A mystery about our solar system – how long is a day on Saturn? – has been solved with new data analysis. This number was hard to calculate because the gas giant does not have a solid surface. There are no landmarks that can be tracked on rotation of the planet. In addition, a magnetic field makes the rotational speed difficult to detect.
Now, NASA scientists have used Cassini probe data to find a final answer: a day on Saturn is ten hours, 33 minutes and 38 seconds long. The new 10:33:38 daily length is slightly shorter than previous estimates, such as the 1981 10:09:22 estimate, which is based on Voyager magnetic field data.
The new number was calculated using Saturn's rings, which Cassini used during his mission from the start of 1997 to the planet's destruction to collect many detailed data in 2017. During his mission Saturn's orbit from 2004, the ship collected high-resolution images of the planet and data about its icy, rocky rings. These data were then used by PhD student Christopher Mankovich to study the wave patterns in the rings.
Mankovich found that the rings acted as a kind of seismometer and responded to vibrations that occurred on the planet. As the interior of the planet vibrates and earthquakes occur, the vibrational frequencies cause fluctuations in the gravitational field of the planet, and these fluctuations are transmitted to the rings. "Particles in the rings can not feel these vibrations in the gravity field," Mankovich explained in a statement. "At certain points in the rings, these vibrations capture their orbital ring particles at just the right time to gradually build up energy, and this energy is carried along as an observable wave."
This means that scientists can now track the movements from within the planet, and from this tracking they can see the planet's rotation. This allowed them to calculate the exact length of a day on Saturn. "The researchers used waves in the rings to look into the interior of Saturn and rustled this long sought, fundamental property of the planet. And it's a really solid result, "said Linda Spilker, the scientist of the Cassini project. "The rings contained the answer."
The newspaper is available in the Physics archive arXiv.