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Thread: Astrobiological papers from Arvix and everywhere

  1. #91
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    A potentially fascinating history of the question of whether we are alone in the universe, but behind a paywall.

    https://ui.adsabs.harvard.edu/abs/20......3C/abstract
    The Extraterrestrial Life Debate from Antiquity to 1900
    Crowe, Michael J. ; Dowd, Matthew F.

    This chapter provides an overview of the Western historical debate regarding extraterrestrial life from antiquity to the beginning of the twentieth century. Though schools of thought in antiquity differed on whether extraterrestrial life existed, by the Middle Ages, the Aristotelian worldview of a unified, finite cosmos without extraterrestrials was most influential, though there were such dissenters as Nicholas of Cusa. That would change as the Copernican revolution progressed. Scholars such as Bruno, Kepler, Galileo, and Descartes would argue for a Copernican system of a moving Earth. Cartesian and Newtonian physics would eventually lead to a view of the universe in which the Earth was one of many planets in one of many solar systems extended in space. As this cosmological model was developing, so too were notions of extraterrestrial life. Popular and scientific writings, such as those by Fontenelle and Huygens, led to a reversal of fortunes for extraterrestrials, who by the end of the century were gaining recognition. From 1700 to 1800, many leading thinkers discussed extraterrestrial intelligent beings. In doing so, they relied heavily on arguments from analogy and such broad principles and ideas as the Copernican Principle, the Principle of Plenitude, and the Great Chain of Being. Physical evidence for the existence of extraterrestrials was minimal, and was always indirect, such as the sighting of polar caps on Mars, suggesting similarities between Earth and other places in the universe. Nonetheless, the eighteenth century saw writers from a wide variety of genres—science, philosophy, theology, literature—speculate widely on extraterrestrials. In the latter half of the century, increasing research in stellar astronomy would be carried out, heavily overlapping with an interest in extraterrestrial life. By the end of the eighteenth century, belief in intelligent beings on solar system planets was nearly universal and certainly more common than it would be by 1900, or even today. Moreover, natural theology led to most religious thinkers being comfortable with extraterrestrials, at least until 1793 when Thomas Paine vigorously argued that although belief in extraterrestrial intelligence was compatible with belief in God, it was irreconcilable with belief in God becoming incarnate and redeeming Earth's sinful inhabitants. In fact, some scientific analyses, such as Newton's determination of the comparative masses and densities of planets, as well as the application of the emerging recognition of the inverse square law for light and heat radiation, might well have led scientists to question whether all planets are fully habitable. Criticism would become more prevalent throughout the nineteenth century, and especially after 1860, following such events as the "Moon Hoax" and Whewell's critique of belief in extraterrestrials. Skepticism about reliance on arguments from analogy and on such broad metaphysical principles as the Principle of Plenitude also led scientists to be cautious about claims for higher forms of life elsewhere in the universe. At the start of the twentieth century, the controversy over the canals of Mars further dampened enthusiasm for extraterrestrials. By 1915 astronomers had largely rejected belief in higher forms of life anywhere in our solar system and were skeptical about the island universe theory.
    Do good work. —Virgil Ivan "Gus" Grissom

  2. #92
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    So, panspermia was not such a dumb idea after all?

    https://arxiv.org/abs/2001.02235

    Transfer of Life by Earth-Grazing Objects to Exoplanetary Systems
    Amir Siraj, Abraham Loeb
    (Submitted on 7 Jan 2020)

    Recently, a 30 cm object was discovered to graze the Earth's atmosphere and shift into a Jupiter-crossing orbit. We use the related survey parameters to calibrate the total number of such objects. The number of objects that could have exported terrestrial microbes out of the Solar System is in the range 2×10^9 − 3×10^11. We find that 10^7−10^9 such objects could have been captured by binary star systems over the lifetime of the Solar System. The total number of objects carrying living microbes on them upon capture is 10−10^3.
    Do good work. —Virgil Ivan "Gus" Grissom

  3. #93
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    Radiation might be a good thing to make some planets habitable for a long period of time.

    https://arxiv.org/abs/1912.02862

    On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide Abundances
    Manasvi Lingam, Abraham Loeb
    (Submitted on 5 Dec 2019 (v1), last revised 24 Jan 2020 (this version, v2))

    The presence of a liquid solvent is widely regarded as an essential prerequisite for habitability. We investigate the conditions under which worlds outside the habitable zones of stars are capable of supporting liquid solvents on their surface over geologically significant timescales via combined radiogenic and primordial heat. Our analysis suggests that super-Earths with radionuclide abundances that are ≳ 10^3 times higher than Earth can host long-lived water oceans. In contrast, the requirements for long-lived ethane oceans, which have been explored in the context of alternative biochemistries, are less restrictive: relative radionuclide abundances of ≳ 10^2 could be sufficient. We find that this class of worlds might be detectable (10σ detection over ∼10 days integration time at 12.8μ m) in principle by the James Webb Space Telescope at distances of ∼10 pc if their ages are ≲ 1 Gyr.
    Do good work. —Virgil Ivan "Gus" Grissom

  4. #94
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    Black hole sun? Could be, says this author, but aliens on planets around black holes would be in deeeep gravity wells. https://arxiv.org/abs/2001.10991
    Do good work. —Virgil Ivan "Gus" Grissom

  5. #95
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    What might life be like on Titan? A new paper peers into the possibilities by looking at how cell membranes might function there.

    https://www.airspacemag.com/daily-pl...urs-180974104/

    On Saturn’s Moon Titan, Living Cells May Be Very Different From Ours
    Yet another good reason to visit this exotic world.
    By Dirk Schulze-Makuch
    airspacemag.com January 31, 2020 1:30PM

    In a new paper published in Science Advances, Hilda Sandström and Martin Rahm from Chalmers University of Technology in Gothenburg, Sweden, consider the possibility of life on Titan—and, more specifically, whether living creatures would need cell membranes to survive.

