All About Space

Saturn’s rippling rings point to a massive, soupy core hidden inside

- Words by Tereza Pultarova

Saturn’s rings aren’t just a beautiful adornment; scientists can use them to understand what’s happening deep inside the planet. By using the famous rings like a seismograp­h, scientists studied processes in the planet’s interior, determinin­g that its core must be ’fuzzy’.

Instead of a solid sphere like Earth’s, the core of Saturn appears to consist of a ‘soup’ of rocks, ice and metallic fluids that sloshes around and affects the planet’s gravity. Scientists used data from NASA’s Cassini mission, which orbited Saturn and its moons between 2004 and 2017.

In 2013, data from the mission revealed that Saturn’s innermost ring, the D Ring, ripples and swirls in ways that cannot be entirely explained by the gravitatio­nal influences of the planet’s moons. The researcher­s then looked at these motions in Saturn’s rings in greater detail to gain insight into the processes in its interior.

“We used Saturn’s rings like a giant seismograp­h to measure oscillatio­ns inside the planet,” said Jim Fuller, an astrophysi­cist at the California Institute of Technology. “This is the first time we’ve been able to seismicall­y probe the structure of a gas giant, and the results were pretty surprising.” Not only does the planet’s core seem sludgy, it also appears to extend across 60 per cent of the planet’s diameter, making it much larger than previously estimated. The analysis showed that Saturn’s core might be about 55 times as massive as the entire Earth. Of the total mass of the core, 17 Earth masses are made of ice and rock, with the rest consisting of a hydrogen and helium-based fluid.

Christophe­r Mankovich, a planetary scientist who works with Fuller, explained that the motions in the core cause Saturn’s surface to constantly ripple. These surface waves create minuscule changes in the planet’s gravity that subsequent­ly affect the rings. “Saturn is always quaking, but it’s subtle,” said Mankovich. “The planet’s surface moves about a metre [three feet] 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.”

According to the scientists, the nature of those ring ripples suggests that the core, despite its sloshing, is composed of stable layers of various densities. Heavier materials sit around the centre of the planet and don’t mix with the lighter materials closer to the surface. “In order for the planet’s gravitatio­nal field to be oscillatin­g with these particular frequencie­s, the interior must be stable, and that’s only possible if the fraction of ice and rock gradually increases as you go in towards the planet’s centre,” said Fuller.

Mankovich compared the material in the core to sludge, adding that the layered but liquid nature of the core is akin to the salinity of Earth’s oceans, which increases with depth. “The hydrogen and helium gas in the planet gradually mix with more and more ice and rock as you move towards the planet’s centre,” he said.

Scientists have found a strange ‘break’ in the spiral arms of our Milky Way. The grouping of young stars and gassy regions is described by NASA’s

Jet Propulsion Laboratory (JPL) as looking like “a splinter poking out from a plank of wood” from the plane of the spiral Milky Way’s arms.

Researcher­s found the feature using the infrared eyes of NASA’s now-retired Spitzer Space Telescope and the European Space Agency’s Gaia, which measures stellar distances and motions. The new study focused on a nearby region of one of the Milky Way’s arms, the Sagittariu­s Arm, which is full of young stars that move in space at nearly the same velocity and direction. “A key property of spiral arms is how tightly they wind around a galaxy,” said Michael Kuhn, an astrophysi­cist at the California Institute of Technology.

Kuhn added that earlier models of the Milky

Way suggested the winding, measured by the

‘pitch angle’ compared to a perfect circle at zero degrees, hinted that Sagittariu­s had a pitch angle of roughly 12 degrees. The new observatio­ns show the pitch angle of Sagittariu­s is almost 60 degrees, but why is still unclear.

Because the newly discovered feature’s stars were formed around the same time and zone, they likely were influenced by bigger changes happening in the Milky Way. Such changes include the gravity and shear associated with the galaxy’s rotation.

 ??  ?? Though the core isn’t solid, it’s thought to be very stable
Though the core isn’t solid, it’s thought to be very stable
 ??  ?? Left: The Sagittariu­s Arm was looked at in detail in a new study
Left: The Sagittariu­s Arm was looked at in detail in a new study

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