I was looking at the MRO image of the Opportunity landing site, and I was struck once again at how incredibly similar the plains on which Oppy landed and the annulus around Victoria look. They could be the exact same landform, looking at it from orbit at MRO's resolution.
The soils and drifts in the annulus also look more like the plains outside of Eagle and Endurance than anything we saw in the dune seas of the "etched" terrain. Granted, the concretions in the annulus are smaller and more conical than the more spherical concretions up north -- but all in all, the surfaces are remarkably similar.
Now, the annulus around Victoria *seems* to be arrayed in an ejecta-like pattern around the crater -- but the crater itself seems too old to exhibit an intact ejecta blanket. And -- and this is the crucial question -- if the terrain in Vickie's annulus is in some way a result of her ejecta blanket, then how do you explain almost identical terrain to the north, which isn't in any way visually associated with any ejecta blanket from any size of an impact?
I'd be tempted to think that such a strong visual similarity would have to indicate similarities in composition and/or origin.
I've read an initial geological analysis of the plains unit. I fail to see why the processes suggested in that analysis (early aqueous alteration, polygonal cracking due to dessication, and finally aeons of aeolian stripping and re-deposition) could cause a very similar unit that seems to be defined by the boundaries of Victoria's ejecta blanket. There are even traces of the same dessicative cracking in the annulus, which seems entirely absent (or masked) in the etched terrain.
Anyone want to take a shot at why these units seem so similar, and if they *are* the product of the same processes, how these processes can modify *only* the annulus around Victoria, not affecting the large drifts and exposed evaporitic sandstone that surround it?
-the other Doug