Abstract
The complex geology of Europa is evidenced by many tectonic and cryomagmatic
resurfacing structures, some of which are "painted" into a more visible
expression by exogenic alteration processes acting on the principal
endogenic cryopetrology. The surface materials emplaced. and affected
by this activity are mainly composed of water ice in some areas,
but in other places there are other minerals involved. Non-ice minerals
are visually recognized by their low albedo and reddish color either
when first emplaced or, more likely, after alteration by Europan
weathering processes, especially sublimation and alteration by ionizing
radiation. While red chromophoric material could be due to endogenic
production of solid sulfur allotropes or other compounds, most likely
the red substance is an impurity produced by radiation alteration
of hydrated sulfate salts or sulphuric acid of mainly internal origin.
If the non-ice red materials or their precursors have a source in
the satellite interior, and if they are not merely trace contaminants,
then they can play an important role in the evolution of the icy
crust, including structural differentiation and the internal dynamics.
Here we assume that these substances are major components of Europa's
cryo/hydrosphere, as some models have predicted they should be. If
this is an accurate assumption, then these substances should not
be neglected in physical, chemical, and biological models of Europa,
even if major uncertainties remain as to the exact identity, abundance,
and distribution of the non-ice materials. The physical chemical
properties of the ice-associated materials will contribute to the
physical state of the crust today and in the geological past. In
order to model the influence of them on the thermal state and the
geology, we have determined the thermal properties of the hydrated
salts. Our new lab data reveal very low thermal conductivities for
hydrated salts compared to water ice. Lower conductivities of salty
ice would produce steeper thermal gradients than in pure ice. If
there are salt-rich layers inside the crust, forming salt beds over
the seafloor or a briny eutectic crust, for instance, the high thermal
gradients may promote endogenic geological activity. On the seafloor,
bedded salt accumulations may exhibit high thermochemical gradients.
Metamorphic and magmatic processes and possible niches for thermophilic
life at shallow suboceanic depths result from the calculated thermal
profiles, even if the ocean is very cold. (C) 2004 Elsevier Inc.
All rights reserved.
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