# Presence of liquid water during the evolution of exomoons orbiting ejected free-floating planets

**Authors:** Giulia Roccetti, Tommaso Grassi, Barbara Ercolano, Karan Molaverdikhani, Aurélien Crida, Dieter Braun, Andrea Chiavassa  
**arXiv:** [2302.04946](https://arxiv.org/abs/2302.04946)  
**Date:** 2023-02-09  
**Summary page:** https://www.summarizepaper.com/en/paper/2302.04946v1/

## Key points

- This study explores the possibility of exomoons orbiting free-floating planets (FFPs) retaining liquid water on their surfaces after ejection from a planetary system.
- The authors perform dynamical simulations to infer the statistics of surviving exomoons around FFPs and investigate the subsequent tidal evolution of their orbital parameters.
- Close-in Earth-mass moons with CO$_2$-dominated atmospheres could retain liquid water for long timescales, depending on the mass of the atmospheric envelope and surface pressure assumed.
- Massive atmospheres are needed to trap heat produced by tidal friction which makes these moons habitable.
- For Earth-like pressure conditions ($p_0$ = 1 bar), satellites could sustain liquid water up to 52 million years (Myr), while higher surface pressures (10 and 100 bar) could extend habitability up to 276 Myr and 1.6 billion years (Gyr), respectively.
- Close-in satellites experience habitable conditions for extended periods of time, remaining bound with the escaping planet during FFP ejection and being less affected by close encounters.
- The presence of an atmosphere with high optical thickness may support the formation and maintenance of oceans of liquid water on these isolated planetary-mass objects' surfaces, making them potential candidates for future astrobiological investigations.

## Summary

This study explores the possibility of exomoons orbiting free-floating planets (FFPs) retaining liquid water on their surfaces after ejection from a planetary system. The authors perform dynamical simulations to infer the statistics of surviving exomoons around FFPs and investigate the subsequent tidal evolution of their orbital parameters. They find that close-in Earth-mass moons with CO$_2$-dominated atmospheres could retain liquid water for long timescales, depending on the mass of the atmospheric envelope and surface pressure assumed. Massive atmospheres are needed to trap heat produced by tidal friction which makes these moons habitable. For Earth-like pressure conditions ($p_0$ = 1 bar), satellites could sustain liquid water up to 52 million years (Myr), while higher surface pressures (10 and 100 bar) could extend habitability up to 276 Myr and 1.6 billion years (Gyr), respectively. Close-in satellites experience habitable conditions for extended periods of time, remaining bound with the escaping planet during FFP ejection and being less affected by close encounters. The presence of an atmosphere with high optical thickness may support the formation and maintenance of oceans of liquid water on these isolated planetary-mass objects' surfaces, making them potential candidates for future astrobiological investigations.