteorite, Arpu Kuilpu, has been classified as an H5 ordinary chondrite. This marks the fifth fall recovered in Australia by the Desert Fireball Network, and the smallest meteoroid ($\simeq 2$ kg) to ever survive entry and be recovered as a meteorite.

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P. Shober, H. Devillepoix, E. Sansom, et. al.
Wed, 16 Feb 22
42/69

Comments: submitted to MAPS

Lithospheric Structure of Venusian Crustal Plateaus [EPA]

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http://arxiv.org/abs/2202.06971


Crustal plateaus are Venusian highlands characterized by tectonized terrains. It is commonly interpreted that their topography is isostatically supported and that they represent fossils of an extinct tectonic regime. Using gravity and topography we perform a comprehensive investigation of the lithospheric structure of six crustal plateaus. We computed the admittance (gravity to topography wavelength-dependent ratio) for each region and compared them to modeled admittances. Three compensation scenarios were tested: Airy isostasy, a surface-loading flexural model, and a flexural model with surface and subsurface loads. Our results show that the topography of most plateaus is supported by crustal thickening and that the addition of a mantle support component is not necessary at the investigated wavelengths. The elastic thickness was constrained to be less than 35 km with a best-fitting average of 15 km, confirming that these regions are consistent with an isostatic regime. The average crustal thickness of the plateaus ranges from 15 to 34 km, and if they are in Airy isostasy, this implies that the global average crustal thickness of Venus is about 20 km. Phoebe Regio is the sole exception of our analysis in that crustal thicknesses that are compatible with the other plateaus are obtained only when a buoyant layer is included. Heat flow estimations computed from the elastic thickness indicate that the plateaus formed under higher heat flow conditions compared to the current global average and could have caused localized melting. Present-day heat flow predictions suggest that eclogitization could occur where the crust is thickest.

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J. Maia and M. Wieczorek
Wed, 16 Feb 22
54/69

Comments: 27 pages, 10 figures

Trajectory, recovery, and orbital history of the Madura Cave meteorite [EPA]

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http://arxiv.org/abs/2202.06641


On the 19th June 2020 at 20:05:07 UTC, a fireball lasting 5.5 s was observed above Western Australia by three Desert Fireball Network observatories. The meteoroid entered the atmosphere with a speed of $14.00 \pm 0.17$ km s$^{-1}$ and followed a $58^{\circ}$ slope trajectory from a height of 75 km down to 18.6 km. Despite the poor angle of triangulated planes between observatories (29$^{\circ}$) and the large distance from the observatories, a well constrained kilo-size main mass was predicted to have fallen just South of Madura in Western Australia. However, the search area was predicted to be large due to the trajectory uncertainties. Fortunately, the rock was rapidly recovered along the access track during a reconnaissance trip. The 1.072 kg meteorite called Madura Cave was classified as an L5 ordinary chondrite. The calculated orbit is of Aten type (mostly contained within the Earth’s orbit), the second time only a meteorite is observed on such an orbit after Bunburra Rockhole. Dynamical modelling shows that Madura Cave has been in near-Earth space for a very long time. The NEO dynamical lifetime for the progenitor meteoroid is predicted to be $\sim87$ Myr. This peculiar orbit also points to a delivery from the main asteroid belt via the $\nu6$ resonance, and therefore an origin in the inner belt. This result contributes to drawing a picture for the existence of a present-day L chondrite parent body in the inner belt.

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H. Devillepoix, E. Sansom, P. Shober, et. al.
Tue, 15 Feb 22
35/75

Comments: N/A

Representation of the gravitational potential of a level ellipsoid by a simple layer [CL]

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http://arxiv.org/abs/2202.05934


A closed-form expression is obtained for the density of a simple layer, equipotential to an oblate level ellipsoid of revolution in an outer space. The potential of any level spheroid of positive mass with the inward direction of attracting force on its surface can be represented in this way. A family of density functions defined on the whole volume of a level ellipsoid of revolution is found. Several density examples are considered.

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D. Milanov
Tue, 15 Feb 22
49/75

Comments: 12 pages, 4 figures

The Metal-Silicate Partitioning of Carbon During Earth's Accretion and its Distribution in the Early Solar System [EPA]

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http://arxiv.org/abs/2202.06809


Carbon is an essential element for the existence and evolution of life on Earth. Its abundance in Earth’s crust and mantle (the Bulk Silicate Earth, BSE) is surprisingly high given that carbon is strongly siderophile (metal-loving) at low pressures and temperatures, and hence should have segregated almost completely into Earth’s core during accretion. Estimates of the concentration of carbon in the BSE lie in the range 100-260 ppm and are much higher than expected based on simple models of core-mantle differentiation. Here we show through experiments at the putative conditions of Earth’s core formation (49-71 GPa and 3600-4000 K) that carbon is significantly less siderophile at these conditions than at the low pressures ($\leq$13 GPa) and temperatures ($\leq$2500 K) of previous large volume press studies, but at least an order of magnitude more siderophile than proposed recently based on an experimental approach that is similar to ours. Using our new data along with previously published results, we derive a new parameterization of the pressure-temperature dependence of the metal-silicate partitioning of carbon. We apply this parameterization in a model that combines planet formation and core-mantle differentiation that is based on astrophysical N-body accretion simulations. Because differentiated planetesimals were almost completely depleted in carbon due to sublimation at high temperatures, almost all carbon in the BSE was added by the accretion of fully-oxidized carbonaceous chondrite material from the outer solar system. Carbon is added to the mantle continuously throughout accretion and its concentration reaches values within the BSE range (e.g. 140$\pm$40 ppm) at the end of accretion. The corresponding final core and bulk Earth carbon concentrations are 1270$\pm$300 ppm and 495$\pm$125 ppm respectively.

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I. Blanchard, D. Rubie, E. Jennings, et. al.
Tue, 15 Feb 22
53/75

Comments: Supplementary material included in pdf

Giant Impact onto a Vesta-Like Asteroid and Formation of Mesosiderites through Mixing of Metallic Core and Surface Crust [EPA]

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http://arxiv.org/abs/2202.06486


Mesosiderites are a type of stony-iron meteorites composed of a mixture of silicates and Fe-Ni metals. The mesosiderite silicates and metals are considered to have originated from the crust and metal core, respectively, of a differentiated asteroid. In contrast, mesosiderites rarely contain the olivine that is mainly included in a mantle. Although a giant impact onto a differentiated asteroid is considered to be a probable mechanism to mix crust and metal materials to form mesosiderites, it is not obvious how such a giant impact can form mesosiderite-like materials without including mantle materials. We conducted numerical simulations of giant impacts onto differentiated asteroids, using the smoothed particle hydrodynamics method, to investigate the detailed distribution of mixed materials on the resultant bodies. For the internal structure of a target body, we used a thin-crust model derived from the magma ocean crystallization model of the asteroid Vesta and a thick-crust and a large-core model suggested from the proximity observation of Vesta by the Dawn probe. In the simulations with the former model, excavation of the metal core requires nearly catastrophic impacts and mantle is exposed over large surface areas. Thus, stony-iron materials produced on its surface are likely to include mantle materials and it is difficult to produce mesosiderite-like materials. Conversely, in the simulations with the latter model, mantle materials are exposed only at impact sites, even when the impacts excavate the metal core, and the formation of a surface with little mantle material and the formation of mesosiderite-like materials are possible. Therefore, our simulations suggest that an internal structure with a thick crust and a large core is more likely as a mesosiderite parent body rather than the thin-crust internal structure inferred from the conventional magma ocean model.

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K. Sugiura, M. Haba and H. Genda
Tue, 15 Feb 22
58/75

Comments: 21 pages, 8 figures, accepted for publication in Icarus

A nitrogen-rich atmosphere on ancient Mars consistent with isotopic evolution models [EPA]

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http://arxiv.org/abs/2202.04825


The ratio of nitrogen isotopes in the Martian atmosphere is a key constraint on the planet’s atmospheric evolution. However, enrichment of the heavy isotope expected due to atmospheric loss from sputtering and photochemical processes is greater than measurements. A massive, multi-bar early CO2-dominated atmosphere and recent volcanic outgassing have been proposed to explain this discrepancy, and many previous models have assumed atmospheric nitrogen rapidly reached a steady state where loss to space balanced volcanic outgassing. Here we show using time-dependent models that the abundance and isotopic composition of nitrogen in the Martian atmosphere can be explained by a family of evolutionary scenarios in which the initial partial pressure of nitrogen is sufficiently high that a steady state is not reached and nitrogen levels gradually decline to present-day values over 4 billion years. Our solutions do not require a multi-bar early CO2 atmosphere and are consistent with volcanic outgassing indicated by both geologic mapping and the atmospheric 36Ar/38Ar ratio. Monte Carlo simulations that include these scenarios estimate that the partial pressure of N2 was 60 – 740 mbar (90% confidence, with a median value of 310 mbar) at 3.8 billion years ago when the valley networks formed. We suggest that such a high nitrogen partial pressure could have contributed substantially to warming on early Mars.

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R. Hu and T. Thomas
Fri, 11 Feb 22
71/71

Comments: Nature Geoscience, published online on February 10, 2022, this https URL

Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth [CL]

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http://arxiv.org/abs/2202.00752


The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements. Previous studies usually focused on the current range of pressure-temperature conditions in the Earth’s mantle and ignored a possible difference in the past, such as the stage of the core-mantle separation. Here, using ab initio evolutionary structure prediction, we find that only two magnesium hydrosilicate phases are stable at megabar pressures, $\alpha$-Mg$_2$SiO$_5$H$_2$ and $\beta$-Mg$_2$SiO$_5$H$_2$, stable at 262-338 GPa and >338 GPa,respectively (all these pressures now lie within the Earth’s iron core). Both are superionic conductors with quasi-one-dimensional proton diffusion at relevant conditions. In the first 30 million years of Earth’s history, before the Earth’s core was formed, these must have existed in the Earth, hosting much of Earth’s water. As dense iron alloys segregated to form the Earth’s core, Mg$_2$SiO$_5$H$_2$ phases decomposed and released water. Thus, now-extinct Mg$_2$SiO$_5$H$_2$ phases have likely contributed in a major way to the evolution of our planet.

Read this paper on arXiv…

H. Li, A. Oganov, H. Cui, et. al.
Thu, 3 Feb 22
28/56

Comments: N/A

Parameter Distributions for the Drag-Based Modeling of CME Propagation [CL]

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http://arxiv.org/abs/2201.12049


In recent years, ensemble modeling has been widely employed in space weather to estimate uncertainties in forecasts. We here focus on the ensemble modeling of CME arrival times and arrival velocities using a drag-based model, which is well-suited for this purpose due to its simplicity and low computational cost. Although ensemble techniques have previously been applied to the drag-based model, it is still not clear how to best determine distributions for its input parameters, namely the drag parameter and the solar wind speed. The aim of this work is to evaluate statistical distributions for these model parameters starting from a list of past CME-ICME events. We employ LASCO coronagraph observations to measure initial CME position and speed, and in situ data to associate them with an arrival date and arrival speed. For each event we ran a statistical procedure to invert the model equations, producing parameters distributions as output.
Our results indicate that the distributions employed in previous works were appropriately selected, even though they were based on restricted samples and heuristic considerations. On the other hand, possible refinements to the current method are also identified, such as the dependence of the drag parameter distribution on the CME being accelerated or decelerated by the solar wind, which deserve further investigation.

