Victoria Crater Vs Big Crater, Visibility Options

[djellison]

I'm not really asking a question really - just posing an issue




Mars Pathfinder was about 2.2km from 'Big Crater' which was about 1.5km wide.

Now - Victoria is only half that size - but it says something about local topography that we cant see it from where we are now - about 3-4km from it.

Doug

[Pando]

Looking at it again I think you are right - Victoria is a much younger crater compared to others nearby (Erebus and another larger one south-southwest).

This image shows an interesting pattern around Victoria (lighter colored terrain), but it's much too large to be ejecta from Viccy (which probably fueled by comment earlier).

There has been much resurfacing due to impacts, and there appear to be some monster ones like the one on the south-east cornier of this image.

I don't know if it's possible to tell though which craters were created during or after the "wet" period at Meridiani.

[dvandorn]

I don't know if it's possible to tell though which craters were created during or after the "wet" period at Meridiani.

Yeah -- that's a challenge. There are a lot of differences between obviously younger craters and ancient, degraded craters, including the old stand-bys of sharpness and blockiness. For example, Endurance and Victoria, while far different in size, look quite similar in morphology (at least from the orbital images) and might well be of similar ages. The cluster of which Erebus is a part is obviously a *lot* older and more degraded.

But, if I'm reading it right, it appears that the ancient cluster has left an uneven terrain that promotes selective wind erosion, while the impacts causing both Endurance and Victoria did not. That might be a matter of the size of the impacts in the cluster, or the interaction of multiple ejecta blankets (assuming the cluster was made all at the same time, which is not a very provable assumoption). But it also might be that the ancient craters struck water-laden target rock and the later impacts of Endurance and Victoria struck mostly dried rocks. My thinking is that the difference in mass of volatiles in the target rock would make a difference in how impacts make the landforms deform, and could cause the relief that has created the etched terrain appearance (explaining why ejecta blankets around ancient craters are still somewhat preserved in the etched terrain, while ejecta blankets around the younger craters have either been completely worn down or are in the process of being flattened out of view).

That's where I'm getting my (admitteldy WAG-ish) hypothesis that the ancient crater cluster was formed when the target rock was water-laden, and following it up with the further supposition that the resulting craters and ejecta were further modified by flowing and/or standing water by "cementing" the ancient craters' ejecta patterns with further overlays of evaporite that has "filled in the cracks" in the ejecta blankets.

I think maybe the *only* way we can establish this kind of stratigraphic sequence in this area is going to be determining if impacts occurred in wet or dry rock -- and especially at this site, where there has been so much erosion of what seems to be a *very* soft and erodable evaporite layer, that's going to be even tougher. But since I observe that the erosion patterns, as well as the erosion results, of obviously older craters seems so different than the erosion patterns we see at the younger, sharper craters, I can't help but come to the conclusion that such a difference in the groundwater state at the time of the impacts may well be a factor...

-the other Doug

[wyogold]

I don't know if it's possible to tell though which craters were created during or after the "wet" period at Meridiani.

Yeah -- that's a challenge. There are a lot of differences between obviously younger craters and ancient, degraded craters, including the old stand-bys of sharpness and blockiness. For example, Endurance and Victoria, while far different in size, look quite similar in morphology (at least from the orbital images) and might well be of similar ages. The cluster of which Erebus is a part is obviously a *lot* older and more degraded.

But, if I'm reading it right, it appears that the ancient cluster has left an uneven terrain that promotes selective wind erosion, while the impacts causing both Endurance and Victoria did not. That might be a matter of the size of the impacts in the cluster, or the interaction of multiple ejecta blankets (assuming the cluster was made all at the same time, which is not a very provable assumoption). But it also might be that the ancient craters struck water-laden target rock and the later impacts of Endurance and Victoria struck mostly dried rocks. My thinking is that the difference in mass of volatiles in the target rock would make a difference in how impacts make the landforms deform, and could cause the relief that has created the etched terrain appearance (explaining why ejecta blankets around ancient craters are still somewhat preserved in the etched terrain, while ejecta blankets around the younger craters have either been completely worn down or are in the process of being flattened out of view).

That's where I'm getting my (admitteldy WAG-ish) hypothesis that the ancient crater cluster was formed when the target rock was water-laden, and following it up with the further supposition that the resulting craters and ejecta were further modified by flowing and/or standing water by "cementing" the ancient craters' ejecta patterns with further overlays of evaporite that has "filled in the cracks" in the ejecta blankets.

I think maybe the *only* way we can establish this kind of stratigraphic sequence in this area is going to be determining if impacts occurred in wet or dry rock -- and especially at this site, where there has been so much erosion of what seems to be a *very* soft and erodable evaporite layer, that's going to be even tougher. But since I observe that the erosion patterns, as well as the erosion results, of obviously older craters seems so different than the erosion patterns we see at the younger, sharper craters, I can't help but come to the conclusion that such a difference in the groundwater state at the time of the impacts may well be a factor...

-the other Doug

If these craters did happen upon "wet" rocks shouldn't it be rather easy to spot when looking at the fracturing within the impacted rocks?

[dvandorn]

If these craters did happen upon "wet" rocks shouldn't it be rather easy to spot when looking at the fracturing within the impacted rocks?

Maybe it will. If my theory is correct, we're just now appraching the edge of the ejecta blankets from the ancient crater cluster. The problem, of course, is that the ejecta blankets have been highly degraded and modified since they were emplaced. I would guess, from the way the terrain looks, that the best shot for seeing exposed ridges of actual ejecta would be in the lightest patches of what looks like outcrop within the etched terrain.

-the other Doug