Ring near edge on illumination, Ring particles are casting shadows Options

[Floyd]

Not only are we seeing the long shadows of moons on the rings, but objects in the rings are now casting shadows. Link

Notice the mini shadows on the bright twisted band just where the moon shadow ends.

One of you who is more adept at image cropping may want to post a cropped blowup.

[sci44]

Nice catch! You have just discovered 11,821 new moonlets!

(x2, rot 18 degrees, crop)



(Credit: NASA / JPL / SSI)

That ring seems to have many more large boulders than the others in frame - its amazing how chaotic it is.

Adjacent frames show the speed the long shadows move:
http://saturn.jpl.nasa.gov/multimedia/imag...9/N00133375.jpg

The large moon shadow here nicely maps out the shape/thickness of the rings:
http://saturn.jpl.nasa.gov/multimedia/imag...9/N00133376.jpg

The Cassini team are going to have fun finding classical names for all those moons..

[Ian R]

Wow - is this the region periodically disturbed by the resonance with Mimas? That would certainly help explain the chaotic appearance of that ringlet.

[scalbers]

Pretty neat. They almost look like the shadow of a mountain range. Actually though are we seeing the shadows of ring irregularities instead? I would think the actual moonlets would usually be too small to resolve. Maybe we're seeing clumps of moonlets that are being warped away from the ring plane (or perhaps simply more dense than the surroundings).

Steve

[ugordan]

Wow, that's seriously wicked. Nice catch, Floyd!

[ElkGroveDan]

Thanks for catching that Floyd. This is amazing. I am utterly fascinated with ring particles and the subtle gravitational phenomena associated with so many distinct masses interacting.

I would think a careful examination of the elongated size and shape of those shadows would result in important data ripe for a new paper on particle size and density.

[sci44]

This is a rough attempt at an animation using frames N00133373.jpg, N00133374.jpg, N00133375.jpg

(http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133374.jpg etc)



(Credit: NASA / JPL / SSI)

There is a little movement in the shadows between frames, I was hoping for more.

[Floyd]

Thanks sci44 for the crop and the movie. I am also surprised at how little the mini shadows change.

[helvick]

It's not all that surprising if we assume that there is very little relative motion between the particles which I'd assume is generally the case unless there's a moonlet nearby disturbing things. Taking an 80000km altitude for the rings (which may be a bit off but it serves for general argument) - the orbital velocity of the particles is around 13km/sec. At that altitude 1 second of arc is remarkably close to 1km so you'd need almost 11 minutes between images to have the particles move by a degree along their orbit.

[dilo]

Excellent finding, Floyd!

Wow - is this the region periodically disturbed by the resonance with Mimas? That would certainly help explain the chaotic appearance of that ringlet.

Ian, this is clearly the outer edge of B-ring, where particles are in 1:2 resonance with Mimas. The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to a sharp cutoff in ring density. These elevated structures could be eventually related to the relatively high inclination of Mimas orbit (1.57°) or to low velocity impacts in such dense region. Just two ideas...
It would be nice to have an estimated height of such features based on shadow lenght... any support on this?

[sci44]

Yes, an excellent find, Floyd!
The first frame of that anim is a bit out - I am sure one of the more experienced UMSF'ers can make a properly calibrated/cleaned up version..
Just watching that GIF - there is actually a trail of disturbance on the left third - from the edge of the ring cutting into the main ring plane - deeper as you go to the left - like the trail of something plowing into the ring at a very shallow angle? Strange. Are these large boulders, or loose collections of small particles? Electrostatic charges are said to play a role with structures like the ring-spokes - is that a factor here? I don't know..

By the way, the sequence of 14 (incrementally numbered) frames with the shadow of (Titan?) cutting across the rings, from
http://saturn.jpl.nasa.gov/multimedia/imag...9/N00133399.jpg
through to
http://saturn.jpl.nasa.gov/multimedia/imag...9/N00133412.jpg
is crying out for an animation - now if only there was an animator here..

[volcanopele]

Most of the moon shadow stuff at the moment is either from Mimas or Tethys.

Very cool animations everyone!

[Astro0]

With Cassini's motion, this is not an easy set of images to register.
Here's my attempt at an animation.
Hard to see if any changes are 'real', 'imagined' or 'artifact'.

[nprev]

All I got to say is WOW, you guys...

Astro, how many minutes does your animation span? (I'm thinking that it must be a fairly hefty period--15 min more or less?--given that moon shadow passing in & out of the FOV.) If that's true, then it's really striking how stable the "mountain silhouette" ring particle shadow pattern remains throughout the period.

Using the word "striking" because my gut feeling (and I'm probably not alone here) was that the rings' behavior must be pretty chaotic at the particle-level scale. That well may be, but not over as short a time scale as might be assumed. Should this be obvious in retrospect?

Just to blue-sky a bit, what if the "chaos threshold" is lower than we expect? By this I mean that perhaps the major ring particles (say 10m or larger) in at least this segment of the ring system have achieved some sort of dynamic equilibrium over time so that they really don't bounce around much relative to their neighbors. It sounds thin to me, too, but you'd think that the system would tend to evolve towards a low-energy state like that over time.

[ElkGroveDan]

I would imagine that the Mimas/Tethys shadows(s) should provide a relative scale to calculate the sizes and the size distribution in that segment. The ratio of the diameter of Mimas to the triangle it's shadow creates should be the same as the ratio of these smaller objects. I wish I had the time to do this myself.