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G. Napoletano, R. Foldes, E. Camporeale, et. al.
Mon, 31 Jan 22
26/55

Comments: 25 pages, 9 figures, accepted for publication by Space Weather Journal. The ICME catalog built for the analysis in Section 3, together with a tool for the data visualization and the module employed for running the PDBM simulations, can be downloaded from this https URL (Napoletano et al., 2021)

Large Impacts onto the Early Earth: Planetary Sterilization and Iron Delivery [EPA]

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http://arxiv.org/abs/2201.09349


Late accretion onto the Hadean Earth included large impacts that could have influenced early habitability, either by sterilizing the planet or alternatively catalyzing the origin of life by delivering iron required to create a reducing environment/atmosphere. We present 3D numerical simulations of 1500-3400 km diameter impacts on the early Earth in order to quantify their effects on planetary habitability. We find sterilizing impact events require larger projectiles than previously assumed, with a 2000-2700 km diameter impactor required to completely melt Earth’s surface and an extrapolated >700 km diameter impactor required for ocean-vaporization. We also find that reducing environments are less likely to arise following large impacts than previously suggested, because >70% of the projectile iron is deposited in the crust and upper mantle where it is not immediately available to reduce surface water and contribute to forming a reducing atmosphere. Although the largest expected late accretion impacts (~1 lunar mass) delivered sufficient iron to the atmosphere to have reduced an entire ocean mass of water, such impacts would also have melted the entire surface, potentially sequestering condensing iron that is not oxidized quickly. The hypothesis that life emerged in the aftermath of large impacts requires an efficient mechanism of harnessing the reducing power of iron sequestered in the crust/mantle, or an origin of life pathway that operates in more weakly-reducing post-impact environments that require smaller quantities of impact-delivered iron.

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R. Citron and S. Stewart
Tue, 25 Jan 22
10/78

Comments: 25 pages, 13 figures (accepted to PSJ)

CaS: a medium for the Ca-S-O cycles and rare metal aggregation in Earth [EPA]

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http://arxiv.org/abs/2201.08615


Oldhamite is a rare mineral only observed naturally in enstatite meteorites (chondrites and achondrites). It has never been observed on terrestrial samples, nor in other meteorite groups. However, under the conditions of 1.5 GPa, 1425K and 0.5 GPa, 1325K, with the oxygen fugacity is in the range of FMQ-2 to FMQ-0.2 (the logfO2 value determined relative to the buffering equilibrium 3Fe2SiO4 + O2 = 2Fe3O4 + 3SiO2; we denote this value FMQ), the oldhamite (CaS) was found during the melt reaction between the pyrrhotite-pentlandite-bearing orthopyroxene and CaCO3. We name this the two-melt mechanism. It is seasonable to infer that the formation of CaS can occur at the interface between the asthenosphere and the oceanic lithosphere under the mid-ocean ridge and during the process of mantle plume intruding into the lithosphere in Earth. CaS is very easy to combine with oxygen to form CaSO4, which probably is the reason why it has never been found in geological samples from Earth. We speculate that part of the anhydrite and gypsum in the black smokers of mid-ocean ridges are related to the oxidation of CaS in the underlying mantle. The Siberian mantle plume can generate CaS when it intruded into the lithosphere. The C and CO in the mantle plume lava with low oxygen fugacity can also react with gypsum in the crust to generate CaS and CO2. When the magma cools, CaS can be oxidized to form CaSO4. During the formation and oxidation of 1 molecule of CaS, 1 molecule of CO2 can be produced, and a half to two moles of O2 will be fixed by CaSO4. This mechanism perhaps is a reason for the reduction of oxygen content in the atmosphere at the Permian-Triassic boundary. The existence of the intermediary product CaS was one of the factors to promote the mass extinction most severe biotic crisis in the past 500 million years at the Permian-Triassic boundary.

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Y. Liu, J. Chen, N. Wu, et. al.
Mon, 24 Jan 22
44/59

Comments: N/A

Sub-surface granular dynamics in the context of oblique, low-velocity impacts into angular granular media [EPA]

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http://arxiv.org/abs/2201.02585


Oblique, low-velocity impacts onto extraterrestrial terrain are an inevitable occurrence during space exploration. We conduct two-dimensional discrete simulations to model such impacts into a bed of triangular grains. Finite element method provides the basis for simulation, enabling the angular grain geometry. Our findings re-create the three classes of impact behavior previously noted from experiments: full-stop, rollout, and ricochet \citep*{Wright2020}. An application of Set Voronoi tessellation assesses packing fraction at a high resolution, revealing how grains shift relative to each other during an impact event. Calculation of Von Mises strain distributions then reveal how grains shift relative to the overall system, leading to the notion of the ‘skin zone’. Intuition would suggest that the region of perturbed grains would grow deeper with higher velocity impacts, results instead show that increasing velocity may actually evoke a change in the grains’ dissipative response that boosts lateral perturbation. Finally, we consider as a whole how sub-surface response could link with impactor dynamics to deepen our understanding of oblique, low-velocity impact events and help to improve mission outcomes.

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P. Miklavčič, H. Askari, P. Sánchez, et. al.
Mon, 10 Jan 22
46/49

Comments: N/A

Towards RNA life on Early Earth: From atmospheric HCN to biomolecule production in warm little ponds [EPA]

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http://arxiv.org/abs/2201.00829


The origin of life on Earth involves the early appearance of an information-containing molecule such as RNA. The basic building blocks of RNA could have been delivered by carbon-rich meteorites, or produced in situ by processes beginning with the synthesis of hydrogen cyanide (HCN) in the early Earth’s atmosphere. Here, we construct a robust physical and non-equilibrium chemical model of the early Earth atmosphere. The atmosphere is supplied with hydrogen from impact degassing of meteorites, sourced with water evaporated from the oceans, carbon dioxide from volcanoes, and methane from undersea hydrothermal vents, and in which lightning and external UV-driven chemistry produce HCN. This allows us to calculate the rain-out of HCN into warm little ponds (WLPs). We then use a comprehensive sources and sinks numerical model to compute the resulting abundances of nucleobases, ribose, and nucleotide precursors such as 2-aminooxazole resulting from aqueous and UV-driven chemistry within them. We find that at 4.4 bya (billion years ago) peak adenine concentrations in ponds can be maintained at ~2.8$\mu$M for more than 100 Myr. Meteorite delivery of adenine to WLPs produce similar peaks in concentration, but are destroyed within months by UV photodissociation, seepage, and hydrolysis. The early evolution of the atmosphere is dominated by the decrease of hydrogen due to falling impact rates and atmospheric escape, and the rise of oxygenated species such as OH from H2O photolysis. Our work points to an early origin of RNA on Earth within ~200 Myr of the Moon-forming impact.

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B. Pearce, K. Molaverdikhani, R. Pudritz, et. al.
Wed, 5 Jan 22
14/54

Comments: Accepted to ApJ, 27 pages (14 main text), 11 figures, 9 tables

The Cassini State of the Moon's inner core [EPA]

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http://arxiv.org/abs/2201.00803


We present a model of the precession dynamics of the Moon that comprises a fluid outer core and a solid inner core. We show that three Cassini states associated with the inner core exist. The tilt angle of the inner core in each of these states is determined by the ratio between the free inner core nutation frequency ($\omega_{ficn}$) and the precession frequency $\Omega_p = 2\pi/18.6$ yr $^{-1}$. All three Cassini states are possible if $|\omega_{ficn}| > 2\pi/16.4$ yr $^{-1}$, but only one is possible otherwise. Assuming that the lowest energy state is favoured, this transition marks a discontinuity in the tilt angle of the inner core, transiting from $-33^\circ$ to $17^\circ$ as measured with respect to the mantle figure axis, where negative angles indicate a tilt towards the orbit normal. Possible Lunar interior density structures cover a range of $\omega_{ficn}$, from approximately half to twice as large as $\Omega_p$, so the precise tilt angle of the inner core remains unknown, though it is likely large because $\Omega_p$ is within the resonant band of $\omega_{ficn}$. Adopting one specific density model, we suggest an inner core tilt of approximately $-17^\circ$. Viscoelastic deformations within the inner core and melt and growth at the surface of a tilted inner core, both neglected in our model, should reduce this amplitude. If the inner core is larger than approximately 200 km, it may contribute by as much as a few thousandths of a degree on the observed mantle precession angle of $1.543^\circ$.

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C. Stys and M. Dumberry
Tue, 4 Jan 22
12/58

Comments: 37 pages, 9 figures

A past lunar dynamo thermally driven by the precession of its inner core [EPA]

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http://arxiv.org/abs/2201.00795


The Cassini state equilibrium associated with the precession of the Moon predicts that the mantle, fluid core and solid inner core precess at different angles. We present estimates of the dissipation from viscous friction associated with the differential precession at the core-mantle boundary (CMB), $Q_{cmb}$, and at the inner core boundary (ICB), $Q_{icb}$, as a function of the evolving lunar orbit. We focus on the latter and show that, provided the inner core was larger than 100 km, $Q_{icb}$ may have been as high as $10^{10}-10^{11}$ W for most of the lunar history for a broad range of core density models. This is larger than the power required to maintain the fluid core in an adiabatic state, therefore the heat released by the differential precession at the ICB can drive a past lunar dynamo by thermal convection. This dynamo can outlive the dynamo from precession at the CMB and may have shutoff only relatively recently. Estimates of the magnetic field strength at the lunar surface are of the order of a few $\mu$T, compatible with the lunar paleomagnetic intensities recorded after 3 Ga. We further show that it is possible that a transition of the Cassini state associated with the inner core may have occurred as a result of the evolution of the lunar orbit. The heat flux associated with $Q_{icb}$ can be of the order of a few mW m$^{-2}$, which should slow down inner core growth and be included in thermal evolution models of the lunar core.

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C. Stys and M. Dumberry
Tue, 4 Jan 22
13/58

Comments: 33 pages, 7 figures

Viscous dissipation in the fluid core of the Moon [EPA]

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http://arxiv.org/abs/2201.00781


The spin axes of the mantle, fluid core and solid inner core of the Moon precess at frequency $\Omega_p=2\pi/18.6$ yr$^{-1}$ though with different orientations, leading to viscous friction at the core-mantle boundary (CMB) and inner core boundary (ICB). Here, we use a rotational model of the Moon with a range of inner core and outer core radii to investigate the relative importance of viscous dissipation at the CMB and ICB, and to show how this dissipation is connected to the phase lead angle ($\phi_p$) of the mantle ahead of its Cassini state. We show that when the inner core radius is $>80$ km and the free inner core nutation frequency $\Omega_{ficn}$ approaches $\Omega_p$, viscous dissipation at the ICB can be comparable to that at the CMB, and in the most extreme cases exceed it by as much as a factor 10. If so, the viscous dissipation in the lunar core projected back in time depends on how $\Omega_{ficn}$ has evolved relative to $\Omega_p$. We further show that constraints on the CMB and ICB radii of the lunar core can in principle be extracted by matching the observed phase lead of $\phi_p=0.27$ arcsec; this requires an improved estimate of tidal dissipation and an accurate model of the turbulent viscous torque. Lastly, when our rotational model is constrained to match $\phi_p=0.27$ arcsec, our results suggest that the viscous dissipation at the ICB is likely insufficient to have ever been above the threshold to power a thermally driven dynamo.

