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T. Nakamura, H. Nakai (NAOJ, Japan), F. Yoshida (Nat'l Central Univ., Taiwan)
Since the discovery by D. Kirkwood in 1866, the orbits in the main asteroid belt with periods commensurable with that of Jupiter have been recognized as locations where no asteroids are found and thereby called "gaps". It is widely believed that asteroid gaps were formed by resonant and chaotic actions caused by the gravity of Jupiter, and they are regarded as a supply source of near-Earth asteroids (NEAs), the majority of which are sub-km-sized. Here we report that, for asteroids smaller than ~1km in diameter, the 3:1 gap (a=2.50AU) substantially does not exist and is almost filled with asteroids. Assuming that the asteroid population inside the gap is in steady state, a distribution as such was constructed from 2 x 104 yr orbital integration of about 5200 existing asteroids near the gap. From the steady-state relative number distribution of asteroids in the gap and the size distribution for km-sized asteroids outside the gap edge which was recently observed by our group, we found that the slope (~ 2.7-3.1) for the cumulative size distribution of km-sized asteroids in the gap is much steeper than that for the corresponding NEAs in size (~1.8: Bottke et al., 2002). This inconsistency and very short dynamical lifetimes (a few Myr) of gap asteroids suggest that the 3:1 resonant gap may not be such a dominant source of NEAs as previously claimed, though it will still be an important one. We found a similar gap-filling effect also in the 7:3 Kirkwood gap (a=2.96AU).
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.