Exomoons in the habitable zones of M dwarfs

TL;DR

This study assesses the habitability, stability, and detectability of exomoons around planets in the habitable zones of M dwarf stars, highlighting potential candidates for long-term habitable moons.

Contribution

It provides an updated catalog of M dwarf exoplanets, analyzes their habitable zones, and identifies specific planets capable of hosting long-term stable habitable exomoons.

Findings

33 exoplanets are in the habitable zones of M dwarfs.

4 planets could host long-term stable habitable exomoons.

Identified candidate systems for future exomoon biosignature surveys.

Abstract

M dwarfs host most of the exoplanets in the local Milky Way. Some of these planets, ranging from sub-Earths to super-Jupiters, orbit in their stars' habitable zones (HZs), although many likely possess surface environments that preclude habitability. Moreover, exomoons around these planets could harbor life for long timescales and thus may also be targets for biosignature surveys. Here we investigate the potential habitability, stability, and detectability of exomoons around exoplanets orbiting M dwarfs. We first compile an updated list of known M-dwarf exoplanet hosts, comprising 109 stars and 205 planets. For each M dwarf, we compute and update precise luminosities with the Virtual Observatory spectral energy distribution Analyzer and Gaia DR2 parallaxes to determine inner and outer boundaries of their HZs. For each planet, we retrieve (or, when necessary, homogeneously estimate) their masses and radii, calculate the long-term dynamical stability of hypothetical moons, and identify those planets that can support habitable moons. We find that 33 exoplanet candidates are located in the HZs of their host stars and that four of them could host Moon- to Titan-mass exomoons for timescales longer than the Hubble time.