Physical properties of Martian meteorites: Porosity and density measurements

Abstract

Abstract-Martian meteorites are fragments of the Martian crust. These samples represent igneous rocks, much like basalt. As such, many laboratory techniques designed for the study of Earth materials have been applied to these meteorites. Despite numerous studies of Martian meteorites, little data exists on their basic structural characteristics, such as porosity or density, information that is important in interpreting their origin, shock modification, and cosmic ray exposure history. Analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planet's surface. We present new data relating to the physical characteristics of twelve Martian meteorites. Porosity was determined via a combination of scanning electron microscope (SEM) imagery/image analysis and helium pycnometry, coupled with a modified Archimedean method for bulk density measurements. Our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample. Preliminary interpretation of the data demonstrates good agreement between porosity measured at 100× and 300× magnification for the shergottite group, while others exhibit more variability. In comparison with the limited existing data for Martian meteorites we find fairly good agreement, although our porosity values typically lie at the low end of published values. Surprisingly, despite the increased data set, there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency. Further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations.

Gabbroic Shergottite Northwest Africa 6963: An intrusive sample of Mars

“…Therefore, in places such as Tharsis, and the younger crust of the northern lowlands, the high density of gabbroic bodies, such as NWA 6963, needs to be taken into account when calculating the crustal thickness. In fact, recent models of the martian crust suggest that the density of the lower crust is ~3.4-3.5 × 10 3 kg/m 3 (or greater), which is consistent with the density of shergottites (Coulson et al 2007) and also consistent with a middle to lower martian crust similar in mineralogy and chemistry to NWA 6963. This might provide an explanation for the so far unsuccessful search for the launch sites of the shergottite martian meteorites (e.g., Hamilton et al 2003;Lang et al 2009).…”

“…Shergottites typically have a density >3 × 10 3 kg/m 3 (Coulson et al 2007), which would reduce the calculated crustal thickness. However, shergottites are approximately 180 m.y.…”

The thermal and physical characteristics of the Gao-Guenie (H5) meteorite

“…There are at least four distinct forms of porosity that can be identified within chondritic meteorites, corresponding to cracks, fractures, vugs, and gaps separating individual chondrules and mineral phases from their surrounding matrix (Flynn, 2004). Connected crack and fracture porosity, however, typically dominates within chondritic meteorites, but shock effects induced during launch and collisional break-up can alter the pristine porosity, and terrestrial weathering may also reduce the pore space through secondary mineral growth (cf., Coulson et al, 2007).…”

The making of Martian meteorite Block Island

“…Indeed, if Block Island truly fell in the late Noachian then it has an age comparable to that of the carbonate and sulphate salts contained with the oldest known Martian meteorite ALH84001 (with a formation age of 4.5 Gyr) collected on Earth (see e.g. Gibson et al 2005; Coulson, Beech & Nie 2007). The general appearance of Block Island (Figs 1 and 4), Shelter Island and Mackinac Island indicates that some considerable differential erosion and pitting of their exposed surfaces have taken place – indeed, their appearance is similar to those displayed by ventifacts formed in desert regions on the Earth (as well as Mars; Bridges 1999; Bridges et al 1999).…”