June 12 2007 Icy Moons (rev 46) Options

[Bjorn Jonsson]

Just wondering... does anybody else live in a constant sense of amazement at the things we see now? I mean, every time we think we've seen the strangest of the strangest, the weirdest of the weird, the universe taps us on the shoulder and whispers "Pssst... look over there..." and we turn around and there's some gorram unbelievably freakish impossible new weirdest of the weird thing staring at us from the Black...

Well, I'm amazed and Cassini has been probably the best ever example of this.

A related observation: I'm amazed at just how different all of these satellites/solar system bodies (and not just those at Saturn) can be from each other, especially when they get reasonably big, say 250+ km in diameter (or length). In fact I probably cannot think of any two solar system bodies above that size that I would have even the slightest difficulties recognizing in global images (unless the resolution were really low). Somehow they each have their own 'personality'. Years ago people expected lots of 'Rheas' out there but instead you've got things like Enceladus, Iapetus, Hyperion and Dione which are totally different from each other (and Titan in a class of its own). The same is true at Jupiter, Uranus and Neptune. Every solar system object seems to be interesting in some way.

[ngunn]

Unbelievable... just unbelievable...

Every solar system object seems to be interesting in some way.

Stu, I share that sentiment 100 percent. Broad brush descriptions of categories of Solar System objects are of very limited use once the details hove into view. Every world and mini-world has a unique history to tell of chance and circumstance within the celestial pinball machine. We live in an age of revelations indeed. Who could not be moved?

[Phil Stooke]

I did a bit of cleaning up and stacking of the Atlas images. Here are the results. The earlier posts were just as good - or better! - but here the significant thing is slight differences between the two views - from the early and late frames of the sequence. I'm not yet sure if a stereo view from these is any good.

Phil

[elakdawalla]

I looked at these in crossed-eye stereo, and I can't decide if I see anything in 3D or if I'm just interpreting shape from shading. I guess maybe there is 3D information contained in the stereo pair, but that the difference in the two points of view is not enough to produce more than a subtle 3D effect.

Nice versions though, much better cleaned up than mine.

And, might I add, what a bizarrely shaped body! Lumpy and smooth at once.

--Emily

[Phil Stooke]

If there is anything in it, I think it has to be this way round:



Phil

[tedstryk]

What a strange moon!

[David]

I'm not sure if I got this right, but I gather that Atlas is shaped something like a spinning-top, with a broad disk shape in the center and two "horns" or mountains on the opposite poles.

If so, then there's an interesting process going on: Atlas is picking up ring particles, of various sizes, on the disk edge, but once accreted they find themselves gravitationally at the furthest point from Atlas' center of gravity; if the are large and massive enough so that they don't easily stick to neighboring particles, they will find themselves rolling (slowly) toward the tops of the "mountains", which paradoxically are gravitationally down. As a result, any large lumpy bits are going to gravitate toward the poles, leaving a smooth equator covered in smaller particles and ring-dust.

Does that sound about right?

[The Messenger]

Just wondering... does anybody else live in a constant sense of amazement at the things we see now? I mean, every time we think we've seen the strangest of the strangest, the weirdest of the weird, the universe taps us on the shoulder and whispers "Pssst... look over there..." and we turn around and there's some gorram unbelievably freakish impossible new weirdest of the weird thing staring at us from the Black...

Unbelievable... just unbelievable...

Unbelievable, or removed from decades of preconception? Wasn't it reasonable, given the standard explanation for how the solar system formed, to assume the moons of Saturn would be a rather dull and homogenious lot? Isn't it more reasonable now to assume Phoebe and Titan may have much more vivid histories; and each of the 'icy' moons of Saturn has their own province?

[Phil Stooke]

David, I think you are combining things which have been said about other small bodies here - a rapidly spinning elongated object, rotating about its short axis, may have the ends of its elongated shape gravitationally lower despite their larger radii. Peter Thomas of Cornell did pioneering work on this phenomenon, which he called dynamic topography, especially with reference to Phobos, Deimos, Gaspra and Ida, in the 90s.

Until new we have not known the shape of Atlas well enough to think about it in this context. My impression is of a "flying saucer" shape with a central bulge - the wrinkly bit we see here - and a big equatorial ridge which now looks as if it extends all around the equator, though a bit irregular. That ridge may be made of ring particles deposited on the satellite, maybe during special events in the history of the system such as an interaction with a ringlet. At this distance from Saturn the dynamic topography would be dominated by Saturn's gravitational gradient across Atlas plus its rather rapid rotation. I'm sure we will see more on this when a full shape model can be constructed.

Phil

[tasp]

Gee, if they are looking for things to do during the extended extended extended mission, a close approach by Cassini to Atlas would be a possibility.

I realize to be close, we would also be close to ring plane crossing, and they like to orient Cassini with the dish forward to absorb the particles, and this would mess up getting a meter or sub meter resolution picture of the accumulated ring goodies.

Just a thought, but would the radar instrument yield useful data on the surface texture, sufficient for use to infer the shapes of the accumulated ring particles ?

This is a unique opprotunity to possibly 'image' Saturnian ring particles and we might want to put some effort into considering this . . .

[tasp]

Just curious musing here:

Would an impact into the accumulated dust donut knock off quite a bit of it, and then might it go back into orbit around Saturn and then re-accrete (re-re-re-accrete ??) back on to Atlas?

Cool if we have a recursive phenomena here.

Is the process of re-accretion going on right now ??