Jupiter’s moons are hotter than they should be, considering their distance from the sun, and scientists at the University of Arizona are explaining why. In a process known as tidal heating, the gravitational push and pull that takes place among the moons seems to be heating them up more than what was expected.
The interiors of some of these icy moons are warmed up enough by tidal heating to contain oceans of liquid water. On one of Jupiter’s largest moons, Io, opposing gravitational forces melt rock into magma.
It was previously assumed that Jupiter itself was responsible for most of the tidal heating, but the researchers determined that the gravitational interactions between the moons have a more powerful effect.
“It’s surprising because the moons are so much smaller than Jupiter. You wouldn’t expect them to be able to create such a large tidal response,” said study lead author Hamish Hay.
By understanding how moons affect each other, experts can gain insight into the evolution of the moon system as a whole. Jupiter has nearly 80 moons, and the four largest are Europa, Ganymede, Io, and Callisto.
“Maintaining subsurface oceans against freezing over geological times requires a fine balance between internal heating and heat loss, and yet we have several pieces of evidence that Europa, Ganymede, Callisto and other moons should be ocean worlds,” said study co-author Antony Trinh.
“Io, the moon closest to Jupiter, shows widespread volcanic activity, another consequence of tidal heating, but at a higher intensity likely experienced by other terrestrial planets, like Earth, in their early history. Ultimately, we want to understand the source of all this heat, both for its influence on the evolution and habitability of the many worlds across the solar system and beyond.”
According to Hay, tidal heating is driven by a phenomenon called tidal resonance.
“Resonance creates loads more heating. Basically, if you push any object or system and let go, it will wobble at its own natural frequency. If you keep on pushing the system at the right frequency, those oscillations get bigger and bigger, just like when you’re pushing a swing. If you push the swing at the right time, it goes higher, but get the timing wrong and the swing’s motion is dampened.”
“These tidal resonances were known before this work, but only known for tides due to Jupiter, which can only create this resonance effect if the ocean is really thin (less than 300 meters or under 1,000 feet), which is unlikely,” explained Hay. “When tidal forces act on a global ocean, it creates a tidal wave on the surface that ends up propagating around the equator with a certain frequency, or period.”
The model created by the researchers indicates that Jupiter’s influence alone cannot cause tidal resonance within the moons because the moons’ oceans are likely too deep. It was not until the scientists accounted for the gravitational influence of the other moons that the tidal forces started to approach the natural frequencies of the moons.
The study is published in the journal Geophysical Research Letters.