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Did tidal heating lead to a rocky Io?

Presentation #315.01 in the session “Io: Geology”.

Published onOct 26, 2020
Did tidal heating lead to a rocky Io?

Jupiter’s four large satellites exhibit a striking gradient in composition from the rocky Io close to Jupiter out to the Icy Callisto. Many previous works have detailed how this gradient might be the result of the formation of the satellites. The possibility that this gradient is the result of tidal heating over solar system history has remained open (Canup and Ward 2009, Dwyer et al. 2013). In this work we aim to test what, if any, mechanisms might allow tidal heating to produce this gradient.

If Io and Europa formed with a ice mass fraction of 30% (comparable to Ganymede and Callisto) a significant amount of energy is needed to remove that. If we extrapolate current estimates for Io’s tidal heating rate through solar system history, we find that roughly 1% of all of Io’s dissipated energy would have needed to go into mass lost. The same calculation requires 10% of Europa’s total dissipated energy. These estimates obviously ignore the fact that Io and Europa’s tidal energy dissipation has varied over solar system history.

In this work we estimate the maximum plausible energy dissipated by Io and Europa over solar system history. This can be compared with the energy needed to remove the initial ice to determine the energy efficiency any process would need to be plausible. We then determine the energy efficiency for a range of processes including atmospheric escape and geysers. Initial results suggest these processes do not have the energy efficiency required to plausibly impact the bulk composition of these moons. This implies that this compositional gradient was the result of the formation process for these satellites.

  1. Canup, R. M., and Ward, W. R. “Origin of Europa and the Galilean satellites.” Europa (2009): 59-83.

  2. Dwyer, C. A., et al. “The influence of imperfect accretion and radial mixing on ice: rock ratios in the Galilean satellites.” Icarus 225.1 (2013): 390-402.


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