Satellite Discovers First Rocky Exoplanet

Feb 4, 2009
By Michael A. Taverna

PARIS - The French-led Corot planet-finding satellite has discovered its first Earth-like planet - the first outside our solar system to be observed directly as it transited in front of its star, and the smallest yet discovered.

The finding, known for a year but only recently confirmed by ground-based telescopes, was announced at a symposium here Feb. 3. It is the latest in a series of startling discoveries since Corot was launched in December 2006 specifically to find terrestrial planets and provide an indication of their relative abundance in the universe.

Performance has been such that scientists think they may find planets similar in size and mass to Earth, and not just bodies in the so-called "Super Earth" category, four to 15 times the size of our planet. The 140 million euro ($180 million) mission also has discovered intriguing details about the internal structures of stars - its second objective - according to Eric Michel, a Paris observatory scientist in charge of Corot astroseismology activities. However, it is too early to confirm these findings, he says.

The new planet, known as Corot-Exo-7b, is less than twice the size of Earth, but its density is still unknown. It is thought to be one of a new class of planets with rock and water present in almost equal amounts, or it could be an ocean planet, a type whose existence has been theorized but never proven.

Determination of the planet's density, still under way, would help solve the puzzle. Preliminary estimates of mass, inferred by radial velocity techniques, show only that it is "less than 11 times that of Earth," but that is only a rough estimate, says Annie Baglin, the Corot principal investigator.

The planet's star is sun-like, but because it takes just 20 hours to orbit the parent star, its surface is too hot (1,000-1,500 deg. C.) to support life. Scientists think the planet may be covered with lava or shrouded in water vapor.

Daniel Rouan, a scientist at the Paris Observatory in charge of Corot extra-solar planet activities, says that some 20 of the 330 or so extra-solar planets discovered to date are in the so-called Super Earth category. However, all but Corot-Exo-7b have been found by radial velocity methods, which give no information on their size or structure.

Radial velocity observations also turned up a second planet in the same solar system as Corot-Exo-7b - a gas giant thought to be the size of Neptune. However, the existence of this second planet has yet to be confirmed. Corot has so far identified seven extra-solar planets, all but Corot-Exo-7b in the gas giant category.

Artist's concept of extrasolar planet: NASA

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