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

摘要

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 meteoroidsfor ejecta 4500–5000 years ago. The meteoroids that come to within 0.05 AU of Earth’s orbit show the correctradiant position, radiant drift, approach speed, radiant dispersion, duration of activity, and distribution of dustat the other node, but meteoroids ejected 5000 years ago by previously proposed parent bodies do not. A morerecent formation epoch is excluded because not enough dust would have evolved into Earth’s path. The totalmass of the stream is about 9 × 1013 kg, similar to that of the remaining comet. Release of so much matterin a short period of time implies a major disruption of the comet at that time. The bulk of this matter stillpasses inside Earth’s orbit, but will cross Earth’s orbit 300 years from now. As a result, the alpha Capricornidsare expected to become a major annual shower in 2220–2420 a.d., stronger than any current annual shower.