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J. Zhang and M. Dumberry
Tue, 4 Jan 22
24/58

Comments: 26 pages, 3 figures

Viscoelastic relaxation within the Moon and the phase lead of its Cassini state [EPA]

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http://arxiv.org/abs/2201.00786


Analyses of Lunar Laser Ranging data show that the spin-symmetry axis of the Moon is ahead of its expected Cassini state by an angle of $\phi_p$ = 0.27 arcsec. This indicates the presence of one or more dissipation mechanisms acting on the lunar rotation. A combination of solid-body tides and viscous core-mantle coupling have been proposed in previous studies. Here, we investigate whether viscoelastic deformation within a solid inner core at the centre of the Moon can also account for a part of the observed phase lead angle $\phi_p$. We build a rotational dynamic model of the Cassini state of the Moon that comprises an inner core, a fluid core and a mantle, and where solid regions are allowed to deform viscoelastically in response to an applied forcing. We show that the presence of an inner core does not change the global monthly Q of the Moon and hence, that the contribution from solid-body tides to $\phi_p$ is largely unaffected by an inner core. However, we also show that viscoelastic deformation within the inner core, acting to realign its figure axis with that of the mantle, can contribute significantly to $\phi_p$ through inner core-mantle gravitational coupling. We show that the contribution to $\phi_p$ is largest when the inner core viscosity is in the range of $10^{13}$ to $10^{14}$ Pa s, when the inner core radius is large and when the free inner core nutation frequency approaches a resonance with the precession frequency of $2\pi/18.6$ yr$^{-1}$.

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O. Organowski and M. Dumberry
Tue, 4 Jan 22
28/58

Comments: 40 pages, 8 figures

Isostatic Modelling, Vertical Motion Rate Variation and Potential Detection of Past-Landslide in the Volcanic Island of Tahiti [CL]

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http://arxiv.org/abs/2201.00196


Intraplate volcanic islands are often considered as stable relief with constant vertical motion and used for relative sea-level curves reconstruction. This study shows that large landslides cause non-negligible isostatic adjustment. The vertical motion that occurred after landslide is quantified using a modelling approach. We show that a giant landslide caused a coastline uplift of 80-110 m for an elastic thickness of 15 km < $T_e$ < 20 km in Tahiti. Theoretical cases also reveal that a coastal motion of 1 m occurred for a landslide involving a displaced volume of 0.2 $km^3$ and influence relative sea-level reconstruction. In Tahiti, a change in the subsidence rate of 0.1 mm/yr (from 0.25 mm/yr to 0.15 mm/yr) occurred during the last 6 kyr and could be explained by a landslide involving a minimum volume of 0.2 $km^3$, $6 \pm 1$ kyr ago.

Read this paper on arXiv…

J. Gargani
Tue, 4 Jan 22
35/58

Comments: N/A

The influence of a fluid core and a solid inner core on the Cassini sate of Mercury [EPA]

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http://arxiv.org/abs/2201.00037


We present a model of the Cassini state of Mercury that comprises an inner core, a fluid core and a mantle. Our model includes inertial and gravitational torques between interior regions, and viscous and electromagnetic (EM) coupling at the boundaries of the fluid core. We show that the coupling between Mercury’s interior regions is sufficiently strong that the obliquity of the mantle spin axis deviates from that of a rigid planet by no more than 0.01 arcmin. The mantle obliquity decreases with increasing inner core size, but the change between a large and no inner core is limited to 0.015 arcmin. EM coupling is stronger than viscous coupling at the inner core boundary and, if the core magnetic field strength is above 0.3 mT, locks the fluid and solid cores into a common precession motion. Because of the strong gravitational coupling between the mantle and inner core, the larger the inner core is, the more this co-precessing core is brought into an alignment with the mantle, and the more the obliquity of the polar moment of inertia approaches that expected for a rigid planet. The misalignment between the polar moment of inertia and mantle spin axis increases with inner core size, but is limited to 0.007 arcmin. Our results imply that the measured obliquities of the mantle spin axis and polar moment of inertia should coincide at the present-day level of measurement errors, and cannot be distinguished from the obliquity of a rigid planet.

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M. Dumberry
Tue, 4 Jan 22
49/58

Comments: 33 pages, 7 figures

Digital Rock Typing DRT Algorithm Formulation with Optimal Supervised Semantic Segmentation [CL]

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http://arxiv.org/abs/2112.15068


Each grid block in a 3D geological model requires a rock type that represents all physical and chemical properties of that block. The properties that classify rock types are lithology, permeability, and capillary pressure. Scientists and engineers determined these properties using conventional laboratory measurements, which embedded destructive methods to the sample or altered some of its properties (i.e., wettability, permeability, and porosity) because the measurements process includes sample crushing, fluid flow, or fluid saturation. Lately, Digital Rock Physics (DRT) has emerged to quantify these properties from micro-Computerized Tomography (uCT) and Magnetic Resonance Imaging (MRI) images. However, the literature did not attempt rock typing in a wholly digital context. We propose performing Digital Rock Typing (DRT) by: (1) integrating the latest DRP advances in a novel process that honors digital rock properties determination, while; (2) digitalizing the latest rock typing approaches in carbonate, and (3) introducing a novel carbonate rock typing process that utilizes computer vision capabilities to provide more insight about the heterogeneous carbonate rock texture.

Read this paper on arXiv…

O. Alfarisi, D. Ouzzane, M. Sassi, et. al.
Mon, 3 Jan 22
30/49

Comments: N/A

The Understanding of Intertwined Physics: Discovering Capillary Pressure and Permeability Co-Determination [CL]

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http://arxiv.org/abs/2112.12784


Although capillary and permeability are the two most important physical properties controlling fluid distribution and flow in nature, the interconnectivity function between them was a pressing challenge. Because knowing permeability leads to determining capillary pressure. Geodynamics (e.g., subsurface water, CO2 sequestration) and organs (e.g., plants, blood vessels) depend on capillary pressure and permeability. The first determines how far the fluid can reach, while the second determines how fast the fluid can flow in porous media. They are also vital to designing synthetic materials and micro-objects like membranes and micro-robotics. Here, we reveal the capillary and permeability intertwined behavior function. And demonstrate the unique physical connectors: pore throat size and network, linking capillary pressure and permeability. Our discovery quantifies the inverse relationship between capillary pressure and permeability for the first time, which we analytically derived and experimentally proved.

Read this paper on arXiv…

O. Alfarisi, D. Ouzzane, M. Sassi, et. al.
Fri, 24 Dec 21
6/58

Comments: N/A

Long-term Trends of Regolith Movement on the Surface of Small Bodies [EPA]

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http://arxiv.org/abs/2112.12460


This paper studies the long-term migration of disturbed regolith materials on the surface of Solar System small bodies from the viewpoint of nonlinear dynamics. We propose an approximation model for secular mass movement, which combines the complex topography and irregular gravitational field. Choosing asteroid 101955 Bennu as a representative, the global change of the dynamical environment is examined, which presents a division of the creeping-sliding-shedding regions for a spun-up asteroid. In the creeping region, the dynamical equation of disturbed regolith grains is established based on the assumption of “trigger-slide” motion mode. The equilibrium points, local manifolds and large-scale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find for a low spin rate, the surface regolith grains flow toward the middle latitudes from the polar/equatorial regions, which is dominated by the gradient of the geopotential. While spun up to a high rate, regolith grains tend to migrate toward the equator, which happens in parallel with a topological shift of the local equilibria at low latitudes. From a long-term perspective, we find the equilibrium points dominate the global trends of regolith movements. Using the methodology developed in this paper, we give a prospect or retrospect to the secular motion of regolith materials during the spin-up process, and the results reveal a significant regulatory role of the equilibria. Through a detailed look at the dynamical scheme under different spin rates, we achieve a macro forecast of the global trends of regolith motion during the spin-up process, which explains the global geologic evolution driven by the long-term movements of regolith materials.

Read this paper on arXiv…

C. Huang, Y. Yu, B. Cheng, et. al.
Fri, 24 Dec 21
55/58

Comments: N/A

The Understanding of Intertwined Physics: Discovering Capillary Pressure and Permeability Co-Determination [CL]

Posted on by

http://arxiv.org/abs/2112.12784


Although capillary and permeability are the two most important physical properties controlling fluid distribution and flow in nature, the interconnectivity function between them was a pressing challenge. Because knowing permeability leads to determining capillary pressure. Geodynamics (e.g., subsurface water, CO2 sequestration) and organs (e.g., plants, blood vessels) depend on capillary pressure and permeability. The first determines how far the fluid can reach, while the second determines how fast the fluid can flow in porous media. They are also vital to designing synthetic materials and micro-objects like membranes and micro-robotics. Here, we reveal the capillary and permeability intertwined behavior function. And demonstrate the unique physical connectors: pore throat size and network, linking capillary pressure and permeability. Our discovery quantifies the inverse relationship between capillary pressure and permeability for the first time, which we analytically derived and experimentally proved.

Read this paper on arXiv…

O. Alfarisi, D. Ouzzane, M. Sassi, et. al.
Fri, 24 Dec 21
14/58

Comments: N/A

Long-term Trends of Regolith Movement on the Surface of Small Bodies [EPA]

Posted on by

http://arxiv.org/abs/2112.12460


This paper studies the long-term migration of disturbed regolith materials on the surface of Solar System small bodies from the viewpoint of nonlinear dynamics. We propose an approximation model for secular mass movement, which combines the complex topography and irregular gravitational field. Choosing asteroid 101955 Bennu as a representative, the global change of the dynamical environment is examined, which presents a division of the creeping-sliding-shedding regions for a spun-up asteroid. In the creeping region, the dynamical equation of disturbed regolith grains is established based on the assumption of “trigger-slide” motion mode. The equilibrium points, local manifolds and large-scale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find for a low spin rate, the surface regolith grains flow toward the middle latitudes from the polar/equatorial regions, which is dominated by the gradient of the geopotential. While spun up to a high rate, regolith grains tend to migrate toward the equator, which happens in parallel with a topological shift of the local equilibria at low latitudes. From a long-term perspective, we find the equilibrium points dominate the global trends of regolith movements. Using the methodology developed in this paper, we give a prospect or retrospect to the secular motion of regolith materials during the spin-up process, and the results reveal a significant regulatory role of the equilibria. Through a detailed look at the dynamical scheme under different spin rates, we achieve a macro forecast of the global trends of regolith motion during the spin-up process, which explains the global geologic evolution driven by the long-term movements of regolith materials.

Read this paper on arXiv…

C. Huang, Y. Yu, B. Cheng, et. al.
Fri, 24 Dec 21
48/58

Comments: N/A

Towards a Classification Scheme for the Rocky Planets based on Equilibrium Thermodynamic Considerations [EPA]

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http://arxiv.org/abs/2112.11404


A classification scheme for rocky planets is proposed, based on a description of the Earth System in terms of the Landau-Ginzburg Theory of phase transitions. Three major equilibrium states can be identified and the associated planetary states or phases are: Earth-like Holocene state; hot Venus-like state; cold Mars-like state. The scheme is based on an approach proposed to understand the Earth transition from the Holocene to the Anthropocene, driven by the impact of the human action on the Earth System. In the present work we identity the natural conditions that cause transformations on the planets forcing them into one of the states identified above. In analysing the relevant physical parameters, one is stroke by the similarities between Earth and Venus, and how likely is that the Anthropocene transition may lead to hot-house Earth scenario.

