Alien "Earths" Less Common Than Expected, Study Says

Alien "Earths" Less Common Than Expected, Study Says

Our Milky Way galaxy may be home to at least two billion Earthlike planets, a new study says.

But don't start making colonization plans just yet: The number is actually far lower than many scientists were expecting, which could make it hard to find other "Earths" in our galaxy, the study authors say.

The new estimate is the first of its kind based on data from NASA's Kepler space telescope, which was designed to search for planets that transit—or cross in front of—their stars, as seen from Earth.

Based on what Kepler's seen so far, the study authors think that up to 2.7 percent of all sunlike stars in the Milky Way host so-called Earth analogs.

"There are about a hundred billion sunlike stars within the Milky Way," said study co-author Joe Catanzarite, a scientist with NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

"Two percent of those might have Earth analogs, so you have two billion Earth analog planets in the galaxy," Catanzarite said.

"Then you start thinking about other galaxies. There are something like 50 billion [in the known universe], and if each one has two billion Earthlike planets, it's mind boggling."

Although the figure seems large, Catanzarite and co-author Michael Shao, also of JPL, say their results actually show that Earths are "relatively scarce."