Characteristics of extrasolar planets emerging with latest find

Press Release From: Carnegie Institution
Posted: Tuesday, September 17, 2002

The international Anglo-Australian Planet Search Team, in part sponsored by the National Science Foundation (NSF), has now found more extrasolar planets in the Southern Hemisphere than any other group. The team's latest find brings the number of extrasolar planets to 100.

And with this total, astronomers are beginning to see patterns in planet characteristics. "When we first started out, we found planets close in to their parent stars," says team member Chris McCarthy of the Carnegie Institution of Washington. "But as the planet search program has matured, we're finding more planets farther out and in nearly circular orbits. This means that we are getting closer to detecting more systems that are similar to our own solar system."

Dr. Hugh Jones, of Liverpool John Moores University in the UK, was the lead astronomer for this latest project, which was supported by three governments. The new planet weighs in at about 1.2 Jupiters. It orbits star Tau 1 Gruis, found in the southern constellation Grus (the crane), 100 light-years from Earth. It is located about the same distance from its star as our asteroid belt is from our Sun (2.5 astronomical units with 1 AU being the Earth-Sun distance). And its orbit is roughly circular.

Based on the 15-year survey, which Paul Butler of Carnegie and Geoff Marcy of U.C. Berkeley have headed at the Lick Observatory, about 12% of the Sun-like stars in our galaxy have planets that can be detected orbiting their stars within about 5 AU. As the body of extrasolar planets grows, more planets are being found farther out. This finding supports the idea that giant planets in solar systems may form at great distances from their stars and later move inward.

The Anglo-Australian Planet Search team includes astronomers from the UK, Australia, and the United States. From the UK: Dr. Hugh R. A. Jones, Liverpool John Moores University, and Dr. Alan J. Penny, Rutherford Appleton Laboratory. From Australia: Dr. Chris G. Tinney, Anglo-Australian Observatory, and Dr. Brad Carter, University of Southern Queensland. From the US: Dr. R. Paul Butler and Dr. Chris McCarthy, Carnegie Institution of Washington, and Dr. Geoffrey W. Marcy, University of California Berkeley and San Francisco State University.

In addition to the NSF, support for this work comes from Anglo-Australian Observatory, which operates and maintains the 3.9-m Anglo-Australian Telescope, (; The Particle Physics and Astronomy Research Council, which funds UK astronomy research, (; and the Australian Telescope Allocation Committee. Also see

The Carnegie Institution of Washington ( has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments in the U.S.: Plant Biology, Global Ecology, Observatories, Embryology, the Geophysical Laboratory, and the Department of Terrestrial Magnetism.

Contact at Carnegie: Chris McCarthy at 202- 478-8862, e-mail; Paul Butler at; Contact at U.C. Berkeley: Geoffrey W. Marcy at

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