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R. P. Binzel, S. J. Bus, T. H. Burbine (Dept. Earth, Atmospheric, and Planetary Sciences, MIT)
A fundamental uncertainty in clarifying the big picture relationship between asteroids and meteorites has been the relationship between the most common asteroids (S-types) and the most common meteorites (ordinary chondrites). Historically, groundbased spectroscopic measurements have shown an apparent mismatch between these asteroid and meteorite types, thus leading to doubt and confusion for asteroid-meteorite interrelationships.
A new big picture has emerged as a result of modern spectroscopic surveys which have extensively sampled main-belt and near-Earth asteroids over a continuous range of sizes down to <1 km. Principal among these has been the MIT Small Main-Belt Asteroid Spectroscopic Survey (SMASS) program that has sampled more than 1000 objects in the main-belt and several hundred in near-Earth and Mars crossing space. About 10% of the smallest asteroids surveyed (~1 km in size) appear spectrally analogous to ordinary chondrite meteorites. Most importantly for clarifying the big picture, a continuous trend is found in the spectral properties which previously separated measurements of S-type asteroids and ordinary chondrite meteorites, where this trend is found to be continuous with respect to diameter.
Our conclusion is that groundbased spectroscopic measurements have now become extensive enough to remove the confusion over the relationship between S-asteroids and ordinary chondrite meteorites. Ordinary chondrites are derived from within the S-asteroid population. Spectroscopically, ordinary chondrites are an end-member of the S-asteroid population, where the size-dependent relationship is the result of collisional processing of the surface, regolith retention, or time-dependent surface evolution. Most specifically, the continuous relationship argues against ordinary chondrite meteorites being derived from a separate sample of small solar system bodies.