Tag Archives: Popular Physics

Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology [EPA]

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http://arxiv.org/abs/2102.05027


Nitrogen dioxide (NO2) on Earth today has biogenic and anthropogenic sources. During the COVID-19 pandemic, observations of global NO2 emissions have shown significant decrease in urban areas. Drawing upon this example of NO2 as an industrial byproduct, we use a one-dimensional photochemical model and synthetic spectral generator to assess the detectability of NO2 as an atmospheric technosignature on exoplanets. We consider cases of an Earth-like planet around Sun-like, K-dwarf and M-dwarf stars. We find that NO2 concentrations increase on planets around cooler stars due to less short-wavelength photons that can photolyze NO2. In cloud-free results, present Earth-level NO2 on an Earth-like planet around a Sun-like star at 10pc can be detected with SNR ~5 within ~400 hours with a 15 meter LUVOIR-like telescope when observed in the 0.2 – 0.7micron range where NO2 has a strong absorption. However, clouds and aerosols can reduce the detectability and could mimic the NO2 feature. Historically, global NO2 levels were 3x higher, indicating the capability of detecting a 40-year old Earth-level civilization. Transit and direct imaging observations to detect infrared spectral signatures of NO2 on habitable planets around M-dwarfs would need several 100s of hours of observation time, both due to weaker NO2 absorption in this region, and also because of masking features by dominant H2O and CO2 bands in the infrared part of the spectrum. Non-detection at these levels could be used to place upper limits on the prevalence of NO2 as a technosignature.

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R. Kopparapu, G. Arney, J. Haqq-Misra, et. al.
Wed, 10 Feb 21
3/64

Comments: Accepted to Astrophysical Journal (in press). 1-D photochemical code from ‘Atmos’ is available at: this https URL

The Dark Matter Enigma [CL]

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http://arxiv.org/abs/2101.10127


In this pedestrian approach I give my personal point of view on the various problems posed by dark matter in the universe. After a brief historical overview I discuss the various solutions stemming from high energy particle physics, and the current status of experimental research on candidate particles (WIMPS). In the absence of direct evidence, the theories can still be evaluated by comparing their implications for the formation of galaxies, clusters and superclusters of galaxies against astronomical observations. I conclude briefly with the attempts to circumvent the dark matter problem by modifying the laws of gravity.

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J. Luminet
Tue, 26 Jan 21
68/84

Comments: 11 pages

On the interplay of solar wind proton and electron instabilities: Linear and quasi-linear approaches [CL]

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http://arxiv.org/abs/2101.07689


Important efforts are currently made for understanding the so-called kinetic instabilities, driven by the anisotropy of different species of plasma particles present in the solar wind and terrestrial magnetosphere. These instabilities are fast enough to efficiently convert the free energy of plasma particles into enhanced (small-scale) fluctuations with multiple implications, regulating the anisotropy of plasma particles. In this paper we use both linear and quasilinear (QL) frameworks to describe complex unstable regimes, which realistically combine different temperature anisotropies of electrons and ions (protons). Thus parameterized are various instabilities, e.g., proton and electron firehose, electromagnetic ion cyclotron, and whistler instability, showing that their main linear properties are markedly altered by the interplay of anisotropic electrons and protons. Linear theory may predict a strong competition of two instabilities of different nature when their growth rates are comparable. In the QL phase wave fluctuations grow and saturate at different levels and temporal scales, by comparison to the individual excitation of the proton or electron instabilities. In addition, cumulative effects of the combined proton and electron induced fluctuations can markedly stimulate the relaxations of their temperature anisotropies. Only whistler fluctuations inhibit the efficiency of proton firehose fluctuations in the relaxation of anisotropic protons. These results offer valuable premises for further investigations in numerical simulations, to decode the full spectrum of kinetic instabilities resulting from the interplay of anisotropic electrons and protons in space plasmas.

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S. Shaaban, M. Lazar, R. López, et. al.
Wed, 20 Jan 21
25/61

Comments: Accepted for publication at MNRAS

Interplanetary Challenges Encountered by the Crew During their Interplanetary Transit from Earth to Mars [EPA]

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http://arxiv.org/abs/2101.04723


Mars is the next destination after Earth to support terrestrial life. Decades of Mars exploration has fascinated space explorers to endeavour for a human expedition. But human Mars enterprise is complicated than conventional mission as the journey is endowed with a profusion of distinct challenges from terrestrial planet to the planetary surface. To perceive and overcome the implications of interplanetary challenges, we conducted a study to manifest every challenge encountered during interplanetary transit from Earth to Mars. Our study concluded entire challenges were attributed to the options for trajectory correction and maneuvering, management of space vehicles, the hazards of exposure to galactic radiation, effects of crew health in a microgravity environment, deficit solar power production, hazards of nuclear elements, psychologic and health effects, interrupted communication interlink from the ground, the complication in fuel pressurization and management, recycling of space wastes, execution of the extra-vehicular activity, and Mars orbital insertion. The main objective of this paper is to underline all possible challenges and its countermeasures for a sustainable crewed mission beyond low earth orbit in forthcoming decades.

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M. M and R. Annavarapu
Thu, 14 Jan 21
14/79

Comments: Conference Presented: 3rd IAA/AAS SciTech Forum 2020 Cyber Edition held virtually at RUDN University, Moscow, Russia from 8-10 December 2020. Accepted by International Program Committee for publication in the Volume of Advances of the Astronautical Sciences. (Manuscript Number: IAA-AAS-SciTech2020-018). Paper holds 12 Pages, 07 Figures and 44 References

The Copernican Principle Rules Out BLC1 as a Technological Radio Signal from the Alpha Centauri System [CL]

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http://arxiv.org/abs/2101.04118


Without evidence for occupying a special time or location, we should not assume that we inhabit privileged circumstances in the Universe. As a result, within the context of all Earth-like planets orbiting Sun-like stars, the origin of a technological civilization on Earth should be considered a single outcome of a random process. We show that in such a Copernican framework, which is inherently optimistic about the prevalence of life in the Universe, the likelihood of the nearest star system, Alpha Centauri, hosting a radio-transmitting civilization is $\sim 10^{-8}$. This rules out, \textit{a priori}, Breakthrough Listen Candidate 1 (BLC1) as a technological radio signal from the Alpha Centauri system, as such a scenario would violate the Copernican principle by about eight orders of magnitude. We also show that the Copernican principle is consistent with the vast majority of Fast Radio Bursts being natural in origin.

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A. Siraj and A. Loeb
Wed, 13 Jan 21
23/70

Comments: 4 pages, 3 figures; submitted for publication

The AstroCamp Project [CL]

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http://arxiv.org/abs/2101.03587


This contribution describes the concept, main structure and goals, and some highlighted outcomes, of the AstroCamp — an international academic excellence program in the field of astronomy and physics created in 2012 and organized by Centro de Astrof\'{\i}sica da Universidade do Porto (CAUP) together with the Paredes de Coura municipality and several national and international partners.

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C. Martins
Tue, 12 Jan 21
56/90

Comments: To appear in the Proceedings of IAU Symposium 367

Are extrasolar Einstein's spinning tops habitable? [EPA]

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http://arxiv.org/abs/2012.14245


Recently, the possibility that putative massive natural satellites (exomoons) of extrasolar Jupiter-like giant planets orbiting main sequence stars may be habitable has gained increasing attention. Typically, such an exomoon is expected to orbit its parent planet in the equatorial plane of the latter, with its spin $\boldsymbol S$ aligned with its orbital angular momentum $\boldsymbol L$ which, in turn, is parallel to the planetary spin $\boldsymbol J$. Thus, if the common tilt of such angular momenta to the satellite-planet ecliptic plane assumes certain values, the overall irradiation experienced by the exomoon may allow it to sustain life as we know it, at least for certain orbital configurations. A telluric body orbiting different gaseous giant primaries at $5-10$ planetary radii $R$ whose spin is initially tilted to the ecliptic by the same angle $\varepsilon_0=23.44^\circ$ as Earth is considered. A similar system does actually exist in our Solar System, being made of Saturn and its moon Titan whose obliquity to the ecliptic is $26.7^\circ$. Here, I show that the de Sitter and Lense-Thirring precessions of the satellite’s spin due to the general relativistic post-Newtonian (pN) field of the host planet may have a non-negligible impact on the exomoon’s habitability through induced long-term variations $\Delta\varepsilon\left(t\right)$ of the obliquity $\varepsilon$ of the satellite’s spin $\boldsymbol S$ to the ecliptic plane which may be as large as tens of degrees over $\simeq 0.1-1$ millions of years.

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L. Iorio
Tue, 29 Dec 20
46/66

Comments: LaTex2e, 19 pages, 3 figures, no tables

Are extrasolar Einstein's spinning tops habitable? [EPA]

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http://arxiv.org/abs/2012.14245


Recently, the possibility that putative massive natural satellites (exomoons) of extrasolar Jupiter-like giant planets orbiting main sequence stars may be habitable has gained increasing attention. Typically, such an exomoon is expected to orbit its parent planet in the equatorial plane of the latter, with its spin $\boldsymbol S$ aligned with its orbital angular momentum $\boldsymbol L$ which, in turn, is parallel to the planetary spin $\boldsymbol J$. Thus, if the common tilt of such angular momenta to the satellite-planet ecliptic plane assumes certain values, the overall irradiation experienced by the exomoon may allow it to sustain life as we know it, at least for certain orbital configurations. A telluric body orbiting different gaseous giant primaries at $5-10$ planetary radii $R$ whose spin is initially tilted to the ecliptic by the same angle $\varepsilon_0=23.44^\circ$ as Earth is considered. A similar system does actually exist in our Solar System, being made of Saturn and its moon Titan whose obliquity to the ecliptic is $26.7^\circ$. Here, I show that the de Sitter and Lense-Thirring precessions of the satellite’s spin due to the general relativistic post-Newtonian (pN) field of the host planet may have a non-negligible impact on the exomoon’s habitability through induced long-term variations $\Delta\varepsilon\left(t\right)$ of the obliquity $\varepsilon$ of the satellite’s spin $\boldsymbol S$ to the ecliptic plane which may be as large as tens of degrees over $\simeq 0.1-1$ millions of years.

Read this paper on arXiv…

L. Iorio
Tue, 29 Dec 20
3/66

Comments: LaTex2e, 19 pages, 3 figures, no tables

Are extrasolar Einstein's spinning tops habitable? [EPA]

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http://arxiv.org/abs/2012.14245


Recently, the possibility that putative massive natural satellites (exomoons) of extrasolar Jupiter-like giant planets orbiting main sequence stars may be habitable has gained increasing attention. Typically, such an exomoon is expected to orbit its parent planet in the equatorial plane of the latter, with its spin $\boldsymbol S$ aligned with its orbital angular momentum $\boldsymbol L$ which, in turn, is parallel to the planetary spin $\boldsymbol J$. Thus, if the common tilt of such angular momenta to the satellite-planet ecliptic plane assumes certain values, the overall irradiation experienced by the exomoon may allow it to sustain life as we know it, at least for certain orbital configurations. A telluric body orbiting different gaseous giant primaries at $5-10$ planetary radii $R$ whose spin is initially tilted to the ecliptic by the same angle $\varepsilon_0=23.44^\circ$ as Earth is considered. A similar system does actually exist in our Solar System, being made of Saturn and its moon Titan whose obliquity to the ecliptic is $26.7^\circ$. Here, I show that the de Sitter and Lense-Thirring precessions of the satellite’s spin due to the general relativistic post-Newtonian (pN) field of the host planet may have a non-negligible impact on the exomoon’s habitability through induced long-term variations $\Delta\varepsilon\left(t\right)$ of the obliquity $\varepsilon$ of the satellite’s spin $\boldsymbol S$ to the ecliptic plane which may be as large as tens of degrees over $\simeq 0.1-1$ millions of years.

Read this paper on arXiv…

L. Iorio
Tue, 29 Dec 20
27/66

Comments: LaTex2e, 19 pages, 3 figures, no tables

Women in academia: a warning on selection bias in gender studies from the astronomical perspective [CL]

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http://arxiv.org/abs/2012.09784


The recent paper by AlShebli et al. (2020) investigates the impact of mentorship in young scientists. Among their conclusions, they state that female prot\’eg\’es benefit more from male than female mentorship. We herein expose a critical flaw in their methodological design that is a common issue in Astronomy, namely “selection biases”. An effect that if not treated properly may lead to unwarranted causality claims. In their analysis, selection biases seem to be present in the response rate of their survey (8.35%), the choice of database, success criterion, and the overlook of the numerous drawbacks female researchers face in academia. We discuss these issues and their implications — one of them being the potential increase in obstacles for women in academia. Finally, we reinforce the dangers of not considering selection bias effects in studies aimed at retrieving causal relations.

