Perhaps the most puzzling thing for the team is the existence of craters that have central mounds the smae height as the surrounding terrain. There is layering in the mounds that matches the layering in the surrounding sides of the craters. If the layers were built up over millions of years, then what caused the material to be removed from around the mounds? There were even some cases of layered mounds that were higher than the surroundings.

Also they found lots of salts in the layers around the rovers, but in answer to a question, there are no carbonates. Mostly sulfates, as though sulphuric acid had seeped up through the rocks and leached out the minerals to form sulfate salts.