Tracking Io's partial melt with tidally modulated convection simulations

Jupiter’s moon Io, where tidal forcing is converted to extensive silicate volcanism, is an ideal setting for linking orbital stresses to heat generation through comparison with Earth volcanism and other tidally heated bodies. However, the total heat generated by tidal dissipation is contingent on the interior structure and distribution of melt, which influence temperature-dependent mechanical properties; this creates complex feedback loops involving tidal dissipation, melt generation and migration, lithospheric loading, and crustal stress states that facilitate magma ascent through deep faults (Keszthelyi et al., 2022). 

The relationship between tidal heating and volcanism on Io therefore depends on the extent and depth of its partial melt, and thus its interior structure. While Io’s interior likely consists of an iron-rich core, silicate mantle, and crust (Breuer et al., 2022), the size of these layers and the likely regions of tidal heat generation are not well constrained. Previous studies suggest that Io’s most strongly heated, dissipative regions will be those containing a degree of partial melt, either through a shallow asthenosphere or in a deeper partially molten mantle (Keane et al., 2023). Given the uncertainty on melt depth and storage, it is difficult to model how Io’s surface magmatism relates to its interior processes, and therefore to fully understand the conversion between tidal stress and energy budgets.  

Using the geodynamical code GAIA (Hüttig et al., 2013) to investigate the combined roles of melt depth and core size, we constructed two- and three-dimensional models of Io. GAIA is a finite-volume code that numerically solves the conservation equations of mass, linear momentum and thermal energy. Our models consider core cooling and radioactive decay as appropriate for a thermal evolution scenario, with tidal heating added per the Maxwell viscosity-dependent treatment of tidal heating by Tobie et al., 2003. Similar to Moore and Webb (2013), we consider fully extrusive cases in which the entire amount of melt produced in Io’s interior is extracted at the surface, followed by vertical downward-advection of cold surface material. Alternatively, we test the effect of magmatic intrusions created at depth, by emplacing only part of the melt produced in the interior at the surface, while the rest remains trapped in the lithosphere. 

Our models were restricted to cases in which Io has a dominantly rocky interior with partial melt concentrations < 30%, in line with recent suggestions that Io lacks a present-day ocean (Park et al., 2025). The mantle viscosity in our models is temperature- and pressure-dependent and follows an Arrhenius law. We include the weakening effect of melt fraction on the viscosity through an additional exponential term that locally decreases the mantle viscosity when non-zero melt fractions are present. In our models, we vary the core size between 650 – 950 km, which we link to a core composition between a pure Fe and an Fe-FeS eutectic. 

As already shown in previous studies (Moore & Webb, 2013; Lourenco et al., 2018; Herrera et al., 2026) melt extraction can play a major role for the thermal state of the lithosphere and affects partial melt production during the planetary history, with fully extrusive scenarios leading to thick and cold lithospheres, with deep melting zones. Highly intrusive models, however, are characterized by thin and warm lithospheres and shallow melt depths.  The results of our simulations will show if and how the depth of partial melt storage within Io can be directly linked to surface heat flux, and the extent to which the predicted degree of melt depends on tidal heating parameters. Following these results, we will aim to predict tidal heating patterns that may be validated with future observational missions. 

 

References

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• Herrera, C., Plesa, A.-C., Maia, J., Breuer, D., 2026. Surface temperature and mantle viscosity influence the cooling efficiency of magmatic styles on Venus (No. EGU26-1018). Presented at the EGU26, Copernicus Meetings. https://doi.org/10.5194/egusphere-egu26-1018
• Hüttig, C., Tosi, N., Moore, W.B., 2013. An improved formulation of the incompressible Navier–Stokes equations with variable viscosity. Physics of the Earth and Planetary Interiors 220, 11–18. https://doi.org/10.1016/j.pepi.2013.04.002
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