http://arxiv.org/abs/2109.04224

The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo, Ru, and Ni isotopic compositions that are intermediate between those of the non-carbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W chronology of Nedagolla indicates that this mixed NC-CC isotopic composition was established relatively late, more than 7 million years after Solar System formation. The mixed NC-CC isotopic composition is consistent with the chemical composition of Nedagolla, which combines signatures of metal segregation under more oxidizing conditions (relative depletions in Mo and W), characteristic for CC bodies, and more reducing conditions (high Si and Cr contents), characteristic for some NC bodies, in a single sample. These data combined suggest that Nedagolla formed as the result of collisional mixing of NC and CC core material, which partially re-equilibrated with silicate mantle material that predominantly derives from the NC body. These mixing processes might have occurred during a hit-and-run collision between two differentiated bodies, which also provides a possible pathway for Nedagolla’s extreme volatile element depletion. As such, Nedagolla provides the first isotopic evidence for early collisional mixing of NC and CC bodies that is expected as a result of Jupiter’s growth.

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F. Spitzer, C. Burkhardt, J. Pape, et. al.
Fri, 10 Sep 21
55/59

Comments: Accepted for publication in Meteoritics & Planetary Science

http://arxiv.org/abs/2108.08382

The study of planets outside our solar system may lead to major advances in our understanding of the Earth, and provide insight into the universal set of rules by which planets form and evolve. To achieve these goals requires applying geoscience’s wealth of Earth observations to fill in the blanks left by the necessarily minimalist exoplanetary observations. In turn, Earth’s many one-offs, e.g., plate tectonics, surface liquid water, a large moon, and life – which have long presented chicken and egg type conundrums for geoscientists – may find resolution in the study of exoplanets possessing only a subset of these phenomena.

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O. Shorttle, N. Hinkel and C. Unterborn
Fri, 20 Aug 21
37/59

Comments: To be published as article 1 in the “Geoscience Beyond the Solar System” issue of Elements magazine, v17 No4

http://arxiv.org/abs/2108.08553

Recent astronomical observations revealed that (225088) Gonggong, a 1000-km-sized trans-Neptunian dwarf planet, hosts an eccentric satellite, Xiangliu, with an eccentricity of approximately 0.3. As the majority of known satellite systems around trans-Neptunian dwarf planets have circular orbits, the observed eccentricity of Gonggong–Xiangliu system may reflect the singular properties of the system. In this study, we assumed that Gonggong–Xiangliu system formed via a giant impact and investigated the following secular tidal evolution of Gonggong–Xiangliu system under the simplifying assumption of homogeneous bodies and of zero orbital inclination. We conducted coupled thermal–orbital evolution simulations using the Andrade viscoelastic model and included higher-order eccentricity functions. The distribution of the final eccentricity from a large number of simulations with different initial conditions revealed that the radius of Xiangliu is not larger than 100 km. We also derived the analytical solution of the semilatus rectum evolution, a function of the radius of Xiangliu. From the point of view of the final semilatus rectum, the radius of Xiangliu was estimated to be close to 100 km. Together with the results of the Hubble Space Telescope observations, our findings suggest Gonggong and Xiangliu have similar albedos.

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S. Arakawa, R. Hyodo, D. Shoji, et. al.
Fri, 20 Aug 21
53/59

Comments: 36 pages, 22 figures. Accepted for publication in AJ

http://arxiv.org/abs/2108.00995

A theoretical model that describes the evolution of a suspension in which crystals can sediment to form a dense cumulate or may produce a light flotation crust has been derived in a companion paper. We use this model to study the thermal history of early accreted planetary bodies accreted during the very early stages of the formation of the solar system. We study the conditions required to form and preserve flotation crusts and basal cumulates, and the implications for the thermal evolution of planetesimals. We calculate the temperature evolution in an early accreted planetesimals internally heated by the decay of $\rm{^{26}Al}$ and $\rm{^{60}Fe}$. For planetesimal with radius $R>30\, \rm{km}$, partial melting reaches 40%, planetesimals undergo a rheological transition and form a magma ocean, i.e.: a suspension from which crystals can segregate and form a floating crust and/or a dense cumulate. Because of the formation of an insulation floating crust, this magma ocean episode is characterized by a relatively long time life, a slow cooling rate, and a weak surface heat flux. The model further predicts a cyclic evolution where episodes of crustal thickening alternate with episodes of melting-induced crustal thinning. These cycles produce in turn an oscillating thermal history and prevent runaway thermal heating of the planetesimals. At the end of the magma ocean episode, when the fraction of crystals becomes larger than 60\%, a transition occurs to solid-state convection in the planetesimal’s mantle. This stage is characterized by high viscous shear stress that tends to erode previously formed crystal deposits. However, the time scale of this erosion process is larger that the lifetime of the planetesimal. Hence solid-state evolution can be described by a well mixed mantle embedded by a metastable crust and a preserved cumulate at its base.

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C. Sturtz, A. Limare, S. Tait, et. al.
Tue, 3 Aug 21
35/90

Comments: 28 pages, 14 figures. Submitted to Journal of Geophysical Research: Planets

http://arxiv.org/abs/2107.03497

Recent discoveries of anomalously bright radar reflections below the Mars South Polar Layered Deposit (SPLD) have sparked new speculation that liquid water may be present below the ice cap. The reflections, discovered in data acquired by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board the Mars Express orbiter, were interpreted as reflections from damp materials or even subsurface ponds and lakes similar to those found beneath Earth’s ice sheets. Recent studies, however, have questioned the feasibility of melting and maintaining liquid water below the SPLD. Herein, we compare radar simulations to MARSIS observations in order to present an alternate hypothesis: that the bright reflections are the result of interference between multiple layer boundaries, with no liquid water present. This new interpretation is more consistent with known conditions on modern Mars.

