Collisional formation of top-shaped asteroids and implications for the origins of Ryugu and Bennu

P Michel; R-L Ballouz; O S Barnouin; M Jutzi; K J Walsh; B H May; C Manzoni; D C Richardson; S R Schwartz; S Sugita; S Watanabe; H Miyamoto; M Hirabayashi; W F Bottke; H C Connolly; M Yoshikawa; D S Lauretta

doi:10.1038/s41467-020-16433-z

Collisional formation of top-shaped asteroids and implications for the origins of Ryugu and Bennu

Nat Commun. 2020 May 27;11(1):2655. doi: 10.1038/s41467-020-16433-z.

Authors

P Michel^#¹, R-L Ballouz^#², O S Barnouin³, M Jutzi⁴, K J Walsh⁵, B H May⁶, C Manzoni⁶, D C Richardson⁷, S R Schwartz⁸, S Sugita⁹, S Watanabe¹⁰, H Miyamoto¹¹, M Hirabayashi¹², W F Bottke⁵, H C Connolly^{8

13}, M Yoshikawa¹⁴, D S Lauretta⁸

Affiliations

¹ Universite Côte d'Azur, Observatoire de la Côte d'Azur, Centre National de la Recherche Scientifique, Laboratoire Lagrange, Nice, France. michelp@oca.eu.
² Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. rballouz@orex.lpl.arizona.edu.
³ The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
⁴ Physics Institute, University of Bern, NCCR PlanetS, Gesellsschaftsstrasse 6, 3012, Bern, Switzerland.
⁵ Southwest Research Institute, Boulder, CO, USA.
⁶ London Stereoscopic Company, London, UK.
⁷ Department of Astronomy, University of Maryland, College Park, MD, USA.
⁸ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
⁹ Department of Earth and Planetary Science, School of Science, The University of Tokyo, Tokyo, Japan.
¹⁰ Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan.
¹¹ Department of System Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan.
¹² Department of Aerospace Engineering, Auburn University, Auburn, AL, USA.
¹³ Department of Geology, School of Earth and Environment, Rowan University, Glassboro, NJ, USA.
¹⁴ Institute of Space and Astronautical Sciences, JAXA, Sagamihara, Japan.

^# Contributed equally.

Abstract

Asteroid shapes and hydration levels can serve as tracers of their history and origin. For instance, the asteroids (162173) Ryugu and (101955) Bennu have an oblate spheroidal shape with a pronounced equator, but contain different surface hydration levels. Here we show, through numerical simulations of large asteroid disruptions, that oblate spheroids, some of which have a pronounced equator defining a spinning top shape, can form directly through gravitational reaccumulation. We further show that rubble piles formed in a single disruption can have similar porosities but variable degrees of hydration. The direct formation of top shapes from single disruption alone can explain the relatively old crater-retention ages of the equatorial features of Ryugu and Bennu. Two separate parent-body disruptions are not necessarily required to explain their different hydration levels.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't