The interesting thing is that earth has a similar structure. The Pacific Ocean is a huge, somewhat round, hole in the crust. That is where the material that is now the moon supposedly came from. If half of Mars' crust is gone, that might, assuming structure indicates history, be where the asteroidal material came from. If so, the present orbits of the main belt asteroids and Mars not be the same as the original main body since before that event but some kind of average.
I wasn't sure that the crust was missing so much as the debris from the impacts altered the surface of the Hemisphere of Craters.
When the Days Were Shorter
Alaska Science Forum (Article #742) | November 11, 1985 | Larry Gedney
Posted on 10/04/2004 10:31:59 AM PDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1234919/posts
New evidence for the Moon's soft middle
New Scientist | 14 February 2002 | Will Knight
Posted on 12/27/2004 2:29:35 PM PST by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1309193/posts
In the shadow of the Moon
New Scientist | 30 January 1999 | editors
Posted on 08/31/2004 8:42:25 AM PDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1203912/posts
regarding:
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=16#16
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=35#35
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=37#37
see:
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=18#18
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=41#41
and:
http://www.freerepublic.com/focus/bloggers/1250694/posts?page=26#26
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=30#30
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=33#33
http://www.freerepublic.com/focus/f-chat/1390424/posts?page=34#34