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M. Dantas, E. Cameron, R. Souza, et. al.
Fri, 18 Dec 20
12/78

Comments: Submitted to Nature Communications on Nov. 27 — comments are welcome

Cometary records revise Eastern Mediterranean chronology around 1240 CE [CL]

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http://arxiv.org/abs/2012.00976


Eirene Laskarina, empress of John III Batatzes of the exiled Byzantine Empire of Nicaea (1204–1261 CE), was an important Eastern Mediterranean figure in the first half of the thirteenth century. We reassess the date of Eirene’s death, which has been variously dated between late 1239 and 1241, with the understanding that narrowing the range in which this event occurred contributes much to understanding the political situation in the area around 1240. George Akropolites, a famous official of the Empire, gives an account that connects Eirene’s death to a comet that appeared “six months earlier”, thus pointing to two comet candidates that were visible from the Eastern Mediterranean between 1239 and 1241, one recorded on “3 June 1239” and the other on “31 January 1240”. Recent historians prefer the former, based on historical circumstances and without a critical assessment of the comet records. We revisit the historical records and reveal that the “3 June 1239” candidate was not a comet. On the other hand, the other candidate, sighted on “31 January 1240”, was a comet, as supported by multiple historical records in multiple regions, and is also a good fit with Akropolites’s narrative. Therefore, we conclude that Eirene died six months after the comet that was seen on 31 January 1240, which places her death in the summer of 1240. Given that the date of her death is crucial for determining some other contemporary events across the Eastern Mediterranean, our results offer a solid basis for further research on the thirteenth-century Eastern Mediterranean.

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K. Murata, K. Ichikawa, Y. Fujii, et. al.
Thu, 3 Dec 20
29/81

Comments: 14 pages, 3 figures, accepted for publication in PASJ

Searching for a message in the angular power spectrum of the cosmic microwave background [IMA]

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http://arxiv.org/abs/2011.14435


The Creator of the universe could place a message on the most cosmic of all billboards, the Cosmic Microwave Background (CMB) sky. It was proposed by Hsu & Zee (2006) to to search for such a message in the CMB angular power spectrum. I process the temperature measurements taken by the Planck and WMAP satellites and extract the binary bit-stream. I estimate the information content of a potential message in the stream as about 1,000 bits. The universality of the message may be limited by the observer-dependent location in space and the finite observation time of order 100 bn years after the big bang. I find no meaningful message in the actual bit-stream, but include it at the end of the manuscript for the interested reader to scrutinize.

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M. Hippke
Tue, 1 Dec 20
57/108

Comments: 4 pages, 2 figures

The Sun Diver: Combining solar sails with the Oberth effect [CL]

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http://arxiv.org/abs/2009.12659


A highly reflective sail provides a way to propel a spacecraft out of the solar system using solar radiation pressure. The closer the spacecraft is to the Sun when it starts its outward journey, the larger the radiation pressure and so the larger the final velocity. For a spacecraft starting on the Earth’s orbit, closer proximity can be achieved via a retrograde impulse from a rocket engine. The sail is then deployed at the closest approach to the Sun. Employing the so-called Oberth effect, a second, prograde, impulse at closest approach will raise the final velocity further. Here I investigate how a fixed total impulse ({\Delta}v) can best be distributed in this procedure to maximize the sail’s velocity at infinity. Once {\Delta}v exceeds a threshold that depends on the lightness number of the sail (a measure of its sun-induced acceleration), the best strategy is to use all of the {\Delta}v in the retrograde impulse to dive as close as possible to the Sun. Below the threshold the best strategy is to use all of the {\Delta}v in the prograde impulse and thus not to dive at all. Although larger velocities can be achieved with multi-stage impulsive transfers, this study shows some interesting and perhaps counter-intuitive consequences of combining impulses with solar sails.

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C. Bailer-Jones
Tue, 29 Sep 20
97/98

Comments: 10 pages, accepted to the American Journal of Physics

Dark Energy: is it `just' Einstein's Cosmological Constant Lambda? [CL]

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http://arxiv.org/abs/2009.10177


The Cosmological Constant Lambda, a concept introduced by Einstein in 1917, has been with us ever since in different variants and incarnations, including the broader concept of Dark Energy. Current observations are consistent with a value of Lambda corresponding to about present-epoch 70% of the critical density of the Universe. This is causing the speeding up (acceleration) of the expansion of the Universe over the past 6 billion years, a discovery recognised by the 2011 Nobel Prize in Physics. Coupled with the flatness of the Universe and the amount of 30% matter (5% baryonic and 25% Cold Dark Matter), this forms the so-called Lambda-CDM standard model, which has survived many observational tests over about 30 years. However, there are currently indications of inconsistencies (`tensions’ ) within Lambda-CDM on different values of the Hubble Constant and the clumpiness factor. Also, time variation of Dark Energy and slight deviations from General Relativity are not ruled out yet. Several grand projects are underway to test Lambda-CDM further and to estimate the cosmological parameters to sub-percent level. If Lambda-CDM will remain the standard model, then the ball is back in the theoreticians’ court, to explain the physical meaning of Lambda. Is Lambda an alteration to the geometry of the Universe, or the energy of the vacuum? Or maybe it is something different, that manifests a yet unknown higher-level theory?

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O. Lahav
Wed, 23 Sep 20
-1760/86

Comments: Invited semi-popular review article, accepted for publication in Contemporary Physics, 21 pages, 14 figures

Clusters of Solar Eclipses in the Maori Era [CL]

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http://arxiv.org/abs/2009.01663


A dozen of high-magnitude solar eclipses accumulated near New Zealand in the 15th century AD when the Maori inhabited the two main islands. Taking today’s capital Wellington as the point of reference, we counted ten events with magnitude larger than 0.9 between 1409 and 1516 AD and two more just below this value. The eclipses need not have been all observed on account of weather conditions. An allusion to a particular event that could be conveyed in a myth is discussed, but the dating turns out far from certain. We take the opportunity here to meet the astronomy of the Maori and their understanding of this natural phenomenon. Moreover, an announcement is made to a cluster of five central eclipses of the sun that will encounter New Zealand from 2035 to 2045.

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E. Khalisi
Fri, 4 Sep 20
-1400/65

Comments: 7 pages, 5 figs, 1 tab, 13 refs

Estimating survival probability using the terrestrial extinction history for the search for extraterrestrial life [EPA]

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http://arxiv.org/abs/2007.09904


Several exoplanets have been discovered to date, and the next step is the search for extraterrestrial life. However, it is difficult to estimate the number of life-bearing exoplanets because our only template is based on life on Earth. In this paper, a new approach is introduced to estimate the probability that life on Earth has survived from birth to the present based on its terrestrial extinction history. A histogram of the extinction intensity during the Phanerozoic Eon is modeled effectively with a log-normal function, supporting the idea that terrestrial extinction is a random multiplicative process. Assuming that the fitted function is a probability density function of extinction intensity per unit time, the estimated survival probability of life on Earth is ~0.15 from the beginning of life to the present. This value can be a constraint on $f_i$ in the Drake equation, which contributes to estimating the number of life-bearing exoplanets.

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K. Tsumura
Tue, 21 Jul 20
-401/75

Comments: 11 pages, 3 figures, 1 table, accepted by Scientific Reports

Monte Carlo estimation of the probability of causal contacts between communicating civilisations [CL]

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http://arxiv.org/abs/2007.03597


In this work we address the problem of estimating the probabilities of causal contacts between civilisations in the Galaxy. We make no assumptions regarding the origin and evolution of intelligent life. We simply assume a network of causally connected nodes. These nodes refer somehow to intelligent agents with the capacity of receiving and emitting electromagnetic signals. Here we present a three-parametric statistical Monte Carlo model of the network in a simplified sketch of the Galaxy. Our goal, using Monte Carlo simulations, is to explore the parameter space and analyse the probabilities of causal contacts. We find that the odds to make a contact over decades of monitoring are low for most models, except for those of a galaxy densely populated with long-standing civilisations. We also find that the probability of causal contacts increases with the lifetime of civilisations more significantly than with the number of active civilisations. We show that the maximum probability of making a contact occurs when a civilisation discovers the required communication technology.

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M. Lares, J. Funes and L. Gramajo
Wed, 8 Jul 20
50/77

Comments: 13 pages, submitted to the International Journal of Astrobiology

The Venus Life Equation [EPA]

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http://arxiv.org/abs/2007.00105


Ancient Venus and Earth may have been similar in crucial ways for the development of life, such as liquid water oceans, land-ocean interfaces, the favorable chemical ingredients and energy pathways. If life ever developed on, or was transported to, early Venus from elsewhere, it might have thrived, expanded and survived the changes that have led an inhospitable surface on Venus today. Today the Venus cloud layer may provide a refugium for extant life. We introduce the Venus Life equation: a theory- and evidence-based approach to calculate the probability of extant life on Venus, L, using three primary factors of life: Origination, Robustness, and Continuity. We evaluate each of these factors using our current understanding of Earth and Venus environmental conditions from the Archean to the present. We find that probability of origination of life on Venus is similar to that of the Earth and argue that the other factors are nonzero, yielding a probability of extant life of Venus of 0.1 or less. The Venus Life Equation identifies poorly understood factors that can be addressed by direct observations with future exploration missions.

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N. Izenberg, D. Gentry, D. Smith, et. al.
Thu, 2 Jul 20
6/64

Comments: Submitted to Astrobiology for Venus Special issue. 25 pages, 3 figures. Also to be submitted as white paper in shortened form to Planetary and Astrobiology Decadal Survey

One of Everything: The Breakthrough Listen Exotica Catalog [IMA]

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http://arxiv.org/abs/2006.11304


We present Breakthrough Listen’s “Exotica” Catalog as the centerpiece of our efforts to expand the diversity of targets surveyed in the Search for Extraterrestrial Intelligence (SETI). As motivation, we introduce the concept of survey breadth, the diversity of objects observed during a program. Several reasons for pursuing a broad program are given, including increasing the chance of a positive result in SETI, commensal astrophysics, and characterizing systematics. The Exotica Catalog is an 865 entry collection of 737 distinct targets intended to include “one of everything” in astronomy. It contains four samples: the Prototype sample, with an archetype of every known major type of non-transient celestial object; the Superlative sample of objects with the most extreme properties; the Anomaly sample of enigmatic targets that are in some way unexplained; and the Control sample with sources not expected to produce positive results. As far as we are aware, this is the first object list in recent times with the purpose of spanning the breadth of astrophysics. We share it with the community in hopes that it can guide treasury surveys and as a general reference work. Accompanying the catalog is extensive discussion of classification of objects and a new classification system for anomalies. We discuss how we intend to proceed with observations in the catalog, contrast it with our extant Exotica efforts, and suggest similar tactics may be applied to other programs.

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B. Lacki, B. Brzycki, S. Croft, et. al.
Tue, 23 Jun 20
48/84

Comments: Submitted to ApJS

Reworking the SETI Paradox: METI's Place on the Continuum of Astrobiological Signaling [CL]

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http://arxiv.org/abs/2006.01167


The Search for Extraterrestrial Intelligence (SETI) has heretofore been a largely passive exercise, reliant on the pursuit of technosignatures. Still, there are those that advocate a more active approach. Messaging Extraterrestrial Intelligence (METI) has had a controversial history within the larger SETI project; it is claimed that the risks involved outweigh any potential benefits. These arguments are ultimately not compelling, result in absurd policy recommendations, and rest on a faulty appreciation of the nature of technosignatures, whose detectability implies intent to signal. Present technology is advancing quickly such that we will soon have great observational reach, to the point of reliably detecting such technosignatures and biosignatures: a capability that can be matched or exceeded elsewhere. To escape the SETI Paradox properly defined, at least one technological civilization must choose not to suppress its own continuum of astrobiological signals, of which METI is merely the most effective endmember. Passive SETI’s low likelihood of success in the short-term is a serious obstacle to sustainable funding, alongside a ‘giggle factor’ enhanced by a pernicious fear of contact. The scientific community must integrate an active approach to better ensure both the continuity and eventual success of the SETI project.

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T. Cortellesi
Wed, 3 Jun 20
47/83

Comments: 15 pages, submitted to JBIS 31 May 2020

Qualitative classification of extraterrestrial civilizations [CL]

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http://arxiv.org/abs/2005.13221


Abridged: The interest towards searches for extraterrestrial civilizations (ETCs) was boosted by the discovery of thousands of exoplanets. We turn to the classification of ETCs for new considerations that may help to design better strategies for ETCs searches. We take a basic taxonomic approach to ETCs and investigate the implications of the new classification on ETCs observational patterns. We use as a counter-example to our qualitative classification the quantitative scheme of Kardashev. We propose a classification based on the abilities of ETCs to modify their environment and to integrate with it: Class 0 uses the environment as it is, Class 1 modifies the it to fit its needs, Class 2 modifies itself to fit the environment and Class 3 ETC is fully integrated with the environment. Combined with the classical Kardashev’s scale our scheme forms a 2d scheme for interpreting ETC properties. The new framework makes it obvious that the available energy is not an unique measure of ETCs, it may not even correlate with how well that energy is used. The possibility for progress without increased energy consumption implies lower detectability, so the existence of a Kardashev Type III ETC in the Milky Way cannot be ruled out. This reasoning weakens the Fermi paradox, allowing the existence of advanced, yet not energy hungry, low detectability ETCs. The integration of ETCs with environment makes it impossible to tell apart technosignatures from natural phenomena. Thus, the most likely opportunity for SETI searches is to look for beacons, specifically set up by them for young civilizations like us (if they want to do that is a matter of speculation). The other SETI window is to search for ETCs at technological level close to ours. To rephrase the saying of A. Clarke, sufficiently advanced civilizations are indistinguishable from nature.