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D. Lalich, A. Hayes and V. Poggiali
Fri, 9 Jul 21
30/62

Comments: N/A

http://arxiv.org/abs/2105.07651

We present a new numerical scheme for one-dimensional conduction problems of a spherical shell. The scheme adopts a solution of the conduction equation in each interval of the chosen discretization that is valid if the fluxes at interval boundaries are constant in time. This piece-wise steady flux (PWSF) numerical scheme is continuous and differentiable in the space domain, which is convenient for implementing the numerical scheme in an energy-conserved thermal evolution model of a planetary core in which a conductive stratified layer develops below the core-mantle boundary when the heat flux is subadiabatic. The influence of a time-variable stratified region on the general evolution of the planetary body is examined, in comparison to imposing an adiabatic temperature profile for the core. By considering stratification in a planetary core where the heat flux is subadiabatic, radial variations in the cooling rate are accounted for whereas otherwise the distribution of energy in the core is fixed by the imposed adiabat. During the growth of the thermally stratified region, the deep part of the core cools more rapidly than the outer part of the core. Therefore, the inner core grows to a larger size and the temperature and heat flux at the core-mantle boundary are higher and larger, respectively, if a stratified region is considered. For the Earth, the implications are likely very minor and can be neglected in thermal evolution studies that are not specifically interested in the stratified region itself. For Mercury, these implications are much larger. For example, the age of the inner core can be underestimated by several billion years if thermal stratification is neglected. Consideration of thermal stratification in the core of Mercury also increases the mantle temperature, leads to a larger heat flux into the lithosphere, and prolongs mantle convection.

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J. Knibbe and T. Hoolst
Tue, 18 May 21
45/77

Comments: N/A

http://arxiv.org/abs/2105.06051

Chondrules are often surrounded by fine-grained rims or igneous rims. The properties of these rims reflect their formation histories. While the formation of fine-grained rims is modeled by the accretion of dust grains onto chondrules, the accretion should be followed by the growth of dust grains due to the shorter growth timescale than the accretion. In this paper, we investigate the formation of rims, taking into account the growth of porous dust aggregates. We estimate the rim thickness as a function of the chondrule fraction at a time when dust aggregate accretion onto chondrules is switched to collisions between these chondrules. Our estimations are consistent with the measured thicknesses of fine-grained rims in ordinary chondrites. However, those of igneous rims are thicker than our estimations. The thickness of igneous rims would be enlarged in remelting events.

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Y. Matsumoto, Y. Hasegawa, N. Matsuda, et. al.
Fri, 14 May 21
25/67

Comments: Accepted for publication in Icarus

http://arxiv.org/abs/2105.05313

The effect of protoplanetary differentiation on the fate of life essential volatiles like nitrogen and carbon and its subsequent effect on the dynamics of planetary growth is unknown. Because the dissolution of nitrogen in magma oceans depends on its partial pressure and oxygen fugacity, it is an ideal proxy to track volatile redistribution in protoplanets as a function of their sizes and growth zones. Using high pressure and high temperature experiments in graphite undersaturated conditions, here we show that the iron loving character of nitrogen is an order of magnitude higher than previous estimates across a wide range of oxygen fugacity. The experimental data combined with metal, silicate and atmosphere fractionation models suggest that asteroid sized protoplanets, and planetary embryos that grew from them, were nitrogen depleted. However, protoplanets that grew to planetary embryo size before undergoing differentiation had nitrogen rich cores and nitrogen poor silicate reservoirs. Bulk silicate reservoirs of large Earth like planets attained nitrogen from the cores of latter type of planetary embryos. Therefore, to satisfy the volatile budgets of Earth like planets during the main stage of their growth, the timescales of planetary embryo accretion had to be shorter than their differentiation timescales, that is, Moon to Mars sized planetary embryos grew rapidly within 1 to 2 million years of the Solar System formation.

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D. Grewal, R. Dasgupta, T. Hough, et. al.
Thu, 13 May 21
33/60

Comments: 44 pages, 6 figures, 9 extended data figures. Nat. Geosci. (2021)

http://arxiv.org/abs/2105.01900

Although spectral surveys and spacecraft missions provide information on small bodies, many important analyses can only be performed in terrestrial laboratories. For now, the total number of parent bodies represented in our meteorites collection is estimated to about 150 parent bodies, of which 50 parent bodies represented by the poorly studied ungrouped chondrites. Linking ungrouped meteorites to their parent bodies is thus crucial to significantly increase our knowledge of asteroids. To this end, the petrography of 25 ungrouped chondrites and rare meteorite groups was studied, allowing grouping into 6 petrographic groups based on texture, mineralogy, and aqueous and thermal parent body processing. Then, we acquired visible-near-infrared reflectance spectroscopy data, in order to compare them to ground-based telescopic observations of asteroids. The reflectance spectra of meteorites were obtained on powdered samples, raw samples and polished sections. Our results showed that sample preparation influences the shape of the spectra, and thus asteroid spectral matching, especially for carbonaceous chondrites. Overall, the petrographic groups defined initially coincide with reflectance spectral groups. We define links between some of the studied ungrouped chondrites and asteroid types that had no meteorite connection proposed before, such as some very primitive type 3.00 ungrouped chondrites to B-type or Cg-type asteroids. We also matched metamorphosed ungrouped carbonaceous chondrites to S-complex asteroids, suggesting that this complex is not only composed of ordinary chondrites or primitive achondrites, as previously established, but may also host carbonaceous chondrites. Conversely, some ungrouped chondrites could not be matched to any known asteroid type, showing that those are potential samples from yet unidentified asteroid types.

