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Nat Geosci. 2019 Apr;12(4):247-252. doi: 10.1038/s41561-019-0330-x. Epub 2019 Mar 19.

Shape of (101955) Bennu indicative of a rubble pile with internal stiffness.

Author information

1
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA (olivier.barnouin@jhuapl.edu).
2
The Centre for Research in Earth and Space Science, York University, Toronto, Ontario, Canada.
3
Planetary Science Institute, Tucson, AZ, USA.
4
Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, Canada.
5
Lockheed Martin Space Systems Company, Denver, CO, USA.
6
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
7
Lunar Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
8
KinetX Aerospace, Inc. Simi Valley, CA, USA.
9
Smithsonian Institution National Museum of Natural History, Washington, DC, USA.
10
Southwest Research Institute, Boulder, CO, USA.
11
Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France.
12
Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, USA.
13
University of Tokyo, Tokyo, Japan.
14
Aizu University, Aizu-Wakamatsu, Japan.
15
Kobe University, Kobe, Japan.
16
Nagoya University, Nagoya, Japan.
17
Institute of Space and Astronautical Science, JAXA, Sagamihara, Japan.

Abstract

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 leading to its current shape. Today, Bennu might follow a different evolutionary pathway, with interior stiffness permitting surface cracking and mass wasting.

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