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V. Ivanov, J. Beamin, C. Caceres, et. al.
Thu, 28 May 20
16/55

Comments: accepted in A&A; 7 pages, 1 figure

The Lyapunov exponents and the neighbourhood of periodic orbits [CL]

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http://arxiv.org/abs/2004.14234


We show that the Lyapunov exponents of a periodic orbit can be easily obtained from the eigenvalues of the monodromy matrix. It turns out that the Lyapunov exponents of simply stable periodic orbits are all zero, simply unstable periodic orbits have only one positive Lyapunov exponent, doubly unstable periodic orbits have two different positive Lyapunov exponents and the two positive Lyapunov exponents of complex unstable periodic orbits are equal. We present a numerical example for periodic orbits in a realistic galactic potential. Moreover, the center manifold theorem allowed us to show that stable, simply unstable and doubly unstable periodic orbits are the mothers of families of, respectively, regular, partially and fully chaotic orbits in their neighbourhood.

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D. Carpintero and J. Muzzio
Thu, 30 Apr 20
6/71

Comments: 5 pages, 1, figure. Accepted for publication in MNRAS

Conspiratorial cosmology. II. The anthropogenic principle [CL]

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http://arxiv.org/abs/2004.00401


We revisit our 2013 claim [arXiv:1303.7476] that the Universe is the result of a conspiratorial plot, and find that it cannot be trusted, as even the belief in this conspiracy likely results from a conspiracy. On the basis of mathematical beauty, the final results of the Planck mission, the exploration of the dark sector by means of occult rituals and symbols, and a powerful new philosophical approach to physics, we demonstrate here that not only the existence of our Universe, but the whole concept of reality has to be rejected as obsolete and generally misleading. By introducing the new concept of the “anthropogenic principle”, we eventually illuminate the darkest corners of the conspiracy behind the conspiracy and briefly discuss some important implications regarding the survival of wo*mankind.

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J. Rachen and U. Gahlings
Thu, 2 Apr 20
43/56

Comments: 8 pages, 1 figure. Submitted to Journal of Comparative Irrelevance (Letters), scheduled to appear in Volume 42 on April 23. Community referee reports welcome until that date (ignored after) to the e-mail address given in the paper

Making It Rain: How Giving Me Telescope Time Can Reduce Drought [IMA]

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http://arxiv.org/abs/2003.13879


In this paper we assess the correlation between recent observing runs (2018 and 2019) and inclement weather, and demonstrate that these observing runs have seen much more rainfall than would otherwise be expected, an increase of over 200%. We further look at a number of observatory sites in areas that are facing or will face drought, and suggest that a strong environmental benefit would follow from telescope allocation committees providing us an inordinate amount of telescope time at facilities located around the globe.

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M. Lund
Wed, 1 Apr 20
25/83

Comments: 8 pages, 3 figures, 3 tables. Submitted to Acta Prima Aprilia

The search for life and a new logic [CL]

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http://arxiv.org/abs/2003.13981


Exploring the Universe is one of the great unifying themes of humanity. Part of this endeavour is the search for extraterrestrial life. But how likely is it that we will find life, or that if we do it will be similar to ourselves? And therefore how do we know where and how to look? We give examples of the sort of reasoning that has been used to narrow and focus this search and we argue that obvious extensions to that logical framework will result in greater success.

Read this paper on arXiv…

D. Scott and A. Frolop
Wed, 1 Apr 20
55/83

Comments: 3 pages

A probabilistic analysis of the Fermi paradox in terms of the Drake formula: the role of the L factor [CL]

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http://arxiv.org/abs/2003.04802


In evaluating the number of technological civilizations N in the Galaxy through the Drake formula, emphasis is mostly put on the astrophysical and biotechnological factors describing the emergence of a civilization and much less on its the lifetime, which is intimately related to its demise. It is argued here that this factor is in fact the most important regarding the practical implications of the Drake formula, because it determines the maximal extent of the “sphere of influence” of any technological civilization. The Fermi paradox is studied in the terms of a simplified version of the Drake formula, through Monte Carlo simulations of N civilizations expanding in the Galaxy during their space faring lifetime L. In the framework of that scheme, the probability of “direct contact” is determined as the fraction of the Galactic volume occupied collectively by the “spheres of influence” of N civilizations. The results of the analysis are used to determine regions in the parameter space where the Fermi paradox holds. It is argued that in a large region of the diagram the corresponding parameters suggest rather a “weak” Fermi paradox. Future research may reveal whether a “strong” paradox holds in some part of the parameter space. Finally, it is argued that the value of N is not bound by N=1 from below, contrary to what is usually assumed, but it may have a statistical interpretation.

Read this paper on arXiv…

N. Prantzos
Wed, 11 Mar 20
16/65

Comments: 9 pages, 5 figures, to appear in MNRAS

Observational Constraints on the Great Filter [EPA]

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http://arxiv.org/abs/2002.08776


The search for spectroscopic biosignatures with the next-generation of space telescopes could provide observational constraints on the abundance of exoplanets with signs of life. An extension of this spectroscopic characterization of exoplanets is the search for observational evidence of technology, known as technosignatures. Current mission concepts that would observe biosignatures from ultraviolet to near-infrared wavelengths could place upper limits on the fraction of planets in the galaxy that host life, although such missions tend to have relatively limited capabilities of constraining the prevalence of technosignatures at mid-infrared wavelengths. Yet search-ing for technosignatures alongside biosignatures would provide important knowledge about the future of our civilization. If planets with technosignatures are abundant, then we can increase our confidence that the hardest step in planetary evolution–the Great Filter–is probably in our past. But if we find that life is commonplace while technosignatures are absent, then this would in-crease the likelihood that the Great Filter awaits to challenge us in the future.

Read this paper on arXiv…

J. Haqq-Misra, R. Kopparapu and E. Schwieterman
Fri, 21 Feb 20
26/67

Comments: Accepted for publication in Astrobiology

Lens Flare: Magnified X-Ray Binaries as Passive Beacons in SETI [HEAP]

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http://arxiv.org/abs/2002.00128


Low mass X-ray binaries (LMXBs) containing neutron stars are both extremely luminous and compact, emitting up to ~10^6 L_sun within a kilometer-scale boundary layer. This combination allows for easy modulation, motivating X-ray SETI. When X-ray lenses smaller than planets (100 – 1,000 km) magnify the LMXB boundary layer, it brightens by a factor of several thousand for about a second. In addition, there should be occultation events where the neutron star is blocked out. Passive X-ray lenses could require little maintenance and the LMXB light source itself shines for millions of years, serving as an effective beacon for interstellar communication. A very large number of lenses would be needed to ensure detection from all directions, however, and gathering material to construct them could be very difficult. Avoiding collisions between lenses and aiming them pose additional challenges. Both “lens flares” and eclipses of LMXBs are easily detectable in the Galaxy, although they would be rare events, occurring once per decade. Our X-ray instruments could detect the flares to several Mpc, but it is unlikely they would be observing the LMXB during a flare.

Read this paper on arXiv…

B. Lacki
Tue, 4 Feb 20
46/52

Comments: Submitted, 15 pages, 4 figures, 1 table. An animated version of Figure 3 is available at this http URL

The Artscience of Planet Formation: import ArtScience.PlanetFormation as AATS [CL]

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http://arxiv.org/abs/2001.01760


The Art, Astronomy, Technology and Society (AATS) project is an artscience collaboration which dwells in the inbetweenness layer of scientific understanding of the origins of planets and the embodied, intuited ways of knowing. One of the oldest and at the same time one of the newest concerns of humanity is “How did the Earth and the planets come to be?”. Planet formation, an intricate and potentially chaotic process, is also very efficient. Every star harbors at least one planet, as evidenced by the high frequency of exoplanet detections. Planet formation must therefore be a frequent process. Yet, learning about the origins of planets has been difficult. Here I share my experience in the AATS artscience project and discuss the nature of artscience collaborations.

Read this paper on arXiv…

S. Pérez
Wed, 8 Jan 20
56/64

Comments: Published in Poi\’esis journal

Beyond Boltzmann: The Potential Energy Distribution of Objects in the Atmosphere [CL]

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http://arxiv.org/abs/2001.02081


Estimates of the number and potential energy of molecules, aerosols, cloud droplets, insects, birds, planes and satellites in the atmosphere yield a distribution which is for potential energies below 10^2 kBT described by the Boltzmann distribution, but for the range from 10^2 kBT to 10^33 kBT by a power law with an exponent of approximately -1. An explanation for this surprising behavior is not found.

Read this paper on arXiv…

H. Hess
Wed, 8 Jan 20
64/64

Comments: 2 pages, 1 figure

There's No Place Like Home (in Our Own Solar System): Searching for ET Near White Dwarfs [CL]

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http://arxiv.org/abs/2001.00673


The preponderance of white dwarfs in the Milky Way were formed from the remnants of stars of the same or somewhat higher mass as the Sun, i.e., from G-stars. We know that life can exist around G-stars. Any technologically advanced civilization residing within the habitable zone of a G-star will face grave peril when its star transitions from the main sequence and successively enters sub-giant, red giant, planetary nebula, and white dwarf stages. In fact, if the civilization takes no action it will face certain extinction. The two alternatives to passive extinction are (a) migrate away from the parent star in order to colonize another star system, or (b) find a viable solution within one’s own solar system. It is argued in this paper that migration of an entire biological population or even a small part of a population is virtually impossible, but in any event, far more difficult than remaining in one’s home solar system where the problem of continued survival can best be solved. This leads to the conclusion that sub-giants, red giants, planetary nebula, and white dwarfs are the best possible candidate targets for SETI observations. Search strategies are suggested.

Read this paper on arXiv…

J. Gertz
Mon, 6 Jan 20
28/49

Comments: 22 pages, 0 figures, accepted for publication in the Journal of the British Interplanetary Society (JBIS), comments welcome

The Inspiring Universe [CL]

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http://arxiv.org/abs/2001.00456


Humans like to find things out. They naturally ask questions and explore the world around them. One observes such behavior already in neonatal infants. Inspiration to further develop such exploratory behavior, the quest to understand and do so deeply, is stimulated by different things, depending on the environment in which one is born and grows up. We thus do not all have the same chances to be inspired. However, there is one exception. Throughout human history humans around the world have stood in awe of the wonders of the sky, the universe. This is a source of inspiration that unites us all. The above considerations and possibly other ones have led to the Universe Awareness (UNAWE) project, which focuses specifically on underprivileged children between the ages of four and ten. Universe Awareness (UNAWE) uses the beauty and grandeur of the Universe to encourage young children, particularly those from an underprivileged background, to have an interest in science and technology and foster their sense of global citizenship from the earliest age.

Read this paper on arXiv…

G. Miley, C. Odman and P. Russo
Fri, 3 Jan 20
14/45

Comments: 15 pages, published version available on Visser, J., & Visser, M. (Eds.). (2020). Seeking Understanding, Brill | Sense, Pages: 119–135

Why SETI Will Fail [CL]

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http://arxiv.org/abs/1912.08386


The union of space telescopes and interstellar spaceships guarantees that if extraterrestrial civilizations were common, someone would have come here long ago.

Read this paper on arXiv…

B. Zuckerman
Thu, 19 Dec 19
47/82

Comments: This article was published in the Sept-Oct 2002 issue of Mercury magazine (published by the Astron. Soc. of the Pacific). Mercury articles were not then available on-line. The present posting is the first on the internet. An electronic (pdf) version of the published article (with some additional words and figures and in color) is available via request at benatastro.ucla.edu

Interstellar communication network. I. Overview and assumptions [CL]

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http://arxiv.org/abs/1912.02616


It has recently been suggested in this journal by Benford (2019) that “Lurkers” in the form of interstellar exploration probes could be present in the solar system. Similarly, extraterrestrial intelligence could send long-lived probes to many other stellar systems, to report back science and surveillance. If probes and planets with technological species exist in more than a handful of systems in our galaxy, it is beneficial to use a coordinated communication scheme. Due to the inverse square law, data rates decrease strongly for direct connections over long distances. The network bandwidth could be increased by orders of magnitude if repeater stations (nodes) are used in an optimized fashion. This introduction to a series of papers makes the assumptions of the communication scheme explicit. Subsequent papers will discuss technical aspects such as transmitters, repeaters, wavelengths, and power levels. The overall purpose is to gain insight into the physical characteristics of an interstellar communication network, allowing us to describe the most likely sizes and locations of nodes and probes.

