[X] My Assistant

[Ant103]

The view toward Beagle is more and more precise.
http://origin.mars5.jpl.nasa.gov/gallery/a...CNP2435R2M1.JPG
The crater place seems to be a bit complex.

[chris]

Looks like lots of chunks lying around. Its going to be very interesting to see how they have interacted with the sand du, er ripples. Which leads me to another thought...

There have been lots of discussions on the tiny craters, etc, and whether they are caused by sapping or are tiny impact craters. I've been puzzling over this for ages (I'm not a geologist, btw). It seems to me that the dunes must be static now, otherwise the wind that we know blows over the plains would fill in the craters by moving the sand. They must have been mobile at some point, otherwise they wouldn't have the wind-sculpted shapes. This means they *must* have been mobile at one point.

I'm finding it hard to understand how slow hardening could result in preservation of the ripple shapes, so it ocurred to me that it might not have been so slow. We know that the apron of Victoria is splash-like, which might imply water. So perhaps the impact released a cloud of water vapour that interacted with the very fine, very dry sand, and essentially fixed it in place.

Am I talking nonsense?

Chris

[CosmicRocker]

It's an odd formation but let's be honest there is absolutely no way the hillock could have dropped into place on top of pre-existing dunes _and_ still have the interface look clean. Well unless there are Martian rubble\regolith moving teams racing around on Airspeeders.
I think Nick's explanation is pretty solid - the dune\ripple forming\moving process is disrupted by this mound because it is higher than the surface zone in which the dune processes are stable\semi stable. Above that zone the conditions are sufficiently different, probably higher wind velocity but it could be something else, to prevent the dunes forming so we get a nice clean rubble pile.
I'm quite glad they are going to poke around in this for a short while, should be very interesting.

I think we are essentially on the same page, in that the rubble pile came first and the ripples later. Whether it is an outlying ejecta block or a remnant of the ejecta blanket is not clear at the moment. But I can't buy into the idea that the hillock is too tall for ripples to form. Haven't we seen ripples as tall and even taller than this mound?