    ==

    https://advances.sciencemag.org/content/6/4/eaax0272

    Can polarity-inverted membranes self-assemble on Titan?
    H. Sandström and M. Rahm
    Science Advances 24 Jan 2020: Vol. 6, no. 4, eaax0272

    Abstract: The environmental and chemical limits of life are two of the most central questions in astrobiology. Our understanding of life’s boundaries has implications on the efficacy of biosignature identification in exoplanet atmospheres and in the solar system. The lipid bilayer membrane is one of the central prerequisites for life as we know it. Previous studies based on molecular dynamics simulations have suggested that polarity-inverted membranes, azotosomes, made up of small nitrogen-containing molecules, are kinetically persistent and may function on cryogenic liquid hydrocarbon worlds, such as Saturn’s moon Titan. We here take the next step and evaluate the thermodynamic viability of azotosome formation. Quantum mechanical calculations predict that azotosomes are not viable candidates for self-assembly akin to lipid bilayers in liquid water. We argue that cell membranes may be unnecessary for hypothetical astrobiology under stringent anhydrous and low-temperature conditions akin to those of Titan.
    Do good work. —Virgil Ivan "Gus" Grissom

  6. #96
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    Quote Originally Posted by Roger E. Moore View Post
    Black hole sun? Could be, says this author, but aliens on planets around black holes would be in deeeep gravity wells. https://arxiv.org/abs/2001.10991
    More on the possibility that black holes can have habitable planets. Still freaks me out to think of it. Infalling debris would clobber those worlds, wouldn't it?

    https://www.sciencemag.org/news/2020...bit-black-hole
    Do good work. —Virgil Ivan "Gus" Grissom

  7. #97
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    Quote Originally Posted by Roger E. Moore View Post
    What might life be like on Titan? A new paper peers into the possibilities by looking at how cell membranes might function there.

    https://www.airspacemag.com/daily-pl...urs-180974104/

    On Saturn’s Moon Titan, Living Cells May Be Very Different From Ours
    Yet another good reason to visit this exotic world.
    By Dirk Schulze-Makuch
    airspacemag.com January 31, 2020 1:30PM

    In a new paper published in Science Advances, Hilda Sandström and Martin Rahm from Chalmers University of Technology in Gothenburg, Sweden, consider the possibility of life on Titan—and, more specifically, whether living creatures would need cell membranes to survive.

    ==

    https://advances.sciencemag.org/content/6/4/eaax0272

    Can polarity-inverted membranes self-assemble on Titan?
    H. Sandström and M. Rahm
    Science Advances 24 Jan 2020: Vol. 6, no. 4, eaax0272

    Abstract: The environmental and chemical limits of life are two of the most central questions in astrobiology. Our understanding of life’s boundaries has implications on the efficacy of biosignature identification in exoplanet atmospheres and in the solar system. The lipid bilayer membrane is one of the central prerequisites for life as we know it. Previous studies based on molecular dynamics simulations have suggested that polarity-inverted membranes, azotosomes, made up of small nitrogen-containing molecules, are kinetically persistent and may function on cryogenic liquid hydrocarbon worlds, such as Saturn’s moon Titan. We here take the next step and evaluate the thermodynamic viability of azotosome formation. Quantum mechanical calculations predict that azotosomes are not viable candidates for self-assembly akin to lipid bilayers in liquid water. We argue that cell membranes may be unnecessary for hypothetical astrobiology under stringent anhydrous and low-temperature conditions akin to those of Titan.
    I confess to not being able to understand the details in these papers at all, except that cell membranes might not be needed for life on Titan. That's pretty radical. Here's a slightly dumbed-down version that goes over my head toward the end of the first paragraph.

    https://phys.org/news/2020-02-polari...turn-moon.html
    Do good work. —Virgil Ivan "Gus" Grissom

  8. #98
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    Even if this habitable-zone planet is not like Earth, it could be quite friendly to life... very weird life.

    https://arxiv.org/abs/2002.11115

    The interior and atmosphere of the habitable-zone exoplanet K2-18b
    Nikku Madhusudhan, Matthew C. Nixon, Luis Welbanks, Anjali A. A. Piette, Richard A. Booth
    (Submitted on 25 Feb 2020)

