Ripples in Saturn's rings reveal planet's 'fuzzy' core

Previously, researchers believed Saturn's core was rocky. But data gathered by NASA's Cassini spacecraft, which orbited the ringed planet for 13 years before intentionally plunging into its atmosphere in 2017, suggests a larger core than previously estimated.

Rather than solid rock, Saturn's core is likely what scientists refer to as "fuzzy," or a slushy mix of ice, rock and metallic fluids.

A study on the findings published Monday in the journal Nature Astronomy.

Oscillations occurring within Saturn's interior cause the planet to move, which creates ripples in the planet's stunning system of rings.

"Saturn is always quaking, but it's subtle," said Christopher Mankovich, lead study author and a postdoctoral scholar research associate in planetary science at the California Institute of Technology, in a statement. "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."

The frequency of the gravitational ripples measured in the rings suggest that Saturn's deep interior is stable. When the planet was forming, its interior formed stable layers as heavy materials like rock and ice moved toward the planet's center and lighter materials rose above them.

"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," said Jim Fuller, study coauthor and assistant professor of theoretical astrophysics at Caltech, in a statement.

Their findings also show that Saturn's core is 55 times more massive than our entire planet. About 17 Earth-masses of the core are made of ice and rock -- the rest is a hydrogen and helium-based fluid. The fuzzy core extends across 60% of the planet's diameter.

The results of this research also align with evidence gathered about Jupiter's core by the ongoing Juno mission, which suggests the largest gas giant in our solar system has a similar core.

"The fuzzy cores are like a sludge," Mankovich said. "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."

These discoveries challenge the current models researchers have regarding how gas giants form. Those models suggest that rocky cores are the first to form, which then pull in gas envelopes around them. But the fuzzy core idea may mean that gas is an earlier part of the formation process.

Spiral patterns in Saturn's rings created by the planet's gravitational field were first observed in 2013 by Matt Hedman, a participating scientist for the Cassini mission and an associate professor in the Physics Department of the University of Idaho.

"Christopher and Jim were able to show that one particular ring feature provided strong evidence that Saturn's core is extremely diffuse," Hedman said in a statement. He did not participate in this study.

"I am excited to think about what all the other ring features generated by Saturn might be able to tell us about that planet," Hedman said.

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