A SEARCH FOR CLUSTERING AMONG THE METEOROID IMPACTS DETECTED BY THE APOLLO LUNAR SEISMIC NETWORK

We examined temporal clustering of meteoroid impacts detected by the Apollo lunar seismic network and found a distinct difference between "small" meteoroids (masses smaller than about 1 kg) and "large" meteoroids (masses larger than about 1 kg). Small meteoroids show strong clustering, many of which are identified with showers known from terrestrial meteor studies. In contrast, little clustering is found for large meteoroids, suggesting that they represent meteoroids of type and origin different from those of the small meteoroids. Overall, 28% of the small events and 15% of the large events occur as clusters. The small meteoroids appear to be mostly cometary, while the large meteoroids may be derived from near-Earth asteroids and short-period comets. Two swarms of large meteoroids detected in June 1975 and January 1977 possibly contain high-density meteoritic objects, and thus may represent "meteorite streams.". © 1991.