    Exoplanets orbiting M dwarfs present a valuable opportunity for their detection and atmospheric characterisation. This is evident from recent inferences of H2O in such atmospheres, including that of the habitable-zone exoplanet K2-18b. With a bulk density between Earth and Neptune, K2-18b may be expected to possess a H/He envelope. However, the extent of such an envelope and the thermodynamic conditions of the interior remain unexplored. In the present work, we investigate the atmospheric and interior properties of K2-18b based on its bulk properties and its atmospheric transmission spectrum. We constrain the atmosphere to be H2-rich with a H2O volume mixing ratio of 0.02−14.8%, consistent with previous studies, and find a depletion of CH4 and NH3, indicating chemical disequilibrium. We do not conclusively detect clouds/hazes in the observable atmosphere. We use the bulk parameters and retrieved atmospheric properties to constrain the internal structure and thermodynamic conditions in the planet. The constraints on the interior allow multiple scenarios between rocky worlds with massive H/He envelopes and water worlds with thin envelopes. We constrain the mass fraction of the H/He envelope to be ≲6%; spanning ≲10^−5 for a predominantly water world to ∼6% for a pure iron interior. The thermodynamic conditions at the surface of the H2O layer range from the super-critical to liquid phases, with a range of solutions allowing for habitable conditions on K2-18b. Our results demonstrate that the potential for habitable conditions is not necessarily restricted to Earth-like rocky exoplanets.


    https://www.sciencealert.com/astrono...y-be-habitable
    Last edited by Roger E. Moore; 2020-Feb-27 at 11:25 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

  9. #99
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    New place to look for aliens?

    https://arxiv.org/abs/2003.09231

    The subsurface habitability of small, icy exomoons
    J. Tjoa, etal.
    (Submitted on 20 Mar 2020)

    Assuming our Solar System as typical, exomoons may outnumber exoplanets. If their habitability fraction is similar, they would thus constitute the largest portion of habitable real estate in the Universe. Icy moons in our Solar System, such as Europa and Enceladus, have already been shown to possess liquid water, a prerequisite for life on Earth. We intend to investigate under what circumstances small, icy moons may sustain subsurface oceans and thus be "subsurface habitable". We pay specific attention to tidal heating. We made use of a phenomenological approach to tidal heating. We computed the orbit averaged flux from both stellar and planetary (both thermal and reflected stellar) illumination. We then calculated subsurface temperatures depending on illumination and thermal conduction to the surface through the ice shell and an insulating layer of regolith. We adopted a conduction only model, ignoring volcanism and ice shell convection as an outlet for internal heat. In doing so, we determined at which depth, if any, ice melts and a subsurface ocean forms. We find an analytical expression between the moon's physical and orbital characteristics and the melting depth. Since this expression directly relates icy moon observables to the melting depth, it allows us to swiftly put an upper limit on the melting depth for any given moon. We reproduce the existence of Enceladus' subsurface ocean; we also find that the two largest moons of Uranus (Titania & Oberon) could well sustain them. Our model predicts that Rhea does not have liquid water. Habitable exomoon environments may be found across an exoplanetary system, largely irrespective of the distance to the host star. Small, icy subsurface habitable moons may exist anywhere beyond the snow line. This may, in future observations, expand the search area for extraterrestrial habitable environments beyond the circumstellar habitable zone.
    Do good work. —Virgil Ivan "Gus" Grissom

  10. #100
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    Life on Mercury? Maybe once, perhaps.

    https://www.nytimes.com/2020/03/24/s...ife-water.html
    Do good work. —Virgil Ivan "Gus" Grissom

  11. #101
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    And yet more on the habitability of black-hole planets.

    https://arxiv.org/abs/1912.01518

    Effects of the general relativistic spin precessions on the habitability of rogue planets orbiting supermassive black holes
    Lorenzo Iorio
    (Submitted on 3 Dec 2019 (v1), last revised 25 Mar 2020 (this version, v3))

    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 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 ε to its orbital plane by tens to hundreds of degrees over a time span of, say, just Δt=400yr , depending on the obliquity η∙ 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. Other scenarios are examined as well.
    Do good work. —Virgil Ivan "Gus" Grissom

  12. #102
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    Tatooine is not likely. Sorry.

    https://arxiv.org/abs/2003.11682

    Earth-size planet formation in the habitable zone of circumbinary stars
    G. O. Barbosa, O. C. Winter, A. Amarante, A. Izidoro, R. C. Domingos, E. E. N. Macau
    (Submitted on 26 Mar 2020)

    In this work is investigated the possibility of close-binary star systems having Earth-size planets within their habitable zones. First, we selected all known close-binary systems with confirmed planets (totaling 22 systems) to calculate the boundaries of their respective habitable zones (HZ). However, only eight systems had all the data necessary for the computation of the HZ. Then, we numerically explored the stability within the habitable zones for each one of the eight systems using test particles. From the results, we selected five systems that have stable regions inside the habitable zones (HZ), namely Kepler-34, 35, 38, 413 and 453. For these five cases of systems with stable regions in the HZ, we perform a series of numerical simulations for planet formation considering disks composed of planetary embryos and planetesimals, with two distinct density profiles, in addition to the stars and host planets of each system. We found that in the case of Kepler-34 and 453 systems no Earth-size planet is formed within the habitable zones. Although planets with Earth-like masses were formed in the Kepler-453, but they were outside the HZ. In contrast, for Kepler-35 and 38 systems, the results showed that potentially habitable planets are formed in all simulations. In the case of the Kepler-413 system, in just one simulation a terrestrial planet was formed within the habitable zone.
    Do good work. —Virgil Ivan "Gus" Grissom

