Stars with Rocky Planets May Be Common

http://blog.wired.com/wiredscience/2008/02/researchers-sta.html

Researchers: Stars with Rocky Planets May Be Common
By John Borland February 18, 2008
Categories: Space

For the last several years, scientists have been discovering new planets elsewhere in the universe at an astonishing rate. Now a group of researchers who have surveyed a large group of stars similar to our own Sun say that potentially life-supporting rocky planets may in fact be extremely common in the Milky Way, circling anywhere from 20 percent to 60 percent of Sun-like stars.

Using the Spitzer Space Telescope, the researchers looked for signs of hot dust at distances plausible for planet formation around various stars, categorized by age.

They found that warm dust at that distance was relatively common around stars that were 10 million to 20 million years old, but that it fell off almost entirely by the time stars were about 300 million years old.

That's about the right time scale to correspond with the time the Earth and other planets are believed to have formed slowly through the collision of smaller bodes, out of the Sun's own dust cloud. Here's University of Arizona astronomer Michael Meyer, who led the study:

"We don't often see warm-dust around stars older than 300 million years. The frequency just drops off. That's comparable to the time scales thought to span the formation and dynamical evolution of our own solar system," he added. "Theoretical models and meteoritic data suggest that Earth formed over 10 to 50 million years from collisions between smaller bodies."

A separate study found dust that some believe is attributable to the process of planet formation around stars that were just 10 million to 30 million years old.

The data can be interpreted different ways. At worst, it appears to show that at least one out of five Sun-like stars has the potential for forming rocky planets, they said. An optimistic interpretation might be that some massive discs of dust would form planets more quickly – and in that case, up to 62 percent of stars could be planet-forming.

But either way, the data seems to show there are plenty of other planets out there.

A paper on the conclusions appeared in the Feb. 1 issue of Astrophysical Journal Letters