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Could Super Earths have Earth like atmospheres?

  1. Aug 7, 2013 #1
    I am wondering if a Super Earth planet with 2x Earths diameter and 8x Earths mass could have atmospheres below 10 bar? If so how could they be formed?

    Im asking because its theorized that super Earths will have thick hydrogen atmospheres. I was wondering if Super Earths could have thinner atmospheres?
    Last edited: Aug 8, 2013
  2. jcsd
  3. Aug 8, 2013 #2


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    If they are hot enough, if there is not enough hydrogen, or if all hydrogen formed chemical bonds... why not.
    They might be rare.
  4. Aug 8, 2013 #3


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    Surface gravity of a planet with parametres as specified would be 2g.
    With the same amount(mass) of atmospheric gasses as on Earth, it'd result in merely 2 bar pressure.

    Additionally, there's a lot of variation in pressure possible for any value of surface gravity. Compare Earth and Venus, with similar values of g and almost two orders of magnitude difference in surface pressure.
  5. Aug 9, 2013 #4
    Lots of Factors

    Some thoughts:
    • The more massive world, with a deeper potential well, is maybe going to hang onto some gases that Earth lost. If it's only twice the mass of Earth then probably not a lot more, but maybe extra water, at least.
    • How deep that potential well will be isn't a trivial question because you have to know how much rock and metal compresses under increased gravity.
    • It's hard to imagine having even a vaguely earthlike atmosphere without plenty of photosynthetic life.
    • Even if the pressure is high at sea level there will be places at high altitude where the pressure is more earthlike - and increased gravity means a thinner atmosphere, so the altitude doesn't need to be all that high.
    • The chains of logic can be complex. If I understand correctly: Venus is hot, so Venus loses its water from its surface, so plate tectonics stops, there's not much weathering, nothing absorbs the CO2, greenhouse effect makes it get hotter, etc..
    • Last time I looked into this I found an elementary planetology lecture notes series on the web. It wasn't hard and that was years ago. Should be even easier now.
  6. Aug 10, 2013 #5


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    The problem with super earths is the greenhouse effect. Yes, it will trap more atmosphere - and more heat. It would need to be in a 'goldilocks' zone to avoid the fate of Venus, or death by freezing. A planet like earth walks a tightrope to remain biologically viable for billions of years
  7. Aug 12, 2013 #6
    Atmosphere on super earths

    I think we may be missing one thing here. Earth has a magnetic field of sufficient strength to protect the atmosphere from being eroded by the solar wind. Without that field, our planet would probably be much less inviting for life....so I would have to presume that some kind of magnetic field, probably from a molten iron core revolving, would have to be part of the equation for atmosphere retention....so if a super earth manages to not have a molten iron core, it might not be able to prevent rapid (comparatively) loss of the atmosphere. Mars has plenty of iron, but I suspect it is locked up in oxides that are solid, and has no molten, moveable core and therefore no magnetic field generating....so combined with less gravity, any atmosphere was driven away. Venus is probably a special case, but I would love to see if there is any high rate erosion of the atmosphere due to it's lack of a magnetic field.....
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