Showing papers by "Gary R. Huss published in 1990"

Ubiquitous interstellar diamond and SiC in primitive chondrites: abundances reflect metamorphism

Abstract: It is shown here that interstellar diamond and SiC were incorporated into all groups of chondrite meteorites. Abundances rapidly go to zero with increasing metamorphic grade, suggesting that metamorphic destruction is responsible for the apparent absence of these grains in most chondrites. In unmetamorphosed chondrites, abundances normalized to matrix content are similar for different classes. Diamond samples from chondrites of different classes have remarkably similar noble-gas constants and isotropic compositions, although constituent diamonds may have come from many sources. SiC seems to be more diverse, partly because grains are large enough to measure individually, but average characteristics seem to be similar from meteorite to meteorite. These observations suggest that various classes of chondritic meteorites sample the same solar system-wide reservoir of interstellar grains.

Meteorite Infall as a Function of Mass: Implications for the Accumulation of Meteorites on Antarctic Ice

Abstract: Antarctic meteorites are considerably smaller, on average, than those recovered elsewhere in the world, and seem to represent a different portion of the mass distribution of infalling meteorites. When an infall rate appropriate to the size of Antarctic meteorites is used (1000 meteorites 10 grams or larger/sq km/1 million years), it is found that direct infall can produce the meteorite accumulations found on eight ice fields in the Allan Hills region in times ranging from a few thousand to nearly 200,000 years, with all but the Allan Hills Main and Near Western ice fields requiring less than 30,000 years. Meteorites incorporated into the ice over time are concentrated on the surface when the ice flows into a local area of rapid ablation. The calculated accumulation times, which can be considered the average age of the exposed ice, agree well with terrestrial ages for the meteorites and measured ages of exposed ice. Since vertical concentration of meteorites through removal of ice by ablation is sufficient to explain the observed meteorite accumulations, there is no need to invoke mechanisms to bring meteorites from large areas to the relatively small blue-ice patches where they are found. Once a meteorite is on a bare ice surface, freeze-thaw cycling and wind break down the meteorite and remove it from the ice. The weathering lifetime of a 100-gram meteorite on Antarctic ice is on the order of 10,000 + or - 5,000 years.

Meteorite mass distributions and differences between Antarctic and non-Antarctic meteorites

Abstract: Meteorite mass distributions provide important insight into real and apparent differences between Antarctic and non-Antarctic meteorites. Antarctic meteorites are typically smaller than non-Antarctic meteorites and represent a different portion of the mass distribution of infalling meteorites. This results from the different methods employed to acquire the collections and from the much smaller effective collecting area for Antarctic meteorites. Comparisons of the proportions and mass distributions of H and L chondrites for different ice fields suggest that previously reported high H to L ratio among Antarctic meteorites compared to witnessed falls results from an unrecognized H5 shower fall that covered the Allan Hills Main and Near Western ice fields in the relatively recent past. The probable presence of unrecognized shower falls among the Antarctic meteorites means that population statistics, even corrected for presently recognized pairing, cannot be used to support the suggestion by Dennison et al. (1986) of a temporal variation in the mixture of meteorites arriving on earth.