31st Annual Meeting of the DPS, October 1999
Session 24. Asteroids: Yarkovsky Effect and Collisions
Contributed Oral Parallel Session, Tuesday, October 12, 1999, 10:30am-12:00noon, Sala Plenaria

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[24.02] Yarkovsky Effect Plus Planetary Perturbations \Longrightarrow Tortuous Meteoroid Paths

J.A. Burns (Cornell U.), W.F. Bottke (Cornell U.), D.P. Rubincam (GSFC)

Using an RMVS N-body integrator, we track meteoroid motions, including both planetary perturbations and the Yarkovsky effect (seasonal and diurnal variants, producing orbital collapse or growth); collisions stochastically alter spin rates and directions. Considering two drift rates, we follow -- for tens of Myr -- one hundred roughly meter-sized bodies started from the positions of each of ten asteroids (e.g., Vesta, Hebe, Maria, Flora, Hestia) scattered across the inner main belt. This region contains the powerful Jovian 3:1 mean-motion resonance and the nu6 secular resonance, as well as numerous weaker three-body (Jupiter, Saturn, meteoroid) and Martian mean-motion resonances. Once modest eccentricities are achieved, orbits can pass near Mars, which significantly affects them.

The resulting dynamics can be quite complex. Depending on the speed and direction of orbital evolution and the particular resonance, particles may i) be captured, increasing e and/or i while a stays constant; or ii) jump across, kicking e, i and a, but bypassing potential ``escape hatches'' from the main belt. Chaos ensues where resonances overlap.

Following convoluted trajectories, which vary with collisional histories, most meteoroids reach Earth-crossing orbits via the 3:1 or \nu6 resonance after tens of Myr in the main belt. These timescales correspond well to the measured cosmic-ray-exposure ages of chondrites and achondrites. Meteoroid sources are, however, less clear; since Yarkovsky drift allows access to a dense forest of resonant sites, nearly any body in the main belt can add to the cumulate meteoroid flux. Ejecta from small parent bodies will dominate the meteoroid flux if the main- belt size-distribution at sub-km sizes is in collisional equilibrium, while big parent bodies dominate if observed population trends for km-sized bodies persist to smaller radii.

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