The main science goal of the CHEOPS mission will be to study the structure of exoplanets smaller than Saturn that are orbiting bright stars with revolution periods below 50 days. With an accurate measure of masses and radii for an unprecedented sample of planets, CHEOPS will set new constraints on the structure and hence on the formation and evolution of planets in the sub-Saturn mass range. In particular, CHEOPS will:
- Determine the mass-radius relation in the planetary mass range from 20 down to 1 Earth mass, with unprecedented precision. In particular CHEOPS will be able to measure radii to a precision of 10%. By targeting stars located anywhere on the sky which are bright enough for precise radial velocity follow-up, CHEOPS will not suffer from the limitations in planet mass associated with fainter stars. CHEOPS will provide a unique and large sample of small planets, with well-measured radii, enabling the robust bulk density estimates needed to test theories of planet formation and evolution to be made.
- Identify planets with atmospheres. CHEOPS will identify planets with significant atmospheres with 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 possible stellar parameters (eg. mass and metallicity).
- Place constraints on planet migration paths. CHEOPS will provide a sufficiently large sample of planets with accurate bulk densities to enable discrimination to be made between common groups of migration path. In particular, CHEOPS will place constraints on possible planet migration paths followed during the formation and evolution of planets for which the clear presence of a massive gaseous envelope cannot be discerned.
- Study energy transport in hot Jupiter atmospheres. CHEOPS will have the capability to detect the phase curve of hot Jupiters, providing information on planet albedos. The mission will bring new constraints on the atmospheric properties of known hot Jupiters that will help in the studies of the physical mechanisms and efficiency of energy transport from the dayside to the night side of the planet.
- Provide unique targets for future ground- and space-based spectroscopic facilities such as the E-ELT and JWST. In particular, CHEOPS will be able to identify planets that are more likely to have a thin envelope, which are prime targets for future habitability studies.
CHEOPS will have the capability to provide precise, time-differential photometric time series at high cadence (1 minute) of a wide range of variable light sources on timescales of ≤ 2 days.
CHEOPS will also offer 20% of open time to the community, which will be allocated through competitive scientific review.