It’s good to see the European Space Agency’s ARIEL mission getting a bit more attention in the media. The Atmospheric Remote-sensing Infrared Exoplanet Large-survey was selected earlier this year as an ESA science mission, scheduled for launch in 2028. Here the goal is to cull a statistically large sample of exoplanets to examine their evolution in the context of their parent stars. Giovanna Tinetti (University College London) is principal investigator.

I would urge seeing ARIEL in the context of a different kind of evolution, that being the gradual growth in our technologies as we continue getting closer to studying the atmospheres of terrestrial-class worlds. For while ARIEL cannot achieve this feat — its focus is on exoplanets of Jupiter-mass down to super-Earths, all on close orbits, with temperatures greater than 320 Celsius — it leverages the fact that high temperature atmospheres keep their various interesting molecules in continual circulation, rather than letting them sink into obscuring layers of cloud. They are thus more easily detected and provide fodder for future work.

Image: Giovanna Tinetti (UCL), principal investigator for ARIEL.

The goal is to study hundreds of transiting exoplanets, looking at the spectra of their atmospheres as they pass in front of their host stars, allowing starlight to filter through the gaseous envelope for analysis. The light emitted by these atmospheres will also be analyzed just before and after the planets pass behind their primaries. Such transmission spectroscopy allows scientists to unlock the composition, temperature and chemical processes at work. No other spacecraft has been so tightly devoted to atmospheric analysis as ARIEL, and here we will be working with a large sample population in search of commonalities and differences. We go from just a few characterized atmospheres to hundreds.

I see that NASA is contributing fine guidance sensors in two photometric bands in an instrument called CASE — Contribution to ARIEL Spectroscopy of Exoplanets — which will observe clouds and hazes at near-infrared as well as visible wavelengths, complementing ARIEL’s other instrument, an infrared spectrometer that operates at longer wavelengths. It will be CASE that measures planetary albedo while examining how clouds influence the composition and other properties of the atmospheres under study. ARIEL should provide abundant insights into how future telescopes can home in on worlds much more like our own.

Image: This artist’s concept shows the European Space Agency’s ARIEL spacecraft on its way to Lagrange Point 2 (L2) – a gravitationally stable, Sun-centric orbit – where it will be shielded from the Sun and have a clear view of the sky. NASA’s JPL will manage the mission’s CASE instrument. Credit: ESA/STFC RAL Space/UCL/Europlanet-Science Office.

Remember that while we await the launch of the James Webb Space Telescope, JWST is by no means a dedicated exoplanet mission, though it will work with a small sample of exoplanets for detailed study as it shares observing time with other investigations. The ARIEL team should be able to draw from JWST’s experience as it homes in on a final target list. Keep in mind as well that ESA’s PLATO mission — PLAnetary Transits and Oscillations of stars — is also in the pipeline, slated for a 2026 launch. As I say, the tools are evolving as our focus sharpens.