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On a ring origin of the equatorial ridge of Iapetus
Guest_AlexBlackwell_*
post Aug 29 2006, 06:18 PM
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Wing Ip just had an interesting Iapetus-related paper published in GRL.
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tasp
post Aug 31 2006, 01:27 PM
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Invoking an atmosphere above a certain very low density will create havoc with the orderly linear progression of the emplacement.

You would wind up with a debris belt all the way around the equator if atmospheric drag forces exceed the magnitude of the differential dynamic spreading affect in the ring materials themselves.


Additionally, due to the enormous volume of space a proto Iapetus would have had to sweep out to accrete itself (and of course its' relatively low orbital speed, too) I think we can infer that heating effects and subsequent melting of Iapetus was uniquely low for a significant moon in our solar system. The 'lumpy' limb of Iapetus seen in the Cassini images also infers a great bearing strength for the Iapetan crust.

Due to its' distance from Saturn, Iapetus would also have experienced a uniquely low rate of tidal heating as it de-spun to tide lock with Saturn. Iapetus had a uniquely ridgid and sturdy crust very early in the game, allowing us the chance to observe some of the most apparently ancient surfaces features yet seen.

I also think we can assume the ring entirely deposited itself onto the Iapetan surface. While the ring spreading effect would tend to 'loft' some material at the high side of the ring system through the Roche limit were it may have had the opprotunity to 'clump up' as we see in the outer reaches of the Saturnian rings, we must also consider drag effects that would have acted on the entire ring system.

Poynting-Robertson effects would have sapped orbital energy from the smaller particles across the ring system, and drag forces from the solar wind and perhaps even the Saturnian magnetotail would have provided a resistive medium for the ring system.


We also note the steepness of the sides of the resulting ridge structure on Iapetus. While I am not an expert in anything, it seems the sides of the ridge are plausibly at the angle of repose for materials deposited from above.


I also cautiously and with all due respect note some of the test footage shown on NASA TV of ice impacts on wing structures during the Columbia accident investigation. Ice was fired at the test samples in a speed range not too far short of the possible touch down speeds of ring materials onto Iapetus. To my untrained eye, (even though the tests appeared to be conducted at room temp and not at -300 F) it appeared the ice did not appreciably wet the surfaces it contacted. Rather, it just tended to pulverize into 'snow'. (in fact, one could see the pulverization occured at the instant of contact, the speed of sound (and fracturing) in the ice being so much higher than the impact speed).

Cryogenically frozen water ice (a plausible ring material) smacking a cryogenically frozen surface in a speed range not exceeding 1500 kph just isn't going to melt much (or vaporize) at impact.



Note, some gas/particle spray liberated at the point of contact will interact with the materials still orbiting above that point. Any material passing through that area of 'spray' will not complete another orbit of Iapetus and will land downrange along the ground track. This is why the main ridge (and the 2 attendants too) slope down away from the high end.
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The Messenger
post Sep 3 2006, 11:22 PM
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QUOTE (tasp @ Aug 31 2006, 07:27 AM) *
I also cautiously and with all due respect note some of the test footage shown on NASA TV of ice impacts on wing structures during the Columbia accident investigation. Ice was fired at the test samples in a speed range not too far short of the possible touch down speeds of ring materials onto Iapetus. To my untrained eye, (even though the tests appeared to be conducted at room temp and not at -300 F) it appeared the ice did not appreciably wet the surfaces it contacted. Rather, it just tended to pulverize into 'snow'. (in fact, one could see the pulverization occured at the instant of contact, the speed of sound (and fracturing) in the ice being so much higher than the impact speed).

What you do not see, even in the high speed film clips, is how much ice is immediately vaporized - perhaps some of it quickly recrystalizing. It is a substantial amount (I will try to find a quantity). During these and similar test, quite heavy steal supporting brackets were deflected and bent.

QUOTE
Cryogenically frozen water ice (a plausible ring material) smacking a cryogenically frozen surface in a speed range not exceeding 1500 kph just isn't going to melt much (or vaporize) at impact.

I have to wonder if this is true. When F-16's collide with the desert at similar velocities, they expect the remains of the pilot to weight 18-25 lbs - if there is no cockpit fire. Virtually all of the liquids - water, uncontained oils and fuel - are immediately vaporized.

