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What is the secret behind Saturn's unique magnetic field?

New simulations from researchers at Johns Hopkins University offer an intriguing look into the planet's interior

This was the spacecraft Cassini’s view from orbit around Saturn on January 2, 2010. Saturn is the second largest planet in our solar system. (NASA/JPL-Caltech/Space Science Institute)

The second largest planet in our solar system, Saturn, is a cosmic marvel. Like its fellow gas giant Jupiter, Saturn is a massive ball made mostly of hydrogen and helium. One of its unique characteristics is its enormous magnetosphere. According to Nasa, Saturn's magnetic field is smaller than Jupiter's. But it is still 578 times as powerful as Earth's.

Now, new simulations from Johns Hopkins University show an intriguing look into Saturn's interior, suggesting that a thick layer of helium rain influences the planet's magnetic field.

The models, which were published recently in the journal AGU Advances, also indicate that Saturn's interior may feature higher temperatures at the equatorial region, with lower temperatures at the high latitudes at the top of the helium rain layer.

It is very difficult to study the interior structures of large gaseous planets, and these findings advance the effort to map Saturn's hidden regions. "By studying how Saturn formed and how it evolved over time, we can learn a lot about the formation of other planets similar to Saturn within our own solar system, as well as beyond it," co-author Sabine Stanley, a Johns Hopkins planetary physicist, says in a news release.

Saturn stands out among the planets in our solar system because its magnetic field appears to be almost perfectly symmetrical around the rotation axis. Detailed measurements of the magnetic field gleaned from the last orbits of Nasa's Cassini mission provide an opportunity to better understand the planet's deep interior, where the magnetic field is generated, lead author Chi Yan, a Johns Hopkins PhD candidate, explains in the release.

Also read: Why do we seek planets outside the solar system?

The magnetic field of Saturn seen at the surface.
The magnetic field of Saturn seen at the surface. (Ankit Barik/Johns Hopkins University)

By feeding data gathered by the Cassini mission, which ended in 2017, into powerful computer simulations similar to those used to study weather and climate, Yan and Stanley explored what ingredients are necessary to produce the dynamo -- the electromagnetic conversion mechanism -- that could account for Saturn's magnetic field.

"One thing we discovered was how sensitive the model was to very specific things like temperature," said Stanley, who is also a Bloomberg Distinguished Professor at Johns Hopkins in the Department of Earth & Planetary Sciences and the Space Exploration Sector of the Applied Physics Lab. "And that means we have a really interesting probe of Saturn's deep interior as far as 20,000 kilometres down. It's a kind of X-ray vision."

The simulations suggest that a slight degree of non-axisymmetry could actually exist near Saturn's north and south poles. "Even though the observations we have from Saturn look perfectly symmetrical, in our computer simulations we can fully interrogate the field," Stanley adds.

Direct observation at the poles would be necessary to confirm this, but the finding could have implications for understanding another problem that has vexed scientists for decades: how to measure the rate at which Saturn rotates, or, in other words, the length of a day on the planet.

Also read: How long is solar system's longest day? Venus has the answer

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