Scientists have discovered an extrasolar planet using a technique known as gravitational microlensing. This is the second such planet found using the method, which measures a planet's effect on light from a distant star. The new planet weighs about three times as much as Jupiter and orbits a star similar to our sun. "This discovery is the tip of the iceberg for microlensing searches," says team member Scott Gaudi of the Harvard-Smithsonian Center for Astrophysics. "With improving technologies and techniques, the first Earth-sized planet may be found by microlensing."

Astronomers using the microlensing technique located their first extrasolar planet just last year. When a massive object such as a star crosses in front of another star located farther away relative to Earth, its gravitational pull bends the light rays and magnifies them. To earthbound observers, this configuration makes the distant star appear brighter, as if a lens was placed in front of it. When the "lens" moves out of the path, the star appears to return to its regular brightness. If a planet is in orbit around the lensing star, scientists can deduce its presence because it affects the process in a predictable way. Observations from around the world, collected by both professional and amateur astronomers alike, were required to collect enough continuous data about this latest microlensing event.

The researchers report that the new planet is orbiting its host star at a distance about three times that separating our planet and the sun. Located approximately 15,000 light-years from Earth, it is also one of the farthest known planets outside our solar system. The scientists hope their new find is just the beginning: "We expect many more discoveries in the coming years," Gaudi predicts. A report describing the exoplanet has been submitted to the Astrophysical Journal.