Characterization of the micrometer scale surface roughness of meteoritic samples

Abstract

This study investigates the key role of boulders, particularly their surface texture, which are primary surface features on small airless planetary bodies, that serve as indicators to better understand the geological history and evolutionary processes undergone by the small bodies and their respective parent bodies. In particular, this study focuses on characterizing the unpolished surface of meteorite samples, which can be likened to the surfaces of boulders on small bodies. We use surface roughness metrics such as the mean (bidirectional) slope and a Hapke mean slope angle in order to characterize the surface texture of the samples. Furthermore, considering a fractal roughness of the surface we estimate the Hurst exponent and the associated scaling factor at an arbitrary scale of ∼60 μm. We find that on the ∼4 μm scale, the mean bidirectional slope and the mean Hapke slope are in the range of 20–40° and 15–35° respectively, with carbonaceous chondrites collectively exhibiting the lowest average value for both. Furthermore, we provide surface roughness measurements for a subsample of the Ryugu sample A0008, which is broadly in agreement with the measurements derived from MASCam data. This study also investigated intra-sample heterogeneities, specifically surface roughness variations between matrix and non-matrix components such as impact melt, shock veins, and chondrules. The results suggest that surface roughness variations exist between these components and the matrix, however, the amplitude of the variation is strongly influenced by the petrological homogeneity of the chosen region of interest.