Alien "Earths" Less Common Than Expected, Study Says
At two billion per galaxy, Earthlike worlds are "relatively scarce."
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.
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