The search for life on other planets is centered on planets beyond our solar system; nevertheless, life could exist much closer than we imagine.
Since the discovery of Europa, a frozen moon of Jupiter, astrobiologists have speculated that under its thick layer of ice, with an orography reminiscent of the ice blocks of our own planet, there could be plate tectonic activity that sustain extraterrestrial life.
Under the assumption that Europe is a frozen body and that it is too far from the Sun to melt the ice, it is necessary that there be another force capable of causing internal heat in Europe.
But there is a viable option: that Europe possess tectonic plates similar to the Earth and that its internal heat, agitated by the great gravitational mass of Jupiter, provokes these movements; which would have important implications in the possibility of life under the ice.
Now, a study published in the Journal of Geophysical Research: Planets , has shown that subduction , the process by which a tectonic plate slides under another and sinks deep into a planet, is physically possible in Europe.
The findings reinforce previous studies of the surface geology of Europe that found regions where the moon’s ice sheet seems to expand in a similar way to the crests of expansion in the middle of the ocean on Earth.
What do subduction movements imply for life?
The surface crust is enriched with chemical elements. Subduction provides a means for this food to come into contact with the oceanic subsoil layers that probably exist under the ice of Europe.
Therefore, if there is life in that ocean, subduction offers a way to supply the nutrients it would need.
According to Brandon Johnson, assistant professor in the Department of Earth, Environmental and Planetary Sciences at Brown University and lead author of the study: “What we show is that, under reasonable assumptions for conditions in Europe, subduction could be happening there as well”.
On Earth, subduction is mainly due to temperature differences between a descending slab and the surrounding mantle. The material of the crust is much colder than the material of the mantle and, therefore, more dense. That density provides the buoyancy necessary to sink a slab deep into the mantle.
Although previous geological studies had hinted that some process similar to subduction could be happening in Europe, it was not clear exactly how that process would work in a frozen world.
There is evidence, researchers say , that the ice of Europa has two layers: a thin outer layer of very cold ice found on a layer of ice convective slightly warmer.
If a plate of the outer ice cap is pushed down into the hotter ice, its temperature quickly heats up to that of the surrounding ice. At this time, the slab would have the same density of the surrounding ice and, therefore, would stop descending.
How could subduction occur in Europe?
But the model developed by Johnson and his colleagues showed a way in which subduction could occur in Europe, regardless of temperature differences . The model showed that if there were variable amounts of salt in the surface ice layer, it could provide the density differences necessary for a slab to subduct.
“Adding salt to an ice slab would be like adding little weight because the salt is more dense than ice,” Johnson said. “Then, instead of the temperature, we showed that differences in the salt content of the ice could allow subduction in Europe.”