Article Posted on : - Oct 29, 2010

A new survey reveals that small planets are more common than large ones, as depicted here in this illustrated bar chart. Photo: NASA/ JPL.

PASADENA (BNS): Astronomers have found Earth-size planets in Milky Way galaxy- nearly one in four of all sun-like stars might have a planet roughly the size of Earth orbiting close around them.

With the help of W.M. Keck Observatory in Hawaii, scientists have searched 166 sun-like stars near to our solar system for five years, ranging from three to 1,000 times the mass of Earth.

The results show more small planets than large ones, indicating small planets are more prevalent in our Milky Way galaxy, according to a new survey, funded by NASA and the University of California.

The study is the most extensive and sensitive planetary census of its kind.

"We studied planets of many masses -- like counting boulders, rocks and pebbles in a canyon -- and found more rocks than boulders and more pebbles than rocks. Our ground-based technology can't see the grains of sand, the Earth-size planets, but we can estimate their numbers," Andrew Howard of the University of California, Berkeley, lead author of the new study, said in a NASA release.

They measured the numbers of planets falling into five groups, ranging from 1,000 times the mass of Earth, or about three times the mass of Jupiter, down to three times the mass of Earth.

The search was confined to planets orbiting close to their stars -- within 0.25 astronomical units, or a quarter of the distance between our sun and Earth.

The astronomers extrapolated from these survey data to estimate that 23 percent of sun-like stars in our galaxy host even smaller planets, the Earth-sized ones, orbiting in the hot zone close to a star. "This is the statistical fruit of years of planet-hunting work," said Marcy. "The data tell us that our galaxy, with its roughly 200 billion stars, has at least 46 billion Earth-size planets, and that's not counting Earth-size planets that orbit farther away from their stars in the habitable zone."

The study is part of a key NASA science programme and will stimulate new theories to explain the significance and impact of these findings.

NASA's Kepler spacecraft is also surveying sun-like stars for planets and is expected to find the first true Earth-like planets in the next few years.