![]() Multiple sources were needed to get a handle on the ringed planet's auroras: In 2014, NASA released images taken from data from Cassini (in infrared, visible light and ultraviolet) as well as the Earth-orbiting Hubble Space Telescope (in ultraviolet wavelengths) that lent insight into how the auroras change over time. Sometimes, it takes multiple spacecraft to get a full picture of what's going on at Saturn. NASA/JPL/ASI/University of Arizona/University of Leicester How soon will the atmosphere at the location of the 2010-2011 storm return to normal? Captured here by Cassini are Tethys at upper right, Enceladus below center and Janus at lower left, along with the planet's rings. In this photo, three very different moons provide targets of great interest for planetary scientists who are studying the Saturn system. A newer direction of research suggests using Saturn's gravity field to learn more about the planet's insides, but this is a work in progress. That paper suggested a rotation period of 10 hours, 32 minutes and 35 seconds, which would imply that Saturn's interior has a "molecular to metallic hydrogen transition about halfway to the planet's center," the paper stated." Since then, however, scientists have found that Saturn's wind speed changes between measurements, making it harder to predict the composition of the interior. In 2007, research led by the University of California's John Anderson and published in the journal Science combined gravitational data with Pioneer and Voyager radio occultation and wind data. The state of Saturn's interior remains a mystery, which makes the length-of-day measurement difficult to obtain. What does the gravity field reveal about the winds, composition, and phase changes of the interior? As of mid-2017, the precise ratio is still not known. At the time, Gautier's group performed several radio occultation measurements near the equator but received different results. The helium-to-hydrogen ratio of 0.034 "is difficult to reconcile with plausible theories of the evolution of the planet," an abstract by the team said. In 2006, a group of scientists led by Daniel Gautier of the Paris Observatory noted that 1980s measurements by the Voyager spacecraft didn't make much sense. Precisely narrowing down the ratio of helium to hydrogen helps scientists understand what the inside of each planet looks like, and how they came to be. These are the elements that principally make up our sun as well as the largest gas giant planets: Jupiter and Saturn. Helium and hydrogen are the two most abundant elements in the universe, and also in our own solar system. What is the mass of Saturn's ring system? ![]() But it's still not known how long a day is on Saturn. In 2011, NASA said the variations in radio-wave periods likely came from changes in high-altitude winds in both hemispheres. "The northern and southern rotational variations also appear to change with the Saturnian seasons, and the hemispheres have actually swapped rates." "Variation in radio waves controlled by the planet's rotation is different in the northern and southern hemispheres," NASA wrote in 2014. Jupiter sends out radio waves that sync with the planet's rotation, but Saturn's emission, called Saturn kilometric radiation, does not do the same thing. At first, scientists thought they could determine that length based on radio waves emitted by the planet, as they did at Jupiter. After more than a decade, Cassini still hasn't closed in on one of Saturn's fundamental properties: how long a day is in its interior (how long it takes to rotate all the way around).
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