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Mysterious Object Might be First Extrasolar Planet Photographed
Space.COM, Jun 3, 2002

The coolest, faintest and possibly the smallest "substellar object" ever photographed was announced yesterday, but researchers don't know exactly what they have found. Observations so far do not allow for a precise determination of the object's distance, which is needed to calculate its mass. If it 1,150 light-years away, as suspected, then it is likely less than 8 million years old and lives amid a cluster of similarly young stars known as the Sigma Orionis system, and its mass would be about that of Jupiter. The object would qualify - by some definitions - as a planet. No planet outside our solar system has ever been photographed. Other Jupiter-mass planets have been found around other stars, but they were detected by an indirect method that notes a gravitational wobble induced in the host star.

If the newly spotted object, called SOri70, is in fact a planet, it would be a strange one, sitting 36,000 times farther away from any its nearest stellar neighbor than Jupiter is from our Sun. There is an unresolved debate among experts as to whether an object so far from a star can be called a planet or not. And no one is sure how it might have formed our how it could end up in such a location. Some models suggest that gaseous objects like Jupiter might form via the gravitational collapse of a cloud of material, similar to how a star forms. But if such an object forms alone in space, and not around a star, can it be called a planet? Regardless, researchers say there is a 20 percent chance the object is closer to us, and thus it would be older, more massive, intrinsically dimmer and classified as a brown dwarf star.

Brown dwarfs are typically many times heavier than Jupiter, but they are not massive enough to trigger the thermonuclear fusion that powers a real star. Brown dwarfs have been found orbiting stars, and other free-floating brown dwarfs have also been detected in recent months. Astronomers who had learned of the finding but had not seen the actual data were unwilling to comment on the results. But one astronomer did tell SPACE.com that if the object is in fact in the Sigma Orionis cluster, then because of its youth it would be brightly emitting infrared radiation as it contracts and cools down. It is possible, the source said, to photograph in the infrared a Jupiter-mass object in this cluster. Victor J. Bejar and Rafael Rebolo, of the Instituto de Astrofisica de Canarias, Tenerife, Spain, both participated in the discovery of SOri70. They responded jointly to a SPACE.com e-mail query and said that if the object turns out to be of planetary mass, they would call it an "isolated planetary mass object." Other researches have suggested the name "free-floating planet."

Regardless of the outcome, the discovery shows the potential for imaging planets in young star systems. "Definitely, very young 'Jupiters' can be directly imaged with current, very large telescopes," Bejar and Rebolo said. "The detection of such objects is an indication that Jupiter-like objects could be populating the space between stars," the researchers said. "They would be extremely faint [when they are older] and therefore they could have been missed in all sky surveys." Researchers say they might be able solve their puzzle by pointing the Hubble Space Telescope at SOri70, but a request for observing time was de
nied. ... Though Hubble's new Advanced Camera for Survey's will spend some time next year attempting the task around another star, the effort is considered a longshot. It involves blocking the light from a bright star to provide an opportunity to see a much dimmer planetary companion. If Hubble does not succeed, most researchers have said, such an image might have to wait a decade or so until a future space telescope is launched.