ESA gets ready to launch a stellar seismologist COROT

ESA gets ready to launch a stellar seismologist COROT to detect and study the vibrations of stars (starquakes) , and aid in the search for extrasolar planets and more particularly the telluric planets.

COROT is an acronym for: COnvection ROtation and planetary Transits.

COROT will contribute to the search for habitable, Earth-like planets around other stars. COROT will do this by detecting planets as they pass in front of their parent stars, blocking some of the light.

From the ground, the only planets detected around other stars have been giant gaseous worlds (Jupiter-like planets), over 10 times the diameter of the Earth. Above the distorting effects of the atmosphere, COROT will be the first spacecraft capable of finding worlds made of rocks, smaller than the gas giants but several times larger than the Earth, itself the biggest rocky planet in the Solar System. Such planets would represent a new, as yet undiscovered, class of world that astronomers believe exists. With COROT, astronomers expect to find between 10-40 of them, together with tens of new gas giants.

In addition, COROT will also be used to detect subtle brightness changes caused by sound waves that resonate through the star. These create a 'starquake' that sends ripples across the star's surface, altering its brightness. The exact nature of the ripples allows astronomers to calculate the star's precise mass, age and chemical composition. The technique is known as asteroseismology and ESA's Solar and Heliospheric Observatory (SOHO) has been taking similar observations of the Sun for years. So, the COROT data is essential to compare the Sun with other stars.

Instead of being an isolated national mission, ESA's involvement places COROT into the European framework to search for habitable planets. In particular, it will open the door to future missions, such as Darwin.

ESA plans to continue its search for Earth-like worlds into the second decade of the century with the launch of Darwin. This flotilla of eight spacecraft will take pictures of Earth-like worlds, allowing scientists to search for signs of life.

The detectors are 4 CCD's 2048 x 2048 wide, (EEV 4280), back thinned, frame transfert, and working in the visible in the MPP mode. They are installed in the focal box, which is at a temperature of -40oC with a variation that is less than 0.05oC per hour.

For the seismology mission, the image spot for a star will be spread out on about 400 pixels, exposure time of 1 second.
A prism, allowing to get a color image of the stars, will be installed before the exoplanet field. It will enable to distinguish the stellar activities of a planetary transit, for the brightest stars.

The afocal telescope is at first constituted of two parabolic mirrors allowing to decrease 3 times the equivalent entry pupil diameter, then 6 dioptric lens allowing to have a 1.1 m focal length. The field of view is a square of 2.8 x 2.8o, half for the seismology mission, the other half for the exoplanet mission.

COROT will be put in a circular polar orbit around the Earth at an altitude of 827 km. The telescope will be pointed to observe perpendicular to its orbit. This ensures there will be no Earth occultations to hinder the observations.

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Credit: ESA/CNES/Active Design