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O. Bertolami and F. Francisco
Wed, 22 Dec 21
45/67

Comments: 9 pages, 2 figures, 1 table

Distant formation and differentiation of outer main belt asteroids and carbonaceous chondrite parent bodies [EPA]

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http://arxiv.org/abs/2112.10284


Volatile compositions of asteroids provide information on the Solar System history and the origins of Earth’s volatiles. Visible to near-infrared observations at wavelengths of $<2.5\ {\rm \mu m}$ have suggested a genetic link between outer main belt asteroids located at $2.5$-$4\ {\rm au}$ and carbonaceous chondrite meteorites (CCs) that show isotopic similarities to volatile elements on Earth. However, recent longer wavelength data for large outer main belt asteroids show $3.1\ {\rm \mu m}$ absorption features of ammoniated phyllosilicates that are absent in CCs and cannot easily form from materials stable at those present distances. Here, by combining data collected by the AKARI space telescope and hydrological, geochemical, and spectral models of water-rock reactions, we show that the surface materials of asteroids having $3.1\ {\rm \mu m}$ absorption features and CCs can originate from different regions of a single, water-rock-differentiated parent body. Ammoniated phyllosilicates form within the water-rich mantles of the differentiated bodies containing NH$_3$ and CO$_2$ under high water-rock ratios ($>4$) and low temperatures ($<70^\circ$C). CCs can originate from the rock-dominated cores, that are likely to be preferentially sampled as meteorites by disruption and transport processes. Our results suggest that multiple large main belt asteroids formed beyond the NH$_3$ and CO$_2$ snow lines (currently $>10$ au) and could be transported to their current locations. Earth’s high hydrogen to carbon ratio may be explained by accretion of these water-rich progenitors.

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H. Kurokawa, T. Shibuya, Y. Sekine, et. al.
Tue, 21 Dec 21
48/86

Comments: 53 pages, 19 figures, 6 tables, accepted for publication in AGU Advances. The journal version will be published as open access at this https URL

Future radioisotope measurements to clarify the origin of deep-ocean 244Pu [HEAP]

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http://arxiv.org/abs/2112.09607


244Pu has been discovered in deep-ocean deposits spanning the past 10 Myr, a period that includes two 60Fe pulses from nearby supernovae. 244Pu is among the heaviest $r$-process products, and we consider whether the 244Pu was created in the supernovae, which is disfavored by model calculations, or in an earlier kilonova that seeded 244Pu in the nearby interstellar medium, which was subsequently swept up by the supernova debris. We propose probing these possibilities by measuring other $r$-process radioisotopes such as 129I and 182Hf in deep-ocean deposits and in lunar regolith.

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X. Wang, A. Clark, J. Ellis, et. al.
Mon, 20 Dec 21
13/59

Comments: 7 pages, 3 figures, 1 table, comments welcome

An Investigation of Libration Heating and the Thermal State of Enceladus's Ice Shell [EPA]

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http://arxiv.org/abs/2112.07038


Tidal dissipation is thought to be responsible for the observed high heat loss on Enceladus. Forced librations can enhance tidal dissipation in the ice shell, but how such librations affect the thermal state of Enceladus has not been investigated. Here we investigate the heating effect of forced librations using the model of Van Hoolst et al. (2013), which includes the elasticity of the ice shell. We find that libration heating in the ice shell is insufficient to match the inferred conductive heat loss of Enceladus. This suggests that either Enceladus is not in a thermal steady state, or additional heating mechanisms beneath the ice shell are contributing the bulk of the power. In the presence of such an additional heat source, Enceladus resides in a stable thermal equilibrium, resisting small perturbations to the shell thickness. Our results do not support the occurrence of a runaway melting process proposed by Luan and Goldreich (2017). In our study, the strong dependence of conductive loss on shell thickness stabilizes the thermal state of Enceladus’s ice shell. Our study implies that thermal runaway (if it occurred) or episodic heating on Enceladus is unlikely to originate from librations of the ice shell.

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W. Shao and F. Nimmo
Wed, 15 Dec 21
3/85

Comments: 22 Pages, 5 figures, published in Icarus

A new versatile method for the reconstruction of scintillator-based muon telescope events [CL]

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http://arxiv.org/abs/2112.07500


This paper presents a new method to process the data recorded with muon telescopes. We have developed this processing method for the plastic scintillator-based hodoscopes located around the volcano La Soufri`ere de Guadeloupe, in the French Lesser Antilles, in order to perform muon radiographies of the lava dome region, strongly impacted by the volcanic hydrothermal activity. Our method relies on particle trajectory reconstruction, performing a fit of the recorded hits in the impacted scintillator bars using a Random Sample Consensus algorithm. This algorithm is specifically built to discriminate outlier points, usually due to noise hits, in the data. Thus, it is expected to significantly improve the signal/noise separation in muon track hits and to obtain higher quality estimates of the particles’ incident trajectories in our detectors. The first analysis of the RANSAC-reconstructed events offers promising results in terms of average density maps. To illustrate the performances of this algorithm, we provide angular resolution and reconstruction efficiency estimates using a GEANT4 simulation of a telescope equipped with four detection matrices. In addition, we also show preliminary results from open-sky data recorded with such telescope at La Soufri`ere de Guadeloupe volcano.

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R. Bajou, M. Rosas-Carbajal and J. Marteau
Wed, 15 Dec 21
78/85

Comments: 6 pages, 7 figures, Muography 2021 workshop proceeding

Ancient and recent collisions revealed by phosphate minerals in the Chelyabinsk meteorite [EPA]

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http://arxiv.org/abs/2112.06038


The collision history of asteroids is an important archive of inner Solar System evolution. Evidence for these collisions is brought to Earth by meteorites, which can preserve impact-reset radioisotope mineral ages. However, as meteorites often preserve numerous mineral ages, their interpretation is controversial. Here, we combine analysis of phosphate U-Pb ages and mineral microtextures to construct a collision history for the highly shocked Chelyabinsk meteorite. We show that phosphate U-Pb ages in the meteorite are independent of thermal history at macro-to-microscales, correlating instead with phosphate microtexture. Isotopic data from pristine phosphate domains is largely concordant, whereas fracture-damaged domains universally display discordance. Combining both populations best constrains upper (4,473 +/- 11 Ma) and lower intercept (-9 +/- 55 Ma, i.e., within error of the present day) U-Pb ages for Chelyabinsk phosphates. We conclude that all phosphate U-Pb ages were completely reset during an ancient high energy collision. Fracture-damaged phosphate domains experienced further Pb-loss during mild collisional heating in the geologically recent past, and must be targeted to properly constrain a lower intercept age. Targeting textural sub-populations of phosphate grains can significantly improve the calculation and interpretation of U-Pb ages, permitting more robust reconstruction of both ancient and recent asteroidal collision histories.

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C. Walton, O. Shorttle, S. Hu, et. al.
Tue, 14 Dec 21
18/98

Comments: Accepted in Nature Communication Earth and Environment

Lifting of Tribocharged Grains by Martian Winds [EPA]

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http://arxiv.org/abs/2112.05471


It is a long-standing open question whether electrification of wind-blown sand due to tribocharging – the generation of electric charges on the surface of sand grains by particle-particle collisions – could affect rates of sand transport occurrence on Mars substantially. While previous wind tunnel experiments and numerical simulations addressed how particle trajectories may be affected by external electric fields, the effect of sand electrification remains uncertain. Here we show, by means of wind tunnel simulations under air pressure of 20 mbar, that the presence of electric charges on the particle surface can reduce the minimal threshold wind shear velocity for the initiation of sand transport, uft, significantly. In our experiments, we considered different samples, a model system of glass beads as well as a Martian soil analog, and different scenarios of triboelectrification. Furthermore, we present a model to explain the values of uft obtained in the wind tunnel that is based on inhomogeneously distributed surface charges. Our results imply that particle transport that subsides, once the wind shear velocity has fallen below the threshold for sustained transport, can more easily be restarted on Mars than previously thought.

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M. Kruss, T. Salzmann, E. Parteli, et. al.
Mon, 13 Dec 21
49/70

Comments: N/A

Hypotheses for Triton's Plumes: New Analyses and Future Remote Sensing Tests [EPA]

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http://arxiv.org/abs/2112.04627


At least two active plumes were observed on Neptune’s moon Triton during the Voyager 2 flyby in 1989. Models for Triton’s plumes have previously been grouped into five hypotheses, two of which are primarily atmospheric phenomena and are generally considered unlikely, and three of which include eruptive processes and are plausible. These hypotheses are compared, including new arguments, such as comparisons based on current understanding of Mars, Enceladus, and Pluto. An eruption model based on a solar-powered, solid-state greenhouse effect was previously considered the leading hypothesis for Triton’s plumes, in part due to the proximity of the plumes to the subsolar latitude during the Voyager 2 flyby and the distribution of Triton’s fans that are putatively deposits from former plumes. The other two eruption hypotheses are powered by internal heat, not solar insolation. Based on new analyses of the ostensible relation between the latitude of the subsolar point on Triton and the geographic locations of the plumes and fans, we argue that neither the locations of the plumes nor fans are strong evidence in favor of the solar-powered hypothesis. We conclude that all three eruption hypotheses should be considered further. Five tests are presented that could be implemented with remote sensing observations from future spacecraft to confidently distinguish among the eruption hypotheses for Triton’s plumes. The five tests are based on the: (1) composition and thickness of Triton’s southern hemisphere terrains, (2) composition of fan deposits, (3) distribution of active plumes, (4) distribution of fans, and (5) surface temperature at the locations of plumes and/or fans. The tests are independent, but complementary, and implementable with a single flyby mission such as the Trident mission concept. We note that, in the case of the solar-driven hypothesis, the 2030s and 2040s may be the last …

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J. Hofgartner, S. Birch, J. Castillo, et. al.
Fri, 10 Dec 21
52/94

Comments: Accepted for publication in Icarus

The InSight HP$^3$ Penetrator (Mole) on Mars: Soil Properties Derived From the Penetration Attempts and Related Activities [IMA]

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http://arxiv.org/abs/2112.04438


The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP$^3$ to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3–5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5-6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure – as was determined through an extensive, almost two years long campaign – was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign — described in detail in this paper — the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole finally reached a depth of 40 cm, bringing the mole body 1–2 cm below the surface. The penetration record of the mole and its thermal sensors were used to measure thermal and mechanical soil parameters such as the thermal conductivity and the penetration resistance of the duricrust and its cohesion. The hammerings of the mole were recorded by the seismometer SEIS and the signals could be used to derive a P-wave velocity and a S-wave velocity and elastic moduli representative of the topmost tens of cm of the regolith. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly consisting of debris from a small impact crater is inferred.

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T. Spohn, T. Hudson, E. Marteau, et. al.
Thu, 9 Dec 21
7/63

Comments: 78 pages 22 figures, , submitted to Space Science Reviews

Testing gravitational redshift base on microwave frequency links onboard China Space Station [IMA]

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http://arxiv.org/abs/2112.02759


In 2022 China Space Station (CSS) will be equipped with atomic clocks and optical clocks with stabilities of $2 \times 10^{-16}$ and $8 \times 10^{-18}$, respectively, which provides an excellent opportunity to test gravitational redshift (GR) with higher accuracy than previous results. Based on high-precise frequency links between CSS and a ground station, we formulated a model and provided simulation experiments to test GR. Simulation results suggest that this method could test the GR at the accuracy level of $(0.27 \pm 2.15) \times10^{-7}$, more than two orders in magnitude higher than the result of the experiment of a hydrogen clock on board a flying rocket more than 40 years ago.

