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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| CHEOPS | 1/2 | https://en.wikipedia.org/wiki/CHEOPS | reference | science, encyclopedia | 2026-05-05T12:43:30.971166+00:00 | kb-cron |
CHEOPS (Characterising Exoplanets Satellite) is a European space telescope. Its objective is to determine the size of known extrasolar planets, which will allow the estimation of their mass, density, composition and their formation. Launched on 18 December 2019, it is the first Small-class mission in ESA's Cosmic Vision science programme. The small satellite features an optical Ritchey–Chrétien telescope with an aperture of 30 cm, mounted on a standard small satellite platform. It was placed into a Sun-synchronous orbit of about 700 km altitude. For the planned mission duration of 3.5 years, CHEOPS is to measure the size of known transiting exoplanets orbiting bright and nearby stars, as well as search for predicted transits of exoplanets previously discovered via radial velocity. Scientists behind the project expect these well-characterised transiting exoplanets to be prime targets for observatories such as James Webb Space Telescope (JWST) or the extremely large telescopes. In 2023, the mission was extended to 2026. During the extended mission CHEOPS is expected to also search for exomoons. CHEOPS also sees trails from other satellites during its observations, since it is in low Earth orbit.
== Spacecraft ==
The satellite has dimensions of approximately 1.5 × 1.5 × 1.5 m (4 ft 11 in × 4 ft 11 in × 4 ft 11 in) and a hexagonal base structure. The satellite bus of the CHEOPS spacecraft is based on the SEOSAT platform. The spacecraft is powered by solar panels that are also part of its sunshield. They provide 60 W continuous power for instrument operations and allow for at least a 1.2 gigabit/day data downlink capacity. A sunshield mounted on the platform protects the radiator and detector housing against the Sun, and it also features solar panels for the electrical power subsystem. The sunshield wraps around the hexagonal bus. The control system is 3-axis stabilized, but nadir locked, ensuring that one of the spacecraft axes is always pointing towards the Earth. During each orbit, the spacecraft slowly rotates around the telescope line-of-sight to keep the focal plane radiator oriented towards cold space, enabling passive cooling of the detector. The typical observation duration is 48 hours. During a typical 48-hour observation CHEOPS has a pointing stability of better than eight arcsec at 95% confidence. Two titanium plaques with thousands of miniaturised drawings by children have been fixed to CHEOPS. Each plaque measures nearly 18 × 24 cm (7.1 × 9.4 in). The plaques, prepared by a team at the Bern University of Applied Sciences were unveiled in a dedicated ceremony at RUAG on 27 August 2018. The individual drawings can be found at the website of CHEOPS by clicking on a map of Europe.
== Instruments == The detector, support electronics, telescope, back-end optics, instrument computer, and thermal regulation hardware are known collectively as the CHEOPS Instrument System (CIS). The required photometric precision is achieved using a single frame-transfer, back-illuminated Charge-coupled device (CCD) detector from Teledyne e2v with 1024 × 1024 pixels and a pixel pitch of 13 μm. The CCD is mounted in the focal plane of the telescope, and is passively cooled to 233 K (−40 °C), with a thermal stability of 10 mK. The telescope is a single medium-size f/8, on-axis Ritchey-Chrétien telescope with a 32 cm (13 in) aperture, mounted on a stiff optical bench. The University of Geneva and the University of Bern provided the powerful photometer. Target star images are deliberately defocussed to help accurate photometry.
== Objectives == Thousands of exoplanets have been discovered by the end of the 2010s; some have minimum mass measurements from the radial velocity method while others that are seen to transit their parent stars have measures of their physical size. Few exoplanets to date have highly accurate measures for both mass and radius, limiting the ability to study the variety in bulk density that would provide clues as to what materials they are made of and their formation history. The main goal of CHEOPS is the accurate measurement of the size (radii) of the exoplanets for which ground-based spectroscopic surveys have already provided mass estimates. Knowing both the mass and the size of the exoplanets will allow scientists to determine the planets' density and thus their approximate composition, such as whether they are gaseous or rocky. CHEOPS is the most efficient instrument to search for shallow transits and to determine accurate radii for known exoplanets in the super-Earth to Neptune mass range (1–6 Earth radius). CHEOPS measures photometric signals with a precision limited by stellar photon noise of 150 ppm/min for a 9th magnitude star. This corresponds to the transit of an Earth-sized planet orbiting a star of 0.9 R☉ in 60 days detected with a S/Ntransit >10 (100 ppm transit depth). For example, an Earth-size transit across a G star creates an 80 ppm depth. The different science objectives require 500 separate target pointings. Assuming 1 hour per pointing the mission duration is estimated at 1175 days or 3.2 years. Together with the 20% of open time available for the community the total duration of the CHEOPS mission is estimated to be 3.5 years.