Density and porosity of stone meteorites: Implications for the density, porosity, cratering, and collisional disruption of asteroids

The grain density, hulk density, and porosity were measured for 19 ordinary chondrite and 5 carbonaceous chondrite meteorites, and the grain density w as measured for an additional 30 ordinary chondrite and 7 carbonaceous chon drite meteorites. The unweathered ordinary chondrites generally have porosi ties ranging from 5 to 25%, while the carbonaceous chondrites have porositi es in the range 10 to 30%. These high porosities indicate that the asteroid al parent bodies from which these chondritic meteorites are derived are por ous, or contain porous regions. The grain densities of all 49 ordinary chondrites are greater than 3.1 g/cc , the grain densities of all 9 anhydrous carbonaceous chondrites are greate r than 3.0 g/cc, and the grain densities of the hydrated carbonaceous chond rites range from 2.5 to 3.0 g/cc. Comparison of these grain densities with spacecraft determinations of the densitiy of the S-type asteroid Ida, 2.6 g /cc, and the anhydrous C-type asteroid Mathilde, 1.3 g/cc, suggests that if these asteroids are composed of material similar in mineralogy to that of the stone meteorites, then Ida and Mathilde must exhibit significant porosi ty. Cratering and collisional disruption are sensitive to the porosity of the t arget. The parent bodies of the ordinary and carbonaceous chondrite meteori tes appear to contain regions of significant porosity, which may affect the ir compression and compaction during impact events. (C) 1999 Academic Press .