Direct N-body Simulations of Satellite Formation around Small Asteroids: Insights from DART’s Encounter with the Didymos System

Author:

Agrusa Harrison F.ORCID,Zhang YunORCID,Richardson Derek C.ORCID,Pravec PetrORCID,Ćuk MatijaORCID,Michel PatrickORCID,Ballouz Ronald-LouisORCID,Jacobson Seth A.ORCID,Scheeres Daniel J.ORCID,Walsh KevinORCID,Barnouin OlivierORCID,Daly R. TerikORCID,Palmer EricORCID,Pajola MaurizioORCID,Lucchetti Alice,Tusberti Filippo,DeMartini Joseph V.ORCID,Ferrari FabioORCID,Meyer Alex J.ORCID,Raducan Sabina D.ORCID,Sánchez PaulORCID

Abstract

Abstract We explore binary asteroid formation by spin-up and rotational disruption considering the NASA DART mission's encounter with the Didymos–Dimorphos binary, which was the first small binary visited by a spacecraft. Using a suite of N-body simulations, we follow the gravitational accumulation of a satellite from meter-sized particles following a mass-shedding event from a rapidly rotating primary. The satellite’s formation is chaotic, as it undergoes a series of collisions, mergers, and close gravitational encounters with other moonlets, leading to a wide range of outcomes in terms of the satellite's mass, shape, orbit, and rotation state. We find that a Dimorphos-like satellite can form rapidly, in a matter of days, following a realistic mass-shedding event in which only ∼2%–3% of the primary's mass is shed. Satellites can form in synchronous rotation due to their formation near the Roche limit. There is a strong preference for forming prolate (elongated) satellites, although some simulations result in oblate spheroids like Dimorphos. The distribution of simulated secondary shapes is broadly consistent with other binary systems measured through radar or lightcurves. Unless Dimorphos's shape is an outlier, and considering the observational bias against lightcurve-based determination of secondary elongations for oblate bodies, we suggest there could be a significant population of oblate secondaries. If these satellites initially form with elongated shapes, a yet-unidentified pathway is needed to explain how they become oblate. Finally, we show that this chaotic formation pathway occasionally forms asteroid pairs and stable triples, including coorbital satellites and satellites in mean-motion resonances.

Funder

National Aeronautics and Space Administration

Grant Agency of the Czech Republic

Istituto Nazionale di Astrofisica

Swiss National Science Foundation

Publisher

American Astronomical Society

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