QUOTE
Note, some gas/particle spray liberated at the point of contact will interact with the materials still orbiting above that point. Any material passing through that area of 'spray' will not complete another orbit of Iapetus and will land downrange along the ground track. This is why the main ridge (and the 2 attendants too) slope down away from the high end.

I like your analysis of the 'bulldozer effect', but I don't see water at any temperature as the source of this ridge deposit - if so, it should look more like drifting snow than Paul Bunyan and his plow.
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ngunn
post Sep 4 2006, 10:13 AM
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QUOTE (The Messenger @ Sep 4 2006, 12:22 AM) *
but I don't see water at any temperature as the source of this ridge deposit - if so, it should look more like drifting snow


Why? Are you assuming that environmental parameters at the time and place of deposition were pretty much as they are there today? If so that's a pretty drastic assumption - and just a bit too convenient in my view - given that we are talking about rather a large mass of material falling from space over an unknown period of time. I imagine something a lot more chaotic and violent, involving a wide range of temperatures and matter in all three states. At the very end of the process, yes, there was probably a fine hail of ice particles falling through near-vacuum onto a deep-frozen surface, but I think things would have been a lot more messy as the bulk of the material was coming down.

In such a situation there is too wide a field of possibilities and too much room for contingency, for example in the pattern of sizes, collisions and perturbations among the larger ring fragments, for a 'tidy' explanation that claims to characterise the whole process from start to finish to be convincing, IMHO.

One thing everyone seems to like (myself included) is the idea that the Iapetan ridge is indeed the remains of a fallen ring. Until this discussion I had not realised the dynamical implications of the remoteness of Iapetus from Saturn - that it could sustain a ring, and perhaps previously a satellite, of its own.
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The Messenger
post Sep 6 2006, 03:21 AM
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QUOTE (ngunn @ Sep 4 2006, 04:13 AM) *
Why? Are you assuming that environmental parameters at the time and place of deposition were pretty much as they are there today?

Yes, Aside from assuming that the belly band started as some kind of ring or dissintegrating moon structure.
QUOTE
In such a situation there is too wide a field of possibilities and too much room for contingency, for example in the pattern of sizes, collisions and perturbations among the larger ring fragments, for a 'tidy' explanation that claims to characterise the whole process from start to finish to be convincing, IMHO.

There are as many potential pitfalls in working backward to find a cause, as there is to working forward to predict an effect. Cassini is doing everything it was designed to do, but we seem to be finding more questions than answers. That's not bad, but it leaves us two options: Make some assumptions and try to prove them wrong on based on the evidence that is here, or wait for another mission.

We need to find better solutions than 'dark stuff' and water ice. We need to narrow down the list of materials by taking a hard look at the physical properties and eliminating what does not fit. What defines the surface besides color? Why are the surfaces of Titan and Iapetus so different from Enceladus and Hyperion?
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TritonAntares
post Sep 6 2006, 08:51 AM
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Hi,
let us anticipate the equatorial ridge was built up by an ancient ring orbiting Iapetus.

How likely is it now for CASSINI to detect any remnants of this former ring structure?
Or put it the other way - is it possible for a ring to vanish completely without leaving any dust particles in orbit?

Therefore a Iapetus ring model must be developed to show how such a ring is behaving over ages.
Iapetus - as most distant large moon of any large planet - should be able to retain a ring for a while.

For mass assumption the ridge mass should be adopted.
There is still the question whether the ring was built up by one major event,
e.g. a large impact like the 'snowman' or the huge southern bassin,
or did Iapetus act like a sort of 'vacuum cleaner' in Saturn's outer vicinity
to collect all kind of interplanetary debris?

Bye.
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ugordan
post Sep 6 2006, 09:03 AM
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The ridge is ancient which means the ring is also ancient. Any material left in orbit would probably be perturbed and dispersed away over a long course of time. I wonder how solar light pressure would evolve the ring particles, gently pushing on them. The ring system was probably very unstable, given Iapetus' weak gravity and probably pretty significant perturbations by Saturn (It's conceivable that after the impact that created the rings, Iapetus' rotational axis wasn't perpendicular to the orbital plane as it is today so Saturn's perturbations might have played a role. This along with the increasing "bulginess" of Iapetus itself would make stable orbits pretty hard to achieve.) I wonder if the impactor would melt Iapetus completely. If so, would it wind up undifferentiated now as it's suggested?
There's also the question of meteoroid bombardment on the rings and scattering them away. Of course, all this is arm-waving without any real numbers to back it up.

