A new estimate released Monday suggests that the Milky Way galaxy is home to at least 17 billion planets similar in size to Earth. It doesn't mean all are potentially habitable, but the sheer number is a welcome starting point in the search for worlds like our own.
Two independent groups came up with the new estimate after a fresh analysis of data gathered by NASA's Kepler spacecraft, launched in 2009 to track down other Earths. The craft spots a planet when it passes in front of the planet's star. (AP)