LINDA WERTHEIMER, host:
In the field of astronomy these days, it is raining planets. Two leading teams of planet hunters, announced this week, they'd found entire solar systems - one with two or three planets, the other with as many as seven. These are not planets that could sustain life. But many scientists say detecting such planets is looking more likely.�NPR's Dan Charles has more.
DAN CHARLES: Many of the world's experts on planets in outer space are playing top this at a scientific conference in southeastern France this week. Among them is Matthew Holman from the Harvard-Smithsonian Center for Astrophysics.
Mr. MATTHEW HOLMAN (Harvard-Smithsonian Center for Astrophysics): There's always, I have to admit, an element of competition. You know, people come and want to show their best work, and they want to surprise their colleagues.�
CHARLES: Holman had to keep his own surprise under wraps for a few days, because it hadn't yet been published. So he just listened as his European competitors claimed the spotlight. Christophe Lovis, from the University of Geneva in Switzerland, announced on Tuesday, his group had discovered a whole collection of planets orbiting a star 127 light-years away.
Mr. CHRISTOPHE LOVIS (University of Geneva): At least five planets, and probably seven - two of them are still a little bit uncertain.�
CHARLES: It's the largest solar system ever seen outside our own. Now, Lovis didn't really see any of those planets.�So far, that's impossible. He watched stars very carefully as they move through space.�If they speed up or slow down a little, at a regular pattern, it shows there's something tugging on them:�the gravitational pull of an orbiting planet.
This has been the most successful planet-hunting technique. But it works best for giant planets close to small stars.�Of the 500 planets discovered so far, most have been like this. One of the new planets that Lovis announced, however, appears to be much smaller. Its mass is just 40 percent greater than Earth.
Mr. LOVIS: We've really moved from giant planets only to any kind of planetary system, with more and more planets, small mass planets and so on. It's really exciting.
CHARLES: And yesterday, Matthew Holman finally got to add his bit of excitement when his discovery was published by the journal Science.
Mr. HOLMAN: We're announcing the discovery of two Saturn-size planets, which we call Kepler 9b and Kepler 9c.
CHARLES: And there's evidence of a third planet, he said, a much smaller one.�Its diameter appears to be just 50 percent larger than Earth's.�
Mr. HOLMAN: If it is confirmed, it would have a radius of about 1.5 times the radius of the Earth.
CHARLES: Holman's discovery, in fact, is an early scientific harvest from NASA's new planet-finding machine, a telescope called Kepler. This instrument is following Earth in its orbit around the sun, staring constantly at a group of 100,000 stars in another corner of our galaxy.�When the light from any of those stars dims slightly, it's evidence that a planet just crossed in front of it.
Now, the planets that scientists have found so far are not what you'd call habitable. The small ones are way too close to their stars.�But Kepler was designed specifically to detect planets just like Earth. And Alan Boss, an astrophysicist at the Carnegie Institution of Washington, is increasingly confident those planets are out there.�
Mr. ALAN BOSS (Astrophysicist, Carnegie Institution of Washington): We're finding more and more evidence that earth-like planets are going to be quite common. We don't have them yet, but we're well on the way towards discovering them.
CHARLES: We'll all have to be patient, though.�A planet just like Earth crosses in front of its star once a year and scientists won't declare it a planet until they see the star's light dim at least three times.��
Dan Charles, NPR News, Washington
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