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Thread: Astrobiological papers from Arvix and everywhere

  1. #121
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    How advances in exoplanetary science are affecting the way in which we search for extraterrestrial intelligence (SETI).


    https://arxiv.org/abs/2007.12645

    Habitability of M dwarfs is a problem for the traditional SETI

    Milan M. Ćirković, Branislav Vukotić

    We consider some implications of the much-discussed circumstellar habitable zones around M-dwarf stars for the conventionally understood radio SETI. We argue that the flaring nature of these stars would further adversely impact local development of radio communication and that, therefore, their circumstellar habitable zones should be preferentially studied by other methods. This is a clear example how diversity of astrobiological habitats is introducing contingency into the cultural evolution, thus undermining the universality of cultural convergence as one of the major premises of the traditional SETI. This is yet another example of how specifics of the physical environment strongly shape cultural evolution taken in the broadest, most inclusive sense.
    Do good work. —Virgil Ivan "Gus" Grissom

  2. #122
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    More on the "location, location, location" aspect of galactic habitability. NOTE: The closer to the Galactic Center, the less desirable the real estate.

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

    https://arxiv.org/abs/2008.09988

    The Impact of Tidal Disruption Events on Galactic Habitability

    E. Pacetti, A. Balbi, M. Lingam, F. Tombesi, E. Perlman

    Tidal Disruption Events (TDEs) are characterized by the emission of a short burst of high-energy radiation. We analyze the cumulative impact of TDEs on galactic habitability using the Milky Way as a proxy. We show that X-rays and extreme ultraviolet (XUV) radiation emitted during TDEs can cause hydrodynamic escape and instigate biological damage. By taking the appropriate variables into consideration, such as the efficiency of atmospheric escape and distance from the Galactic center, we demonstrate that the impact of TDEs on galactic habitability is comparable to that of Active Galactic Nuclei. In particular, we show that planets within distances of ∼0.1-1 kpc could lose Earth-like atmospheres over the age of the Earth, and that some of them might be subject to biological damage once every ≳ 10^4 yrs. We conclude by highlighting potential ramifications of TDEs and argue that they should be factored into future analyses of inner galactic habitability.

    ------

    https://arxiv.org/abs/2008.01419

    The Habitability of the Galactic Bulge

    Amedeo Balbi, Maryam Hami, Andjelka B. Kovačević

    We present a new investigation of the habitability of the Milky Way bulge, that expands previous studies on the Galactic Habitable Zone. We discuss existing knowledge on the abundance of planets in the bulge, metallicity and the possible frequency of rocky planets, orbital stability and encounters, and the possibility of planets around the central supermassive black hole. We focus on two aspects that can present substantial differences with respect to the environment in the disk: (i) the ionizing radiation environment, due to the presence of the central black hole and to the highest rate of supernovae explosions and (ii) the efficiency of putative lithopanspermia mechanism for the diffusion of life between stellar systems. We use analytical models of the star density in the bulge to provide estimates of the rate of catastrophic events and of the diffusion timescales for life over interstellar distances.
    Do good work. —Virgil Ivan "Gus" Grissom

  3. #123
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    Might aliens communicate with each other by using FRBs (fast radio bursts)?


    https://arxiv.org/abs/2006.08493

    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

  4. #124
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    I wonder if some of these radio bursts might answer several questions.

    Putting things in orbit around magnetars and such could give power, but perhaps also produce heavier elements.

    If asteroids are bombarded over deep time— might that allow for more gold to be generated than stellar collisions alone account for?

  5. #125
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    Re: Lunar Opportunities for SETI
    The great thing about farside is that it is always shielded from Earth and that you can find natural craters that would dwarf the lamented Arecibo.
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  6. #126
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    The first contact we get might be with a much older, more powerful civilization.


