Space mission

ULiège takes part in the CHEOPS mission

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ESA has just launched its first space mission dedicated to the in-depth study of already known exoplanets. Called CHEOPS (CHaracterising ExOPlanet Satellite), the satellite - whose baffle and door were designed and assembled at the Centre Spatial de Liège - aims to measure the size, mass and some atmospheric characteristics of already identified exoplanets orbiting bright nearby stars. The University of Liège is leading the Belgian participation in this mission, which is expected to last three and a half years.


aunched on the 18 December 2019 from the Kourou base in French Guiana, by a Soyuz rocket, CHEOPS - CHaracterising ExOPlanet Satellite - is the first European Space Agency (ESA) space mission dedicated to observing exoplanetary transits by very high precision photometry on bright stars already known to host exoplanet. The mission, led by Switzerland, includes the participation of several European countries* including Belgium. And it is the University of Liège that is leading this Belgian participation to the mission, with in particular the astrophysicists Valérie Van Grootel, Laetitia Delrez and Michaël Gillon,, members of its scientific team and its board.

"CHEOPS will not attempt to discover new exoplanets as did previous missions," explains Valérie Van Grootel, a FNRS Research associate at the STAR Research Unit. The mission aims to monitor and observe exoplanets that we already know in order to study them in more detail. "The small space telescope, which has a mirror 32 cm in diameter, is dedicated to the study of exoplanets using the so-called transit method, i.e. by measuring the apparent drop in brightness of the system when the planet "transits" its host star, i.e. passes in front of it. "These data will allow us to measure the planet's radius very accurately," says Laetitia Delrez, PostDoc researcher at the STAR and ASTROBIOLOGY research units. By combining this information with measurements from ground-based telescopes, its density can be obtained, allowing the structure of the planet to be estimated. This is a first step towards a deeper understanding of exoplanets. »

CHEOPS will be placed in orbit at an altitude of 700 km, which will ensure that observations are not disturbed by the Earth's atmosphere. The satellite will be able to measure very precise radii for a large sample of planets whose masses have already been estimated from data taken from the ground. "Our TRAPPIST and SPECULOOS telescopes allow us to make observations but they remain limited in terms of accuracy," explains Michaël Gillon, FNRS Senior Research Associate at the ASTROBIOLOGY Research Unit. CHEOPS will provide additional accuracy in the measurement of transits of exoplanets that are out of range of telescopes on the ground, which will allow us to obtain very accurately the radii of these exoplanets.

The satellite, which was mainly manufactured in Switzerland, passed through the hands of engineers from the Centre Spatial de Liège who manufactured the door and the baffle, a critical hardware component of the satellite. "The baffle makes it possible to attenuate straylights that disturb the high-precision measurement of the transits , explains Jean-Yves Plesseria, head of the CSL's Thermo-mechanical Laboratory, an applied research centre of ULiège specialising in the design, integration and calibration of space observation instruments whose expertise is recognised throughout the world.

The main scientific objectives of the CHEOPS mission are to measure the size of Planets with masses between the Earth and Neptune in orbit around bright stars and to provide appropriate targets for future in-depth studies of the planets' atmosphere in this mass range in order to understand their formation, evolution and surface conditions. A key step in the characterization of planets outside our Solar System.

The first data are expected in early April 2020.


CHEOPS, a european satellite to study exoplanets

The CHEOPS space telescope aims to measure the size of known transiting exoplanets orbiting bright and nearby stars as well as search for transits of exoplanets previously discovered via radial velocity.

 * The European Agency's CHEOPS mission is led by a consortium of 11 countries: Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Sweden, Spain, Switzerland and the United Kingdom.

ESA Cheops brochure


VAN GROOTEL Valérie - STAR Research Institute I Faculty of Science

DELREZ Laetitia I STAR Reseach Institue I ASTROBIOLOGY Research Unit I Faculty of Science

GILLON Michaël I ASTROBIOLOGY Research Unit I Faculty of Science

PLESSERIA Jean-Yves I Centre Spatial de Liège (Liège Space Center)

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