Presence of water on exomoons orbiting free-floating planets: a case study

TL;DR

This study models exomoons orbiting free-floating planets, demonstrating that under certain conditions, they can retain enough water to potentially support primordial life, despite smaller water quantities than Earth.

Contribution

It provides a detailed atmospheric and chemical model showing conditions for liquid water stability on exomoons around free-floating planets, a novel scenario in astrobiology.

Findings

Liquid water can exist on exomoons under specific conditions.

The water amount is smaller than Earth's oceans but potentially sufficient for life.

Cosmic rays control the chemical equilibrium timescale in the exomoon atmosphere.

Abstract

A free-floating planet is a planetary-mass object that orbits around a non-stellar massive object (e.g. a brown dwarf) or around the Galactic Center. The presence of exomoons orbiting free-floating planets has been theoretically predicted by several models. Under specific conditions, these moons are able to retain an atmosphere capable of ensuring the long-term thermal stability of liquid water on their surface. We model this environment with a one-dimensional radiative-convective code coupled to a gas-phase chemical network including cosmic rays and ion-neutral reactions. We find that, under specific conditions and assuming stable orbital parameters over time, liquid water can be formed on the surface of the exomoon. The final amount of water for an Earth-mass exomonoon is smaller than the amount of water in Earth oceans, but enough to host the potential development of primordial life. The chemical equilibrium time-scale is controlled by cosmic rays, the main ionization driver in our model of the exomoon atmosphere.