ARIEL is a European mission being planned to answer fundamental questions about how planetary systems form and evolve. ARIEL will investigate the atmospheres of several hundreds planets orbiting distant stars. It is one of three candidate missions selected by the European Space Agency (ESA) for its next medium class science mission, due for launch in 2026. The ARIEL mission concept has been developed by a consortium of more than 50 institutes from 12 countries, including UK, France, Italy, Germany, the Netherlands, Poland, Spain, Belgium, Austria, Denmark, Ireland, Portugal.

During its 3.5-year mission, ARIEL will observe hundreds of exoplanets ranging from Jupiter- and Neptune-size down to super-Earth and Earth-size in a wide variety of environments. The main focus of the mission will be on exotic, hot planets in orbits very close to their star. Hot exoplanets represent a natural laboratory in which to study the chemistry and formation of exoplanets. In cooler planets, different gases separate out through condensation and sinking into distinct cloud layers. The scorching heat experienced by hot exoplanets overrides these processes and keeps all molecular species circulating throughout the atmosphere.

ARIEL will have a meter-class mirror to collect visible and infrared light from distant star systems. The analysis of ARIEL spectra and photometric data will allow to extract the chemical fingerprints of gases and condensates in the planets’ atmospheres, including the elemental composition for the most favorable targets. It will also enable the study of thermal and scattering properties of the atmosphere
as the planet orbit around the star.

ARIEL will be placed in orbit at Lagrange Point L2 to maximise the thermal stability and field of regard, and therefore its options for observing exoplanets discovered previously by other missions.