[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.

[tasp]

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.

Spent some more time looking at the picture.

Will run some ideas out:

The smooth bottom crater with the landslide covering a 1/3 of it is blasted out of the slumped original basin wall.

After that crater formed, the wall slumped again, I'm thinking the impact loosened and/or 'sharpened' up the basin wall enough so that it again collapsed into the new crater. The 'lumpiness' of the terrrain around the crater is similar to the 'lumpiness' in the slide in the crater.




Additionally, after looking at the new Iapetus map (see the other thread) and looking at this picture, the long 'trench' running up the right side of the picture that ends near the 3 craters arranged at 90, 90 and 180 degrees to each other is also close to an isolated segment of the equatorial ridge structure.

It is not very pronounced, but the alignment to the rest of the thing is right on.

Cassini website photo N00026206.3 might be a good one to look at.

I will try to find it and may be able to provide some better coordinatess for seeing it.

Might be some of the better resolution view of it we have.

[TritonAntares]

...
Cassini website photo N00026206.3 might be a good one  to look at.

I will try to find it and may be able to provide some better coordinatess for seeing it.

Here we go...

Date: 12/31/04
Distance: 183.276 km

The equatorial ridge ends at the same point where the trench ends (or begins).
Coincidence?
The CREB and its smooth bottom crater with the landslide are on a lengthened thought line from the ridge.
Coincidence?

Phuh,... Iapetus is a really large walnut to crack...


We really need more encounters to this strange moon - not only the Sep.2007 fly-by...
But concerning this, later...
Bye.