Convection and Melt Migration in Io’s Mantle

Abstract:

Heating from tidal dissipation is so extreme on Io that its mantle is partially molten, and it is the most volcanically active body in the solar system. The detection of an induced magnetic field in Io suggests that the partially molten layer in the interior is at least 50 km thick and at least 20% molten [1]. The presence of this magma changes the nature of convection. Stagnant lid convection alone cannot produce Io’s high observed surface heat flux [2], and Io’s surface shows no evidence of plate tectonics. Instead, Io loses most of its internal heat through magma migration and volcanic eruptions or the ‘heat pipe mechanism’. Previous studies of heat loss from Io’s mantle have considered either migration of magma [3] or convection of solid mantle material [e.g. 4], but not both. Here we present numerical simulations that include both processes allowing for the first self-consistent test of the hypothesized heat-pipe mechanism on Io. We use the mantle convection code StagYY, which includes the generation, segregation, and eruption of magma, to conduct two-dimensional numerical simulations in Cartesian geometry considering a region ¼ the width of Io’s mantle and the full depth of Io’s mantle. We find that Io has a partially molten mantle, which is consistent with the detected induced magnetic field. Furthermore, our simulations demonstrate the viability of the heat pipe mechanism on Io. We find that Io loses two orders of magnitude more internal heat via magmatic eruption than via conduction through its stagnant lid. These magmatic eruptions are the source of Io’s high heat flux. Although the average heat flux from magmatic eruptions is equal to Io’s observed heat flux, the magmatic heat flux oscillates around this value with time, which is consistent with the variable nature of volcanic eruptions despite our simplified parameterization of eruption.

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