Understanding the distribution of near-Earth asteroids

We have deduced the orbital and size distributions of the near-Earth astero ids (NEAs) by (i) numerically integrating NEAs from their source regions to their observed orbits, (ii) estimating the observational biases and size d istribution associated with asteroids on those orbits, and (iii) creating a model population that can be fit to the known NEAs. We predict that there are similar to 900 NEAs with absolute magnitude Less than 18 (that is, kilo meter-sized), of which 29, 65, and 6% reside on Amor, Apollo, and Aten orbi ts, respectively. These results suggest that roughly 40% of the kilometer-s ized NEAs have been found. The remainder, on highly eccentric and inclined orbits, are more difficult to detect.