ARIEL (Atmospheric Remote‐sensing Infrared Exoplanet Large‐survey) mission
In March 2018, ESA selected ARIEL as part of its Cosmic Vision plan. The mission addresses one of the key themes of Cosmic Vision: What are the conditions for planet formation and the emergence of life? The nature of planets orbiting stars in other systems will be the focus for ESA’s fourth medium-class science mission, to be launched in mid 2028. 1)
Thousands of exoplanets have already been discovered with a wide range of masses, sizes and orbits, but there is no apparent pattern linking these characteristics to the nature of the parent star. In particular, there is a gap in our knowledge of how the planet’s chemistry is linked to the environment where it formed, or whether the type of host star drives the physics and chemistry of the planet’s evolution.
ARIEL will address fundamental questions on what exoplanets are made of and how planetary systems form and evolve by investigating the atmospheres of hundreds of planets orbiting different types of stars, enabling the diversity of properties of both individual planets as well as within populations to be assessed.
Observations of these worlds will give insights into the early stages of planetary and atmospheric formation, and their subsequent evolution, in turn contributing to put our own Solar System in context.
“ARIEL is a logical next step in exoplanet science, allowing us to progress on key science questions regarding their formation and evolution, while also helping us to understand Earth’s place in the Universe,” says Günther Hasinger, ESA Director of Science. ”ARIEL will allow European scientists to maintain competitiveness in this dynamic field. It will build on the experiences and knowledge gained from previous exoplanet missions.”
The mission will focus on warm and hot planets, ranging from super-Earths to gas giants orbiting close to their parent stars, taking advantage of their well-mixed atmospheres to decipher their bulk composition. Ariel will measure the chemical fingerprints of the atmospheres as the planet crosses in front of its host star, observing the amount of dimming at a precision level of 10–100 parts per million relative to the star. As well as detecting signs of well-known ingredients such as water vapor, carbon dioxide and methane, it will also be able to measure more exotic metallic compounds, putting the planet in context of the chemical environment of the host star.
For a select number of planets, ARIEL will also perform a deep survey of their cloud systems and study seasonal and daily atmospheric variations.
ARIEL’s meter-class telescope will operate at visible and infrared wavelengths. It will be launched on ESA’s new Ariane 6 rocket from Europe’s spaceport in Kourou in mid 2028. It will operate from an orbit around the second Lagrange point, L2, 1.5 million kilometers directly ‘behind’ Earth as viewed from the Sun, on an initial four-year mission.
Following its selection by ESA’s Science Program Committee, the mission will continue into another round of detailed mission study to define the satellite’s design. This would lead to the ‘adoption’ of the mission – presently planned for 2020 – following which an industrial contractor will be selected to build it.
ARIEL was chosen from three candidates, competing against the space plasma physics mission THOR (Turbulence Heating ObserveR) and the high-energy astrophysics mission XIPE (X-ray Imaging Polarimetry Explorer).
The mission's Principal Investigator is Professor Giovanna Tinetti, from UCL (University College London), who will lead the mission science. STFC (Science and Technology Facilities Council) of RAL Space will manage the overall European consortium building the payload, which will be assembled and tested in Harwell, Oxfordshire. Other UK involvement will come from Cardiff University, Oxford University and the UK Astronomy Technology Center. UK industry can also expect to be involved in the satellite's construction and operations. 2)
Figure 1: A hot planet transits in front of its parent star in this artist impression of an exoplanet system (image credit: ESA/ATG medialab, CC BY-SA 3.0 IGO)
In April 2019, the ARIEL project launched a global competition series to find innovative solutions for the interpretation and analysis of exoplanet data. The first ARIEL Data Challenge invites professional and amateur data scientists around the world to use Machine Learning (ML) to remove noise from exoplanet observations caused by starspots and by instrumentation. 3)
The ARIEL Data Challenge Series was announced at the UK Exoplanet Community Meeting (EXOM) 2019 in London.Details of the ARIEL Data Challenge Series 2019 are available at: http://ariel-datachallenge.space
”The aim of launching the ARIEL Data Challenges is to build a wide international collaboration from our own research community and from other data analysis fields to develop a diverse range of solutions to the complex computational problems faced by the mission," said Prof Giovanna Tinetti of UCL, who is principal investigator of the ARIEL mission.
Figure 2: The ARIEL Data Challenge Series 2019 (image credit: ARIEL Consortium)
• December 7, 2021: ESA and Airbus have signed a contract to move forward with the design and construction of the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, Ariel, planned for launch in 2029. 4)
- Ariel is the third in a trio of dedicated exoplanet missions conceived by ESA focusing on various aspects of this rapidly evolving subject area. It will follow Cheops, which launched in 2019, and Plato, scheduled for launch in 2026.
