CATASTROPHIC FRAGMENTATION OF ASTEROIDS - EVIDENCE FROM METEORITES

Meteorites are impact-derived fragments from approximate to 85 parent bodies. For seven of these bodies, the meteorites record evidence sugg esting that they may have been catastrophically fragmented. We identif y three types of catastrophic events : (a) impact and reassembly event s >4.4 Gy ago, involving molten or very hat parent bodies (>1200 degre es C); this affected the parent bodies of the ureilites, Shallowater, and the mesosiderites. In each case, the fragments cooled rapidly (app roximate to 1-1000 degrees C day(-1)) and then reassembled. (b) Later impacts involving cold bodies which, in some cases, reassembled, this occurred on the H and L ordinary chondrite parent bodies. The L parent body probably suffered another catastrophic event about 500 My ago. ( c) Recent impacts of cold, multi-kilometer-sized bodies that generated meter-sized meteoroids; this occurred on the parent bodies of the III AB irons (650 My ago), the IVA irons (400 My ago), and the H ordinary chondrite (7 My ago).