Survivability of moon systems around ejected gas giants

Abstract

We examine the effects that planetary encounters have on the moon systems of ejected gas giant planets. We conduct a suite of numerical simulations of planetary systems containing three Jupiter-mass planets (with the innermost planet at 3 AU) up to the point where a planet is ejected from the system. The ejected planet has an initial system of 100 test-particle moons. We determine the survival probability of moons at different distances from their host planet, measure the final distribution of orbital elements, examine the stability of resonant configurations, and characterize the properties of moons that are stripped from the planets. We find that moons are likely to survive in orbits with semi-major axes out beyond 200 planetary radii (0.1 AU in our case). The orbital inclinations and eccentricities of the surviving moons are broadly distributed and include nearly hyperbolic orbits and retrograde orbits. We find that a large fraction of moons in two-body and three-body mean-motion resonances also survive planetary ejection with the resonance intact. The moon-planet interactions, especially in the presence of mean-motion resonance, can keep the interior of the moons molten for billions of years via tidal flexing, as is seen in the moons of the gas giant planets in the solar system. Given the possibility that life may exist in the subsurface ocean of the Galilean satellite Europa, these results have implications for life on the moons of rogue planets-planets that drift through the galaxy with no host star.

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

“…To maintain the temperature above the freezing point, the orbital parameters need to be constrained in time. As previously discussed, albeit surviving moons around ejected gas giants are expected to exist up to 0.1 au from the hosting planet, closer orbits (& 0.01 au) are in general more probable (Rabago and Steffen 2019). Figurefig1 shows that, given the same pressure conditions, for the same eccentricity value, smaller semi-major axis implies warmer environments.…”

“…Williams (2013) show that Earth-sized objects can be captured by a gas giant planet, thus leading to a massive satellite. Since such a planet-moon system could survive an ejection from their stellar system, as reported in the models of Rabago and Steffen (2019), we assume a configuration of a secondary object (i.e. the moon orbiting around the FFP) with a mass of 1 M ⊕ (and gravity g = 980 cm s −2 ) orbiting around a 1 M J object, that allows to produce a significant amount of tidal heating to obtain liquid water when the atmosphere is not irradiated by any significant external radiation.…”

“…To model the dynamics of the planet-moon system, we assume that the FFP has been ejected from its host system by e.g. a perturbation from a gas giant planet, and it retained at least one of its moons after the ejection, as for example discussed in Debes and Sigurdsson (2007); Hong et al (2018) and Rabago and Steffen (2019). The orbital parameters of the planet-moon system depend on the gravitational interaction during the ejection.…”

“…The orbital parameters of the planet-moon system depend on the gravitational interaction during the ejection. Rabago and Steffen (2019) presented 77 simulations finding that 47% of the moons are likely to remain bond to the planet, and that the final semi-axis of a survived moon is <0.1 au (for comparison Jupiter's largest moons are within 0.01 au), but favouring the innermost orbits, as the number of moons is roughly inversely proportional to the final semi-axis a (namely, the probability of having a closer object after the ejection is higher). The final eccentricity e is mostly between 10 −3 and 1 (Hong et al 2018).…”

“…We choose a range of semi-major axis and eccentricity following Debes and Sigurdsson (2007); Hong et al (2018); Rabago and Steffen (2019), with the former ranging between 0.8 × 10 −3 and 1.4 × 10 −2 au, while the latter between 10 −3 and 5 × 10 −1 . We assume a primary object (i.e.…”