Like our own Moon, Callisto rotates in the same period as it revolves, so it always keeps the same face toward Jupiter. Its distance from Jupiter is about 2 million kilometers, and it orbits the planet in 17 days. This makes it a convenient object with which other, more active, worlds can be compared. We begin our discussion of the Galilean moons with the outermost one, Callisto, not because it is remarkable but because it is not. Table 12.1 Callisto: An Ancient, Primitive World We include Titan, Saturn’s one big moon, here for comparison.) Table 12.1 summarizes some basic facts about these large moons (plus our own Moon for comparison). (Beginning in 2004, we received an even greater bonanza of information about Titan, obtained from the Cassini spacecraft and its Huygens probe, which landed on its surface. More recently, the Juno spacecraft, also a Jupiter orbiter, has provided a few close looks at Ganymede and Europa. Explain how tidal forces generate the geological activity we see on Europa and Ioįrom 1996 to 1999, the Galileo spacecraft careered through the jovian system on a complex but carefully planned trajectory that provided repeated close encounters with the large Galilean moons.Describe the major distinguishing characteristic of Io.Explain what may be responsible for the unusual features on the icy surface of Europa.Explain the evidence for tectonic and volcanic activity on Ganymede. Describe the major features we can observe about Callisto and what we can deduce from them.The findings of this study were published in the journal Geophysical Research Letters, and they can be accessed here.įor weather, science, and COVID-19 updates on the go, download The Weather Channel App (on Android and iOS store).By the end of this section, you will be able to: 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.Īll 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. However, this current model functions on the assumption that the tidal resonances never get too extreme. 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. 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. 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.Īs 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. 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. “You wouldn't expect them to be able to create such a large tidal response.”įor any moon to experience tidal resonance, their oceans must be tens to hundreds of kilometers thick. “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. The tidal heating is what causes the interiors of the moons to heat-up, and it is driven by a phenomenon called tidal resonance. But now, a new study has found that moon-moon interactions may be more responsible for the heating than the Gas Giant.Įssentially, 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. 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. And on the planet’s innermost moon, Io, the heat is intense enough to melt rocks into magma. 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.
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