Those are stars. There are actually 9 stars theoretically visible if you stretch the image and search hard enough, but they're awfully faint.
I don't have the exact amount of motion blur available, but the hand-wavey answer is: not much. At least, not for a given exposure. Each exposure lasts for around a second (some less, some for a a bit more). In that time, the spacecraft doesn't move a lot as far as its view of distant objects like Saturn and the moons are concerned. (My quick calculation says perhaps a few tenths of a pixel for the longest exposures. For most exposures, much less than that.) On the other hand, this mosaic is made up of many exposures and in the total time it took to take all of the images, there was distinct movement of both spacecraft and moons.
Iapetus Monolith: the long axis of the shadow points to the moon casting the shadow. Pretty sure (but not certain, nor able to check from my current location) in this case, the moon is to the right since I can't see the shadow of the planet anywhere on the rings, here.
(I should add that when I say that *I* haven't had a chance to analyze these images for possible morphology changes, I meant "I". It's possible someone else in our team has noticed something and I'm not in the loop. I don't want it to sound like I'm the only one who can do this, I'm just using the singular 'cause I can't speak for others right now.)
I haven't had a chance to really analyze these images yet, but I don't *think* that the morphology changes much (if any) over the course of the movie. The density of the ring between us and the moon does change a lot from ring radius to ring radius, so we often see the shadow clipped or striped, but that's an illusion due to the photometry.
That said, if there is significant variation of the shadow with location in the rings, one possible cause is an out-of-plane component to the ring. We're looking at that now. If we find anything, I'm sure we'll announce it. :-)
The "horizontal" component (I prefer "radial") is due to the moon's passage. It happens any time a nearby moon passes a group of particles. It's actually those waves that we used to find Pan and Daphnis since they're diagnostic of the moon's presence. The vertical waves are due to the moon's vertical motion. They only occur for a moon on an inclined orbit.
So there's not really a particularly close connection between the two waves, other than the moon is the cause. You always get the radial, but you don't always get the vertical.
Aleksandar, to address your question about ripples below the ring plane: it's a bit complicated. It turns out that Daphnis warps the whole edge of the gap so that everything moves up and down together. However, some *parts* of the edge move further up or down than others, leading to the rippled edge. So where you don't see a long shadow here, the edge is still lifted up, just not very far (probably a tenth of a kilometer or so).
If there *were* shadows being cast of the other side of the rings, we would probably be able to see them. We've seen shadows of moons through the A ring before, anyway.
Yep, we actually started the research to study the relationship between the mass of the moonlet and the amplitude of the edge waves. Since we were doing computer simulations, when we found out that Daphnis has an inclined orbit, it was pretty easy to study that aspect, too. It was pretty cool to see how the edges of the rings would get vertical ripples from the interaction with the moon. (So, yes, it was a prediction we had made.) Serendipitously, these images came down just as the paper was about to be published and the journal was kind enough to allow us to add one of these to the paper.
Which lack of symmetry do you mean? On the one hand, on a given edge (inner or outer) of the gap, you only see ripples on one side of the moon. This is simply because the particles on the other side have not yet encountered the moon. (They're "upstream" if you will.) However, there is also an asymmetry between the two edges as well. This, we think, is due to Daphnis' orbital eccentricity (which means the two edges get forced differently at different times in Daphnis' orbit) and the fact that one edge is in a resonance with the moon Prometheus. Some members of the Imaging Team are studying this even now; watch for more about this in the future as the unravel the story further!
Actually, that's pretty much the shape that we expected. Remember that the shadow is stretched in one direction (north-south) and not in the other, so the spherical moon casts an (approximately) elliptical shadow. You can simulate this yourself with a ball and the Sun early in the morning or late in the evening. (Or, if you prefer, with a table lamp shining obliquely onto the floor.)
mipsandbips: If you're suggesting that Daphnis has been ablated by collisions, that actually seems to be the reverse of what we found in our 2007 paper (Porco et al., 2007 in Science). It looks more like Daphnis grew out of ring material in the A ring. It would be almost impossible to add more material to Daphnis now since tidal and centrifugal forces would tend to pull it off more strongly than gravity would hold it.
Also note that if Daphnis were larger, the gap would also be larger. In fact, the gap edge would probably be too far away for Daphnis to make physical contact. (Think about Pan in the Encke gap.)
But I do like how you think! Collisions have almost certainly done a lot of shape Daphnis!
We might see the penumbra of Titan on the rings, although without running the numbers, I'm thinking probably not.
As for other moons... stay tuned. :-)
Red_dragon: I don't believe we'll be seeing Titan's shadow on the rings this equinox. Titan is on the wrong side of the planet on the day of equinox and by the time it makes it back around, the Sun will already be too high again.
Actually, their inclinations are around 7.5 degrees and 4 degrees (http://ssd.jpl.nasa.gov/?sat_elem). However, you have the right tilts for them, which dominate the effects. So yep, their equinoxes are potentially quite different from Saturn's.
Sorry, I don't know where the December date come from. The Titanic equinox is certainly shifted slightly from Saturn's equinox, but I'm pretty sure it can't be more than a few weeks. Here's why: Titan's orbital inclination is only 0.3 degrees to Saturn's equatorial plane, so if its spin axis is perpendicular to its orbital plane (I believe it is), that's how different its spin is from Saturn's. In that case, the farthest the equinoxes could be apart is around 20 days. (The time difference could be a lot less, depending on the orientation of Titan's orbit.)
Hope that helps!
-- John Weiss
Andrew: Saturnian equinox is 11 August 2009. Earth will cross the ring plane about a month after equinox thanks to the slight relative inclinations in the two planets' orbits.