Read this paper on arXiv…

M. Hippke
Fri, 6 Dec 19
11/78

Comments: AJ in press

Searching for a standard Drake equation [CL]

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http://arxiv.org/abs/1912.01783


In the 20th century the scientific search for extraterrestrial intelligence began, and the Drake equation was proposed to estimate the number of extraterrestrial species humanity could attempt to detect, N. This paper discusses the need to update and standardize this equation. A new and more accurate expression is deduced which contains the classic equation as a particular case, and its advantages are discussed. A necessary condition is also stated for its use in scientific contexts: if N is defined as the total number of civilizations like ours then N = 1, given that we exist, and consequently the working hypothesis of the SETI project can be expressed as N>1. In this case, the Drake equation is being applied in a scientific way, because it is trying to test a hypothesis based on evidence.

Read this paper on arXiv…

J. Molina
Thu, 5 Dec 19
47/71

Comments: 15 pages, 3 tables

Effects of the general relativistic spin precessions on the habitability of rogue planets orbiting supermassive black holes [EPA]

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http://arxiv.org/abs/1912.01518


Recently, the possibility that many starless telluric planets may form around supermassive black holes (SMBHs) receiving an energy input from the hole’s accretion disk which, under certain not implausible circumstances, may make them habitable in a terrestrial sense has gained increasing attention. In particular, an observer on a planet orbiting at distance $r=100$ Schwarzschild radii from a SMBH with mass $M_\bullet = 1\times 10^8\,\mathrm{M}\odot$ in a plane slightly outside the equator of the latter would see the gravitationally lensed accretion disk with the same size of the Sun as seen from the Earth. Moreover, the accretion rate might be set in such a way that the apparent disk’s temperature would be identical to that of the solar surface. We demonstrate that the post-Newtonian (pN) de Sitter and Lense-Thirring precessions of the spin axis of such a world would change, among other things, its tilt $\varepsilon$ to its orbital plane by tens to hundreds of degrees over a time span of, say, just $\Delta t =400\,\mathrm{yr}$, depending on the obliquity $\eta\bullet$ of the SMBH’s spin to the orbital plane. Thus, such relativistic effects would have a relevant impact on the long term habitability of the considered planet. It is plausible arguing that much stronger effects would likely alter the sky as seen from the fictional planets appearing in the movie \textit{Interstellar}, which orbit much closer to the event horizon of the SMBH Gargantua.

Read this paper on arXiv…

L. Iorio
Wed, 4 Dec 19
10/58

Comments: LaTex2e, 15 pages, 2 figures, no tables

Black Hole Genesis and origin of inertia [CL]

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http://arxiv.org/abs/1910.10819


I propose that if the universe was born as a baby universe on the other side of the event horizon of a black hole existing in a parent universe, then the corresponding white hole provides the absolute inertial frame of reference in the universe. The principle of relativity then allows to construct an infinity of other inertial frames. Consequently, this scenario could give the origin of inertia and complete Einstein’s general theory of relativity by making it consistent with Mach’s principle.

Read this paper on arXiv…

N. Popławski
Wed, 30 Oct 19
6/77

Comments: 2 pages

Nebula-Relay theory: a new theory about the origin of life on the Earth [CL]

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http://arxiv.org/abs/1910.06396


In this paper, we introduced a new theory, the Nebula-Relay theory, to explain the origination of life on the Earth. In our model, the seeds of life on Earth was formatted at pre-solar system and filled in the entire nebula after the dead of pre-Solar star. So we divide the history of Earth life into three epochs: the formation of seeds in the pre-solar epoch, seeds sleep in the nebula epoch and the life evolution epoch. Our model could avoid the problems of abiogenesis and panspermia model and provides testable predictions. At the same time, our model dissolve the Fermi Paradox naturally.

Read this paper on arXiv…

L. Feng
Wed, 16 Oct 19
7/56

Comments: 6 pages, 1 figure

Life on Miller's Planet: The Habitable Zone Around Supermassive Black Holes [CL]

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http://arxiv.org/abs/1910.00940


In the science fiction film $Interstellar$, a band of intrepid astronauts sets out to explore a system of planets orbiting a supermassive black hole, searching for a world that may be conducive to hosting human life. While the film legitimately boasts a relatively high level of scientific accuracy, it is still restricted by Hollywood sensitivities and limitations. In this paper, we discuss a number of additional astrophysical effects that may be important in determining the (un)inhabitable environment of a planet orbiting close to a giant, accreting black hole. Foremost among these effects is the blueshift and beaming of incident radiation on the planet, due to the time dilation of an observer orbiting very close to the black hole. This results in high-energy flux incoming from surrounding stars and background radiation, with significant implications for habitability.

Read this paper on arXiv…

J. Schnittman
Thu, 3 Oct 19
54/59

Comments: based on talk given at Library of Congress, May 2016, available here: this https URL

Synergy between Art and Science: Collaboration at the South Pole [CL]

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http://arxiv.org/abs/1908.08812


We present the result of a cross-disciplinary collaboration between Prof. Donald Fortescue of the California College of the Arts in San Francisco and the Dr. Gwenhael de Wasseige of the IceCube Collaboration. The work presented was initiated during Fortescue’s US National Science Foundation funded Antarctic Artists and Writers Fellowship at the South Pole in the austral summer of 2016/17. One outcome of this collaboration is the video work Axis Mundi – a timelapse movie captured during 24 hours at the South Pole, combined with a simultaneous sampling of IceCube data transduced into sound. Axis Mundi captures the rotation of the Earth in space, the transient motions of the atmosphere, and the passage of subatomic particles through the polar ice, to provide a means for us to physically engage with these phenomena. We detail how both the timelapse and the transduction of atmospheric muon data have been realized and discuss the benefits of such a collaboration.

Read this paper on arXiv…

D. Fortescue and G. Wasseige
Mon, 26 Aug 19
15/55

Comments: Presented at the 36th International Cosmic Ray Conference (ICRC 2019). See arXiv:1907.11699 for all IceCube contributions

The aromatic Universe [GA]

Posted on by

http://arxiv.org/abs/1908.05918


The rich molecular structures of polycyclic aromatic hydrocarbons — essentially planar flakes of fused benzene rings — and their fullerene cousins are revealed through their vibrational and electronic spectra.

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A. Candian, J. Zhen and A. Tielens
Mon, 19 Aug 19
6/46

Comments: The following article appeared in Physics Today, November 2018, page 38

The Nine Axes of Merit for Technosignature Searches [IMA]

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http://arxiv.org/abs/1908.02683


The diverse methodologies and myriad orthogonal proposals for the best technosignatures to search for in SETI can make it difficult to develop an effective and balanced search strategy, especially from a funding perspective. Here I propose a framework to compare the relative advantages and disadvantages of various proposed technosignatures based on nine “axes of merit”. This framework was first developed at the NASA Technosignatures Workshop in Houston in 2018 and published in that report. I give the definition and rationale behind the nine axes as well as the history of each axis in the SETI and technosignature literature. These axes are then applied to three example classes of technosignature searches as an illustration of their use. An open-source software tool is available to allow technosignature researchers to make their own version of the figure.

Read this paper on arXiv…

S. Sheikh
Thu, 8 Aug 19
11/78

Comments: Submitted, waiting for review

Copernicanism and the Typicality in Time [CL]

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http://arxiv.org/abs/1907.08947


How special (or not) is the epoch we are living in? What is the appropriate reference class for embedding the observations made at the present time? How probable — or else — is anything we observe in the fulness of time? Contemporary cosmology and astrobiology bring those seemingly old-fashioned philosophical issues back into focus. There are several examples of contemporary research which use the assumption of typicality in time (or temporal Copernicanism) explicitly or implicitly, while not truly elaborating upon the meaning of this assumption. The present paper brings attention to the underlying and often uncritically accepted assumptions in these cases. It also aims to defend a more radical position that typicality in time is not — and cannot ever be — well-defined, in contrast to the typicality in space, and the typicality in various specific parameter spaces. This, of course, does not mean that we are atypical in time; instead, the notion of typicality in time is necessarily somewhat vague and restricted. In principle, it could be strengthened by further defining the relevant context, e.g., by referring to typicality within the Solar lifetime, or some similar restricting clause.

Read this paper on arXiv…

M. Ćirković and A. Balbi
Tue, 23 Jul 19
61/72

Comments: 19 pages, 2 figure, accepted for publication in “International Journal of Astrobiology”

The Breakthrough Listen Search for Extraterrestrial Intelligence [IMA]

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http://arxiv.org/abs/1907.05519


The discovery of the ubiquity of habitable extrasolar planets, combined with revolutionary advances in instrumentation and observational capabilities, have ushered in a renaissance in the millenia-old quest to answer our most profound question about the Universe and our place within it – Are we alone? The Breakthrough Listen Initiative, announced in July 2015 as a 10-year 100M USD program, is the most comprehensive effort in history to quantify the distribution of advanced, technologically capable life in the universe. In this white paper, we outline the status of the on-going observing campaign with our primary observing facilities, as well as planned activities with these instruments over the next few years. We also list collaborative facilities which will conduct searches for technosignatures in either primary observing mode, or commensally. We highlight some of the novel analysis techniques we are bringing to bear on multi-petabyte data sets, including machine learning tools we are deploying to search for a broader range of technosignatures than was previously possible.

Read this paper on arXiv…

V. Gajjar, A. Siemion, S. Croft, et. al.
Mon, 15 Jul 19
24/38

Comments: Astronomy and Astrophysics Decadal Survey 2020, APC white paper, To be published in BAAS

Gamow's Cyclist: A New Look at Relativistic Measurements for a Binocular Observer [CL]

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http://arxiv.org/abs/1906.11642


The visualisation of objects moving at relativistic speeds has been a popular topic of study since Special Relativity’s inception. While the standard exposition of the theory describes certain shape-changing effects, such as the Lorentz-contraction, it makes no mention of how an extended object would appear in a snapshot or how apparent distortions could be used for measurement. Previous work on the subject has derived the apparent form of an object, often making mention of George Gamow’s relativistic cyclist thought experiment. Here, a rigorous re-analysis of the cyclist, this time in 3-dimensions, is undertaken for a binocular observer, accounting for both the distortion in apparent position and the relativistic colour and intensity shifts undergone by a fast moving object. A methodology for analysing binocular relativistic data is then introduced, allowing the fitting of experimental readings of an object’s apparent position to determine the distance to the object and its velocity. This method is then applied to the simulation of Gamow’s cyclist, producing self-consistent results.

Read this paper on arXiv…

E. Cryer-Jenkins and P. Stevenson
Mon, 1 Jul 19
44/52

Comments: 18 pages, 15 figures. Submitted to Proc. Roy. Soc. A

Catching Gravitational Waves With A Galaxy-sized Net Of Pulsars [CL]

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http://arxiv.org/abs/1906.07568


Until recently, the only way to observe the Universe was from light received by telescopes. But we are now able to measure gravitational waves, which are ripples in the fabric of the Universe predicted by Albert Einstein. If two very dense objects (like black holes) orbit each other closely, they warp space and send out gravitational waves. For black holes that are similar in mass to the Sun, scientists use the LIGO detector on Earth. But for the biggest black holes in the Universe (billions of times more massive than the Sun), scientists monitor a net of rapidly-spinning neutron stars (called pulsars) across the Milky Way. Any gravitational wave passing by will change how long radio signals from these pulsars take to get to Earth. The NANOGrav Collaboration monitored 34 of these pulsars over 11 years, in an attempt to detect gravitational waves from giant black holes.

Read this paper on arXiv…

S. Taylor
Wed, 19 Jun 19
5/60

Comments: Pedagogical article on gravitational-waves and pulsar-timing arrays written for a young audience

How much of the Solar System should we leave as Wilderness? [CL]

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http://arxiv.org/abs/1905.13681


“How much of the Solar System should we reserve as wilderness, off-limits to human development?” We argue that, as a matter of policy, development should be limited to one eighth, with the remainder set aside. We argue that adopting a “1/8 principle” is far less restrictive, overall, than it might seem. One eighth of the iron in the asteroid belt is more than a million times greater than all of the Earth’s estimated iron reserves and may suffice for centuries. A limit of some sort is needed because of the problems associated with exponential growth. Humans are poor at estimating the pace of such growth, so the limitations of a resource are hard to recognize before the final three doubling times which take utilization successively from 1/8 to 1/4 to 1/2, and then to the point of exhaustion. Population growth and climate change are instances of unchecked exponential growth. Each places strains upon ouru available resources. Each is a problem we would like to control but attempts to do so at this comparatively late stage have not been encouraging. Our limited ability to see ahead suggests that we should set ourselves a ‘tripwire’ that gives us at least 3 doubling times as leeway, i.e. when 1/8 of Solar System resources are close to being exploited. At a 3.5 percent growth rate for the space economy, comparable to that of the iron use from the beginning of the Industrial Revolution until now, the 1/8 point would be reached after 400 years. At that point the 20 year doubling time of a 3.5 percent growth rate means that only 60 years would remain to transition the economic system to new “steady state” conditions. The rationale for adopting the 1/8 principle now is that it may be far easier to implement in principle restrictions at an early stage, rather than later, when vested and competing interests have come into existence.

