In a new paper accepted to Nature Astronomy and written by Caltech’s Christopher Mankovich and Jim Fuller, the pair used data taken with the Cassini spacecraft of Saturn’s gravity field to analyze the composition and some of the structure of Saturn’s core. They also examined a wave in Saturn’s C-ring, the closest ring to the planet, because those oscillations can be used to help determine that composition, similar to how we use earthquakes here on Earth to understand the interior of our own planet.

Now, some of you may have this picture in your head of a light fluffy cloud of Saturn with a hard, rocky, metallic core at the center. But it turns out while that core does have about 17 Earth masses of rock and ice, there is also a lot of hydrogen and helium mixed in. The entire core is actually 55 Earth masses, more than half of the total mass of Saturn. This means that the core is not a tight little ball; it’s more like a fluffy ball.

So Saturn, like comedian Gabriel Iglesias, is fluffy.

And this work also helps us understand more about how Saturn formed. The previous theory was that a rocky core formed and began to collect dust and gas. Then the heavier materials sank to the center and formed a compact core like I mentioned above. Afterward, that core continued to attract more hydrogen and helium, which are actually liquid under Saturn’s gravity, until we have the gas giant we have today.

Now, scientists think that the gas and rock and ice all got pulled into one fluffy, extended core, and this new paper provides evidence for that formation theory. Instead of a sudden differentiation between the rocks and ice and the gas, there is a gradual increase in the gas content and decrease in the rock and ice content, which reflects a more gradual development of the core over time. And now we have a much better picture of just how Saturn is structured, at least from an observational standpoint.

While it is awesome to be able to directly observe things like Saturn’s rings to measure the inside structure of Saturn, sometimes, you just can’t measure things the way you’d like, so you have to combine the power of computer models with what observations you have and see what theory allows you to discover. 

Another team of Saturn studying researchers used Cassini’s precise measurements of Saturn’s magnetic field to build models of the planet’s interior. It turns out, to get as nice and neat a magnetic field as Saturn happens to have, you have to have a very particular internal structure. Beyond that fluffy core we just discussed, these models, published in AGU Advances by C Yan and S Stanley, take into consideration the near-perfect alignment between Saturn’s rotational axis and magnetic axis – an alignment not seen elsewhere – and study what must be true to see what we see. 

According to Stanley: One thing we discovered was how sensitive the model was to very specific things like temperature. And that means we have a really interesting probe of Saturn’s deep interior as far as 20,000 kilometers down. It’s a kind of X-ray vision. 

Their results hint at a thick layer of helium rain that influences the planet’s magnetic field, and they also indicate we need another mission to Saturn, this time one that can view Saturn’s Poles, so we can better understand Saturn and all its weird and wonderful beauty.

More Information

ScienceNews article

“A diffuse core in Saturn revealed by ring seismology,” Christopher Mankovich and Jim Fuller, submitted to ArXiv (preprint)

Johns Hopkins University press release

“Recipe for a Saturn‐Like Dynamo,” C. Yan and S. Stanley, 2021 May 5, AGU Advances