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W. Shen, P. Zhang, Z. Shen, et. al.
Tue, 7 Dec 21
30/91

Comments: 6 pages, 5 figures

Near-Infrared reflectance spectroscopy of sublimating salty ice analogues. Implications for icy moons [EPA]

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http://arxiv.org/abs/2112.03063


The composition of the surface of the Galilean icy moons has been debated since the Galileo mission. Several chemistries have been proposed to explain the composition of the non-icy component of the moon’s surfaces, notably, sulphuric acid hydrates and magnesium and sodium sulphates. More recently, magnesium and sodium chlorides have been proposed to explain features observed in ground-based observations. We have considered four salts (NaCl, Na2SO4, MgSO4 and MgCl2) with various concentrations, to produce salty ice analogues. Granular particles were produced by a flash-freezing procedure. Additionally, compact slabs of salty ices were produced by a slow crystallisation of salty liquid solution. These two methods mimic the end-members (plumes and slow ice block formation) for producing hydrated salty ices on the surface of icy moons such as Europa and Ganymede. We have monitored the near-infrared (NIR) evolution of our salty ices during sublimation, revealing differences between the granular particles and the slabs. The slabs formed a higher amount of hydrates and the most highly hydrated compounds. Granular ices must be formed from a more concentrated salty solution to increase the amount of hydrates within the ice particles. The sublimation of salty ices removed all excess water ice efficiently, but the dehydration of the salts was not observed. The final spectra of the slabs were most flattened around 1.5 and 2.0 {\mu}m, especially for the Na2SO4, MgCl2 and MgSO4, suggesting the presence of stable, highly hydrated compounds. We find that Na2SO4, MgCl2 and MgSO4 are most compatible with the non-icy component at the surface of the icy moons as observed by the NIMS instrument on Galileo and by ground-based observations.

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R. Cerubini, A. Pommerol, Z. Yoldi, et. al.
Tue, 7 Dec 21
53/91

Comments: 71 pages with 16 figures

The InSight HP^3 mole on Mars: Lessons learned from attempts to penetrate to depth in the Martian soil [IMA]

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http://arxiv.org/abs/2112.03234


The NASA InSight mission payload includes the Heat Flow and Physical Properties Package HP^3 to measure the surface heat flow. The package was designed to use a small penetrator – nicknamed the mole – to implement a string of temperature sensors in the soil to a depth of 5m. The mole itself is equipped with sensors to measure a thermal conductivity as it proceeds to depth. The heat flow would be calculated from the product of the temperature gradient and the thermal conductivity. To avoid the perturbation caused by annual surface temperature variations, the measurements would be taken at a depth between 3 m and 5 m. The mole was designed to penetrate cohesionless soil similar to Quartz sand which was expected to provide a good analogue material for Martian sand. The sand would provide friction to the buried mole hull to balance the remaining recoil of the mole hammer mechanism that drives the mole forward. Unfortunately, the mole did not penetrate more than a mole length of 40 cm. The failure to penetrate deeper was largely due to a few tens of centimeter thick cohesive duricrust that failed to provide the required friction. Although a suppressor mass and spring in the hammer mechanism absorbed much of the recoil, the available mass did not allow a system that would have eliminated the recoil. The mole penetrated to 40 cm depth benefiting from friction provided by springs in the support structure from which it was deployed. It was found in addition that the Martian soil provided unexpected levels of penetration resistance that would have motivated to designing a more powerful mole. It is concluded that more mass would have allowed to design a more robust system with little or no recoil, more energy of the mole hammer mechanism and a more massive support structure.

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T. Spohn, T. Hudson, L. Witte, et. al.
Tue, 7 Dec 21
58/91

Comments: 34 pages, 15 figures, submitted to Adnaves in Space Research

Constraints on the production of phosphine by Venusian volcanoes [EPA]

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http://arxiv.org/abs/2112.00140


The initial reports of the presence of phosphine in the cloud decks of Venus has led to the suggestion that volcanism was the source of phosphine, through volcanic phosphides ejected into the clouds. Here we examine the idea that mantle plume volcanism, bringing material from the deep mantle to the surface, could generate observed amounts of phosphine through interaction of explosively erupted phosphide with sulfuric acid clouds. Direct eruption of deep mantle phosphide is unphysical, but shallower material could contain traces of phosphide, and could be erupted to the surface. Explosive eruption that efficiently transported material to the clouds would require ocean:magma interactions or subduction of hydrated oceanic crust, neither of which occur on modern Venus. The transport of erupted material to altitudes coinciding with the observations of phosphine is consequently very inefficient. Using the model proposed by Truong and Lunine as a base case, we estimate that an eruption volume of at least 21,600 km3/year would be required to explain the presence of 1 ppb phosphine in the clouds. This is greater than any historical terrestrial eruption rate, and would have several detectable consequences for remote and in situ observations to confirm. More realistic lithospheric chemistry or atmospheric photochemistry require even more volcanism.

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W. Bains, O. Shorttle, S. Ranjan, et. al.
Thu, 2 Dec 21
20/61

Comments: The paper expands on and confirms the results of Bains et al. 2021 arXiv:2009.06499 and provides further constrains on the model of the production of phosphine on Venus proposed by Truong and Lunine this https URL

Very weak carbonaceous asteroid simulants I: mechanical properties and response to hypervelocity impacts [EPA]

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http://arxiv.org/abs/2111.15279


The two on-going sample return space missions, Hayabusa2 and OSIRIS-REx are going to return to Earth asteroid regolith from the carbonaceous near-Earth asteroids Ryugu and Bennu. The two main processes that lead to regolith production are the micrometeorite bombardment and the thermal cracking. Here we report the production of a weak simulant material, analogue to carbonaceous meteorites with a CM-like composition, following the preliminary compositional results for Bennu and Ryugu. This asteroid simulant has compressive and flexural strength 1.8+/-0.17 and 0.7+/-0.07 MPa, respectively. The thermal conductivity (in air) of the simulant at room temperature is between 0.43 and 0.47 W/m/K. In order to distinguish the type of regolith that is produced by each of these processes, we present and discuss the results of the experimental campaign focused on laboratory hypervelocity impacts, using the 2-stage light-gas gun of the University of Kent, that mimic the micrometeorite bombardment. We find that this process produces both monomineralic and multimineralic fragments, resulting in a difficulty to distinguish the two processes, at least on these weak materials.

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C. Avdellidou, A. DiDonna, C. Schultz, et. al.
Wed, 1 Dec 21
50/110

Comments: N/A

Early differentiation of magmatic iron meteorite parent bodies from Mn-Cr chronometry [EPA]

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http://arxiv.org/abs/2111.15291


Magmatic iron meteorite groups such as IIAB, IIIAB and IVA, represent the largest sampling of extraterrestrial core material from the earliest accreted distinct planetary bodies in the solar system. Chromium isotope compositions of chromite/daubreelite from seven samples, translated into 53Cr/52Cr model ages, provide robust time information on planetary core formation. These ages range within 1.5 Ma after formation of calcium-aluminium-rich inclusions (CAIs) and define the time of metal core formation in the respective parent bodies, assuming metal-silicate separation was an instantaneous event that induced strong chemical fractionation of Mn from the more siderophile Cr. The early core formation ages support accretion and differentiation of the magmatic iron meteorite parent bodies to have occurred prior to the chondrule formation interval. The calibration of Mn-Cr ages with established Hf-W ages of samples from the same magmatic iron meteorite groups constrains the initial E53Cr of the solar system to -0.30, and thus lower than previously estimated.

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A. Anand, J. Pape, M. Wille, et. al.
Wed, 1 Dec 21
82/110

Comments: Accepted for publication in Geochemical Perspective Letters

Applications for CryoSat2 satellite magnetic data in studies of Earth's core field variations [EPA]

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http://arxiv.org/abs/2111.14538


We use 20 years of magnetic field measurements from the Oersted, CHAMP and Swarm satellite missions, supplemented by calibrated platform magnetometer data from the CryoSat2 satellite, to study time variations of the Earth’s core field at satellite altitude and at the core-mantle boundary (CMB). From the satellite data we derive composite time series of the core field secular variation (SV) with 4month cadence, at 300 globally distributed Geomagnetic Virtual Observatories (GVO). GVO radial SV series display regional fluctuations with 5-10 years duration and amplitudes reaching 20 nT/yr, most notably at low latitudes over Indonesia (2014), over South America and the South Atlantic (2007, 2011 and 2014), and over the central Pacific (2017). Applying the Subtractive Optimally Localized Averages (SOLA) method, we map the SV at the CMB as a collection of locally averaged SV estimates. We demonstrate that using 2-year windows of CryoSat2 data, it is possible to reliably estimate the SV and its time derivative, the secular acceleration (SA), at the CMB, with a spatial resolution, corresponding to spherical harmonic degree 10. Along the CMB geographic equator, we find strong SA features under Indonesia from 2011-2014, under central America from 2015 to 2019, and sequences of SA with alternating sign under the Atlantic during 2004-2019. We find that data from CryoSat2 make a valuable contribution to the emerging picture of sub-decadal core field variations. Using 1 year windows of data from the Swarm satellites, it is possible to study SA changes at low latitudes on timescales down to 1 year, with spatial resolution corresponding to spherical harmonic degree 10. We find strong positive and negative SA features appearing side-by-side in the Pacific in 2017, and thereafter drift westward.

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M. Hammer, C. Finlay and N. Olsen
Tue, 30 Nov 21
75/105

Comments: N/A

New evidence for wet accretion of inner solar system planetesimals from meteorites Chelyabinsk andBenenitra [EPA]

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http://arxiv.org/abs/2111.13804


We investigated the hydrogen isotopic compositions and water contents of pyroxenes in two recent ordinary chondrite falls, namely, Chelyabinsk (2013 fall) and Benenitra (2018 fall), and compared them to three ordinary chondrite Antarctic finds, namely Graves Nunataks GRA 06179, Larkman Nunatak LAR 12241, and Dominion Range DOM 10035. The pyroxene minerals in Benenitra and Chelyabinsk are hydrated ($\sim$0.018-0.087 wt.$\%$ H$2$O) and show D-poor isotopic signatures ($\delta$D${SMOW}$ from -444$\unicode{x2030}$ to -49$\unicode{x2030}$). On the contrary, the ordinary chondrite finds exhibit evidence of terrestrial contamination with elevated water contents ($\sim$0.039-0.174 wt.$\%$) and values (from -199$\unicode{x2030}$ to -14$\unicode{x2030}$). We evaluated several small parent body processes that are likely to alter the measured compositions in Benenitra and Chelyabinsk, and inferred that water-loss in S-type planetesimals is minimal during thermal metamorphism. Benenitra and Chelyabinsk hydrogen compositions reflect a mixed component of D-poor nebular hydrogen and water from the D-rich mesostases. 45-95$\%$ of water in the minerals characterized by low $\delta$D$_{SMOW}$ values was contributed by nebular hydrogen. S-type asteroids dominantly composed of nominally anhydrous minerals can hold 254-518 ppm of water. Addition of a nebular water component to nominally dry inner Solar System bodies during accretion suggests a reduced need of volatile delivery to the terrestrial planets during late accretion.

