Measuring the rotation of Saturn is actually a more complicated job than you might think. That’s because Saturn is just a ball of hydrogen and helium, without any solid surface features that you can measure from day to day. Saturn’s rotation is even more complicated than that, since different parts of the planet rotate at different speeds. So asking what the rotation of Saturn is depends on which part of the planet you’re talking about.
The visible features of Saturn rotate at different rates depending on their latitude (distance from the equator). Astronomers have developed three different systems for measuring the rotational speed of Saturn. System I is for regions around the planet’s equator. The System I rotation speed is 10 hours and 14 minutes. Above and below the Equatorial Belt is called System II. Here the rotation speed is 10 hours and 39 minutes.
System III is based on the rotation of Saturn’s magnetic field, and was measured by NASA’s voyager spacecraft. They determined that Saturn’s magnetic field takes 10 hours and 39 minutes to complete a rotation. But here’s a strange mystery. The rotation of the magnetic field was measured again by NASA’s Cassini spacecraft in 2004, and it found that the rotation of the magnetic field had slowed down to 10 hours and 45 minutes. So it appears that the rotation of Saturn can change over time.
We have written many articles about Saturn for Universe Today. Here’s an article that goes into much more detail about the process of measuring a day on Saturn.
We have recorded a podcast just about Saturn for Astronomy Cast. Click here and listen to Episode 59: Saturn.