Personally, though, this ring idea seems too far-fetched for me.

BTW, Cassini did a pretty entensive search for moonlets during a recent fairly close approach. AFAK, no objects or ring remnants were seen.


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Posts in this topic
- AlexBlackwell   On a ring origin of the equatorial ridge of Iapetus   Aug 29 2006, 06:18 PM
- - volcanopele   okay, now a ring around Iaptetus is an interesting...   Aug 29 2006, 06:20 PM
- - AlexBlackwell   Here's an interesting passage from the conclud...   Aug 29 2006, 06:25 PM
- - Michael Capobianco   Does the paper address why the equatorial ridge do...   Aug 29 2006, 06:40 PM
|- - David   QUOTE (Michael Capobianco @ Aug 29 2006, 06...   Aug 29 2006, 07:05 PM
|- - Decepticon   QUOTE (Michael Capobianco @ Aug 29 2006, 02...   Aug 29 2006, 11:56 PM
|- - JRehling   Roughly speaking, I guess the fact that the ridge ...   Aug 30 2006, 01:07 AM
- - jsheff   Would this process also explain the albedo assymet...   Aug 29 2006, 07:06 PM
|- - tasp   QUOTE (jsheff @ Aug 29 2006, 02:06 PM) Wo...   Sep 10 2006, 01:35 AM
- - AlexBlackwell   QUOTE (Michael Capobianco @ Aug 29 2006, 08...   Aug 29 2006, 07:44 PM
- - tasp   An object skimming the surface of Iapetus will hav...   Aug 30 2006, 05:11 AM
- - AlexBlackwell   There was a brief blurb about this paper yesterday...   Aug 30 2006, 07:53 PM
- - Rob Pinnegar   I guess this idea probably originated with those i...   Aug 30 2006, 09:41 PM
|- - tasp   QUOTE (Rob Pinnegar @ Aug 30 2006, 04:41 ...   Aug 30 2006, 11:29 PM
- - dvandorn   Does Iapetus' ridge have to have been created ...   Aug 31 2006, 12:04 AM
|- - tasp   Maintaining focus (or collimation) of the strand ...   Aug 31 2006, 03:02 AM
|- - David   I think I understand the idea to be one of a low-v...   Aug 31 2006, 07:23 AM
- - ngunn   Under the scenario proposed I would expect volatil...   Aug 31 2006, 10:00 AM
|- - ugordan   QUOTE (ngunn @ Aug 31 2006, 11:00 AM) Cou...   Aug 31 2006, 11:18 AM
|- - ngunn   QUOTE (ugordan @ Aug 31 2006, 12:18 PM) M...   Aug 31 2006, 11:50 AM
|- - ugordan   The point I was trying to make is the greatest tem...   Aug 31 2006, 12:08 PM
|- - ngunn   QUOTE (ugordan @ Aug 31 2006, 01:08 PM) A...   Aug 31 2006, 12:38 PM
- - ngunn   One other point - the 'catastrophic atmosphere...   Aug 31 2006, 01:06 PM
- - tasp   Invoking an atmosphere above a certain very low de...   Aug 31 2006, 01:27 PM
|- - ngunn   QUOTE (tasp @ Aug 31 2006, 02:27 PM) Invo...   Aug 31 2006, 02:01 PM
|- - The Messenger   QUOTE (tasp @ Aug 31 2006, 07:27 AM) I al...   Sep 3 2006, 11:22 PM
|- - ngunn   QUOTE (The Messenger @ Sep 4 2006, 12:22 ...   Sep 4 2006, 10:13 AM
||- - The Messenger   QUOTE (ngunn @ Sep 4 2006, 04:13 AM) Why?...   Sep 6 2006, 03:21 AM
||- - ngunn   QUOTE (The Messenger @ Sep 6 2006, 04:21 ...   Sep 6 2006, 08:15 AM
|||- - JRehling   A comment on followup missions: Whatever future mi...   Sep 6 2006, 12:02 PM