Read this paper on arXiv…

M. Elvis and T. Milligan
Mon, 3 Jun 19
24/59

Comments: 18 pages, 0 figures, 1 table. Submitted version of paper published in Acta Astronautica

Does the evolution of complex life depend on the stellar spectral energy distribution? [EPA]

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http://arxiv.org/abs/1905.07343


This paper presents the proportional evolutionary time hypothesis, which posits that the mean time required for the evolution of complex life is a function of stellar mass. The “biological available window” is defined as the region of a stellar spectrum between 200 to 1200 nm that generates free energy for life. Over the $\sim$4 Gyr history of Earth, the total energy incident at the top of the atmosphere and within the biological available window is $\sim$10$^{34}$ J. The hypothesis assumes that the rate of evolution from the origin of life to complex life is proportional to this total energy, which would suggest that planets orbiting other stars should not show signs of complex life if the total energy incident on the planet is below this energy threshold. The proportional evolutionary time hypothesis predicts that late K- and M-dwarf stars (M < 0.7 M${\odot}$) are too young to host any complex life at the present age of the universe. F-, G-, and early K-dwarf stars (M > 0.7 M${\odot}$) represent the best targets for the next generation of space telescopes to search for spectroscopic biosignatures indicative of complex life.

Read this paper on arXiv…

J. Haqq-Misra
Mon, 20 May 19
43/44

Comments: Accepted for publication in Astrobiology

SETI in Russia, USSR and the post-Soviet space: a century of research [IMA]

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http://arxiv.org/abs/1905.03225


Studies on extraterrestrial civilisations in Russia date back to the end of the 19th century. The modern period of SETI studies began in the USSR in the early 1960s. The first edition of the I.S. Shklovsky’s book {\it Universe, Life, Intelligence} published in 1962 was a founding stone of SETI research in the USSR. A number of observational projects in radio and optical domains were conducted in the 1960s – 1990s. Theoretical studies focused on defining optimal spectral domains for search of artificial electromagnetic signals, selection of celestial targets in search for ETI, optimal methods for encoding and decoding of interstellar messages, estimating the magnitude of astro-engineering activity of ETI, and developing philosophical background of the SETI problem. Later, in the 1990s and in the first two decades of the 21st century, in spite of acute underfunding and other problems facing the scientific community in Russia and other countries of the former Soviet Union, SETI-oriented research continued. In particular, SETI collaborations conducted a number of surveys of Sun-like stars in the Milky Way, searched for Dyson spheres and artificial optical signals. Several space broadcasting programs were conducted too, including a radio transmission toward selected stars. Serious rethinking was given to incentives for passive and active participation of space civilisations in SETI and CETI. This paper gives an overview of past SETI activities. It also gives a comprehensive list of publications by authors from Russia, the Soviet Union and the post-Soviet space, as well as some SETI publications by other authors. The rich heritage of SETI research presented in the paper might offer a potentially useful background and starting point for developing strategy and specific research programs of the near future.

Read this paper on arXiv…

L. Gindilis and L. Gurvits
Thu, 9 May 19
7/59

Comments: 51 pages, 4 figures, 179 references

Persistence of Technosignatures: A Comment on Lingam and Loeb [CL]

Posted on by

http://arxiv.org/abs/1905.03146


In a recent paper in this journal, Lingam and Loeb (2018) develop an excellent heuristic for searches for biosignatures vs. technosignatures. We consider two ways in which their approach could be extended and sharpened, with focus on durability of technosignatures. We also note an important consequence of the adopted heuristic which offers strong support to the ideas of the Dysonian SETI.

Read this paper on arXiv…

M. Ćirković, B. Vukotić and M. Stojanović
Thu, 9 May 19
40/59

Comments: Accepted for publication in Astrobiology

Ensuring Uninterrupted Power Supply to Lunar Installations Through an Organic Rankine Cycle [IMA]

Posted on by

http://arxiv.org/abs/1904.03944


We propose using the temperature gradients between the Moon’s surface and the soil at a certain depth to power an Organic Rankine Cycle that could supply a permanent installation, particularly at night, when solar power is not available. Our theoretical and engineering considerations show that, with existing working fluids and quite feasible technical requirements, it is possible to continuously yield $25\,{\rm kW}$ to sustain a 3 member crew.

Read this paper on arXiv…

F. Francisco and O. Bertolami
Tue, 9 Apr 19
61/105

Comments: 8 pages, 3 tables, 3 figures

Advanced Aspects of the Galactic Habitability [CL]

Posted on by

http://arxiv.org/abs/1904.01062


Context. Astrobiological evolution of the Milky Way (or the shape of its “astrobiological landscape”) has emerged as one of the key research topics in recent years. In order to build precise, quantitative models of the Galactic habitability, we need to account for two opposing tendencies of life and intelligence in the most general context: the tendency to spread to all available ecological niches (conventionally dubbed “colonization”) and the tendency to succumb to various types of existential catastrophes (“catastrophism”). These evolutionary tendencies have become objects of study in fields such as ecology, macroevolution, risk analysis, and futures studies, while a serious astrobiological treatment has been lacking so far. Aims. Our aim is to numerically investigate the dynamics of opposed processes of expansion (panspermia, colonization) and extinction (catastrophic mechanisms) of life in the Galaxy. Methods. We employ a new type of numerical simulation based on 1D probabilistic cellular automaton with very high temporal resolution, in order to study astrobiological dynamics. Results. While the largest part of the examined parameter space shows very low habitability values, as expected, the remaining part has some observationally appealing features that imply, among other things, a reduction in the amount of fine-tuning necessary for resolving the Fermi paradox. Conclusions. Advanced aspects of Galactic habitability are amenable to precision studies using massive parallel computer simulations. There are regions of parameter space corresponding to a quasi-stationary state satisfying observable constraints and possessing viable SETI targets.

Read this paper on arXiv…

V. Đošović, B. Vukotić and M. Ćirković
Wed, 3 Apr 19
45/68

Comments: N/A

Possibility of a coordinated signaling scheme in the Galaxy and SETI experiments [IMA]

Posted on by

http://arxiv.org/abs/1904.00536


We discuss a Galaxy-wide coordinated signaling scheme with which a SETI observer needs to examine a tiny fraction of the sky. The target sky direction is determined as a function of time, based on high-precision measurements of a progenitor of a conspicuous astronomical event such as a coalescence of a double neutron star binary. In various respects, such a coordinated scheme would be advantageous for both transmitters and receivers, and might be widely prevailing as a tacit adjustment. For this scheme, the planned space gravitational-wave detector LISA and its follow-on missions have a potential to narrow down the target sky area by a factor of $10^{3\textit{-}4}$, and could have a large impact on future SETI experiments.

Read this paper on arXiv…

N. Seto
Tue, 2 Apr 19
8/90

Comments: 4 pages, 3 figures, accepted for publication in ApJL

Worlds in Migration [CL]

Posted on by

http://arxiv.org/abs/1903.12437


In this paper we discuss an alternative track for migration that can explain the existence of Hot Jupiters observed in close orbits around their stars based on a novel interpretation of established work. We also discuss the population of sub-Earth rogue planets that would be created via this migration method, which would be on the order of 2 to 40 billion, many of which would still be present in the Galaxy and potentially detectable.

Read this paper on arXiv…

M. Lund
Mon, 1 Apr 19
13/56

Comments: 5 pages, 1 figure. Submitted to Acta Prima Aprilia

The Long Night: Modeling the Climate of Westeros [CL]

Posted on by

http://arxiv.org/abs/1903.12195


Many previous authors have attempted to find explanations for Westeros’s climate, characterized by a generally moderate, Earth-like climate punctuated by extremely long and cold winters, separated by thousands of years. One explanation that has been proposed is that the planet orbits in a Sitnikov configuration, where two equal-mass stars (or a star and a black hole) orbit each other on slightly eccentric orbits, and the planet moves along a line through the barycenter perpendicular to the primaries’ orbital plane (Freistetter & Gr\”utzbauch 2018). We modify an intermediate-complexity GCM to include the effects of such an orbit and integrate it for thousands of years to determine whether such an orbit can a) be habitable and b) explain the climatic variations observed by the inhabitants of Westeros, in both double-star and star-black hole configurations. While configurations with low primary eccentricity and initial conditions that permit only small excursions from the ecliptic plane are habitable, these orbits are too stable to explain Westerosi climate. We find that while orbits with more bounded chaos are able to produce rare anomalously long and cold winters similar to Westeros’s Long Night, huge variations in incident stellar flux on normal orbital timescales should render these planets uninhabitable. We note that the presence of an orbital megastructure, either around the planet or the barycenter, could block some of the sunlight during crossings of the primaries’ orbital plane and preserve Westeros’s habitability. While we find that bounded chaotic Sitnikov orbits are a viable explanation for Westeros’s Long Night, we propose that chaotic variations of the planet’s axial tilt or semimajor axis, potentially due to torques from nearby planets or stars, may be a more realistic explanation than Sitnikov orbits.

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A. Paradise, A. Obertas, A. O’Grady, et. al.
Mon, 1 Apr 19
23/56

Comments: 11 pages, 7 figures; submitted to Acta Prima Aprilia

Looking for Lurkers [IMA]

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http://arxiv.org/abs/1903.09582


A recently discovered group of nearby co-orbital objects is an attractive location for extraterrestrial intelligence (ETI) to locate a probe to observe Earth while not being easily seen. These near-Earth objects provide an ideal way to watch our world from a secure natural object. That provides resources an ETI might need: materials, a firm anchor, concealment. These have been little studied by astronomy and not at all by SETI or planetary radar observations. I describe these objects found thus far and propose both passive and active observations of them as possible sites for ET probes.

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J. Benford
Mon, 25 Mar 19
8/71

Comments: 12 pages, 7 figures, 1 table

Searching for Technosignatures: Implications of Detection and Non-Detection [EPA]

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http://arxiv.org/abs/1903.06550


The search for technosignatures from the Galaxy or the nearby universe raises two main questions: What are the possible characteristics of technosignatures? and How can future searches be optimized to enhance the probability of detection? Addressing these questions requires an interdisciplinary approach, combining i) the study of Anthropocene as a planetary transition and thus a possible proxy also for other planets, ii) the active search for technosignatures in the radio/optical and infrared range, and iii) the statistical modelling of technosignatures and Bayesian inference methods to learn from both detection and non-detection. This strategy (combining modelling and observations) offers the best scientific opportunity in the next decade to discover the possible existence of technological civilizations beyond Earth.

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J. Haqq-Misra, A. Berea, A. Balbi, et. al.
Mon, 18 Mar 19
86/102

Comments: Science white paper submitted to the Astro2020 Decadal Survey. arXiv admin note: substantial text overlap with arXiv:1801.00052

A Shiny New Method for SETI: Specular Reflections from Interplanetary Artifacts [EPA]

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http://arxiv.org/abs/1903.05839


Glints of light from specular reflection of the Sun are a technosignature of artificial satellites. If extraterrestrial intelligences have left artifacts in the Solar System, these may include flat mirror-like surfaces that also can glint. I describe the characteristics of the resulting flashes. An interplanetary mirror will appear illuminated for several hours, but if it is rotating, its glint may appear as a train of optical pulses. The resulting glints can be very bright, but they will be seen only if the mirror happens to reflect sunlight to the Earth. The detection of large mirrors is limited mainly by the fraction oriented to reflect sunlight toward Earth. I give rough calculations for the expected reach of each exposure of Pan-STARRS1, LSST, and Evryscope for mirror glints. A single exposure of Pan-STARRS1 has an effective reach of 10^-9 – 10^-7 AU^3 for interplanetary mirrors with effective areas of 10 m^2, depending on rotation rate. Over several years, Pan-STARRS1 might accumulate a reach ~10^5 times greater than this, as it tiles the sky and different mirrors enter and exit a favorable geometry.

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B. Lacki
Fri, 15 Mar 19
47/67

Comments: 13 pages, 8 figures, submitted

Introduction: Detectability of Future Earth [CL]

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http://arxiv.org/abs/1902.08035


Earth’s future detectability depends upon the trajectory of our civilization over the coming centuries. Human civilization is also the only known example of an energy-intensive civilization, so our history and future trajectories provide the basis for thinking about how to find life elsewhere. This special issue of Futures features contributions that consider the future evolution of the Earth system from an astrobiological perspective, with the goal of exploring the extent to which anthropogenic influence could be detectable across interstellar distances. This collection emphasizes the connection between the unfolding future of the Anthropocene with the search for extraterrestrial civilizations. Our rate of energy consumption will characterize the extent to which our energy-intensive society exerts direct influence on climate, which in turn may limit the ultimate lifetime of our civilization. If the answer to Fermi’s question is that we are alone, so that our civilization represents the only form of intelligent life in the galaxy (or even the universe), then our responsibility to survive is even greater. If we do find evidence of another civilization on a distant exoplanet, then at least we will know that our trajectory can be managed. But as long as our searches turn up empty, we must stay vigilant to keep our future secure.

