Astronomers Find Solar System Like Our Own

Aug. 16 -- For the first time, astronomers have detected a multi-planet solar system that is much like our own.

The system, located in the constellation, Ursa Major, which includes the Big Dipper, resembles ours by the way its two detected planets are in nearly circular orbits around their sun.

"The discovery of planets in circular orbits is exciting because they are so rare," said Paul Butler of the Carnegie Institution of Washington. Butler collaborated with Debra Fischer, an assistant research astronomer at the University of California, Berkeley, who made the main discovery.

Like Ours, Uniquely Regular

Unlike the some 70 solar systems discovered in the past decade, this system is unique for its regularity. The most recent detection was a planet, at least three-quarters the size of Jupiter, orbiting the star 47 Ursae Majoris in the Big Dipper, about 51 light years from Earth.

Previously, in 1996, astronomers had detected another planet, about 2.5 times the size of Jupiter, orbiting this 7-billion-year-old star. The two planets, which are likely gaseous, both appear to be orbiting in near perfect circles.

Other recent solar system discoveries have revealed planets that orbit their suns in more erratic patterns.

"Every new planetary system reveals some new quirk that we didn't expect," said UC Berkeley astronomy professor Geoffrey Marcy. "We've found planets in small orbits and wacky eccentric orbits. With 47 Ursae Majoris, it's heartwarming to find a planetary system that finally reminds us of our solar system."

Based on past discoveries, the astronomers estimate about five percent of solar systems may contain planets with circular orbits like our own.

The two planets' distance to their star is greater than the space between Mars and our sun, but less than Jupiter's distance from the sun. That places them beyond the zone normally considered habitable for life.

Life-Hosting Planet Unlikely

It's possible that an Earth-like terrestrial planet is tucked within the habitable region around the star and it's just not yet visible to astronomers. But Fisher says the prospect is unlikely. Computer simulations suggest the habitable zone of the star is rendered too unstable by the close presence of the two gaseous planets.