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

Olivier Barnouin , M. Daly (1) , E. Palmer (2) , R. Gaskell (2) , J. Weirich , C. Johnson , M. Al Asad , J. Roberts (3) , M. Perry , H. Susorney , R. Daly (4) , E. Bierhaus , J. Seabrook , R. Espiritu , A. Nair , L. Nguyen (5) , G. Neumann , C. Ernst , W. Boynton , M. Nolan (6) , C. Adam , M. Moreau (7) , B. Rizk (8) , C. Drouet D’aubigny , E. Jawin , K. Walsh , P. Michel , S. Schwartz (9) , R.-L. Ballouz , E. Mazarico , D. Scheeres , J. Mcmahon , W. Bottke , S. Sugita (10) , N. Hirata , S.-I. Watanabe , K. Burke , D. Dellagiustina , C. Bennett , D. Lauretta , Marc Bernacki (11) , Daniel Pino Muñoz (11)

1 IHU-LIRYC
2 PSI - Planetary Science Institute [Tucson]
3 Centre of Ecology and Hydrology
4 inconnu
5 Axe 1 : procédés céramiques
6 Institute of Northern Engineering
7 IM2NP - Institut des Matériaux, de Microélectronique et des Nanosciences de Provence
8 LPL - Lunar and Planetary Laboratory [Tucson]
9 ISTerre - Institut des Sciences de la Terre
10 Institute of Ecology
11 CEMEF - Centre de Mise en Forme des Matériaux

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.

Mots clés: Asteroids comets and Kuiper belt; Geomorphology; Structural geology

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Sciences de l'ingénieur [physics]

Olivier Barnouin, M. Daly, E. Palmer, R. Gaskell, J. Weirich, et al.. Shape of (101955) Bennu indicative of a rubble pile with internal stiffness. Nature Geoscience, 2019, ⟨10.1038/s41561-019-0330-x⟩. ⟨hal-02381693⟩