Determination of bulk density for small meteorite fragments via visible light 3‐D laser imaging

Abstract

Abstract-Bulk density is an important intrinsic property of meteorites, but the necessary bulk volume measurement is difficult to do in a truly nondestructive way. Archimedean methods involving the displacement of a 40-100 lm beads ''fluid'' are commonly applied, but can encounter systematic errors. Herein, we report a visible light laser imaging technique for the nondestructive measurement of meteorite surface features, allowing for the subsequent assembly of 3-D volumetric models; the method is particularly applicable to small meteorite fragments and to fragile specimens. We have acquired laser image data for 24 fragments from 18 ordinary chondrites, carbonaceous chondrites, and achondrites, with masses ranging from 265.0 to 1.2 g. Laser imaging bulk density is consistent between sister fragments of meteorites down to sizes of about 0.5 cm 3 , an order of magnitude smaller than can be reliably measured with Archimedean beads techniques. Uncertainty is less than 2% for fragments >4 cm 3 , and typically between 2 and 4% for small fragments <4 cm 3 . For 10 fragments, 3-D laser imaging volumes are on average 1.3% smaller than those obtained with Archimedean beads. In a wider comparison using 21 meteorite fragments, 3-D laser imaging bulk densities are on average 2.14 ± 2.36% greater than the corresponding Archimedean method literature values for these meteorites. Difficulties in the procedure of 3-D image alignment may lead to a slight overestimation of meteorite bulk density, and so laser imaging-based bulk densities are maximum estimates that can be viewed as being complementary to the minimum bulk density estimates obtained using Archimedean beads methods.

Determining meteoroid bulk densities using a plasma scattering model with high-power large-aperture radar data

“…Any non-physical densities, which comprise 5-10% of the data, were removed. The highest density meteoroids have densities consistent with the measured meteorites of McCausland et al (2011) and relative populations consistent with the optical meteor measurements of Kikwaya et al (2011). Once again selection effects are evident, since compared to these other methods, our HPLA radar approach allows measurement of meteoroids with lower densities that either do not reach the Earth's surface or do not result in significant optical emission.…”

3‐D laser images of splash‐form tektites and their use in aerodynamic numerical simulations of tektite formation

“…2 and 3 of Fry et al [2013]; Table 1). The error associated with model building is estimated to be <2%, based on the coefficient of variation among three different operators evaluated in an earlier study (McCausland et al 2011). Assembling 3-D models of tektites proved to be laborious for two reasons.…”

“…Recently, three-dimensional (3-D) imaging using noncontact high-resolution laser digitizers has become available. This technique has been applied to a variety of hand samples of stony (Smith et al 2006;McCausland et al 2011) and iron (Fry et al 2012;Fry 2013) meteorites, and to drill cores (Olson 2013).…”

Large spinel grains in a CM chondrite (Acfer 331): Implications for reconstructions of ancient meteorite fluxes

“…This equals to 1 Mg-Al-Cr-spinel grain >28 lm per 5 9 10 À3 g CM meteorite. A micrometeorite of cubic shape with a diameter of 200 lm, a size that is common among micrometeorites (Love and Brownlee 1993), and with the bulk density of 2.2 g cm À3 (mean of CM meteorites; Macke et al 2011; for comparison see e.g., Flynn et al 1999, McCausland et al 2011, weighs 1.76 9 10 À5 g. This means that 1 in 284 CM micrometeorites would yield a spinel grain >28 lm.…”