Understanding the Near-Earth Object Population: the 2004 Perspective

Abstract

Over the last several decades, evidence has steadily mounted that asteroids and comets have impacted the Earth over solar system history. This population is commonly referred to as “near-Earth objects” (NEOs). By convention, NEOs have perihelion distances q ≤ 1.3AU and aphelion distances Q ≥ 0.983AU (e.g. Rabinowitz et al. 1994). Subcategories of the NEO population include the Apollos (a ≥ 1.0AU; q ≤ 1.0167AU) and Atens (a < 1.0AU; Q ≥ 0.983AU), which are on Earth-crossing orbits, and the Amors (1.0167AU < q ≤ 1.3AU) that are on nearly-Earth-crossing orbits and can become Earthcrossers over relatively short timescales. Another group of related objects that have not yet been considered part of the “formal” NEO population are the IEOs, or those objects located inside Earth’s orbit (Q < 0.983AU). To avoid confusion with standard conventions, I treat the IEOs here as a population distinct from the NEOs. The combined NEO and IEO populations are comprised of bodies ranging in size from dustsized fragments to objects tens of kilometers in diameter (Shoemaker 1983).