Powering the Galilean Satellites with Moon‐Moon Tides

Abstract

There is compelling evidence for subsurface water oceans among the three outer Galilean satellites and evidence for an internal magma ocean in the innermost moon, Io. Tidal forces from Jupiter periodically deform these bodies, causing heating and deformation that, if measured, can probe their interior structures. In addition to Jupiter‐raised tides, each moon also raises tides on the others. We investigate moon‐moon tides for the first time in the Galilean moons and show that they can cause significant heating through the excitation of high‐frequency resonant tidal waves in their subsurface oceans. The heating occurs both in the crust and ocean and can exceed that of other tidal sources and radiogenic decay if the ocean is inviscid enough. The resulting tidal deformation can be used to constrain subsurface ocean thickness. Our understanding of the thermal‐orbital evolution and habitability of the Jovian system may be fundamentally altered as a result.

Building the Galilean moons system via pebble accretion and migration: A primordial resonant chain

“…The bottom panel shows that the amplitude of the resonant angle associated with the Laplacian resonant slightly increases at ∼ 8 Myrthe moment when the outermost satellite leaves the resonance with the second outermost satellite -but the three innermost satellites remain locked in this configuration. Therefore, our results also suggest that the Galilean satellite system is a primordial resonant chain, where Callisto was once in resonance with Ganymede but left this configuration via divergent migration due to dynamical tides (Fuller et al 2016;Downey et al 2020;Lari et al 2020;Hay et al 2020;Durante et al 2020;Idini & Stevenson 2021). Of course, a complete validation of this result may require self-consistent simulations modeling tidal planet-satellite dissipation effects but this is beyond the scope of this paper.…”

“…Thus, we propose that Callisto -the outermost Galilean satellite -was originally locked in resonance with Ganymede but left this primordial configuration via divergent migration due to tidal dissipative effects (Fuller et al 2016;Downey et al 2020). We also proposed that the orbital eccentricities of the Galilean satellites were much higher in the past and were damped to their current values via tidal dissipation without destroying the resonant configuration of the innermost satellites (Fuller et al 2016;Downey et al 2020;Lari et al 2020;Hay et al 2020;Durante et al 2020;Idini & Stevenson 2021). Finally, we proposed that the Galilean system represents a primordial resonant chain that did not become unstable after the circumplanetary gas disk dispersal.…”

“…These water reservoirs are then rapidly lost via hydrodynamic escape, partially (or fully) drying the two innermost satellites (Bierson & Nimmo 2020). Additional water loss may be driven by giant impacts during their formation and enhanced tidal heating effects caused by the Laplacian resonance (Dwyer et al 2013;Hay et al 2020). Different from Io and Europa, the high concentrations of water-ice in Ganymede and Callisto suggest formation in cold and volatile-rich environments of the CPD (Schubert et al 2004), very likely outside the disk snowline where very limited water loss via hydrodynamic escape took place, if any at all.…”

Compositional Layering in Io Driven by Magmatic Segregation and Volcanism

“…However, there were significant challenges to the magma‐ocean model as proposed in Keszthelyi et al (2004). For example, once partial melting exceeds ∼20%, the shear modulus drops to the point that tidal dissipation cannot match the surface heat flow (Bierson & Nimmo, 2016; Moore, 2003; Renaud & Henning, 2018), limiting the possible thickness of such a high‐melt‐fraction layer (however, dissipation in a magma ocean may be significant Hay et al, 2020; Tyler et al, 2015). Furthermore, applying a different thermal model to the Pillan eruption, its temperature was revised down to ∼1600 K (Keszthelyi et al, 2007).…”

Compositional layering in Io driven by magmatic segregation and volcanism

“…However, there were significant challenges to the magma-ocean model as proposed in Keszthelyi et al (2004). For example, once partial melting exceeds ∼ 20%, the shear modulus drops to the point that tidal dissipation cannot match the surface heat flow (Moore, 2003;Bierson & Nimmo, 2016;Renaud & Henning, 2018), limiting the possible thickness of such a high-melt-fraction layer (however, dissipation in a magma ocean may be significant (Tyler et al, 2015;Hay et al, 2020)). Furthermore, applying a different thermal model to the Pillan eruption, its temperature was revised down to ∼ 1600 K (Keszthelyi et al, 2007).…”