Study: Billions of Earth-size planets in Milky Way

LONG BEACH, Calif. (AP) — Astronomers estimate one in six stars in our Milky Way galaxy has a planet the size of Earth orbiting it. That translates to at least 17 billion Earth-size planets.

It doesn't mean these planets are all habitable, but it's an encouraging sign for scientists hunting for worlds like our own.

Two independent groups came up with similar estimates after a fresh analysis of data from NASA's Kepler spacecraft, launched in 2009 to track down other Earths. The findings were presented Monday at the American Astronomical Society in Long Beach, Calif.

The goal has long been to discover a planet similar in size to Earth that's located in the so-called Goldilocks zone — a place that's not too hot and not too cold, where water might exist in liquid form.