A rock has to get off of the body where it formed, it has to travel through space, then it has to land safely on a new body, and once it get there it has to find a congenial environment. Of the three, landing is probably the easiest. |
It's completely possible that there's no water involved at all and that what we're seeing are just dry flows of dust and sand. You can get massive flows of material that's completely dry and ends up having pretty much the same shape as if they were wet. |