[Paper Review] Ariel: Enabling planetary science across light-years

G. Tinetti, Paul Eccleston+316 more|arXiv (Cornell University)|Apr 10, 2021

Spacecraft Design and Technology27 citations

TL;DR

Ariel is a 2029 ESA medium-class mission designed to survey about 1000 exoplanets in visible and infrared to determine their chemical compositions and thermal structures.

ABSTRACT

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 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. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution.

Motivation & Objective

• Motivate a mission to study exoplanet atmospheres and formation history beyond the Solar System.
• Enable statistical planetary science by observing a diverse exoplanet sample.
• Provide measurements of chemical compositions and thermal structures across many planets.
• Demonstrate a mission architecture that achieves stable, broad spectral coverage with infrared capabilities.

Proposed method

• Use an off-axis Cassegrain telescope with a 1100 mm by 730 mm ellipse primary mirror.
• Operate two simultaneous instruments, FGS and AIRS, covering 0.5–7.8 μm.
• Place the spacecraft in an L2 orbit for thermal stability and wide field-of-regard.
• Passively cool the payload module with V-Groove radiators; actively cool AIRS detectors with a Ne JT cooler.
• Develop the payload through a consortium of institutions across multiple ESA countries and NASA.

Experimental results

Research questions

• RQ1 How does the atmospheric composition of a statistically significant sample of exoplanets correlate with planetary formation and evolutionary pathways?
• RQ2 What are the thermal structures of transiting exoplanets, and how do they vary with star type, planet mass, and orbit?
• RQ3 Can a large, homogeneous spectral dataset constrain models of planetary atmospheres and formation scenarios across diverse exoplanets?
• RQ4 What pipeline and instrumentation performance are required to achieve precise chemical and thermal measurements across 0.5–7.8 μm?

Key findings

• Ariel is adopted as the fourth medium-class mission in ESA’s Cosmic Vision programme and targeted for launch in 2029.
• The mission will survey about 1000 extrasolar planets in visible and infrared wavelengths.
• Ariel uniquely targets chemical composition and thermal structures of hundreds of transiting exoplanets.
• The payload comprises an off-axis Cassegrain telescope and two instruments (FGS and AIRS) covering 0.5–7.8 μm simultaneously.
• The spacecraft is optimally placed at L2 with passive cooling for most hardware and active Ne JT cooling for AIRS detectors.
• The Ariel payload is developed by a broad consortium spanning 16 ESA countries and includes NASA contributions; the study report was ESA-reviewed in 2020.