I hope someone can clear up some issues about Mars's atmosphere, specifically: -- Since most evidence indicates that Mars once had surface water, I assume that it must have had a considerably more substantial atmoshpere than it currently has. --- A magnetic field is necessary for the preservation of such an atmosphere, as is the case on earth. ---The fact that Mars no longer has a magnetic field implies that its field vanished at some point and that explains the dissaperance of the atmosphere in sufficient density to preserve surface water. This all seems reasonable to me but I'm guessing at most of it. Anyone out there care to comment on the validity of these points?