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J.S. Stuart (MIT Lincoln Laboratory)
I present a model for the bias-corrected population of near-Earth objects (NEOs). Discovery observations and physical measurements are naturally biased toward objects having the highest albedos - as generally these objects have brighter apparent magnitudes. Thus, they are more likely to be discovered and observed. The population model presented here is based on a bias correction method applied to albedo (Delbo, M. et al. 2003 submitted Icarus) and spectral (Binzel, R.P. 2003 in preparation) measurements of the NEOs.
I find that the bias-corrected, fractional abundances of the taxonomic complexes are as follows: A-0.2%; C-10%, D-17%, O-0.5%, Q-14%, R-0.1%, S-22%, U-0.4%, V-1%, X-34%. Overall, the bias-corrected mean albedo for the whole NEA population is 0.14±0.02 . Using this mean albedo, an absolute magnitude of 17.8 ±0.1 translates to an estimated diameter of 1 km. I find that there are 1090 ± 180 NEAs with diameters larger than 1 km.
Next, I determine the impact frequency, and collision energy distribution for impacts of NEAs into the Earth and Moon. Globally destructive collisions (~1021 J) of asteroids 1 km or larger strike the Earth once every 0.60 ±0.1 Myr on average. Regionally destructive collisions with impact energy greater than 4x1018 J (~200 m diameter) strike the Earth every 47,000 ±6,000 years. Collisions in the range of the Tunguska event (4-8x1016 J) occur every 2000-3000 years. The rate of formation of craters expected from the NEAs is found to be in close agreement with the observed number of craters on the Earth and on the Moon.
These results are a summary of Stuart, J.S, Observational Constraints on the Number, Albedos, Sizes, and Impact Hazards of the Near-Earth Asteroids. PhD Thesis, Massachusetts Institute of Technology, Cambridge, MA, USA. 2003.
This work was sponsored by NASA and by the Department of the Air Force under Air Force Contract F19628-00-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the United States Government.
If you would like more information about this abstract, please follow the link to http://www.mit.edu/~stuarts/StuartPhDThesis2003.pdf. 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.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.