Independent Perspective News

SAN FRANCISCO, California (Reuters) -- A huge planet which scientists believed to be orbiting around a distant star has been shown to be an optical illusion -- a discovery which could take several more "planets" off the list of worlds beyond our solar system, according to researchers. Astronomer Gregory Henry of Tennessee State University said his analysis revealed that the "planet" -- one of several far-flung discoveries announced with great fanfare two years ago -- was actually a trick of light created by giant "star spots" on its sun's surface.

"The existence of this planet was certainly an illusion," Henry said in an interview Wednesday. "It is easy to be fooled."

Teams of astronomers have thus far identified some 101 so-called "extrasolar" planets, with each discovery fueling hopes that one day humans may be able to locate far-off worlds capable of supporting life. But Henry said his new analysis, published in the current edition of the Astrophysical Journal, showed that a small number of them could simply be optical tricks.

Henry and his colleagues took a new look at the star identified as HD 192263, which both California and Swiss researchers said in 1999 had large, gaseous Jupiter-like planet swinging around it in a tight orbit.

As with all planet-hunting teams, the astronomers did not see the actual planet around the star, which lies some 63 light years from Earth.

But they reached their conclusion by detecting a tell-tale "wobble" in the star which would indicate the gravitational pull exerted by an orbiting planet.

What's in a wobble?

Henry and his team took a closer look at that wobble, using an array of telescopes on an Arizona mountaintop to take precise measurements of the star's brightness. They concluded that the "wobble" was in fact caused by the passage of large dark "star spots" across the star's surface -- creating a light signature similar to that of an orbiting planet.

When they determined that the star spot moved across the star at precisely the interval attributed to the supposed planet, they knew they had disproved the theory, he said.

"What they saw were the back and forth motion of the lines of the (light) spectrum, and from that they inferred that the star must be wobbling, and from that they inferred that there must be a planet," Henry said. "This shows that that chain of inference was wrong."

Henry stressed that most of the 100 or so extrasolar planets thus far detected are in orbit around far older stars, which are unlikely to have the "star spot" phenomenon.

"This is not waving a flag and saying all of these planets are going to disappear. Far from it. Ninety-five percent of them are absolutely secure, but there could be a small number of planets that have been announced which haven't been checked in enough detail to make sure they are real," he said.

Steven Vogt, a University of California-Santa Cruz astronomer who was among those who made the planet announcement for HD 192263, said he agreed with Henry's conclusions and that the university's world-famous "planet hunting" teams would be alert to such discrepancies in future. With about 1000 stars now being examined for possible worlds, Vogt said it was inevitable that a small number of "bogies" would turn up false positive results.

"We were pretty skeptical about this one to begin with," Vogt said, noting that his group had asked Henry to do his star brightness study to double-check their theory about the star's possible planet. "We try to de-bogify these things, but it takes time," he said.