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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 30 2006, 05:11 AM
Post #2


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An object skimming the surface of Iapetus will have a velocity of ~1500 km/hr. (under 1000 mph)

For cryogenic water ice, (~-300 F) I suspect vaporization upon impact would be nil. There may be a 'blast of particles though.



Consider a ring around Iapetus (glossing over how it got there, for the moment).

What happens to the lowest orbiting particle?

It strikes the highest point along the Iapetan equator.

What happens to the second lowest orbiting particle?

It hits the first one.


You originally start to form a pile. At some point in time, you literally run out of room in the pile area (insufficient kinetic energy of the oncoming particles) and the pile starts to accrete only into the direction of the oncoming particles. (analogy-you plow snow from all over your driveway into one pile, eventually, your pickup is not powerful enough to cram the pile any higher, and if you keep shoving snow into the pile, always from the same direction, you will start to form an elongated pile, and the pile will lengthen into the path of the oncoming snowplow)

The orbitally decaying ring system will form a ridge. Ridge 'grows' into the oncoming stream of material. Process concludes when ring material is depleted.

Iapetus had enough ring material to make a ridge 90 to 120 degrees long.


An atmosphere is not necessary for the process to occur. Differential ring spreading (transference of angular momentum radially across a ring system is well understood. Check out the Planetary Rings chapter in The New Solar System. That chapter also outlines clearly how a cloud of debris in virtually any orbital inclination will eventually settle into an equatorial ring system.


That the ridge is observed to be non-continuous may be due to the ridge suffering subsequent cratering damage, or perhaps settlement due to crustal overloading.


The best Cassini images also show perfectly (less subsequent crating damage) symetrical diverging 'attendent' ridges (the off ramps). I cannot imagine any internal geological process that could make such elegant matched attendents. They are the 'smoking gun' for declaring an external process made the ridge.

(the attendants can be explained by a percentage of the ring system being inclined to the equator. Twice each orbit for the inclined material, it will cross the equator. Once, from north to south, and once from south to north. The high spot on the ridge 'synchronizes' the simultaneous equal deposition of material into 2 matched divering stuctures.)


(I suspect at the contact point with the high spot on the surface for the inclined material, a small debris cloud forms, and material orbiting above that spot at the instant of the lower materials contact will be subjected to a drag force and accumulate down range.)

-or-

As the material deposits into the ridge structure, a point is reached where the spin axis of Iapetus shifts a few degrees (like unbalancing a gyro with a small weight) and Iapetus starts preceesing underneath the still descending ring system, the high spot still penetrates the ring plane twice per rotation, and the symmetrical attendant ramp form as before.

-or-

A large (unrelated) impact occurs somewhere on Iapetus and it knocks the spin access off a few degrees. Effect is still the same as above.



Why don't we see ridges any where else?

Iapetus is the most remote from it's primary, satellite we have seen so far. Tidal effects (causing the ring system to not form in the first place on other moons) are uniquely low at Iapetus (also one of the reasons we will not see a ridge system on either Pluto or Charon).

Also, Iapetus plods along at 5000 kph (or is it mph?, doesn't matter) in it's orbit around Saturn. Iapetus probably accreted very slowly (compared to the other satellites) and perhaps had a solid crust far earlier in its' history than the other moons, the impact heat being reduced by the lower incoming velocities and longer periods to radiate the heat away. Also, Al 27 heating in the accretable materials of Iapetus had longer to radiate away.

Iapetus is the closest we get to a 'cold formed' moon considering its' size.


We may see some equatorial ridge structures on the larger KBO's, if there are enough of them that are spherical (think about it), remote enough, and had an originating oblique impact to orbit a ring forming debris cloud.

This post has been edited by tasp: Aug 30 2006, 05:15 AM
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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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