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New Evidence Points To Icy Plate Tectonics On Europa (gizmodo.com)
According to new research published today in Journal of Geophysical Research: Planets, Europa has what it takes to support plate tectonics. "Using computer models, a team lead by Brown University planetary scientist Brandon Johnson was able to demonstrate the physical feasibility of icy plates driving deep into the icy interior in a processes similar to what's seen on Earth," reports Gizmodo. "Excitingly, this same process could be delivering important minerals to the ocean below, heightening the moon's status a potentially habitable world." From the report: Europa has surface features reminiscent of Earth's mid-ocean ridges. For astronomers, this hinted at geological processes akin to subduction zones, where, on Earth, tectonic plates slide underneath another, sinking deep into the planet's interior. Several years ago, researchers Simon Kattenhorn and Louise Prockter posited this explanation when they noticed that a 20,000 square-kilometer (7,722 square-mile) chunk of ice had mysteriously disappeared from Europa's surface. Their explanation was that Europa's surface, like a gigantic jigsaw puzzle, is composed of tectonic plates, and that occasionally a plate of ice will sink beneath the other into warmer layers below. But this observational evidence of extension and spreading needed to be supported by geophysical reality. To that end, Johnson's team ran a computer simulation to see if it was possible for ice to sink in this way.
On our planet, subduction is primarily driven by differences in temperature between a descending slab and the surrounding mantle. Dense crustal material features a negative buoyancy that drives it down into the mantle. The Brown University scientists figured a similar thing happens on Europa, but with ice. In the case of Europa, the researchers surmised that the moon has two frozen layers -- an outer lid of very cold ice that sits above a layer of slightly warmer convecting ice. Their models showed that subduction is indeed possible in this alien environment, but only if the outer shell contains varying amounts of salt. This added ingredient provides the necessary density differences for a slab to conduct.
On our planet, subduction is primarily driven by differences in temperature between a descending slab and the surrounding mantle. Dense crustal material features a negative buoyancy that drives it down into the mantle. The Brown University scientists figured a similar thing happens on Europa, but with ice. In the case of Europa, the researchers surmised that the moon has two frozen layers -- an outer lid of very cold ice that sits above a layer of slightly warmer convecting ice. Their models showed that subduction is indeed possible in this alien environment, but only if the outer shell contains varying amounts of salt. This added ingredient provides the necessary density differences for a slab to conduct.
Io is right next door (so to speak), and spews forth a lot of material from its volcanoes. Some of that material makes it into the Jovian space between the moons. Jupiter's magnetic field is a transport mechanism.
Also: we know that tons - literally, tons - of extraplanetary material rains down on the Earth each day. Jupiter, being as massive as it is, probably sucks up a lot more. Europa is a small target, but is traveling through this inward flux of material and is sure to pick some up.
Anyway, we have no idea what conditions are required for life to start. There may well be a minimum energy requirement which europa doesn't even get close to. Also you need some kind of energy gradiant. In an ocean sealed off dozens or even hundreds of km below the surface I suspect that gradient is shallow in the extreme.
Features such as Conamara chaos show extensive melt-through and rafting. That does not happen with an icy crust hundreds of kilometres thick.
The ice shell is probably less than 10km thick in most places and occasionally much thinner. Gives ample opportunity for surface materials (irradiated by the sun and radiation from jupiter) to be recycled into the subsurface ocean.