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J. Haqq-Misra
Fri, 22 Feb 19
23/52

Comments: Introduction to the special issue on the Detectability of Future Earth, published in Futures (volume 106, pages 1-44)

The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion and Steady States [CL]

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http://arxiv.org/abs/1902.04450


We model the settlement of the galaxy by space-faring civilizations in order to address issues related to the Fermi Paradox. We explore the problem in a way that avoids assumptions about the intent and motivation of any exo-civilization seeking to settle other planetary systems. We first consider the speed of an advancing settlement via probes of finite velocity and range to determine if the galaxy can become inhabited with space-faring civilizations on timescales shorter than its age. We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. The results of these models demonstrate that the Milky Way can be readily ‘filled-in’ with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates. We then consider the question of the galactic steady-state achieved in terms of the fraction of settled planets. We do this by considering the effect of finite settlement civilization lifetimes on the steady states. We find a range of parameters for which the galaxy supports a population of interstellar space-faring civilizations even though some settleable systems are uninhabited. Both results point to ways in which Earth might remain unvisited in the midst of an inhabited galaxy. Finally we consider how our results can be combined with the finite horizon for evidence of previous settlements in Earth’s geologic record. Our steady-state model can constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart’s famous “Fact A” (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the galaxy.

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J. Carroll-Nellenback, A. Frank, J. Wright, et. al.
Wed, 13 Feb 19
49/62

Comments: N/A

Numerical constraints on the size of generation ships from total energy expenditure on board, annual food production and space farming techniques [CL]

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http://arxiv.org/abs/1901.09542


In the first papers of our series on interstellar generation ships we have demonstrated that the numerical code HERITAGE is able to calculate the success rate of multi-generational space missions. Thanks to the social and breeding constraints we examined, a multi-generational crew can safely reach an exoplanet after centuries of deep space travel without risks of consanguinity or genetic disorders. We now turn to addressing an equally important question : how to feed the crew? Dried food stocks are not a viable option due to the deterioration of vitamins with time and the tremendous quantities that would be required for long-term storage. The best option relies on farming aboard the spaceship. Using an updated version of HERITAGE that now accounts for age-dependent biological characteristics such as height and weight, and features related to the varying number of colonists, such as infertility, pregnancy and miscarriage rates, we can estimate the annual caloric requirements aboard using the Harris-Benedict principle. By comparing those numbers with conventional and modern farming techniques we are able to predict the size of artificial land to be allocated in the vessel for agricultural purposes. We find that, for an heterogeneous crew of 500 people living on an omnivorous, balanced diet, 0.45 km2 of artificial land would suffice in order to grow all the necessary food using a combination of aeroponics (for fruits, vegetables, starch, sugar, and oil) and conventional farming (for meat, fish, dairy, and honey).

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F. Marin, C. Beluffi, R. Taylor, et. al.
Tue, 29 Jan 19
4/62

Comments: 12 pages, 14 figures, 3 tables, accepted for publication in JBIS

Gravitational collapse and structure formation in an expanding universe with dark energy [CL]

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http://arxiv.org/abs/1803.04267


Observations show that the expansion of the Universe is accelerating. This requires that the dominant constituent of matter in the Universe has some unusual properties like negative pressure. This exotic component has been given the name dark energy. We work with the simplest model of dark energy, the cosmological constant introduced by Einstein. We study the evolution of spherical over-densities in such a model and show that there is a minimum over-density required for collapse: perturbations with a smaller amplitude do not collapse. This threshold is interesting as even perturbations with a positive over-density and negative energy do not collapse in finite time. Further, we show that perturbations with an amplitude larger than, but comparable to the threshold value, take a very long time to collapse. We compare the solutions with the case when dark energy is absent.

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M. Rajvanshi, T. Chakraborty and J. Bagla
Thu, 17 Jan 19
11/51

Comments: 17 pages, 7 figures. Accepted for publication in Resonance, journal of science education

A search for technosignatures from TRAPPIST-1, LHS 1140, and 10 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz [EPA]

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http://arxiv.org/abs/1901.04057


As part of our ongoing search for technosignatures, we collected over three terabytes of data in May 2017 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused primarily on planetary systems in the Kepler field, but also included scans of the recently discovered TRAPPIST-1 and LHS 1140 systems. We present the results of our search for narrowband signals in this data set with techniques that are generally similar to those described by Margot et al. (2018). Our improved data processing pipeline classified over $98\%$ of the $\sim$ 6 million detected signals as anthropogenic Radio Frequency Interference (RFI). Of the remaining candidates, 30 were detected outside of densely populated frequency regions attributable to RFI. These candidates were carefully examined and determined to be of terrestrial origin. We discuss the problems associated with the common practice of ignoring frequency space around candidate detections in radio technosignature detection pipelines. These problems include inaccurate estimates of figures of merit and unreliable upper limits on the prevalence of technosignatures. We present an algorithm that mitigates these problems and improves the efficiency of the search. Specifically, our new algorithm increases the number of candidate detections by a factor of more than four compared to Margot et al. (2018).

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P. Pinchuk, J. Margot, A. Greenberg, et. al.
Tue, 15 Jan 19
3/83

Comments: 17 pages, 9 figures

Interstellar Probes: The Benefits to Astronomy & Astrophysics [CL]

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http://arxiv.org/abs/1901.04422


Long range observations in the field of astronomy have opened up our understanding of the Solar System, the Galaxy and the wider Universe. In this paper we discuss the idea of direct in-situ reconnaissance of nearby stellar systems, using robotic probes. In particular, we consider what additional knowledge can be learned that can only be obtained by such close encounters. This may include calibration of existing measurements, detailed observations of stellar winds, astrometry measurements of stellar parallax, refinement of our understanding of physics through the use of long baseline interferometers. In addition, getting close to an exoplanet will enable detailed knowledge of planetary interiors, surface processes, geological evolution, atmospheric composition and climate, internal seismology, detailed surface morphology and even the speculative possibility of detecting the presence of microbial life, detailed palaeontology or even indigenous life-forms. We argue that astronomical remote sensing should be pursued in parallel with in-situ reconnaissance missions by robotic probes, so that both can enhance the discoveries and performance of the other. This work is in support of Project Starshot; an effort to send a Gram-scale probe towards another star at 0.2c within the next two decades, and return images and other data to the Earth. Presented at the 47th IAA Symposium on Future Space Astronomy and Solar System Science Missions. Session on Space Agency Strategies and Plans.

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K. Long
Tue, 15 Jan 19
7/83

Comments: 7 pages, 1 figure, 1 table, Presented at 47th IAA Symposium on Future Space Astronomy & Solar System Missions. Submitted to Acta Astronautica 19th December 2018

Why planetary and exoplanetary protection differ: The case of long duration Genesis missions to habitable but sterile M-dwarf oxygen planets [CL]

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http://arxiv.org/abs/1901.02286


Time is arguably the key limiting factor for interstellar exploration. At high speeds, flyby missions to nearby stars by laser propelled wafersats taking 50-100 years would be feasible. Directed energy launch systems could accelerate on the other side also crafts weighing several tons to cruising speeds of the order of 1000\,km/s (c/300). At these speeds, superconducting magnetic sails would be able to decelerate the craft by transferring kinetic energy to the protons of the interstellar medium. A tantalizing perspective, which would allow interstellar probes to stop whenever time is not a limiting factor. Prime candidates are in this respect Genesis probes, that is missions aiming to offer terrestrial life new evolutionary pathways on potentially habitable but hitherto barren exoplanets.
Genesis missions raise important ethical issues, in particular with regard to planetary protection. Here we argue that exoplanetary and planetary protection differ qualitatively as a result of the vastly different cruising times for payload delivering probes, which are of the order of millennia for interstellar probes, but only of years for solar system bodies. Furthermore we point out that our galaxy may harbor a large number of habitable exoplanets, M-dwarf planets, which could be sterile due to the presence of massive primordial oxygen atmospheres. We believe that the prospect terrestrial life has in our galaxy would shift on a fundamental level in case that the existence of this type of habitable but sterile oxygen planets will be corroborated by future research. It may also explain why our sun is not a M dwarf, the most common star type, but a medium-sized G-class star.

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C. Gros
Wed, 9 Jan 19
31/46

Comments: in press

On times and shadows: the observational analemma [CL]

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http://arxiv.org/abs/1812.10719


The observation that the shadows of objects change during the course of the day and also for a fixed time during a year led curious minds to realize that the Sun could be used as a timekeeper. However, the daily motion of the Sun has some subtleties, for example, with regards to the precise time at which it crosses the meridian near noon. When the Sun is on the meridian, a clock is used to ascertain this time and a vertical stick determines the angle the Sun is above the horizon. These two measurements lead to the construction of a diagram (called an analemma) as an extremely useful resource for the teaching of astronomy. In this paper we report on the construction of this diagram from roughly weekly observations during more than a year.

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A. Gangui, C. Lastra and F. Karaseur
Mon, 31 Dec 18
39/57

Comments: Published version available at this http URL

NASA and the Search for Technosignatures: A Report from the NASA Technosignatures Workshop [IMA]

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http://arxiv.org/abs/1812.08681


This report is the product of the NASA Technosignatures Workshop held at the Lunar and Planetary Institute in Houston, Texas, in September 2018. This workshop was convened by NASA for the organization to learn more about the current field and state of the art of searches for technosignatures, and what role NASA might play in these searches in the future. The report, written by the workshop participants, summarizes the material presented at the workshop and incorporates additional inputs from the participants. Section 1 explains the scope and purpose of the document, provides general background about the search for technosignatures, and gives context for the rest of the report. Section 2 discusses which experiments have occurred, along with current limits on technosignatures. Section 3 addresses the current state of the technosignature field as well as the state-of-the-art for technosignature detection. Section 4 addresses near-term searches for technosignatures, and Section 5 discusses emerging and future opportunities in technosignature detection.

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N. Participants
Fri, 21 Dec 18
24/72

Comments: Edited by Dawn Gelino (NExScI) and Jason Wright (PSU); Chapter Leads: Natalie Batalha (UCSC), Svetlana Berdyugina (KIS/PLANETS), Emilio Enriquez (UCB), Shubham Kanodia (PSU), Andrew Siemion (UCB), Jason Wright (PSU), Shelley Wright (UCSD)

Six Strange Facts About`Oumuamua [CL]

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http://arxiv.org/abs/1811.08832


`Oumuamua is nothing like we expected or seen before in the Solar System.

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A. Loeb
Tue, 27 Nov 18
48/74

Comments: Published in Observations, Scientific American (November 20, 2018); this https URL

Creating music based on quantitative data from variable stars [IMA]

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http://arxiv.org/abs/1811.02930


In this work we show a technique that allows for the musical interpretation of the brightness variations of stars. This method allows composers a lot of freedom to incorporate their own ideas into the score, based on the melodic line generated from the quantitative data obtained from the stars. There are a wide number of possible applications for this technique, including avant-garde music creation, teaching and promotion of the association between music and science.

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C. Droppelmann and R. Mennickent
Thu, 8 Nov 18
46/72

Comments: Accepted for publication in Journal of the American Association of Variable Star Observers

Engaging the Public with Supernova and Supernova Remnant Research Using Virtual Reality [IMA]

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http://arxiv.org/abs/1811.01542


On 21 April 2018, the citizens of Wako, Japan, interacted in a novel way with research being carried out at the Astrophysical Big Bang Laboratory (ABBL) at RIKEN. They were able to explore a model of a supernova and its remnant in an immersive three-dimentional format by using virtual reality (VR) technology. In this article, we explain how this experience was developed and delivered to the public, providing practical tips for and reflecting on the successful organisation of an event of this kind.

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G. Ferrand and D. Warren
Tue, 6 Nov 18
13/77

Comments: CAPjournal Issue 24 October 2018 this https URL

Algol as Horus in the Cairo Calendar: the possible means and the motives of the observations [CL]

Posted on by

http://arxiv.org/abs/1810.06412


An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck with the period of 2.850 days. Previous astronomical, astrophysical and statistical analyses of CC support the idea that this was the period of the eclipsing binary Algol three millennia ago. However, next to nothing is known about who recorded Algol’s period into CC and especially how. Here, we show that the ancient Egyptian scribes had the possible means and the motives for such astronomical observations. Their principles of describing celestial phenomena as activity of gods reveal why Algol received the title of Horus.

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S. Porceddu, L. Jetsu, T. Markkanen, et. al.
Tue, 16 Oct 18
9/83

Comments: 34 pages, 6 figures, accepted in Open Astronomy

Exploring the Kuiper Belt with Sun-diving Solar Sails [IMA]

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http://arxiv.org/abs/1810.00407


We discuss a possibility to survey many Kuiper Belt Objects (KBO) with a single launch using a few smallscale spacecraft, each equipped with solar sails, which could be unfurled from a single interplanetary bus at the perihelion of that craft’s solar orbit. Each small-scale spacecraft would carry a scientific payload and would be directed to intersect one or more KBOs. The proposed scenario is the following: the sails are carried as a payload to a relatively small heliocentric distance (0.1 – 0.3 AU). Once at the perihelion, the sails are deployed. Besides electromagnetic propulsion due to the solar radiation, another mechanism could be convenient: thermal desorption, a physical process of mass loss which can provide additional thrust as heating liberates atoms, embedded on the surface of a solar sail. Therefore, the sails experience additional propulsive force due to the thermal desorption that dramatically increases the distance that sails travel per year.

