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.

[Michael Capobian...]

Well, I'm still a bit skeptical as well. For one thing, a spreading ridge of upwelling material often produces a multiple ridge like we're seeing in the close-ups. I would really love to see those detailed shots of the ridge superimposed in context on the map of Iapetus.

So, with the ring-emplacement, we have an interesting theory, but we don't have enough high-resolution images to really test it. Here are some observations after staring at these images far too long:

* The ridge extends from about 50 degrees to 210 degrees, only a little more than half way around Iapetus.

* It's visible only in Cassini Regio. There's no sign of it in Roncevaux Terra, some of which the Saturnshine images show at high resolution.

* Although at large scales there appears to be an equatorial marking at the Eastern edge of Cassini Regio, it doesn't show much topography, is primarily an albedo feature, and may be coincidental.

* The ridge is discontinuous in Western CR, which is not consistent with ring-emplacement. There is a large crater superimposed on it there, but would a large impact create the pattern we see?

* In the area of Cassini Regio west of the landslide basin, the ridge seems to peter out and stops entirely well before reaching the presumed ejecta blanket of the basin.


I think the 2007 encounter will resolve many of the issues here, especially the nature of the ridge in Western CR. If it actually is discontinuous west of the superimposed crater, that will be a very important data point. Not to mention the nature of the white mountains and how the dark material is distributed there. I still believe that a flyby for close-up imaging of the Snowman/Moat would be extremely valuable to understand the dark/light interface, and the likelihood of Iapetan internal activity. If there is a remnant of the ridge there, perhaps wiped out by the Snowman impact, it might help understand the ridge as well.

Michael