Using new data from the NASA spacecraft Cassini, researchers believe they have solved a mystery of solar system science for a long time: the duration of a day in Saturn. Ten hours, 33 minutes and 38 seconds.
It is a figure that has denied planetary scientists for decades, because the gas giant does not have a solid surface with milestones to continue while it is rotating, and has an unusual magnetic field that hides the rotation speed of the planet.
The answer, it turned out, was hidden in the rings.
During Cassini Saturn's orbits, the instruments examined the frozen and rocky rings in unprecedented details. Christopher Mankovich, a graduate in astronomy and astrophysics at the University of California, Santa Cruz, used the data to study pattern patterns within the rings.
His work determined that the rings responded to the vibrations within the planet, acting similarly to the seismomers used to measure the movement caused by earthquakes. The interior of Saturn vibrates at frequencies that cause variations in its gravitational field. The rings, in turn, detect these movements in the field.
"Particles along the rings can not stop feeling these oscillations in the field of gravity," said Mankovich. "In specific locations of the rings, these oscillations capture ring particles at the right time in their orbits to accumulate energy, and that energy is transmitted as an observable wave."
The investigation of Mankovich, published on January 17 of the Astrophysical Journal, describes how he developed models of Saturn's internal structure that coincided with the waves of the rings. This allowed him to follow the movements of the interior of the planet and, therefore, its rotation.
The rotation speed at 10:33:38 that the analysis produced is several minutes faster than previous estimates in 1981, which were based on NASA's Voyager ship's radio signals.
Voyager data, which estimated the day at 10:39:23, was based on information on the magnetic field. Cassini also used data from the magnetic field, but previous estimates range from 10:36 a.m. to 10:48.
Scientists often rely on magnetic fields to measure the rotation rates of the planets. The magnetic axis of Jupiter, like the one on the Earth, is not aligned with its axis of rotation. So it turns as the planet rotates, allowing scientists to measure a periodic radio waves signal to achieve the rotational speed. However, Saturn is different. Its unique magnetic field is perfectly aligned with its axis of rotation.
This is the reason why finding the ring has been key to taking charge of the duration of the day. Saturn scientists are anxious to have the answer to such a central question about the planet.
"The researchers used waves in the rings to look at Saturn's interior, leaving this fundamental and fundamental feature of the planet, and it is a very solid result," said Cassini project scientist Linda Spilker "The rings kept the answer".
The idea that Saturn's rings could be used to study the seismology of the planet was suggested for the first time in 1982, long before possible, the necessary observations.
Co-author Mark Marley, now at the NASA's Ames Research Center in California's Silicon Valley, deepened the idea of his Ph.D. thesis in 1990, showing how the calculations could be made and predicted where the signatures of Saturn's rings would be. He also pointed out that the mission of Cassini, then in the planning stages, would be able to make the necessary observations to prove the idea.
"Two decades later, in the last years of the Cassini mission, scientists analyzed the mission data and found ring functions in the locations of Mark's predictions," said co-author Jonathan Fortney , professor of astronomy and astrophysics at UC Santa Cruz and member of the Cassini team. "This current job seeks to take advantage of these observations."
Cassini's mission ended in September 2017 when, with little fuel, he deliberately plunged into the Saturn atmosphere by the mission team, who wanted to avoid breaking the boat towards the moons of the planet, polluting them.
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. The NASA Air Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for the Director of the NASA Science Mission, Washington. JPL designed, developed and mounted the Cassini orbiter. The radar instrument was built by JPL and the Italian Space Agency, working with members of the United States and several European countries.
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