ERC Consolidator Grant worth almost €2 million for Paul Mollière
 

Paul Mollière, leader of the independent research group on exoplanet atmospheric modeling and retrieval in Laura Kreidberg's "Astrophysics of Exoplanets" department at the Max Planck Institute for Astronomy (MPIA) in Heidelberg has been awarded one of the highly coveted and lucrative grants from the European Research Council (ERC). His project, entitled "From photons to storms: Revealing the 3D structure of giant exoplanet atmospheres," will be funded by an ERC Consolidator Grant worth almost 2 million euros.

Since the first exoplanet—a planet orbiting another sun-like star—was discovered in 1995, more than 6,000 such alien worlds have been found by 2025. Despite this large number of known exoplanets, studying their atmospheres is a challenge. This is because the signal the planet's atmosphere causes on the telescope detector is tiny when compared to the bright emission of its host star. Yet, methods that reveal this signal exist. One example is to study the  atmospheres of exoplanets during so-called transits. This method takes advantage of the fact that the orbital plane of a planet may happen to be aligned in space in such a way that, as seen from Earth, it can pass in front of its star – similar to what the planets Mercury and Venus occasionally do in our solar system. The periodic dimming of the starlight, and how this dimming varies with wavelength (i.e., the color of the light in which we observe a transit), then reveals the absorption of molecules in the atmosphere of an exoplanet.

But not only transits allow us to study planetary atmospheres, astronomers can use a wide array of approaches. For example, in some cases the planetary emission can be made visible directly (i.e., a picture of the planet can be taken “next to its star”). With the James Webb Space Telescope (JWST) astronomers can study atmospheric effects in greater detail than ever before, and the situation will become even better once the Extremely Large Telescope (ELT) comes online later in this decade. This is highly interesting because the planets in our solar system show that planetary atmospheres are complex 3D systems that evolve over time. While we can observe this in impressive detail on our own planets, such observations are not possible with exoplanets because they are too far away to take pictures of their surfaces — even with the largest telescopes.

However, information on the 3D structure of exoplanet atmospheres is encoded in their spectra. For example, time-dependent flux variations allow us to trace how the atmosphere changes as a planet rotates. When taking such measurements at high spectral resolution we can also see how molecular absorption lines are shifted and deformed over time, which encodes wind speeds and rotation in a planet's atmosphere, due to the well-known Doppler effect.

These effects are detectable at high significance in observations with JWST and the upcoming ELT, opening a new window into the 3D studies of exoplanet atmospheres. Observations will allow us to uncover the intertwined processes that determine atmospheric dynamics (like rotation, radiative forcing, clouds formation and their radiative feedback, disequilibrium chemistry, drag, and much more).

In spite of these awesome observational prospects, no methods exist that can extract the 3D atmospheric properties from the aforementioned observations reliably. This is precisely the aim of Paul Molliere's project, proposed under the acronym VORTEX, which is now being funded by the ERC.

"The incoming data is so rich in information, requiring models of such a high complexity, that state-of-the-art analysis methods have prohibitively long runtimes, while their fidelity is not sufficiently tested. Here VORTEX will come into play: by building a strong and focussed team of experts in atmospheric 3D modeling and fitting, leveraging the latest developments in machine learning inference we will break this fundamental barrier and characterize exoplanet atmospheres in 3D," says Paul Molliere.

The European Research Council has now allocated just under €2 million to the VORTEX project for a period of five years. The project is expected to start in the course of 2026. The substantial funding will make it possible to set up a dedicated team working on the VORTEX goals that is led by Paul Mollière and that will contain two postdocs, and three doctoral students.

The ERC offers various funding programs as part of its program. All applications for funding must demonstrate the excellence of the scientists involved, but above all the outstanding significance of the proposed projects.

Further information:
Paul Mollière's website
ERC press release

KJ/PM