Exoplanet Search Begins with French Launch of Corot Telescope Satellite

William Atkins
Wednesday, 27 December 2006 22:40

Science - Space

The 1,400-pound (630-kilogram) Corot will perform its mission from a polar orbit about the Earth at an average altitude of 557 miles (896 kilometers). It carries a 30-centimeter telescope and a charge-coupled device (CCD) with the ability to detect exoplanets smaller than are currently known. More information about Corot resides at: http://smsc.cnes.fr/COROT/ and http://www.esa.int/esaSC/120372_index_0_m.html.

The existence of exoplanets has been presumed at least as far back as the time of Dutch astronomer Christian Huygens (1629-1695). However, even today, exoplanets are difficult to observe directly because planets use reflected light from stars, which are hundreds of millions of times dimmer than the stars themselves. In fact, as of October 2006 (according to the International Astronomical Union [IAU]), only 208 exoplanets have so far been discovered. These exoplanets contain masses from the size of the planet Jupiter to about 15 Jupiter masses.

During its 2.5-year mission, Corot will be able to detect exoplanets smaller than Jupiter, which makes the mission very important because it will find planets that scientists have so far been unable to observe. In fact, astronomers are expecting to discover planets that are one-and-one-half Earth sizes or larger. The Corot telescope also has the ability to analyze the interior of the stars about which these planets orbit (what is generally termed astroseismology), including the acoustical rumblings that take place within stars (what is called starquakes).

The Corot spacecraft will direct its search to a different field every 150 days, while observing about 10,000 stars at a time. It detects exoplanets by observing transits, which are passages of a planet directly between its star and the Earth. When a transit occurs, the apparent brightness of a star dims for a few minutes; often times only by one percent or so. Corot begins its mission with an observation of the center of the Milky Way galaxy. Philippe Boudy, a representative for the French National Center of Space Studies recently said, “What everybody has in mind is this tremendous question of is there life elsewhere in the universe, or are we alone. Corot won’t be able to tell us that, but it will be able to tell us what type of planets is orbiting other stars and how common they are.” The Corot mission team is hopeful of finding about 200 exoplanets.

A number of other exoplanet missions are planned within the next few years. NASA will launch the Kepler Space Telescope in November 2008. Its purpose is to search about 100,000 stars (using the transit method) over a four-year period to determine if any Earth-sized or smaller planets are orbiting those stars. The Kepler mission, in an Earth-trailing orbit about the Sun, will have a mass of about 2,290 pounds (1,039 kilograms), an aperture of 3.11 feet (0.95 meters), and a primary mirror of 4.59 feet (1.4 meter).

NOTE: Under a new definition provided by the IAU in August 2006, a planet within the Earth’s solar system is officially defined as a “celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit”. For exoplanets outside of the solar system, the term ‘Sun’ can be replaced with ‘star’.