|Cosmic Vision Themes||What are the conditions for planet formation and the emergence of life?|
|Key Science Questions||What are exoplanets made of?
How do planets and planetary systems form?
How do planets and their atmospheres evolve over time?
|Primary goal||To perform a large-scale survey of a statistically well defined, diverse sample of about 1000 exoplanets, ranging from gas giants to rocky planets and preferentially in the hot to temperate zones of F- to M-type stars, and compile a catalogue of planetary compositions and properties|
|Wavelengths||Visible and infrared photometry: 0.50-0.55 µm, 0.8-1.0 µm, 1.0-1.2 µm
Infrared spectroscopy: two medium-resolution channels (1.95-3.9 µm and 3.9-7.8 µm) and one low-resolution channel (1.25-1.95 µm)
|Payload||An off-axis Cassegrain telescope (elliptical primary mirror of 1.1m x 0.7m, effective collecting area 0.64 m2), diffraction limited at 3 μm
Ariel medium-resolution InfraRed Spectrometer (AIRS) covering the 1.95 – 7.80 μm wavelength range
A Fine Guidance System (FGS) module with three narrow-band visible to near-infrared photometer channels (two used as guidance sensors as well as for science) and a low-resolution near-infrared spectrometer
|Orbit||An eclipse-free (Earth-Moon) large amplitude halo orbit around the Sun-Earth L2 point|
|Lifetime||Nominal 4-year operational timeline, with a potential extended science operations phase lasting for two further years|
|Launch||Ariel is foreseen to launch in 2029|
|Type||Medium (M-class) mission|
Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, will study how planets and planetary systems form and evolve by surveying a large, diverse sample of approximately 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. In March 2018, Ariel was selected as M4, the fourth medium-sized (M-class) mission in ESA’s Cosmic Vision Plan.
Ariel will address one of the key questions within ESA's 2015-2025 Cosmic Vision Plan: What are the conditions for planet formation and the emergence of life?
Despite the large numbers of different exoplanets that have been discovered to date, there is still no clear link between the presence, size, or orbital parameters of a planet and the nature of its parent star. To understand more about exoplanets and exoplanetary systems, an unbiased large-scale survey of exoplanets is required — to perform such a survey is Ariel's key observational objective.
Ariel will study the nature of the exoplanets themselves, both as individuals and as populations, and monitor their host stars for stellar activity. Using both transit and eclipse spectroscopy (in near infrared wavelengths) and photometry (in visible wavelengths), Ariel will explore the properties and atmospheres of approximately 1000 transiting planets, including preferentially warm and hot gas giants, Neptunes, super-Earths, and Earth-sized planets, and seek to understand what planets are made of and how planetary systems form and evolve.