Scientist challenges existence of planet outside solar system Sighting from pulsations of star, Canadian says


A Canadian astronomer has challenged evidence for the existence of the first planet reported found around another Sun-like star, saying that the phenomenon observed is actually caused by the star's own pulsations, not the gravitational effects of an unseen planetary companion.

"The presence of a planet is not required to explain the data," the astronomer, David F. Gray of the University of Western Ontario in London, Ontario, concluded in an article being published today in the journal Nature.

If true, the findings would mean retracting the report of one of the most sensational astronomical discoveries in recent years: the detection 16 months ago of an object half the mass of Jupiter orbiting unusually close to the star 51 Pegasi. Other astronomers confirmed the detection and went on to find at least seven more planets around other stars; the existence of three of them could also be questioned in light of the new research.

But the discoverers of these new planets beyond the solar system were not ready to concede anything. Another study, they noted, had found nothing comparable to the behavior of light from 51 Pegasi that Gray ascribed to the star's pulsations rather than to the star's wobbling motions caused by the gravity of a nearby large planet.

Also, they argued, the star does not show the brightness variations that should accompany the kind of oscillations that Gray proposes.

Gray's conclusion "is unconfirmed and seems extraordinarily premature," four astronomers involved in the discovery wrote in a joint statement distributed to other scientists over the Internet.

The apparent existence of the 51 Pegasi planet was detected by Michel Mayor and Didier Queloz of the Geneva Observatory in Switzerland. The discovery was confirmed by Geoffrey W. Marcy and R. Paul Butler of San Francisco State University, who subsequently detected most of the other extrasolar planets.

Alan P. Boss, a theoretical astrophysicist at the Carnegie Institution of Washington, said he found the discoverers' arguments against Gray's hypothesis to be persuasive but not final. "I don't think it's quite time to declare the 51 Pegasi planet dead," he said.

Pub Date: 2/27/97

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