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L. Ruggiu, P. Beck, J. Gattacceca, et. al.
Thu, 6 May 21
31/55

Comments: N/A

http://arxiv.org/abs/2105.00753

Almost three decades ago, the problem of long term polar wander on a dynamic planet was formulated and simplified within the framework of normal mode theory. The underlying simplifications have been debated ever since, recently in a series of papers by Hu et al. 2017a, 2017b, and 2019, who clarify the role of neglecting short-term relaxation modes of the body. However, the authors still do not solve the governing equations in full, because they make approximations to the Liouville equation (LE). In this paper I use a time domain approach and for previously studied test loads I solve both the relaxation of the body and the LE in full. I also compute the energy balance of true polar wander (TPW) in order to analyze the existing LE approximations. For fast rotating bodies such as the Earth, I show that the rotation axis is always aligned with the maximum principal axis of inertia (w||MMOI) once free oscillations are damped. The w||MMOI assumption is also re-derived theoretically. Contrary to previous beliefs, I demonstrate that it is not necessarily linked to the quasi-fluid simplification of the body’s viscoelastic response to loading and rotation, but that it is an expression of neglecting the Coriolis and Euler forces in the equation of motion. For slowly rotating bodies such as Venus, the full LE together with energy analysis indicate that previous estimates of TPW in the normal direction need to be revisited. The numerical code LIOUSHELL is made freely available.

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V. Patočka
Tue, 4 May 21
59/72

Comments: to be submitted to JGR:Planets

http://arxiv.org/abs/2104.10924

Mars northern polar latitudes are known to harbor an enhanced 3 ${\mu}$m spectral signature when observed from orbit. This may indicate a greater amount of surface adsorbed or bound water, although it has not yet been possible to easily reconcile orbital observations with ground measurements by Phoenix. Here we reprocessed OMEGA/Mars Express observations acquired during the Northern summer to further characterize this 3 ${\mu}$m absorption band increase. We identify the presence of a new specific spectral signature composed of an additional narrow absorption feature centered at 3.03 ${\mu}$m coupled with an absorption at ${\lambda}$ ${\geq}$ 3.8 ${\mu}$m. This signature is homogeneously distributed over a bright albedo open ring surrounding the circumpolar low-albedo terrains between ~ 68°N and 76°N and ~ 0°E and 270°E. This location includes the Phoenix landing site. This feature shows no time variability and can be confidently attributed to a seasonally stable surface component. All together, the stability, spectral shape and absence of significant correlation with other signatures in the 1 $-$ 2.5 ${\mu}$m range discard interpretations relying on water ice or easily exchangeable adsorbed water. The exact full spectral shape cannot be easily reproduced by pure minerals samples, although sulfates, notably lowly hydrated Ca-sulfates, provide interesting comparisons. A modification of the chemical or physical properties of the soil, potentially involving additional sulfates contaminants, or modification of the hydration state of sulfates, and/or modification of their grains size, seems a plausible explanation to this observation, which may then indicate geologically recent water alteration at high northern latitudes.

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A. Stcherbinine, M. Vincendon, F. Montmessin, et. al.
Fri, 23 Apr 2021
2/48

Comments: Submitted to Icarus

http://arxiv.org/abs/2103.16242

Collision and disruption processes of proto-planetary bodies in the early solar system are key to understanding the genesis of diverse types of main-belt asteroids. Mesosiderites are stony-iron meteorites that formed by mixing of howardite-eucrite-diogenite-like crust and molten core materials and provide unique insights into the catastrophic break-up of differentiated asteroids. However, the enigmatic formation process and the poorly constrained timing of metal-silicate mixing complicate the assignment to potential parent bodies. Here we report high-precision uranium-lead dating of mesosiderite zircons by isotope dilution thermal ionization mass spectrometry, revealing initial crust formation 4,558.5 +/- 2.1 million years ago and metal-silicate mixing at 4,525.39 +/- 0.85 million years. The two distinct ages coincide with the timing of crust formation and a large-scale reheating event on the eucrite parent body, likely the asteroid Vesta. This chronological coincidence corroborates that Vesta is the parent body of mesosiderite silicates. Mesosiderite formation on Vesta can be explained by a hit-and-run collision 4,525.4 million years ago that caused the thick crust observed by NASA’s Dawn mission and explains the missing olivine in mesosiderites, howardite-eucrite-diogenite meteorites, and vestoids.

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M. Haba, J. Wotzlaw, Y. Lai, et. al.
Wed, 31 Mar 2021
58/62

Comments: 45 pages, 4 figures, Supplementary Information

http://arxiv.org/abs/2103.02868

An accurate understanding of the relationship between the impact conditions and the degree of shock-induced thermal metamorphism in meteorites allows the impact environment in the early Solar System to be understood. A recent hydrocode has revealed that impact heating is much higher than previously thought. This is because plastic deformation of the shocked rocks causes further heating during decompression, which is termed post-shock heating. Here we compare impact simulations with laboratory experiments on the impact devolatilization of calcite to investigate whether the post-shock heating is also significant in natural samples. We calculated the mass of CO$_2$ produced from the calcite, based on thermodynamics. We found that iSALE can reproduce the devolatilization behavior for rocks with the strength of calcite. In contrast, the calculated masses of CO2 at lower rock strengths are systematically smaller than the experimental values. Our results require a reassessment of the interpretation of thermal metamorphism in meteorites.

