Jupiter moon Europa’s deforming ice appears as a surprising generator of heat, raising possibilities about its subsurface ocean, according to researchers from Brown University.
The findings comes as excitement is building up for the entry of NASA’s Juno exploration into Jupiter’s orbit this coming summer, as well as future missions that will probe the ice moon’s potential to support life.
Using computer modeling and lab experiments, the team found that tidal dissipation — a phenomenon caused by the planet’s massive gravitational field — could be causing Europa’s fragmented ice to create far greater heat than previously believed.
These Jovian moons have shown plenty of surprises since the NASA probes in the 1970s and 1990s. While scientists expected to find cold and lifeless locations, says lead researcher Christine McCarthy, striking surfaces on those satellites astounded them.
“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,” she explains, adding that the only way to produce enough heat for these processes occurring far from the sun is through tidal dissipation.
It has been established that Europa features a huge subsurface ocean of liquid shielded by a fragmented and icy crust appearing to move like Earth’s continental plates. Tidal pressures produced during its Jupiter orbit create an internal dynamo, mildly heating the moon from its core and maintains the ocean’s liquid form.
The icy plates’ motions are believed to create their internal heat via the frictional mechanisms at their boundaries. Heat is dissipated when there is recurring tidal flexing of the moon crust at the boundaries, a process akin to someone repeatedly bending a metal coat hanger.
But the particulars of this icy process were hardly understood, with simply mechanical models failing to generate the kind of heat fluxes creating the tectonics. So the team ran experiments to better understand the process.
McCarthy simulated what is happening in the crust of Europa by putting ice samples into a kind of compression device, therefore measuring how much deformation and heating are present.
It was previously thought that the heat produced in the process hailed from friction occurring between the ice grains, meaning the size of the grains directly influenced the heating. However, the experiment demonstrated a lack of difference in heat flux given varying ice grain sizes.
This suggested that the heating emerged from microscopic defects in the ice’s crystalline lattice as the ice was deformed. More heat was generated with greater deformation.
Research collaborator Reid Cooper says that as McCarthy discovered, ice showed to be an order of magnitude better dissipative than thought, relative to currently used models. Understanding the physics behind this, he adds, will lead to a more intimate look at the thickness of Europa’s shell and, as a result, the ocean chemistry, which is critical if one is looking for signs of life.
Studies like this contribute to a greater insight into the potential livability of Europa’s subsurface ocean, especially in light of NASA plans to choose instruments for its future Europa Clipper mission to study the Jovian world.
The findings were published June 1 in the journal Earth and Planetary Science Letters.
