Other
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1033r&link_type=abstract
American Astronomical Society, DPS meeting #28, #10.33; Bulletin of the American Astronomical Society, Vol. 28, p.1103
Other
Scientific paper
There is mounting evidence that most km-sized objects in the solar system are ``rubble-piles'', fragile objects composed of loose collections of smaller components all held together by self-gravity rather than tensile strength. The evidence includes: (a) the paucity of fast rotating km-sized asteroids (Harris, 1996, LPSC 27, 977); (b) the tidal disruption of Comet Shoemaker-Levy 9 (SL9) and observations of crater chains on the Moon and Galilean satellites (Schenk et al., 1996, Icarus 121, 149); (c) observations of extremely large craters on Phobos, Gaspra, and Ida; and (d) hydrocode models that realistically treat asteroid impacts (Love and Ahrens, 1996, Icarus, in press). Accordingly, we predict that Earth's tidal forces play a major role in the evolution of rubble-pile Earth-crossing objects (ECOs). By modeling close encounters between the Earth and our rubble-piles (for details, see Bottke et al., this issue), we found that Earth's tidal forces can make the progenitors undergo: (a) ``SL9-type'' disruption (formation of clumps of roughly equal size along the fragment train; this outcome may explain specific crater chains seen on the Moon); (b) mass shedding (over half of the primary remains intact; in many cases, the shed fragments go into orbit around the progenitor, producing binary asteroids, which could explain the population of doublet craters seen on the terrestrial planets (Bottke and Melosh, 1996, Nature 381, 51)); (c) reshaping accompanied by spin-up or spin-down (this mechanism could explain the large aspect ratio (2.76), unusual shape, and short rotation period (5.2 hours) of 1620 Geographos as well as the short rotation periods of many other ECOs). Mass shedding events for ECOs occur more frequently at low velocities relative to Earth than at high velocities, corresponding to low (e, i) values. Thus, Earth's tidal forces should be most effective at disrupting large ECOs (and producing small bodies) in this region. This localized disruption mechanism may explain observations by Rabinowitz et al. (1993, Nature 363, 704), who claim to see an ``excess'' number of small ECOs (D < 50 m) at low (e, i) relative to their expectation based on the number of large ECOs seen elsewhere.
Bottke William F.
Richardson Chris D.
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