Thrilling Times in Search for Small Expoplanets

The French COROT satellite has detected the smallest extrasolar planet ever found, one only twice the diameter of Earth. Although it orbits a star similar to the sun, it is so close to the star that no life could survive there.

The new exoplanet, given the unromantic name COROT-Exo-7b, apparently is the first that is rocky, like Earth, rather than a giant gasbag like Jupiter, Saturn, Uranus and Neptune. The discovery means humanity is closer to finding Earthlike exoplanets.

The COROT project is led by the French Space Agency, CNES (for Centre National d’Etudes Spatiales), with participation by the European Space Agency. Also partners in COROT are Austria, Belgium, Brazil, Germany and Spain.

While the Europeans are ahead of America in the small exoplanet race, my money’s on NASA finding the first truly Earthlike planet around another star.

The difficulty in finding Earthlike planets probably isn’t that they are rare, but that detecting something so tiny light years away is much harder than finding a big, obvious planet. The gravity of large planets tugs more on their host stars, causing the stars to wobble in a way that is easier to measure. And, obviously, bigger planets are easier to see when they cross the disks of their stars.

The latest tally of exoplanets is 339, says a web site maintained by NASA’s Jet Propulsion Laboratory in Pasadena. The site, PlanetQuest, adds that the current count is “Stars with planets: 287. Earthlike planets: 0.”

While the COROT discovery is not Earthlike, it seems to be the closest yet to a planet with a composition similar to ours.

“The density of the planet is still under investigation: it may be rocky like Earth and covered with liquid lava,” says a press release issued Feb. 3 by the European Space Agency. “It may also belong to a class of planets that are thought to be made up of water and rock in almost equal amounts.” The release says the new planet could be “a very hot and humid place.”

Orbiting its star every 20 hours, the planet is so close to the star that its temperature is estimated at approximately 1800 degrees Fahrenheit to more than 2,700 F.

COROT was launched on Dec. 27, 2006. Using a telescope about 12 inches in diameter, the satellite measures the light of stars and is able to determine when a planet comes across the face of a star by the dimming. Every 150 days, COROT will switch its observations from northern to southern, or southern to northern, regions above Earth. Its astronomers believe they will be able to find between 10 and 40 rocky worlds and “tens of new gas giants” in each field it studies.

However, while the technique can find exoplanets about twice as wide as Earth, it cannot spot anything as small as our planet. For that, the European Space Agency plans to launch the Darwin project sometime in the next ten years. With four or five spacecraft working in tandem, according to ESA, Darwin “will take pictures of Earth-like worlds, allowing scientists to search for signs of life.”

But don’t count NASA out. Chances are, it will discover an Earthlike world before ESA does.

On March 5, a spacecraft called Kepler is to launch from Cape Canaveral, Fla. Its purpose is to “find Earth-size planets orbiting stars like our sun in a zone where liquid water could exist,” says a news release sent out by NASA on Thursday.

Next Thursday, 3 p.m. MST, NASA will brief reporters on Kepler at its headquarters in Washington. The briefing is to be carried on NASA TV.

The image below is an illustration provided by the European Space Agency showing how COROT detects planets.

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