The near-earth object population: Connections to comets, main-belt asteroids, and meteorites

Near-Earth objects (NEOs) owe their origins to both the main-belt asteroids and comets. They include (by definition) precursors for all meteorite samples. Thus understanding NEO connections is central to the modern study of small bodies in our solar system and serves as the principal focus of this chapter. Herein we also briefly highlight how the proximity of near-Earth objects enables detailed study of the smallest known and most accessible natural objects in space, and we provide links to other chapters addressing these aspects more fully. The success of Japan’s Hayabusa mission sample return yields a definitive link between the most common class of near-Earth asteroids and one of the most common meteorites, a watershed whose ground truth enables a deeper level of understanding and new questions. We can now investigate the near-Earth population to pinpoint specific main-belt source regions for broad taxonomic classes and specific meteorite types in addition to estimating the extinct comet contribution. Spectral properties combined with long-term orbital modeling reveal a strong role played by planetary encounters to resurface (and likely reshape) many objects. Outstanding puzzles remain for many of the newly revealed details; their resolution will generate new insights to the basic physical processes governing small bodies.