On a ring origin of the equatorial ridge of Iapetus |
On a ring origin of the equatorial ridge of Iapetus |
Guest_AlexBlackwell_* |
Aug 29 2006, 06:18 PM
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Guests |
Wing Ip just had an interesting Iapetus-related paper published in GRL.
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Sep 7 2006, 03:03 PM
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Member Group: Members Posts: 903 Joined: 30-January 05 Member No.: 162 |
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. |
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Sep 7 2006, 03:50 PM
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Member Group: Members Posts: 288 Joined: 28-September 05 From: Orion arm Member No.: 516 |
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: So, if there is really an older feature below a ring-built belt we could eventually be in trouble with the ring's age....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. 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. |
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Sep 8 2006, 10:44 AM
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
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? |
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Sep 8 2006, 11:05 AM
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
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. -------------------- |
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Sep 8 2006, 01:56 PM
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#6
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Member Group: Members Posts: 509 Joined: 2-July 05 From: Calgary, Alberta Member No.: 426 |
Two things today:
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. (1) Hmmm. You may just have come up with a device to explain the inward spiralling of the rings. Saturn's ring system is pretty much flatter than a board. Presumably it gets hit by objects from time to time (comets, meteroroids and the like) that would be able to scatter ring particles into inclined orbits. However, any such particles will end up in a ring-crossing orbit, and will end up hitting other ring particles and getting re-absorbed into the rings. Each impact will of course add net momentum (and angular momentum) to the ring system, but over time these should average to zero -- and even if they didn't, tidal effects from Saturn and the moons ought to be more than capable of keeping things in order. A ring around Iapetus, though, would experience perturbations from Saturn that would warp the ring. It probably wouldn't warp it like an old vinyl LP record left out in the sun -- instead it would tend to "smudge" the ring perpendicular to Iapetus' equatorial plane. The ring would constantly be trying to flatten itself out through the mechanism described above, i.e. ring particles would constantly be hitting each other from "above" and "below". Any component of a collision perpendicular to the ring plane would take net energy away from the ring system, and though I haven't done the math, I'm betting that this would tend to cause the ring to spiral in towards Iapetus over time. Wild hypothesizing: If you look at the distribution of dust in the asteroid belt, there are concentrations about 9 degrees above and below the ecliptic. This is thought to be due to particles from a recent major asteroid-asteroid collision. Due to their inclined orbits, the dust particles spend a disproportionate amount of time away from the ecliptic, and tend to "collect" at +- 9 degees altitude. Perhaps the perturbations from Saturn could have been responsible for an analogous "three-layered" structure in the proto-Iapetan ring, that is reflected in the mass distribution of the ridge structure? (I have to be honest -- I don't believe this for a minute -- and am just tossing it out here as an idea.) (2) The recently posted image that shows the "triple structure" of the ridge is in fact the one I referred to the other week. Great. Now, are we absolutely certain that those three parallel lines are three parallel ridges and not some other type of linear structure within a single ridge? This was my reason for asking about it in the first place. Perhaps it would be possible to produce a stereo pair to get some altitude information? There were quite a few images taken of this region during the New Year's distant flyby. I have no idea how to do that sort of thing, unfortunately. [Edit: I was typing this post when Tasp put up his above message -- which also covers the topic of "ring flattening". Neat coincidence, that.] |
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