Modeling optical roughness and firstorder scattering processes from OSIRISREx color images of the rough surface of asteroid (101955) Bennu
Abstract
The dark asteroid (101955) Bennu studied by NASA' s OSIRISREx mission has a boulderrich and apparently dustpoor surface, providing a natural laboratory to investigate the role of singlescattering processes in rough particulate media. Our goal is to define optical roughness and other scattering parameters that may be useful for the laboratory preparation of sample analogs, interpretation of imaging data, and analysis of the sample that will be returned to Earth. We rely on a seminumerical statistical model aided by digital terrain model (DTM) shadow raytracing to obtain scattering parameters at the smallest surface element allowed by the DTM (facets of ~10 cm). Using a Markov Chain Monte Carlo technique, we solved the inversion problem on all fourband images of the OSIRISREx mission' s top four candidate sample sites, for which highprecision laser altimetry DTMs are available. We reconstructed the a posteriori probability distribution for each parameter and distinguished primary and secondary solutions. Through the photometric image correction, we found that a mixing of low and average roughness slope best describes Bennu's surface for up to 90^{∘} phase angle. We detected a low nonzero specular ratio, perhaps indicating exposed subcentimeter monocrystalline inclusions on the surface. We report an average roughness RMS slope of 27_{5}^{∘+1}, a specular ratio of 2.6_{0.8}^{+0.1}%, an approx. singlescattering albedo of 4.64_{0.09}^{+0.08}% at 550 nm, and two solutions for the backscatter asymmetric factor, ξ^{(1)} =  0.360 ± 0.030 and ξ^{(2)} =  0.444 ± 0.020, for all four sites altogether.
 Publication:

Icarus
 Pub Date:
 March 2021
 DOI:
 10.1016/j.icarus.2020.114106
 arXiv:
 arXiv:2010.04032
 Bibcode:
 2021Icar..35714106H
 Keywords:

 Asteroid Bennu;
 Asteroids;
 surfaces;
 Radiative transfer;
 Image processing;
 Photometry;
 Astrophysics  Earth and Planetary Astrophysics;
 Physics  Computational Physics;
 Physics  Geophysics;
 Physics  Optics
 EPrint:
 15 pages, 11 figures