The ESA/Ariel mission will address some fundamental questions on the composition and formation of exoplanets, in the frame of the ESA Cosmic Vision Program. Ariel is to be launched in 2029. It will use the technique of transit spectroscopy in the near-infrared (1.1-7.8 μm), observing host stars during planetary transit or eclipses, obtained on around one thousand transiting planets. It will provide an extensive statistical study on planets from Earth-size to gas giants around a range of host star types, in complement to James Webb Space Telescope and ground-based observatories observations. The unique performances of Ariel are to record simultaneously the whole wavelength range from about 1 to 8 μm, to record up to ∼ 1000 targets for statistical purpose and to study in parallel host star activity with planetary spectra thanks to its visible channel concurrent observations. The international consortium, led by G. Tinetti (UK), will procure to ESA the instrument and subsystems, including the telescope and the spectrometers. The Ariel satellite will consist in a telescope (elliptical mirror 1100 mm x 730 mm size) with radiatively cooled optics below 60K. The telescope feeds two separate instruments : The FGS (Fine Guide Sensor), providing three photometric channels (0.5-0.6 micron ; 0.8-1.1 micron and 1.10-1.95 μm, the latter with coarse spectral resolution R ≥ 15) The AIRS (Ariel Infra-Red Spectrometer) is a two channels grating spectrometer (1.95-3.9 μm with R ≥ 100 and 3.9-7.9 μm with R ≥ 30) The exoplanet spectra are retrieved from transit and/or eclipse observations on the target with data processing including calibration of photometric/spectral science spectra, with timely public release of data to maximize science return of Ariel. Within the consortium, the French participation (co-PIs JP Beaulieu \& PO Lagage) is supported by CNES and will be in charge principally of : - 1. AIRS (Ariel infrared spectrometer) instrument o optical module (including detectors & Cold Front End Electronics) and cryoharnesses including with full calibration at detector and instrument level o AIRS instrument detector control unit t with acceptance by the AMC systems team - 2 Contribution to management and systems engineering o for the Instrument Operations and Science Data Centre (IOSDC); o contribute to algorithm, software definition, and data processing of the SGS and to the observations and scheduling. A description of the AIRS instrument is given in a companion paper(Amiaux et al. this session). In preparation of the Ariel future observations, science schools are annually organized for the training of new PhD students or post-doctoral. The first French Ariel school in 2019 has already been followed by the publication of 4 papers (ARESI, II, III, IV) References Ariel Definition Study Report ESA-SCI (2020) in press. Tinetti, Giovanna, Drossart, Pierre; Eccleston, Paul et al., A chemical survey of exoplanets with ARIEL. 2018ExA, 46, 135T Puig, Ludovic, Pilbratt, Göran, et al. The Phase A study of the ESA M4 mission candidate ARIEL. 2018ExA, 46,211P Encrenaz, Thérèse, Tinetti, G., Coustenis, A. Transit spectroscopy of temperate Jupiters with ARIEL: a feasibility study. 2018ExA, 46, 31E Edwards, Billy, Changeat, Quentin, et al. ARES I: WASP-76 b, A Tale of Two HST Spectra 2020AJ, 160, 8E Skaf, Nour, Bieger, Michelle Fabienne, et al. ARES II. Characterizing the Hot Jupiters WASP-127 b, WASP-79 b, and WASP-62b with the Hubble Space Telescope 2020AJ, 160, 109S Pluriel, William; Whiteford, Niall, et al. ARES III. Unveiling the Two Faces of KELT-7 b with HST WFC3 2020AJ, 160, 112P Gloria Guilluy, Amelie Gressier, et al. ARES IV: Probing the Atmospheres of the Two Warm Small Planets HD 106315 C and HD 3167 C with HST/WFC3 CAMERA. Submitted to AJ.