Cheops (CHaracterising ExOPlanets Satellite), is a small Switzerland satellite will be launched by the European Space Agency (ESA) in 2017.
This small space telescope measuring 33 cm in diameter and 1.2 meters long focal operating in visible light and equipped with a CCD sensor, on the band of wavelengths from 0.4 to 1.1 micron. The orbit of the satellite will be located at 800 km altitude. Its mission is to study the characteristics of exoplanets from 1 to 6 terrestrial radius with unprecedented accuracy. It uses the method of photometric precision is to observe the cyclical variations of brightness of stars selected.
The passage of a exoplanet between the Earth and a star induces a change in light that reaches us from this star. The decrease in brightness of the star and the size of the planet is determined by the degree of impairment of luminous flux emitted. Its instrument is designed to study the characteristics of exoplanets have already been detected by the spectroscopic method used by large telescopes of La Silla Observatory (3.6 m) telescope or observatory in Hawaii (10.4 m). When a star is accompanied by a planet, one and other turn around the center of mass of the gravitational system they form. Given the mass much larger of the star, the center is much closer to the latter than the planet. Even the barycenter lies inside the star, it is not exactly in the center of it. The star therefore shows some variation caused by the presence of the planet.
Cheops can not see the planet, but discern these variations in the spectrum of the light emitted by the star. By Doppler effect, it appears more red if it moves away from the observer, bluer when it comes close.
By measuring these variations Cheops determines the characteristics of the planets (mass, size, density) that accompany it. In our solar system we observe a slight oscillation of the Sun on a cycle of 12 years, which corresponds to the gravity of Jupiter cycle.
Corot (ESA, 2006-2011), Kepler (NASA, 2009-2015) and Cheops (ESA, 2017-2021) work on the same principle, but Cheops target its observations on nearby exoplanets (10-100 al), and selected not at random from thousands of stars far (1000-10000 al) in the galaxy, as in the case of Corot and Kepler.
Corot has detected more than 600 candidates, including 25 transits were confirmed by terrestrial observations. Kepler has detected more than 2000 candidates of which 77 were confirmed transits. The telescope Cheops will analyze planets already discovered, i.e. those that pass in front of their stars, but the images will be low quality and even blurred.
The next possible step will be in the years 2020-2030 where exoplanets will be analyzed and photographed directly in the search for extraterrestrial life.
Cheops telescope will probe the atmosphere of "hot Jupiters" knowned, identifi.e. exoplanets that have a significant atmosphere, provide specific targets for monitoring large telescopes.
Characteristics of exoplanets will surprise us again.
In a few years we have learned that gas giants can exist on short-period orbits close to their stars, that exoplanets exist on non-coplanar orbits outside the equatorial plane of the star and that are exoplanets retrograde, they rotate in opposite directions on their orbits.
Image: Astronomers have discovered thousands of exoplanets. The European Commission Cheops is designed to analyze the characteristics of confirmed exoplanets. The method used is method of transits, micro eclipses caused by the passage of a planet in front of its star. In this picture you can see Venus during the Transit June 6, 2012 0:32 (UT).