Powering the Galilean Satellites with Moon-Moon Tides

Resonant ocean thicknesses at different forcing frequencies. a) Location of Europa's first three largest resonant rotational-gravity modes as a function of forcing frequency and ocean thickness, for both zonal (m = 0) and sectoral (m = 2) degree-2 modes. The sole resonant mode in the non-rotating limit is shown in red. b) Frequency decomposition of the sectoral degree-2 tidal potential at Europa due to Jupiter, Io, and Ganymede. c) Heating in Europa’s ocean and crust due to two frequency components of the tidal forcing; diurnal, eastward Jupiter-forcing (blue) and westward Io-forcing at ten times Europa's orbital frequency (orange), for a drag coefficient α = 10−9 s−1 . The dotted line uses α = 10−6 s−1 . The crust is 10 km thick with a melting viscosity of 1017 Pa s.

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.

Hamish C. F. C. Hay, Antony Trinh, Isamu Matsuyama
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: Geophysical Research Letters, 47, 2020, e2020GL088317
DOI: 10.1029/2020GL088317
Cite as: arXiv:2008.02825 [astro-ph.EP] (or arXiv:2008.02825v1 [astro-ph.EP] for this version)
Submission history
From: Hamish Hay
[v1] Thu, 6 Aug 2020 18:05:18 UTC (5,912 KB)

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