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Greenhouse Effect Could Extend Habitable Zone in Alien Solar Systems
The distant region beyond Saturn is too cold for liquid water, a necessity for life as we know it. But new research indicates that rocky planets far from their parent star could generate enough heat to keep water flowing - if their atmospheres were made up primarily of hydrogen.
Planets near their suns reap the benefits of light and heat, while those farther away must endure colder temperatures. But the new research indicates that planets with hydrogen-rich atmospheres could contain liquid at their surface even out to fifteen times the distance between the Earth and the Sun.
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That kind of talk was in general before we knew much about what the poles were actually made of. For quite a while, I believe the general consensus was that the North polar cap was almost entirely water, while the South was almost entirely Carbon Dioxide. I believe the current consensus is that both are majority water. Further, climate modelling back in the 90s was not what it is today, and I'm not sure that current models would agree with the suggestion that evaporating the polar caps would result in a 70 K temperature rise planetwide.
-Josh
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As with many ideas about Mars' climate, the pendulum swings back and forth on how much CO2 is sequestered in the polar caps. It used to be thought there was enough to raise the surface pressure to several bar (something of this magnitude would be required for that quoted 70 K temperature increase). But it was then discovered, as Josh pointed out, that the caps are mostly water. The only apparent CO2 was a small permanent residual deposit visible at the South pole. So the pendulum swung the other way and over the past decade or so people got into the mindset that no significant permanently frozen CO2 deposits exist. However, the amount of CO2 that could be "hiding" inside the polar caps is not well constrained, and could theoretically be as much as a few 100 mbar. Recent radar work has found pockets in the South polar cap of relatively pure CO2 forming a reservoir comparable to the entire current atmosphere. There is also the possibility of CO2 clathrates, which we currently have no clear way of observing from orbit. Some sort of lander would need to be needed to find unequivocal evidence. This might be an area of interest over the next decade as the pendulum swings back toward a view favorable to significant CO2 deposits in the caps (albeit not as large as originally believed).
"Everything should be made as simple as possible, but no simpler." - Albert Einstein
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