NASA's orbiting Kepler telescope has discovered its first planet in the habitable zone of another star. By "habitable," astronomers mean that a planet could harbor temperatures conducive to liquid water—and maybe life.
The new planet, Kepler 22b, orbits somewhat closer to its host star than Earth does to the sun. “The star is some 600 light-years away.” NASA's Bill Borucki, who leads the Kepler mission, in a December 5th teleconference.
That star is a bit cooler than the sun. "So if the greenhouse warming were similar on this planet, and it had a surface, its surface temperature would be something like 72 Fahrenheit—a very pleasant temperature here on Earth."
Kepler 22b is more than twice as large as Earth. One big caveat is that it may not be rocky, like Earth is. It could instead be a gas planet like Neptune. If that were the case, prospects for life there would be rather dim.
Kepler ought to find even better candidates for life in the near future. The satellite has now tentatively identified more than 2,300 possible planets—about 50 of them in the habitable zone—that await confirmation in the years to come.
[The above text is a transcript of this podcast.]