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E. Ancona, R. Kezerashvili and G. Matloff
Tue, 2 Oct 18
38/84

Comments: 6 pages, 6 figures

Recommendations from the Ad Hoc Committee on SETI Nomenclature [CL]

Posted on by

http://arxiv.org/abs/1809.06857


The Ad Hoc Committee on SETI Nomenclature was convened at the suggestion of Frank Drake after the Decoding Alien Intelligence Workshop at the SETI Institute in March 2018. The purpose of the committee was to recommend standardized definitions for terms, especially those that are used inconsistently in the literature and the scientific community. The committee sought to recommend definitions and terms that are a compromise among several desirable but occasionally inconsistent properties for such terms:
1) Consistency with the historical literature and common use in the field; 2) Consistency with the present literature and common use in the field; 3) Precision of meaning; 4) Consistency with the natural (i.e. everyday, non-jargon) meanings of terms; 5) Compatibility with non-English terms and definitions.
The definitions in this report are restricted to technical, SETI contexts, where they may have jargon senses different from their everyday senses. In many cases we include terms only to deprecate them (in the sense of “to withdraw official support for or discourage the use of…in favor of a newer or better alternative”, Merriam-Webster sense 4).
This is a consensus document that the committee members all endorse; however, in many cases the individual members have (or have expressed in the past) more nuanced opinions on these terms that are not fully reflected here, for instance Alm\’ar (2008, Acta Astronautica, 68, 351), Denning (2008, NASA-SP-2009-4802 Ch. 3 pp.63-124), and Wright (2018, arXiv:1803.06972).

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J. Wright, S. Sheikh, I. Almár, et. al.
Thu, 20 Sep 18
10/55

Comments: 10pp, to be presented at the NASA Technosignatures Workshop in Houston, TX, USA Sep. 26-28, 2018

A Novel Entry, Descent and Landing Architecture for Mars Landers [CL]

Posted on by

http://arxiv.org/abs/1809.00062


Landing robotic spacecrafts and humans on the surface of Mars has become one of the technological needs for humans. To accomplish this intent, we need to land an enormous number of cargoes, crewed modules, scientific laboratories and return vehicles on Mars. In this entailing condition, there are many incidences of the crash landing of landers leading to complete demolition of lander modules. Crash landing occurs due to numerous circumstances. Significant problems and their proportions were illustrated in Fig.1. Moreover, existences of deformable shock absorbers like aluminium honeycomb and crushable carbon fibres in landing gears are not feasible for high scale mass and crewed landing, as a consequence it may cause impairment of landing module. Furthermore, in the interim of EDL performance, one of the most challenging tasks for lander is landing and switching EDL events within the limited span of 5 to 8 minutes. Scrutinizing this concern, we are proposing a novel shock absorbing landing gear system that will be more accomplishable for large-scale and frequent landing missions. This paper relies on the theoretical proposal for the practical design of landing gear system and we expect that subject to any obstruction in EDL sequence, this mechanical system will enable soft-landing thereby increasing the probability of success in forthcoming landing missions. Hence, our ultimate aim is to protect lander modules and its instruments during the course of landing phase.

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M. M and R. A
Fri, 7 Sep 18
42/65

Comments: 19 pages, 16 figues, 3 tables

Limitations of Chemical Propulsion for Interstellar Escape from Habitable Zones around Low-Mass Stars [CL]

Posted on by

http://arxiv.org/abs/1808.08141


The habitable zones of low-mass stars are characterized by escape speeds that can be a few times higher than the Earth’s orbit around the Sun. Owing to the exponential dependence of the required fuel mass on the terminal speed for chemical rockets, interstellar travel may not be easy for technological species inhabiting planets around M-dwarfs.

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M. Lingam and A. Loeb
Mon, 27 Aug 18
8/46

Comments: Accepted for publication in Research Notes of the AAS; 3 pages

Around the Pleiades [IMA]

Posted on by

http://arxiv.org/abs/1808.02968


We present a calculation of the distance to the Pleiades star cluster based on data from Gaia DR2. We show that Gaia finally settles the discrepancy between the values derived from Hipparcos and other distance determinations. The technical level of the presentation is adequate for the interested layperson.

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G. Abramson
Fri, 10 Aug 18
38/45

Comments: N/A

Yes, Aboriginal Australians Can and Did Discover the Variability of Betelgeuse [CL]

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http://arxiv.org/abs/1808.01862


Recently, a widely publicized claim has been made that the Aboriginal Australians discovered the variability of the red star Betelgeuse in the modern Orion, plus the variability of two other prominent red stars: Aldebaran and Antares. This result has excited the usual healthy skepticism, with questions about whether any untrained peoples can discover the variability and whether such a discovery is likely to be placed into lore and transmitted for long periods of time. Here, I am offering an independent evaluation, based on broad experience with naked-eye sky viewing and astro-history. I find that it is easy for inexperienced observers to detect the variability of Betelgeuse over its range in brightness from V = 0.0 to V = 1.3, for example in noticing from season-to-season that the star varies from significantly brighter than Procyon to being greatly fainter than Procyon. Further, indigenous peoples in the Southern Hemisphere inevitably kept watch on the prominent red star, so it is inevitable that the variability of Betelgeuse was discovered many times over during the last 65 millennia. The processes of placing this discovery into a cultural context (in this case, put into morality stories) and the faithful transmission for many millennia is confidently known for the Aboriginal Australians in particular. So this shows that the whole claim for a changing Betelgeuse in the Aboriginal Australian lore is both plausible and likely. Given that the discovery and transmission is easily possible, the real proof is that the Aboriginal lore gives an unambiguous statement that these stars do indeed vary in brightness, as collected by many ethnographers over a century ago from many Aboriginal groups. So I strongly conclude that the Aboriginal Australians could and did discover the variability of Betelgeuse, Aldebaran, and Antares.

Read this paper on arXiv…

B. Schaefer
Tue, 7 Aug 18
29/68

Comments: N/A

Relative Likelihood of Success in the Searches for Primitive versus Intelligent Extraterrestrial Life [CL]

Posted on by

http://arxiv.org/abs/1807.08879


We estimate the relative likelihood of success in the searches for primitive versus intelligent life on other planets. Taking into account the larger search volume for detectable artificial electromagnetic signals, we conclude that both searches should be performed concurrently, albeit with significantly more funding dedicated to primitive life. Our analysis suggests that the search for technosignatures may potentially merit a minimum funding level of $\$1$ million per year.

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M. Lingam and A. Loeb
Wed, 25 Jul 18
46/60

Comments: 19 pages; 0 figures

Securing Fuel for Our Frigid Cosmic Future [CL]

Posted on by

http://arxiv.org/abs/1806.07170


Advanced civilizations will likely migrate into rich clusters of galaxies, which host the largest reservoirs of matter bound by gravity against the accelerated cosmic expansion.

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A. Loeb
Wed, 20 Jun 18
41/58

Comments: 3 pages, accepted for publication in Scientific American

Life Versus Dark Energy: How An Advanced Civilization Could Resist the Accelerating Expansion of the Universe [CEA]

Posted on by

http://arxiv.org/abs/1806.05203


The presence of dark energy in our universe is causing space to expand at an accelerating rate. As a result, over the next approximately 100 billion years, all stars residing beyond the Local Group will fall beyond the cosmic horizon and become not only unobservable, but entirely inaccessible, thus limiting how much energy could one day be extracted from them. Here, we consider the likely response of a highly advanced civilization to this situation. In particular, we argue that in order to maximize its access to useable energy, a sufficiently advanced civilization would chose to expand rapidly outward, build Dyson Spheres or similar structures around encountered stars, and use the energy that is harnessed to accelerate those stars away from the approaching horizon and toward the center of the civilization. We find that such efforts will be most effective for stars with masses in the range of $M\sim (0.2-1) M_{\odot}$, and could lead to the harvesting of stars within a region extending out to several tens of Mpc in radius, potentially increasing the total amount of energy that is available to a future civilization by a factor of several thousand. We also discuss the observable signatures of a civilization elsewhere in the universe that is currently in this state of stellar harvesting.

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D. Hooper
Fri, 15 Jun 18
33/54

Comments: 11 pages, 4 figures

Computing the minimal crew for a multi-generational space travel towards Proxima Centauri b [IMA]

Posted on by

http://arxiv.org/abs/1806.03856


The survival of a genetically healthy multi-generational crew is of a prime concern when dealing with space travel. It has been shown that determining a realistic population size is tricky as many parameters (such as infertility, inbreeding, sudden deaths, accidents or random events) come into play. To evaluate the impact of those parameters, Monte Carlo simulations are among the best methods since they allow testing of all possible scenarios and determine, by numerous iterations, which are the most likely. This is why we use the Monte Carlo code HERITAGE to estimate the minimal crew for a multi-generational space travel towards Proxima Centauri b. By allowing the crew to evolve under a list of adaptive social engineering principles (namely yearly evaluations of the vessel population, offspring restrictions and breeding constraints), we show in this paper that it is possible to create and maintain a healthy population virtually indefinitely. A initial amount of 25 breeding pairs of settlers drives the mission towards extinction in 50 +/- 15% of cases if we completely forbid inbreeding. Under the set of parameters described in this publication, we find that a minimum crew of 98 people is necessary ensure a 100% success rate for a 6300-year space travel towards the closest telluric exoplanet known so far.

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F. Marin and C. Beluffi
Tue, 12 Jun 18
15/79

Comments: 8 pages, 6 figures, 2 tables. Accepted for publication in JBIS

Locating Planets in Sky Using Manual Calculations [CL]

Posted on by

http://arxiv.org/abs/1806.01649


In this article, we describe a very simple technique to locate naked-eye planets in the sky, to an accuracy of $\sim 1^{\circ}$. The procedure, comprising just three steps, involves very simple manual calculations for planetary orbits around the Sun; all one needs are the initial specifications of planetary positions for some standard epoch and the time periods of their revolutions. After applying a small correction for the orbital ellipticity, appearance of a planet relative to Sun’s position in sky, as seen by an observer from Earth, is found using a scale and a protractor (found inside a school geometry box).

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A. Singal
Wed, 6 Jun 18
18/68

Comments: 8 pages, 4 tables, 2 figures

Experimental Tests of Spirituality [CL]

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http://arxiv.org/abs/1806.01661


We currently harness technologies that could shed new light on old philosophical questions, such as whether our mind entails anything beyond our body or whether our moral values reflect universal truth.

Read this paper on arXiv…

A. Loeb
Wed, 6 Jun 18
55/68

Comments: 2 pages, accepted for publication in Scientific American

Lets Talk About Black Hole Singularities [CL]

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http://arxiv.org/abs/1805.05865


Does the collision of black hole singularities imprint an observable quantum signature on the resulting gravitational wave signal?

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A. Loeb
Wed, 16 May 18
27/92

Comments: 2 pages, to be published in Scientific American

The Reclassification of Asteroids from Planets to Non-Planets [EPA]

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http://arxiv.org/abs/1805.04115


It is often claimed that asteroids’ sharing of orbits is the reason they were re-classified from planets to non-planets. A critical review of the literature from the 19th Century to the present shows this is factually incorrect. The literature shows the term asteroid was broadly recognized as a subclass of planet for 150 years. On-going discovery of asteroids resulted in a de facto stretching of the concept of planet to include the ever smaller bodies. Scientists found utility in this taxonomic identification as it provided categories needed to argue for the leading hypothesis of planet formation, Laplace’s nebular hypothesis. In the 1950s, developments in planet formation theory found it no longer useful to maintain taxonomic identification between asteroids and planets, Ceres being the sole exception. At approximately the same time, there was a flood of publications on the geophysical nature of asteroids showing them to be geophysically different than the large planets. This is when the terminology in asteroid publications calling them planets abruptly plunged from a high level of usage where it had hovered during the period 1801 – 1957 to a low level that held constant thereafter. This marks the point where the community effectively formed consensus that asteroids should be taxonomically distinct from planets. The evidence demonstrates this consensus formed on the basis of geophysical differences between asteroids and planets, not the sharing of orbits. We suggest attempts to build consensus around planetary taxonomy not rely on the non-scientific process of voting, but rather through precedent set in scientific literature and discourse, by which perspectives evolve with additional observations and information, just as they did in the case of asteroids.

