ESA is preparing for the launch of the first in a series of three exoplanet missions designed to tackle different aspects of the evolving field of exoplanet science. CHEOPS, the Characterising Exoplanet Satellite, is scheduled for launch in late 2019, and will make precise measurements of planets known to be orbiting around nearby bright stars. It will focus particularly on stars with Earth- to Neptune-sized planets. By determining the size of the planet, and combining this with known measurements of the planets' masses, CHEOPS will allow the density of the planet to be estimated, and therefore enable a first step towards characterising the nature of these planets – from lava worlds to rocky Earth-like planets, to gas planets or even ocean worlds.
The artist's impressions depicted in this montage imagine some of the different types of exoplanets and their host stars that might be studied by CHEOPS.
In the next decade, PLATO, the PLAnetary Transits and Oscillations of stars mission will be launched. It is a next-generation planet hunter with an emphasis on the properties of rocky planets in orbits up to the 'habitable zone' – where liquid water can exist on the planet's surface – around Sun-like stars. It will also investigate seismic activity in stars, which will enable precise characterisation of the planet's host star, including its age, providing insight into the age and evolutionary state of the planet system.
Also scheduled to launch in the next decade, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey mission, ARIEL, will take exoplanet characterisation one step further, performing a chemical census of a large and diverse sample of exoplanets by analysing their atmospheres. This will enable the study of exoplanets both as individuals and, importantly, as populations, in greater detail than ever.
CHEOPS will also help provide targets for other missions, including the international James Webb Space Telescope, which will be used to search for the signatures of water and methane, important elements in our quest for signs of habitability.
Together with CHEOPS, these future missions will keep ESA at the forefront of exoplanet research well beyond the next decade, and will build on answering the fundamental question: what are the conditions for planet formation and the emergence of life?