- Ariel will study the composition of exoplanets, 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 exoplanets, linking them to the host star’s environment. This will fill a significant gap in our knowledge of how the planet’s chemistry is linked to the environment where it formed, or if and how the type of host star drives the physics and chemistry of the planet’s evolution.
Figure 3: Artist's rendition of ESA's Ariel exoplanet satellite (image credit: Airbus)
- Observations of these worlds will give insights into the early stages of planetary and atmospheric formation, and their subsequent evolution, in turn contributing to the understanding of our own Solar System. They could help us find out whether there is life elsewhere in our Universe and if there is another planet like Earth.
- “With this milestone for the Ariel mission we celebrate the continuation of the outstanding relationship with our industry partners to keep Europe at the forefront of excellence in the field of exoplanet research well into the next decade and beyond,” says Günther Hasinger, ESA’s Director of Science.
- The contract was celebrated between the two parties with a small ceremony at ESA headquarters in Paris on 6 December.
- “It is an exciting phase in a mission to move forward with a chosen design and assign a prime contractor,” adds Jean-Christophe Salvignol, ESA’s Ariel Project Manager.
- Airbus will lead the European industrial consortium building the satellite and provide expertise and support to ESA for the development of the payload module. The Toulouse facility in France will be the main site for designing, manufacturing and integrating the spacecraft elements, while Airbus Stevenage in the UK will lead the engineering of the avionics, radio frequency communication and electrical design of the platform.
Figure 4: ESA’s new and future exoplanet missions. ESA’s trifecta of dedicated exoplanet missions – Cheops, Plato and Ariel – will also be complemented with the upcoming James Webb Space Telescope mission (image credit: ESA)
- “Airbus has extensive experience of leading ground-breaking science missions, including Juice, Gaia, Solar Orbiter, Lisa Pathfinder and Cheops, on which we are building for ESA’s latest science mission, Ariel,” said Jean-Marc Nasr, head of Space Systems at Airbus.
Figure 5: Artist impression of an exoplanet system (image credit: ESA)
• November 12, 2020: ESA’s exoplanet mission Ariel, scheduled for launch in 2029, has moved from study to implementation phase, following which an industrial contractor will be selected to build the spacecraft. 5)
- Ariel, the Atmospheric remote-sensing infrared exoplanet large-survey mission, addresses one of the key themes of ESA’s Cosmic Vision program: What are the conditions for planet formation and the emergence of life? Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of around 1000 planetary atmospheres simultaneously in visible and infrared wavelengths.
- It is the first mission dedicated to measuring the chemical composition and thermal structures of exoplanets, linking them to the host star’s environment. This will fill a significant gap in our knowledge of how the planet’s chemistry is linked to the environment where it formed, or whether the type of host star drives the physics and chemistry of the planet’s evolution.
- Observations of these worlds will give insights into the early stages of planetary and atmospheric formation, and their subsequent evolution, in the process also helping us to understand how our own Solar System fits into the bigger picture of the overall cosmos.
- Ariel was selected in 2018 as the fourth medium-class science mission in ESA’s Cosmic Vision plan. It was ‘adopted’ by ESA during the Agency’s Science Program Committee meeting on 12 November, paving the way towards construction.
Figure 6: The first discoveries of exoplanets in the 1990s, by ground-based observatories, completely changed our perspective of the Solar System and opened up new areas of research that continues today. This infographic highlights the main space-based contributors to the field, including not only exoplanet-dedicated missions, but also exoplanet-sensitive missions, past, present and future (image credit: ESA)
- “Ariel will enable planetary science far beyond the boundaries of our own Solar System,” says Günther Hasinger, ESA’s Director of Science. “The adoption of Ariel cements ESA’s commitment to exoplanet research and will ensure European astronomers are at the forefront of this revolutionary field for the next decade and well beyond.”
- Ariel will be ESA’s third dedicated exoplanet mission to launch within a ten-year period, with each mission tackling a unique aspect of exoplanet science. Cheops, the Characterizing ExOPlanet Satellite, launched in December 2019, is already producing world-class science, Plato, the PLAnetary Transits and Oscillations of stars mission, will be launched in the 2026 timeframe to find and study extrasolar planetary systems, with a special emphasis on rocky planets around Sun-like stars in the habitable zone – the distance from a star where liquid water can exist on a planet’s surface. Ariel, planned to launch in 2029, will focus on warm and hot planets, ranging from super-Earths to gas giants orbiting close to their parent stars, taking advantage of their well-mixed atmospheres to decipher their bulk composition.