    https://arxiv.org/abs/2010.12358

    Contact Inequality -- First Contact Will Likely Be With An Older Civilization

    David Kipping, Adam Frank, Caleb Scharf

    First contact with another civilization, or simply another intelligence of some kind, will likely be quite different depending on whether that intelligence is more or less advanced than ourselves. If we assume that the lifetime distribution of intelligences follows an approximately exponential distribution, one might naively assume that the pile-up of short-lived entities dominates any detection or contact scenario. However, it is argued here that the probability of contact is proportional to the age of said intelligence (or possibly stronger), which introduces a selection effect. We demonstrate that detected intelligences will have a mean age twice that of the underlying (detected + undetected) population, using the exponential model. We find that our first contact will most likely be with an older intelligence, provided that the maximum allowed mean lifetime of the intelligence population, τmax, is > e times larger than our own. Older intelligences may be rare but they disproportionality contribute to first contacts, introducing what we call a 'contact inequality', analogous to wealth inequality. This reasoning formalizes intuitional arguments and highlights that first contact would likely be one-sided, with ramifications for how we approach SETI.
    Do good work. —Virgil Ivan "Gus" Grissom

  7. #127
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    QUOTE: As we near the end of the year, what were the biggest stories related to the search for life beyond Earth? It seems fitting that we start with a loss—of the Arecibo Telescope in Puerto Rico.

    https://www.airspacemag.com/daily-pl...020-180976585/
    Do good work. —Virgil Ivan "Gus" Grissom

  8. #128
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    Robust stellar flares might not prevent life on exoplanets, could facilitate its detection.

    QUOTE: If there is life on M and K dwarf exoplanets, previous work hypothesizes that stellar flares might make it easier to detect. For example, stellar flares can increase the abundance of life-indicating gasses (such as nitrogen dioxide, nitrous oxide and nitric acid) from imperceptible to detectable levels. "Space weather events are typically viewed as a detriment to habitability," Chen said. "But our study quantitatively shows that some space weather can actually help us detect signatures of important gases that might signify biological processes."

    https://phys.org/news/2020-12-robust...xoplanets.html

    https://scitechdaily.com/alien-life-...space-weather/
    Do good work. —Virgil Ivan "Gus" Grissom

  9. #129
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    Two planetary articles with peculiar intertwined headlines about the past of Earth and Venus--we were them and they were us.

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

    Venus was once more Earth-like, but climate change made it uninhabitable.

    https://earthsky.org/space/venus-was...climate-change

    ===

    Early Earth Was No Inviting Blue Planet—It Was More Like Venus.

    https://www.airspacemag.com/daily-pl...nus-180976534/
    Do good work. —Virgil Ivan "Gus" Grissom

  10. #130
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    Planets, planets, literally everywhere. Life everywhere, too? A planet called KOI-5Ab orbits in a triple-star system with a skewed configuration.

    https://phys.org/news/2021-01-planet...ar-skewed.html
    Do good work. —Virgil Ivan "Gus" Grissom

  11. #131
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    Good news for photosynthesis under red-dwarf skies!

    https://arxiv.org/abs/2101.04448

    Super-Earths, M Dwarfs, and Photosynthetic Organisms: Habitability in the Lab

    R. Claudi, E. Alei, M. Battistuzzi, L. Cocola, M. S. Erculiani, A. C. Pozzer, B. Salasnich, D. Simionato, V. Squicciarini, L. Poletto, N. La Rocca

    In a few years, space telescopes will investigate our Galaxy to detect evidence of life, mainly by observing rocky planets. In the last decade, the observation of exoplanet atmospheres and the theoretical works on biosignature gasses have experienced a considerable acceleration. The~most attractive feature of the realm of exoplanets is that 40\% of M dwarfs host super-Earths with a minimum mass between 1 and 30 Earth masses, orbital periods shorter than 50 days, and radii between those of the Earth and Neptune (1--3.8 R⊕). Moreover, the recent finding of cyanobacteria able to use far-red (FR) light for oxygenic photosynthesis due to the synthesis of chlorophylls d and f, extending in vivo light absorption up to 750\ nm, suggests the possibility of exotic photosynthesis in planets around M dwarfs. Using innovative laboratory instrumentation, we exposed different cyanobacteria to an M dwarf star simulated irradiation, comparing their responses to those under solar and FR simulated lights.~As expected, in FR light, only the cyanobacteria able to synthesize chlorophyll d and f could grow. Surprisingly, all strains, both able or unable to use FR light, grew and photosynthesized under the M dwarf generated spectrum in a similar way to the solar light and much more efficiently than under the FR one. Our findings highlight the importance of simulating both the visible and FR light components of an M dwarf spectrum to correctly evaluate the photosynthetic performances of oxygenic organisms exposed under such an exotic light~condition.
    Do good work. —Virgil Ivan "Gus" Grissom

