Gehrels proposes two sources: debris gouged out of the moon when other, larger asteroids slam into it; or further breakup of main-belt asteroids
already fragmented by collisions within the belt.
A possible collision involving the large main-belt asteroid
(596) Scheila', 121(1), 4 (2011);
229255) Andrewelliott is a small main-belt asteroid
probably some 2-3km in diameter.
In contrast, he is at a loss to explain another discovery-a body that sports a tail yet orbits as if it were a main-belt asteroid
There are 187 main-belt asteroids
larger than 100 km in diameter, and 474 that are larger than 50 km.
The T-Tauri outbursts stripped a portion of Mercury's incompletely condensed protoplanet and transported it to the region between Mars and Jupiter where it fused with in-falling oxidized condensate from the outer regions of the Solar System forming the parent matter of ordinary chondrite meteorites, the main-Belt asteroids
, and veneer for the inner planets, especially Mars.
MBCs are main-belt asteroids
situated at a distance of between 2 and 3.