|||- - ugordan   QUOTE (JRehling @ Sep 6 2006, 01:02 PM) A...   Sep 6 2006, 12:29 PM
|||- - mchan   QUOTE (ugordan @ Sep 6 2006, 05:29 AM) Tr...   Sep 6 2006, 11:15 PM
|||- - ugordan   QUOTE (mchan @ Sep 7 2006, 12:15 AM) I do...   Sep 7 2006, 06:58 AM
||- - TritonAntares   Hi, let us anticipate the equatorial ridge was bui...   Sep 6 2006, 08:51 AM
||- - ugordan   The ridge is ancient which means the ring is also ...   Sep 6 2006, 09:03 AM
|||- - ngunn   QUOTE (ugordan @ Sep 6 2006, 10:03 AM) Pe...   Sep 6 2006, 12:41 PM
||- - ngunn   QUOTE (TritonAntares @ Sep 6 2006, 09:51 ...   Sep 6 2006, 09:05 AM
||- - tasp   QUOTE (TritonAntares @ Sep 6 2006, 03:51 ...   Sep 9 2006, 02:32 PM
|- - JRehling   QUOTE (The Messenger @ Sep 3 2006, 04:22 ...   Sep 5 2006, 04:44 PM
- - tasp   And this, consider the oblique impactor that may h...   Aug 31 2006, 01:33 PM
- - ngunn   Note the following sentence already quoted by Alex...   Aug 31 2006, 02:52 PM
- - tasp   I am having trouble seeing how the precipitating l...   Aug 31 2006, 03:56 PM
- - Rob Pinnegar   You mention "attendant ridges". This was...   Aug 31 2006, 05:20 PM
- - ngunn   On multiple ridges - perhaps the emplacement of th...   Sep 1 2006, 11:26 AM
- - tasp   I admit a certain favoring of an oblique impact kn...   Sep 1 2006, 01:45 PM
- - ngunn   This discussion has become really interesting. I...   Sep 1 2006, 02:52 PM
- - ngunn   Just found John Rehling's rather nice diagram ...   Sep 4 2006, 01:49 PM
|- - TritonAntares   Hi, I've just been back from a 1-week-vacation...   Sep 5 2006, 10:27 AM
- - ngunn   I did ask the other day for someone to re-post an ...   Sep 6 2006, 02:08 PM
|- - ugordan   QUOTE (ngunn @ Sep 6 2006, 03:08 PM) I di...   Sep 6 2006, 02:15 PM
- - djellison   Links to that place are not a good idea. Can peop...   Sep 6 2006, 02:13 PM
|- - ngunn   QUOTE (djellison @ Sep 6 2006, 03:13 PM) ...   Sep 6 2006, 02:31 PM
|- - Themisto   QUOTE (ngunn @ Sep 6 2006, 04:31 PM) Sorr...   Sep 6 2006, 03:06 PM
- - djellison   That's better We used to worry about mention...   Sep 6 2006, 03:10 PM
- - ngunn   OK let's see if this works.. http://www.aaw-d...   Sep 6 2006, 03:45 PM
- - tasp   3 intersecting ridges, all describing segments of ...   Sep 6 2006, 06:47 PM
|- - ngunn   QUOTE (tasp @ Sep 6 2006, 07:47 PM) The f...   Sep 7 2006, 08:51 AM
- - tasp   Some of the criteria that seem to be needed for us...   Sep 7 2006, 02:58 PM
|- - ngunn   QUOTE (tasp @ Sep 7 2006, 03:58 PM) Some ...   Sep 7 2006, 03:45 PM
- - tasp   We may find Iapetan like ridge structures on a per...   Sep 7 2006, 03:03 PM
|- - TritonAntares   Hi, before we should keep on speculating whether t...   Sep 7 2006, 03:50 PM
|- - ngunn   QUOTE (TritonAntares @ Sep 7 2006, 04:50 ...   Sep 8 2006, 10:44 AM
|- - ugordan   I have absolutely no idea on which internal proces...   Sep 8 2006, 11:05 AM
||- - ngunn   QUOTE (ugordan @ Sep 8 2006, 12:05 PM) I ...   Sep 8 2006, 12:04 PM
|||- - ugordan   QUOTE (ngunn @ Sep 8 2006, 01:04 PM) On g...   Sep 8 2006, 12:25 PM