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K. Kurosawa, H. Genda, S. Azuma, et. al.
Fri, 5 Mar 21
3/64

Comments: 30 pages, 4 figures, 1 Supporting Information, accepted for publication in Geophysical Research Letters

http://arxiv.org/abs/2103.02571

Dynamical scenarios of terrestrial planets formation involve strong perturbations of the inner part of the solar system by the giant-planets, leading to enhanced impact velocities and subsequent collisional erosion. We quantitatively estimate the effect of collisional erosion on the resulting composition of Earth, and estimate how it may provide information on the dynamical context of its formation. We simulate and quantify the erosion of Earth’s crust in the context of Solar System formation scenarios, including the classical model and Grand Tack scenario that invokes orbital migration of Jupiter during the gaseous disk phase (Walsh et al., 2011; Raymond et al., 2018). We find that collisional erosion of the early crust is unlikely to produce an excess of about 6% of the Sm/Nd ratio in terrestrial rock samples compared to chondrites for most simulations. Only Grand Tack simulations in which the last giant impact on Earth occurred later than 50 million years after the start of Solar System formation can account for such an offset. However, this time frame is consistent with current cosmochemical and dynamical estimates of the Moon forming impact (Chyba, 1991; Walker, 2009; Touboul et al.,2007, 2009, 2015; Pepin and Porcelli, 2006; Norman et al., 2003; Nyquist et al., 2006; Boyet et al.,2015). Such a late fractionation in the Sm/Nd ratio is unlikely to be responsible for a 20-ppm $^{142}$Nd excess in terrestrial rocks due to the half life of the radiogenic system. Additionally, such a large and late fractionation in the Sm/Nd ratio would accordingly induce non-observed anomalies in the $^{143}$Nd/$^{144}$Nd ratio. Considering our results, the Grand Tack model with a late Moon-forming impact cannot be easily reconciled with the Nd isotopic Earth contents.

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L. Allibert, S. Charnoz, J. Siebert, et. al.
Thu, 4 Mar 21
77/83

Comments: 22 pages, 3 figures, supplementary, to be published

http://arxiv.org/abs/2103.02374

The tectonic regime of rocky planets fundamentally influences their long-term evolution and cycling of volatiles between interior and atmosphere. Earth is the only known planet with active plate tectonics, but observations of exoplanets may deliver insights into the diversity of tectonic regimes beyond the solar system. Observations of the thermal phase curve of super-Earth LHS 3844b reveal a solid surface and lack of a substantial atmosphere, with a temperature contrast between the substellar and antistellar point of around 1000 K. Here, we use these constraints on the planet’s surface to constrain the interior dynamics and tectonic regimes of LHS 3844b using numerical models of interior flow. We investigate the style of interior convection by assessing how upwellings and downwellings are organized and how tectonic regimes manifest. We discover three viable convective regimes with a mobile surface: (1) spatially uniform distribution of upwellings and downwellings, (2) prominent downwelling on the dayside and upwellings on the nightside, and (3) prominent downwelling on the nightside and upwellings on the dayside. Hemispheric tectonics is observed for regimes (2) and (3) as a direct consequence of the day-to-night temperature contrast. Such a tectonic mode is absent in the present-day solar system and has never been inferred from astrophysical observations of exoplanets. Our models offer distinct predictions for volcanism and outgassing linked to the tectonic regime, which may explain secondary features in phase curves and allow future observations to constrain the diversity of super-Earth interiors.

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T. Meier, D. Bower, T. Lichtenberg, et. al.
Thu, 4 Mar 21
79/83

Comments: Accepted for publication in The Astrophysical Journal Letters; 9 pages, 5 figures; summary available at this http URL

http://arxiv.org/abs/2102.11534

Fireballs are infrequently recorded by seismic sensors on the ground. If recorded, they are usually reported as one-off events. This study is the first seismic bulk analysis of the largest single fireball data set, observed by the Desert Fireball Network (DFN) in Australia in the period 2014-2019. The DFN typically observes fireballs from cm-m scale impactors. We identified 25 fireballs in seismic time series data recorded by the Australian National Seismograph Network (ANSN). This corresponds to 1.8% of surveyed fireballs, at the kinetic energy range of 10$^6$ to 10$^{10}$ J. The peaks observed in the seismic time series data were consistent with calculated arrival times of the direct airwave or ground-coupled Rayleigh wave caused by shock waves by the fireball in the atmosphere (either due to fragmentation or the passage of the Mach cone). Our work suggests that identification of fireball events in the seismic time series data depends both on physical properties of a fireball (such as fireball energy and entry angle in the atmosphere) and the sensitivity of a seismic instrument. This work suggests that fireballs are likely detectable within 200 km direct air distance between a fireball and seismic station, for sensors used in the ANSN. If each DFN observatory had been accompanied by a seismic sensor of similar sensitivity, 50% of surveyed fireballs could have been detected. These statistics justify the future consideration of expanding the DFN camera network into the seismic domain.

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T. Neidhart, K. Miljković, E. Sansom, et. al.
Wed, 24 Feb 21
13/64