- In the coming months, industry will be asked to make bids to supply spacecraft hardware for Ariel. Around summer next year, the prime industrial contractor will be selected to build it.
- The mission’s payload module, which includes a one meter-class cryogenic telescope and associated science instruments, is provided by the Ariel Mission Consortium. The consortium comprises more than 50 institutes from 17 European countries. NASA also contributes to the payload.
- “After an intensive period working on the preliminary design concepts and on the consolidation of the required technologies to demonstrate the mission feasibility, we are ready to move Ariel forward to the implementation stage,” says ESA’s Ariel study manager Ludovic Puig.
Figure 7: Detecting exoplanets with the transit method. This animation shows a planet whose orbit is aligned in such a way that it crosses the disc of its parent star as seen from Earth: during these transits, the star appears less bright. By detecting these periodic decreases of brightness over time, it is possible to detect the presence of the planet orbiting the star (video credit: ESA)
- The telescope’s spectrometers will measure the chemical fingerprints of a planet as it crosses in front of – ‘transits’ – its host star, or passes behind it – an ‘occultation’. The measurements will also enable astronomers to observe the dimming of the host star by the planet with a precision of 10–100 parts per million relative to the star.
- Ariel will be able to detect signs of well-known ingredients in the planets’ atmospheres such as water vapor, carbon dioxide and methane. It will also detect more exotic metallic compounds to decipher the overall chemical environment of the distant solar system. For a select number of planets, Ariel will also perform a deep survey of their cloud systems and study seasonal and daily atmospheric variations.
- “With Ariel we will take exoplanet characterization to the next level by studying these distant worlds both as individuals and, importantly, as populations, in much greater detail than ever before possible,” says ESA’s Ariel study scientist Göran Pilbratt.
- “Our chemical census of hundreds of solar systems will help us understand each planet in context of the chemical environment and composition of the host star, in turn helping us to better understand our own cosmic neighborhood,” adds ESA’s Ariel project scientist Theresa Lueftinger.
- “We’re pleased to enter the implementation phase of the Ariel mission,” says ESA’s Ariel project manager Jean-Christophe Salvignol. “We’re moving towards the optimal spacecraft design for answering fundamental questions about our place in the cosmos.”
- Ariel is planned for launch on ESA’s new Ariane 6 rocket from Europe’s spaceport in Kourou, French Guiana. It will operate from an orbit around the second Sun-Earth Lagrange point, L2, 1.5 million kilometers directly ‘behind’ Earth as viewed from the Sun, on an initial four-year mission. The ESA-led Comet Interceptor mission will share the ride into space.
Launch: The Ariel spacecraft is anticipated to launch on ESA’s new Ariane 6, together with the Comet Interceptor mission (Ref. 4).
Orbit: Ariel will operate from the second Lagrange point (L2), 1.5 million km directly ‘behind’ Earth as viewed from the Sun, on an initial four year mission. Thanks to its very stable thermal and mechanical design, the spacecraft will be able to carry out long term observations of the same exoplanet system for a duration of between 10 hours and up to 3 days.
“Launch may still seem a long way ahead for Ariel, but we are firmly on the road to a wonderful science mission, which will further broaden our understanding of solar system science well beyond the boundaries of our own planetary neighborhood,” says Theresa Lueftinger, ESA Ariel Project Scientist.
The mission’s payload module, which includes a one meter-class cryogenic telescope and associated science instruments, is provided by the Ariel Mission Consortium. The consortium comprises more than 50 institutes from 17 European countries. NASA also contributes to the payload.
1) ”ESA's next science mission to focus on nature of exoplanets,” ESA, 20 March 2018, URL: http://m.esa.int/Our_Activities/Space_Science/
2) ”UK team to lead European mission to study new planets,” Space Daily, 21 March 2018, URL: http://www.spacedaily.com/reports/UK_team_to_lead_European_mission_to_study_new_planets_999.html
”ARIEL Data Challenge Series launched to build global community
for exoplanet data solutions,” 17 April 2019, URL: https://arielspacemission.files.wordpress.com
4) ”Airbus will build ESA’s Ariel exoplanet satellite,” ESA Science & Exploration, 7 December 2021, URL: https://www.esa.int/Science_Exploration/Space_Science
5) ”Ariel moves from blueprint to reality,” ESA Science & Exploration, 12 November 2020, URL: https://www.esa.int/Science_Exploration/Space_Science/Ariel_moves_from_blueprint_to_reality
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).