A new NASA survey indicates that Earth-sized planets are now thought to be common in the galaxy, and thus, probably the universe. As many as one in four stars similar to the sun could have Earth-sized planets orbiting them.
From the press release:
Nearly one in four stars similar to the sun may host planets as small as Earth, according to a new study funded by NASA and the University of California.
The study is the most extensive and sensitive planetary census of its kind. Astronomers used the W.M. Keck Observatory in Hawaii for five years to search 166 sun-like stars near our solar system for planets of various sizes, ranging from three to 1,000 times the mass of Earth.
All of the planets in the study orbit close to their stars. The results show more small planets than large ones, indicating small planets are more prevalent in our Milky Way galaxy.
“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,” said Andrew Howard of the University of California, Berkeley, lead author of the study. “Earth-size planets in our galaxy are like grains of sand sprinkled on a beach — they are everywhere,” Howard said.
The study is in the Oct. 29 issue of the journal Science.”
See also the University of California press release. These findings would appear to confirm the preliminary findings from the Kepler space telescope as well, in that smaller rocky worlds are more common than larger gas giants, which bodes well in the search for life.