Amazing Ring Ripples


Two shepherding moons continue to affect Saturn’s F ring in this amazing image captured by Cassini. Pandora on the outside of the ring and Prometheus on the inside, periodically create what are called “streamer-channels,” seen here in the F ring. The potato-shaped Prometheus pulls a streamer of material from the ring and leaves behind a dark channel. During its 14.7-hour orbit of Saturn, Prometheus (102 kilometers, or 63 miles across) reaches the point in its elliptical path, called apoapse, where it is farthest away from Saturn and closest to the F ring, and the moon’s gravity is just strong enough to draw a “streamer” of material out of the core region of the F ring.

The creation of such streamers and channels occurs in a cycle that repeats each Prometheus orbit: when Prometheus again reaches apoapse, it draws another streamer of material from the F ring. But since Prometheus orbits faster than the material in the ring, this new streamer is pulled from a different location in the ring about 3.2 degrees (in longitude) ahead of the previous one.

In this way, a whole series of streamer-channels is created along the F ring. In some observations, 10 to 15 streamer-channels can easily be seen in the F ring at one time.

Click here to watch a movie of streamer channels being created, from images taken in 2005.

This view looks toward the northern, sunlit side of the rings from about 10 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 20, 2009. The view was obtained at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn. Image scale is 13 kilometers (8 miles) per pixel.

More information about the Cassini.
The Cassini imaging team homepage.

Source: Cassini

13 Replies to “Amazing Ring Ripples”

  1. So it would appear that the rings settled into the ‘shells’ around Saturn’s electromagnetic field lines based on the type of material (heavier closer in, lighter further out) distributed due to impacts or just the formation of the planet, and we’re directly viewing the accretion of rocky bodies by their orbit pulling material from these rings. Might this be exactly the same thing that happened to form the planets? Oh man, here’s a really awesome idea. If you have electromagnetic field lines that determine where material has a tendency to build up, might a change in the field (moving in or out) cause matter to tend to follow? Over time, making an orbit more elliptical, or less?

  2. @ Jon:
    Where in this paper is electromagnetism mentionned?
    What is “Saturn’s electromagnetic field”?

  3. Maybe the strange gravitational phenomena due to embedded or shepherding moonlets is indicative of similar ring dynamics of Jupiter, Uranus and Neptune. To be sure, the other three gas giants sport markedly different ring systems compared to Saturn, but the orbital dynamics of these ring systems may share much in common.

  4. Speaking of rings in the Saturn system, Emily Lakdawalla has a post today about a ring around Rhea! 😀

  5. I think that the next Saturn mission must include a little add-on ring explorer probe. Send it in on a suicide mission, snapping piccies all the way down. I want higher res, damn it!

    I think that what I’m feeling is the spacecraft equivalent of aperture fever. In this case – screw more aperture – too expensive for what I want. Get me closer!

  6. Years ago when I was working on orbital dynamics I worked some problems with orbital debris and the statistics of their orbital configurations. I deformed the problem slightly and put an electric charge on the smallest pieces ~ 10-100 microns, to compute numerically their orbits. What I found was they ended up in spiralling orbits near the poles. The Lorentz force deformed the orbit into something resembling the MHD jets from black holes or neutron stars. The orbit would drop down to some limit and then bounce back up and so forth spiralling around as if a bead moving on a tube.

    It is tempting to think there are electromagnetic interactions involved, but they don’t seem to work. If there are electrical currents in the rings these would tend to be pushed by the Loretnz force in directions normal to the orbit of the rings. This then set up dynamics similar to the precession of a gyroscope, sending the angular momentum vector of the orbit tilting and …, wel this end up pushing the particle into a tight spiral orbit around the poles.

    As for a probe to study the rings, you would want a probe tjat enters the rings and navagates between them with some sort of power system. We would get some inside views of the rings.


  7. @ LC: interesting!

    Is this what’s involved in the ring spokes? I’ve been reading electrostatic interaction is the cause, never realized it could be Lorentz force. But, they don’t seem to go far from the ring plane.

    How would particles acquire, and keep, a charge?

    I totally support a ring probe! Back in 2004 I had hoped Cassini would see individual ring particles…

  8. The Lorentz force is due to the motion of a charged particle in a magnetic field. Saturn has such a field, and charged particles in the rings would execute the strange motion I mention above. For charge separations in a complex system that might be a bit different. We might consider charge separations in the rings. This might be induced by charged particles (protons etc) caught in Saturn’s magnetic field passing through the ring material. This then might have complex dipole structure which is string enough to prevent particles from moving off the plane of ring by Lorentz force. So for a test case a dipole, two charges electrostatically bound or attracted to each other. would by the Lorentz force move radially in and out depending on their charge. The electrostatic interaction would resist this motion, but of course is ~1/r^2 is it behavior. Then you would have to consider a continuum of material behaving this way.

    Remember, this only makes sense for particles which are remarkably small, on the order of 10-100 microns. It would take enormous amounts of charge to displace the motion by Lorentz force of a particle on the order of kilograms in mass.

    I suppose to think about this it amounts to a curious problem that borders classical mechanics. electromagnetism and plasma physics. If the rings of Saturn exhibit some level of EM physics then this similar to a plasma of sorts.

    I have of course wondered if there were such physics in the rings of Saturn. They have such extraordinary levels of structure, which makes me question whether this is purely due to very weak gravity force.

    Indeed a probe that moves parallel to the orbital motion of the rings would be very important I should think. The probe moving with the material could send various optical and IR radition out to make an optical scatter (Mie scatter) estimate of the distribution of particle sizes. The probe could capture some particles to do some chemical analysis, the motion of particles maybe tracked and so forth.


  9. “a curious problem that borders classical mechanics. electromagnetism and plasma physics”

    [shivers] A problem that borders plasma physics borders insanity. (Well, in some cases.) This compound problem I wouldn’t touch with a pole. [/shivers]

    But a probe, sure. That way one could get to a lot of gas planet & ring physics, methinks. Better make room for a series of small and fast probes, where the latest sets the agenda for the next.

    Let’s hit Saturn with “a probe gun”!

  10. I concur with Astrofiend, Crowell and Manu, either a parallel probe or a ring intersection mission to Saturn would return a wealth of information about not only about Saturn’s rings but ring dynamics, origins and ring evolution in general.

  11. So if a force similar to the Lorentz force does turn out to be involved, I think it’s pretty safe to say that these forces are dynamic based on the evolution of internal dynamics in stars and planets and that just as with a plasma engine, a little force exhibited over a very long period of time could have an impact on bodies in motion near these lines.

    I dunno, based on our observations of larger gas giants in close orbits to their stars, I think it’s possible that that could be the end stage of a solar system. Due to frame dragging and the evolution of the star itself, the orbits of outer planets begin to decay and they essentially come inward and collide away until what’s left is all that mass circling a star, or maybe a binary pair of stars.

  12. I am thinking of doing a little numerical exercise on this. It might tax my machine a bit, but I could compute some configurations of charged particles in this orbit and see if anything emerges.

    Cheers LC

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