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Saturn’s rings are jiggling, delightfully enough, due to its wobbly core

Saturn Makes Waves in its Own Rings

Our solar system is full of wonders, like the beauty of Saturn’s rings. But these rings aren’t static — recent research shows that they are gently jiggling.

Astronomers from the California Institute of Technology looked at data about Saturn from the now-defunct Cassini mission which orbited the planet between 2004 and 2017. They investigated the planet’s core, and found that it is not solid, as some previously thought, but is what Caltech describes as “a diffuse soup of ice, rock, and metallic fluids,” which makes for a type of call technically called a fuzzy core.

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An illustration of Saturn and its "fuzzy" core.
An illustration of Saturn and its “fuzzy” core. Caltech/R. Hurt (IPAC)

The researchers were able to determine both the composition and the size of the core — which stretches across 60% of the planet’s diameter — by looking at the rings. “We used Saturn’s rings like a giant seismograph to measure oscillations inside the planet,” explained co-author Jim Fuller, assistant professor of theoretical astrophysics at Caltech. “This is the first time we’ve been able to seismically probe the structure of a gas giant planet, and the results were pretty surprising.”

The fuzzy core has a profound effect on the planet. “The fuzzy cores are like a sludge,” explains the lead author of the study, Christopher Mankovich. “The hydrogen and helium gas in the planet gradually mix with more and more ice and rock as you move toward the planet’s center. It’s a bit like parts of Earth’s oceans where the saltiness increases as you get to deeper and deeper levels, creating a stable configuration.”

This sludge oscillates slightly, which makes the whole planet jiggle. In turn, this causes ripples in the rings which the Cassini data showed.

“Saturn is always quaking, but it’s subtle,” says Mankovich. “The planet’s surface moves about a meter every one to two hours like a slowly rippling lake. Like a seismograph, the rings pick up the gravity disturbances, and the ring particles start to wiggle around.”

As well as being a delightful mental image, this finding leads to questions about how gas giants form. The current leading theory of their formation is that they begin with a rocky core. Over time, this core attracts gas through gravity, and these gases eventually form part of the planet. But if Saturn has a fuzzy core, it raises the question of whether gas is a key part of the formation of gas giants earlier than previously thought.

The findings are published in the journal Nature Astronomy.

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