Despite being so far away from the Sun, Jupiter’s moons are hot—hotter than they should be!
The beautiful, icy moons are known to contain interiors warm enough to host oceans of liquid water. And on the planet’s innermost moon, Io, the heat is intense enough to melt rocks into magma.
Previously, researchers believed that Jupiter was the sole reason behind most of the heating associated with Io’s internal ocean of magma as well as the liquid interiors of its three icy Galilean moons: Europa, Ganymede, and Callisto. But now, a new study has found that moon-moon interactions may be more responsible for the heating than the Gas Giant.
Essentially, the researchers have found that the moons gravitationally tug at each other and create friction—a process called tidal heating—while Jupiter itself stretches and squishes them. The tidal heating is what causes the interiors of the moons to heat-up, and it is driven by a phenomenon called tidal resonance.
“It’s surprising because the moons are so much smaller than Jupiter,” said the paper’s lead author Hamish Hay, a postdoctoral fellow at the Jet Propulsion Laboratory in Pasadena, California. “You wouldn’t expect them to be able to create such a large tidal response.”
However, they do just that.
For any moon to experience tidal resonance, their oceans must be tens to hundreds of kilometers thick. Incidentally, the oceans on Jupiter’s moons are so thick, that the planet’s influence alone is incapable of creating tides with the right frequency to resonate with the moons. It was only when the researchers added in the gravitational influence of the other moons that they started to see tidal forces approaching the natural frequencies of the moons.
As the tides generated by other moons resonate with a moon’s frequency, they serve as an energy source and excite the subsurface lunar oceans near their natural frequencies. This leads to the generation of fast-flowing tidal waves, which effectively release significant amounts of heat into the oceans and crusts of Io and Europa.
Subsequently, these moons begin experiencing more heating than that caused by Jupiter alone, and in extreme cases, it could also result in the melting of ice or rock internally, especially on Io.
However, this current model functions on the assumption that the tidal resonances never get too extreme. In future studies, Hay and his team of researchers intend to see what happens when they lift that constraint, and also study the true depth of the oceans within these moons.
All in all, getting a complete picture of how these moons influence each other is crucial, as it could shed light on how Jupiter’s wonderful moon system evolved as a whole, and also improve our understanding of how ocean worlds in compact systems evolve.
The findings of this study were published in the journal Geophysical Research Letters, and they can be accessed here.