Breakup and structure of an H-chondrite parent body - The H-chondrite flux over the last million years

Two distinct groups of H chondrites are identified which have respectively induced thermoluminescence peak temperatures above 190 C (AC) and below 190 C (BC). Metallographic cooling rate determinations confirm that the AC group cools at very high rates relative to the latter group. The AC group members have cosmic ray exposure ages of about 8 Myr. Antarctic meteorite of the BC group have cosmic ray exposure ages greater than 20 Myr. Modern H-chondrite falls, which are all of the BC group, have cosmic ray exposure ages of 8 and above 20 Myr. The data show that the abundance of the AC group is directly related to terrestrial age. It is suggested that both the AC group and part of BC group were produced by an impact event at approximately 8 Myr and that the small sizes of the AC group made them prone to destruction, allowing the BC group to dominate the modern H-chondrite flux.