By Marc Kaufman
Thursday, August 26, 2010; 6:26 PM
NASA's Kepler spacecraft has discovered the first confirmed planetary system with more than one planet "transiting" or crossing in front of a central star.
The discovery came from observing some 156,000 stars for seven months as part of a pioneering search for Earth-sized planets outside our solar system. The findings were published in Thursday's issue of the journal Science.
Kepler's ultra-precise camera measures tiny decreases in a star's brightness caused by the orbiting of the planet as it crosses in front of its sun. The size of the planets can be determined by measuring these temporary dips.
Two planets in the newly discovered system, 2,000 light years away, are Saturn-sized and a third possible planet is a "super-Earth," one-and-a-half times the size of our planet. That planet is the size thought to be potentially habitable, but it orbits too close to its star to support any life.
In June, scientists submitted findings for peer review that identified more than 700 potential planet candidates detected in the first 43 days of Kepler's planet search. The data included five additional candidate systems that appear to exhibit more than one transiting planet.
Kepler's results are tested and confirmed by ground-based telescopes that use a different method of determining if planets are present.