Impact of melt accumulation on tidal heat production in Europa’s mantle

Volcanic activity at Europa’s seafloor is one of the key questions regarding the habitability of its subsurface ocean. The suitable conditions for hydrothermalism on Europa’s seafloor are conditioned by the heat released from the underlying silicate mantle, supplied by both radiogenic and tidal heating. The orbital resonance between Io, Europa, and Ganymede forces their orbit and maintains non-zero eccentricities. Tidal heating due to eccentricity tides on Io is so extreme that it  produces intense volcanism.  Even though tidal heating  in Europa’s silicate mantle is expected to be much weaker than on Io due to its greater distance to Jupiter,   Běhounková et al. [1] showed that it may still be sufficient to maintain Europa’s mantle in a partially molten state  for several tens to hundred millions of years, particularly during periods of increased eccentricity. Due to inefficient melt transport through the thick lithosphere of Europa [2], melt produced during periods of enhanced eccentricity may accumulate and in turn affect the tidal heating, as it is the case for Io, implying a possible runaway melt process in the silicate interior of Europa.   In this context, the goal of this study is to evaluate the effect of melt accumulation on the tidal heat production of Europa’s silicate mantle. For that purpose, we follow the approach developed to model the solid tides in Io’s partially molten interior [3], taking into account the effect of melt on the viscoelastic properties of the mantle. We adapt it to the context of Europa, corresponding to a deeper and thinner asthenosphere than on Io. We show that, whatever the partially molten layer thickness, melt accumulation increases tidal heat production and tidal dissipation even exceeds radiogenic heating. For equivalent volume of accumulated melt, the thinner the layer, the more pronounced this effect is. Our results show that the accumulation of melt, over timescales consistent with the 3D model prediction of Běhounková et al. [1], may significantly affect the tidal dissipation amplitude and its pattern. The potential presence of such melt accumulations may be tested by future measurements by Europa Clipper and JUICE from the combined analysis of gravimetric, altimetric and magnetic data, which might reveal long-wavelength anomalies which could be confronted to our model prediction.   [1] Běhounková et al., GRL, 48(3), e2020GL090077 (2021),  [2] Bland and Elder, GRL, 49(5), e2021GL096939 (2022). [3] Kervazo et al., A&A, 650, A72 (2021)