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The Iapetus Ridge, decayed ring hypothesis revisited
ngunn
post Dec 14 2010, 09:26 AM
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Well well! A ring is back in the reckoning, and this time originating from the breakup of a former sub-satellite. (I'm sure I've seen that somewhere before wink.gif )

http://www.spacedaily.com/reports/How_Iape..._Ridge_999.html

EDIT: How did I miss this abstract? http://www.agu.org/cgi-bin/SFgate/SFgate?l...fm10%2ffm10.txt

EDIT: Link back to the earlier thread kicked off by the original Wing Ip paper: http://www.unmannedspaceflight.com/index.php?showtopic=3122
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DrShank
post Dec 14 2010, 02:18 PM
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QUOTE (ngunn @ Dec 14 2010, 03:26 AM) *
Well well! A ring is back in the reckoning, and this time originating from the breakup of a former sub-satellite. (I'm sure I've seen that somewhere before wink.gif )

http://www.spacedaily.com/reports/How_Iape..._Ridge_999.html


yes it does. Folks are starting to do some serious simulations and finding it's rather easy. It also relates to our Rhea ring deposit story. Stereomoons.blogspot.com. We see series of blue spots on the equator just like Iapetus except no high ridge. In our Icarus paper we argued that Rhea and Iapetus both had rings but Rhea ring had much less mass
Paul


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Phil Stooke
post Dec 14 2010, 02:35 PM
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The geometric arguments seem to fit the ring hypothesis perfectly. As long as you can actually make the ring build up into a ridge instead of digging a groove, you're OK. In other words, the astronomy works, now for the geological part of the story.

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Hungry4info
post Dec 14 2010, 03:13 PM
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I'm not sure I understand (or it could be my definition of "ring" is incomplete). I interpreted this as a moon being tidally ripped apart and dropped onto Iapetus, making a nice lumpy line. Since this ridge on Iapetus does not completely encircle Iapetus, the idea of a ring seemed unreasonable to me. Would it be more accurate to call it a ring arc?


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ngunn
post Dec 14 2010, 03:22 PM
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H4 - check out the earlier thread I linked back to where various scenarios were worked over pretty thoroughly (by amateur standards). I think the ridge would have formed complete but later large impacts created gaps.
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tasp
post Dec 14 2010, 06:56 PM
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If those 'serious simulations' show ring edge warping at Iapetus from the distant Saturn, due to the Iapetan orbital inclination, then Joseph Burns' ideas and predictions about ring warping (born out already at Neptune) would neatly explain the short diverging attendant ridges. Check out the Planetary Rings chapter in The New Solar System. (I haven't seen the new edition, hope it is still included!)

Exciting times we live in!

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DrShank
post Dec 16 2010, 06:44 AM
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story just appeared in WiredScience! so i guess that officially makes it cool.

http://www.wired.com/wiredscience/2010/12/iapetus-ridge/

its an interesting story cause it continues to develop, and whatever the details about how the ring material got into orbit (there are several competing ideas tho most are related in some way), this feature exposed a new dynamical complexity to the Solar System.


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ngunn
post Dec 16 2010, 10:03 AM
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It seems to me that in the general case where a big collision lifts material into orbit around the target body some of that material will find itself above synchronous orbit and some below. The material above spirals outward producing satellites like Charon and our own Moon. The material below spirals inward eventually impacting the surface to form geometrically perfect equatorial surface features. In the case of Iapetus any above-synchronous material has probably been lost to Iapetus by now though it could still be in orbit around Saturn. In the case of Earth any equatorial feature produced by inward spiralling material has long since been erased by the planet's active processes. What about Pluto? Could it perhaps be the world where both features are preserved, a big satellite and a soon-to-be-discovered fossil ring? And what about Mars? Two moons, one spiralling in and one spiralling out. Were they both formed in this same way? What kind of equatorial feature will Phobos produce when it eventually descends to the Martian surface?

If the new simulations are telling us that this kind of thing is 'easy' maybe we should ask if it could have happened elsewhere too. Venus? Mercury? Perhaps most worlds are really cousins of 'weird' Iapetus but in some cases the evidence has left the scene or still remains to be discovered.

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scalbers
post Dec 23 2010, 08:08 PM
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QUOTE (ngunn @ Dec 14 2010, 04:22 PM) *
H4 - check out the earlier thread I linked back to where various scenarios were worked over pretty thoroughly (by amateur standards). I think the ridge would have formed complete but later large impacts created gaps.

Some of these gaps may be in the brighter longitudes. In these areas I wonder if we're seeing where the gaps are and whether impacts would account for them. In the dark areas Turgis seems to be a good example of such an impact.


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tasp
post Dec 23 2010, 08:16 PM
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I haven't seen mention of Ganelon as possibly being an interesting crater to consider for the moon and/or ring forming impact. With the lower resolution of the Cassini images of that area, I doubt we can get crater count derived age to rule out or rule in Ganelon.


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scalbers
post Dec 31 2010, 10:26 PM
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Any connection of this to the "lite" band on Tethys (e.g. in post #12 below)?

http://www.unmannedspaceflight.com/index.p...mp;#entry114175

Perhaps not as I see Dr. Shank in another thread attributed the Tethys band to electron bombardment related to the magnetic field.

http://www.unmannedspaceflight.com/index.php?showtopic=6846


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DrShank
post Jan 1 2011, 04:37 PM
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QUOTE (scalbers @ Dec 31 2010, 04:26 PM) *
Any connection of this to the "lite" band on Tethys (e.g. in post #12 below)?

http://www.unmannedspaceflight.com/index.p...mp;#entry114175

Perhaps not as I see Dr. Shank in another thread attributed the Tethys band to electron bombardment related to the magnetic field.

http://www.unmannedspaceflight.com/index.php?showtopic=6846



Agreed. The Tethys and Mimas bands are very wide (250+ km) and no relief. The Iapetus ridge is a few 10s of km wide but very topographic. The Tethys ridge (see seperate thread) is narrow but does not follow equator. A bit confusing but 3 distinct phenomena. Electrons in the first case, Ring reaccretion (probably) in the second (also seen faintly in the Rhea string of blue pearls), and ejecta deposition in the third.


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ngunn
post Jan 28 2011, 07:01 PM
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Here is a relevant LPSC abstract: http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2562.pdf

I checked back to post 1 to compare this with the AGU 2010 abstract and found my link there went to the wrong abstract. I've now edited it there but for completeness here it is again: http://www.agu.org/cgi-bin/SFgate/SFgate?l...fm10%2ffm10.txt

There are interesting differences between the two scenarios.
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stevesliva
post May 11 2011, 06:17 PM
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http://www.technologyreview.com/blog/arxiv/26752/

QUOTE
Harold Levison and buddies at the Southwest Research Institute in Boulder, Colorado, have hit on an explanation for the other two puzzling features: Iapetus's bulge and ridge.
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ngunn
post May 11 2011, 07:17 PM
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That's a really clear and succinct article. Thanks for posting it. However it proceeds in Odyssean fashion with the more recent (sublimation) story preceding the more ancient (despinning and ring) one. For me the icing on the cake in the extraordinary tale of Iapetus is the fact that the despinning that left it with such long days was an essential prerequisite to the runaway sublimation. It's all one story really - a tale of the unexpected if ever there was one.
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