Quantification of porosity and surface roughness in laboratory measurements of the bidirectional reflectance of asteroid surface analogues

Tatsuya Sakai,Akiko M Nakamura

doi:10.1186/bf03351807

Abstract

Abstract We studied the effects of the surface roughness and porosity of a sample layer on its light-scattering properties in laboratory experiments using fly ash, iron, graphite, and olivine powders. Three types of surface structure were prepared: compacted, knocked, and fluffy surfaces. The surface roughness is represented by the mean slope angle of small facets on the surface. We found a positive correlation between the surface roughness and the porosity of the layer. The bidirectional reflectance of the surface at the wavelength of a He-Ne laser (633 nm) was measured to illustrate the influence of surface structure on scattering properties, with the incidence angle fixed at 0°, while varying the phase angle from 2 to 80°. The reflectance of a relatively rough surface was lower than that of a relatively smooth one for all of the materials measured. The reflectance measured at 30° in phase angle decreased by between ∼25 and ∼60%. This effect may explain the discrepancy between the absolute reflectance in previous laboratory results and the observed results for C class asteroids (Kamei and Nakamura, 2002; Nakamura et al., 2002).

Highlights

Laboratory photometric phase curves of meteorite powders place constraints on meteorite-asteroid connections and the surface structure of asteroids
We report on the relationship between porosity and surface roughness, and the effect on the bidirectional reflectance
Summary To quantify the effects of the surface structure of a powdery layer on its light scattering properties, bidirectional reflectance was measured in the laboratory using powdery surfaces with various degrees of roughness and porosity

Summary

Introduction

Laboratory photometric phase curves of meteorite powders place constraints on meteorite-asteroid connections and the surface structure of asteroids. In previous studies of the bidirectional reflectance of meteorite powders, the sample surfaces were smoothed using a spatula (Kamei and Nakamura, 2002; Tomita et al, 2003). These studies found that (1) the surfaces of meteorite powders had shallower phase curves than those of most asteroids and (2) the surfaces made of carbonaceous-chondrite powders were up to 200% as bright as asteroid 253 Mathilde (Kamei and Nakamura, 2002; Nakamura et al, 2002). The surface is probably rougher and more porous than laboratory surfaces smoothed using a spatula

Methods

Results

Conclusion