CHEOPS

CHEOPS, or Characterising Exoplanet Satellite, is an ESA space telescope designed to study exoplanets through high-precision transit photometry. Its primary objective is to measure the radii of transiting planets orbiting bright, nearby stars with unprecedented accuracy, thereby constraining planetary densities and informing models of composition and structure. The mission also provides precise transit ephemerides to support follow-up observations with current and future facilities.

The mission was selected in 2012 as part of ESA’s Small Missions/Cosmic Vision programme. CHEOPS is operated by a European consortium led by Switzerland and includes partners from several member states. The spacecraft carries a 32-centimeter-aperture telescope and a high-precision CCD photometer that observes in a broad optical band, roughly spanning 330 to 1100 nanometers, to maximize photometric stability and signal.

CHEOPS was launched on 18 December 2019 atop a Vega rocket from the Guiana Space Centre in Kourou, French Guiana. It operates in a near-equatorial Sun-synchronous low-Earth orbit at an altitude of about 700 kilometers, enabling stable thermal conditions and continuous monitoring of target stars during transits.

In operation, CHEOPS observes individual target stars during predicted transit windows, measuring tiny dips in brightness with high accuracy. The resulting light curves yield accurate planetary radii and help refine densities, compositions, and models of exoplanetary atmospheres. The mission is designed for a multi-year nominal duration with potential extensions, and its observations support broader exoplanet science goals by improving transit timing and ephemerides for future studies.