51 Pegasi: A Star without a Planet?

By Cowen, Ron | Science News, March 1, 1997 | Go to article overview

51 Pegasi: A Star without a Planet?


Cowen, Ron, Science News


In the hearts and minds of many astronomers, the universe teems with stars executing tiny pirouettes, pulled to and fro by unseen planets. That vision, buoyed by the indirect detection of at least eight planets orbiting sunlike stars, may prove correct, but a controversial new report states that the first such planet simply isn't there.

That's the contention of David F. Gray of the University of Western Ontario in London, who argues in the Feb. 27 Nature that the nearby star 51 Pegasi, similar in mass to the sun, doesn't wobble back and forth, as Swiss astronomers had reported. Moreover, he suggests reevaluating three other planet finds.

In 1995, Michel Mayor and Didier Queloz of Geneva Observatory reported that certain wavelengths of light absorbed by 51 Pegasi shifted periodically to redder and bluer wavelengths, as if the star were receding from and approaching Earth every 4.2 days. They ascribed this motion to the tug of an unseen planet about half the mass of Jupiter orbiting the star more closely than Mercury orbits the sun. Geoffrey W. Marcy and R. Paul Butler, both of San Francisco State University and the University of California, Berkeley, confirmed the finding (SN: 10/21/95, p. 260).

After examining the star's spectra with a higher-resolution instrument, Gray concluded that a more subtle characteristic-the shape of an absorption peak-varies along with the periodically shifting wavelength. Astronomers do not think a planet would change the shape of a spectral peak. Gray proposes that only something intrinsic to the star-most likely large-scale oscillations of gas at its surface-can account for both the periodic change in the geometry of the spectral peak and the previously detected shift in wavelength. The two other teams, he says, were fooled by the star's complex oscillations, which mimic the wobble a planet might have induced.

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