Shepherd Moons and Jovian Rings


When I was an undergraduate, I remember how we looked on with amazement as the first images of Saturn’s ring system were sent back from Voyager. While Pioneer sent back the first images while I was still a freshman, the detailed images from Voyager were astonishingly better – and they showed a detailed structure in the ring system that was a total surprise.

I remember looking at an picture of a braided ring structure, and seeing the spokes clearly and hearing my professors saying there’s no way gravity can do such a thing.

Years later we realized the connection between Saturn’s complicated ring system and Saturn’s nearly as complicated collection of moons. The moons, especially those that orbit in very nearly the same path are the reason for the ring structures – and the effect is most often caused by “shepherding“.

As someone who had to try to explain all this, I was never satisfied that I was successful. I had graphs, I tried to demonstrate the effect with balls rolled along a lab table, I tried getting the students up and moving and “playing Saturn”.

So I’m quite envious of those teaching Astronomy today because they have these wonderful new movies of actual shepherding of Jupiter’s rings that were taken by the Pluto probe as it makes it’s way across the solar system:

“The New Horizons spacecraft took the best images of Jupiter’s charcoal-black rings as it approached and then looked back at Jupiter in February 2007. This sequence of pictures from the Long Range Reconnaissance Imager (LORRI) shows the well-defined lanes of gravel- to boulder-sized material composing the bulk of the rings; labels point out how these narrow rings are confined in their orbits by small ‘shepherding’ moons (Metis and Adrastea).”

Just so cool. And it comes with a movie too!

Read the rest here: New Horizons Web Site

The Author

Episcopal bishop, dad, astronomer, erstwhile dancer...


  1. Paul Martin says

    You could do an impressive multimedia sermon for Good Shepherd Sunday. It would certainly be a unique way of approaching the subject.

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