Read this paper on arXiv…

P. Metzger, M. Sykes, A. Stern, et. al.
Mon, 14 May 18
25/54

Comments: 27 pages, 4 figures

The Breakthrough Starshot System Model [IMA]

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http://arxiv.org/abs/1805.01306


Breakthrough Starshot is an initiative to prove ultra-fast light-driven nanocrafts, and lay the foundations for a first launch to Alpha Centauri within the next generation. Along the way, the project could generate important supplementary benefits to solar system exploration. A number of hard engineering challenges remain to be solved before these missions can become a reality.
A system model has been formulated as part of the Starshot systems engineering work. This paper presents the model and describes how it computes cost-optimal point designs. Using the model, three scenarios are examined: A 0.2 c mission to Alpha Centauri, a 0.01 c solar system precursor mission, and a ground-based test facility based on a vacuum tunnel. All assume that the photon pressure from a 1.06 {\mu}m wavelength beam accelerates a circular dielectric sail. The 0.2 c point design assumes \$0.01/W lasers, \$500/m$^2$ optics, and \$50/kWh energy storage to achieve \$8.3B capital cost for the ground-based beam director. In contrast, the energy needed to accelerate each sail costs \$7M. Beam director capital cost is minimized by a 4.2 m diameter sail that is accelerated for 10 min. The 0.01 c point design assumes \$1/W lasers, \$10k/m$^2$ optics, and \$100/kWh energy storage to achieve \$517M capital cost for the beam director and \$8k energy cost to accelerate each 19 cm diameter sail. The ground-based test facility assumes \$100/W lasers, \$1M/m$^2$ optics, \$500/kWh energy storage, and \$10k/m vacuum tunnel. To reach 20 km/s, fast enough to escape the solar system from Earth, takes 0.3 km of vacuum tunnel, 16 kW of lasers, and a 0.9 m diameter telescope, all of which costs \$6M.
The system model predicts that, ultimately, Starshot scales to cruise velocities of greater than 0.9 c.

Read this paper on arXiv…

K. Parkin
Fri, 4 May 18
4/65

Comments: N/A

Spaceflight from Super-Earths is difficult [CL]

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http://arxiv.org/abs/1804.04727


Many rocky exoplanets are heavier and larger than the Earth, and have higher surface gravity. This makes space-flight on these worlds very challenging, because the required fuel mass for a given payload is an exponential function of planetary surface gravity, $\sim 3.3\,\exp(g_{\rm 0})$. We find that chemical rockets still allow for escape velocities on Super-Earths up to 10x Earth mass. More massive rocky worlds, if they exist, would require other means to leave the planet, such as nuclear propulsion.

Read this paper on arXiv…

M. Hippke
Mon, 16 Apr 18
22/52

Comments: Serious version of the April Fool’s idea (arXiv:1803.11384). Submitted on April 4th 2018

Interstellar Escape from Proxima b is Barely Possible with Chemical Rockets [CL]

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http://arxiv.org/abs/1804.03698


A civilization in the habitable zone of a dwarf star might find it challenging to escape into interstellar space using chemical propulsion.

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A. Loeb
Thu, 12 Apr 18
9/54

Comments: 3 pages, accepted for publication in Scientific American

Role of stellar physics in regulating the critical steps for life [CL]

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http://arxiv.org/abs/1804.02271


We use the critical step model to study the major transitions in evolution on Earth. We find that a total of five steps represents the most plausible estimate, in agreement with previous studies, and use the fossil record to identify the potential candidates. We apply the model to Earth-analogs around stars of different masses by incorporating the constraints on habitability set by stellar physics including the habitable zone lifetime, availability of ultraviolet radiation for prebiotic chemistry, and atmospheric escape. The critical step model suggests that the habitability of Earth-analogs around M-dwarfs is significantly suppressed. The total number of stars with planets containing detectable biosignatures of microbial life is expected to be highest for K-dwarfs. In contrast, we find that the corresponding value for intelligent life (technosignatures) should be highest for solar-mass stars. Thus, our work may assist in the identification of suitable targets in the search for biosignatures and technosignatures.

Read this paper on arXiv…

M. Lingam and A. Loeb
Tue, 10 Apr 18
11/79

Comments: 34 pages; 5 figures

Independent Discovery of a Sub-Earth in the Habitable Zone Around a Very Close Solar-Mass Star [CL]

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http://arxiv.org/abs/1804.00419


With the wealth of planets that have been discovered over the past $\sim$ 20 years, the field can broadly be divided into two regimes. For understanding broad occurrence and formation rates, large numbers of planets allow for population statistics to be calculated, and this work preferentially tends towards fainter planets (and fainter host stars) to allow for a large number of detections. The second regime is the detailed understanding of a single planet, with particular consideration to planetary structure and atmosphere, and in this case benefits from finding individual planets (and host stars) that are very close, and subsequently, very bright. The closest of these also provide very novel possibilities for exploration if they are close enough that travel time to them is relatively low, something that would be extremely unlikely for more distant planets. Here, we announce the independent discovery of a sub-earth planet orbiting in the habitable zone of a very close solar-mass star using a novel processing technique and observations from the Kilodegree Extremely Little Telescope (KELT).

Read this paper on arXiv…

M. Lund, R. Siverd and P. Stibbons
Tue, 3 Apr 18
3/57

Comments: 6 pages, 3 figures, submission for Sunday’s Acta Prima Aprilia

Super-Earths in need for Extremly Big Rockets [CL]

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http://arxiv.org/abs/1803.11384


Many rocky exoplanets are heavier and larger than Earth, so-called “Super-Earths”. Some of these may be habitable, and a few may be inhabited by Super-Earthlings. Due to the higher surface gravity on these worlds, space-flight is much more challenging. We find that chemical rockets still allow for escape velocities on Super-Earths up to 10x Earth mass. Much heavier rocky worlds, if they exist, will require using up most of the planet as chemical fuel for the (one) launch, a rather risky undertaking. We also briefly discuss launching rockets from water worlds, which requires Alien megastructures.

Read this paper on arXiv…

M. Hippke
Mon, 2 Apr 18
9/39

Comments: N/A

Sitnikov in Westeros: How Celestial Mechanics finally explains why winter is coming in Game of Thrones [CL]

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http://arxiv.org/abs/1803.11390


“Winter is coming”. As far as meteorological predictions go, the words of House Stark are both trivial and not very helpful for a scientific analysis to explain the chaotic sequence of the seasons in the world of “Game of Thrones”. The natives of Westeros have failed to develop a feasible model to understand and predict the coming and duration of their winters. And although the scientists of Earth have brought forth many different mechanisms to explain the seasons, all of them are found wanting (at least by us). Nobody seems to have discovered the one and only true and working mechanism to explain the coming and going of winters on Westeros and thus it is up to us to introduce the world to the might of the often ignored Sitnikov problem. That very special configuration of two stars and one planet is ideally suited to explain everything that needs to be explained and uncover the real reason for the coming of winter.

Read this paper on arXiv…

F. Freistetter and R. Grutzbauch
Mon, 2 Apr 18
12/39

Comments: 10 pages, 3 figures

Implications of Neutron Star Mergers for Extraterrestrial Civilizations [CL]

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http://arxiv.org/abs/1803.04919


The economy and fate of extraterrestrial civilizations should depend on the abundance of gold and uranium, made in neutron star mergers.

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A. Loeb
Wed, 14 Mar 2018
23/61

Comments: 3 pages, no figures, published in Scientific American

A search for Extraterrestrial Intelligence (SETI) toward the Galactic Anticenter with the Murchison Widefield Array [CL]

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http://arxiv.org/abs/1803.00524


Following from the results of the first systematic modern low frequency Search for Extraterrestrial Intelligence (SETI) using the Murchison Widefield Array (MWA), which was directed toward a Galactic Center field, we report a second survey toward a Galactic Anticenter field. Using the MWA in the frequency range of 99 to 122 MHz over a three hour period, a 625 sq. deg. field centered on Orion KL (in the general direction of the Galactic Anticenter) was observed with a frequency resolution of 10 kHz. Within this field, 22 exoplanets are known. At the positions of these exoplanets, we searched for narrow band signals consistent with radio transmissions from intelligent civilisations. No such signals were found with a 5-sigma detection threshold. Our sample is significantly different to the 45 exoplanets previously studied with the MWA toward the Galactic Center Tingay et al.(2016), since the Galactic Center sample is dominated by exoplanets detected using microlensing, hence at much larger distances compared to the exoplants toward the Anticenter, found via radial velocity and transit detection methods. Our average effective sensitivity to extraterrestrial transmiter power is therefore much improved for the Anticenter sample. Added to this, our data processing techniques have improved, reducing our observational errors, leading to our best detection limit being reduced by approximately a factor of four compared to our previously published results.

Read this paper on arXiv…

S. Tingay, C. Tremblay and S. Croft
Fri, 2 Mar 18
29/61

Comments: Six pages, two figures. Accepted for publication in ApJ

Area Coverage of Expanding E.T. Signals in the Galaxy: SETI and Drake's N [CL]

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http://arxiv.org/abs/1802.09399


The Milky Way Galaxy contains an unknown number, $N$, of civilizations that emit electromagnetic radiation (of unknown wavelengths) over a finite lifetime, $L$. Here we are assuming that the radiation is not produced indefinitely, but within $L$ as a result of some unknown limiting event. When a civilization stops emitting, the radiation continues traveling outward at the speed of light, $c$, but is confined within a shell wall having constant thickness, $cL$. We develop a simple model of the Galaxy that includes both the birthrate and detectable lifetime of civilizations to compute the possibility of a SETI detection at the Earth. Two cases emerge for radiation shells that are (1) thinner than or (2) thicker than the size of the Galaxy, corresponding to detectable lifetimes, $L$, less than or greater than the light-travel time, $\sim 100,000$ years, across the Milky Way, respectively. For case (1), each shell wall has a thickness smaller than the size of the Galaxy and intersects the galactic plane in a donut shape (annulus) that fills only a fraction of the Galaxy’s volume, inhibiting SETI detection. But the ensemble of such shell walls may still fill our Galaxy, and indeed may overlap locally, given a sufficiently high birthrate of detectable civilizations. In the second case, each radiation shell is thicker than the size of our Galaxy. Yet, the ensemble of walls may or may not yield a SETI detection depending on the civilization birthrate. We compare the number of different electromagnetic transmissions arriving at Earth to Drake’s $N$, the number of currently emitting civilizations, showing that they are equal to each other for both cases (1) and (2). However, for $L < 100,000$ years, the transmissions arriving at Earth may come from distant civilizations long extinct, while civilizations still alive are sending signals yet to arrive.

Read this paper on arXiv…

C. Grimaldi, G. Marcy, N. Tellis, et. al.
Tue, 27 Feb 18
85/85

Comments: 10 pages, 2 figures, to be published in PASP

Rejuvenating the Contract of Academia With Society [CL]

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http://arxiv.org/abs/1802.05289


Academia owes the public a fresh look at its education and research mission. First and foremost, researchers must communicate the results of their latest studies in a truthful and meaningful way. Second, the traditional boundaries among disciplines should be blurred since innovation often blossoms along these boundaries. Third, universities should develop courses which are relevant for the skills required in the job market today. Finally, professors should mentor the future leaders of science, technology, arts and humanities and not just replicate themselves.

Read this paper on arXiv…

A. Loeb
Mon, 19 Feb 18
21/41

Comments: 3 pages, Accepted for publication in Scientific American

Interstellar communication. IX. Message decontamination is impossible [IMA]

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http://arxiv.org/abs/1802.02180


A complex message from space may require the use of computers to display, analyze and understand. Such a message cannot be decontaminated with certainty, and technical risks remain which can pose an existential threat. Complex messages would need to be destroyed in the risk averse case.

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M. Hippke and J. Learned
Thu, 8 Feb 18
9/43

Comments: 3 pages, comments welcome

Stability and self-organization of planetary systems [EPA]

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http://arxiv.org/abs/1801.08575


We show that stability of planetary systems is intimately connected with their internal order. An arbitrary initial distribution of planets is susceptible to catastrophic events in which planets either collide or are ejected from the planetary system. These instabilities are a fundamental consequence of chaotic dynamics and of Arnold diffusion characteristic of many body gravitational interactions. To ensure stability over astronomical time scale of a realistic planetary system — in which planets have masses comparable or those of planets in the solar system — the motion must be quasi-periodic. A dynamical mechanism is proposed which naturally evolves a planetary system to a periodic state from an arbitrary initial condition. A planetary self-organization predicted by the theory is similar to the one found in our solar system.

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R. Pakter and Y. Levin
Mon, 29 Jan 18
6/54

Comments: N/A

Fine-Tuning, Complexity, and Life in the Multiverse [CL]

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http://arxiv.org/abs/1801.06944


The physical processes that determine the properties of our everyday world, and of the wider cosmos, are determined by some key numbers: the ‘constants’ of micro-physics and the parameters that describe the expanding universe in which we have emerged. We identify various steps in the emergence of stars, planets and life that are dependent on these fundamental numbers, and explore how these steps might have been changed, or completely prevented, if the numbers were different. We then outline some cosmological models where physical reality is vastly more extensive than the ‘universe’ that astronomers observe (perhaps even involving many ‘big bangs’), which could perhaps encompass domains governed by different physics. Although the concept of a multiverse is still speculative, we argue that attempts to determine whether it exists constitute a genuinely scientific endeavor. If we indeed inhabit a multiverse, then we may have to accept that there can be no explanation other than anthropic reasoning for some features our world.

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M. Livio and M. Rees
Tue, 23 Jan 18
11/85

Comments: Chapter for the book Consolidation of Fine Tuning, 17 pages, 3 figures