Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface

K. Walsh , E. Jawin , R.-L. Ballouz , Olivier Barnouin , E. Bierhaus , H. Connolly , J. Molaro , T. Mccoy , M. Delbo’ , C. Hartzell , M. Pajola (1) , S. Schwartz (2) , D. Trang , E. Asphaug (3) , K. Becker , C. Beddingfield , C. Bennett , W. Bottke , K. Burke , B. Clark , M. Daly (4) , D. Dellagiustina , J. P. Dworkin (5) , C. Elder , D. Golish , A. Hildebrand , R. Malhotra (6) , J. Marshall (7) , P. Michel , M. Nolan (8) , M. Perry , B. Rizk (9) , A. Ryan , S. Sandford , D. Scheeres , H. Susorney , F. Thuillet , D. Lauretta , Marc Bernacki (10) , Daniel Pino Muñoz (10)

1 CISAS - Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo”
2 ISTerre - Institut des Sciences de la Terre
3 SESE - ASU School of Earth and Space Exploration
4 IHU-LIRYC
5 GSFC - NASA Goddard Space Flight Center
6 National Dairy Research Institute
7 SETI Institute
8 Institute of Northern Engineering
9 LPL - Lunar and Planetary Laboratory [Tucson]
10 CEMEF - Centre de Mise en Forme des Matériaux

Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennu’s expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.

Mots clés: Geomorphology; Asteroids comets and Kuiper belt; Early solar system

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

K. Walsh, E. Jawin, R.-L. Ballouz, Olivier Barnouin, E. Bierhaus, et al.. Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface. Nature Geoscience, 2019, ⟨10.1038/s41561-019-0326-6⟩. ⟨hal-02381710⟩