[Previous] | [Session 6] | [Next]
L. Dones, H. F. Levison (Southwest Research Institute), K. J. Zahnle (NASA Ames Research Center)
Impact rates on the Moon and (presumably) Earth were orders of magnitude higher than they are now when the late lunar basins formed about 3900 Myr ago. Small bodies that remained in the inner solar system after the Earth and Moon formed have been suggested as possible basin-forming impactors (Wetherill 1975). As part of a study to determine whether various classes of small bodies might have produced the Late Heavy Bombardment, we have integrated the orbits of 200 test particles in the 0.7-1.3 AU region. The particles initially had circular orbits with zero inclination to the ecliptic. The integration included all the planets and was run for 100 Myr. 42% of the particles survived for 100 Myr; 23.5% hit Earth; 14% hit Venus; 14% hit the Sun; and 0.5% hit Mars. At late times the number, N, of particles that survive for time t goes as N = A - B log t, where A and B are constants (cf. Holman and Wisdom 1993, Evans and Tabachnik 1999). Using this law, we predict that about 10% of the particles would had survived to the time of the Late Heavy Bombardment, some 600 Myr after the solar system formed. Thus accretional leftovers are plausible impactors for producing the late lunar basins. However, if the Moon underwent a ''cataclysm,'' i.e., a sharp increase in the impact rate some 3900 Myr ago, some additional process, such as tidal disruption of a multi-100 km planetesimal by the Earth or Venus, would need to be invoked (Hartmann et al. 2000).
Evans, N.W., and Tabachnik, S. (1999). Possible long-lived belts in the inner solar system. Nature 399, 41-43.
Hartmann, W.K., Ryder, G., Dones, L., and Grinspoon, D. (2000). The time-dependent intense bombardment of the primordial Earth/Moon system. In Origin of the Earth and Moon (R. Canup and K. Righter, Eds.). Univ. Arizona Press and Lunar and Planetary Institute.
Holman, M.J., and Wisdom, J. (1993). Dynamical stability in the outer solar system and the delivery of short period comets. Astron. J. 105, 1987-1999.
Wetherill, G.W. (1975). Late heavy bombardment of the moon and terrestrial planets. In: Lunar Science Conference, 6th, Proceedings, Volume 2. Pergamon, New York, pp. 1539-1561.
If you would like more information about this abstract, please follow the link to http://www.boulder.swri.edu/~luke. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.
The author(s) of this abstract have provided an email address for comments about the abstract: luke@boulder.swri.edu