for National Geographic News
Another Earth? Not yet.
But astronomers say they're getting ever closer to finding planets more like Earth around sunlike stars.
Christophe Lovis of Switzerland's Observatory of Geneva and colleagues announced that they have found a solar system containing three rocky, medium-size planetsthe smallest so-called extrasolar planets that have ever been observed.
The rocky, Neptune-size planets are orbiting a star called HD 69830, barely visible with the naked eye near the southern constellation Puppis.
One of the planets is in the star's "habitable zone," where liquid water could exist on its surface, the researchers said.
The astronomers report their discovery in tomorrow's issue of the journal Nature.
Scientists have discovered almost 200 extrasolar planets so far. The first one was found in 1995 by Michel Mayor, an astronomer at the University of Geneva who is also an author of the new study.
Mayor said one of the most exciting aspects of the new discovery is that the planets are the smallest yet found, proving that astronomers' techniques are getting sharp enough to someday detect distant planets the size of Earth.
"These objects are still not Earth twins, but the amazing progress suggests that the dream to detect real 'Earths' could be possible," Mayor said.
NASA's Spitzer Space Telescope recently spotted HD 69830, about 41 light-years away, as part of a wider survey. The telescope found that the star had an unusually strong infrared signal.
Astronomers said last month that they think the signal is caused by a belt of asteroids that's about as far from the star as Earth is from the sun.
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