Publié le 5 décembre 2017

Pascal Tremblin, an ERC starting grant laureate, presents his ATMO project

Pascal Tremblin from CEA Paris-Saclay explains that the James Webb Space Telescope (JWST) will be launched in spring 2019 as the successor to the Hubble Space Telescope. It is expected to revolutionize what astronomers understand from exoplanet atmospheres.

Which molecules are present in the atmosphere of exoplanets? What are their mass, radius and age? Do they have clouds, convection (atmospheric turbulence), or a large-scale circulation induced by the irradiation from their host star? These questions are fundamental in exoplanetology to better understand planet formation and exoplanet habitability.

The ATMO project aims at better understanding the role of convective processes and atmospheric circulation in the chemistry of exoplanets' atmosphere by using numerical simulations of these processes on the largest supercomputers in Europe. Astronomers will then be able to predict and interpret the mass, radius, and chemical composition of exoplanets that will be observed with future missions such as JWST.Example of numerical simulations of fingering convection in the interior of stars - Brown et al. 2013 ApJ 768 34

It has been recently suggested that a well-known convective instability happening in the Earth's ocean, called the "thermohaline" convection and triggered by water salinity gradient, has an analog in extraterrestrial atmospheres: this "fingering" convection could be triggered by chemical transitions. This process is poorly understood in exoplanets. A detailed analysis of the convective instability and its interaction with the atmospheric circulation induced by the irradiation from their host star will be performed in the ATMO project.

Pascal Tremblin aims at performing high-resolution numerical simulations to characterize the impact of convective instability on the temperature gradient of the atmosphere of an exoplanet. This impact can be directly observed in the light spectrum of the exoplanet with visible and infrared telescopes. A quantitative analysis of this process is mandatory before interpreting the light spectrum of the exoplanet to deduce its chemical composition and ultimately the presence of biomarkers.

Interview with Pascal Tremblin, 2017 ERC starting grant holder

Could you present your research background as well as your research activity?

I finished my PhD in 2012 at the department of Astrophysics at CEA Paris-Saclay, studying the impact of massive stars on molecular clouds in the interstellar medium, with hydrodynamics numerical simulations. I then did a three-year postdoc at the University of Exeter (UK) studying chemistry and radiative transfer in exo-atmospheres. I proposed that an analog of thermohaline convection, fingering convection triggered by chemical transitions, can occur in these atmospheres. Since 2015, I have been back at CEA Paris-Saclay with a permanent position as Engineer/Scientist in numerical simulations at the Maison de la Simulation.

You’ve just been granted an ERC Starting grant. Why do you think this funding can be helpful to conduct your research?

With my PhD expertise on hydrodynamics numerical simulations and my postdoc expertise on the physics of exoplanets' atmospheres, the missing part was to link both expertises to perform hydrodynamics numerical simulations of fingering convection. These simulations are extremely difficult and costly in terms of supercomputer resources. This ERC starting grant is the key to build an expert research team on the subject. This team will design the necessary numerical tools and be able to get access to the European largest supercomputers.

What were your reasons for applying for an ERC grant?

My postdoc at the University of Exeter was part of an ERC advanced grant. I have seen from the inside of an ERC project how this type of funding brings resources and the autonomy to conduct research at the highest level.

Where do you see yourself in 2022, at the end of your project?

At the end of the project, I will probably be trying to apply for an ERC Consolidator grant to extend the use of the newly designed numerical tools in the project in other fields of research, e.g. oceanography or atmospheric sciences.

What kind of support did you receive to prepare your proposal ?

I have received strong support from Université Paris-Saclay to write the proposal and to prepare the interview. I am quite sure that it would have been very difficult to get the funding without this support. As scientists, we are quite often too deeply buried in the research and related technical challenges. Advisors at Université Paris-Saclay have helped me to step back and put the science into perspective in order to show to the ERC panel how important my project is.

Given your experience, what advice would you give those who want to apply for this grant?

My advice is to take the time to think and write the proposal. I started this process one year before the call. Then you have the time to write and circulate the B1 part among your colleagues in order to get as much feedback as you can. It is also clearly thanks to this feedback from experts representative of the ERC panel that I was able to get this important funding.


To learn more:

ATMO website: