Astronomy8 papers
Binary asteroids
IŽ
Ivana Milić Žitnik
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intermediate
Rotational breakup as the origin of small binary asteroids
Kevin J. Walsh et al. (2008)
- Published
- Jul 1, 2008
- Journal
- Nature · Vol. 454 · No. 7201
- DOI
- 10.1038/nature07078
At a Glance
Simulations show YORP spin-up can shed equatorial rubble that re-accretes into close, circular satellites matching small binary asteroids.
Summary
This paper identifies a single formation pathway that can explain why small binaries in both near-Earth and inner main-belt populations look so similar. Using rubble-pile simulations under gradual YORP-driven spin-up, the authors show that equatorial material is shed and, if collisions are sufficiently dissipative and the primary stays nearly axisymmetric, the debris efficiently accretes into a close satellite on a low-eccentricity orbit. The model naturally produces “top-shaped” primaries with equatorial ridges, consistent with detailed radar constraints for (66391) 1999 KW4, and predicts that secondaries are built mostly from the primary’s surface material. The work shifts small-binary origins away from impacts or repeated tidal encounters toward a slow, radiatively driven rotational-disruption cycle, with implications for surface refreshment and binary lifetimes via BYORP/tides.
Method Snapshot
Discrete-element (N-body) simulations of cohesionless rubble piles are slowly spun up to mimic YORP, tracking mass shedding and gravitational reaccumulation into satellites.
Background
Basic asteroid dynamics and radiative torques (YORP), plus familiarity with rubble-pile mechanics and orbital elements.