Abstract

The anti-Jovian hemisphere of Europa (the hemisphere opposite the one facing Jupiter) displays a complex array of fractures, including roughly concentric and arcuate ones. The geometry of this intriguing pattern on the icy surface of Europa resembles the textural features displayed by perlitic volcanic glass. We argue that fast cooling of a rhyolitic magma may serve as an analogue for fast supercooling of water leading to formation of amorphous ice (glassy water). We envisage two possible scenarios for ice melting and subsequent extremely fast supercooling: (1) massive subglacial volcanic activity or (2) a large impact on the anti-Jovian hemisphere. We suggest that extremely fast formation of amorphous ice on Europa would result in a fracture pattern geometrically equivalent to that observed in perlitic glass. Fast supercooling of water will initially lead to brine retention in the ice phase; however, after some time these brines would be laterally rejected toward fractures. Furthermore, as solidification progresses downward, a shrinking ocean would increase brine concentration. These brines would eventually escape to the surface via the fracture network. Finally, high-pressure crystallization of salts within fractures may provide an efficient mechanism for differential plate separation, horizontal movement, and formation of new fractures.

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