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Z. Jin, M. Bose, T. Lichtenberg, et. al.
Tue, 30 Nov 21
82/105

Comments: 18 pages, 7 figures, accepted for publication in The Planetary Science Journal

Aggregation of Sub-mm Particles in Strong Electric Fields under Microgravity Conditions [EPA]

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http://arxiv.org/abs/2111.13402


Dust emission mechanisms as one aspect of wind-driven particle motion on planetary surfaces are still poorly understood. The microphysics is important though as it determines dust sizes and morphologies which set sedimentation speeds and optical properties. We consider the effects of tribocharging in this context as grains in wind driven granular matter charge significantly. This leads to large electric fields above the granular bed. Airborne dielectric grains are polarized in these electric fields, which leads to attractive forces between grains. To simulate aggregation under these conditions we carried out drop tower experiments using tracer particles, mimicking the gas coupling behavior of small dust grains in terms of high surface to mass ratios and efficient gas drag. Under microgravity, the particles are released into an observation chamber in which an alternating electric field up to 80 kV/m is applied. Without electric field no aggregation can be observed on timescales of seconds. However, polarization instantly leads to aggregation of particles when the field is switched on and long chains aligned to the electric field form. Scaled to dust entrained into planetary atmospheres, fine and coarse grain fractions might readily form aggregates after being liberated. Under certain natural conditions, aggregates might therefore start chain-like or at least a chain-like appearance is favored. If atmospheric influences on their stability are small, aerodynamic and optical properties might depend on this.

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F. Jungmann, M. Kruss, J. Teiser, et. al.
Mon, 29 Nov 21
45/94

Comments: N/A

Condensation of cometary silicate dust using an induction thermal plasma system I. Enstatite and CI chondritic composition [EPA]

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http://arxiv.org/abs/2111.10955


Glass with embedded metal and sulfides (GEMS) is a major component of chondritic porous interplanetary dust particles. Although GEMS is one of the most primitive components in the Solar System, its formation process and conditions have not been constrained. We performed condensation experiments of gases in the system of Mg-Si-O (MgSiO3 composition) and of the S-free CI chondritic composition (Si-Mg-Fe-Na-Al-Ca-Ni-O system) in induction thermal plasma equipment. Amorphous Mg-silicate particles condensed in the experiments of the Mg-Si-O system, and their grain size distribution depended on the experimental conditions (mainly partial pressure of SiO). In the CI chondritic composition experiments, irregularly shaped amorphous silicate particles of less than a few hundred nanometers embedded with multiple Fe-Ni nanoparticles of ~<20 nm were successfully synthesized. These characteristics are very similar to those of GEMS, except for the presence of FeSi instead of sulfide grains. We propose that the condensation of amorphous silicate grains smaller than a few tens of nanometers and with metallic cores, followed by coagulation, could be the precursor material that forms GEMS prior to sulfidation.

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T. Kim, A. Takigawa, A. Tsuchiyama, et. al.
Tue, 23 Nov 21
41/84

Comments: N/A

Growth and evolution of secondary volcanic atmospheres: I. Identifying the geological character of warm rocky planets [EPA]

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http://arxiv.org/abs/2111.05161


The geology of Earth and super-Earth sized planets will, in many cases, only be observable via their atmospheres. Here, we use the creation of volcanic atmospheres as a key window into planetary geochemistry. We couple volcanic outgassing with atmospheric chemistry models to simulate the growth of C-O-H-S-N atmospheres in thermochemical equilibrium, aiming to establish what information about the planet’s mantle fO2 and bulk silicate H/C ratio can be determined by atmospheric observation. Warm (800 K) volcanic atmospheres develop distinct compositional groups as the mantle fO2 is varied, which can be identified using sets of (often minor) indicator species: Class O, representing an oxidised mantle and containing SO2 and sulfur allotropes; Class I, formed by intermediate mantle fO2’s and containing CO2, CH4, CO and COS; and Class R, produced by reduced mantles, containing H2, NH3 and CH4. These atmospheric classes are largely independent of the bulk silicate H/C ratio. However, the H/C ratio does affect the dominant atmospheric constituent, which can vary between H2, H2O, CO2 and CH4 once the chemical composition has stabilised to a point where it no longer changes substantially with time. This final state is dependent on the mantle fO2, the H/C ratio, and time since the onset of volcanism. Superchondritic H/C enrichment to the level of Earth (H/C = 0.99 +/- 0.42) and higher can only be inferred for planets with reduced mantles producing Class R atmospheres. On warm, volcanically active planets, mantle fO2 could be identifiable from atmospheric observations using JWST.

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P. Liggins, S. Jordan, P. Rimmer, et. al.
Wed, 10 Nov 21
27/63

Comments: Submitted to JGR:Planets

An investigation of factors affecting high-precision Sr isotope analyses (87Sr/86Sr and δ88/86Sr) by MC-ICP-MS [CL]

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http://arxiv.org/abs/2111.02942


The abundance and fractionation of the stable strontium (Sr) isotope system are being increasingly utilized to move forward our understanding in geological and cosmological processes. Two analytical techniques are commonly used to measure stable Sr isotopes: 1) double-spike thermal ionization mass spectrometry (DS-TIMS) and 2) Zr-doped sample-standard bracketing multi-collector inductively coupled plasma mass spectrometry (Zr-doped SSB via MC-ICP-MS). Relative to DS-TIMS, Zr-doped SSB via MC-ICP-MS allows simultaneous determinations of both 87Sr/86Sr and 88Sr/86Sr ratios, increasing measurement efficiency and sample throughput. However, this technique is currently associated with greater uncertainties in measurement precision and accuracy. In this study, we evaluated potential factors that can affect the quality of Sr isotope measurements during Zr-doped SSB. Our tests show that incomplete Sr recovery during chromatographic separation, mismatches of Sr and Zr concentrations and acid molarity between sample and bracketing standard, and cation contamination could all affect the precision and accuracy of Sr isotope measurements. We present evidence that, with updated preparation procedures and diligent concentration checks, a long-term reproducibility (2{\sigma}SD: 87Sr/86Sr = +/-0.000015 and {\delta}88/86Sr = +/-0.03 permil) comparable to that of DS-TIMS is achievable when using the Zr-doped SSB method via MC-ICP-MC.

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J. Wang, D. Asael, N. Planavsky, et. al.
Fri, 5 Nov 21
49/72

Comments: N/A

Study of spectrally resolved thermoluminescence in Tsarev and Chelyabinsk chondrites with a versatile high-sensitive setup [EPA]

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http://arxiv.org/abs/2111.01405


Thermoluminescence (TL) research provides a powerful tool for characterizing radiation-induced processes in extraterrestrial matter. One of the challenges in studying the spectral features of the natural TL of stony meteorites is its weak intensity. The present work showcases the capabilities of a high-sensitive original module for measuring the spectrally resolved TL characteristics of the Chelyabinsk and Tsarev chondrites. We have analyzed the emission spectra and glow curves of natural and induced TL over the 300 – 650 nm and RT – 873 K ranges. A quasi-continuous distribution of traps active within the 350 – 650 K range was found in the silicate substructure of both meteorites under study. Based on the general order kinetic formalism and using the natural TL data, we also estimated the activation energies of 0.86 and 1.08 eV for the Chelyabinsk and Tsarev chondrites, respectively.

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A. Vokhmintsev, A. Henaish, T. Sharshar, et. al.
Wed, 3 Nov 21
74/106

Comments: 7 pages, 4 figures, 2 tables, 18 references; Keywords: TL spectroscopy; ordinary chondrite; Chelyabinsk LL5; Tsarev L5; activation energy

Reproducing size distributions of swarms of barchan dunes on Mars and Earth using a mean-field model [CL]

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http://arxiv.org/abs/2110.15850


We apply a mean-field model of interactions between migrating barchan dunes, the CAFE model, which includes calving, aggregation, fragmentation, and mass-exchange, yielding a steady-state size distribution that can be resolved for different choices of interaction parameters. The CAFE model is applied to empirically measured distributions of dune sizes in two barchan swarms on Mars, three swarms in Morocco, and one in Mauritania, each containing ~1000 bedforms, comparing the observed size distributions to the steady-states of the CAFE model. We find that the distributions in the Martian swarm are very similar to the swarm measured in Mauritania, suggesting that the two very different planetary environments however share similar dune interaction dynamics. Optimisation of the model parameters of three specific configurations of the CAFE model shows that the fit of the theoretical steady-state is often superior to the typically assumed log-normal. In all cases, the optimised parameters indicate that mass-exchange is the most frequent type of interaction. Calving is found to occur rarely in most of the swarms, with a highest rate of only 9\% of events, showing that interactions between multiple dunes rather than spontaneous calving are the driver of barchan size distributions. Finally, the implementation of interaction parameters derived from 3D simulations of dune-pair collisions indicates that sand flux between dunes is more important in producing the size distributions of the Moroccan swarms than of those in Mauritania and on Mars.

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D. Robson, A. Annibale and A. Baas
Mon, 1 Nov 21
21/58

Comments: 30 Pages, 10 figures, Submitted to Physica A: Statistical Mechanics and its Applications

Numerous chondritic impactors and oxidized magma ocean set Earth's volatile depletion [EPA]

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http://arxiv.org/abs/2110.12195


Earth’s surface environment is largely influenced by its budget of major volatile elements: carbon (C), nitrogen (N), and hydrogen (H). Although the volatiles on Earth are thought to have been delivered by chondritic materials, the elemental composition of the bulk silicate Earth (BSE) shows depletion in the order of N, C, and H. Previous studies have concluded that non-chondritic materials are needed for this depletion pattern. Here, we model the evolution of the volatile abundances in the atmosphere, oceans, crust, mantle, and core through the accretion history by considering elemental partitioning and impact erosion. We show that the BSE depletion pattern can be reproduced from continuous accretion of chondritic bodies by the partitioning of C into the core and H storage in the magma ocean in the main accretion stage and atmospheric erosion of N in the late accretion stage. This scenario requires a relatively oxidized magma ocean ($\log_{10} f_{\rm O_2}$ $\gtrsim$ $\rm{IW}$$-2$, where $f_{\rm O_2}$ is the oxygen fugacity, ${\rm IW}$ is $\log_{10} f_{\rm O_2}^{\rm IW}$, and $f_{\rm O_2}^{\rm IW}$ is $f_{\rm O_2}$ at the iron-w\”{u}stite buffer), the dominance of small impactors in the late accretion, and the storage of H and C in oceanic water and carbonates in the late accretion stage, all of which are naturally expected from the formation of an Earth-sized planet in the habitable zone.

