On a ring origin of the equatorial ridge of Iapetus Options

[Guest_AlexBlackwell_*]

Wing Ip just had an interesting Iapetus-related paper published in GRL.

[Guest_AlexBlackwell_*]

Does the paper address why the equatorial ridge doesn't go all the way around Iapetus?

And why would the decay of such a ring produce a ridge rather than a chain of impact craters?

Given that I'm quoting liberally from the paper, I wish it were available

As described in the classical diffusive accretion model [Pringle, 1981], collisional interaction among the ring particles will lead to the inward and outward radial dispersal of the ring material. If Iapetus possessed a thick atmosphere at that time, the ring particles would drift inward systematically because of gaseous drag. What kind of ring mass is required to build the ridge system? While the height of the ridge reaches as much as 20 km at some locations [Denk et al., 2000; Porco et al., 2005], there are also peaks only a few km high or less [Denk et al., 2005b]. Just for the sake of estimate, the maximum ring mass can be computed to be Δm = 2πRIΔw Δh ρ ~ 4.4 × 1021 g for Δw ~ 50 km, Δh ~ 20 km and ρ ~ 1 g cm−3 for water ice composition. This mass is equivalent to an object of 74 km-radius with a mass of 0.1% of that of Iapetus. A better inventory would require more complete information on the height distribution of the ridge system around Iapetus. The important thing here is that the impact site of the ring particles must be defined by the intersection of the ring plane and the satellite surface which is the equator. A possible consequence of the surface impact is simply that regions with prior ring mass injection would tend to intercept more material – at grazing angle - because of their greater heights. This effect might help to partially explain the non-uniform height distribution of the ridge system as mentioned above. On the other hand, local geological process plus cratering events could also contribute to the disruption of the equatorial ridge (T. Denk, private communication, 2005).

...The surface landing mechanism [of the ring particles] might be assisted by the formation of a boundary layer between the satellite surface and the inner edge of the ring system. The viscous heating in slowing down the ring particles would lead to the pulverization and even partial liquification of the infalling material. The bulk of the ridge system might then be built up bit by bit as a sort of sandpile but in a grand scale It is required that the surface of Iapetus should be solidified already at this stage. Otherwise, no trace of the ring remnant would be able to remain. In the final phase, the residual ring system would gradually disappear because of destructive bombardment and erosion by the interplanetary stray bodies.

Would this process also explain the albedo assymetry on Iapetus?

I doubt it.