Resonant Removal of Exomoons During Planetary Migration

Abstract

Jupiter and Saturn play host to an impressive array of satellites, making it reasonable to suspect that similar systems of moons might exist around giant extrasolar planets. Furthermore, a significant population of such planets is known to reside at distances of several Astronomical Units (AU), leading to speculation that some moons thereof might support liquid water on their surfaces. However, giant planets are thought to undergo inward migration within their natal protoplanetary disks, suggesting that gas giants currently occupying their host star's habitable zone formed farther out. Here we show that when a moon-hosting planet undergoes inward migration, dynamical interactions may naturally destroy the moon through capture into a so-called evection resonance.Within this resonance, the lunar orbit's eccentricity grows until the moon eventually collides with the planet. Our work suggests that moons orbiting within about ∼10 planetary radii are susceptible to this mechanism, with the exact number dependent on the planetary mass, oblateness, and physical size. Whether moons survive or not is critically related to where the planet began its inward migration, as well as the character of interlunar perturbations. For example, a Jupiter-like planet currently residing at 1 AU could lose moons if it formed beyond ∼5 AU. Cumulatively, we suggest that an observational census of exomoons could potentially inform us on the extent of inward planetary migration, for which no reliable observational proxy currently exists.

Ploonets: formation, evolution, and detectability of tidally detached exomoons

“…For instance, the perturbations experienced by a moon during its evolution could drive its disruption or escape. Thus, in the host-planet migration phase, the moon can either be ejected via "evection resonance" (Spalding, Batygin & Adams 2016) or by planet-planet scattering (Gong et al 2013;Hong et al 2018). As a result, when the moon-planet system reaches its final configuration in a close-in orbit (Namouni 2010), the tidal interplay with the planet and the star would push the moon towards large circumplanetary orbits where it can be perturbed and lost (Alvarado-Montes, .…”

Innocent Bystanders: Orbital Dynamics of Exomoons During Planet–Planet Scattering

“…The Hill stability criterion, Roche limit, stellar tidal stripping, tidal decay, planet migration, direct planet perturbation, and planetary close encounters are among the mechanisms that can destabilize the orbits of exomoons (Barnes & O'Brien 2002;Domingos et al 2006;Donnison 2010;Frouard & Yokoyama 2013;Holman & Wiegert 1999;Kane 2017;Payne et al 2013;Sasaki et al 2012;Namouni 2010;Spalding et al 2016). The stability of distant satellites (a s > 0.1 R H ), which would be classified as irregular satellites in the Solar System, in planet-planet scattering, are investigated by Gong et al (2013) and Nesvorný et al (2007).…”

Disruption of planetary orbits through evection resonance with an external companion: circumbinary planets and multiplanet systems

“…This resonance was first studied in the context of the Moon-Earth-Sun system by Touma & Wisdom (1998), who showed that the resonance between the Moon's orbital precession due to the Earth's oblateness and the periodic perturbation of the Sun could give the Moon a significant eccentricity in its early evolution, which later produce the misalignment of the Moon's orbit. Recently, Spalding, Batygin & Adams (2016) studied the evolution of exomoons during planetary migration, and showed that evection resonance could induce eccentricity growth of exomoons, leading to their collisions with the host planet.…”