  13. #103
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    How to find dolphins on Altair 5 (or any other waterworld)

    https://arxiv.org/abs/2004.03631
    Detectability of Life Using Oxygen on Pelagic Planets and Water Worlds
    Donald M Glaser, Hilairy Ellen Hartnett, Steven J. Desch, Cayman T. Unterborn, Ariel Anbar, Steffen Buessecker, Theresa Fisher, Steven Glaser, Stephen R. Kane, Carey M. Lisse, Camerian Millsaps, Susanne Neuer, Joseph G. ORourke, Nuno Santos, Sara Imari Walker, Mikhail Zolotov
    (Submitted on 7 Apr 2020)
    The search for life on exoplanets is one of the grand scientific challenges of our time. The strategy to date has been to find (e.g., through transit surveys like Kepler) Earth-like exoplanets in their stars habitable zone, then use transmission spectroscopy to measure biosignature gases, especially oxygen, in the planets atmospheres (e.g., using JWST, the James Webb Space Telescope). Already there are more such planets than can be observed by JWST, and missions like the Transiting Exoplanet Survey Satellite and others will find more. A better understanding of the geochemical cycles relevant to biosignature gases is needed, to prioritize targets for costly follow-up observations and to help design future missions. We define a Detectability Index to quantify the likelihood that a biosignature gas could be assigned a biological vs. non-biological origin. We apply this index to the case of oxygen gas, O2, on Earth-like planets with varying water contents. We demonstrate that on Earth-like exoplanets with 0.2 weight percent (wt%) water (i.e., no exposed continents) a reduced flux of bioessential phosphorus limits the export of photosynthetically produced atmospheric O2 to levels indistinguishable from geophysical production by photolysis of water plus hydrogen escape. Higher water contents >1wt% that lead to high-pressure ice mantles further slow phosphorus cycling. Paradoxically, the maximum water content allowing use of O2 as a biosignature, 0.2 wt%, is consistent with no water based on mass and radius. Thus, the utility of an O2 biosignature likely requires the direct detection of both water and land on a planet.
    Do good work. —Virgil Ivan "Gus" Grissom

  14. #104
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    Recently a fossil in Australia was identified as the possible ancestor of all animals. Would the ancestor of all life on another world look just the same?

    https://forum.cosmoquest.org/showthr...ralian-fossils
    Do good work. —Virgil Ivan "Gus" Grissom

  15. #105
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    The naked mole rat might be the most truly alien critter on Earth that isn't an extremophile microbe.

    https://www.airspacemag.com/daily-pl...dst-180970220/
    Do good work. —Virgil Ivan "Gus" Grissom

  16. #106
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    Look for alien life around white dwarf stars? Didn't they blow up real big once, and now they're eating their own planets?

    https://www.universetoday.com/145921...arch-for-life/
    Do good work. —Virgil Ivan "Gus" Grissom

  17. #107
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    I bet this question has not occurred to you: is the Kuiper Belt full of aliens?

    https://ui.adsabs.harvard.edu/abs/20....382M/abstract
    Is the Kuiper Belt Inhabited?
    Matloff, G.
    Abstract: The Sun's Kuiper Belt (located about 30-50 Astronomical Units from the Sun) is a volatile-rich region containing very many objects in the ~10-20 km size range. An expedition to our solar system would encounter this region before it reached the Sun's habitable zone. It has been speculated that alien space habitats in this region could be detected by infrared or visible light transmissions. Recent data from the Gaia space observatory reveals that our solar system is approached very closely by Sun- like stars at intervals of ~ one million years. Properly timed expeditions to Sol might be less time consuming than commonly believed. It is argued here that the probability of our outer solar system being colonized during the distant past is not small. Even if alien space habitats no longer exist, artifacts of failed or abandoned colonization attempts might be discovered. Recent exploration of the Kuiper Belt has revealed fascinating anomalies. It is possible that humans are not the first technological terrestrial civilization. Evidence for such a possibility might also be searched for among small Kuiper Belt Objects.
    Publication: Journal of the British Interplanetary Society, Vol. 72, pp. 382-385
    Pub Date: November 2019

    And a very similar paper....

    https://ui.adsabs.harvard.edu/abs/20....318R/abstract
    Colonizing the Plutoids: The Key to Human Expansion into the Galaxy
    Roy, K. I.; Kennedy, R. G.; Fields, D. E.
    Abstract" Pluto-type worlds (plutoids) are far more numerous in our solar system than initially thought with hundreds, maybe thousands, of them existing in the Kuiper belt and Oort cloud. Other stars are likely to also possess many such worlds. These worlds possess almost limitless quantities of water and substantial quantities of nitrogen, which are two limiting ingredients necessary for terraforming planets in the inner solar system. Assuming that faster-than-light travel is impractical, that artificial gravity is only possible via circular motion, that humans remain basically unchanged, and that humanity's expansion into the solar system and beyond is desirable, then exploiting the resources of, and establishing bases and even colonies on, icy plutoids may become essential for human expansion into space. Such colonies face problems involving gravity, radiation, energy supply and complex ecologies. This paper attempts to address those issues and outline what such colonies might look like. This type of colony offers humanity, and perhaps other species, the ability to establish settlements at otherwise undesirable locations, including red and brown dwarf stars. Such colonies could even be established in orphan planets in interstellar space, far from any star.
    Publication: Journal of the British Interplanetary Society, vol. 66, p. 318-327
    Pub Date: 2013
    Do good work. —Virgil Ivan "Gus" Grissom

  18. #108
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    Quote Originally Posted by Roger E. Moore View Post
    Look for alien life around white dwarf stars? Didn't they blow up real big once, and now they're eating their own planets?

    https://www.universetoday.com/145921...arch-for-life/
    Most are not eating their own planets. They're just more noticeable that way.

