The Formation of Terraces on Asteroid (101955) BennuOPEN ACCESS 

O. S. Barnouin, M. G. Daly, J. A. Seabrook, Y. Zhang, F. Thuillet, P. Michel, J. H. Roberts, R. T. Daly, M. E. Perry, H. C. M. Susorney, E. R. Jawin, R.-L. Ballouz, K. J. Walsh, M. M. Sevalia, M. M. Al Asad, C. L. Johnson, E. B. Bierhaus, R. W. Gaskell, E. E. Palmer, J. Weirich, B. Rizk, C. Y. Drouet D’Aubigny, M. C. Nolan, D. N. DellaGiustina, D. J. Scheeres, J. W. McMahon, H. C. Connolly, D. C. Richardson, C. W. V. Wolner, D. S. Lauretta

JGR Planets
First Published: 31 March 2022


“The surface of the rubble-pile asteroid (101955) Bennu has been characterized in detail by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission. By examining global and local digital terrain models, we observed that Bennu possesses terraces, that is, a series of roughly latitude-parallel, step-like slope breaks. These partially circumscribe the poles and extend east-west over several longitudinal quadrants at mid- to high (≥30°) latitudes. The terraces are subtle in amplitude, with heights ranging from 1 to 5 m. They often exhibit back-wasting that results in V-shaped scarps that open downslope in some locations. When boulders >5–10 m are absent at or near a terrace, the steeper portion (the drop) of the terrace lacks rocks, whereas the flatter portion (the bench) of the terrace has accumulations of rocks at its crest. When boulders >5–10 m are present, their steep downslope faces often make up the drop from the terrace crest, and they retain debris upslope, thereby enhancing the terrace structure. A geotechnical stability analysis indicates that Bennu’s surface is likely unstable and that surface cohesion is <0.6 Pa. Bennu’s terraces strongly resemble scarps generated in laboratory and numerical simulations of a cohesionless granular bed as the slope of the bed increases quasi-statically. We conclude that terraces are probably actively forming on Bennu as its surface slowly fails owing to creep induced by spin acceleration.”