The European Space Agency (ESA) has given the green light to a space telescope that will study the atmospheres of planets outside our Solar System.


The telescope’s mission is to look at the links between a planet’s chemistry and its environment by charting approximately 1,000 known planets outside our own Solar System, known as exoplanets. The information will provide scientists with a full picture of what exoplanets are made of, how they were formed and how they will evolve.

The Atmospheric Remote-sensing Infrared Exoplanet Large-survey (Ariel) has undergone a rigorous review process throughout 2020 and is now due for launch in 2029.

With funding from the UK Space Agency (UKSA), UK research institutions – including UCL, Cardiff University and the University of Oxford – are playing a critical role in the mission by providing leadership, contributing expertise, vital hardware and software, and shaping its goals.

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The Science and Technology Facilities Council’s (STFC) RAL Space, Technology Department and UK Astronomy Technology Centre have also offered essential support.

Once in orbit, Ariel will rapidly share its data with the general public, inviting space enthusiasts and budding astronomers to use the data to help select targets and characterise stars.

The spectrographs aboard the observatory will study the light that filters through a planet’s atmosphere as it passes across the face of its host star, revealing chemical fingerprints of gases that shroud the body. The instruments will also try to refine estimates of a planet’s temperature.

Ariel will be able to detect signs of well-known ingredients in the planets’ atmospheres such as water vapour, carbon dioxide and methane. For a select number of planets, it will also perform a deep survey of their cloud systems and study seasonal and daily atmospheric variations.

“We are the first generation capable of studying planets around other stars," said Professor Giovanna Tinetti, principal investigator for Ariel from UCL. “Ariel will seize this unique opportunity and reveal the nature and history of hundreds of diverse worlds in our galaxy. We can now embark on the next stage of our work to make this mission a reality.”

Some 4,374 worlds have been confirmed in 3,234 systems since the first exoplanet discoveries in the early 1990s.


This mission will focus on planets unlikely to host life as we know it – from extremely hot to temperate, from gaseous to rocky planets. It will also look at planets orbiting close to their parent stars and those of different masses, particularly ones that are heavier than a few Earth masses.

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What does it mean if an exoplanet is 'habitable'?

All forms of life that we know of depend on one critical component: liquid water. So, in the search for life, astronomers focus on planets where liquid water could exist, which they call 'habitable'.

Every star has a 'habitable zone', also called the 'Goldilocks zone', where it is not too hot and not too cold. A planet in the habitable zone gets the right amount of energy from the star to support liquid water. Any closer in to the star and water would boil, and any further out and it would freeze.

However, this doesn't guarantee that liquid water would exist on a planet in the habitable zone. The planet's atmosphere could be too thick, raising the temperature even higher. And even if liquid water does exist on the planet, habitable doesn't mean inhabited.

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Sara RigbyOnline staff writer, BBC Science Focus

Sara is the online staff writer at BBC Science Focus. She has an MPhys in mathematical physics and loves all things space, dinosaurs and dogs.