On the Diversity of M-Star Astrospheres and the Role of Galactic Cosmic Rays Within

TL;DR

This study models the astrospheres of M-type stars and estimates how galactic cosmic rays penetrate these environments, highlighting their potential impact on the habitability of orbiting exoplanets.

Contribution

It provides the first numerical estimates of galactic cosmic ray modulation within M-star astrospheres using 3D MHD models and a 1D transport model.

Findings

V374 Peg has a larger astrosphere than the Sun.

Proxima Centauri and LHS 1140 have comparable or smaller astrospheres than the Sun.

GCR impact on Proxima Centauri b and LHS 1140 b affects habitability considerations.

Abstract

With upcoming missions such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (ELT), and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL), we soon will be on the verge of detecting and characterizing Earth-like exoplanetary atmospheres for the first time. These planets are most likely to be found around smaller and cooler K- and M-type stars. However, recent observations showed that their radiation environment might be much harsher than that of the Sun. Thus, the exoplanets are most likely exposed to an enhanced stellar radiation environment, which could affect their habitability, for example, in the form of a hazardous flux of energetic particles. Knowing the stellar radiation field, and being able to model the radiation exposure on the surface of a planet is crucial to assess its habitability. In this study, we present 3D magnetohydrodynamic (MHD)-based model efforts investigating M-stars, focusing on V374 Peg, Proxima Centauri, and LHS 1140, chosen because of their diverse astrospheric quantities. We show that V374 Peg has a much larger astrosphere (ASP) than our Sun, while Proxima Centauri and LHS 1140 most likely have ASPs comparable or even much smaller than the heliosphere, respectively. Based on a 1D transport model, for the first time, we provide numerical estimates of the modulation of Galactic cosmic rays (GCRs) within the three ASPs. We show that the impact of GCRs on the Earth-like exoplanets Proxima Centauri b and LHS 1140 b cannot be neglected in the context of exoplanetary habitability.