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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

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