Atmospheric mass loss and stellar wind effects in young and old systems I: comparative 3D study of TOI-942 and TOI-421 systems

TL;DR

This study compares atmospheric mass loss and stellar wind interactions in young and old planetary systems, highlighting the importance of stellar wind effects and XUV spectra in interpreting atmospheric escape observations.

Contribution

It provides the first 3D modeling comparison of young and old systems, emphasizing stellar wind interactions and spectral energy distribution effects on atmospheric escape signatures.

Findings

Stellar wind interactions are crucial for interpreting young planet atmospheres.

XUV spectral distribution significantly affects Ly-alpha absorption modeling.

Young planets exhibit stronger atmospheric mass loss due to stellar wind effects.

Abstract

At young ages, when radiation from the host star is high, and the planet is hot and inflated after formation, planetary atmospheric mass loss can be extremely strong compared to older planets. In turn, stellar winds are faster and denser for young stars compared to evolved main-sequence stars. Their interaction with escaping planetary atmospheres can substantially affect atmospheric mass loss rates, as well as the observable signatures of escaping atmospheres, with both effects expected to occur differently for young and evolved planets. We perform a comparative study of two systems around stars of similar masses but very different ages (50~Myr and 9~Gyr): TOI-942 and TOI-421. Both stars host two sub-Neptune-like planets at similar orbits and in similar mass ranges, which allows a direct comparison of the atmospheric escape and interactions with the stellar winds in the young and old systems. We perform the 3D atmospheric modeling of the four planets in TOI-942 and TOI-421 systems and make the theoretical predictions of possible observational signatures in Ly-alpha absorption. We find that accounting for the stellar wind interacting with planetary atmospheres is crucial for the interpretation of the observations for young planets. Additionally, we show that a particular energy distribution along the XUV spectra has a minor effect on the atmospheric mass-loss rates, but it is of crucial importance for modeling the Ly-alpha absorption and therefore for interpretation of observations.