MINOR PLANET 2002 EX12 (=169P/NEAT) AND THE ALPHA CAPRICORNID SHOWER

Minor planet 2002 EX12 (=comet 169P/NEAT) is identified as the parent body of the alpha Capricornid shower, based on a good agreement in the calculated and observed direction and speed of the approaching meteoroids for ejecta 4500-5000 years ago. The meteoroids that come to within 0.05 AU of Earth's orbit show the correct radiant position, radiant drift, approach speed, radiant dispersion, duration of activity, and distribution of dust at the other node, but meteoroids ejected 5000 years ago by previously proposed parent bodies do not. A more recent formation epoch is excluded because not enough dust would have evolved into Earth's path. The total mass of the stream is about 9 x 10(13) kg, similar to that of the remaining comet. Release of so much matter in a short period of time implies a major disruption of the comet at that time. The bulk of this matter still passes inside Earth's orbit, but will cross Earth's orbit 300 years from now. As a result, the alpha Capricornids are expected to become a major annual shower in 2220-2420 A.D., stronger than any current annual shower.