Meteoroid streams as sources for meteorite falls: a status report

From their circumstances of fall (year, day, and, sometimes, petrographic type) five clusters of H4–6 chondrites have been identified statistically as deriving from separate meteoroid streams. Using another criterion, the meteoritesʹ contents of volatile trace elements (Ag, Bi, Cd, Cs, In, Rb, Se, Te, Tl, Zn) determined using radiochemical neutron activation analysis, and treated by multivariate statistical analysis techniques, three of the five clusters are distinguishable from the random background of observed falls. These data indicate that distinct H chondrite sources with primary thermal histories distinguishable from those of random sources provided H4–6 chondrites that fell in May, 1855–1895, and in September–October, 1812–1992. Thus, both in the short-term, and the long-term (> 50 kyr) as evidenced by Antarctic H4–6 chondrites, time-dependent variations occur in the Earthʹs sampling of common meteorites. The source-variations indicated by our data apparently reflect the existence of meteoroid streams which complete the hierarchy of comet streams, asteroid streams and fireball streams of asteroidal origin established by others.