An Earth sized planet circling a near by star is said to have the proper conditions for sustaining life, and according to at least one expert it's almost certain that it does.
Gliese 581g is said to have a surface and has enough gravity to hold an atmosphere. "Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent," Prof Steven Vogt said during a press briefing. "I have almost no doubt about it." Vogt led the team of scientist who discovered the planet.
Gliese 581g is located 20 light years away from Earth in the constellation Libra and is said to have an estimated average surface temperature of between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius). So, it's no vacation hot spot.
All of a sudden I'm not so skeptical about the UN's Alien Ambassador appointment :)