The ESA Ariel mission is ready for implementation

Ariel, the “atmospheric remote sensing infrared exoplanet large survey” mission, is the European Space Agency’s Cosmic Vision M4 (medium-class number 4) science mission. It has recently gone through an implementation approval (“adoption”), with a planned launch in 2029. Ariel, together with two other M4 candidate missions (THOR and XIPE), was recommended in June 2015 to enter an assessment study, consisting of a Phase 0 at the ESA internal Concurrent Design Facility study followed by a Phase A with parallel industrial studies. The Phase A was concluded in March 2018 with the selection of Ariel as the M4 mission endorsed by the ESA Science Programme Committee (SPC). Phase B1 was subsequently initiated, and was concluded by the Mission Adoption Review in mid-2020, followed by the formal adoption of Ariel in November 2020 by the SPC. Ariel is a survey-type mission dedicated to the characterisation of exoplanets by performing a chemical census. Using the differential technique of transit/eclipse spectroscopic observations, Ariel will obtain transmission and/or emission spectra of the atmospheres of a large (~1000) and diverse sample of known exoplanets covering a wide range of masses, densities, equilibrium temperatures, orbital properties and host-star characteristics. This will include hot Jupiters to warm Super-Earths, orbiting A to M spectral class host stars. This paper reports on the Ariel Phase 0/A/B1 study, including the conclusions of the reviews that were conducted in 2020 to close the study and support the adoption process.