The OSIRIS-REx mission’s observation campaigns  using the PolyCam instrument, part of the OSIRIS-REx Camera Suite (OCAMS) [2 3], have returned images of the surface of near-Earth asteroid (NEA) (101955) Bennu at a resolution unprecedented for a planetary surface. These images resolved cavities on Bennu’s boulders (Fig. 1) that are near-circular in shape and have diameters ranging from 5 cm to 5 m. We made hundreds of measurements of these cavities in image and laser altimeter data  and found more than 100 boulders that exhibit at least one on their surface.
The most likely mechanism for the creation of these cavities is impacts. We use our observations of mini-craters on Bennu’s boulders and strength scaling models to derive the disruption threshold of monolithic C-complex objects. We subsequently use counting statistics of craters on meter-scale boulders to estimate Bennu’s residence time in near-Earth space.
Acknowledgements This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. P.M. acknowledges support from the Centre National d’Études Spatiales and from the Academies of Excellence on Complex Systems and Space, Environment, Risk and Resilience of the Initiative d’EXcellence “Joint, Excellent, and Dynamic Initiative” (IDEX JEDI) of the Université Côte d’Azur. We are grateful to the entire OSIRIS-REx team for making the encounters with Bennu possible.
Lauretta et al. (2017) Space Science Reviews, 212, 925.
Rizk, B. et al. (2018) Space Science Reviews, 214, 26.
Golish, D.R. et al. (2020) Space Science Reviews, 216, 12.
Daly, M. G., et al. (2020) Science Advances, In Review.