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Astronomers Spy Possible Planet

28 May 1998 7:00 pm
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Scientists believe they have for the first time eyeballed a planet outside our solar system. A team headed by Susan Terebey of the Extrasolar Research Corporation in Pasadena, California, spotted the putative planet while studying an image of a nearby star-forming region made with the Hubble Space Telescope. The planet appears to have been ejected by its parent stars and was caught hurtling into space. According to NASA scientist Ed Weiler, the observation "could turn out to be the most important discovery by Hubble in its 8-year history."

Planets orbiting stars other than the sun are notoriously hard to see because they are obscured by the stars' glare. So far, detections of these so-called exoplanets have all been indirect. In this case, however, the planet was displaced far enough from its orbit around a binary star to show up on the image. It's connected to the binary by a clearly visible trail--a luminous filamentary structure that Terebey's team interprets to be a tunnel burrowed through the interstellar dust. Although the object is dark and obscured by dust, Hubble's infrared NICMOS camera picked up its feeble heat radiation, left over from its formation. Scientists estimate the planet is about 300,000 years old and 450 light-years away. They put the mass of the object--apparently a gas giant like Jupiter--at 2 to 3 times the mass of Jupiter, the largest planet in the solar system.

Astronomers have yet to confirm that the object really is a planet, warns David Black of NASA's Lunar and Planetary Institute in Houston. He says "this is an exciting observation," but notes that even a slight error in the age determination--related to its brightness, from which its mass can be inferred--could push the mass of the object high enough to make it a brown dwarf: a "failed star" larger than a planet but not massive enough for hydrogen fusion to occur in the core. Adam Burrows of the University of Arizona, Tucson, adds that there's a remote possibility that "this is a chance alignment" of a distant star with the foreground binary star, and that the bright filament is unrelated to it.

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