The Exoplanets group concentrates on the observation and characterisation of planets outside our solar system, and focuses in particular on the study of atmospheric structure and evolution. To this end, the group makes use of a wide range of observational facilities, including the Hubble Space Telescope and the 8-m ESO Very Large Telescopes.

The group analyses mostly transiting planets, for which atmospheric studies are possible. Transiting planets offer unique opportunities for the study of exoplanet atmospheres, as we can observe them passing in front and behind their host star. During an occultation, the host star blocks the flux emerging from the planetary dayside. By comparing the flux in- and out-of occultation, one can measure the planet-to-star brightness ratio. Observations in different pass-bands yield a measure of the planetary emission spectrum, which encodes information on planetary atmospheric structure, composition, and energy balance.

Transit observations allow one to study the composition of planetary atmospheres in greater detail, as the stellar light is filtered through the planetary atmosphere on its way to the observer. Then, spectrally resolved transit observations allow one to probe the planetary transmission spectrum and infer the elemental and molecular signatures contained in it.

IWF is involved in a number of projects using the above techniques to study bright transiting systems with close-in planets. Multi-wavelength observations from ground- and space-based facilities (ESO/VLT, Gemini, Spitzer, and HST) are used to study the atmospheres of key exoplanets in transmission and emission, and detect the absorption and scattering signatures of chemical elements, molecules and haze components. The group employs ultraviolet observations obtained with HST to characterize the physical and chemical properties of the upper atmosphere of close-in planets to constrain atmospheric escape and evolution models. Finally, the star–planet interaction phenomenon is studied by measuring stellar activity at different wavelengths looking for magnetic and physical interactions (e.g., planet-to-star mass transfer).

The group is also heavily involved in the preparations for the CHEOPS (CHaracterizing ExOPlanets Satellite) and CUTE (Colorado Ultraviolet Transit Experiment) missions and the future exploitation of their data. CHEOPS is the first European mission fully dedicated to the study of exoplanets. The main goal of the mission is the detection and analysis of transits for stars already known to host planets. CUTe is a NASA 6U CubeSat mission dedicated to the study of exoplanet atmospheric escape through the observation of planetary transits at ultraviolet wavelengths.