Super-Earths point to crowded universe

— -- So, Sir Isaac Newton, it turns out, was no slouch: Amid his accomplishments in math, physics and optics, he prophesied the glut of planets discovered in the last two decades circling nearby stars. The 1713 edition of the venerable astronomer's Principia Mathematica describes our own solar system — "this most beautiful system of the sun, planets, and comets" — and speculates, "the fixed stars are the centers of other like systems."

The story of these "extrasolar" planets gained its latest chapter last week, at a Paris colloquium for France's Centre National D'Etudes Spatiales space telescope, COROT. The telescope searches a swath of nearby stars for signs of dimming caused by planets passing in front of them, so-called "transit" planets, and one reported at the colloquium, COROT-Exo-7b, was among the smallest yet detected, less than twice the size of the Earth, but much hotter.

"For the first time, we have unambiguously detected a planet that is 'rocky' in the same sense as our own Earth," said COROT's Malcolm Fridlund, in a European Space Agency statement. "This discovery is a very important step on the road to understanding the formation and evolution of our planet."

Almost 340 planets have been detected orbiting nearby stars, according to the catalogue maintained by Paris Observatory astronomer Jean Schneider. Most discovered since 1995 are Jupiter-sized, or larger, worlds, many of them "roaster" planets that nearly graze their star.

The last few years have brought reports of "Super-Earths," planets like COROT-Exo-7b that only outweigh our planet by a bit.

"Finding Super-Earths, roughly a dozen of them, has been profound, a major leap forward," says theorist Alan Boss of the Carnegie Institute of Washington, author of The Crowded Universe: The Search for Living Planets, released today. Judged by the rate of recent discoveries, about 30% of nearby stars likely possess planets in Earth's weight class, he says.

COROT's report clears the way for the planned March 5 launch of NASA's $591 million Kepler mission, a larger transit-spotting telescope that should be able to spot Earth-sized planets in the "habitable zone" around stars, where water neither boils away or freezes away.