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Astronomers Find Jupiter-Size Planet Found Orbiting Star in Big Dipper
Astronomers Find Jupiter-Size Planet Found Orbiting Star in Big Dipper
15 Aug 2001
(Source: NASA Headquarters)

Donald Savage
Headquarters, Washington
(Phone: 202/358-1547)

Amber Jones
National Science Foundation, Arlington, VA
(Phone: 703/292-8070)

RELEASE: 01-166

A team of astronomers has found a Jupiter-sized planet orbiting a faint nearby star similar to our Sun, raising intriguing prospects of finding a solar system like our own.

The planet is the second found orbiting the star 47 Ursae Majoris in the Big Dipper, also known as Ursa Major or the Big Bear. The new planet is at least three-fourths the mass of Jupiter and orbits the star at a distance that, in our Solar System, would place it beyond Mars but within the orbit of Jupiter.

"Astronomers have detected evidence of more than 70 extrasolar planets," said Morris Aizenman, a senior science advisor at the National Science Foundation (NSF). "Each discovery brings us closer to determining whether other planetary systems have features like those of our own."

"For the first time we have detected two planets in nearly circular orbits around the same star," said team member Debra Fischer of the University of California at Berkeley. "Most of the 70 planets people we have found to date are in bizarre solar systems, with short periods and eccentric orbits close to the star. As our sensitivity improves we are finally seeing planets with longer orbital periods, planetary systems that look more like our Solar System."

The planet-search team, which is supported by NASA and the National Science Foundation, Arlington, VA, has been instrumental in finding a majority of the planets outside our Solar System (also called extrasolar planets). Besides Fischer, the team includes Geoffrey Marcy, also of Berkeley, Paul Butler of the Carnegie Institution of Washington, Steve Vogt of the University of California at Santa Cruz and Gregory Laughlin of NASA's Ames Research Center, Mountain View, CA. Their report on the new planet has been submitted to the Astrophysical Journal.

A few years ago, Marcy and Butler discovered a planet more than twice the mass of Jupiter in a circular orbit around the same star. The star is one of 100 that the scientists have targeted since 1987 in their search for evidence of extrasolar planets. Using telescopes at the University of California's Lick Observatory, they measure changes in the characteristics of light emitted by the stars. Those changes, they believe, signal the presence of a planet periodically pulling the star toward or away from Earth.

Fischer was able to see the periodic wobble from the second planet, smaller and farther from the star than the first, because of improved instrumentation.

The star is a yellow star similar to the sun, probably about seven billion years old and located about 51 light-years from Earth. A light-year, the distance light travels in one year, is approximately 6 trillion miles.

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

A list of extrasolar planets is available at:
Images are available at:

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Last Updated: 20 Aug 2001