January 17, 2006

	Mouse over image to see binary star motion
	This pair of images, taken 39 years apart, reveal the star Gliese 777A moving in sync with its companion, relative to the background stars. Two planets (not visible) recently were discovered circling Gliese 777A.

(PLANETQUEST) -- In the most comprehensive survey of its kind, Georgia State University astronomers have found that about one in five known extrasolar planetary systems include more than one sun.

Principal investigator Deepak Raghavan, a doctoral student at Georgia State University, sifted data on 131 extrasolar planetary systems over a two-year period and confirmed that 26 of those systems were binary, or two-star systems. Three others were found to be trinary, or triple-star systems.

"We used to think planets would not form in binary systems, but we now see they are quite common," Raghavan said Wednesday during a press conference at the American Astronomical Society Meeting in Washington, D.C. "These results show that planets are quite hardy. They survive in a variety of environments."

The study findings will help answer questions about how planets form, how stellar companions either help or hurt planet formation, and how orbital characteristics of planets could be affected by stellar companions, Raghavan said.

To conduct their survey, Raghavan and his colleagues examined Internet archives of sky images taken over a 30- to 40-year period, then followed up with new telescope observations to confirm or deny if systems have stellar companions. In addition to the 29 confirmed multi-star systems, the team has seven more candidates to check.

Over that past decade, astronomers have discovered more than 150 planets around stars other than the sun, but none so far are considered hospitable to life. Nonetheless, Raghavan said the team's unexpected findings inspire speculation of life very different from ours.

"It's cool to think about living on a planet where it gets dark or you have seasons changing a lot more than ours do, and just wondering how that would affect hypothetical life," Raghavan said.

Written by Randal Jackson/PlanetQuest