vinces99 writes with this excerpt from the UW news service: "It might be easier than previously thought for a planet to overheat into the scorchingly uninhabitable 'runaway greenhouse' stage, according to new research (abstract, article paywalled) by astronomers at the University of Washington and the University of Victoria. In the runaway greenhouse stage, a planet absorbs more solar energy than it can give off to retain equilibrium. As a result, the world overheats, boiling its oceans and filling its atmosphere with steam, which leaves the planet glowing-hot and forever uninhabitable, as Venus is now. One estimate of the inner edge of a star's 'habitable zone' is where the runaway greenhouse process begins. The habitable zone is that ring of space around a star that's just right for water to remain in liquid form on an orbiting rocky planet's surface, thus giving life a chance. Revisiting this classic planetary science scenario with new computer modeling, the astronomers found a lower thermal radiation threshold for the runaway greenhouse process, meaning that stage may be easier to initiate." If correct, the habitable zone shrinks a bit and a few exoplanets might lose their potentially habitable status. And the Earth will leave the habitable zone in a billion and a half or so years as the Sun gets brighter.
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