Is first life-friendly exoplanet an 'eyeball'?

IN DECEMBER, a pair calling themselves "The Benevolent Fisted Rulers" offered up 4-hectare plots of Gliese 581 g, the most habitable exoplanet yet discovered,Setting aside the ethics of exoplanetary land grabs, the move seems a touch premature. The alien world is 20 light years away and its very existence is not confirmed. Still, if the planet does exist, it is possible that it has some good exo-real estate.

Raymond Pierrehumbert at the University of Chicago examined the range of climates that Gliese 581 g might have and found one that would have a pool of water on one side, making it look like an eyeball. Even if further observations disprove the existence of Gliese 581 g, the work could help determine the habitability of exo-Earths still to be discovered.

First spotted in September via wobbles in the light emitted by its host star, Gliese 581 g is likely to be rocky. That, combined with the fact that it orbits the star at just the right, "Goldilocks" distance to provide the warmth needed for liquid water, made it the first planet discovered outside our solar system with the potential to host life.

But Gliese 581 g also differs from Earth. For a start, it orbits its dim, red dwarf star so closely that its year lasts just 37 days. This boosts the chance that its star's gravitational tug has caused the planet to spin at the same rate that it moves around the star, so that one side of the planet always faces the star and the other is always dark. Pierrehumbert assumed that the planet is indeed locked in this configuration when he looked at the various climates it might support.

One option is that the planet has no atmosphere. Although all water on the surface would remain frozen, at least there would be no gas to transport heat away from the starlit side. This could keep temperatures there high enough to thin the ice, allowing light that could support life to reach liquid water beneath the surface.


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