Comments: accepted for publication in PASA

http://arxiv.org/abs/2102.07634

The CM carbonaceous chondrite meteorites provide a record of low temperature aqueous reactions in the early solar system. A number of CM chondrites also experienced short-lived, post-hydration thermal metamorphism at temperatures of 200C to over 750C. The exact conditions of thermal metamorphism and the relationship between the unheated and heated CM chondrites are not well constrained but are crucial to understanding the formation and evolution of hydrous asteroids. Here we have used position-sensitive-detector X-ray diffraction (PSD-XRD), thermogravimetric analysis (TGA) and transmission infrared (IR) spectroscopy to characterise the mineralogy and water contents of 14 heated CM and ungrouped carbonaceous chondrites. We show that heated CM chondrites underwent the same degree of aqueous alteration as the unheated CMs, however upon thermal metamorphism their mineralogy initially (300 to 500C) changed from hydrated phyllosilicates to a dehydrated amorphous phyllosilicate phase. At higher temperatures (over 500C) we observe recrystallisation of olivine and Fe-sulphides and the formation of metal. Thermal metamorphism also caused the water contents of heated CM chondrites to decrease from 13 wt percent to 3 wt percent and a subsequent reduction in the intensity of the 3 micron feature in IR spectra. We estimate that the heated CM chondrites have lost 15 to 65 percent of the water they contained at the end of aqueous alteration. If impacts were the main cause of metamorphism, this is consistent with shock pressures of 20 to 50 GPa. However, not all heated CM chondrites retain shock features suggesting that some were instead heated by solar radiation. Evidence from the Hayabusa2 and ORSIRS-REx missions suggest that dehydrated materials may be common on the surfaces of primitive asteroids and our results will support upcoming analysis of samples returned from asteroids Ryugu and Bennu.

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A. King, P. Schofield and S. Russell
Tue, 16 Feb 21
38/63

Comments: Accepted for publication in Geochimica et Cosmochimica Acta

http://arxiv.org/abs/2102.01939

It has been shown that temperature cycles on airless bodies of our Solar System can cause damaging of surface materials. Nevertheless, propagation mechanisms in the case of space objects are still poorly understood. Present work combines a thermoelasticity model together with linear elastic fracture mechanics theory to predict fracture propagation in the presence of thermal gradients generated by diurnal temperature cycling and under conditions similar to those existing on the asteroid Bennu. The crack direction is computed using the maximal strain energy release rate criterion, which is implemented using finite elements and the so-called G$\theta$ method (Uribe-Su\’arez et al. 2020. Eng. Fracture Mech. 227:106918). Using the implemented methodology, crack propagation direction for an initial crack tip in different positions and for different orientations is computed. It is found that cracks preferentially propagate in the North to South (N-S), in the North-East to South-West (NE-SW) and in the North-West to South-East (NW-SE) directions. Finally, thermal fatigue analysis was performed in order to estimate the crack growth rate. Computed value is in good agreement with available experimental evidence.

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D. Uribe, M. Delbo, P. Bouchard, et. al.
Thu, 4 Feb 21
32/57

Comments: To be published in Icarus-Journal

http://arxiv.org/abs/2102.01281

Northwest Africa (NWA) 11042 is a heavily shocked achondrite with medium-grained cumulate textures. Its olivine and pyroxene compositions, oxygen isotopic composition, and chromium isotopic composition are consistent with L chondrites. Sm-Nd dating of its primary phases shows a crystallization age of 4100 +/- 160 Ma. Ar-Ar dating of its shocked mineral maskelynite reveals an age of 484.0 +/- 1.5 Ma. This age coincides roughly with the breakup event of the L chondrite parent body evident in the shock ages of many L chondrites and the terrestrial record of fossil L chondritic chromite. NWA 11042 shows large depletions in siderophile elements (<0.01 times CI) suggestive of a complex igneous history involving extraction of a Fe-Ni-S liquid on the L chondrite parent body. Due to its relatively young crystallization age, the heat source for such an igneous process is most likely impact. Because its mineralogy, petrology, and O isotopes are similar to the ungrouped achondrite NWA 4284 (this work), the two meteorites are likely paired and derived from the same parent body.

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Z. Vaci, C. Agee, M. Humayun, et. al.
Wed, 3 Feb 21
54/61

Comments: N/A

http://arxiv.org/abs/2012.15300

This is a study of the history of the asteroids in the main asteroid belt. Collisions have been the dominant process. Every asteroid has been impacted by others a multitude of times, with consequences of cratering, erosion, spin increments, fragmentation, and occasional catastrophic disruption and dispersion. Extensive information for asteroid orbits, sizes, shapes, composition, and rotation rates of those asteroids is now available. Those are a result of their history, but to interpret them requires understanding the processes. That understanding can be improved by simulations of the history. A simulation needs robust models of the dynamical and collisional events. Such models have evolved substantially in the last few decades. Here I present current models, a method, and a code “SSAH” for stochastic simulations of the history of the main belt. That code gives a framework upon which existing and future models can be based. The results lead to new paradigms for asteroid histories including the distribution of spins; the irrelevance of strength spin limits; the “unusual” spins of 2001 OE84; and of large slow-spinning tumbling objects (Mathilde); the “V-shape” in the spin versus diameter plot; the non-Maxwellian distribution of spins of a given diameter range; the numbers of expected tumblers, and more. At the same time, the simulations expose gaps in our knowledge that require further research. The SSAH code is freely available for the use of others.

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K. Holsapple
Fri, 1 Jan 21
57/103

Comments: Manuscript has 79 pages, including 35 Figures and 3 Tables

http://arxiv.org/abs/2012.15300

This is a study of the history of the asteroids in the main asteroid belt. Collisions have been the dominant process. Every asteroid has been impacted by others a multitude of times, with consequences of cratering, erosion, spin increments, fragmentation, and occasional catastrophic disruption and dispersion. Extensive information for asteroid orbits, sizes, shapes, composition, and rotation rates of those asteroids is now available. Those are a result of their history, but to interpret them requires understanding the processes. That understanding can be improved by simulations of the history. A simulation needs robust models of the dynamical and collisional events. Such models have evolved substantially in the last few decades. Here I present current models, a method, and a code “SSAH” for stochastic simulations of the history of the main belt. That code gives a framework upon which existing and future models can be based. The results lead to new paradigms for asteroid histories including the distribution of spins; the irrelevance of strength spin limits; the “unusual” spins of 2001 OE84; and of large slow-spinning tumbling objects (Mathilde); the “V-shape” in the spin versus diameter plot; the non-Maxwellian distribution of spins of a given diameter range; the numbers of expected tumblers, and more. At the same time, the simulations expose gaps in our knowledge that require further research. The SSAH code is freely available for the use of others.

