PLATO and CHEOPS are two European Space Agency missions aimed at characterising exoplanets.

CHEOPS is an S-class mission (small mission in ESA’s science program) which aims to characterise exoplanets already known to be orbiting around nearby bright stars. CHEOPS will target Earth- to Neptune-sized planets.

PLATO is an M-class mission (medium size mission) aimed at finding terrestrial exoplanets in orbits out to the habitable zone (HZ) of solar-type stars (up to orbits of one year), and characterising their bulk properties to determine their habitability. PLATO focuses on the discovery of new planetary systems.

CHEOPS will target planets that already have a mass estimate from ground based observations. PLATO, on the other hand, will first find new planets then facilitate ground based follow-up observations so that the masses of the newly discovered planets can be measured. For both missions, ground based observations are vital as they will (in combination with space based observations) allow for accurate measurements of the bulk density of the planets. This will provide information about the approximate composition of the planet, such as whether it is rocky or gaseous.

For PLATO to be efficient at finding new planetary systems it has to simultaneously observe a large number of stars. This is achieved by having a wide field of view, which is made possible by the 26 PLATO telescopes. Since CHEOPS will instead specifically observe one pre-defined target at a time, there is no need for a wide field of view making a single, larger telescope suitable.

CHEOPS is expected to observe ~500 targets. For each target, CHEOPS will provide an accurate estimate for the planetary radius of validated planets with known masses. These observations will provide valuable data for constraining the mass-radius relation of exoplanets. 20% of the time will be open time available for the community to develop new science programmes.

PLATO is expected to provide accurate parameters for planets on orbits similar to the terrestrial planets in the Solar System. This will allow for comparative exoplanetology for planets orbiting at distances up to about 1 AU. PLATO will also provide the ages for a large number of planetary systems (~10% accuracy for bright, solar-like stars). This will not only help us understand how planets form, but also help us understand the structure of the Milky Way. PLATO offers a Guest Observer program with 8% of the data rate being offered to the community, roughly equivalent to 40,000 targets per pointing.

Telescope aperture 12 cm (diamter of a CD) 32 cm
Number of telescopes 24 regular + 2 fast read out 1
Wavelength range 500-1000 nm 400 – 1100 nm
On sky pixel size 15 arc seconds 1 arc second
Main targets Bright, Sun-like stars Known exoplanet host stars with a V-magnitude ≤ 12 anywhere in the sky
Main objective Detect Earth sized planets in the habitable zone Characterise transiting exoplanets orbiting bright host stars
Mission duration 4 years 3.5 years
Orbit L2 (1.5 Million km from Earth) Sun-synchronous, 650-800 km altitude
Noise <= 50 ppm in 1hr (for main sample, up to V ~ 11 Sun-like star)
<= 800 ppm in 1 hour (for M-dwarfs)
<= 100 ppm in 1 hr (up to a V ~ 11 Sun-like star)
Type M-class mission S-class mission