Earlier, it was assumed that the planet Jupiter was responsible for most of the tidal heating associated with the moons’ liquid interiors. But a new study comes with another reason.
The study conducted by scientists from the University of Arizona suggests that Jupiter’s moon’s interactions might be responsible for tidal heating associated with the moons’ liquid interiors.
The paper’s lead author Hamish Hay, a postdoctoral fellow at the Jet Propulsion Laboratory in Pasadena, California, said, “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.”
Understanding how the moons impact each other is significant because it can reveal insight into the moon system’s evolution overall. Jupiter has almost 80 moons, the four biggest of Io, Europa, Ganymede, and Callisto.
Co-author Antony Trinh, a postdoctoral research fellow in the Lunar and Planetary Lab, said, “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.”
“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.”
The trick to tidal heating is a phenomenon called tidal Resonance.
Hay said, “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.”
“Each moon’s natural frequency depends on the depth of its ocean. 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) unlikely. 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.”
As per the scientists’ model, Jupiter’s impact alone can’t create tides with the right frequency to resonate with the moons because the moons’ oceans are excessively thick. It’s only when the researchers added in the other moons’ gravitational influence that they started to see tidal forces approaching the natural frequencies of the moons.
When the tides generated by other objects in Jupiter’s moon system match each moon’s resonant frequency, the moon begins to experience more heating than that due to tides raised by Jupiter alone. In the most extreme cases, this could result in the melting of ice or rock internally.
When the tides generated by other objects in Jupiter’s moon system match each moon’s resonant frequency, the moon begins to experience more heating than that due to tides raised by Jupiter alone. In the most extreme cases, this could result in the melting of ice or rock internally.
Hay said, “For moons to experience tidal Resonance, their oceans must be tens to hundreds of kilometers—at most a few hundred miles—thick, which is in range of scientists’ current estimates. However, there are some caveats to the researchers’ findings.”
“The model assumes that tidal resonances never get too extreme. Now, we want to return to this variable in the model and see what happens when they lift that constraint.”
In future studies, scientists hope to infer the actual depth of the oceans within these moons.
Journal Reference:
- Hamish C. F. C. Hay et al., Powering the Galilean Satellites with Moon‐Moon Tides, Geophysical Research Letters (2020). DOI: 10.1029/2020GL088317