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K. Holsapple
Fri, 1 Jan 21
48/103

Comments: Manuscript has 79 pages, including 35 Figures and 3 Tables

http://arxiv.org/abs/2012.02576

A giant collision is believed to be at the origin of the Pluto-Charon system. As a result, the initial orbit and spins after impact may have substantially differed from those observed today. More precisely, the distance at periapse may have been shorter, subsequently expanding to its current separation by tides raised simultaneously on the two bodies. Here we provide a general 3D model to study the tidal evolution of a binary composed of two triaxial bodies orbiting a central star. We apply this model to the Pluto-Charon binary, and notice some interesting constraints on the initial system. We observe that when the eccentricity evolves to high values, the presence of the Sun prevents Charon from escaping because of Lidov-Kozai cycles. However, for a high initial obliquity for Pluto or a spin-orbit capture of Charon’s rotation, the binary eccentricity is damped very efficiently. As a result, the system can maintain a moderate eccentricity throughout its evolution, even for strong tidal dissipation on Pluto.

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A. Correia
Mon, 7 Dec 20
62/69

Comments: 14 pages, 10 figures

http://arxiv.org/abs/2011.15066

Mercury’s crust has a complex structure resulting from a billion years of volcanism. The surface variations in chemical composition have been identified from orbit by the spacecraft MESSENGER. Combining these measurements with laboratory experiments on partial melting, we estimate which variations in surface density and degree of mantle melting are required to produce surface rocks. If the surface density is representative of the deep crustal density, more than one half of crustal thickness variations in the northern hemisphere are explained by lateral variations in mantle melting. The crust is thin below the magnesium-poor Northern Volcanic Plains whereas the thickest crust is found in the magnesium-rich region located at mid-northern latitudes in the Western Hemisphere. The magnesium-rich region is thus not due to an early impact but rather to extensive mantle melting. The thickness-melting relation has also been observed for the oceanic crust on Earth and might be a common feature of terrestrial planets.

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M. Beuthe, B. Charlier, O. Namur, et. al.
Tue, 1 Dec 20
58/108

Comments: 11 pages of main text, 37 pages with supplements; 3+12 figures, 1+1 tables

http://arxiv.org/abs/2011.15097

Isostasy explains why observed gravity anomalies are generally much weaker than what is expected from topography alone, and why planetary crusts can support high topography without breaking up. Classical isostasy, however, neglects internal stresses and geoid contributions to topographical support, and yields ambiguous predictions of geoid anomalies. Isostasy should instead be defined either by minimizing deviatoric elastic stresses within the elastic shell, or by studying the dynamic response of the body in the long-time limit. I implement here the first option by formulating Airy isostatic equilibrium as the response of an elastic shell to surface and internal loads. Isostatic ratios are defined in terms of deviatoric Love numbers which quantify deviations with respect to a fluid state. The Love number approach separates the physics of isostasy from the technicalities of elastic-gravitational spherical deformations, and provides flexibility in the choice of the interior structure. Since elastic isostasy is invariant under a global rescaling of the shell shear modulus, it can be defined in the fluid shell limit, which reveals a deep connection with viscous isostasy. If the shell is homogeneous, minimum stress isostasy is dual to a variant of elastic isostasy called zero deflection isostasy, which is less physical but simpler to compute. Each isostatic model is combined with general boundary conditions applied at the surface and bottom of the shell, resulting in one-parameter isostatic families. At long wavelength, the influence of boundary conditions disappears as all isostatic families members yield the same isostatic ratios. At short wavelength, topography is supported by shallow stresses so that Airy isostasy becomes similar to either pure top or bottom loading. The isostatic ratios of incompressible bodies with three homogeneous layers are implemented in freely available software.

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M. Beuthe
Tue, 1 Dec 20
67/108

Comments: 65 pages, 12 figures, 5 tables

http://arxiv.org/abs/2011.14800

Dissipation of ocean potential energy is proposed by Tyler (2020) as a new mechanism leading to possible high-power states for Enceladus. I show here that this process actually results from viscoelastic dissipation within the crust. For plausible values of Enceladus’s ocean thickness, crustal dissipation can be computed with the standard approach of static deformations of solid layers by equilibrium tides.

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M. Beuthe
Tue, 1 Dec 20
100/108

Comments: 12 pages, 2 figures

http://arxiv.org/abs/2011.04964

FTIR measurement on MK immediately after its fall, shows a unique doublet around 10 micrometer, significantly different from many ordinary CM2 chondrites, where only a singlet around 10 micrometer is observed. Also, a very faint 11.2 micrometer feature in MK indicates the absence of anhydrous silicates, olivine and thus complete serpentinization of anhydrous silicates due to severe aqueous alteration on parent body. Raman studies show a low peak metamorphic temperature around 0 {\deg}C and consistent with the absence of peak corresponding to tochilinite in FTIR spectrum, which forms at higher temperature. The first thermogravimetric measurement was carried out within 24 hrs. of MK fall, showing 10% weight loss in 400-770 {\deg}C range and is consistent with TGA on another MK fragment of same batch after 30 months, confirming no environmental impact on the water bound to hydrated clay. This large weight loss also rules out any post aqueous alteration thermal event suffered by MK and signify the presence of hydrated clay. The measured ratio of MgO/FeO is about 0.56, and sulfur weight is 3.4 %. Recently, based on only aqueous alteration Potin et al. (Potin et al. 2020), classified MK as CM1, implying MK should be utmost altered CM, whereas Ray et al. (Ray et al 2018), as equivalent to Paris like (CM2.7), least aqueous altered. However, if we combine the observed aqueous alteration, MgO/FeO weight ratio, and sulfur weight % together will provide a more comprehensive understanding for MK, and thus, we classify it as CM2.3.insted CM1 or CM(2.7-2.9).

