NASA's Cassini spacecraft observed Saturn's ring system in unprecedented detail, and a team of planetary scientists from the University of California Santa Cruz and NASA's Ames Research Center have now used these observations to revise the gas giant's rotation period. According to their calculations, the length of one day on Saturn is 10 hours 33 minutes and 38 seconds – 53 seconds longer than an estimate made three years ago.
"We now have the length of Saturn's day when we thought we couldn't find it," said Cassini project researcher Dr. Linda Spilker, a planet researcher at NASA's Jet Propulsion Laboratory.
"They used the rings to look into Saturn's interior and drive out this much sought after, basic quality on the planet. And that is a really solid result. The rings kept the answer."
University of California Santa Cruz researcher Christopher Mankovich and Colleagues studied wave patterns created within Saturn's rings of the planet's inner vibrations.
The ring seems like an extremely sensitive seismograph by responding to vibrations in the planet itself.
Like the earth's vibrations from an earthquake, Saturn responds to disturbances by vibrating at frequencies determined by its internal structure. Hot-powered convection in the interior is the most likely source of vibration.
These internal fluctuations cause the density at a particular location in the world to change, making the gravitational field outside the planet oscillate at the same frequencies. 19659005] "The particles in the whole rings can't help feeling these fluctuations in the gravity field," Mankovich said.
"At certain places in the rings, these oscillations capture ring particles at the right time in their orbits to gradually build up energy and that energy is carried away as an observable wave."
"Most of the waves that observed in Saturn's rings is due to the gravitational effect of the moons that orbit outside the rings, "said University of California Santa Cruz professor Jonathan Fortney, co-author of the study.
"But some of the functions of the rings are due to the actual oscillations on the planet itself, and we can use them to understand the internal evolution and internal structure of the e-planet."
The team developed a set of models of Saturn's inner structure, them to predict the frequency spectrum of Saturn's inner vibrations and compare these predictions with the waves observed by Cassini in Saturn's C ring.
One of the most important results is the new calculation of Saturn's rotational speed, which has been surprisingly difficult to measure.
"As a giant planet, Saturn does not have a solid surface with landmarks that could be traced as it rotates," the researchers explained.
"Saturn is also unusual in having its magnetic axis almost perfectly aligned with its axis of rotation."
"Jupiter's magnetic axis, like the Earth's, is not aligned with its axis of rotation, which means that the magnetic pole swings around as the planet rotates. so astronomers can measure a periodic signal in radio waves and calculate the rotational speed. "
The results appear from Astrophysical Journal . Christopher Mankovich et al . 2019. Cassini Call Seismology as a Probe of Saturn's Interior. I. Stiff rotation. 871, 1; doi: 10.3847 / 1538-4357 / aaf798