Scientific rationale

Space weather encompasses the effect of stellar energetic particles, flares and coronal mass ejections (CMEs) on exoplanets orbiting cool stars (image credit: Stephenie Brophy Lee). Our understanding of these processes for cool stars other than the Sun is still limited. Based on our knowledge of the Sun, magnetic fields must play a fundamental role in the production of stellar energetic particles, flares and CMEs. Zeeman-Doppler imaging results indicate that active stars, such as young stars or M dwarfs, have large-scale stellar surface magnetic field strengths orders of magnitude stronger than the Sun’s. What does this mean for the acceleration of stellar CMEs and stellar energetic particles? Do these phenomena affect exoplanets in ways that can be detected? While most cool stars are expected to host exoplanets, the number of known planet-hosting stars with stellar magnetic field maps remains small. They provide us with a unique opportunity to potentially probe stellar properties through star-planet interactions. The goal of our session is to improve our understanding of how exoplanets can be used as a diagnostic of space weather.

The key open questions that our session will contribute to are:

How do we predict XUV (X-ray and Extreme Ultraviolet) radiation from cool stars? Stellar XUV radiation is the most important parameter for affecting an exoplanet atmosphere. JWST observations have already detected the first signature of UV photochemistry in an exoplanet atmosphere. X-ray and EUV stellar radiation can also generate planetary winds if enough of the radiation is deposited in the planetary atmosphere. Escaping atmospheres have already been detected among planet-hosting cool stars (e.g. GJ436 b). Using these observations of planetary atmospheres, models constrained stellar wind parameters. Although we have some understanding of the X-ray emission from cool stars, we do not have proper constraints on EUV emission.

What are the stellar energetic particle fluxes from cool stars? Are stellar energetic particles also accelerated efficiently at the location of flares? Can stellar optical flare rates be used to predict stellar energetic particle fluxes? There is much to understand about the acceleration of stellar energetic particles by cool stars. For the Sun, energetic particles are accelerated at the location of flares and CME shock fronts. Recent modelling efforts indicate that active stars with fast CMEs should accelerate particles to higher energies than the Sun.

What can exoplanet observations tell us about space weather? How do stellar energetic particles, CMEs and flares affect exoplanet atmospheres? Chemical modelling of exoplanet atmospheres is key to understand how high-energy phenomena alter the chemical composition of different types of exoplanet atmospheres. The enhanced plasma density and radiation during CMEs and flares will undoubtedly change exoplanet atmosphere dynamics. Flares photoionise and photodissociate different species in exoplanet atmospheres changing their chemical abundances. On the other hand, CMEs that interact directly with the upper atmosphere of exoplanets could strip the atmosphere significantly.

Question submission

The splinter session will include an interactive discussion. We would like to solicit questions from the community in advance, to prepare the discussion in an effective way. The questions will remain anonymous. Please fill in this form.