581 c

Astronomers have found a roughly-Earth-class planet orbiting the red dwarf star Gliese 581. The planet is estimated to be five times as massive as the earth, and has a temperature between 32 and 104 (no units provided, I hope they mean F, a salubrious planet it would be!).

The significance of this is that it is the first detection of this class of planet outside the solar system, and that it might the first of many, many such discoveries.