    And WDs are hot for billions of years, possibly enough time for life to redevelop.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  19. #109
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    Microbic life in hydrogen-dominated atmospheres? Could be, by this paper.

    https://arxiv.org/abs/2005.01668
    [Submitted on 4 May 2020]
    Laboratory studies on the viability of life in H2-dominated exoplanet atmospheres
    S. Seager, J. Huang, J.J. Petkowski, M. Pajusalu
    Theory and observation for the search for life on exoplanets via atmospheric "biosignature gases" is accelerating, motivated by the capabilities of the next generation of space- and ground-based telescopes. The most observationally accessible rocky planet atmospheres are those dominated by molecular hydrogen gas, because the low density of H2-gas leads to an expansive atmosphere. The capability of life to withstand such exotic environments, however, has not been tested in this context. We demonstrate that single-celled microorganisms (E. coli and yeast) that normally do not inhabit H2-dominated environments can survive and grow in a 100% H2 atmosphere. We also describe the astonishing diversity of dozens of different gases produced by E. coli, including many already proposed as potential biosignature gases (e.g., nitrous oxide, ammonia, methanethiol, dimethylsulfide, carbonyl sulfide, and isoprene). This work demonstrates the utility of lab experiments to better identify which kinds of alien environments can host some form of possibly detectable life.
    Do good work. —Virgil Ivan "Gus" Grissom

  20. #110
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    How to classify extraterrestrial civilizations?

    https://arxiv.org/abs/2005.13221
    Qualitative classification of extraterrestrial civilizations
    Valentin D. Ivanov, Juan Carlos Beamin, Claudio Caceres, Dante Minniti
    [Submitted on 27 May 2020]
    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.
    Do good work. —Virgil Ivan "Gus" Grissom

  21. #111
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    New study: "...we calculate that there should be around 36 active civilizations in our Galaxy."

    https://phys.org/news/2020-06-intell...fe-galaxy.html
    Do good work. —Virgil Ivan "Gus" Grissom

  22. #112
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    Fast radio bursts as interstellar civilization signals?

    https://arxiv.org/abs/2006.08493
    [Submitted on 15 Jun 2020]
    A Quantitative Assessment of Communicating Extra-Terrestrial Intelligent Civilizations in the Galaxy and the Case of FRB-like Signals
    Bing Zhang (UNLV)
    A formula is proposed to quantitatively estimate the signal emission rate of Communicating Extra-Terrestrial Intelligent civilizations (CETIs) in the Galaxy. I suggest that one possible type of CETI signal would be brief radio bursts similar to fast radio bursts (FRBs). A dedicated search for FRB-like artificial signals in the Galaxy for decades may pose a meaningful upper limit on the emission rate of these signals by CETIs. The Fermi-Hart paradox is answered in terms of not having enough observing times for this and other types of signals. Whether humans should send FRB-like signals in the far future is briefly discussed.
    Do good work. —Virgil Ivan "Gus" Grissom

  23. #113
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    The race to discover new forms of alien technosignatures is on.

    QUOTE: A civilization, by nature, will need to find a way to produce energy, and, Frank says, "there are only so many forms of energy in the universe. Aliens are not magic."

    https://phys.org/news/2020-06-intell...res-clues.html
    Do good work. —Virgil Ivan "Gus" Grissom

  24. #114
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    Does the lifetime of a communicating civilization or the number of communicating civilizations made more difference in the probability of contact?

    https://arxiv.org/abs/2007.03597
    [Submitted on 7 Jul 2020]
    Monte Carlo estimation of the probability of causal contacts between communicating civilisations
    Marcelo Lares, José Funes, Luciana Gramajo
    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.
    Do good work. —Virgil Ivan "Gus" Grissom

  25. #115
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    Another look at the "faint young Sun" paradox, which is more complicated than it seems.

