Statistics – Computation
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29s.446b&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 446
Statistics
Computation
Asteroids, Collision Parameters, Ejecta, Hypervelocity Impact, Probability Distribution Functions, Radiation Belts, Computational Astrophysics, Earth Orbital Environments, Monte Carlo Method
Scientific paper
Recent discoveries of small Earth-approaching asteroids by the 0.9-m Spacewatch telescope (referred to here as S-SEAs) reveal more bodies with diameter D less than 50 m than had previously been inferred from the distribution of larger bodies (D greater than 100 m). Assuming that the S-SEA observations represent a steady-state excess of small bodies in that orbital space, candidate sources are impact ejecta from one (or more) terrestrial planets, collisional fragments from the main belt, or collisional break-up of a larger Earth-crossing asteroid. To determine the most viable provenance region for the S-SEAs, we track test bodies as they dynamically and collisionally evolve from each possible source. We then compare their most probable evolutionary paths with the dynamical constraints given by observations. We use the Monte Carlo dynamical evolution code of Melosh and Tonks, modified to include an impact disruption model based on a map (in orbital a, e, i space) of collision probabilities and mean impact velocities found using actual main-belt and near-Earth asteroid orbits. These results show that bodies with high eccentricities disrupt more frequently than bodies with low eccentricities, due to high-impact velocities and the large amount of time spent near aphelion among main belt projectiles. Our results show that main-belt objects exiting the 3:1 and dot-nu6 resonances when they become Earth crossing are unlikely to become S-SEAs. Furthermore, though frequent impacts with the main belt would produce fresh collisional debris, there is no reason for the process to create the clear excess of small bodies seen as S-SEAs. However, planetary ejecta from either the Earth-Moon system or Venus could produce a small-body excess spanning the current S-SEA orbits within about 10 m.y. after ejection. Ejecta from these regions is collisionally decoupled from the main belt, allowing it to survive and maintain its steep size-frequency distribution.
Bottke William F. Jr.
Greenberg Richard
Melosh Henry Jay
Nolan Michael C.
Vickery Ann M.
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