CHEOPS is the ESA space telescope launched in 2019 to characterize known exoplanets.
CHEOPS stands for Characterising Exoplanets Satellite. Unlike a survey mission designed mainly to discover large numbers of new planets, it focuses on measuring the sizes of already known planets, especially those orbiting bright, nearby stars. When combined with mass measurements from radial-velocity observations, its radius measurements let astronomers estimate density and infer whether a world is likely rocky, gaseous, or somewhere between.
The spacecraft launched on 18 December 2019 aboard a Soyuz rocket from Europe's spaceport in French Guiana. Its telescope operates in low Earth, Sun-synchronous orbit and uses highly precise photometry: it watches a star dim slightly when a planet crosses, or transits, its disk. CHEOPS deliberately defocuses stellar images across many detector pixels to improve measurement stability.
A common mix-up is confusing CHEOPS with NASA's Kepler or TESS. Those missions were primarily planet-finding surveys, whereas CHEOPS is a follow-up observatory built to refine the physical properties of selected worlds. Its results also help identify promising targets for atmospheric studies with larger telescopes such as JWST.