At a recent meeting of the American Astronomical Society, Bill Borucki, principal investigator for NASA's planet-finding Kepler spacecraft, provided an update on Kepler's hunt for distant worlds, especially those Earth-like planets that might be habitable:

“We are finding Earth-size planets. Not in the habitable zone. We are looking for planets and finding a few big planets in the habitable zone. Okay, and we are trying to take what we have found and ask, if you see a few how do you extrapolate to the many? When you see a planet by a transit, the orbit has to be in your line of sight. But most orbits won't be. Well, we can correct for that. It's like rolling dice—what are the odds of getting snake eyes? One in 36. So if you get snake eyes there's probably 35 times that you'd roll and you wouldn't get them, for example.

“So we can do the same thing. We can tell in our galaxy there must be billions of planets. Probably on the order of a billion planets in the habitable zone of their stars. That's pretty crude right now—we're refining it—but we're getting the first statistics that are allowing us to make those estimates.”

In next week's episode, Borucki will tell us when Kepler will answer the big question—are habitable, Earth-like planets rare or common?

—John Matson

[The above text is a transcript of this podcast.]