Photometric models of disk-integrated observations of the OSIRIS-REx target Asteroid (101955) Bennu

We used ground-based photometric phase curve data of the OSIRIS-REx target Asteroid (101955) Bennu and low phase angle data from Asteroid (253) Mathilde as a proxy to fit Bennu data with Minnaert, Lommel-Seeliger, (RObotic Lunar Orbiter) ROLO, Hapke, and McEwen photometric models, which capture the global light scattering properties of the surface and subsequently allow us to calculate the geometric albedo, phase integral, spherical Bond albedo, and the average surface normal albedo for Bennu. We find that Bennu has low reflectance and geometric albedo values, such that multiple scattering is expected to be insignificant. Our photometric models relate the reflectance from Bennu's surface to viewing geometry as functions of the incidence, emission, and phase angles. Radiance Factor functions (RADFs) are used to model the disk-resolved brightness of Bennu. The Minnaert, Lommel-Seeliger, ROLO, and Hapke photometric models work equally well in fitting the best ground-based photometric phase curve data of Bennu. The McEwen model works reasonably well at phase angles from 20° to 70°. Our calculated geometric albedo values of 0.047-0.014+0.012,0.047-0.014+0.005, and 0.048-0.022+0.012 for the Minnaert, the Lommel-Seeliger, and the ROLO models respectively are consistent with the geometric albedo of 0.045 ± 0.015 computed by Emery et al. (Emery, J.P. et al. [2014]. Icarus 234, 17-35) and Hergenrother et al. (Hergenrother, C.W. et al. [2014]. ). Also, our spherical Bond albedo values of 0.016-0.004+0.005,0.015-0.001+0.003, and 0.015-0.005+0.007 for the Minnaert model, Lommel-Seeliger, and ROLO models respectively are consistent with the value of 0.017 ± 0.002 presented by Emery et al. (Emery, J.P. et al. [2014]. Icarus 234, 17-35). On the other hand, the semi-physical models such as the Hapke model, where several assumptions and approximations were necessary, and the McEwen model are not supported by the global disk-integrated data, indicating that disk-resolved measurements will be necessary to constrain these models, as expected.