Density, porosity, and magnetic susceptibility of achondritic meteorites

Abstract

Abstract-As part of a large-scale survey of meteorite bulk and grain densities, porosities, and magnetic susceptibilities, we measured these properties for 174 stones from 106 achondritic meteorites. These include four lunar meteorites, 15 stones from 10 shergottites, nakhlites, and chassignites (SNCs), 96 stones from 56 howardites, eucrites, and diogenites (HEDs), 17 stones from nine aubrites, two angrites, and 16 stones from 10 ureilites, four stones of three acapulcoites, as well as four stones of three lodranites, and 15 stones from eight primitive achondrites. Those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities, on an average, than the more primitive achondrites, which have a higher percentage metal. A notable exception is the one chassignite in the study (Chassigny), which has a high grain density of 3.73 ± 0.04 g cm )3 . Ureilites have magnetic susceptibilities consistent with primitive achondrites, but lower grain densities. Porosities do not vary considerably between most of the groups, with most stones 5-14% porous, although on an average, ureilites and brachinites have lower porosities, with most stones less than 7% porous. For primitive achondrites, the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites, with a reduction in grain density, magnetic susceptibility, and porosity as compared with unweathered falls. For lunites, SNCs, and HEDs, no such effect is observed. We also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites, nakhlites, and chassignites from each other. Shergottites and nakhlites have low grain densities (averaging 3.31 and 3.41 g cm )3 , respectively) whereas Chassigny is 3.7 g cm )3 . In magnetic susceptibility, shergottities and chassignites are similar (averaging 2.85 and 2.98 in log units of 10 )9 m 3 kg )1 , respectively) with nakhlites averaging higher at 3.42.

Internal structure and physical properties of the Asteroid 2008 TC3 inferred from a study of the Almahata Sitta meteorites

“…Comparing the bulk density data to other ureilites, all but one of the measured Almahata Sitta bulk densities are slightly lower than the ureilite mean of 3.22 g/cm 3 reported in Macke et al (2011).…”

“…In addition, the grain volume of one sample was measured using a Quantachrome Ultrapyc 1000 He pycnometer. The standard error of this device has been shown to be less than ±0.1 cm 3 (Macke et al, 2011).…”

Physical properties of the ESA Rosetta target asteroid (21) Lutetia

“…Perhaps more realistically, meteorite bulk densities should be considered instead. These are significantly lower -e.g., CO/CV appear to be, on average, about 0.6 g.cm −3 lower (Macke et al 2009). …”

“…Grain densities for stony meteorites range from ∼2.3 g cm −3 for CI/CM carbonaceous chondrites (Consolmagno et al 2008) to ∼3.0−3.6 g cm −3 for CO/CV (Flynn et al 1999) to ∼3.6 g cm −3 for EC (Macke et al 2009). Our best model yields densities of 4.3 or 3.5 g cm −3 , which are among the higher densities yet tabulated for asteroids.…”

Multi-color, rotationally resolved photometry of asteroid 21 Lutetia from OSIRIS/Rosetta observations

“…An alternative interpretation excludes significant porosity and probably a rubble-pile internal structure for Lutetia. In this context, we can directly compare the above result with the grain densities of meteorites: ∼2.3 g cm −3 for CI and CM, ∼3.5 g cm −3 for CO and CV, 3.6 to 3.7 g cm −3 for CH, and 4.4 to 4.6 g cm −3 for stony-iron meteorites (Britt & Consolmagno 2003;Consolmagno et al 2008;Macke et al 2009). Excluding the CI and CM, they are all compatible with the present uncertainty range of the density of Lutetia.…”