ARIEL is an ambitious mission planned to answer fundamental questions about how planetary systems form and evolve by investigating the atmospheres of several hundred planets orbiting stars other than the Sun. It is one of three candidate missions selected by the European Space Agency (ESA) for its next medium class science mission, M4, due for launch in 2026. The essential nature of exoplanets is still something of a mystery: despite finding nearly 4000 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 500 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 planets in orbits very close to their star, or orbiting stars much brighter than our Sun. 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 8 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 maximize its options for observing exoplanets discovered previously by other missions.
Aim of our participation
The ARIEL mission concept is developed by a consortium of more than 50 institutes from 12 countries. The Institute of Space Sciences is one of the co-I institutes and participates in several aspects of the mission. In 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, the entire Instrument Control Unit simulator, and the mechanisms of the secondary mirror refocusing system.
The ARIEL mission was selected as an ESA M4 candidate in late 2015. The Institute of Space Sciences team contributes to the Telescope Control Unit (TCU) design, a mission-critical subsystem devoted to thermal diagnostics, and calibration lamp and secondary mirror control. The TCU is included in the Warm Front-end Electronics package and is a critical companion of the Instrument Control Unit. The Institute of Space Sciences has also been leading the design of the mission planning strategy that is a key building block of the Science Operations Assumptions Document (SOAD) and is the basis to define the Science Ground Segment of the mission. The mission planning strategy has been derived from an exhaustive mission performance analysis that has been elaborated using Artificial Intelligence technologies (i.e., Evolutionary Algorithms). The latter has been carried out taking into account the survey design and the multiple scheduling scenarios that maximize the scientific return and properly balance the scientific return and the operation optimization for the full estimated lifetime of ARIEL. The final mission proposal was submitted for the ESA Mission Selection Review (MSR) in March 2017. The outcome of the Assessment Phase of the candidate missions was evaluated by a dedicated Senior Science Committee that issued a recommendation in October 2017 to select the ARIEL mission for the M4 launch slot. This is now pending approval by the Space Program Committee of ESA expected to take place in March 2018.
Senior Institute members involved
, J. Colomé