    https://arxiv.org/abs/2007.03423
    [Submitted on 7 Jul 2020]
    Habitability of the early Earth: Liquid water under a faint young Sun facilitated by strong tidal heating due to a nearby Moon
    René Heller (1), Jan-Peter Duda (2), Max Winkler (3), Joachim Reitner (2), Laurent Gizon (1,4) ((1) Max Planck Institute for Solar System Research, Göttingen, (2) Göttingen Centre of Geosciences, Georg-August-University Göttingen, (3) Max Planck Institute for Extraterrestrial Physics, Garching, (4) Institute for Astrophysics, Georg-August-University of Göttingen)
    Geological evidence suggests liquid water near the Earth's surface as early as 4.4 gigayears ago when the faint young Sun only radiated about 70 % of its modern power output. At this point, the Earth should have been a global snowball. An extreme atmospheric greenhouse effect, an initially more massive Sun, release of heat acquired during the accretion process of protoplanetary material, and radioactivity of the early Earth material have been proposed as alternative reservoirs or traps for heat. For now, the faint-young-sun paradox persists as one of the most important unsolved problems in our understanding of the origin of life on Earth. Here we use astrophysical models to explore the possibility that the new-born Moon, which formed about 69 million years (Myr) after the ignition of the Sun, generated extreme tidal friction - and therefore heat - in the Hadean and possibly the Archean Earth. We show that the Earth-Moon system has lost about 3e31 J, (99 % of its initial mechanical energy budget) as tidal heat. Tidal heating of roughly 10 W/m^2 through the surface on a time scale of 100 Myr could have accounted for a temperature increase of up to 5 degrees Celsius on the early Earth. This heating effect alone does not solve the faint-young-sun paradox but it could have played a key role in combination with other effects. Future studies of the interplay of tidal heating, the evolution of the solar power output, and the atmospheric (greenhouse) effects on the early Earth could help in solving the faint-young-sun paradox.
    Do good work. —Virgil Ivan "Gus" Grissom

  26. #116
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    Suppose... we wanted to detect a massive sublight-speed interstellar spacecraft entering our solar system. How would we do that? One solution here.

    https://arxiv.org/abs/2007.04892
    [Submitted on 9 Jul 2020]
    Detectability of Thermal Emission from Sub-Relativistic Objects
    Thiem Hoang, Abraham Loeb
    We calculate the surface temperature and the resulting brightness of sub-relativistic objects moving through the Solar system due to collisional heating by gas and radiative heating by solar radiation. The thermal emission from objects of size ≳100 m and speed of ≳0.1c, can be detected by the upcoming James Webb Space Telescope out to a distance of ∼100 au. Future surveys could therefore set interesting limits on the abundance of fast-moving interstellar objects or spacecraft.
    Do good work. —Virgil Ivan "Gus" Grissom

  27. #117
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    No luck hunting for technosignatures--except our own.


    https://arxiv.org/abs/2011.05265

    A Search for Technosignatures Around 31 Sun-like Stars with the Green Bank Telescope at 1.15-1.73 GHz

    Jean-Luc Margot, Pavlo Pinchuk, Robert Geil, Stephen Alexander, Sparsh Arora, Swagata Biswas, Jose Cebreros, Sanjana Prabhu Desai, Benjamin Duclos, Riley Dunne, Kristy Kwan Lin, Shashwat Goel, Julia Gonzales, Alexander Gonzalez, Rishabh Jain, Adrian Lam, Briley Lewis, Rebecca Lewis, Grace Li, Mason MacDougall, Christopher Makarem, Ivan Manan, Eden Molina, Caroline Nagib, Kyle Neville, Connor O'Toole, Valerie Rockwell, Yoichiro Rokushima, Griffin Romanek, Carlyn Schmidgall, Samar Seth, Rehan Shah, Yuri Shimane, Myank Singhal, Armen Tokadjian, Lizvette Villafana, Zhixian Wang, In Yun, Lujia Zhu, Ryan S. Lynch

    We conducted a search for technosignatures in April of 2018 and 2019 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused on regions surrounding 31 Sun-like stars near the plane of the Galaxy. We present the results of our search for narrowband signals in this data set as well as improvements to our data processing pipeline. Specifically, we applied an improved candidate signal detection procedure that relies on the topographic prominence of the signal power, which nearly doubles the signal detection count of some previously analyzed data sets. We also improved the direction-of-origin filters that remove most radio frequency interference (RFI) to ensure that they uniquely link signals observed in separate scans. We performed a preliminary signal injection and recovery analysis to test the performance of our pipeline. We found that our pipeline recovers 93% of the injected signals over the usable frequency range of the receiver and 98% if we exclude regions with dense RFI. In this analysis, 99.73% of the recovered signals were correctly classified as technosignature candidates. Our improved data processing pipeline classified over 99.84% of the ~26 million signals detected in our data as RFI. Of the remaining candidates, 4539 were detected outside of known RFI frequency regions. The remaining candidates were visually inspected and verified to be of anthropogenic nature. Our search compares favorably to other recent searches in terms of end-to-end sensitivity, frequency drift rate coverage, and signal detection count per unit bandwidth per unit integration time.

    ======

    Nearby habitable-zone super-Earth has water, maybe? Good news?

    https://arxiv.org/abs/2011.08815

    Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b

    Billy Edwards, Quentin Changeat, Mayuko Mori, Lara O. Anisman, Mario Morvan, Kai Hou Yip, Angelos Tsiaras, Ahmed Al-Refaie, Ingo Waldmann, Giovanna Tinetti

    Atmospheric characterisation of temperate, rocky planets is the holy grail of exoplanet studies. These worlds are at the limits of our capabilities with current instrumentation in transmission spectroscopy and challenge our state-of-the-art statistical techniques. Here we present the transmission spectrum of the temperate Super-Earth LHS 1140b using the Hubble Space Telescope (HST). The Wide Field Camera 3 (WFC3) G141 grism data of this habitable zone (Teq = 235 K) Super-Earth (R = 1.7 R⊕), shows tentative evidence of water. However, the signal-to-noise ratio, and thus the significance of the detection, is low and stellar contamination models can cause modulation over the spectral band probed. We attempt to correct for contamination using these models and find that, while many still lead to evidence for water, some could provide reasonable fits to the data without the need for molecular absorption although most of these cause also features in the visible ground-based data which are nonphysical. Future observations with the James Webb Space Telescope (JWST) would be capable of confirming, or refuting, this atmospheric detection.