  12. #132
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    According to astronomers at Villanova University, the best stars for life are one step along the Hertzsprung-Russell chart of star types - that is, K-type stars, which are orange stars a little cooler than the Sun, and a little warmer than a red dwarf. "K-dwarf stars are in the 'sweet spot,' with properties intermediate between the rarer, more luminous, but shorter-lived solar-type stars (G stars) and the more numerous red dwarf stars (M stars)," explained Villanova astronomer and astrophysicist Edward Guinan. "The K stars, especially the warmer ones, have the best of all worlds. If you are looking for planets with habitability, the abundance of K stars pump up your chances of finding life."

    https://www.sciencealert.com/astrono...ould-host-life
    Do good work. —Virgil Ivan "Gus" Grissom

  13. #133
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    Planets almost since the universe began. Chances of life in the universe look better, maybe?

    Astronomers Find an Astonishing 'Super-Earth' That's Nearly as Old as The Universe. Around one of the galaxy's oldest stars, an orange dwarf named TOI-561 just 280 light-years away, astronomers have found three orbiting exoplanets - one of which is a rocky world 1.5 times the size of Earth, whipping around the star on a breakneck 10.5-hour orbit. Obviously an exoplanet so close to its star isn't likely to be habitable, even if it is rocky like Earth, Venus and Mars. It would have a temperature of 2,480 Kelvin, tidally locked with a magma ocean on the permanent day side. But the TOI-561 system, planets and all, is one of the oldest ever seen, at an estimated age of around 10 billion years. That's more than twice as old as the Solar System, nearly as old as the Universe itself, and evidence that rocky exoplanets can remain stable for a very long time. "TOI-561 b is one of the oldest rocky planets yet discovered," said astronomer Lauren Weiss of the University of Hawai'i. "Its existence shows that the universe has been forming rocky planets almost since its inception 14 billion years ago."

    https://www.sciencealert.com/an-asto...s-the-universe
    Do good work. —Virgil Ivan "Gus" Grissom

  14. #134
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    Life in Elliptical Galaxies: Hot Spheroids, Fast Stars, Deadly Comets?

    Brian C. Lacki

    Elliptical galaxies have dynamically hot (σ1D ~ 100--300 km s−1) populations of stars, and presumably, smaller objects like comets. Because interstellar minor bodies are moving much faster, they hit planets harder and more often than in the local Galaxy. I estimate the rates for Chicxulub-scale impacts on an Earth-size planet in elliptical galaxies as a potential habitability constraint on intelligent life. Around most stars in a normal elliptical galaxy, these planets receive only ~ 0.01--0.1 Gyr−1, although hazardous rates may be common in certain compact early-type galaxies. About ~10% of the stellar mass is in a region where the rate is >10 Gyr−1, large enough to dominate the mass extinction rate. This suggests that elliptical galaxies have an exclusion zone several hundred parsecs in radius around their centers for the evolution of intelligent life.

    https://arxiv.org/abs/2101.11833
    Do good work. —Virgil Ivan "Gus" Grissom

  15. #135
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    Could game theory help discover intelligent alien life? New research from the University of Manchester suggests using a strategy linked to cooperative game playing known as 'game theory' in order to maximize the potential of finding intelligent alien life. "In game theory there are a class of games known as coordination games involving two players who have to cooperate to win but who cannot communicate with each other. When we engage in SETI we, and any civilisation out there trying to find us, are playing exactly this kind of game. So, if both we and they want to make contact, both of us can look to game theory to develop the best strategy." Dr. Kerins dubs his idea "Mutual Detectability." It states that the best places to look for signals are planets from which we would be capable of determining that Earth itself may be inhabited.

    https://phys.org/news/2021-01-game-t...lien-life.html
    Do good work. —Virgil Ivan "Gus" Grissom

  16. #136
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    Arsenic and (Very) Old Life. This normally toxic substance might have been useful in the oxygen-deprived environment of early Earth.

    https://www.airspacemag.com/daily-pl...obe-180976876/
    Do good work. —Virgil Ivan "Gus" Grissom

  17. #137
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    Failed attempt to detect laser light from Proxima Centauri.

