Astronomers have for the first time used the bending of light waves by a star to identify a planet 17,000 light-years away, an achievement that could set the stage for the discovery of more extrasolar planets, especially smaller planets similar in size to Earth.
Researchers have so far identified more than 100 extrasolar planets by observing slight wobbles in a star's trajectory caused by a planet circling it or by observing small changes in a star's brightness when a planet passes in front of it.
But those methods work only for planets larger than Jupiter, and most of the planets discovered so far orbit very close to their stars - indicating that the planetary systems are not very much like our own.
Although the planet discovered using the new technique, called gravitational microlensing, is about the size of Jupiter, the method should work equally well with smaller planets, researchers said. In addition, the newly discovered planet, in the constellation Sagittarius, orbits its star at a distance of about three astronomical units (one AU equals the distance from Earth to the sun), and that star is a red dwarf similar to our sun.
The fact that the newly discovered planet orbits its star at such a distance means there could be smaller planets, more like Earth, Venus and Mars, orbiting it more closely, said Philippe Crane, who is in charge of the search for such planets at the National Aeronautics and Space Administration.
The new technique relies on the fact that powerful gravitational fields can bend light rays, a phenomenon first predicted by Albert Einstein. When a nearby star passes between an earthbound telescope and a more distant star, its gravity acts like a telescopic lens, bending and focusing light from the distant star so that it appears much brighter than it otherwise would.
About 13 years ago, Princeton University astronomer Bohdan Paczynski and his student Shude Mao suggested this microlensing capability could be used to find extrasolar planets.
"I'm thrilled and delighted to see that old idea come true," Paczynski said yesterday in a telephone news conference announcing the finding. The report will be published in the May 10 issue of Astrophysical Journal Letters.
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