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.

[tasp]

We may find Iapetan like ridge structures on a percentage of the larger KBOs.

Not sure NASA wold mass produce New Horizon clones and start launching them en masse to the outer solar system ( [laugh] ), but it would be interesting to have a few more examples to study.

[TritonAntares]

Hi,
before we should keep on speculating whether the equatorial ridge was built by an ancient Iapetian ring,
we should take a closer look at the ridge, e.g. if there are older structures below it - what could answer its built up...

Here again what I wrote half a year ago - and an interesting pic:

One question to answer should be:
What is older, the equatorial ridge or its surrunding/overlaying area, speak the craters?

Therefore I compared these two shots of the 'belly band':

Visible left is a large bassin (large pink circle) in the western part of CR cut by the part of the ridge with the 'white peaks'.
Thus the crater must be older than them, even if its central peak (small pink circle) doesn't coincide with the 'white peak' NW of it
and it is also lower. So you could guess the ridge there is fairly young, maybe eruptive....

In the right image another part of the ridge in central CR is shown. It seems to be quite old.
Lots of craters (red circles) crashed into it and disturbed its line.
The craters in the blue circles look somehow tilted, probably raised up by the ridge.
But due to bad resolution this is difficult to discern...

And don't forget there is no evidence for the ridge east of CR, only some uncertain albedo features.

Is the equatorial ridge powered by some longitudinal subsurfaced source or is there a gravitational cause from one direction?
The belts different heights and ages then could be explained by a longitudinal shift over a longterm period.

So, if there is really an older feature below a ring-built belt we could eventually be in trouble with the ring's age....

For me speaking,
I'm more convinced of an internal origin of the belt - probably connected with a large impact and/or some internal processes.

This ring theory sounds too strange and unlikely...
But planets around a neutron star did that as well ...

Bye.

[ngunn]

Hi,
This ring theory sounds too strange and unlikely... Bye.

That makes you the second poster here, along with Ugordan, to be sceptical of the whole idea. Any particular reason for this, or just a general hunch? As an undergraduate in 1970 I remember arguing with my geology professor about the origin of lunar craters. His line was "Why invoke an exotic external cause when there's a perfectly natural geological explanation?"

With hindsight it seems surprising that fossil ring structures were not predicted ahead of the Iapetus discovery, given the ubiquity of rings when things break up in the vicinity of other things, plus the fact that most ring material will inevitably spiral inward over time and has to end up somewhere.

So, A QUESTION: Has anybody here come across a prior prediction of fossil ring structures, either in the scientific literature, in fiction, or in informal communications?

[ugordan]

I have absolutely no idea on which internal process could create the ridge, but I am skeptical of the ring hypothesis mainly because I don't see it very likely that smallish Iapetus could have enough gravity to align the orbiting debris along its equatorial plane. Isn't that possible only due to the rotational bulge at the equator? Iapetus has a small radius so a 16 hour rotation wouldn't produce centrifugal forces as big as on a body twice the radius. The bulge would be lower. Therefore, orbiting debris would be unlikely to align into an quatorial ring that easily. An equatorial ring maintained long enough, even due to Saturn's perturbations? I also don't like the explanation on why the ridge isn't complete around the equator. And how does it all fit with the dark stuff? Why is the color of the dark stuff practically identical to Hyperion's color, only differing in albedo?

There's just too much magic fairy work here, IMHO.

[ngunn]

I have absolutely no idea on which internal process could create the ridge, but I am skeptical of the ring hypothesis mainly because I don't see it very likely that smallish Iapetus could have enough gravity to align the orbiting debris along its equatorial plane. Isn't that possible only due to the rotational bulge at the equator? Iapetus has a small radius so a 16 hour rotation wouldn't produce centrifugal forces as big as on a body twice the radius. The bulge would be lower. Therefore, orbiting debris would be unlikely to align into an quatorial ring that easily. An equatorial ring maintained long enough, even due to Saturn's perturbations? I also don't like the explanation on why the ridge isn't complete around the equator. And how does it all fit with the dark stuff? Why is the color of the dark stuff practically identical to Hyperion's color, only differing in albedo?

There's just too much magic fairy work here, IMHO.

Very useful to have specific doubts expressed, thanks. On getting the ring to be flat and thin - an equatorial bulge helps but I don't think it's essential. I admit I have no idea about the timescale required for flattening the ring or for it's destabilisation by Saturn. We will have to see if a proper scientific rebuttal along these lines emerges in due course. I would just point out that if the ring material came from a former subsatellite rather than from a randomly oriented collision it would have been pretty near the equatorial plane to start with. If in addition the former satellite was made of rather loosely bound material the process of smearing it out at the Roche limit could have been quite orderly. It would simply have 'poured' itself (as it were) into a flat sheet. On the unusual albedo features - I think they are much younger than the underlying solid structure of Iapetus.

[ugordan]

On getting the ring to be flat and thin - an equatorial bulge helps but I don't think it's essential.

It actually might be essential. A perfectly spherical object will act as a point gravity source (barring mascons) and it won't exert any torques that change the orbital plane of an object. At least I think so.

If in addition the former satellite was made of rather loosely bound material the process of smearing it out at the Roche limit could have been quite orderly. It would simply have 'poured' itself (as it were) into a flat sheet. On the unusual albedo features - I think they are much younger than the underlying solid structure of Iapetus.

Again, I don't know how strong Iapetus' tidal force could be to do this sort of thing and overcome disruptive perturbations by Saturn. I'd be much more comfortable with the ring idea if there was a simulation showing it's dynamically possible. Beyond that, all this seems just arm-waving. Or my gut feelings vs. your gut feelings.

[ngunn]

It actually might be essential. A perfectly spherical object will act as a point gravity source (barring mascons) and it won't exert any torques that change the orbital plane of an object. At least I think so.
Again, I don't know how strong Iapetus' tidal force could be to do this sort of thing and overcome disruptive perturbations by Saturn. I'd be much more comfortable with the ring idea if there was a simulation showing it's dynamically possible. Beyond that, all this seems just arm-waving. Or my gut feelings vs. your gut feelings.

Just arm waving certainly! I don't claim to be doing anything else, but it's fun anyway. Ring flattening - I thought that a ring would eventually flatten itself due to mutual interactions between the particles???

[ugordan]

Yeah, but why would it flatten itself along the equatorial plane if the particles were ejected on a random inclination? They don't know / don't particularly care about the equator.