|
A few months ago there was a great deal of talk about the
exoplanet Gliese 581 g, in orbit around a red dwarf about 20 light years away. After being in the news for being the first that could have liquid water, it has once again made the news because it may not even exist.
This uncertainty has nonetheless not stopped some opportunists from selling part of the surface on e-bay!
Neither has the possible inexistence of Gliese 581 g has stopped researchers from trying to work out what the surface of the planet may look like, in the presence or absence of an atmosphere.
An initial assumption has been that the spin period of the planet is synchronized with its rotation, so that the same hemisphere always faces the star, keeping the other permanently in darkness, and probably frozen.
According to Raymond Pierrehumbert, of the University of Chicago, the hemisphere exposed to the stellar light could have an enormous liquid ocean, likely covered by a layer of ice.
If there is actually no atmosphere, there would be no greenhouse effect, but nor would there be an efficient way to transport heat away from the ocean, that although frozen on the surface, would be liquid at depths where the light could still penetrate, an essential condition for the support of any life.
Pierrehumbert maintains that the scenario most likely to support life is that in which Gliese 581 g has an atmosphere rich in carbon dioxide (CO2). This could create a greenhouse effect able to maintain a completely liquid ocean, covering about 1/4 of the circumference of the planet if
the CO2 accounted for as much as 20% of the atmosphere. In this case Gliese 581 g would look like a "gigantic eyeball with a liquid pupil".
Although this is little more than speculation, the possible scenarios described in The Astrophysical Journal by Pierrehumbert could well be applied to planets other than Gliese 581 g, if this planet turns out not to exist.
|
