A new study estimates that one in four sun-like stars have Earth-sized planets — far more than previously thought. It challenges current theories on how planets form, and may mean a greater chance of finding habitable worlds.
Astronomers at UC Berkeley observed 166 G and K stars — stars similar to our sun — within 80 light years of Earth and tallied up the detectable planets from each star. According to their report in today's Science, they estimated that 1.6 percent of the sun-like stars in their sample had Jupiter-size planets and 12 percent had super-Earths (3-10 Earth masses). Extrapolating these findings, they estimate that 23 percent of these planets have Earth-sized planets.
Now, it's important to note that none of these Earth-sized planets would be habitable. Current detection methods allow astronomers only to detect super-Earths that are close to their stars. But that's what's so interesting. According to current models of planet formation and migration, after their birth in a protoplanetary disk, planets should spiral inward because of interactions with the gas in the disk. If this were true, then the inner region of solar systems would be devoid of planets. But the Berkeley study found Earth-like planets likely do exist in the inner ring — and chances are we will find more planets further out in these solar systems' habitable zones as detection technology improves and the Kepler Mission turns its telescope on these systems.
Andrew Howard and Geoffrey Marcy, who led the study, warn that this 23 percent is a very rough, very early estimate, but they're encouraged that it will mean the discovery of far more Earth-sized planets than previously predicted.
Based on these statistics, Howard and Marcy, who is a member of NASA's Kepler mission to survey 156,000 faint stars in search of transiting planets, estimate that the telescope
will detect 120-260 "plausibly terrestrial worlds" orbiting some 10,000 nearby G and K dwarf stars with orbital periods less than 50 days.