Gliese 581g, Or Not?

Since the announcement last fall of the discovery of the first exoplanet that might be habitable, Gliese 581g, several studies have been done, some of which have concluded the world doesn't exist.

The star Gliese 581 is only 30 percent the mass of the Sun, and is 20 light years away. It has four confirmed planets, and two more that are controversial-- they may or may not actually exist. The entire Gliese 581 system so far known orbits within the area of Earth's orbit about the Sun. That makes untangling the mathematics of the interactions of four, or six, worlds in such a crowded volume of space quite challenging. Presumably, too, it's possible that one or more planets might exist beyond the group we know about, which would add another factor to a complex mathematical situation. Under those circumstances, given the basis for establishing the existence of these worlds are tiny wobbles of Gliese 581 resulting from gravitational interaction with planets, it's not surprising there are disagreements.

Paul Vogt, co-discoverer of 581g, stands by that discovery. He says his team looked at hundreds of possibilities, and that the existence of 581g in the habitable zone of its star is the simplest explanation that fits the data. We shall see.