“Hidden in the Rings” –Cassini Data Solves Mystery of Length of Saturn Day

Cassini Finale

 

 

“The researchers used waves in the rings to peer into Saturn’s interior, and out popped this long-sought, fundamental characteristic of the planet. And it’s a really solid result,” said Cassini Project Scientist Linda Spilker. “The rings held the answer.”

Using new data from NASA’s Cassini spacecraft, researchers believe they have solved a longstanding mystery of solar system science: the length of a day on Saturn. It’s 10 hours, 33 minutes and 38 seconds. The figure has eluded planetary scientists for decades, because the gas giant has no solid surface with landmarks to track as it rotates, and it has an unusual magnetic field that hides the planet’s rotation rate.

The answer, it turned out, was hidden in the rings.

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During Cassini’s orbits of Saturn, instruments examined the icy, rocky rings in unprecedented detail. Christopher Mankovich, a graduate student in astronomy and astrophysics at UC Santa Cruz, used the data to study wave patterns within the rings.

His work determined that the rings respond to vibrations within the planet itself, acting similarly to the seismometers used to measure movement caused by earthquakes. The interior of Saturn vibrates at frequencies that cause variations in its gravitational field. The rings, in turn, detect those movements in the field.

“Particles throughout the rings can’t help but feel these oscillations in the gravity field,” Mankovich said. “At specific locations in the rings these oscillations catch ring particles at just the right time in their orbits to gradually build up energy, and that energy gets carried away as an observable wave.”

Mankovich’s research, published Jan. 17 by Astrophysical Journal, describes how he developed models of Saturn’s internal structure that would match the rings’ waves. That allowed him to track the movements of the interior of the planet – and thus, its rotation.

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The rotation rate of 10:33:38 that the analysis yielded is several minutes faster than previous estimates in 1981, which were based on radio signals from NASA’s Voyager spacecraft. The analysis of Voyager data, which estimated the day to be 10:39:23, was based on magnetic field information. Cassini used magnetic field data, too, but earlier estimates ranged from 10:36 all the way to 10:48.

The Daily Galaxy via NASA/JPL 

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