Density and Porosity of Stone Meteorites: Implications for the Density, Porosity, Cratering, and Collisional Disruption of Asteroids

Abstract

The grain density, bulk density, and porosity were measured for 19 ordinary chondrite and 5 carbonaceous chondrite meteorites, and the grain density was measured for an additional 30 ordinary chondrite and 7 carbonaceous chondrite meteorites. The unweathered ordinary chondrites generally have porosities ranging from 5 to 25%, while the carbonaceous chondrites have porosities in the range 10 to 30%. These high porosities indicate that the asteroidal parent bodies from which these chondritic meteorites are derived are porous, 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 greater than 3.0 g/cc, and the grain densities of the hydrated carbonaceous chondrites 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 porosity. Cratering and collisional disruption are sensitive to the porosity of the target. The parent bodies of the ordinary and carbonaceous chondrite meteorites appear to contain regions of significant porosity, which may affect their compression and compaction during impact events.