Determining the length of a day on a planet is usually quite easy. You just choose a landmark and wait until it reaches the exact same point twice in rotation and you have an answer. For astronomers who study Saturn, it's not that easy.
Saturn has no visible landmarks to track, and its gas atmosphere does not offer many clues about how fast it actually rotates. In addition, the magnetic field also hides the speed of the rotating body. The researchers were confused about how to track the planet's rotation, but using data from NASA's Cassini spacecraft, the code finally cracked.
Christopher Mankovich, a graduate student at UC Santa Cruz, found that Cassini's observations of Saturn's fine ring structure really hold the key to determining the rate at which Saturn itself rotates. Mankovich carefully observed the subtle wave patterns inside the ring, determined that the waves were caused by a specific location on the planet as he spun, and tracking them could solve rotational puzzles once and for all.
"The particles throughout the ring cannot help feeling this oscillation in the gravitational field," Mankovich said in a statement. "In certain locations within the ring, this oscillation captures ring particles at the right time in their orbit to gradually build up energy, and that energy is carried as observable waves."
Using this data, Mankovich can determine that one day on Saturn lasts for 10 hours, 33 minutes, and 38 seconds. A few decades ago, astronomers who used magnetic field data from Voyager estimated that one day Saturn was 10 hours, 39 minutes and 23 seconds. This new study helps to clarify these initial estimates a little, and offers the most accurate measurements in a day on planet rings.