In article <8eq11eFdmdU1@mid.individual.net>,
Greg Goss wrote:
>Naraht wrote:
>
>>This is more sort of a research question.
>>
>>Presuming a planet with more or less the same makeup of the solid
>>portion, the same age, and same distance from the sun, how large or
>>small can the planet be to be habitable by humans? I *think* the
>>primary issue is that if it is larger than a certain size then the
>>planet won't lose the Hydrogen/Helium in the atmosphere and become a
>>close in Gas Giant and if it is smaller than a certain size, it won't
>>keep it's Oxygen long enough (which puts the minimum somewhat larger
>>than Mars (or would Mars have kept its oxygen if it had a
>>Magnetosphere)).
>
>Niven's various stories in the seventies figured that Earth would have
>kept too much atmosphere if it hadn't had a moon stirring the top and
>pulling off air molecules and tossing them around.
That's an idea he got from Thomas Gold, one that turned out to be, like
so many other Gold ideas [1], wrong.
As it happens, Venus and Earth have about the same amount of CO2. It's
just that almost all of Earth's is locked away in the crust and almost
all of Venus' isn't.
1: But not all, so his ideas can't just be dismissed out of hand.
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