image Stellar radiation, magnetism and exoplanets image Stellar radiation, magnetism and exoplanets image Stellar radiation, magnetism and exoplanets image Stellar radiation, magnetism and exoplanets

Stellar radiation, magnetism and exoplanets

The continuous flow of matter that escapes from stars, known as stellar winds, carries particles along the stellar magnetic field lines and permeates the entire exoplanetary system, interacting with exoplanets in different ways. In particular, weakly or non-magnetised planets, such as Mars, can have their atmosphere eroded, or even stripped away, by the stellar wind. In magnetised planets, such as the Earth, their magnetic field acts as a shield against the stellar wind producing a bow shock between the two magnetospheres. To characterise the interactions between stars and exoplanets, Arago will study stellar winds and their impact on exoplanets.
In addition, exoplanets orbiting close to their host star are subject to intense stellar irradiation. This increased heating causes the planetary atmosphere to inflate and escape. This can be probed during planetary transits, when the high-energy stellar radiation is transmitted through the exoplanet's atmosphere. Finally, photochemistry due to UV stellar irradiation can mimic the signature of biomarkers in the atmosphere of exoplanets.
Star-planet interactions can furthermore be probed thanks to anomalous stellar activity enhancement synchronised with the orbiting planet. Close-in planets are expected to have the strongest interactions with their host star, producing tidal bulges in the star that drive flows and waves, and thus influence activity. Likewise, the interaction between the stellar and planetary magnetic fields and magnetospheres can increase stellar activity and produce additional heating of the chromosphere and corona. It is therefore crucial to characterise the host star and the star-planet interactions to interpret the atmospheric spectra of exoplanets.
Understanding the various aspects of star-planet interactions and their impact, e.g., on stellar dynamics and evolution and on the planet\u2019s atmosphere and orbital evolution, will allow us to define the environmental conditions for the emergence of life on rocky planets. Specifically, Arago will study the impact of stellar properties on space weather, irradiation on the planetary surface, and biomarkers. Attention will be given to systems similar to the Sun-Earth system as well as to young or evolved Suns, in order to infer insights into the history of our own Solar system.