![]() ![]() They were working on lots of other science too, and were very successful, but they failed to solve the problem of its rotation rate. The Cassini magnetometer and radio and plasma wave science teams spent the rest of the mission trying to find a signal in their data that accurately represented the rotation rate of Saturn. They are measuring something rotating, but it's not the bulk rotation of the planet. ![]() Later on in the Cassini mission, the team realized that their data showed different rotation rates in the northern and southern hemispheres! Clearly, the method of using radio emissions to measure Saturn's rotation rate did not work the way it did at other giant planets. One - or both - of the measurements was wrong. (That's 10.8 hours.) Saturn didn't slow down between Voyager in 1981 and Cassini in 2004 there is no force in the solar system that could have made such a massive planet slow its rotation so much, so rapidly. The answer - 10 hours, 45 minutes, 45 ± 36 seconds - was more than 6 minutes longer than the Voyager measurement. When Cassini got to Saturn, it also measured Saturn's rotation rate from its radio emissions. Voyager precisely measured the day lengths of Jupiter ( 9h 55m 29.71s), Uranus ( 17h 14.4m ± 0.6m), and Neptune ( 16h 6.5m ± 0.4m) as well as Saturn. If the magnetic field has any angle to the rotation pole, then the magnetic field sweeps around the planet like the beam of a lighthouse, and there's a pulsing to the radio emissions in time with the planet's rotation rate. All the giant planets have magnetic fields. Electrons zipping around in magnetic fields generate radio emissions. Voyager measured the rotation rates of all four outer planets using their radio emissions. (Jupiter rotates fast, too, and is also oblate, but less so.) It's so fast that Saturn is very clearly oblate - it's dramatically fatter at the equator than the poles, 10 percent wider than it is high. The Voyager missions gave us one answer: 10 hours, 39 minutes, 24 seconds (that is, 10.7 hours). "How long is one day on Saturn?" is such a seemingly simple question. ![]() Is there life elsewhere? Why is Venus different from Earth? If I lived on Saturn, how long would a day be there? I often argue that a reason that space science is so accessible is that the questions that space scientists ask are very easy questions for the general public to understand. I actually think that's kind of wonderful. One of the Cassini mission's goals was to figure out how long a day on Saturn is. That's how it happens that I'm writing today about a new measurement of the rotation period of Saturn that is different from past measurements. Scientists! Post your preprints on Twitter! A science writer might notice it and write about it. ![]()
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