The total exoplanet tally now stands at about 3,200, and Kepler has found 2,235 of them as according to NASA officials.
“We now know that exoplanets are common, most stars in our galaxy have planetary systems and a reasonable fraction of stars in our galaxy have potentially habitable planets,” Paul Hertz, Astrophysics Division director at NASA Headquarters in Washington, D.C., said. “Knowing this, is the first step toward addressing the question, ‘Are we alone in the universe?'”
Indeed, data gathered by Kepler and other instruments suggest that about 25 percent of all the “normal” (main-sequence) stars in the Milky Way harbor roughly Earth-size planets in their habitable zones, that just-right range of distances at which liquid water can exist on a world’s surface.
There are at least 70 billion main-sequence stars in the galaxy, said Kepler mission scientist Natalie Batalha, of NASA’s Ames Research Center in Moffett Field, California.
“You can see, doing the math, that you’re talking about tens of billions of potentially habitable, Earth-sized planets out there in the galaxy,” Batalha said.