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H. Sakuraba, H. Kurokawa, H. Genda, et. al.
Tue, 26 Oct 21
48/109

Comments: 17 pages, 4 figures (comprising 11 panels in total), 1 table, Methods, and Supplementary Information (available online: this https URL)

Dynamic Split Tensile Strength of Basalt, Granite, Marble and Sandstone: Strain rate dependency and Fragmentation [CL]

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http://arxiv.org/abs/2110.10072


The scope of this study is to understand the strength behaviour and fragment size of rocks during indirect, quasi-static, and dynamic tensile tests. Four rocks with different lithological characteristics namely, basalt, granite, sandstone and marble are selected. The Brazilian disc experiments are performed over a range of strain rates from 10-5 /s to 2.7×101 /s using a hydraulic loading frame and a split-Hopkinson bar. Over the range of strain rates, our measurements of dynamic strength increase are in good agreement with the universal theoretical scaling relationship of Kimberley et al. (2013). Dynamic fragmentation during a split tension mode receives very little attention and not much information is available about the generated fragment size distributions. The fragments fall into two distinct groups based on the nature of failure, coarser primary fragments and finer secondary fragments. The degree of fragmentation is assessed in terms of characteristic strain rate and is compared with existing theoretical tensile fragmentation models. The primary fragment size are less sensitive to strain rate, particularly at lower strain rates. The size of secondary fragment has a strong strain rate dependency over the entire testing range. Marble and sandstone are found to generate more pulverized secondary debris when compared to basalt and granite. Further, it is shown that the mean fragment sizes of primary and secondary fragments are well described by a power law function of strain rate.

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V. Padmanabha, F. Schaefer, A. Rae, et. al.
Wed, 20 Oct 21
43/67

Comments: 32 Pages, 11 Figures and 3 Tables

Dynamic Split Tensile Strength of Basalt, Granite, Marble and Sandstone: Strain rate dependency and Fragmentation [CL]

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http://arxiv.org/abs/2110.10072


The scope of this study is to understand the strength behaviour and fragment size of rocks during indirect, quasi-static, and dynamic tensile tests. Four rocks with different lithological characteristics namely, basalt, granite, sandstone and marble are selected. The Brazilian disc experiments are performed over a range of strain rates from 10-5 /s to 2.7×101 /s using a hydraulic loading frame and a split-Hopkinson bar. Over the range of strain rates, our measurements of dynamic strength increase are in good agreement with the universal theoretical scaling relationship of Kimberley et al. (2013). Dynamic fragmentation during a split tension mode receives very little attention and not much information is available about the generated fragment size distributions. The fragments fall into two distinct groups based on the nature of failure, coarser primary fragments and finer secondary fragments. The degree of fragmentation is assessed in terms of characteristic strain rate and is compared with existing theoretical tensile fragmentation models. The primary fragment size are less sensitive to strain rate, particularly at lower strain rates. The size of secondary fragment has a strong strain rate dependency over the entire testing range. Marble and sandstone are found to generate more pulverized secondary debris when compared to basalt and granite. Further, it is shown that the mean fragment sizes of primary and secondary fragments are well described by a power law function of strain rate.

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V. Padmanabha, F. Schaefer, A. Rae, et. al.
Wed, 20 Oct 21
29/67

Comments: 32 Pages, 11 Figures and 3 Tables

The number and location of Jupiter's circumpolar cyclones explained by vorticity dynamics [EPA]

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http://arxiv.org/abs/2110.09422


The Juno mission observed that both poles of Jupiter have polar cyclones that are surrounded by a ring of circumpolar cyclones. The North Pole holds eight circumpolar cyclones and the South Pole possesses five, with both circumpolar rings positioned along latitude ~84{\deg} N/S. Here we explain the location, stability, and number of the Jovian circumpolar cyclones by establishing the primary forces that act on them, which develop because of vorticity gradients in the background of a cyclone. In the meridional direction, the background vorticity varies owning to the planetary sphericity and the presence of the polar cyclone. In the zonal direction, the vorticity varies by the presence of adjacent cyclones in the ring. Our analysis successfully predicts the latitude and number of circumpolar cyclones for both poles, according to the size and spin of the respective polar cyclone. Moreover, the analysis successfully predicts that Jupiter can hold circumpolar cyclones while Saturn currently cannot. The match between the theory and observations implies that vortices in the polar regions of the giant planets are largely governed by barotropic dynamics, and that the movement of other vortices at high-latitudes is also driven by interaction with the background vorticity.

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N. Gavriel and Y. Kaspi
Tue, 19 Oct 21
3/98

Comments: 13 Pages, 8 figures

Dependence of the initial internal structure of chondrule rim on dust size distribution [EPA]

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http://arxiv.org/abs/2110.08564


Coarse objects in chondrites such as chondrules and CAIs are mostly coated with fine-grained rims (FGRs). FGRs can be formed on the surface of free floating chondrules in a turbulent nebula, where dust aggregation also occurs. A former study has reported that the morphology of the dust populations accreting onto chondrules affects the initial structures of FGRs. It was revealed that, if monomer grains accrete onto chondrules, the smaller grains tend to accumulate near the surface of chondrules, and FGRs exhibit grain size coarsening from the bottom to the top. However, the study did not consider the effect of temporal growth of dust aggregates on FGRs formation. In this study, we calculate the aggregation of polydisperse monomer grains and their accretion onto chondrules. The following two different stages of dust aggregation can be identified: the monomer-aggregation stage and the BCCA-like stage. In the monomer-aggregation stage, monomer grains are incorporated into aggregates when the average aggregate size reaches the size of the monomer. In the BCCA-like stage, aggregates evolve fractally in a fashion similar to that of single size monomer grains. Based on the results of the previous study, we obtain the requisite conditions for chondrules to acquire monomer-accreting FGRs with grain size coarsening observed in some chondrites. In the case of similar size distribution as that of Inter Stellar Medium (ISM), the maximum grain size of $>$ $1$ $\mu$m is widely ($\alpha$ $<$ $10^{-3}$) required for monomer accretion, while if turbulent intensity in a nebula is extremely weak ($\alpha$ $<$ $10^{-5}$), a maximum grain size $\sim$ $10$ $\mu$m is required. The monomer size distributions having larger mass fraction in the large grains compared to ISM might be necessary for the effective grain size coarsening.

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H. Kaneko, S. Arakawa and T. Nakamoto
Tue, 19 Oct 21
42/98

Comments: 56 pages, 20 figures, 6 tables. Accepted for publication in Icarus

Paleomagnetic evidence for a disk substructure in the early solar system [EPA]

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http://arxiv.org/abs/2110.09500


Astronomical observations and isotopic measurements of meteorites suggest that substructures are common in protoplanetary disks and may even have existed in the solar nebula. Here, we conduct paleomagnetic measurements of chondrules in CO carbonaceous chondrites to investigate the existence and nature of these disk sub-structures. We show that the paleomagnetism of chondrules in CO carbonaceous chondrites indicates the presence of a 101 $\pm$ 48 $\mu$T field in the solar nebula in the outer solar system ($\sim$3 to 7 AU from the Sun). The high intensity of this field relative to that inferred from inner solar system ($\lesssim$3 AU) meteorites indicates a factor of $\sim$5 to 150 mismatch in nebular accretion between the two reservoirs. This suggests substantial mass loss from the disk associated with a major disk substructure, possibly due to a magnetized disk wind.

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C. Borlina, B. Weiss, J. Bryson, et. al.
Tue, 19 Oct 21
67/98

Comments: 16 pages, 3 figures, published in Science Advances

Earth's accretion inferred from iron isotopic anomalies of supernova nuclear statistical equilibrium origin [EPA]

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http://arxiv.org/abs/2110.06045


Nucleosynthetic Fe isotopic anomalies in meteorites may be used to reconstruct the early dynamical evolution of the solar system and to identify the origin and nature of the material that built planets. Using high-precision iron isotopic data of 23 iron meteorites from nine major chemical groups we show that all iron meteorites show the same fundamental dichotomy between non-carbonaceous (NC) and a carbonaceous (CC) meteorites previously observed for other elements. The Fe isotopic anomalies are predominantly produced by variation in 54Fe, where all CC iron meteorites are characterized by an excess in 54Fe relative to NC iron meteorites. This excess in 54Fe is accompanied by an excess in 58Ni observed in the same CC meteorite groups. Together, these overabundances of 54Fe and 58Ni are produced by nuclear statistical equilibrium either in type Ia supernovae or in the Si/S shell of core-collapse supernovae. The new Fe isotopic data reveal that Earth’s mantle plots on or close to correlations defined by Fe, Mo, and Ru isotopic anomalies in iron meteorites, indicating that throughout Earth’s accretion, the isotopic composition of its building blocks did not drastically change. While Earth’s mantle has a similar Fe isotopic composition to CI chondrites, the latter are clearly distinct from Earth’s mantle for other elements (e.g., Cr and Ni) whose delivery to Earth coincided with Fe. The fact that CI chondrites exhibit large Cr and Ni isotopic anomalies relative to Earth’s mantle, therefore, demonstrates that CI chondrites are unlikely to have contributed significant Fe to Earth.

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T. Hopp, N. Dauphas, F. Spitzer, et. al.
Wed, 13 Oct 21
53/80

Comments: 1 Table, 9 Figures

Towards Adaptive Simulations of Dispersive Tsunami Propagation from an Asteroid Impact [CL]

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http://arxiv.org/abs/2110.01420


The long-term goal of this work is the development of high-fidelity simulation tools for dispersive tsunami propagation. A dispersive model is especially important for short wavelength phenomena such as an asteroid impact into the ocean, and is also important in modeling other events where the simpler shallow water equations are insufficient. Adaptive simulations are crucial to bridge the scales from deep ocean to inundation, but have difficulties with the implicit system of equations that results from dispersive models. We propose a fractional step scheme that advances the solution on separate patches with different spatial resolutions and time steps. We show a simulation with 7 levels of adaptive meshes and onshore inundation resulting from a simulated asteroid impact off the coast of Washington. Finally, we discuss a number of open research questions that need to be resolved for high quality simulations.

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M. Berger and R. LeVeque
Tue, 5 Oct 21
11/72

Comments: 16 pages, 5 figures, submitted to Proc. International Congress of Mathematicians, 2022

Nucleosynthetic Pt isotope anomalies and the Hf-W chronology of core formation in inner and outer solar system planetesimals [EPA]

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http://arxiv.org/abs/2109.15250


The 182Hf-182W chronology of iron meteorites provides crucial information on the timescales of accretion and differentiation of some of the oldest planetesimals of the Solar System. Determining accurate Hf-W model ages of iron meteorites requires correction for cosmic ray expo-sure (CRE) induced modifications of W isotope compositions, which can be achieved using in-situ neutron dosimeters such as Pt isotopes. Until now it has been assumed that all Pt isotope variations in meteorites reflect CRE, but here we show that some ungrouped iron meteorites display small nucleosynthetic Pt isotope anomalies. These provide the most appropriate starting composition for the correction of CRE-induced W isotope variations in iron meteorites from all major chemical groups, which leads to a ~1 Ma upward revision of previously reported Hf-W model ages. The revised ages indicate that core formation in non-carbonaceous (NC) iron meteorite parent bodies occurred at ~1-2 Ma after CAI formation, whereas most carbonaceous (CC) iron meteorite parent bodies underwent core formation ~2 Ma later. We show that the younger CC cores have lower Fe/Ni ratios than the earlier-formed NC cores, indicating that core formation under more oxidizing conditions occurred over a more protracted timescale. Thermal modeling of planetesimals heated by 26Al-decay reveals that this protracted core formation timescale is consistent with a higher fraction of water ice in CC compared to NC planetesimals, implying that in spite of distinct core formation timescales, NC and CC iron meteorite parent bodies accreted about contemporaneously within ~1 Ma after CAI formation, but at different radial locations in the disk.

