[X] My Assistant

[Rob Pinnegar]

While looking over some pictures of Iapetus from the New Year's 2005 flyby, I came across this:



I'm not sure that we've been paying this image enough attention. For one thing, this big crater, on the edge of the big Saturn-facing basin, has a nice bright white ice band that extends most of the way around its edge. This has got to have some implications both for emplacement of Cassini Regio, and perhaps the thickness of the dark material as well. Also, this crater seems to have virtually no impacts inside it, which points to a recent origin -- and that in turn can place some age limits on Cassini Regio, which has to be even younger.

There's also that strange "flow feature" on the crater's floor. The hypothesis that was originally put forth to explain this was that part of the basin wall had caved in and caused a big landslide. The thing that bothers me about this idea is that it doesn't explain the shape of the crater's outline, which looks as if it really should extend a bit farther out beyond the basin wall. Shouldn't a landslide have caused the crater's outline to be deformed outwards on that side, not inwards?

Also, I've never been comfortable with the idea of a landslide extending over that much distance. Iapetus' low gravity has been cited as a reason for this, but that also would limit the amount of gravitational potential energy available to get the slide going. We probably need a bigger energy source.

So I wonder if this flow feature wasn't caused by a landslide at all, but instead was formed at the same time as the crater, as the shock wave caused by the impact reflected off of the basin wall? I don't know if this could explain the sharp boundary of the flow region, but it's probably worth considering, at least.

[hendric]

If you look at the image kinda squinty-eyed, you do see that there is a faint outline that extends beyond the crater into the highlands to the right. It could be a vastly older, highly degraded basin, or it could be slumping caused by the landslide.

[TritonAntares]

If you look at the image kinda squinty-eyed, you do see that there is a faint outline that extends beyond the crater into the highlands to the right.  It could be a vastly older, highly degraded basin, or it could be slumping caused by the landslide.

I guess you mean the red lined ancient crater rim.

The red marked area below the crater for sure is an also vast landslide.
My impression of the giant bassin is, that it could be a kind of caldera not an impact structure...
Hints are the circled craters at the edge of the bassin.
One looks to be tilted, the two others left somehow to be cut off...
...anyway it looks like the bottom below them collapsed. Even a caldera incident...
But this could also be some shadow effects...

Any other ideas?

Bye.