[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

[dvandorn]

Looking at the bedding in the ripples, you can see that there are some compositional changes over time in the grain deposition. That's the only way you get this kind of bedding.

So, the layers in the ripples (which seem relatively evenly spaced) speak to epochs of ripple deposition, I think. The way that the layers tend to have partially-cemented surfaces (similat to the cementing we see on the surfaces of the ripples today) hint that each of these layers was once the surface of the ripple.

So, what could occur in epochs on Mars that would result in the building of material on top of existing, surface-cemented (and therefore probably relaytively static for a time) ripples?

Cyclic, drastic climate change, due to Mars' extreme wobble, could just fit the model. I think.

So, perhaps we are seeing layering in these ripples that is built up every time Mars goes through a given portion of its extreme climate cycle. Possibly, you only get rapid ripple/dune deposition during those times when the maximum amount of Mars' atmosphere is gaseous for the greatest amount of time during the year. I'm not sure which portion of the climate cycle would offer these conditions -- but I bet the planetary climatologists will have it all figured out in a decade or two...

-the other Doug