The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to the formation of binary asteroids.
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ANSYS Mechanical APDL is commercially available (https://www.ansys.com/services/training-center/structures/introduction-to-ansys-mechanical-apdl).
The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Spacecraft tracking data and ancillary files will be available via the Planetary Data System (PDS) (https://sbn.psi.edu/pds/resource/orex/). Data are delivered to the PDS according to the OSIRIS-REx Data Management Plan available in the OSIRIS-REx PDS archive. Higher-level products, for example, slope maps, will be available in the PDS one year after departure from the asteroid.
Journal peer review information: Nature Astronomy thanks Matthias Grott, David Polishook and Yang Yu for their contribution to the peer review of this work.
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This material is based upon work supported by NASA under contract NNM10AA11C issued through the New Frontiers Program. Work by M.G.D., C.L.J., M.M.A.A. and H.C.M.S. was supported by the Canadian Space Agency. A portion of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. P.M. acknowledges funding support from the French space agency CNES and from the Academies of Excellence: ‘Complex systems’ and ‘Space, environment, risk, and resilience’, part of the IDEX JEDI of the Université Côte d’Azur. B.R. acknowledges support from the Royal Astronomical Society in the form of a research fellowship. P.T. acknowledges support from NASA’s OSIRIS-REx Participating Scientist Program through grant 80NSSC18K0280. M.H. acknowledges support from the Department of Aerospace Engineering at Auburn University.
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The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations
Nature Communications (2019)
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Nature Astronomy (2019)