"Ten years ago, we knew of no extrasolar planets," says John Bally, an astronomer at the University of Colorado in Boulder. "Now we're discovering planets almost weekly."
Or as Sylvain Korzennik, a researcher at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., put it: "Extrasolar planets are everywhere in the sky."
In addition to simply boosting the count of planets, new technologies are letting scientists begin to analyze the chemical makeup of their finds. Water molecules have been spotted in the atmosphere of at least one new planet. The fingerprints of elements such as carbon, oxygen, sodium, silicon and iron have shown up.
So far, none of the known exoplanets seems likely to harbor life. That's because almost all the discoveries are what are known as gas giants, as big as or bigger than our own Jupiter.
Most of them huddle close to their stars - inside Mercury's orbit if they were in our solar system - and are far too hot for liquid water, an essential ingredient for life as we know it.
Many orbit so rapidly that their years last only a few days.
"The known exoplanets are very different from our own," says Sara Seager, a planetary scientist at the Massachusetts Institute of Technology.
The reason astronomers are finding mostly big, close-in planets is that they're easier to detect than Earth-size objects. Planet hunters are confident, however, that new telescopes soon will be able to identify smaller, solid bodies in Earthlike orbits in the so-called "habitable zone": close enough, but not too close, to their stars to permit liquid water and perhaps life.
"No question there are habitable planets out there," Seager says. "Whether they are inhabited is uncertain."
The pace of discovery is bound to increase. A European planet-hunting satellite named Corot was launched in December and reported its first discovery May 3.
