Now We Know the Length of a Day on Saturn

Feb 17, 2019

Remember back in 2017 when the Cassini space craft dove through Saturn’s rings and plunged to its death in Saturn’s atmosphere? Well, like the Mars rover Opportunity, Cassini’s legacy lives on in the data it sent back.

And now, thanks to that data, scientists have figured out that a day on Saturn lasts 10 hours, 33 minutes, and 38 seconds. Plus or minus a minute or two.

Figuring out the length of a day on Saturn was tricky because it’s a fluid planet, which means you can't just track features on the surface and time how long they take to go around.

Jupiter is a fluid planet, too, but it has a magnetic field that rotates with it. So scientists can track a day on Jupiter by watching the magnetic field.

“But for Saturn…its magnetic field as far as we can tell is perfectly aligned with its rotation axis,” said UC Santa Cruz graduate student Chris Mankovich. “Which means that you can stare, and stare, and stare at the magnetic field and it just doesn't change.”

Instead, Mankovich used Saturn’s “ring seismology” to determine that Saturn is spinning five to eight minutes faster than the most commonly cited rotation rate.

“We think that old rate was not really tracking the inside of the planet,” Mankovich told Living Lab Radio.

“If you look closely at the rings, you can find waves,” he said. “And, in general, those waves are the product of satellites orbiting Saturn just pulling and pushing on the rings.”

The waves are caused by Saturn oscillating in a way that's a lot like earth shaking after an earthquake.

“It turns out that the frequencies of the planet’s oscillations are really strong function of how quickly it rotates,” he said.

Next, Mankovich would like to better understand another class of waves that are closer to Saturn’s core. Ultimately, he’d like to know what makes up the center of Saturn.  

“So, whether or not there is a solid core, how big it is, and whether or not a solid core might have eroded over time,” he said.

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