Like others have said, its not unexpected that some water remains, however its also possible (especially due to its location) that the object that caused this i

Like others have said, its not unexpected that some water remains, however its also possible (especially due to its location) that the object that caused this impact was made of ice. I'm not sure if Mars suffers impacts from it, but impacts from sources such as the Oort Cloud (http://en.wikipedia.org/wiki/Oort_cloud http://en.wikipedia.org/wiki/Oort_cloud) often contain ice and other materials. There are other examples if you search around. The universe is a big and crazy thing, the possibilities of what can and have happened are almost endless.