Research: Waves in Saturn's rings provide precise measurement of planet rotation rate –


Saturn's distinctive rings were observed in unprecedented detail at NASA's Cassini spacecraft, and scientists have now used those observations to probe the interior of the giant planet and obtain the first precise determination of its rotation rate. The length of a day on Saturn, according to their calculations, is 10 hours 33 minutes and 38 seconds.

The researchers studied wave patterns created within the Saturn's rings of the planet's internal vibration. In fact, these rings act as a very sensitive seismograph by responding to vibrations within the planet itself.

Similar to Earth's vibrations of an earthquake, Saturn responds to perturbations by vibrating at frequencies determined by its internal structure. Heat-driven interior convection is the most likely source of these vibrations. The internal oscillations bake the density at any particular location within the planet to oscillate, which causes the gravitational field outside the planet to be at the same frequencies.

"Particles in these rings feel the oscillation in the gravitational field. In places where the oscillation has been rated with ring orbits, energy begins and becomes a wave," explained Christopher Mankovich, a graduate student in Astronomy and Astrology. At UC Santa Cruz.

Mankovich is the leader of a paper, published on 17 January Astrophysical magazineComparing the wave patterns in the rings with the Saturn interior structure.

Most of the waves observed in Saturn's rings are due to the Moons' gravitational effects outside the rings, co-starring Jonathan Fortney, Astronomy Professor and Astrophysics at UC Santa Cruz. "But some of the rings' features are due to the oscillations of the planet itself, and we can use these to understand the planet's internal oscillations and internal structures," he said.

Mankovich developed a set of models of the Saturn's internal structure, used them to predict the frequency spectrum of Saturn's internal vibrations, and compared the predictions with the waves observed by Cassini in Saturn's C ring. One of the main results of his analysis was the new calculation of Saturn's rotation, which was surprisingly difficult to measure.

Like a gas giant planet, Saturn has no solid surface with landmarks that could be tracked as it rotates. Saturn is also unusual in that its magnetic axis is almost aligned with its rotational axis. Jipiter's magnetic axis, like Earth's, is not aligned with its rotational axis, which means that the magnetic pole swings around as the planet rotates, enabling astronomers to measure periodic signals into radio waves and calculate the rotation rate.

The rotation rate of 10:33:38 determined by Mankovich's analysis is several minutes faster than previous estimates based on Vyager and Cassini spacecraft radios.

"We now have the length of Saturn's day, when we think we would not be able to find it," said Casinini Project Scientist Linda Spiler. "They used the rings to appear in Saturn interior, and to remove this long-looking, fundamental quality of the planet. And it's a really tough result. Those rings were the answer."

The idea that Saturn's rings could be used to study the cosmology of the planet was first suggested in 1982, long before the necessary observations are possible. Afterwards Marley Marki, now at NASA's Ames Research Center in Silicon Valley, subsequently flattened out the idea for his Ph.D. 1990's thesis showed how the calculations could be done, and predicted what features in Saturn's rings would be. He also noted that the Cassini mission, then in the planning stages, would be able to make the observations needed to try this idea.

"Two decades later, the Cassini data were viewed and ringing features found at Mark's predictions," Fortney said.


University of California – Santa Cruz. Originally written by Theme Stephens. .

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