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F. Spitzer, C. Burkhardt, F. Nimmo, et. al.
Fri, 1 Oct 21
14/65

Comments: Accepted for publication in Earth and Planetary Science Letters

Large-scale Vortices in Rapidly Rotating Rayleigh-Bénard Convection at Small Prandtl number [CL]

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http://arxiv.org/abs/2109.14289


One prominent feature in the atmospheres of Jupiter and Saturn is the appearance of large-scale vortices. However, the sustaining mechanism of these large-scale vortices remains unclear. One possible mechanism is that these large-scale vortices are driven by rotating convection. Here we present numerical simulation results on rapidly rotating Rayleigh-B\’enard convection at a small Prandtl number $Pr=0.1$ (close to the turbulent Prandtl numbers of Jupiter and Saturn). We have identified four flow regimes in our simulation: multiple small vortices, coexisted large-scale cyclone and anticyclone, large-scale cyclone, and turbulence. The formation of large-scale vortices requires two conditions to be satisfied: the vertical Reynolds number is large ($Re_{z}\ge 400$), and the Rossby number is small ($Ro\leq 0.4$). Large-scale cyclone first appears when $Ro$ decreases to be smaller than 0.4. When $Ro$ further decreases to be smaller than 0.1, coexisted large-scale anticyclone emerges. We have studied the heat transfer in rapidly rotating convection. The result reveals that the heat transfer is more efficient in the anticyclonic region than in the cyclonic region. Besides, we find that 2D effect increases and 3D effect decreases in transporting convective flux as rotation rate increases. We find that aspect ratio has an effect on the critical Rossby number for the emergence of large-scale vortices. Our results provide helpful insights on understanding the dynamics of large-scale vortices in gas giants.

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T. Cai
Thu, 30 Sep 21
70/82

Comments: Accepted to ApJ

A method to distinguish between micro- and macro-granular surfaces of small Solar System bodies [EPA]

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http://arxiv.org/abs/2109.12833


The surface granularity of small Solar System bodies is diverse through the different types of planetary bodies and even for specific objects it is often not known in detail. One of the physical properties that strongly depends on the surface structure is the surface temperature. In highly porous media with large voids, radiation can efficiently transport heat, whereas more compact, micro-porous structures transport the heat primarily by conduction through the solid material. In this work, we investigate under which conditions a macro-porous surface can be distinguished from a micro-porous one by simply measuring the surface temperature. In our numerical simulations, we included circular and elliptical orbits with and without obliquity and varied the rotation period of the considered objects. We found that daily temperature cycles are rather insensitive to the specific surface granularity. However, the surface temperature at sunrise shows significant dependency on the material structure and this effect becomes even more pronounced when the solar intensity increases. By measuring the sunrise temperature as a function of insolation at noon, a differentiation between micro- and macro-granular surface structures is possible. In this paper, we provide a strategy how remote sensing can be used to derive the surface structure of small Solar System bodies.

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D. Bischoff, B. Gundlach and J. Blum
Tue, 28 Sep 21
50/89

Comments: accepted by MNRAS

The Tidal-Thermal Evolution of the Pluto-Charon System [EPA]

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http://arxiv.org/abs/2109.13206


Existence of subsurface oceans on the satellites of the giant planets and Trans-Neptunian objects has been predicted for some time. Oceans on icy worlds exert a considerable influence on the dynamics of the ice-ocean system and, because of the astrobiological potential, represent an important objective for future missions. The Pluto-Charon system is representative of an icy moon orbiting a dwarf planet formed from the remnants of a giant impact. Evolution of icy moons is primarily controlled by the mode and efficiency of heat transfer through the outer ice shell, which is influenced by the presence of impurities, by tidal dissipation in the ice shell, and the radioactive element budget in the core. Previous studies on the evolution of the Pluto-Charon system considered either only the thermal or the tidal evolution, and in the cases where both were considered, the important effect of the presence of impurities in the liquid oceans was not addressed. We consider the joint tidal-thermal evolution of the system by combining a comprehensive tidal model that incorporates a viscoelastic tidal response with a parameterized convection model developed for icy worlds. This approach enables an extensive analysis of the conditions required for formation and maintenance of subsurface liquid oceans to the present. Our results show that because of fast circularization and synchronization of the orbits, tidal heating is only important during the early stages of evolution (<1 Myr). We test the sensitivity of our results to the initial orbital and thermal parameters. In all the cases, oceans on Pluto are always predicted to remain liquid to the present, ranging from 40 km to 150-km thick, whereas oceans on Charon have solidified. This is supported by New Horizons observations of extensional faults on Pluto and both extensional and compressional faults on Charon.

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A. Bagheri, A. Khan, F. Deschamps, et. al.
Tue, 28 Sep 21
68/89

Comments: N/A

Early habitability and crustal decarbonation of a stagnant-lid Venus [EPA]

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http://arxiv.org/abs/2109.08756


Little is known about the early evolution of Venus and a potential habitable period during the first one billion years. In particular, it remains unclear whether or not plate tectonics and an active carbonate-silicate cycle were present. In the presence of liquid water but without plate tectonics, weathering would have been limited to freshly produced basaltic crust, with an early carbon cycle restricted to the crust and atmosphere. With the evaporation of surface water, weathering would cease. With ongoing volcanism, carbonate sediments would be buried and sink downwards. Thereby, carbonates would heat up until they become unstable and the crust would become depleted in carbonates. With CO$_2$ supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more CO$_2$.
We assess the habitable period of an early stagnant-lid Venus by employing a coupled interior-atmosphere evolution model accounting for CO$_2$ degassing, weathering, carbonate burial, and crustal decarbonation. We find that if initial surface conditions allow for liquid water, weathering can keep the planet habitable for up to 900 Myr, followed by evaporation of water and rapid crustal carbonate depletion. For the atmospheric CO$_2$ of stagnant-lid exoplanets, we predict a bimodal distribution, depending on whether or not these planets experienced a runaway greenhouse in their history. Planets with high atmospheric CO$_2$ could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric CO$_2$ would indicate active silicate weathering and thereby a habitable climate.

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D. Höning, P. Baumeister, J. Grenfell, et. al.
Tue, 21 Sep 21
40/85

Comments: N/A

Forecasting GICs and geoelectric fields from solar wind data using LSTMs: application in Austria [CL]

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http://arxiv.org/abs/2109.08624


The forecasting of local GIC effects has largely relied on the forecasting of dB/dt as a proxy and, to date, little attention has been paid to directly forecasting the geoelectric field or GICs themselves. We approach this problem with machine learning tools, specifically recurrent neural networks or LSTMs by taking solar wind observations as input and training the models to predict two different kinds of output: first, the geoelectric field components Ex and Ey; and second, the GICs in specific substations in Austria. The training is carried out on the geoelectric field and GICs modelled from 26 years of one-minute geomagnetic field measurements, and results are compared to GIC measurements from recent years. The GICs are generally predicted better by an LSTM trained on values from a specific substation, but only a fraction of the largest GICs are correctly predicted. This model had a correlation with measurements of around 0.6, and a root-mean-square error of 0.7 A. The probability of detecting mild activity in GICs is around 50%, and 15% for larger GICs.

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R. Bailey, R. Leonhardt, C. Möstl, et. al.
Mon, 20 Sep 21
15/53

Comments: N/A

Spatiotemporal Characterization of VIIRS Night Light [CL]

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http://arxiv.org/abs/2109.06913


The VIIRS Day Night Band sensor on the Suomi NPP satellite provides almost a decade of observations of night light. The daily frequency of sampling, without the temporal averaging of annual composites, requires the distinction between apparent changes of imaged night light related to the imaging process and actual changes in the underlying sources of the light being imaged. This study characterizes night light variability over a range of spatial and temporal scales to provide a context for interpretation of changes on both subannual and interannual time scales. This analysis uses a combination of temporal moments, spatial correlation and Empirical Orthogonal Function (EOF) analysis. A key result is the pervasive heteroskedasticity of VIIRS monthly mean night light. Specifically, the monotonic decrease of temporal variability with increasing mean brightness. Anthropogenic night light is remarkably stable on subannual time scales. Overall variance partition derived from the eigenvalues of the spatiotemporal covariance matrix are 88%, 2% and 2% for spatial, seasonal and interannual variance in the most diverse geographic region on Earth (Eurasia). Heteroskedasticity is present in all areas for all months, suggesting that much, if not most, of observed month-to-month variability may result from luminance of otherwise stable sources subjected to multiple aspects of the imaging process varying in time. Given the skewed distribution of all night light arising from radial peripheral dimming of bright sources, even aggregate metrics using thresholds must be interpreted in light of the fact that much larger numbers of more variable low luminance pixels may statistically overwhelm smaller numbers of stable higher luminance pixels and cause apparent changes related to the imaging process to be interpreted as actual changes in the light sources.

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C. Small
Thu, 16 Sep 21
24/54

Comments: 18 pages, 6 figures

Thermal history of matrix forsterite grains from Murchison based on high-resolution tomography [EPA]

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http://arxiv.org/abs/2109.06942


Protoplanetary disks are dust- and gas-rich structures surrounding protostars. Depending on the distance from the protostar, this dust is thermally processed to different degrees and accreted to form bodies of varying chemical compositions. The primordial accretion processes occurring in the early protoplanetary disk such as chondrule formation and metal segregation are not well understood. One way to constrain them is to study the morphology and composition of forsteritic grains from the matrix of carbonaceous chondrites. Here, we present high-resolution ptychographic X-ray nanotomography and multimodal chemical micro-tomography (X-ray diffraction and X-ray fluorescence) to reveal the early history of forsteritic grains extracted from the matrix of the Murchison CM2.5 chondrite. The 3D electron density maps revealed, at unprecedented resolution (64~nm), spherical inclusions containing Fe-Ni, very little silica-rich glass and void caps (i.e., volumes where the electron density is consistent with conditions close to vacuum) trapped in forsterite. The presence of the voids along with the overall composition, petrological textures, and shrinkage calculations is consistent with the grains experiencing one or more heating events with peak temperatures close to the melting point of forsterite ($\sim$2100~K) and subsequently cooled and contracted, in agreement with chondrule-forming conditions.

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G. Perotti, H. Sørensen, H. Haack, et. al.
Thu, 16 Sep 21
42/54

Comments: 15 pages, 11 figures, accepted for publication in ApJ

The Timing of Alluvial Fan Formation on Mars [EPA]

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http://arxiv.org/abs/2109.05407


The history of rivers on Mars is an important constraint on Martian climate evolution. The timing of relatively young, alluvial fan-forming rivers is especially important, as Mars’ Amazonian atmosphere is thought to have been too thin to consistently support surface liquid water. Previous regional studies suggested that alluvial fans formed primarily between the Early Hesperian and the Early Amazonian. In this study, we describe how a combination of a global impact crater database, a global geologic map, a global alluvial fan database, and statistical models can be used to estimate the timing of alluvial fan formation across Mars. Using our global approach and improved statistical modeling, we find that alluvial fan formation likely persisted into the last ~2.5 Gyr, well into the Amazonian period. However, the data we analyzed was insufficient to place constraints on the duration of alluvial fan formation. Going forward, more crater data will enable tighter constraints on the parameters estimated in our models and thus further inform our understanding of Mars’ climate evolution.

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S. Holo, E. Kite, S. Wilson, et. al.
Tue, 14 Sep 21
26/88

Comments: Accepted by The Planetary Science Journal