EXOPLANETS | Space instruments & demonstrators

EXOPLANETS | Space instruments & demonstrators

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 one of the three candidate missions which compete for ESA's fourth M-class mission, with a launch date in 2025. ARIEL would analyze the atmospheres of at least 500 planets orbiting close to nearby stars, to determine their chemical composition and physical conditions. The results would help scientists better understand planet formation, putting our own solar system in context.

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 the 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 with help of 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 SRON scientist Michiel Min.

With Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large-survey) astronomers will be able to take an important step further on the road to analyzing exoplanets. Ariel will gather spectra of warm planets 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: 1) What are exoplanets made of? 2) How do exoplanets form and evolve?

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


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

ARIEL will be able to study planets with a mass a few times the mass of the Earth (super Earths) 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 be able to take a spectrum of the planet itself. From analyzing the spectrum we can deduce the planets composition, temperature structure and the characteristics of clouds in the atmosphere, if any. Warm exoplanets have well mixed atmospheres. This means that if we study the upper layers of the atmosphere we can be pretty certain that this paints an accurate picture of the the whole atmosphere. Another advantage is that these planets will not have many clouds which will disturb the measurements.


ARIEL will have an infrared spectrometer between 2 and 8 micrometers with a spectral resolution of about 100. A fine guidance sensor will ensure stability of the pointing but will also chart the variations in the stars atmosphere. ARIEL is probably going to use European detectors. SRON will provide the cold front-end electronics for the currently anticipated European detectors in ARIEL.