The CHaracterizing ExOPlanet Satellite (CHEOPS) is the first ESA S-type mission, and will be the first to search for transits by means of ultrahigh precision photometry on bright stars already known to host planets, with an expected launch in October/November 2019. By being able to point its 30-cm telescope and detectors at nearly any location on the sky, it will provide the unique capability of determining accurate radii for a subset of those planets for which the mass has already been estimated. It will also provide precision radii for new planets discovered by ground-based transit surveys (Neptune-size and smaller). CHEOPS is designed as a dedicated survey mission for transit photometry capable of observing a large, diverse and well-defined planet sample within its 3.5-year mission lifetime.

Among the planets observed by CHEOPS, super-Earths will take a privileged position. They are the larger and more massive siblings of our Earth but will permit many studies of processes that are extremely relevant and important to the structure and evolution of our atmosphere. CHEOPS will identify planets with significant atmospheres in a range of masses, distances from the host star, and stellar parameters. Using observations of a sample of planets with and without significant gaseous envelopes, CHEOPS will be able to constrain the critical core mass (in the case of runaway gas accretion) or the loss of primordial H/He atmospheres as a function of the distance to the star and possibly stellar parameters (mass, metallicity).
Artist's impression of CHEOPS, the Characterising Exoplanet Satellite, with an exoplanet system in the background. Copyright: ESA/ATG medialab
Aim of the ourparticipation
The Institute of Space Sciences is involved in the scientific aspects of the CHEOPS mission through its participation in the Mission Board and Core Science Team.

Recent  developments
The mission successfully completed its construction phase during 2018 and has fulfilled all milestones for launch in October/November 2019. Because of its modest size and weight, it will be launched as a secondary passenger. The Science Team has worked on fine-tuning the science case and on defining the transiting planet sample that CHEOPS will observe. In this latter aspect, the synergy with the TESS mission from NASA, which was launched in April 2018, is evident (TESS will discover hundreds of planet candidates that CHEOPS can observe). To exploit this, the Institute of Space Sciences team has been leading the joint TESS-CHEOPS team and has explored and established the benefits of the collaboration.

Senior Institute members involved

I. Ribas
Institute of Space Sciences (IEEC-CSIC)

Campus UAB, Carrer de Can Magrans, s/n
08193 Barcelona.
Phone: +34 93 737 9788
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An institute of the Consejo Superior de Investigaciones Científicas

An institute of the Consejo Superior de Investigaciones Científicas
Affiliated with the Institut d'Estudis Espacials de Catalunya

Affiliated with the Institut d'Estudis Espacials de Catalunya