Effects of Magnetic Fields on the Location of the Evaporation Valley for Low-Mass Exoplanets

TL;DR

This paper investigates how planetary magnetic fields influence atmospheric mass-loss rates and the resulting distribution of exoplanet radii, impacting our understanding of their core composition.

Contribution

It introduces the role of magnetic fields in modifying atmospheric escape and the radius distribution minimum for low-mass exoplanets.

Findings

Magnetic fields can significantly reduce atmospheric mass-loss rates.

Lower mass-loss rates shift the radius distribution minimum.

Implications for core composition estimates of exoplanets.

Abstract

The observed distribution of radii for exoplanets shows a bimodal form that can be explained by mass-loss from planetary atmospheres due to high energy radiation emitted by their host stars. The location of the minimum of this radius distribution depends on the mass-radius relation, which in turn depends on the composition of planetary cores. Current studies suggest that super-Earth and mini-Neptune planets have iron-rich and hence largely Earth-like composition cores. This paper explores how non-zero planetary magnetic fields can decrease the expected mass-loss rates from these planets. These lower mass-loss rates, in turn, affect the location of the minimum of the radius distribution and the inferred chemical composition of the planetary cores.