Linking stellar flares and spots to exoplanet atmospheric escape and photochemistry

Determine how stellar flare and starspot activity on exoplanet host stars drives atmospheric escape and alters photochemical processes within exoplanet atmospheres, specifying the mechanisms and conditions under which these effects occur.

Background

The white paper argues that stellar magnetic activity—manifested through flares, spots, and faculae—can dominate atmospheric chemistry, ionization, and escape in close-in terrestrial planets, particularly around M dwarfs. While photometric surveys have cataloged flares, the lack of time-resolved spectroscopy leaves the translation from stellar activity to atmospheric outcomes poorly constrained.

A next-generation 12-m class facility with integral-field and multi-object spectroscopy is proposed to capture flare spectral energy distributions and chromospheric diagnostics with sufficient cadence to quantify how transient stellar events drive atmospheric escape and photochemistry.

References

Here are the major open questions that the next big telescope developed by ESO will address through conducting a decadal spectroscopic survey of young, active exoplanet hosts: How do flare and spot activity translate into atmospheric escape and photochemistry on exoplanets?

— Transients as Determinants of Habitability  (2512.12456 - Majidi et al., 13 Dec 2025) in Section 3 (Key Questions)

We do not include haze production in our Archean Earth cases, so further work will be necessary to understand how the variance of UV flux from M stars across stellar age impacts photochemical haze production.

— The Effects of M Star Age Dependent Ultraviolet Emission on Detecting and Interpreting Exoplanet Biosignatures  (2608.19328 - Davis et al., 19 Aug 2026) in Section 4.6, page 20

We note that the results shown in this study are products of only quiescent UV emission, and the impact of differences in flare rates and energies across stellar age on terrestrial atmospheres will need further study.

— The Effects of M Star Age Dependent Ultraviolet Emission on Detecting and Interpreting Exoplanet Biosignatures  (2608.19328 - Davis et al., 19 Aug 2026) in Section 4.6, page 20

Furthermore, our M-star simulations indicate that after repeated flares the planet might approach a quasi-steady state ozone column depth. Unfortunately, 180~days is not sufficient to confirm this result and longer simulations are required.

— Preparing for the Early eVolution Explorer: The Impact of Flare Temperature on Ozone Column Depth in Earth-Like Atmospheres  (2608.23548 - Crouse et al., 24 Aug 2026) in Section 5, Conclusions