HR: 10:20h
AN: P42A-01    [Abstracts]
TI: Origin of Impacting Objects in the Inner Solar System
AU: * Strom, R G
EM: rstrom@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AU: Malhotra, R
EM: renu@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AU: Ito, T
EM: tito@cc.nao.ac.jp
AF: National Astronomical Observatory, Osawa 2-21-1 Mitaka, Tokyo, 181-8588 Japan
AU: Yoshida, F
EM: yoshdafm@cc.nao.ac.jp
AF: National Astronomical Observatory, Osawa 2-21-1 Mitaka, Tokyo, 181-8588 Japan
AU: Kring, D A
EM: kring@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AB: The impact crater record in the inner Solar System is the result of two impacting populations with different size distributions and ages. The 'old' population, responsible for the period of Late Heavy Bombardment that ended about 3.8 Ga ago, is virtually identical in size distribution to the present main belt asteroids. In order to preserve the size distribution, the mechanism that ejected the asteroids from the main belt must have been a gravitational event. This mechanism was probably an epoch of orbital migration of the outer planets. These results support the hypothesis that the period of Late Heavy Bombardment in the inner Solar System was a cataclysm that occurred about 3.9 Ga and lasted from about 20 to 150 My. The second population, responsible for craters younger than about 3.8 Gy, matches the size distribution of near Earth asteroids. These impactors are also derived from the asteroid belt, but by a combination of chaotic gravitational resonances and non-gravitational processes (the Yarkovski Effect) that are size-dependent, yielding a different size distribution. These results imply that the Moon and inner planets were resurfaced about 3.9 Ga by the period of Late Heavy Bombardment. Consequently, the cratering record cannot be used to date surfaces older than about 3.9 Ga. Surfaces younger than about 3.8 Gy can be dated by using the impact flux of near Earth asteroids at different inner planets.
DE: 6022 Impact phenomena (5420, 8136)
DE: 6040 Origin and evolution
DE: 6205 Asteroids
SC: Planetary Sciences [P]
MN: Fall Meeting 2005