Artist’s impression of four exoplanets such as those that will be investigated by ESA’s Characterising Exoplanet Satellite, Cheops. 

Cheops will make measurements of alien worlds that will help determine their nature. It will focus on Earth-to-Neptune sized planets orbiting nearby bright stars, and will measure the size of the planet as it transits in front of the star.

Combined with known information about the mass of the planet, these data will enable scientists to distinguish between a dense rocky world or rather more gaseous, a water-world or an ice-rich planet – as represented from left to right in this artist impression.

Cheops will identify which planets are rather more similar in composition to Mercury, Venus, Earth and Mars in our own Solar System, or if they resemble small versions of the outer Solar System’s gas giants like Neptune or Uranus. It will also be able to identify hot-Jupiters – large gas planets similar in mass and size to Jupiter but orbiting very close to their host stars – or rather smaller and rocky lava worlds orbiting close to their star.

This first-step characterisation of these worlds – many with no Solar System equivalents – is a critical process towards understanding the formation, origin and evolution of these small exoplanets.

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