Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - FOUR ACES (Future of upper atmospheric characterisation of exoplanets with spectroscopy)
Teaser
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...
Summary
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
The beginning of this first period was dedicated to hiring the team: I hired two PhD students (J. Seidel and L. Dos Santos in June 2017 and September 2017, respectively) and three postdocs (V. Bourrier, J. Hoeijmakers and T. Kuntzer in October 2017, November 2017 and March 2018, respectively). All work packages are staffed according to plan and fully operational.
Over this first period, the team has produced 27 articles in international refereed journals. Milestone results include:
- 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 first 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).
All these results have been the object of press releases and media coverage.
We are providing in attachment the artist\'s impressions commissioned to illustrate these milestone results. These illustrations have been made with a will to mix accurate science and imagination to capture the attention and the imagination of the public (while stressing that they are not real images; a common issue with realistic artist\'s impressions). They have been disseminated through the social networks and at several exhibitions.
Final results
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. 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.