A MODEL FOR CRYOVOLCANISM ON EUROPA BASED ON HEAT TRANSFER & DYNAMICS

Europa, the smallest of Jupiter’s Galilean satellites, has a relatively young surface that may be due, at least in part, to cryovolcanic processes. The likelihood for cryovolcanism to occur on Europa hinges on the ability of icy magmas to retain heat while traversing the lithosphere.

Terrestrial volcanic processes occur when diapirism, diking and/or complex subsurface plumbing systems, capped by vertical conduits, deliver superheated magma to Earth's surface. One or more of these same processes would initiate cryovolcanism on Europa. In an effort to place constraints on the conditions under which cryovolcanic eruptions might occur, we have modeled the ascent of cryomagmas originating from the base of the ice shell of this intriguing satellite. Based upon magmatic heat transfer, dynamics, and brine composition, and assuming a geothermal gradient of 5.77 K/km, we present models for the transport of icy magmas to Europa’s surface via diapirsm, diking, and conduit transport.

Assuming that Europa’s lithosphere is currently in a steady-state, Stefan-type conductive regime, we find that the ice shell is approximately 30 km thick. Based on this value of lithospheric thickness, preliminary results from our model indicate that cryomagmatic diapirs with radii of 1km and 5km must travel in excess of 2x10^-4m/s and 2x10^-6m/s, respectively, to arrive at Europa’s surface at warm enough temperatures to initiate cryovolcanic events. Equivalent volumes of cryomagma ascending through the lithosphere in conduits must travel at least 5x10^-6m/s, if the conduit has a radius of 0.21km, and 5x10^-8m/s, if transported in a larger conduit with a radius on the order of 2km, in order to reach the surface prior to solidification. Finally, dikes that are on the order of 0.02 km thick must have propagation speeds of at least 1x10^-2m/s, while their 0.1km thick counterparts must have propagation speeds of at least 2x10^-4m/s, to deliver cryomagmas to the surface before solidification takes place. Based on heat transfer considerations, these results tell us that a slow-moving dike can deliver cryomagmas warm enough to facilitate cryovolcanism to the surface of Europa in, at most, approximately 5 years, while a slow moving diapir can take hundreds of years to deliver the same volume of melt to the surface at an equivalent temperature.