31st Annual Meeting of the DPS, October 1999
Session 12. Near Earth Asteroids Posters
Poster Group I, Monday-Wednesday, October 11, 1999, , Kursaal Center

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[12.05] Tiny Asteroids: Three Contradictory Lines of Evidence for their Numbers

D. P. O'Brien, R. Greenberg (LPL)

A consistent theory for the collisional evolution of the asteroidal population must reconcile several lines of observational evidence. An obvious constraint on collisional evolution models [1] is the observed main-belt asteroid population. However, a successful model must also be consistent with the numbers of small, sub-meter sized bodies inferred from the cosmic ray exposure (CRE) ages of meteorites and the observed cratering records on Ida and Gaspra [2,3]. The current model that best reproduces the main belt population, by Durda et. al. [1], is not consistent with the numbers of sub-meter sized bodies implied by these constraints.

In order to address this problem, we are attempting to increase the lifetimes of meter-sized objects within the collisional model to make them more consistent with the CRE ages of meteorites. The lifetime of meter-sized bodies is controlled, in a large part, by the number of cm-scale objects capable of destroying them. The number of cm-scale meteorite-killing 'bullets' can be reduced in several ways. First, an overabundance of mm-scale objects will reduce the number of cm-scale 'bullets' and thus increase the lifetime of meter-scale objects. An overproduction of mm-sized fragments, due to the fact that they are near the grain size of stony material, has this effect. Also, assuming that cm-scale bodies are weaker than that obtained by simple extrapolation from larger bodies, i.e. flattening the strength curve at small sizes, reduces the number of cm-scale 'bullets' as well and thus increases the lifetimes of meter-sized bodies.

Our model applies these effects to increase the lifetimes of meteorite-sized bodies towards CRE values while still reproducing the size distribution of observable asteroids. Future work will involve reconciling both the CRE ages and collisional model with the asteroidal cratering records of Ida and Gaspra.

References: [1] Durda, D. D., et. al. 1998. Icarus 135; [2] Greenberg, R., et. al. 1996. Icarus 120; [3] Greenberg, R., et. al. 1994. Icarus 107.

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