Physical Properties of Near-Earth Objects

Abstract

The population of near-Earth objects (NEOs) contains asteroids, comets, and the precursor bodies for meteorites. The challenge for our unterstanding of NEOs is to reveal the proportions and relationships between these categories of solar-system small bodies and their source(s) of resupply. Even accounting for strong bias factors in the discovery and characterization of higher-albedo objects. NEOs having S-type spectra are proportionally more abundant than within the main asteroid belt as a whole. This, an inner asteroid belt origin (where S-type objects dominate) is implied for most NEOs. The identification of a cometary contribution within the NEO population remains one of a case-by-case examination of unusual objects, and the sum of evidence suggests that comets contribute at most only a few percent of the total. With decreasing size and younger surfaces (due to presumably shorter collisional lifetimes for smaller objects), NEOs show a transition in spectral properties toward resembling the most common meteorites, the ordinary chondrites. Ordinary chondritelike objects are no longer rare among the NEOs, and at least qualitatively it is becoming understandable why these objects comprise a high proportion of meteorite falls. Comparisons that can be performed between asteroidal NEOs and their main-belt counterparts suggest that the physical properties (e.g. rotation states, configurations, spectral colors, surface scattering) of NEOs may be represantative of main-belt asteroids (MBAs) at similar (but presently unobservable) sizes.