Theoretical models of tidal dissipation in Io’s interior have provided support for a global subsurface melt layer. The extremely high temperature of the lava erupting on Io’s surface also hints at an extremely hot interior consistent with an internal magma ocean. However, the only direct evidence of a subsurface magma ocean in Io is provided by the electromagnetic induction response observed by Galileo (Khurana et al. 2011, Science, 332, 1186).
Using Jupiter’s rotating magnetic field as a sounding signal, Khurana et al. (2011) analyzed the response of Io observed during four different flybys of Io by the spacecraft Galileo, and showed that the magnetic field response is global, variable and in sync with the time varying field of Jupiter. Modeling of this signature shows that the induction response from a completely solid mantle model is inadequate to explain the magnetometer observations. However, a layer of asthenosphere > 50 km in thickness with a rock melt fraction ≥ 20% is adequate to accurately model the observed magnetic field.
In this presentation, after summarizing our current knowledge of Io’s interior from Galileo’s induction measurements, I will outline a scheme to further infer properties of Io’s interior, especially its internal temperature profile, by marrying the principles of thermodynamics with those of electromagnetism. In particular, we would obtain guidance on stable mineral phases and their physical properties (such as density, melt state and electrical conductivity) from thermodynamic principles whereas how the resulting internal conductivity profile affects the magnetic environment around Io from electromagnetic theory. I will also explore how induction measurements could be obtained at multiple frequencies from a future mission and be used to constrain both the location and the thickness of the magma ocean.
Finally, I will explore the consequences of the global magma ocean of Io on its physical properties such as the current sites of tidal energy dissipation, the absence of an internal magnetic field and a lack of plate tectonics on its surface.