|||- - ngunn   QUOTE (ugordan @ Sep 8 2006, 01:25 PM) It...   Sep 8 2006, 12:45 PM
|||- - ugordan   Yeah, but why would it flatten itself along the eq...   Sep 8 2006, 12:50 PM
||- - Rob Pinnegar   Two things today: QUOTE (ugordan @ Sep 8 200...   Sep 8 2006, 01:56 PM
|- - ynyralmaen   QUOTE (ngunn @ Sep 8 2006, 12:44 PM) So, ...   Sep 8 2006, 11:34 AM
||- - ngunn   QUOTE (ynyralmaen @ Sep 8 2006, 12:34 PM)...   Sep 8 2006, 12:12 PM
|- - tasp   QUOTE (ngunn @ Sep 8 2006, 05:44 AM) So, ...   Sep 8 2006, 01:33 PM
- - Bill Harris   This has been a fascinating discussion. Before Ca...   Sep 8 2006, 12:56 PM
- - ngunn   Hello Bill - nice to know it's not just the 4 ...   Sep 8 2006, 01:18 PM
|- - tasp   QUOTE (ngunn @ Sep 8 2006, 08:18 AM) Hell...   Sep 8 2006, 01:40 PM
- - tasp   Some where here at UMSF is a nice map of Iapetus (...   Sep 8 2006, 02:27 PM
- - tasp   I will note that Iapetus is subject to the smalles...   Sep 8 2006, 02:30 PM
|- - ugordan   However, the surface gravity at Iapetus is also va...   Sep 8 2006, 02:38 PM
- - tasp   I also point out that the New Solar System books...   Sep 8 2006, 02:36 PM
- - tasp   Virtually all solar system objects are believed to...   Sep 8 2006, 02:52 PM
- - ngunn   Is this the one? http://photojournal.jpl.nasa.gov/...   Sep 8 2006, 02:54 PM
|- - tasp   QUOTE (ngunn @ Sep 8 2006, 09:54 AM) Is t...   Sep 8 2006, 02:59 PM
|- - ugordan   Iapetus is undeniably oblate, but the question is ...   Sep 8 2006, 03:04 PM
|- - tasp   QUOTE (ugordan @ Sep 8 2006, 10:04 AM) Ia...   Sep 9 2006, 05:31 AM
- - hendric   I still don't see how the two divergent ridges...   Sep 8 2006, 05:54 PM
|- - TritonAntares   QUOTE 37th DPS Meeting, 4-9 September 2005 Session...   Sep 8 2006, 08:29 PM
||- - tasp   QUOTE (TritonAntares @ Sep 8 2006, 03:29 ...   Sep 9 2006, 05:28 AM
||- - ngunn   QUOTE (TritonAntares @ Sep 8 2006, 09:29 ...   Sep 9 2006, 08:59 AM
||- - tasp   QUOTE (ngunn @ Sep 9 2006, 03:59 AM) . . ...   Sep 9 2006, 01:56 PM
||- - ngunn   QUOTE (tasp @ Sep 9 2006, 02:56 PM) I hav...   Sep 9 2006, 09:56 PM
|- - tasp   QUOTE (hendric @ Sep 8 2006, 12:54 PM) I ...   Sep 9 2006, 05:10 AM
- - tasp   Also, check out the big elongated crater at 0 to 3...   Sep 9 2006, 05:35 AM
- - tasp   Just noticed I did not address moonlets below sync...   Sep 9 2006, 09:00 PM
- - tasp   I am thinking we aren't going to see an Iapeta...   Sep 10 2006, 01:00 AM
- - tasp   Speaking of New Horizons, how far out can it produ...   Sep 10 2006, 01:11 AM
- - tasp   Regarding perturbations of a possible Iapetan ring...   Sep 10 2006, 05:08 PM
- - Michael Capobianco   Well, I'm still a bit skeptical as well. For o...   Sep 10 2006, 05:18 PM
- - tasp   Of course, the most interesting bit of the ridge s...   Sep 10 2006, 06:00 PM
- - ngunn   So much to reply to (no, it isn't driving me t...   Sep 10 2006, 08:05 PM
- - tasp   QUOTE (ngunn @ Sep 10 2006, 03:05 PM) On ...   Sep 11 2006, 02:42 AM
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