145;Distant planet is optical illusion146;

Teams of astronomers have thus far identified some 101 so-called 8216;8216;extrasolar8217;8217; planets, with each discovery fuelling 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 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.

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 8216;8216;wobble8217;8217; in the star which would indicate the gravitational pull exerted by an orbiting planet.

Henry and his team took a closer look at that 8220;wobble8221; and concluded that it was in fact caused by the passage of large dark 8216;8216;star spots8217;8217; across the star8217;s surface 8212; 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.