[EMAIL PROTECTED] Solar systems like ours may be rare
URL to an interesting article from MSNBC _http://www.msnbc.msn.com/id/25784858/_ (http://www.msnbc.msn.com/id/25784858/) First paragraphs " As humans look farther into the universe and discover more and more planets beyond the sun, many wonder how typical our own solar system is. Often astronomers in the planet-hunting business say discoveries of Earth-like worlds are just around the corner. But a new study indicates our setup may be rare indeed. A group of astronomers surveyed sun-like stars in the Orion nebula open cluster and found that fewer than 10 percent have enough surrounding dust to make Jupiter-sized planets. ____________________________________ "We think that most stars in the galaxy are formed in dense, Orion-like regions, so this implies that systems like ours may be the exception rather than the rule," said researcher Joshua Eisner, an astrophysicist at the University of California, Berkeley. That's important because giant planets like Jupiter may be instrumental in fostering life on rocky worlds like Earth. Eisner and his team observed about 250 stars in the million-year-old Orion Nebula, looking for dense disks of dust surrounding the stars that could be forming planets. They found that only about 10 percent of the stars emitted radiation in the frequency that would indicate they have these proto-planetary disks of warm dust. And only 8 percent of the stars surveyed had dust disks with masses greater than one-hundredth the mass of the sun, a mass thought to be the lower limit for formation of Jupiter-sized planets. These findings seem to agree with what planet hunters are finding so far when they use radial velocity studies to detect extrasolar planets around other stars. (The radial velocity approach involves looking for a wobble in a star's motion caused by the slight gravitational pull of an orbiting planet.) "The current numbers are suggesting 6 to 10 percent of stars have Jupiter-sized planets, which is exactly consistent with our findings," Eisner told SPACE.com. The researchers will detail their findings in the Aug. 10 issue of the Astrophysical Journal. Snapshot in time Still, it's too soon to completely despair of finding the universe filled with Jupiters around other suns. Since the survey only looked at dust around the stars, and would not have detected any already-formed planets, it could be that some of those sun-like stars already had planets. Slide show (javascript:SSOpen('10913792','0');) _Month in Space_ (javascript:SSOpen('10913792','0');) See highlights from the shuttle Discovery’s flight, the Phoenix Mars Lander mission and much more in June’s roundup of cosmic pictures. more photos "Perhaps we're only detecting the stars that have not formed planets yet," said John M. Carpenter, an astronomer at Caltech who worked with Eisner on the Orion research. "Perhaps some other stars already formed planets. It's only a snapshot in time and as you look at other clusters at different ages you can build up a better picture." Other scientists agree there are many unanswered questions about solar systems beyond our own. "As the precision with which we can measure improves, we find more planets," said Harvard planet hunter David Charbonneau, who was not involved in the Orion study. "The rate of occurrence has gone up since we started looking." He said it's too soon to tell for sure whether Earth's system is atypical, but studies that look at whether other stars have the raw materials necessary to form solar systems like our own can help. "Certainly knowing that there is enough stuff around stars to make planets is a crucial step," he said."
