Thursday, April 12, 2018

Cryomagma on Europa


Lesage et al


Europa's surface exhibits morphological features associated with a low craters density that demonstrate a recent internal activity. In particular, the morphology of the smooth plains covering parts of the surface, and their relationship to the surrounding terrains suggest that they result from viscous liquid extrusions. Furthermore, recent literature explains the emplacement of liquid-related features, such as double ridges, lenticulae and chaos by the presence of liquid reservoirs beneath the surface. We model the ascent of liquid water through a dike or a pipe-like conduit, from a sub-surface reservoir to Europa's surface and derive the eruption time-scale and the total volume extruded at the end of the eruption, depending on the chamber volume and depth. We also estimate the freezing time of the sub-surface reservoir necessary to trigger an eruption. Considering available data for density and eutectic temperature of salt impurities recently proposed for Europa, we discuss their effect on the cryomagma freezing time and ascent. For plausible volumes and depths varying between 0.1 km3 ≤ V ≤ 10 km3 and 100 m ≤ H ≤ 10 km, the total extruded cryolava volume ranges from 105 to 108 m3 and the time scale of the eruptions varies from few minutes to few tens of hours. The freezing time-scale of the cryomagma pocket varies with the cryomagma composition: it varies between 102 to 103 years for a pure water cryomagma and from 102 to 104 years for a briny cryomagma.

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