Plate Tectonics on Jupiter’s Moon Could Reveal Hidden Ocean
Kevin Stacey, 6 Dec 17
       

(Credit: NASA/JPL-Caltech/SETI Institute)

The icy shell of Jupiter’s moon Europa may have plate tectonics similar to those on Earth, a new study suggests.


“If indeed there’s life in that ocean, subduction offers a way to supply the nutrients it would need…”


The presence of plate tectonic activity could have important implications for the possibility of life in the ocean thought to exist beneath the moon’s surface.

The study, published in the Journal of Geophysical Research: Planets, uses computer modeling to show that subduction—when a tectonic plate slides underneath another and sinks deep into a planet’s interior—is physically possible in Europa’s ice shell.

The findings bolster earlier studies of Europa’s surface geology that found regions where the moon’s ice shell looks to be expanding in a way that’s similar to the mid-ocean spreading ridges on Earth. The possibility of subduction adds another piece to the tectonic puzzle.

Exciting findings

“We have this evidence of extension and spreading, so the question becomes where does that material go?” says Brandon Johnson, an assistant professor in the earth, environmental, and planetary sciences department at Brown University and a lead author of the study.

“On Earth, the answer is subduction zones. What we show is that under reasonable assumptions for conditions on Europa, subduction could be happening there as well, which is really exciting,” says Johnson.

Part of the excitement, Johnson says, is that surface crust is enriched with oxidants and other chemical food for life. Subduction provides a means for that food to come into contact with the subsurface ocean scientists think probably exists under Europa’s ice.

“If indeed there’s life in that ocean, subduction offers a way to supply the nutrients it would need,” Johnson says.

Salt and subduction

On Earth, subduction is driven largely by differences in temperature between a descending slab and the surrounding mantle. Crustal material is much cooler than mantle material, and therefore denser. That increased density provides the negative buoyancy needed to sink a slab deep into the mantle.

Though previous geological studies had hinted that something like subduction could be happening on Europa, it wasn’t clear exactly how that process would work on an icy world.

There’s evidence, Johnson says, that Europa’s ice shell has two layers: a thin outer lid of very cold ice that sits atop a layer of slightly warmer, convecting ice. If a plate from the outer ice lid was pushed down into the warmer ice below, its temperature would quickly warm to that of the surrounding ice. At the point, the slab would have the same density of the surrounding ice and would therefore stop descending.

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