Apr 24 2009
Gliese 581
It was another good week for planetary astronomy, with the announcement of the discovery of the smallest exoplanet (planet orbiting another star) yet, only twice Earth’s mass, orbiting the red dwarf Gliese 581. The planet, dubbed Gliese 581 e, orbits very closely, and would be too hot for life as we know it. However, in other news from the same system, one of the earlier discovered planets (we now know of four) Gliese 581 c, is orbiting in the habitable zone, which means liquid water could exist. It’s a big planet, Neptune-size, and may very well be a water world. Of course any moons it has (which would be too small for us to detect yet, even if they were large by our standards) would also be in the habitable zone.
Currently exoplanets are named after their parent star with a lowercase letter in the order found, with “a” reserved for the star itself. Thus Gliese 581 c was the second planet discovered orbiting that star, the recent Gliese 581 e the fourth. This has nothing to do with the traditional (at least in sci-fi) convention of using roman numerals to indicate position from the star; until we discover all the planets a star has, we won’t know the order. But at the moment, until we discover more, Gliese 581 e would be Gliese 581 I, and Gliese 581 c would be Gliese 581 III.
Gliese 581 is only about 20 lightyears from here, within T-Space. I really need to set a story there.
