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Planetary News: Extrasolar Planets (2007)International Team Announces Discovery of 28 New Exoplanets29 May, 2007
The most prolific team of planet hunters, responsible for detecting over half of the exoplanets known to date, has announced the discovery of 28 new planets orbiting distant stars. The discovery represents the combined work of the California and Carnegie Planet Search team and the Anglo-Australian Planet Search team, and it brings the total number of known exoplanets to 236. The news was announced last week by Jason T. Wright and John Asher Johnson of U.C. Berkeley at a meeting of the American Astronomical Society (AAS) which took place in Honolulu. According to the presenters, the planets were detected separately over the past two years and described in scientific publications, but this is the first time that the entire group is considered together as a group. “We’ve added 12 percent to the total [of known exoplanets], and we’re very proud of that” said Wright. This provides new planetary systems so that we can study their properties as an ensemble.”Wright said the research teams have become much more sophisticated in their analyses of the stellar wobbles caused by orbiting planets, enabling them to detect the weaker wobbles caused by smaller planets as well as planets farther from their parent stars. The California and Carnegie Planet Search team is headed by Geoffrey Marcy, professor of astronomy at UC Berkeley; Paul Butler of the Carnegie Institution of Washington; Debra Fischer of San Francisco State University; and Steve Vogt, professor of astronomy at UC Santa Cruz. The Anglo-Australian Planet Search team is headed by Chris Tinney of the University of New South Wales and Hugh Jones of the University of Hertfordshire. Of the 28, Wright singled out an exoplanet discovered by their teams two years ago as "extraordinarily rich." Circling the star Gliese 436 (GJ 436), a red M dwarf only 30 light years from Earth, was an ice-giant planet the teams calculated to be at least 22 Earth masses, slightly larger than the mass of Neptune (17 Earth masses). After the discovery in 2004 and publication of the exoplanet's orbit earlier this year, a Belgian astronomer, Michael Gillon at Liege University, observed the planet crossing in front of the star - the first Neptune-sized planet observed to transit a star. By combining the radial velocity data provided by the discoverers with the transit data, Gillon and colleagues were able to calculate the planet’s mass, 22.4 that of Earth, its size, and its density. "From the density of two grams per cubic centimeter - twice that of water - it must be 50 percent rock and about 50 percent water, with perhaps small amounts of hydrogen and helium," Marcy said. "So this planet has the interior structure of a hybrid super-Earth/Neptune, with a rocky core surrounded by a significant amount of water compressed into solid form at high pressures and temperatures." Its short, 2.6-day orbit around Gliese 436 means the exoplanet is very close to the star - only 3percent of the sun-Earth distance - making it a hot Neptune, Wright said. It also has an eccentric orbit, not a circular orbit like most giant planets found orbiting close to their parent stars. This orbit, in fact, suggests that the star may have another planetary companion in a more distant orbit. "I'm sure people will immediately follow up and try to measure the atmospheric composition of this planet." Wright predicted. The California and Carnegie Planet Search team uses telescopes at the University of California's Lick Observatory and the W. M. Keck Observatory in Hawaii. The Anglo-Australian Planet Search team uses the Anglo-Australian Observatory. Did you like this article? Send
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