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Thread: Circumstellar habitable zone -hypothetical innermost edge?

  1. #1
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    Question Circumstellar habitable zone -hypothetical innermost edge?

    This article suggests that the habitable zone for hypothetical Dune like desert worlds actually extends all the way in to Mercury's orbit:

    http://adsabs.harvard.edu/abs/2013ApJ...778..109Z

    >>We explore the minimum distance from a host star where an exoplanet could potentially be habitable in order not to discard close-in rocky exoplanets for follow-up observations. We find that the inner edge of the Habitable Zone for hot desert worlds can be as close as 0.38 AU around a solar-like star, if the greenhouse effect is reduced (~1% relative humidity) and the surface albedo is increased.<<

    Is this plausible? It sounds like what they've done is played with this tool:

    http://www.astro.indiana.edu/gsimonel/temperature1.html

    If you increase the surface albedo and decrease the greenhouse effect, then it says that even planets very close to the sun could have Earth-like temperatures, but a lot about it seems very unconvincing. For a start, doesn't Mercury have trouble spinning, because it is close to being tidally locked to the sun? So a day on Mercury is very long and so the side with the daylight gets heated up a lot more whereas the night side cools down a lot.

    On the other hand, there are gypsum sand dunes in the Mexican desert, aren't there? I read somewhere that gypsum has an albedo of 85 and if this is true, then could a hypothetical planet exist with a surface of gypsum sand that would cool itself down a lot through surface albedo?

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    Quote Originally Posted by Aetherium View Post
    On the other hand, there are gypsum sand dunes in the Mexican desert, aren't there? I read somewhere that gypsum has an albedo of 85 and if this is true, then could a hypothetical planet exist with a surface of gypsum sand that would cool itself down a lot through surface albedo?
    Would a gypsum-covered planet with minimal water and tidally locked, be able to support life?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    At absolute most, my guess would be that it would only support microbial life.

    But that was the question I was putting to the regulars here. Does that Harvard hypothesis look plausible, or does it look poorly researched.

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    Quote Originally Posted by Aetherium View Post
    Is this plausible? It sounds like what they've done is played with this tool:

    ... could a hypothetical planet exist with a surface of gypsum sand that would cool itself down a lot through surface albedo?
    Yes, it is very easy to to play with tools and maths to find a special case solution that solves a given problem, but that special case is nowhere near stable over time.

    For our hypothetical planet, the question is how long would it exist with a surface of gypsum sand? If it's close to the sun, it's going to get a lot of asteroid strikes and infalling dust, and so get dirty very quickly.
    Last edited by Ufonaut99; 2017-Oct-29 at 12:50 AM. Reason: added infalling dust

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    Quote Originally Posted by Aetherium View Post
    Does that Harvard hypothesis look plausible, or does it look poorly researched.
    Plausible in what sense? In the sense that, if we do find alien life, that it is likely found on the type of planets this study explores? Probably not.

    Or do you mean plausible for the purpose stated in the study itself: "in order not to discard close-in rocky exoplanets for follow-up observations"? I'm not equipped to judge whether the study was done well or poorly (it's available, if anyone wants to read it), but that quote means that they are purposely looking for the very extreme lower bound. So if they do come up with conclusions that it is barely possible, but only in the rarest of circumstances, well, that's what they were trying to find, no?
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