How Saturn shakes its rings

As well as its moons, Saturn itself can create "waves" in its rings. Credit: NASA / JPL / Space Science Institute
As well as its moons, Saturn itself can create “waves” in its rings.
Credit: NASA / JPL / Space Science Institute

Saturn’s rings are one of the most beautiful sights in the solar system. They are an amazing planetary phenomenon – countless bits of rock, ice and dust orbiting the planet in relatively paper-thin rings, which, when seen from above, kind of look like a giant vinyl record (remember those?). Saturn’s many moons can affect the rings’ appearance due to their gravitational pull. Now, new research shows how Saturn itself can do this also, essentially “shaking” its rings.

The gravitational pull from the moons creates “waves” in the rings, a bit like ripples in water. Most of these are in the outer A ring, the main ring closest to the moons. Others, though, are in the C ring, closest to the planet. Since the moons couldn’t cause these waves, being too far away, their formation is now thought to be caused by Saturn itself.

Matthew Hedman and Philip Nicholson at Cornell University used data from the Cassini spacecraft to reach their conclusions. As Hedman states, “We found that Saturn probably is affecting the rings just as the moons do.” They were able to map six waves in the C ring in detail, by measuring how starlight from background stars is absorbed in the ring.

According to Jonathan Fortney at the University of California, “It’s incredibly important. It opens up the possibility of using seismic data to understand the structure of a giant planet, which has been phenomenally successful for the sun and for Earth.”

Basically, as material in Saturn’s interior moves around, it affects the planet’s gravitational field, which in turn creates waves in the rings.

As well as providing new information about the structure and behaviour of the rings, the study should help scientists learn more about the interior of the planet itself. This can then be applied to other gas giant planets in other solar systems as well. As Hedman notes, “Jupiter and Saturn provide close-by versions of what gas-giant planets are, so if we can understand the interior structure of these guys pretty well, we should be able to better understand other giant planets too.”

The new findings will be published in a future issue of The Astronomical Journal.

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