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We've been taking a look at the models that have been done of the runaway greenhouse and the moist greenhouse to try to understand the time scale for the loss of the oceans. The first thing you realize when you look at these models is that it has not been done in a very sophisticated way. Not because the people that have done it are unsophisticated -- Jim Kasting is the best in the business, and his models are state of the art. But the state of the art is not that good.
So, how can one do a better job at modeling the longevity of oceans on a Venus-like planet? I say 'Venus-like planet' because the problem is applicable not just to Venus, but to terrestrial planets on the inner edge of the habitable zone anywhere in the galaxy, or other galaxies.
In the greenhouse-era Venus, Venus still has surface water, and the atmosphere is largely water vapor. The oceans are evaporating, hydrogen is being lost to space. When we put in clouds in our model, we found that the clouds act to cool the planet significantly during that greenhouse phase. Temperatures are significantly lower.
Another intriguing thing about early Venus is that it may have had an oxygen-rich atmosphere. You had this massive loss of hydrogen to space from water, and what's left is all that oxygen. We've heard a lot about the rise of oxygen being important in the development of complex life on Earth. Perhaps Venus was a warm, wet planet with an oxygenated atmosphere much earlier than Earth.
By the way, one further implication for habitability bears mentioning. If Venus once had life, and there's no good reason to think that it couldn't have, then we can ask what happened to this life when the oceans disappeared. One possibility is that it simply died out once its habitat vanished. But life is tenacious and highly adaptable. So I think that it is possible that Venusian life migrated to an atmospheric niche when the surface water dried up.