    A Search for Optical Laser Emission from Proxima Centauri

    Geoffrey W. Marcy

    A search for laser light from Proxima Centauri was performed, including 107 high-resolution, optical spectra obtained between 2004 and 2019. Among them, 57 spectra contain multiple, confined spectral combs, each consisting of 10 closely-spaced frequencies of light. The spectral combs, as entities, are themselves equally spaced with a frequency separation of 5800 GHz, rendering them unambiguously technological in origin. However, the combs do not originate at Proxima Centauri. Otherwise, the 107 spectra of Proxima Centauri show no evidence of technological signals from lasers or any optical light in a narrow range of wavelengths. This search would have revealed lasers pointed toward Earth having a power of 20 to 120 kilowatts and located within the 1.3au field of view centered on Proxima Centauri, assuming a benchmark laser launcher having a 10-meter aperture.

    https://arxiv.org/abs/2102.01910
    Do good work. —Virgil Ivan "Gus" Grissom

  18. #138
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    Resolving the History of Life on Earth by Seeking Life As We Know It on Mars

    Christopher E. Carr

    An origin of Earth life on Mars would resolve significant inconsistencies between the inferred history of life and Earth's geologic history. Life as we know it utilizes amino acids, nucleic acids, and lipids for the metabolic, informational, and compartment-forming subsystems of a cell. Such building blocks may have formed simultaneously from cyanosulfidic chemical precursors in a planetary surface scenario involving ultraviolet light, wet-dry cycling, and volcanism. However, early Earth was a water world, and the timing of the rise of oxygen on Earth is inconsistent with final fixation of the genetic code in response to oxidative stress. A cyanosulfidic origin of life could have taken place on Mars via photoredox chemistry, facilitated by orders of magnitude more sub-aerial crust than early Earth, and an earlier transition to oxidative conditions. Meteoritic bombardment may have generated transient habitable environments and ejected and transferred life to Earth. The Mars 2020 Perseverance Rover offers an unprecedented opportunity to confirm or refute evidence consistent with a cyanosulfidic origin of life on Mars, search for evidence of ancient life, and constrain the evolution of Mars' oxidation state over time. We should seek to prove or refute a Martian origin for life on Earth alongside other possibilities.

    https://arxiv.org/abs/2102.02362
    Do good work. —Virgil Ivan "Gus" Grissom

  19. #139
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    Can super-Earth interior dynamics set the table for habitability?

    https://phys.org/news/2021-02-super-...itability.html
    Do good work. —Virgil Ivan "Gus" Grissom

  20. #140
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    A truly unique way of looking at air pollution on alien worlds.

    Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology

    Ravi Kopparapu, Giada Arney, Jacob Haqq-Misra, Jacob Lustig-Yaeger, Geronimo Villanueva

    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.

    https://arxiv.org/abs/2102.05027
    Do good work. —Virgil Ivan "Gus" Grissom

  21. #141
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    Interstellar travel is essential to the long-term survival of a space civilization, says paper.

    Minimal conditions for survival of technological civilizations in the face of stellar evolution

    Brad Hansen, Ben Zuckerman

    The ease of interstellar rocket travel is an issue with implications for the long term fate of our own and other civilizations and for the much-debated number of technological civilizations in the Galaxy. We show that the physical barrier to interstellar travel can be greatly reduced if voyagers are patient, and wait for the close passage of another star. For a representative time of ∼1 Gyr, characteristic of the remaining time that Earth will remain habitable, one anticipates a passage of another star within ∼1500~AU. This lowers the travel time for interstellar migration by ∼ two orders of magnitude compared with calculated travel times based on distances comparable to average interstellar separations (i.e., ∼1 pc) in the solar vicinity. We consider the implications for how long-lived civilizations may respond to stellar evolution, including the case of stars in wide binaries, and the difficulties of identifying systems currently undergoing a relevant close encounter. Assuming that life originates only around G-type stars, but migrates primarily to lower mass hosts when the original system becomes uninhabitable, the fraction of extant technological civilizations that exist as diaspora can be comparable to the fraction that still orbit their original host stars.

    https://arxiv.org/abs/2102.05703
    Last edited by Roger E. Moore; 2021-Feb-12 at 01:05 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

  22. #142
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    I think by the time stellar evolution becomes a problem for any hypothetical intelligent life, interstellar travel will either be a long-since solved problem, or a moot point.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  23. #143
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    A technosignature-search paper listing many sorts of things to look for (not limited to Dyson spheres).

