Europa’s compositional evolution is not well constrained. Observations
only provide approximations of the current interior structure of Europa.
However, dynamic models [Hussmann & Spohn 2004] resolve the
magnitude of interior heating produced by tidal interaction over time.
We couple the heat production to thermodynamic and chemical equilibrium
models Perple_X [Connolly 2005], Rcrust [Mayne+ 2016] and
CHIM-XPT [Reed 1998] to compute compositional changes of the
interior and ocean. Assuming that Europa’s interior is not molten now, a
Fe core could have accommodated up to 24 wt % S during accretion,
assuming chondritic accretion material. However, a metal-silicate
segregated magma ocean was needed to allow such high S content in the
core. More likely, accretion proceeded with low impact rates that
allowed heat dissipation. Based on this and experimental metal-silicate
partition behavior, Europa’s core contains ~1 wt % S.
Two mantle melting events were calculated corresponding to putative
events in Europa’s thermal-orbital evolution: a first event that melted
up to 30 vol % of the volatile-rich silicate shell, at pressures of 2.5
– 1.2 GPa ≥4 Ga ago, and a possible melting event ~1.3
Ga ago resulting from increased dissipation as the mantle’s rigidity
increased [Hussmann & Spohn 2004]. Melt intrusive to extrusive
ratios (I/E) for Europa are unknown, but eruption to the ocean-rock
interface would have been hindered by high stress needed to cause
fracture propagation and melt migration at depth [Byrne+ 2018].
Assuming I/E = 10, <7 wt % melt would have erupted (Fig 1).
Even if lava erupted during the first event, limited heat transfer from,
and dehydration of, the mantle may not have prevented the second event
from occurring. Considering Europa’s volcanism enables us to predict the
minerals likely to have influenced the ocean’s composition and the
mineralogy of concurrent water-rock activity. Erupted lava reacting with
the ocean results in water-to-rock ratio dependent proportions of
sulfides, saponite, chlorite and carbonates. We will describe
implications for the ocean’s composition and habitability. A part of the
research was carried out at the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics
and Space Administration. Copyright 2018. All rights reserved.