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Planet-star interaction

The variability of the host star in extra-solar systems is mostly treated as intrinsic noise while looking for exoplanets. Magnetic active stars, as many M dwarves, are left outside possible targets or undergo a noise reduction strategy to reveal a possible exoplanet signal. Starspots cause line distortions in the RV measurements, while frequent flares may affect the transit technique. Observations in different photometric bands, especially in optical to infrared bands can help to exclude exoplanets candidates: a periodic signal coming from the Active Regions (ARs) can be related to the host star rotation since this is wavelength-dependent, while a transiting exoplanet is related to a non chromatic signal. A further interest is rising since relatively young system (100 Myr) are very active and hitherto excluded from surveys, while they are interesting for studying planetary formation.

Recently, a change of paradigm is ongoing: to consider stellar activity as a significant signal needed to characterize at best the exo-planetary system. High intensity stellar flares and coronal emission from stellar active regions have the potential to strip an otherwise habitable planet of its atmosphere and water. Using our solar system as a Rosetta stone it is possible to infer the boundaries of the host star influence in the system, in terms of interplanetary medium, stellar-planet interaction and particle transport. Ultraviolet photons from the host star influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets. At present, a more in-depth study of the ultraviolet spectra of M dwarfs is needed, in order to predict and interpret the spectra of potentially habitable planets. UV emission from the host star can significantly preclude even the existence of a planetary atmosphere. Another key aspect is the presence of a magnetosphere and the possibility for the exoplanet to be protected from atmospheric erosion by its internal magnetic field. Auroral observations has been observed only in a case for a giant exoplanet, but may help in understanding space weather events in exo-planetary systems.

This very complex physical systems can be studied using an interdisciplinary approach combining knowledge from solar physics, solar system planetary science and climatology communities. One interesting line of investigation is to use planets in our solar system as a benchmark/analog model, therefore using what we know from direct observations (either in situ or from flybys) to infer the properties of planetary systems around other stars.

Related Researchers

F. Berrilli, C. Cagnazzo, D. Galuzzo, S. Ivanovski, A. Mura

Related Projects

WorkPackage P1: Host Star vs Planet Climate

WorkPackage P2: Stellar Activity and Habitability