Evaluation of ground-based optical surveys for near-Earth asteroids

Near-Earth asteroids (NEAs) pose a long-term hazard to the Earth and its inhabitants as a result of impacts such as the Tunguska event of 1908, and especially from still larger, although even less frequent events. An evaluation is presented of the ability of ground-based telescope systems to inventory the population of NEAs, as a function of telescope parameters, NEA size and albedo, and duration of the survey. The optimum strategy for surveying appears to be to cover the entire visible sky every month, rather than covering a smaller area of sky to a fainter threshold of detection. An optimally designed and operated system consisting of two or three 1 m telescopes should be able to achieve ∼ 75% completeness of survey down to a size of 1 km diameter, in 10 years of operation. To achieve a completeness > 90% in the same time would require several telescopes of 2–3 m aperture. Achieving near-completeness down to the size of the smallest NEAs capable of causing significant ground damage (∼ 70 m diameter) on a timescale of 10 years appears impractical with present technology, however because of the long timescale of events, even present or soon-to-start surveys are likely to discover the next Earth-impacting body before it hits.