NASA’s Ames Research Center in Mountain View says that the agency’s Kepler mission, dedicated to locating planets orbiting stars other than our sun, has found its first rocky planet. That makes it a cousin of sorts to our favorite planet, Earth, which is also rocky (as opposed to gaseous, like Jupiter, Saturn, and the hundreds of other planets discovered to date around distant stars).

The planet announced today, called Kepler 10-B, is far denser than the Earth and orbits much closer to its star, meaning that it’s uninhabitable from the point of view of known life forms. If you’ve got questions about Kepler 10-B, NASA’s sponsoring a live web chat at 12:30 p.m. today with Natalie Batalha, a professor of physics and astronomy at San Jose State University and deputy science team lead for NASA’s Kepler Mission. Here’s the link:

Excerpt from the press release on the new discovery:

MOFFETT FIELD, Calif. — NASA’s Kepler mission confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.

The discovery of this so-called exoplanet is based on more than eight months of data collected by the spacecraft from May 2009 to early January 2010.

“All of Kepler’s best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our sun,” said Natalie Batalha, Kepler’s deputy science team lead at NASA’s Ames Research Center in Moffett Field, Calif., and primary author of a paper on the discovery accepted by the Astrophysical Journal. “The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it’s beginning to pay off.”

Kepler’s ultra-precise photometer measures the tiny decrease in a star’s brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star.

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet’s surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.

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