@blob
The pic you linked is a render based on the picture from the rover.
If you back up the tree a couple of levels you get to
here where you can look at the pictures.
As to the lightness at the bottom of the trench, the site says that "[t]he brightness of the newly-exposed soil is thought to be either intrinsic to the soil itself, or a reflection of the Sun." Or? Or? Any other ideas or does that about cover the options?
Anyway, if you look about the landing site, there are plenty of outcrops of material lighter than the surface of the dust. Unfortunately the pic is only B&W and there is no good reference in it to figure out the actual brightness. How light or dark should shadows be on Mars, and what colour are the rover's wheels when they're at home?
I suspect the light material is some sort of material that reflects more light than the darker material. Can I write NASA press releases now?
