Direct $N$-body simulations of satellite formation around small asteroids: insights from DART's encounter with the Didymos system

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 $\sim 2-3\%$ 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 co-orbital satellites and satellites in mean motion resonances.

41 pages, 23 figures, accepted to PSJ, movies available at https://zenodo.org/doi/10.5281/zenodo.8387043

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Cited by in corpus (7)

• The Dynamical State of the Didymos System Before and After the DART Impact
• The Yarkovsky effect on the long-term evolution of binary asteroids
• Rapid formation of binary asteroid systems post rotational failure: a recipe for making atypically shaped satellites
• High-Speed Boulders and the Debris Field in DART Ejecta
• The binary Yarkovsky effect on the primary asteroid with applications to singly synchronous binary asteroids
• Considering contact forces during the formation of planetesimals by gravitational collapse: mutual orbits, spin states, and shapes
• Secondary impact debris in the Didymos system: what could be observed by Hera?