    ------

    A Trojan-planet detected at LHS 1140? Is this a first?

    https://arxiv.org/abs/2010.06928

    Planetary system LHS 1140 revisited with ESPRESSO and TESS

    J. Lillo-Box, P. Figueira, A. Leleu, L. Acuña, J.P. Faria, N. Hara, N.C. Santos, A. C. M. Correia, P. Robutel, M. Deleuil, D. Barrado, S. Sousa, X. Bonfils, O. Mousis, J.M. Almenara, N. Astudillo-Defru, E. Marcq, S. Udry, C. Lovis, F. Pepe

    LHS 1140 is an M dwarf known to host two known transiting planets at orbital periods of 3.77 and 24.7 days. The external planet (LHS 1140 b) is a rocky super-Earth that is located in the middle of the habitable zone of this low-mass star, placing this system at the forefront of the habitable exoplanet exploration. We further characterize this system by improving the physical and orbital properties and search for additional planetary-mass components in the system, also exploring the possibility of co-orbitals. We collected 113 new radial velocity observations with ESPRESSO over a 1.5-year time span with an average photon-noise precision of 1.07 m/s. We determine new masses with a precision of 6% for LHS 1140 b (6.48±0.46 M⊕) and 9% for LHS 1140 c (mc=1.78±0.17 M⊕), reducing by half the previously published uncertainties. Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140 b might be iron-enriched. In both cases, the water content is compatible to a maximum fraction of 10-12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet LHS 1140 b. Our results also provide evidence for a new planet candidate in the system (md = 4.8 ± 1.1 M⊕) on a ~78.9-day orbital period, which is detected through three independent methods. The analysis also allows us to discard other planets above 0.5 M⊕ for periods shorter than 10 days and above 2 M⊕ for periods up to one year. Finally, our analysis discards co-orbital planets of LHS 1140 b down to 1 M⊕. Indications for a possible co-orbital signal in LHS 1140 c are detected in both radial velocity and photometric data, however. The new characterization of the system make it a key target for atmospheric studies of rocky worlds at different stellar irradiations

    ============

    A radio telescope in lunar orbit or on the Moon might help SETI enormously.

    https://arxiv.org/abs/2009.12689

    Lunar Opportunities for SETI

    Eric J. Michaud, Andrew P. V. Siemion, Jamie Drew, S. Pete Worden

    A radio telescope placed in lunar orbit, or on the surface of the Moon's farside, could be of great value to the Search for Extraterrestrial Intelligence (SETI). The advantage of such a telescope is that it would be shielded by the body of the Moon from terrestrial sources of radio frequency interference (RFI). While RFI can be identified and ignored by other fields of radio astronomy, the possible spectral similarity between human and alien-generated radio emission makes the abundance of artificial radio emission on and around the Earth a significant complicating factor for SETI. A Moon-based telescope would avoid this challenge. In this paper, we review existing literature on Moon-based radio astronomy, discuss the benefits of lunar SETI, contrast possible surface- and orbit-based telescope designs, and argue that such initiatives are scientifically feasible, both technically and financially, within the next decade.

    ----

    https://arxiv.org/abs/2011.04671

    The limits of cosmology: role of the Moon

    Joseph Silk

    The lunar surface allows a unique way forward in cosmology, to go beyond current limits. The far side provides an unexcelled radio-quiet environment for probing the dark ages via 21 cm interferometry to seek elusive clues on the nature of the infinitesimal fluctuations that seeded galaxy formation. Far-infrared telescopes in cold and dark lunar polar craters will probe back to the first months of the Big Bang and study associated spectral distortions in the CMB. Optical and IR megatelescopes will image the first star clusters in the universe and seek biosignatures in the atmospheres of unprecedented numbers of nearby habitable zone exoplanets. The goals are compelling and a stable lunar platform will enable construction of telescopes that can access trillions of modes in the sky, providing the key to exploration of our cosmic origins.

    ============

    Using gravitational lenses to focus interstellar communications lines.

    https://arxiv.org/abs/2009.01866

    Interstellar communication network. II. Deep space nodes with gravitational lensing

    Michael Hippke

    Data rates in an interstellar communication network suffer from the inverse square law due to the vast distances between the stars. To achieve high (Gbits/s) data rates, some combination of large apertures and high power is required. Alternatively, signals can be focused by the gravitational lenses of stars to yield gains of order 10^9, compared to the direct path. Gravitational lens physics imposes a set of constraints on the sizes and locations of receivers and apertures. These characteristics include the minimum and maximum receiver size, the maximum transmitter size, and the heliocentric receiver distance. Optimal sizes of receivers and transmitters are of order meters. Such small devices allow for the capture of the main lobe in the beam while avoiding the temporal smearing which affects larger apertures. These and other properties can be used to describe the most likely parameters of a lensed communication network, and to determine exact position of communication nodes in the heliocentric reference frame.
    Last edited by Roger E. Moore; 2020-Nov-22 at 06:54 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

