A COLLECTION OF DIVERSE MICROMETEORITES RECOVERED FROM 100 TONNES OF ANTARCTIC BLUE ICE

STUDIES of meteorites and interplanetary dust particles (IDPs) have provided constraints on the formation and evolution of the Solar System 1, and have identified pre-solar interstellar grains 2-4. Here we describe a new type of meteoritic material, intermediate in size between meteorites and IDPs. Melting and filtering of approximately 100 tonnes of blue ice near Cap Prudhomme, Antarctica, yielded greater-than-or-equal-to 7,500 irregular, friable particles and approximately 1,500 melted spherules, approximately 100-mu-m in size, both showing a 'chondritic' composition suggestive of an extraterrestrial origin 5,6. For the present work, we analysed the composition and texture of 51 irregular particles and 25 spherules. The irregular particles appear to be unmelted, and have similarities with the fine-grained matrix of primitive carbonaceous chondrites, but are extremely diverse in composition. Isotopic analysis of trapped neon confirms an extraterrestrial origin for 16 of 47 irregular particles and 2 of 19 spherules studied, and strongly suggests that they were exposed in space as micrometeoroids. These large Antarctic micrometeorites constitute a new family-or at least a new population-of Solar System objects, in a mass range corresponding to the bulk of extraterrestrial material accreted by the Earth today.