Scientists are also ecstatic about the precision of the mission’s observations, which they say reflect the fact that instruments are performing better than predicted. ESA project scientist Malcolm Fridlund estimates the performance of the ESA-built telescope baffle to be 60% better than foreseen and other instruments are working an order of magnitude better than expected.
Instrument performance was illustrated by the second planet found by Corot, named Corot-exo-2b. The discovery, made after a 140-day sequence of observations – Corot’s third – and a record 78 transits, demonstrated an error level of just 160 parts per million over 2.5 min., and identified parameters with remarkable precision. It was determined that the planet has an average density of 1.5 grams per cu. cm. – slightly higher than Jupiter’s – and orbits its parent star in 1.74 days from a distance about six times the stellar radius.
At the same time, Corot’s asteroseismology sensor detected the presence of periodic modulations on Corot-exo-2b’s parent star itself, which scientists said was probably a sign that the star’s rotation varies between the two poles. The star is similar to the Sun, but somewhat more massive, cooler and more active. Two other stars comparable to the Sun, HD49933 and HD181420, have also shown solar-type oscillations.
Mission leaders think the superior payload performance could eventually allow Corot to observe planets with an accuracy as good as one part per 100,000 – sufficient to discover terrestrial bodies the size of Earth. It was originally thought that such discoveries would have to await the launch of NASA’s Kepler observatory later this year, and that Corot’s observations would be limited to so-called Super Earths – rocky planets two or three times the size of Earth (AW&ST Jan. 1, 2007, p. 35).
Scientists say Corot may even be able to detect subtle variations in the stellar light reflected by the exoplanets, giving an inkling of their chemical makeup. Astronomers had initially thought this would have to be left for later missions such as ESA’s Darwin, still in the study phase.
Corot is designed to provide a wide-field survey of planets by observing a large number of stars–up to 12,000 at once–free from the background disturbances that affect ground-based telescopes. It does so by analyzing the behavior of light emitted by the target star: A sudden dip in luminar intensity may indicate a planet transiting in front of it. Combining space- and ground-based measurements makes it possible to determine the radius, mass and period of extrasolar planets. Analysis of oscillations in the curve can give clues to the age, rotation, composition and internal processes of the parent star itself.
The extremely high accuracy of the sensors, combined with the long period of observation (up to 150 days), makes it possible to obtain measurements with unprecedented accuracy.
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