On a ring origin of the equatorial ridge of Iapetus Options

[Guest_AlexBlackwell_*]

Wing Ip just had an interesting Iapetus-related paper published in GRL.

[ngunn]

So much to reply to (no, it isn't driving me to distraction - far from it) - but only a few minutes available. On no ridge rings on Pluto or Charon - I agree, unfortunately, but there's always an outside chance since we don't really know their histories. Anyhow Pluto will get one when Charon disintigrates.

On the intimate details of ring emplacement - very good, I'm almost buying it. However I don't think the basic thesis would be under serious threat even if your details turn out to be wrong.

I'm going to go away and extend my d cubed times m over M table to some more objects, like Ceres and the moons of Uranus. Will post anything interesting I find.

[tasp]

On the intimate details of ring emplacement - very good, I'm almost buying it. However I don't think the basic thesis would be under serious threat even if your details turn out to be wrong.

I don't know how thoroughly I have cosidered this topic (I don't know what I don't know, after all) but I have gone over quite a few variations of all this.

Before I encountered and understood the differential ring spreading process as outlined in the New Solar System book, I labored trying to figure out a mechanism to get the ring down on the surface of Iapetus. I considered Iapetus' remoteness from perturbing bodies to imply an extremely long lived ring system. Cool if we want to see one in this epoch, but it doesn't help explain the pictures we have now. I put a great deal of effort into establishing that Iapetus is not to far off the mark from Triton and Pluto to have had an extremely tenuous atmosphere eons ago when the sun was somewhat dimmer. The atmospheric drag emplaced the ring. Unfortunately, that generates a feature that doesn't look like the ridge system on Iapetus.

I have also spent time gyrating the center of mass of Iapetus during the ring emplacement. I get thinking of precessing the axis of a gyroscope as analogous to Iapetus unbalancing during emplacement. The ring system just isn't massive enough, and/or emplaced quickly enough to do anything bizarre to the Iapetan spin axis. While interesting to think about, it doesn't really help us understand how the ring descended and emplaced the ridge structure.

I do have some technical trades backgrounds, and frequently thought of lathes, specifically, machining the inside of a cylindrical piece of metal. Interesting analogy, but tough to explain on a messageboard.

The diverging attendent ridges I consider to be the 'brass ring' here. Explain them, and you have the whole thing nailed down air tight. Realizing that inclined structures in the ring could emplace just like that, and alternatively, that Iapetus could have it's spin axis deflected by a few degrees during emplacement (perhaps by a big impactor) and generate the exact same feature again was fun.

The ring idea seems to tell all actually.

The ring particles actually orbited in the same direction as the ridge tapers downward. (Assuming the pics aren't inverted and I understand the orientation of everything here, as seen on the map earlier in this thread, from left to right)

It would have been possible, and perfectly safe, to stand directly beneath the ring during emplacement in what I call landslide basin. One could have actually approached the ring fairly closely from the sides too, but having meter sized boulders whizzing past your face at just under 1000 MPH would have been a bit scary. Even discerning motion in the ring system would have been difficult from far enough away for the unaided human eye.

I am thinking the rings were white, or light colored. And the fine grooving we see in Saturn's rings would have been greatly diminished here, or absent entirely. Having the inner edge of the ring descending so low to the surface (no corresponding dusky ring analog here) would have presented a very different appearance from Saturn's rings. (and to my aesthetics, less visually appealing, they would not seem to be floating above the moon, but rather resting upon it).


Due to the pretty intense 'meat grinder' effect of lofting the materials in the first place, then collapsing to the Laplacian plane, followed by the incessant bump and grind of the dynamical ring spreading process, I suspect the ring particles to have been pretty uniform size wise, although I don't know if we are talking walnut sized chunks or Volkswagen sized chunks.

The upper edge of the ring, I feel, was rather constrained at or near the Roche limit. Drag forces would have always been sapping energy from the ring system, and the ring spreading process would have worked primarily on the low side of the ring, not the top. We wouldn't have seen any little moons spun off the high side. And as it follows, the entire ring system would have eventually emplacedonto the Iapetan surface.


The absolute fastest the ring system could have emplaced, would, I feel, be in the hundreds of years range. There are some formulas for figuring ring spreading speed, but I will let others chew numbers for this. Heck, an upper limit for ring emplacement time might be up to many thousands of years, but not millions. That some 'straggler' chunks in the ring plane might have persisted for longer periods isn't too important, this all happened billions of years ago (no I am not going to do crater counts to calculate surface ages, either) anyhow, and are nowhere near as interesting as the main phase of the emplacement process.


What a fun moon this has turned out to be. Hope Allen gets lucky and photographs some especially weird and bizarre Kuiper belt objects!