Astronomers Pioneer Planet Discovery

The discovery of OGLE-TR-56b, a planet light years away from earth in the constellation Sagittarius, has helped researchers from the Harvard-Smithsonian Center for Astrophysics to validate a new technique for finding planets in the farthest reaches of the galaxy.

The new approach to locating planets, called the transit technique, depends upon observing changes in the level of brightness of light that distant stars emit.

As a planet orbits a star, it occasionally comes between the star’s light and the earth, creating an eclipse-like effect that subtly dims the light from that star.

Dr. Guillermo Torres, an astrophysicist at the Smithsonian Center who worked on the OGLE, or Optical Gravitational Lensing Experiment, said the method was less complicated than previous attempts to find planets.

“We began by recording the brightness of several stars every night over a two month period,” he said.

Cabot Professor of Astronomy Dimitar Sasselov, a lead researcher in OGLE, compared viewing these eclipses to spotting a mosquito in front of a searchlight hundreds of miles away.

Robert Noyes, an Astronomer at the Smithsonian Center, said the OGLE researchers did excellent detective work.

“Many stars can masquerade as planets,” he said. When a star interferes with another star’s light emission, the dimming effect is much greater than that of a planet.

After detecting about 60 light-dimming bodies as potential planet candidates, the researchers used a series of telescopes to provide clues about which interfering bodies were too large to be planets.

The scientists used the largest telescope in the world, the Keck I in Hawaii, to take the final measurements to determine OGLE-TR-56b was a planet.

This is the first time that the transit technique has actually been used to discover a planet.

While rains of hot iron plummet to the surface of OGLE-TR-56b, which is roughly the size of Jupiter, astronomers hope that this new, more direct technique can now be used to find earth-sized planets with raindrops of water.

NASA will launch a mission in 2006 named Kepler to use the transit technique to check for the existence of earth-sized planets.

“In space you can measure smaller drops in brightness with much higher precision than on the ground,” Torres said.

Once the more efficient transit technique has located earth size planets, another NASA mission will follow Kepler between 2012 and 2015 to check for life on these planets.

—Staff writer Wendy D. Widman can be reached at widman@fas.harvard.edu.