COROT << kaw ROH >> is an Earth-orbiting telescope once used to study the interiors of distant stars and to search for planets outside our solar system. It accomplished both tasks by monitoring distant stars for small changes in brightness. COROT was developed by France, the European Space Agency (ESA) , and several other countries. It was launched in December 2006 and took its first images in January 2007. Mission planners intended COROT to operate for about 21/2 years, but the mission was extended several times. The satellite officially ended observations on June 24, 2013.
COROT stands for CO_nvection, _RO_tation, and planetary _T_ransits. The words _convection and rotation in COROT’s name refer to the mission’s research on the structure of stars. Astronomers can learn about a star’s interior by studying vibrations that originate within the star, in much the same way that geologists study earthquakes to learn about Earth’s interior. In the case of a star, the vibrations produce tiny changes in brightness. By measuring these variations, COROT enabled scientists to model the interior of the star. For instance, they could determine the thickness of the star’s convection zone, a subsurface layer made up of churning clumps of hot gas. They could also calculate how fast different regions of the star rotate around its center.
COROT searched for planets outside the solar system, called extrasolar planets or exoplanets, by detecting the drop in brightness that occurs when an orbiting planet passes between its star and Earth, an event known as a transit. Astronomers had previously used the transit technique to discover and study exoplanets with ground-based telescopes. But Earth’s atmosphere distorts some of the light that reaches ground-based telescopes, limiting their ability to detect small changes in brightness. As a result, most of the planets discovered from the ground have been giant, gaseous planets—much like Jupiter—whose transits cause relatively large drops in their stars’ brightness. Because COROT observed above Earth’s atmosphere, it could detect the smaller drops in brightness caused by the transits of small, rocky planets more like Earth. In 2009, the COROT team announced the discovery of the first exoplanet with a rocky surface. The team named the planet COROT 7b. In March 2010, the COROT team announced the discovery of a planet with a temperature and composition similar to those of planets in our solar system. Named COROT 9b, the planet has a surface temperature similar to Earth’s and a chemical composition resembling that of Saturn and Jupiter.
COROT gathered light using a primary (main) mirror about 11 inches (27 centimeters) in diameter. An electronic camera converted the light into a signal that was analyzed on a computer. The formal observation portion of the COROT mission included short and long observation runs. During a long run, COROT continuously watched a single region of space for about 150 days. During a short run, lasting roughly 20 days, COROT continuously monitored neighboring areas. The long runs concentrated on planetary transit research. The short runs emphasized research on the structure of stars. Overall, the mission was intended to study in detail the interior vibrations of about 100 stars and search for planets around tens of thousands of stars. If a planet transited its star three or more times during a run, scientists could determine the planet’s period or “year.”
