Towards a consistent thermal-orbital model for the Galilean satellites

In the coming decade, the JUICE and Europa Clipper spacecraft will both visit Jupiter’s Galilean satellites, a joint exploration in great part motivated by the presence of subsurface oceans on Europa, Ganymede, and possibly Callisto. A key aspect of our investigation of these moons as potential extraterrestrial habitats is the long-term thermal-orbital evolution of the Galilean system. Our present knowledge of these moons is mostly based on the findings of the Galileo mission, among which the discovery of the aforementioned subsurface oceans. Earth-based astrometric observations, on the other hand, have brought constraints on the current evolution of the Laplace resonance between the three innermost Galilean moons (Io, Europa, and Ganymede) (Lainey et al., 2009).

However, the origin and history of the Laplace resonance, and the dynamical evolution of the system in general, still remain poorly constrained. The moons’ surfaces bear witness of past changes in the system’s orbital configuration (Greenberg, 2010), possibly hinting at periods of enhanced tidal heating due to increased eccentricity. Such episodes could be accompanied by a thinning of the ice shell and growth of the ocean layer, and a possible melting of  the rocky mantle (Behounkova et al., 2021). However, the level of magmatic activity at the seafloor and its potential expression at the surface should strongly depend on the duration and periodicity of these periods of increased eccentricity.  They are intrinsically linked to the system’s orbital resonance history and, as such, evidence the strong coupling between the evolution of the moons’ orbits and interiors.

While extensive orbital and thermal evolution studies of the Galilean satellites have been separately conducted, coupled thermal-orbital analyses remain limited in number and scope (Showman et al., 1997; Hussmann and Spohn, 2004; Bland et al., 2009). To work towards a coherent reconstruction of the system’s evolution, we therefore propose to couple a N-body dynamical model with existing, state-of-the-art interior models to consistently account for the intricate feedback between the moons’ orbits, tidal heating, and thermal evolution of the moons’ interiors.

As a first step towards such a consistent solution, we will exploit our N-body dynamical model to investigate the moons’ recent orbital history and specifically investigate potential periods of enhanced eccentricities over the last few hundreds million years. As the thermal evolution takes place over significantly longer timescales, averaged orbital configurations can be fed to interior modelling tools to continuously update tidal parameters throughout the orbital propagation. We aim to both place constraints on past tidal heating episodes and identify families of possible orbital evolution scenarios, eventually benefiting the interpretation of JUICE and Europa Clipper’s unprecedented characterisation of the present-day Galilean system.

 

References

Běhounková, M., et al. "Tidally induced magmatic pulses on the oceanic floor of Jupiter's moon Europa." Geophysical Research Letters 48.3 (2021): e2020GL090077.

Bland, M.T., Showman, A.P., and Tobie, G. "The production of Ganymede's magnetic field." Icarus 198.2 (2008): 384-399.

Greenberg, R. "The icy Jovian satellites after the Galileo mission." Reports on Progress in Physics 73.3 (2010): 036801.

Hussmann, H., and Spohn, T. "Thermal-orbital evolution of Io and Europa." Icarus 171.2 (2004): 391-410.

Lainey, V., et al. "Strong tidal dissipation in Io and Jupiter from astrometric observations." Nature 459.7249 (2009): 957-959.

Showman, A.P., Stevenson, D.J., and Malhotra, R. "Coupled orbital and thermal evolution of Ganymede." Icarus 129.2 (1997): 367-383.