SCIENCE NEWS / Sunday January 31, 1999
Two new extrasolar planets - 12 in total now

Astronomers have discovered two new planets orbiting sunlike stars, bringing to an even dozen the official number of such orbiting bodies. In separate work, a team has found graphic evidence that a star hosts a complete planetary system. The findings are described in the Sept. 26 Science News.

One of the newly found extrasolar planets is the first whose average distance from its parent star is nearly the same as Earth's distance from the sun. The planet, however, is far heavier than Earth, at least 1.36 times as massive as Jupiter, and has a much more elongated orbit. The planet ventures closer to its host star than Venus' average distance from the sun and farther away than Mars' average distance. It orbits the star HD210277, which is 68 light-years away from Earth.

The other new planet orbits its parent star, HD187123, more closely than any other planet found so far. Its circular orbit lies at a distance less than one-ninth the average separation between the sun and Mercury, the solar system's innermost planet. HD187123 lies 156 light-years away from Earth. Both planets were detected by a team that includes R. Paul Butler of the Anglo-Australian Observatory in Epping, Australia, and Geoffrey W. Marcy of San Francisco State University and the University of California, Berkeley. The team will report the discovery of the closely orbiting planet in an upcoming PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC.

Researchers believe that massive, closely orbiting stars form at a Jupiterlike distance from their parent stars and migrate inward by flinging out dust from the circumstellar disk of debris that spawned them. In observing the vicinity of the star, 55 Rho1 Cancri, known to harbor a massive, closely orbiting planet, another team of researchers has found a dusty disk. The disk extends as far out from the star as the Kuiper belt, a reservoir of comets, lies from the sun, but the disk appears to contain 10 times as much dust.

Astronomers David E. Trilling and Robert H. Brown of the University of Arizona in Tucson believe the disk may be the star's own Kuiper belt. They excess dust, they suggest, represents debris flung out by the massive planet and could be material left over from the formation of several planets. The disk is the first to be seen around an ordinary, middle-aged star, Trilling notes. "There's real evidence that this is a fully mature planetary system," he says.