Rings of Saturn : four views

Rings of Saturn are one of the most visually exciting and fascinating cosmic sights.

Given the picture of the rings and knowing that the Saturn is about 120,000 km, it seems that the rings have a diameter of about 250,000 km. And based on the picture, I would have guessed that the thickness of the ring must be about 5,000 – 10,000 km.

And of course that is wrong. The first time I looked it up, I was told that the rings are about 1-2 km thick… impossible, I said to myself. How can that be? Especially with 60 moons – and Titan which is the largest moon in the solar system, there must be tidal forces and forces that act asymmetrically when the moons are on the different sides of the planet. How can a complex system like that produce a sharp ring on 1-2 km.

And then we all learned that the thickness of the rings might actually be 10-30 meters!

Things in physics are never this sharp; they are always fuzzy, and have gradient. but thickness of 10 meters for a ring that has a diameter of 250,000 km is just unfathomable.

The rings are also dynamic, in the sense that the clusters within the ring come and go; dissolve and re-form somewhere; yet manage to stay within 10-30 meters.

Some have argued that the rings remain so tight because of all those moons – the moons act like traffic cops and keep them in line. Yah, sure.. take 60 orbiting objects of different size and different placement and they all conspire to have a razor sharp plane where everything settles down! May be it is true, but I just don’t buy it, not yet, anyway.

I see it, I read about it, I see all the calculations, but my astonishment is never diminished.

The physics is most interesting when the results are hard to fathom; The laws of physics retain the right to astonish you.

Sort of reminds me of a friend of mine – an aerospace engineer, who was doing his postdoc on helicopter dynamics. And once a while, he would just whirl his textbook or the journal he was reading and exclaim “I still don’t understand how this damn thing flies!!!’…. I sympathize with him, I still don’t understand how the rings of Saturn are so sharp and so stable.

here are four views of the rings:

(1) Sketch of Saturn by Galileo in 1616 and first sketch of a gap in the rings by Cassini from 1676.

(2) A short video of Saturn and its rings – from Bad Astronomy

(3) Sounds of Saturn rings – rings are very active source of radio waves. Cassini space craft captured these radio sounds.

(4) A-F rings and various gaps. The images in this view were obtained on May 9, 2007. Image scale is about 6 kilometers per pixel.

Talk Like a Physicist