Can Moons Exist around the Habitable-zone Planet K2-18b?

TL;DR

This study investigates the potential for exomoons around the habitable-zone planet K2-18b, concluding that tidal interactions make moon survival unlikely, thus challenging moon-based habitability for similar short-period planets.

Contribution

It provides the first detailed dynamical analysis of exomoon stability around K2-18b considering tidal effects using N-body simulations.

Findings

Exomoons around K2-18b are unlikely to survive due to rapid tidal-driven migration.

Any moons would have short lifetimes, not exceeding 10 million years.

Tidal interactions significantly reduce the likelihood of stable exomoons around short-period habitable-zone planets.

Abstract

K2-18b closely orbits a nearby M3 dwarf within its habitable zone, where this planet could be either a super-Earth or a mini-Neptune. Recent studies using transit spectroscopy suggest that it is Hycean in nature, but this classification is currently controversial. We use the N-body integrator rebound and its extension library reboundx to investigate the possibility of exomoons around K2-18b. Due to tidal interactions that induce outward migration, we find that any moons would be extremely unlikely. If formed, their lifetimes would be relatively short, not exceeding 10 Myr assuming Earth-like or Neptune-like tidal parameters for K2-18b. Recent studies estimate the stellar (and system) lifetime as 3 Gyr, which is significantly longer than the tidal migration timescale. We show that exomoons are unlikely to survive around K2-18b due to rapid tidal-driven migration, casting doubt on moon-based habitability scenarios for short-period M-dwarf planets in general.