There may be more Earth-size planets in the universe than astronomers suspect, according to a University of California-Berkeley study published Thursday.
Using NASA's powerful Keck telescope in Hawaii, university astronomers Andrew Howard and Geoffrey Marcy tracked 166 sun-like stars within 80 light-years of Earth, according to their report published in Thursday's edition of the journal Science.
Howard and Marcy found a notable number of planets of the smallest size currently detectable: about three times the size of Earth.
"If we extrapolate down to Earth-size planets - between one-half and two times the mass of Earth - we predict that you'd find about 23 for every 100 stars," Howard said in a press release.
"This is the first estimate based on actual measurements of the fraction of stars that have Earth-size planets," Marcy said.
"What this means," Howard added, "is that, as NASA develops new techniques over the next decade to find truly Earth-size planets, it won't have to look too far."
The trick is to find planets that are the optimal distance from their stars to provide the right temperature range for liquid water and to sustain life, they wrote.
The research was funded by NASA and the W.M. Keck Observatory, which is operated by the University of California and the California Institute of Technology.
The study found just 33 planets circling 22 stars, but previous models had predicted very few or no planets in those ranges, Marcy said.
"One of astronomy's goals is to find eta-Earth, the fraction of Sun-like stars that have an Earth," Howard said. "This is a first estimate, and the real number could be one in eight instead of one in four. But it's not one in 100, which is glorious news."