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A. Dixit, R. Tripathi, S. Kumar, et. al.
Wed, 11 Nov 20
55/69

Comments: Submitted to MAPS

http://arxiv.org/abs/2010.00870

The detection of liquid water by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) at the base of the south polar layered deposits in Ultimi Scopuli has reinvigorated the debate about the origin and stability of liquid water under present-day Martian conditions. To establish the extent of subglacial water in this region, we acquired new data, achieving extended radar coverage over the study area. Here, we present and discuss the results obtained by a new method of analysis of the complete MARSIS dataset, based on signal processing procedures usually applied to terrestrial polar ice sheets. Our results strengthen the claim of the detection of a liquid water body at Ultimi Scopuli and indicate the presence of other wet areas nearby. We suggest that the waters are hypersaline perchlorate brines, known to form at Martian polar regions and thought to survive for an extended period of time on a geological scale at below-eutectic temperatures.

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S. Lauro, E. Pettinelli, G. Caprarelli, et. al.
Mon, 5 Oct 20
7/61

Comments: N/A

http://arxiv.org/abs/2009.10093

We consider how chondrules, once-molten mm-sized spheres filling the oldest meteorites, may have formed as the thermally processed fallout from planetesimal collisions in the primordial solar nebula. We focus on the cloud of hot and dense silicate vapor released from a collision, and its expansion into cold and rarefied nebular hydrogen. Collisional particle debris, including chondrule precursors, are entrained by the cloud and melted by it, via gas conduction and radiation emitted by dust grains that condense out of the cloud. Conduction and radiation lock vapor, dust, and proto-chondrules to a common temperature, which falls as the cloud expands. Latent heat released by condensation slows cooling at first, but eventually radiative losses hasten it so that all remaining vapor condenses, leaving behind a pressure-less cavity which nebular gas backfills. Particles that are not too large are swept back in; of these, those that are not too small can sediment at drag-limited terminal velocities onto the planetesimal remains before solar tides tear them away. Particles that re-agglomerate with their parent thus have a specific size range: $\sim$1 mm in the asteroid belt, and $\sim$10 $\mu$m in the proto-Kuiper belt, for nebular densities comparable to the minimum-mass solar nebula. Thermal histories of chondrules in asteroids, and chondrule-like particles in the short-period comet 81P/Wild-2, are reproduced for colliding planetesimals of order 100 km in radius, matching the dominant sizes of Solar System minor bodies. If asteroids were born big and nebular gas densities decayed monotonically, then our model predicts older chondrules have larger maximum sizes and cooled more slowly. Problems, including the efficiency of chondrule production and the origin of CAIs, are discussed.

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N. Choksi, E. Chiang, H. Jr., et. al.
Wed, 23 Sep 20
-1754/86

Comments: Submitted to MNRAS

http://arxiv.org/abs/2007.15187

The external galactic key factor for developing of massive geochronological boundaries, as well as mass extinctions (ME) is proved based on chronological relationships of the impulses of globally short processes. External galactic key factor is also proved based on the coincidence of the scales of their developing processes, their regular periodicity in the formation of the boundaries of the Phanerozoic epochs and the presence of a unifying complex of cause-effect relationships for boundary processes. The hypotheses of the impact origin of ocean basins and plumes are substantiated, the assumptions about the unsteady nature of the Spiral Arms and the rotational acceleration of the Milky Ways core are confirmed.

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R. Nigmatzyanov
Fri, 31 Jul 20
-636/69

Comments: Published in the journal Otechestvennaya geologiya [National geology], 2015, 3. pp.70-83

http://arxiv.org/abs/2007.12037

Hydrogen in rocky planet atmospheres has been invoked in arguments for extending the habitable zone via N2-H2 and CO2-H2 greenhouse warming, and providing atmospheric conditions suitable for efficient production of prebiotic molecules. On Earth and Super-Earth-sized bodies, where H2-rich primordial envelopes are quickly lost to space, volcanic outgassing can act as a hydrogen source, provided it balances with the loss rate from the top of the atmosphere. Here, we show that both Earth-like and Mars-like planets can sustain atmospheric H2 fractions of several percent across relevant magmatic fO2 ranges. In general this requires hydrogen escape to operate somewhat less efficiently than the diffusion limit. We use a thermodynamical model of magma degassing to determine which combinations of magma oxidation, volcanic flux, and hydrogen escape efficiency can build up appreciable levels of hydrogen in a planet’s secondary atmosphere. On a planet similar to the Archean Earth and with a similar magmatic fO2, we suggest that the mixing ratio of atmospheric hydrogen could have been in the range 0.2-3%. A planet erupting magmas around the Iron-Wustite (IW) buffer (i.e., ~3 log fO2 units lower than Archean Earth’s), but with otherwise similar volcanic fluxes and H2 loss rates to early Earth, could sustain an atmosphere with approximately 10-20% H2. For an early Mars-like planet with magmas around IW, but a lower range of surface pressures and volcanic fluxes compared to Earth, an atmospheric H2 mixing ratio of 2-8% is possible. On early Mars, this H2 mixing ratio could be sufficient to deglaciate the planet. However, the sensitivity of these results to primary magmatic water contents and volcanic fluxes show the need for improved constraints on the crustal recycling efficiency and mantle water contents of early Mars.

