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Thread: What do you think is the most likely explanation for the Fermi paradox?

  1. #1051
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    Quote Originally Posted by Colin Robinson View Post
    Do you think Venus is less likely for life than Mars? Why?
    I do, primarily because known upper atmosphere life is largely dependent on interaction with the greater biosphere. Venus' conditions would seem to make such a niche much more tenuous.

    Underground and Arctic life that we know of has direct access to moisture and minerals and protections which give such life forms something of an advantage, IMO.



    Glad you mentioned sunlight and abiogenesis.

    It's true that the ice moons including Titan get a lower flux of energy from the sun than Earth or Mars.

    But due to the composition of Titan's atmosphere (hydrogenating rather than oxidising), it's able to turn a substantial part of the solar energy it gets into chemical energy. E.g. by producing acetylene (C2H2) alongside free hydrogen (H2) in its ionosphere. This is comparable to what happened in the Urey/Miller experiment, and to what presumably happened in Earth's atmosphere 4 billion years ago, when abiogenesis occurred.

    That's one reason I think Titan may tell us more than Mars about questions like how common or uncommon abiogenesis is throughout the Galaxy.
    Well, it would tell us something about organic chemistry under cryo conditions. We still have no idea if such conditions could originate life. As you said, it takes more than the right molecules.

    I think Enceladus and Europa might be places to watch. They're thought to have oxygenation from radiation flux on the ice, making for plenty of potential chemical "oomph".
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  2. #1052
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    I would put Mars first because, based on the evidence we have, conditions underground in some places could be able to support Earth life (at least some single cell life). It has a decent chance of having earthlike microenvironments. I’m not aware of anything similar elsewhere. Europa’s possible oceans would likely be very different from Earth environments, for example.

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  3. #1053
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    Quote Originally Posted by Noclevername View Post
    I do, primarily because known upper atmosphere life is largely dependent on interaction with the greater biosphere. Venus' conditions would seem to make such a niche much more tenuous.

    Underground and Arctic life that we know of has direct access to moisture and minerals and protections which give such life forms something of an advantage, IMO.





    Well, it would tell us something about organic chemistry under cryo conditions. We still have no idea if such conditions could originate life. As you said, it takes more than the right molecules.

    I think Enceladus and Europa might be places to watch. They're thought to have oxygenation from radiation flux on the ice, making for plenty of potential chemical "oomph".
    I'd agree that Enceladus and Europa are intriguing worlds. They are two more reasons why Mars should not be thought of as the only place in the Solar System where we might conceivably find extraterrestrial life.

    But what about the point you made in your last message, about relevance of sunshine to life? How much energy from the Sun reaches the subsurface ocean of Europa?
    Last edited by Colin Robinson; 2021-Jan-01 at 07:43 AM.

  4. #1054
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    Quote Originally Posted by Van Rijn View Post
    I would put Mars first because, based on the evidence we have, conditions underground in some places could be able to support Earth life (at least some single cell life). It has a decent chance of having earthlike microenvironments. I’m not aware of anything similar elsewhere.
    That line of argument is presumably why the idea of life on Mars gets so much attention.

    But we don't know whether the sort of Earthlike microenvironments which may exist on Mars are enough for a living ecosystem to function.

    David Grinspoon thinks microenvironments may not be enough. Like James Lovelock, he sees life on Earth as the property of a global biosphere, in which living things and non-living things (such as atmospheric composition) have co-evolved, i.e. developed together.

    So he expects life activity beyond Earth to be found on a planet or moon which, like Earth, is active in other ways, such as having cycles of liquid formation and evaporation, and an atmosphere which is far from chemical equilibrium.
    Last edited by Colin Robinson; 2021-Jan-01 at 08:32 AM.

  5. #1055
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    Quote Originally Posted by Colin Robinson View Post
    But we don't know whether the sort of Earthlike microenvironments which may exist on Mars are enough for a living ecosystem to function.
    Of course, but I thought the discussion was about how one would order worlds in terms of most likely to least likely to have habitable environments. I’d put Mars at the top because, based on current evidence, it is the most likely to have microenvironments that could support some kinds of earth life. Whereas for others we generally have to posit various significant differences from Earth life to survive anywhere.

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  6. #1056
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    Quote Originally Posted by Colin Robinson View Post
    I'd agree that Enceladus and Europa are intriguing worlds. They are two more reasons why Mars should not be thought of as the only place in the Solar System where we might conceivably find extraterrestrial life.

    But what about the point you made in your last message, about relevance of sunshine to life? How much energy from the Sun reaches the subsurface ocean of Europa?
    I never said it was the only place.

    I consider Mars more likely than the ice moons specifically because of sunlight. But the moons do have alternative sources of energy.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Van Rijn View Post
    Of course, but I thought the discussion was about how one would order worlds in terms of most likely to least likely to have habitable environments. I’d put Mars at the top because, based on current evidence, it is the most likely to have microenvironments that could support some kinds of earth life. Whereas for others we generally have to posit various significant differences from Earth life to survive anywhere.
    Have you seen this essay by Peter Vickers of Durham University — Alien life is out there, but our theories are probably steering us away from it?

    He suggests that perhaps we've been thinking about life and habitability too narrowly. "Under-explored areas need exploring, and we can’t know in advance what we will find."

    It seems to me that Venus and Titan are under-explored in comparison with Mars.

    Over the last half century, study of the Solar System, and of exo-planets, has shown that planetary environments are very diverse.

    Other worlds have all sorts of significant differences from Earth. So perhaps we should be open to the possibility that life on other worlds has significant differences from Earth life?

    Diversity of biospheres may explain why we don't see colonists from other worlds here on Earth.

    A very diverse Galaxy means that would-be colonists would face a different environmental challenge on every world they tried to colonise.

    The challenges may be too great for colonisation to work at all; or may mean that even the most successful colonising life-forms spread through the Galaxy at a rate vastly slower than predicted by people like Michael Hart and Robin Hanson.
    Last edited by Colin Robinson; 2021-Jan-01 at 08:19 PM.

  8. #1058
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    Ideally we could explore everywhere in detail and our resources could be allocated by the experts' best judgement.

    As far as colonizing, I agree trying to integrate yourself into an alien biosphere would be much harder than establishing a closed artificial one. Even given best possible compatibility, there's sure to be major differences.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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