Modelling the performance of the instruments of the Exo-planet characterization satellite Ariel

To date there are in excess of three thousand confirmed exoplanets and two thousand more awaiting confirmation, with many more to come thanks to ongoing (TESS, CHEOPS) and upcoming (PLATO) missions. To truly understand and characterize these planets, ARIEL, a satellite due to launch in 2028, will perform transit spectroscopy of a set of such planets to establish their atmospheric composition. This ESA mission combines two instruments ranging from the visible to mid-infrared wavelengths, with the shorter wavelengths also having the dual purpose of aiding in fine tuning the spacecraft pointing. Its operation in the Sun-Earth second lagrangian point combined with low temperature operation and stable pointing requirements provide a set of challenges for a spectrometer. These are being addressed by an international consortium of 17 countries, producing a design for a satellite payload which will perform spectroscopy of approximately 1000 exoplanets in a four-year mission. Even so, detailed modelling of the payload performance and its relation to the spacecraft pointing will be key to make sure that maximum information and efficiency can be extracted from the ARIEL data once it is launched.