The CHEOPS mission

Abstract

The CHaracterising ExOPlanet Satellite (CHEOPS) was selected on October 19, 2012, as the first small mission (S-mission) in the ESA Science Programme and successfully launched on December 18, 2019, as a secondary passenger on a Soyuz-Fregat rocket from Kourou, French Guiana. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys. The expected photometric precision will also allow CHEOPS to go beyond measuring only transits and to follow phase curves or to search for exo-moons, for example. Finally, by unveiling transiting exoplanets with high potential for in-depth characterisation, CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres. To reach its science objectives, requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars (stellar radius of 0.9R⊙) in the magnitude range 6 ≤ V ≤ 9 by achieving a photometric precision of 20 ppm in 6 hours of integration time. In the case of K-type stars (stellar radius of 0.7R⊙) of magnitude in the range 9 ≤ V ≤ 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration time. This precision has to be maintained over continuous periods of observation for up to 48 hours. This precision and stability will be achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter, on-axis Ritchey-Chrétien telescope. The nearly 275 kg spacecraft is nadir-locked, with a pointing accuracy of about 1 arcsec rms, and will allow for at least 1 Gbit/day downlink. The sun-synchronous dusk-dawn orbit at 700 km altitude enables having the Sun permanently on the backside of the spacecraft thus minimising Earth stray light. A mission duration of 3.5 years in orbit is foreseen to enable the execution of the science programme. During this period, 20% of the observing time is available to the wider community through yearly ESA call for proposals, as well as through discretionary time approved by ESA’s Director of Science. At the time of this writing, CHEOPS commissioning has been completed and CHEOPS has been shown to fulfill all its requirements. The mission has now started the execution of its science programme.

The Nature and Origins of Sub‐Neptune Size Planets

“…Early results on this topic from further analysis of Kepler/K2 data have yielded tentative evidence that super-Earths form in gas poor disks around low-mass stars (Cloutier & Menou, 2020), and that the mass-loss timescale for these planets around stars with masses ≳1 M ⊙ is approximately a Gyr, which is a potential signpost to the core-powered mechanism (Berger et al, 2020). Continuing work on this topic is currently enabled through the detection of transiting planets around bright stars by NASA's TESS mission (launched 2018;Ricker et al, 2015) and ESA's CHEOPS mission (launched 2019;Benz et al, 2020), and will be furthered by ESA's PLATO mission (scheduled for launch in 2026; Rauer et al, 2014).…”

Exploiting the transit timing capabilities of Ariel

“…4 as the result of better determination of orbital parameters timing variations of Exoplanets project (TASTE, [16,38]), the Next-Generation Transit Survey (NGTS, [58]), and the ExoClock Project 9 (within the Ariel Ephemerides Working Group), or space missions, i.e. Transiting Exoplanet Survey Satellite (TESS, [48]), CHaracterizing ExOPlanets Satellite (CHEOPS, [3,7]), PLAnetary Transits and Oscillations of stars (PLATO, [47]). Thanks to TESS and to the extended operations TESS will also be of great advantage for the ephemeris recovery of almost all the Kepler/K2 targets on the ecliptic and most of the targets on the sky.…”

“…We are aware that emcee code should be used with caution when space of the parameters has a number of dimension greater than 10, but it has been extensively used in exoplanet literature showing great performances in different cases. Furthermore, using a parameterization that reduces the correlation among parameters and that allows the algorithm to evenly sample the parameter space can mitigate this issue 3. In the impact parameter we took into account the eccentricity and the argument of pericenter as in[59] and[26].…”

The NASA High-Resolution Speckle Interferometric Imaging Program: Validation and Characterization of Exoplanets and Their Stellar Hosts

“…As new exoplanet transit missions such as K2 (Howell et al, 2014), and the currently operating missions TESS (Ricker et al, 2015) and CHEOPS (Benz et al, 2020) come along, follow-up high-resolution (sub-arcsecond) imaging continues to be needed and in larger amounts than before. While Gaia can resolve companions down to near 1.0 arcsec and a bit closer using additional observations over time, e.g., EDR3; (Fabricius et al, 2016), it does not reach the spatial resolution of speckle imaging.…”