Future of upper atmospheric characterisation of exoplanets with spectroscopy

Project Information

FOUR ACES

Grant agreement ID: 724427

DOI

10.3030/724427

Project closed

EC signature date 27 January 2017

Start date 1 June 2017

End date 31 May 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 999 475,00

EU contribution

€ 1 999 475,00

Coordinated by

UNIVERSITE DE GENEVE
Switzerland

Periodic Reporting for period 4 - FOUR ACES (Future of upper atmospheric characterisation of exoplanets with spectroscopy)

Reporting period: 2021-12-01 to 2023-05-31

Summary of the context and overall objectives of the project

Planets beyond our Solar System (exoplanets) exhibit a huge variety of sizes, levels of insolation and structures. Understanding this diversity is the key to reconstruct the history of all planetary systems, including our own. One key science driver is the possibility of life on another planet. To find out, we analyse the atmospheres of exoplanets, hoping to find chemical disequilibrium in their composition. Finding life on another planet will have a strong impact on how we understand the origin of life on Earth. The main challenges are to find exoplanets similar to Earth, determine whether they are able to host life and probe their atmospheres with sufficient precision to detect their chemical composition. We are able to do that for exoplanets extremely close to their stars, which are too hot to be habitable. Studying these hot exoplanets, we realised that they are losing their atmosphere, which is literally evaporating. Atmospheric evaporation produces huge clouds of gas around the planet, which yield strong observational signatures. In contrast, the signature of atoms or molecules low in the atmosphere of a planet are much more difficult to detect. Therefore, the main idea behind this ERC project is to use atmospheric evaporation as a magnifying glass to probe the atmospheric properties of exoplanets, from gaseous giants to Earth-like planets.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The FOUR ACES core team was composed by the following persons:
- Prof. Vincent Bourrier was a senior postdoctoral fellow within the team (2017-2020); he is now an Assistant Professor at Université de Genève (Switzerland)
- Dr Adrien Deline was a senior postdoctoral fellow within the team (2019-2022); he is now Support Scientist at the CHEOPS Science Operations Centre at Université de Genève (Switzerland)
- Dr Leonardo Dos Santos did his PhD thesis (2017-2021) within the team; he is now an Assistant Astronomer at the Space Telescope Science Institute in Baltimore (USA)
- Dr Jens Hoeijmakers was a postdoctoral fellow within the team (2017); he is now an Associate Senior Lecturer at Lund University (Sweden)
- Dr Thibault Kuntzer was a postdoctoral fellow within the team (2018-2019); he is now an Application Development Engineer at APCO Technologies SA (Switzerland)
- Dr Dominique Petit dit de la Roche was a postdoctoral fellow within the team (2021); she is now a postdoctoral fellow at Université de Genève (Switzerland)
- Dr Julia Seidel did her PhD thesis (2017-2021) within the team; she is now an ESO Fellow at European Southern observatory Santiago (Chile)
The team worked in close collaboration with scientists from the Exoplanet Team of the Department of Astronomy at Université de Genève and in particular with Dr Lorenzo Pino and Dr Martin Turbet. The team was involved in several international consortia, namely the ESPRESSO Consortium and the CHEOPS Consortium. By the end of the action, the team has been involved in 176 articles in international refereed journals. These articles have received over 5,700 citations (source: NASA ADS). The core team members produced 34 of these articles as first authors and two PhD theses. Seven articles were published in high-impact, multidisciplinary journals (Nature or Science); 3 of these were led by the core team members. Publications are freely available on arXiv.org.

Milestone results are
- The theoretical discovery that oceans of water could never condensed at the surface of Venus (Turbet et al. 2021, Nature 598, 276; PR: https://www.unige.ch/communication/communiques/en/2021/y-a-t-il-eu-des-oceans-sur-venus/)
- The detection of transits from a lukewarm, volatile-rich super-earths around a naked eye star (Delrez et al. 2021, Nature Astronomy 5, 775; PR: https://www.esa.int/Science_Exploration/Space_Science/Cheops/Unique_exoplanet_photobombs_Cheops_study_of_nearby_star_system)
- The measurement of the hot temperature of an ultra hot gas giant with the CHEOPS space telescope - the first scientific result of the mission (Lendl et al. 2020, A&A 643, L94; PR: https://sci.esa.int/web/cheops/-/first-results-from-cheops-esa-s-exoplanet-observer-reveals-extreme-alien-world)
- The detection of iron condensation across the nightside of an ultra hot gas giant exoplanet (Ehrenreich et al. 2020, Nature 580, 597; PR: https://www.eso.org/public/news/eso2005/)
- The discovery of a misaligned planetary system, where the planet is evaporating (Bourrier et al. 2018a, Nature 553, 477; PR: https://www.unige.ch/communication/communiques/en/2017/cdp181217/)
- The detection of metallic vapour in a giant exoplanet hotter than a star (Hoeijmakers et al. 2018, Nature 560, 453; PR: https://www.unige.ch/communication/communiques/en/2018/iron-and-titanium-in-the-atmosphere-of-an-exoplanet/).
- The first detection of helium escaping from a bloated exoplanet (Spake et al. 2018, Nature 557, 68) and the first detailed measurement of the shape and dynamics of an escaping cloud of helium around an exoplanet (Allart et al. 2018, Science 362, 1384; PR: https://www.unige.ch/communication/communiques/en/2018/une-planete-gonflee-comme-un-ballon/).
- The detection of a second case of evaporating Neptune-mass exoplanet (Bourrier et al. 2018b, A&A 620, A147; PR: http://hubblesite.org/news_release/news/2018-52).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have demonstrated that atmospheric evaporation is common for Neptune-mass exoplanets and can be strong enough to explain the lack of such planets very close to their stars. This is the first strong clue of the impact that stellar irradiation has on the evolution of exoplanets. We have also opened the way for a new way to probe escaping atmospheres by uncovering the signature of helium in several exoplanets and use 3D models to interpret the signature. This signature is readily observable using high-resolution spectroscopy in the near-infrared, meaning that we can now observe atmospheric escape from the ground (previously, only the Hubble Space Telescope could detect the hydrogen escaping from exoplanets in the ultraviolet). In contrast with the hydrogen signature, the helium signature is unaffected by the interstellar medium and we can thus access most known exoplanets, creating the first big survey for atmospheric evaporation. These ground-breaking results were not expected until the end of the project. We will thus use it to substantially orient the scientific programmes of several new instruments the team is involved with, including ESPRESSO at the VLT and NIRPS at the ESO 3.6m telescope. With ESPRESSO, we could scan the surface of a giant exoplanet; we measured a difference in the chemical composition at two location on the planet. We concluded from this that iron atoms present as a gas on the evening side of the planet must condense (rain or snow) during the night. This provides a new way to trace extreme climates on highly irradiated exoplanets.

Artist's impression representing the dry surface of Venus 4 Gyr ago with all water still in the sky

Artist's impression showing the condensation of iron at the twilight zone of an ultrahot gas giant

Visit "Exoplanets: Art, Science & Fiction" at https://my.matterport.com/show/?m=sv2XDfTu3sQ

Artist's impression showing the orbital misalignment of an evaporating Neptune-mass exoplanet

Artist's impression showing the possible internal structures of exoplanets in the Nu2 Lupi system

Artist's impression showing the detection of escaping helium from a Neptune-mass exoplanet

Artist's impression showing the discovery of metallic vapour on an extremely hot gas giant

Artist's impression representing the CHEOPS space telescope in front of an ultrahot gas giant