A RECENT METEORITE SHOWER IN ANTARCTICA WITH AN UNUSUAL ORBITAL HISTORY

The Antarctic meteorite collection has proved to be a source of many i mportant discoveries, including a number of previously unknown or very rare meteorite types. A thermoluminescence (TL) survey of meteorite s amples recovered by the 1988/89 European expedition and pre-1988 Ameri can expeditions to the Allan Hills Main blue ice field resulted in the discovery of 15 meteorites with very high TL levels (> 100 krad at 25 0 degrees C in the glow curve). It is likely that these samples are fr agments of a single meteoroid body which: (1) fell very recently and ( 2) experienced a decrease in orbital perihelia from greater than or eq ual to 1.1 AU to 1 AU within the last 10(5) yr. Carbon-14 data for two of the samples confirm their young terrestrial age compared to most A ntarctic meteorites. Studies of the cosmogenic isotopes in at least on e non-Antarctic meteorite, which also has very high natural TL, Jilin, indicate that the meteorite experienced a multi-stage irradiation his tory, the most recent stage being 0.4 Ma in duration following a major break-up of the object. These meteorites, and the few equivalent mode rn falls, are the only documented samples from bodies which were recen tly in Earth-approaching (Amor) orbits (i.e., with perihelion > 1.0 AU ), as opposed to the Earth-crossing (Apollo) orbits which are the sour ce of most other meteorites. Their rarity indicates that such rapid or bit changes are unusual for meteoroid bodies and may be the result of isolated, large break-up events.