NASA Today: Space rock recovery

I've got a better idea: send a trapping spacecraft to the Asteroid Belt, and 
bring us back a sample from there, so we can determine if that stuff has the same density and characteristics as stuff from Mars. Let's find out if parts of the surface of Mars are now making up that crushed rock and gravel in that belt out there between Mars and Jupiter. My pet theory says 'Yes'. And don't look now, but our Moon and Mars have a calculated mean density of approximately 3.9 grams per cubic centimeter, which is considerably lower than the three other terrestrial planets. Did our moon originate in Mars, before that meteoroid punctured Mars' crust about three and a half billion years ago? Perhaps. But we won't know if we don't investigate the possibilities.