Friday, August 27, 2010;
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 findings, published in Thursday's issue of the journal Science, came from observing about 156,000 stars for seven months as part of a pioneering search for Earth-size planets outside our solar system.
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 the size of Saturn, and a third possible planet is a "super-Earth," 11/2 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 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 by ground-based telescopes that use a different method of determining if planets are present.
If confirmed, the Earth-size planet would be the first of its kind found by Kepler, a one-ton spacecraft launched in the spring. Earlier this week, a European team using ground-based telescopes and spectrographs detected a planet that might be even smaller, with a mass only 1.4 times that of Earth. It is circling a star 127 light-years away.
The Kepler telescope observes star systems and their possible planets many times before determining whether exoplanets are present. As a result, Kepler's full capabilities and successes won't be known for months or years.
- Marc Kaufman