51 Pegasi: Planet, Not Pulsation

By Ken Croswell

Published abridged in New Scientist (December 13, 1997).

Planet hunters can breathe a sigh of relief--it looks as if there really is a planet orbiting the star 51 Pegasi. Their delight comes at the expense of a rival theory which claimed that the planet was simply a mirage.

In 1995, Michel Mayor and Didier Queloz of the Geneva Observatory reported that 51 Pegasi is wobbling from the gravitational pull of an orbiting planet. It was the first planet ever found around another Sunlike star.

Early in 1997, however, David Gray of the University of Western Ontario in Canada asserted that 51 Pegasi's planet did not exist. Instead, he said, the star is pulsating, which causes the periodic change in its spectrum that planet hunters had mistaken for a planet.

Other astronomers have now searched for the alleged pulsation but failed to find it. One team, led by Timothy Brown of the High Altitude Observatory in Boulder, Colorado, used a telescope at Mount Hopkins in Arizona to obtain high-quality spectra of 51 Pegasi. If the star were pulsating, the shapes of its spectral lines should vary. But they remained constant. The results, which several other teams have confirmed, will appear in Astrophysical Journal Letters.

The planet's discoverers have welcomed the news. "We are very glad," says Mayor.

Gray was not rejoicing, however. "It's disappointing that it looks like we're not going to be able to analyze oscillations on this star," says Gray, because such oscillations would have probed the star's interior. "On the other hand, the people who study planets will be delighted to have one of their planets back."

Ken Croswell is the author of Planet Quest and Magnificent Universe.

"An excellent introduction to a branch of astronomy that may eventually help to establish the presence or absence of life elsewhere in the universe...Fascinating and worthwhile."--New York Times Book Review. See all reviews of Planet Quest here.

"Elegant and eloquent."--Washington Post. See all reviews of Magnificent Universe here.

KenCroswell.com

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