Habitable Zones & Global Climate

Presence Of Liquid Water During The Evolution Of Exomoons Orbiting Ejected Free-floating Planets

By Keith Cowing
Status Report
February 12, 2023
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Presence Of Liquid Water During The Evolution Of Exomoons Orbiting Ejected Free-floating Planets
Probability density function, calculated as the KDE, to find a moon at a certain surface temperature as a function of time. Different panels show increasing surface pressures. The hatched area represents the HZ, and the contour lines show the 5th, 50th, and 95th percentiles of the distributions. We note that the presence of more massive and substantial atmospheres increases the surface temperature of the moons and the number of moons inside the HZ. Increasing p0 also increases the timescale spent in the HZ. Above the HZ areas, we report the probability for a moon orbiting a FFP to lie in the HZ during its lifetime. The normalization of the KDE is analogous to Fig. 4. — astro-ph.EP

Free-floating planets (FFPs) can result from dynamical scattering processes happening in the first few million years of a planetary system’s life.

Several models predict the possibility, for these isolated planetary-mass objects, to retain exomoons after their ejection. The tidal heating mechanism and the presence of an atmosphere with a relatively high optical thickness may support the formation and maintenance of oceans of liquid water on the surface of these satellites.

In order to study the timescales over which liquid water can be maintained, we perform dynamical simulations of the ejection process and infer the resulting statistics of the population of surviving exomoons around free-floating planets. The subsequent tidal evolution of the moons’ orbital parameters is a pivotal step to determine when the orbits will circularize, with a consequential decay of the tidal heating.

We find that close-in (a≲25RJ) Earth-mass moons with CO2-dominated atmospheres could retain liquid water on their surfaces for long timescales, depending on the mass of the atmospheric envelope and the surface pressure assumed. Massive atmospheres are needed to trap the heat produced by tidal friction that makes these moons habitable. For Earth-like pressure conditions (p0 = 1 bar), satellites could sustain liquid water on their surfaces up to 52 Myr. For higher surface pressures (10 and 100 bar), moons could be habitable up to 276 Myr and 1.6 Gyr, respectively. Close-in satellites experience habitable conditions for long timescales, and during the ejection of the FFP remain bound with the escaping planet, being less affected by the close encounter.

Giulia Roccetti, Tommaso Grassi, Barbara Ercolano, Karan Molaverdikhani, Aurélien Crida, Dieter Braun, Andrea Chiavassa

Comments: 21 pages, 12 figures, accepted for publication on International Journal of Astrobiology
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2302.04946 [astro-ph.EP] (or arXiv:2302.04946v1 [astro-ph.EP] for this version)
Submission history
From: Giulia Roccetti
[v1] Thu, 9 Feb 2023 21:32:11 UTC (1,283 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