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
Post
#1
|
Guests |
Wing Ip just had an interesting Iapetus-related paper published in GRL.
|
|
|
Sep 7 2006, 02:58 PM
Post
#2
|
|
Member Group: Members Posts: 903 Joined: 30-January 05 Member No.: 162 |
Some of the criteria that seem to be needed for us to see such a feature are
*ancient surface *object needs to approximate a sphere *object may need to be remote from other objects (our own moon does not seem to have low circular orbits stable enough for there to be enough time for a ring system to form and emplace. Materials in randomly inclined lunar orbits will contact the lunar surface prior to colapse to the Laplacian plane) *object needs to have a surface sufficiently solid and rigid for the materials to emplace on *object needs a very low density (prefer none) atmosphere or materials will drop all around the equator. (we may see such structures someday, but they won't look like the Iapetan ridge formation). *object needs to be somewhere an appropriate glancing impact can loft materials is likely to occur. Iapetus may have encountered an 'outie' satellite of Saturn or a displaced Saturnian Trojan object |
|
|
Sep 7 2006, 03:45 PM
Post
#3
|
|
Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
Some of the criteria that seem to be needed for us to see such a feature are *ancient surface *object needs to approximate a sphere *object may need to be remote from other objects (our own moon does not seem to have low circular orbits stable enough for there to be enough time for a ring system to form and emplace. Materials in randomly inclined lunar orbits will contact the lunar surface prior to coplace to the Laplacian plane) *object needs to have a surface sufficiently solid and rigid surface for the materials to emplace on *object needs a very low density (prefer none) atmosphere or materials will drop all around the equator. (we may see such structures someday, but they won't look like the Iapetan ridge formation). *object needs to be somewhere an appropriate glancing impact can loft materials is likely to occur. Iapetus may have encountered an 'outie' satellite of Saturn or a displaced Saturnian Trojan object I've been having similar thoughts about the criteria. The only one of yours I would dispute is the last. I think an equally likely source for ring material is a sub-satellite that fragments at the Roche limit - no collision required. On 'ancient surface' I would prefer to say something like 'primitive' surface since in principle at least a ring-forming event does not have to be ancient (after all we see rings round the giant planets now that are probably not ancient, at least in their present form). On 'remote from other objects' I have been doing some rough calculations of a parameter that I think should relate to the capacity of a body to retain independent satellites or rings. It uses 3 quantities: mass of the world in question, m, mass of the most significant perturbing body, M, and the distance between them, d. As the strength of tidal forces falls off as the cube of distance so the formula becomes: d cubed multiplied by m over M. Using this formula all the major planets, including Mercury, come out orders of magintude ahead of all the solar system moons - no surprise there, though interestingly Pluto scores almost as highly as Jupiter. Of the moons, Luna and Titan score highest. Our moon could not have retained a ring at an early stage if it was much closer to the Earth then, but it could now! Titan could well have had subsatellites or rings early on but there would be no evidence left. Next comes Japetus, then Callisto. I haven't done the calculations for KBOs besides Pluto but they should all come out MUCH higher than Japetus, so definitely good places to look for ring ridges. On the contingent circumstances that would determine the type of great circle feature formed - there's the presence of any atmosphere certainly, but also the nature and quantity of the ring materials, the size distribution of the ring 'particles', the degree of tidal perturbation of the ring, and the rate of infall of material and the temperatures reached in the process, to mention just the most obvious ones. |
|
|
Lo-Fi Version | Time is now: 27th September 2024 - 09:50 AM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |