Detecting Biosignatures with RISTRETTO and ANDES


PI: Prof. Christophe Lovis, Prof. Emeline Bolmont

Collaborators: The RISTRETTO and ANDES consortium, the Generic PCM developers’ team (LMD, Paris), Jérémy Leconte (LAB, Bordeaux)

Funding: NCCR PlanetS

Dates: 01/08/2022 – 31/07/2026

A major objective of the exoplanet field is to characterize the atmospheres and surfaces of rocky exoplanets orbiting within the habitable zone of their host star. This will allow us to place the Earth in the broader context of the terrestrial planet population in our Galaxy, and ultimately probe the occurrence of life elsewhere in the Universe. From an observational point of view, accessing temperate rocky exoplanets is extremely challenging due to their small sizes and weak atmospheric signatures. JWST is currently opening the way by studying a number of such objects using transit spectroscopy, in particular the TRAPPIST-1 system. However, there are intrinsic limitations to the transit spectroscopy approach which call for alternative methods to be explored. From the ground, a promising new avenue is the combination of high contrast and high spectral resolution, which enables the direct detection of exoplanets close to the diffraction limit of the telescope. The Department of Astronomy is involved in three upcoming instruments that will implement this technique: RISTRETTO at the VLT, ANDES at the ELT, and in the farther future PCS also at the ELT.

Two aspects are being pursued in this project: the development of the instrument and the preparation for future observations in terms of scientific return.

For the first aspect, several engineers and technicians from the Department of Astronomy are working on RISTRETTO to develop the spectrograph and the adaptive optics system. The spectrograph is currently in the manufacturing phase, and will be integrated and tested in 2024-2025. The front-end including the adaptive optics system is in a preliminary design phase. It will feature a novel coronagraphic integral-field unit concept working at the diffraction limit of the telescope, which will allow RISTRETTO to resolve Proxima-b and other exoplanets from their host stars.

For the second aspect, climate simulations of the sample of rocky planets these instruments will target should be performed. As little is known about these planets, we are investigating how factors like atmospheric composition, rotation and tidal heating impact the climate of these planets. To do so, we are using the generic PCM to study these effects and determine if they can be observed.



  • One PhD (Muskan Shinde): Development of the adaptive optics for RISTRETTO
  • One PhD (Mathilde Houelle): Climate simulations of the terrestrial planets which will be targeted by ANDES.