The shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennu’s shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, north–south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting.
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Most of the image and digital terrain analyses shown were undertaken with the JHUAPL Small Body Mapping Tool (SBMT). It is available for the analysis of a broad suite of asteroid and comet data at sbmt.jhuapl.edu. On release of the OSIRIS-REx data by the PDS, a version of SBMT with those data will be made publicly available. The spherical harmonic assessment was performed using the Spherical Harmonic Transform Library hosted at Mathworks (https://www.mathworks.com/matlabcentral/fileexchange/43856-real-complex-spherical-harmonic-transform-gaunt-coefficients-and-rotations). The SPC code used to develop the GDTM of Bennu can be made available with special permission. Please contact the corresponding author for additional information on how.
Raw through to calibrated data sets 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, the GDTM) discussed here will be available in the PDS one year after departure from the asteroid.
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This material is based on work supported by NASA under contract NNM10AA11C issued through the New Frontiers Program. The Canadian team members were supported by the Canadian Space Agency. P.M. acknowledges funding support from the French space agency CNES and from Academies of Excellence: Complex systems and Space, environment, risk, and resilience, part of the IDEX JEDI of the Université Côte d’Azur.
The authors declare no competing interests.
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Barnouin, O.S., Daly, M.G., Palmer, E.E. et al. Shape of (101955) Bennu indicative of a rubble pile with internal stiffness. Nat. Geosci. 12, 247–252 (2019). https://doi.org/10.1038/s41561-019-0330-x
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