ARIEL will characterise the atmospheres of hundreds of planets orbiting stars other than our Sun.
By observing the spectrum of the light blocked by an exoplanet atmosphere, we are able to identify the molecular content of these atmospheres and search for signs of possible clouds. (ESA)

ARIEL is ESA’s fourth M-class mission, with a launch date in 2029. ARIEL will analyze the atmospheres of at least 500 planets in close orbit around their parent star, to determine their chemical composition and physical conditions. The results will help scientists better understand planet formation, putting our own solar system in context. SRON is involved in the calibration and testing of the detectors in ARIEL.

Exoplanet studies constitute a major challenge for today’s telescopes. The reflected light from planets is a great deal weaker than the light coming from the stars they orbit. A popular trick astronomers use – for instance in the PLATO mission – is to measure the decrease in starlight when the planets travel in front of their star (transit method). The measured dip in starlight tells us a lot about the size of the planet. From Earth we can determine the mass of the planet using the Doppler method. This gives a first indication of the planet’s composition: light-weight or heavy material. Click here to see a short film about exoplanets with Michiel Min, head of SRON’s exoplanet programme.

ARIEL (Atmospheric Remote-Sensing Infrared Exoplanet Large-survey) will be able to take the characterization of exoplanets to the next level The space telescope will gather spectra of warm exoplanets we have already discovered using the transit method. These spectra provide us with information on the molecular content of the atmospheres and potential cloud coverage. The fundamental questions SRON scientists will address are:

  • What are exoplanets made of?
  • How do exoplanets form and evolve?

When the mission is selected by ESA, SRON will contribute crucial detector electronics.


ARIEL will measure transits of at least 500 planets in three years. For some planets one transit will be enough to get a good spectrum, whereas others will need up to ten transits. SRON will participate in the analysis and interpretation of the scientific data.

ARIEL will study a broad range of planets: from those of a few Earth masses (super Earths) up to so called hot Jupiters—massive planets that orbit the star closely. By taking a spectrum when the planet is in front of (transit), behind (pure starlight) or beside (star and planetary light) the star, we will get a spectrum of the planet itself. From this we will deduce the planet’s composition, temperature structure and the characteristics of clouds in the atmosphere, if any. ARIEL’s target—warm exoplanets—have well-mixed atmospheres, soif we study the upper layers of the atmosphere we can be pretty certain that this paints an accurate picture of the whole atmosphere. Another advantage of warm planets is that they probably have few clouds disturbing the measurements.


ARIEL will have an infrared spectrometer for wavelengths between 2 and 8 micrometers with a spectral resolution of about 100. A fine guidance sensor will ensure stability of the pointing and chart variations in the planets’ atmospheres. SRON is involved in the calibration and testing of the detectors in ARIEL. Also, scientists from SRON and other institutes in The Netherlands are strongly involved in performance simulation, instrument definition and scientific data analysis for the mission.