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W. F. Bottke, Jr. (Cornell U.), D. P. Rubincam (GSFC), J. A. Burns (Cornell U.)
The Yarkovsky effect, a radiation force produced by the anisotropic reradiation of sunlight, causes 0.1-10 m bodies to undergo semimajor axis, eccentricity, and inclination changes as a function of their spin, orbit, size, and material properties. Accordingly, it may play an important role in delivering meteoroids to main belt resonances (and hence to Earth). To check this, we formulated two variants of the Yarkovsky force: ``diurnal'' (dependent on the body's spin rate and longitudinal temperature distribution) and ``seasonal'' (dependent on the body's mean motion around the Sun and its latitudinal temperature distribution) and included them into a symplectic N-body integration routine (RMVS3). Tests of our code against known benchmarks (Rubincam 1998; Farinella et al. 1998) show excellent agreement with their semimajor axis drift rates (+/- 0.01-0.001 AU/Myr for meter-sized basaltic objects).
We have used this code to test whether the Yarkovsky effect delivers meteoroids to the 3:1 and/or v6 resonances slowly enough to explain the cosmic-ray-exposure (CRE) ages of stony and iron meteorites (~10-50 Myr and ~ 1 Gyr, respectively). Note that an object's dynamical lifetime after entering these resonance is typically 2-3 Myr. To demonstrate how the Yarkovsky effect works, we will present movies showing that stony bodies, started from a variety of locations in the inner main belt, spiral into a resonance within a few tens of Myr (consistent with CRE data). Thus, since nearly any inner main belt body can produce meteorites, we can no longer say whether large asteroids, with huge collision cross sections, or small asteroids, which lose nearly all ejecta during collisions, dominate the flux of meteoroids reaching Earth. In addition, we find that iron meteoroids, with different thermal properties, evolve slowly enough to match CRE data. Yarkovsky forces also cause some small bodies to undergo significant inclination changes, which may provide an alternate escape route.
The author(s) of this abstract have provided an email address for comments about the abstract: bottke@astrosun.tn.cornell.edu