for National Geographic News
Scientists have discovered a new planet they call a "super-Earth" in a solar system 9,000 light-years away.
The icy, rocky planet, which weighs 13 times as much as Earth, orbits the outer region of its solar system, around a so-called red dwarf star that is about half as big as our sun.
The planet dominates a region similar to the one in our solar system that is populated by the gas giants Jupiter and Saturn. Scientists believe the planet likely didn't accumulate enough gas to grow to giant proportions. (See an interactive map of our solar system.)
"We've never been able to see these failed Jupiter cores before," said Andrew Gould, an astronomer at Ohio State University in Columbus who is leading the research.
He suggests, however, that icy super-Earths are common and that about 35 percent of all stars have them.
Gould leads an international effort called the Microlensing Follow-Up Network (MicroFUN), in which astronomers search for planets using a phenomenon called gravitational microlensing. This occurs when a big object such as a star crosses in front of another star. The gravity of the foreground star bends the light rays from the more distant star and magnifies them like a lens.
"This [technique] has opened up a different area of study observationally for extrasolar planets," Gould said.
If the foreground star has a planet in its orbit, the planet's gravity can distort the light further, and thus signal its presence. The precise alignment required for the effect, however, means that each microlensing event lasts for only a brief time.
"People have thought about this theoretically but just didn't have any way to actually see what was going on," Gould said.
The discovery is reported today in a paper posted at the Web site arXiv.org.
Not Enough Gas
The planet, which has been named OGLE-2005-BLG-169Lb, is probably a mixture of ice and rock. Its terrestrial nature has prompted scientists to dub it a super-Earth, but its distance from its star chills it to -330ºF (-201ºC), making it too cold for liquid water and, presumably, life.