On March 29th, 2015 we learned about

Saturn spins at 1/632 RPM

Earth rotates once every 23 hours, 56 minutes and 4 seconds. We round that up to 24 hours, and call it a day. Mars takes around 24 hours, 37 minutes, Venus takes a whopping 243 days. Measuring a day on gas giants like Saturn is much trickier though, since there are no surface features to track from space. For this reason, we still aren’t completely sure how long Saturn takes to rotate, but new estimates are closing in on that figure.

Since Saturn is covered in swiftly moving clouds, we can’t see it’s rocky surface to track any stationary object’s rotation time. Tracking changes in the magnetic field in the 1980s gave us the first estimate of 10 hours and 39 minutes. Later measurements from the Cassini satellite moved that up to 10 hours and 45 minutes. The latest estimates, made by combining gravitational pull, estimates of the planet’s core’s density and statistical analysis, put a day on Saturn at 10 hours, 32 minutes and 45 seconds, give or take 46 seconds.

Why worry about Saturn’s schedule?

The interest in these measurements isn’t because we want to plan our day out whenever we get a chance to visit Saturn. Knowing the length of a day can actually helps inform us about the wind speed on the surface, the planet’s structure, and how it originally formed. These methods can then hopefully be applied to studying other planets outside our solar system.


My kindergartner asked: Why we don’t fly Cassini down to the surface to take a look at exactly what’s going on there? Once the satellite got too close, aside from needing to dodge ice and rock surrounding the planet, it doesn’t have the engines necessary to overcome the gravity experienced on the surface, most likely ending the mission.

Source: A Day's A Day The World Around — But Shorter On Saturn by Geoff Brumfiel, The Two-Way

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