  28. #118
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    Two views on the likelihood of mass extinctions on Earth from phenomena in the skies.

    https://arxiv.org/abs/2007.15975

    Gamma Rays from UltraCompact Minihaloes: Effects on the Earth's Atmosphere and Links to Mass Extinction Events

    M. Sarkis, G. Beck, B. C. Thomas

    Recent studies of the effects on the Earth's atmosphere by astrophysical sources, such as nearby gamma-ray bursts or supernovae, have shown that these events could lead to severe changes in atmospheric composition. Depletion of ozone, the most notable of these changes, is extremely dangerous to living organisms as any decrease in ozone levels leads to an increase in the irradiance of harmful solar radiation at the Earth's surface. In this work we consider dark matter as an astrophysical source of gamma rays, by the annihilation and decay of WIMPs found within dark compact halo objects known as UltraCompact Minihaloes (UCMHs). We calculate the fluence of gamma rays produced in this way and simulate the resulting changes to terrestrial ozone levels using the Goddard Space Flight Center 2D Atmospheric Model. We also calculate the rate at which such events would occur, using estimates for the mass distribution of these haloes within the Milky Way. We find that the ozone depletion from UCMHs can be significant, and even of similar magnitude to the levels which have been linked to the cause of the Late-Ordovician mass extinction event. However, the probability of such encounters over the Earth's entire history is relatively low. This suggests that, while dark compact objects like UCMHs could have had an impact on the Earth's biosphere, other astrophysical phenomena like gamma-ray bursts or supernovae seem a more likely source of these effects.

    ------

    https://arxiv.org/abs/2009.14078

    Gamma Ray Bursts: Not so Much Deadlier than We Thought

    Brian C. Thomas (Washburn University), Dimitra Atri (NYU Abu Dhabi), Adrian L. Melott (Univ. of Kansas)

    We analyze the additional effect on planetary atmospheres of recently detected gamma-ray burst afterglow photons in the range up to 1 TeV. For an Earth-like atmosphere we find that there is a small additional depletion in ozone versus that modeled for only prompt emission. We also find a small enhancement of muon flux at the planet surface. Overall, we conclude that the additional afterglow emission, even with TeV photons, does not result in a significantly larger impact over that found in past studies.
    Do good work. —Virgil Ivan "Gus" Grissom

  29. #119
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    Galactic real estate: it's always location, location, location for the best possible places to live.


    https://arxiv.org/abs/2009.13539

    The best place and time to live in the Milky Way

    R. Spinelli, G. Ghirlanda, F. Haardt, G. Ghisellini, G. Scuderi

    Among the most powerful cosmic events, supernovae (SNe) and gamma-ray bursts (GRBs) can be highly disruptive for life: their radiation can be harmful for biota or induce extinction by removing most of the protective atmospheric ozone layer on terrestrial planets. Nearby high-energy transient astrophysical events have been proposed as possible triggers of mass extinctions on Earth. We aim at assessing the habitability of the Milky Way (MW) along its cosmic history against potentially disruptive astrophysical transients with the scope of identifying the safest places and epochs within our Galaxy. We also test the hypothesis that long GRBs had a leading role in the late Ordovician mass extinction event (~440 Myrs ago). We characterise the habitability of the MW along its cosmic history as a function of galactocentric distance of terrestrial planets. We estimate the dangerous effects of transient astrophysical events (long/short GRBs and SNe) with a model which binds their rate to the specific star formation and metallicity evolution within the Galaxy along its cosmic history. Our model also accounts for the probability of forming terrestrial planets around FGK and M stars. Until ~6 billion years ago the outskirts of the Galaxy were the safest places to live, despite the relatively low density of terrestrial planets. In the last ~4 billion years, regions between 2 and 8 kpc from the center, featuring a higher density of terrestrial planets, became the best places for a relatively safer biotic life growth. We confirm the hypothesis that one long GRB had a leading role in the late Ordovician mass extinction event. In the last 500 Myrs, the safest galactic region is comprised between 2 and 8 kpc from the center of the MW, whereas the outskirts of the Galaxy have been sterilized by 2-5 long GRBs.
    Do good work. —Virgil Ivan "Gus" Grissom

  30. #120
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    Multiple stars systems can have habitable zones, too. This comes with excellent illustrations.


    https://arxiv.org/abs/2009.00144

    Habitable Zones in Binary Star Systems: A Zoology

    Siegfried Eggl, Nikolaos Georgakarakos, Elke Pilat-Lohinger

    Several concepts have been brought forward to determine where terrestrial planets are likely to remain habitable in multi-stellar environments. Isophote-based habitable zones, for instance, rely on insolation geometry to predict habitability, whereas radiative habitable zones take the orbital motion of a potentially habitable planet into account. Dynamically informed habitable zones include gravitational perturbations on planetary orbits, and full scale, self consistent simulations promise detailed insights into the evolution of select terrestrial worlds. All of the above approaches agree that stellar multiplicity does not preclude habitability. Predictions on where to look for habitable worlds in such environments can differ between concepts. The aim of this article is to provide an overview of current approaches and present simple analytic estimates for the various types of habitable zones in binary star systems.
    Do good work. —Virgil Ivan "Gus" Grissom

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