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J.S. Stuart (MIT)
Three years of search data from the Lincoln Near-Earth Asteroid Research (LINEAR) project allow us to estimate the size and shape of the near-Earth asteroid population. To calibrate the limiting magnitude of the LINEAR search, we restrict ourselves to nights with stable weather. We are left with 375,000 square degrees of sky coverage and over 1300 NEA detections. A simulation of discovery circumstances for the range of absolute magnitude and orbital parameters of the detected asteroids is used to determine the detection probabilities. From these detection probabilities, the biases of the survey are estimated, allowing us to calculate the total population from that which is observed. We previously presented (DPS2000) a population estimate that used an assumption for the shape of the population over the semi-major axis and eccentricity dimensions. In this work we remove that assumption and derive estimates over absolute magnitude (H), semi-major axis, eccentricity, and inclination. As in the previously presented work, we find that the NEAs are more highly inclined than the currently known population and more highly inclined than other estimates. The number of NEAs with H<18 is found to be in the range 1150 to 1400.
We also investigate the requirements for a search system to complete the Spaceguard goal of discovering 90% of the 1 km NEAs by 2008, assuming that the real population is similar to the model derived here. Since the albedo distribution of the NEAs is currently unknown, we cannot fully evaluate progress toward the Spaceguard goal. However, if we assume that H=18 corresponds to a diameter of 1 km, then a single telescope similar to LINEAR requires 40 years to reach 90% completeness. If the albedo distribution of the asteroids is such that 1 km corresponds to H=17.5, then 30 years are required. The opposite case of low average albedo, setting the 1 km target at H=18.5, requires 60 years. A coordinated collection of telescopes capable of searching the entire available sky each lunation to limiting magnitude V ~ 20.5 is necessary to complete the Spaceguard goal in 10 years from system inception, assuming that H=18 corresponds to 1 km.
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 Air Force. The author obtains financial support from the Lincoln Scholars Program at MIT Lincoln Laboratory.