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P. Liggins, O. Shorttle and P. Rimmer
Fri, 24 Jul 20
-539/53

Comments: Submitted with reviewer comments to Earth and Planetary Science Letters

http://arxiv.org/abs/2007.09021

Aims: The secondary atmospheres of terrestrial planets form and evolve as a consequence of interaction with the interior over geological time. We aim to quantify the influence of planetary bulk composition on interior–atmosphere evolution to aid the interpretation of future observations of terrestrial exoplanet atmospheres.
Methods: We use a geochemical model to determine the major-element composition of planetary interiors (MgO, FeO, and SiO$_2$) following the crystallization of a magma ocean after planet formation, predicting a compositional profile of the interior as an initial condition for our long-term thermal evolution model. Our 1D evolution model predicts the pressure-temperature structure of the interior which we use to evaluate near-surface melt production and subsequent volatile outgassing. Volatiles are exchanged between the interior and atmosphere according to mass conservation.
Results: Based on stellar compositions reported in the Hypatia catalog, we predict that about half of rocky exoplanets have a mantle that convects as a single layer (whole-mantle convection), and the other half exhibit double-layered convection due to the presence of a mid-mantle compositional boundary. Double-layered convection is more likely for planets with high bulk planetary Fe-content and low Mg/Si-ratio. We find that planets with low Mg/Si-ratio tend to cool slowly because their mantle viscosity is high. Accordingly, low-Mg/Si planets also tend to lose volatiles swiftly through extensive melting. Moreover, the dynamic regime of the lithosphere (plate tectonics vs. stagnant lid) has a first-order influence on the thermal evolution and volatile cycling. These results suggest that the composition of terrestrial exoplanetary atmospheres can inform about the dynamic regime of the lithosphere, and the thermo-chemical evolution of the interior.

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R. Spaargaren, M. Ballmer, D. Bower, et. al.
Mon, 20 Jul 20
-348/85

Comments: 14 pages, 10 figures, submitted to Astronomy and Astrophysics

http://arxiv.org/abs/2007.00610

Magmatic segregation and volcanic eruptions transport tidal heat from Io’s interior to its surface. Several observed eruptions appear to be extremely high temperature ($\geq$ 1600 K), suggesting either very high degrees of melting, refractory source regions, or large amounts of viscous heating on ascent. To address this ambiguity, we develop a model that couples crust and mantle dynamics to a simple compositional system. We analyse the model to investigate chemical structure and evolution. We demonstrate that magmatic segregation and volcanic eruptions lead to differentiation of the mantle, the extent of which depends on how easily high temperature melts from the more refractory lower mantle can migrate upwards. We propose that Io’s highest temperature eruptions originate from this lower mantle region, and that such eruptions act to limit the degree of compositional differentiation.

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D. Spencer, R. Katz, I. Hewitt, et. al.
Thu, 2 Jul 20
22/64

Comments: Submitted to Journal of Geophysical Research: Planets

http://arxiv.org/abs/2006.02589

The next step on the path toward another Earth is to find atmospheres similar to those of Earth and Venus – high-molecular-weight (secondary) atmospheres – on rocky exoplanets. Many rocky exoplanets are born with thick (> 10 kbar) H$_2$-dominated atmospheres but subsequently lose their H$_2$; this process has no known Solar System analog. We study the consequences of early loss of a thick H$_2$ atmosphere for subsequent occurrence of a high-molecular-weight atmosphere using a simple model of atmosphere evolution (including atmosphere loss to space, magma ocean crystallization, and volcanic outgassing). We also calculate atmosphere survival for rocky worlds that start with no H$_2$. Our results imply that most rocky exoplanets orbiting closer to their star than the Habitable Zone that were formed with thick H$_2$-dominated atmospheres lack high-molecular-weight atmospheres today. During early magma ocean crystallization, high-molecular-weight species usually do not form long-lived high-molecular-weight atmospheres; instead they are lost to space alongside H$_2$. This early volatile depletion also makes it more difficult for later volcanic outgassing to revive the atmosphere. However, atmospheres should persist on worlds that start with abundant volatiles (for example, waterworlds). Our results imply that in order to find high-molecular-weight atmospheres on warm exoplanets orbiting M-stars, we should target worlds that formed H$_2$-poor, that have anomalously large radii, or which orbit less active stars.

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E. Kite and M. Barnett
Fri, 5 Jun 20
69/70

Comments: N/A

http://arxiv.org/abs/2005.00349

Mars is currently at the center of scientific debate regarding proposed ancient river morphological landscapes on the planet. An increased curiosity in the geomorphology of Mars and its water history, therefore, has led to an effort to better understand how those landscapes formed. Many studies, however, consist of patchwork investigations that have not thoroughly examined proposed ancient fluvial processes on Mars from an Earth analog perspective. The purpose of this investigation, therefore, is to compare known fluvial features on Moenkopi Plateau with proposed paleopotamologic features on Mars. The search for analogs along the Moenkopi Plateau was due to the similarities in fluvial erosion, influenced and modified by eolian activity, primarily from Permian through Jurassic age. By analyzing orbital imagery from two cameras onboard NASA Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment and the Context Camera and paralleling it with imagery obtained from the U.S. Geological Survey and an unmanned aircraft operating over the Moenkopi Plateau, this investigation identified similar fluvial morphology. We interpret, therefore, that the same fluvial processes occurred on both planets, thereby reinforcing the history of water on Mars.

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A. Paris and L. Tognetti
Mon, 4 May 20
43/55

Comments: 14 pages, 12 Figures