Europa’s icy exterior might be what keeps its subsurface ocean from freezing

Europa's Icy Exterior Might Be What Keeps Its Ocean From Freezing-2

Although situated far away from the sun, Jupiter’s moon Europa is a treasure trove of unique physical characteristics, including an abundance oxygen and subsurface running water, which together make it one of the most likely places for extraterrestrial life. According to a new research, the ocean remains liquid, despite very low surface temperature, thanks to the heat generated by continual heaving and falling of the moon’s icy crust under Jupiter’s gravitational pull.

Discovered back in 1610 by Galileo, Europa is one of the four Galilean moons of Jupiter, with the others being Ganymede, Callisto and Io. Named after Zeus’ lover, the satellite is around 4.5 billion years old, and is sixth from Jupiter in terms of distance. Space probe flybys in recent decades have revealed the presence of a water-ice crust and a rarefied atmosphere composed mainly of oxygen. It is believed to possess a rocky mantle and an iron core, similar to our own planet. Speaking about the Jovian moons, Christine McCarthy of Columbia University said:

[Scientists] had expected to see cold, dead places, but right away they were blown away by their striking surfaces. There was clearly some sort of tectonic activity—things moving around and cracking. There were also places on Europa that look like melt-through or mushy ice.

Europa's Icy Exterior Might Be What Keeps Its Ocean From Freezing-1

Europe’s surface temperature never rises above minus 260 degrees Fahrenheit (or minus 160 degrees Celsius) near the equator, and minus 370 degrees Fahrenheit (around minus 220 degrees Celsius) at the poles. Despite such low temperatures, researchers believe that there is a huge global ocean running underneath the moon’s outer crust. According to one hypothesis, Jupiter’s tremendous gravitational pull causes the satellite’s icy shell to continually heave and fall, generating sufficient heat to keep the water liquid.

As part of a recent research, a team of geoscientists from Columbia and Brown universities has come to the conclusion that this process, known as tidal dissipation, could produce far more heat in Europa’s frigid environment than previously thought. Published in the journal Earth and Planetary Science Letters, the work could help astronomers estimate the thickness of the moon’s icy crust with greater accuracy. McCarthy, who likened the process to the action of repeatedly bending a metal coat hanger, explained:

If you bend it back and forth, you can feel it making heat at the junction. The way it does that is that internal defects within that metal are rubbing past each other, and it’s a similar process to how energy would be dissipated in ice.

Up until now, researchers relied on mechanical models to analyze Europa’s frosty surface. Although such models pointed to the presence of sub-surface running water, they failed to provide a proper explanation for the kind of heat fluxes that would be required to create such tectonics. Working alongside Reid Cooper in the laboratory, McCarthy placed ice samples in a specially-designed compression apparatus. The samples, according to the team, were subjected to cyclical loads, undergoing repeated deformation and rebounding.

To determine the amount of heat generated during the process, McCarthy and her team measured the lag time between the application of the load and the distortion of the ice. Previously, it was assumed that friction between ice grains is responsible for generating a major chunk of the heat. If that were indeed the case, the amount of heat produced would be dependent on the size of the grains. In the new study, however, the scientists were able to attain similar results, irrespective of the grain size. The heat, the researchers believe, likely comes from defects in the crystal lattice of ice, formed as a result of repeated deformation. Cooper of Brown University added:

Christine discovered that, relative to the models the community has been using, ice appears to be an order of magnitude more dissipative than people had thought. The beauty of this is that once we get the physics right, it becomes wonderfully extrapolative. Those physics are first order in understanding the thickness of Europa’s shell. In turn, the thickness of the shell relative to the bulk chemistry of the moon is important in understanding the chemistry of that ocean. And if you’re looking for life, then the chemistry of the ocean is a big deal.

According to the team, the new study could help unravel the various mysteries surrounding Europa and its hidden ocean.

Source: Brown University

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