[#3Fan]

Plus topographical studies show that the plastered side is sitting on top of the exposed unplastered side.

Let me rephrase that. Topographical studies (or studies of the crust) show that the loose pastered debris is sitting on top of a former surface that is visible on the unplastered side.

[RightWhale]

It could be that. There is the lower side that is relatively uncratered and the high side that is extensively cratered. Whether the low side is what was left after removal of material, or the high side is material that was added is a question that might be resolved by extensive geological digging. It seems that each successful probe to Mars raises questions but answers little.

When they taught in the 50s the story of where the moon came from, they had diagrams showing the moon material being ripped from one side of the earth's crust presumably where the Pacific Basin is today. Something similar could have happened to Mars, but there is of course nothing left of this material except the two small pieces Phobos and Deimos, if they came from that event and aren't just some kind of captured asteroids. There is no reason to expect that a captured asteroid would settle into a circular orbit except that is what happens apparently around Jupiter and Saturn. What could circularize such orbits when there are only a couple of small moons?