ARIEL (Atmospheric Remote-sensing Exoplanet Large-survey) is an ambitious mission planned to answer fundamental questions about how planetary systems form and evolve by investigating the atmospheres of a statistically significant sample pf planets orbiting stars other than the Sun. It was selected by the European Space Agency (ESA) for its M4 medium class science mission, due for launch in 2028.
The essential nature of exoplanets is still something of a mystery: despite finding thousands of exoplanets no discernible pattern has been found linking the presence, size or orbital parameters of a planet to what its parent star is like.
ARIEL is designed to study a statistically large sample of exoplanets to answer questions, such as how is the chemistry of a planet linked to the environment in which it forms, or is its birth and evolution driven by its host star. During its 3.5-year mission, ARIEL will observe over 1000 exoplanets ranging from hot-Jupiters to super-Earths in a wide variety of environments. While some of the planets observed may be habitable, the main focus of the mission will be on exotic, hot, giant and Neptune-size planets in orbits very close to their star.
ARIEL will have a meter-class mirror to collect infrared light from distant star systems and to focus it to a spectrometer. This will cover a wavelength range from 0.6 to 7 micro-meters, which is ideally suited to extract the chemical fingerprints of gases in the planets’ atmospheres, as the planet passes in front or behind the star, in which is called the transit or occultation.
The spacecraft will be placed in orbit at Lagrange Point 2 (L2), a gravitational balance point beyond the Earth’s orbit, where the spacecraft is shielded from the Sun and has a clear view of the whole night sky. This will maximise its options for observing exoplanets discovered previously by other missions.
The ARIEL mission concept is developed by a consortium of more than 70 institutes from 17 countries. The IEEC is one of the co-PI institutes and leads the Spanish contribution, which also includes the Instituto de Astrofísica de Canarias and the Universidad Politécnica de Madrid. The IEEC participates in several aspects of the mission. On the scientific side, we study the effects of stellar activity on transit spectroscopy, due to the spectrophotometric variability caused by starspots, and we collaborate in the selection of the target sample. On the technical side, we lead the mission planning task by using our expertise on scheduling techniques to optimize operations and study the impact of mission design requirements. Also, we are responsible for the design of the Telescope Control Unit (which monitors the telescope sensors and operates the secondary mirror) and the design and manufacturing of the mechanisms of the secondary mirror refocusing system (M2M).