Ariel will survey the atmosphere of approximately 1,000 transiting and eclipsing planets throughout its expected four-year mission.
The target planets will vary in size from gas giants to mysterious sub-Neptunes and super-Earths orbiting stars of various spectral classes. Ariel will focus on "hot" planets (temperatures in excess of 400 K, 120°C) with a well-mixed, dynamic atmosphere.
Ariel will be able to detect molecules such as water, methane, carbon monoxide, carbon dioxide, ammonium hydroxide and cyanide, as well as measure the chemical composition and structure of these planetary atmospheres and detect clouds. It will also be able to provide meteorological data by observing some planets over long periods. Finally, scientists will be able to deduce the composition of the planet cores from the temperature and composition of the atmosphere.
Ariel consists of a space telescope with an elliptical primary mirror (1.10 x 0.73 metres). It will host two instruments to analyse the planets' atmospheres.
The Ariel InfraRed Spectrometer (AIRS) covers wavelengths ranging from 1.95 to 7.8 microns, with a spectral resolution R=30-200.
A Fine Guidance System (FGS) covers the 0.5- to 1.2-micron range with photometric channels and a low-resolution spectrograph bridging the gap from 1.2 to 1.95 microns.
The instrument payload will be passively cooled to 55 K (–218°C) by thermal shields and the AIRS detectors actively cooled to an operating temperature of 35 K (-238°C).
The mission is coordinated by Principal Investigator Giovanna Tinetti and the United Kingdom Space Agency who lead a consortium of over 60 institutes from 15 European countries. France and Italy are the two main partners, with many contributions from across Europe: Austria, Belgium, Czech Republic, Denmark, Germany, Hungary, Ireland, Netherlands, Poland, Portugal, Spain and Sweden. The United States are supplying FGS components through NASA.
The French team comprising the CNES, CEA and CNRS is responsible for designing, building and delivering the AIRS. CEA-Irfu is managing the project, with major contributions from the laboratories of the CNRS and its partners: the Institute of Spatial Astrophysics (IAS), the Laboratory of Space Studies and Astrophysics Instrumentation (LESIA) and the Paris Institute of Astrophysics (IAP). The CNES, the contracting authority, offers its expertise as and when required. French laboratories are also involved in preparing and analysing the data from Ariel, and in the scientific operation of the mission.