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Rotational breakup as the origin of small binary asteroids.
Kevin J Walsh1, Derek C Richardson, Patrick Michel
1UMR 6202 Cassiopée, University of Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France. kwalsh@oca.eu
Nature
|July 11, 2008
Summary
The thermal YORP effect can explain how small asteroids develop satellites. This mechanism causes rubble pile asteroids to spin up, shedding mass that forms a close-orbiting secondary body.
Area of Science:
- Planetary Science
- Astronomy
- Astrophysics
Background:
- Asteroids with satellites are observed across the Solar System, from near-Earth asteroid pairs to Kuiper Belt objects.
- Small asteroid binaries, common in near-Earth and inner main-belt populations, feature rapidly rotating primaries and close, circular secondary orbits.
- Approximately 15% of asteroids smaller than 10 km in diameter possess satellites, yet the formation mechanism for these binaries remained unclear.
Purpose of the Study:
- To investigate the formation mechanism of small asteroid binaries.
- To explain the common characteristics of asteroid binaries in different dynamic populations.
Main Methods:
- Modeling the spin-up of 'rubble pile' asteroids using the thermal YORP effect.
- Analyzing mass shedding from critically spinning bodies and satellite accretion conditions.
- Comparing model-generated binary properties with observed asteroid systems.
Main Results:
- The thermal YORP effect provides a unified mechanism for forming asteroid binaries in both near-Earth and main-belt populations.
- Mass shed from a slowly spinning, elongated primary asteroid accretes into a satellite under specific conditions.
- The model successfully reproduces the observed properties of small asteroid binaries, including their orbital characteristics and the example of 1999 KW(4).
Conclusions:
- The thermal YORP effect is the primary mechanism responsible for creating small asteroid binaries.
- This mechanism explains the prevalence and characteristics of satellites around small asteroids.
- The findings reconcile observations of asteroid binaries in distinct dynamical environments.
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