    Concepts for future missions to search for technosignatures

    Hector Socas-Navarro, Jacob Haqq-Misra, Jason T. Wright, Ravi Kopparapu, James Benford, TechnoClimes 2020 workshop participants

    New and unique opportunities now exist to look for technosignatures (TS) beyond traditional SETI radio searches, motivated by tremendous advances in exoplanet science and observing capabilities in recent years. Space agencies, both public and private, may be particularly interested in learning about the community's views as to the optimal methods for future TS searches with current or forthcoming technology. This report is an effort in that direction. We put forward a set of possible mission concepts designed to search for TS, although the data supplied by such missions would also benefit other areas of astrophysics. We introduce a novel framework to analyze a broad diversity of TS in a quantitative manner. This framework is based on the concept of ichnoscale, which is a new parameter related to the scale of a TS cosmic footprint, together with the number of potential targets where such TS can be searched for, and whether or not it is continuous in time.

    https://arxiv.org/abs/2103.01536
    Do good work. —Virgil Ivan "Gus" Grissom

  24. #144
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    More theorizing on the likelihood of finding signals from alien civilizations.

    Longevity is the key factor in the search for technosignatures.

    Amedeo Balbi, Milan M. Ćirković

    It is well-known that the chances of success of SETI depend on the longevity of technological civilizations or, more broadly, on the duration of the signs of their existence, or technosignatures. Here, we re-examine this general tenet in more detail, and we show that its broader implications were not given the proper significance. In particular, an often overlooked aspect is that the duration of a technosignature is in principle almost entirely separable from the age of the civilization that produces it. We propose a classification scheme of technosignatures based on their duration and, using Monte Carlo simulations, we show that, given an initial generic distribution of Galactic technosignatures, only the ones with the longest duration are likely to be detected. This tells us, among other things, that looking for a large number of short-lived technosignatures is a weaker observational strategy than focusing the search on a few long-lived ones. It also suggests to abandon any anthropocentric bias in approaching the question of extraterrestrial intelligence. We finally give some ideas of possible pathways that can lead to the establishment of long-lived technosignatures.

    https://arxiv.org/abs/2103.02923
    Do good work. —Virgil Ivan "Gus" Grissom

  25. #145
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    Oumuamua Is Not a Probe Sent to our Solar System by an Alien Civilization

    Ben Zuckerman

    Oumuamua, the first known object of extrasolar origin seen to enter our Solar System, has multiple unusual characteristics that, taken together, are very difficult to explain with conventional astronomical entities like asteroids and comets. Consequently, it has been hypothesized that Oumuamua is an interstellar probe that was constructed by an alien civilization. We demonstrate that the accomplishments that can be achieved with large space telescopes/interferometers in the alien's planetary system will completely quench any motivation for construction and launch of an Oumuamua-like probe. The absence of any such motivation proves that Oumuamua is not an alien creation.

    https://arxiv.org/abs/2103.05559
    Do good work. —Virgil Ivan "Gus" Grissom

  26. #146
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    Quote Originally Posted by Roger E. Moore View Post
    The absence of any such motivation proves that Oumuamua is not an alien creation.
    Also the complete lack of any evidence that it is an alien creation.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  27. #147
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    Researcher theorizes worlds with underground oceans support, conceal life.

    https://phys.org/news/2021-03-theori...s-conceal.html

    QUOTE: "Interior water ocean worlds are better suited to provide many kinds of environmental stability, and are less likely to suffer threats to life from their own atmosphere, their star, their solar system, and the galaxy, than are worlds like Earth, which have their oceans on the outside," said Stern.
    Do good work. —Virgil Ivan "Gus" Grissom

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