Spitzer Albedos of Near-Earth Objects

Abstract

Thermal infrared observations are the most effective way to measure asteroid diameter and albedo for a large number of near-Earth objects (NEOs). Major surveys like NEOWISE, NEOSurvey, ExploreNEOs, and NEOLegacy find a small fraction of high albedo objects that do not have clear analogs in the current meteorite population. About 8% of Spitzer-observed NEOs have nominal albedo solutions greater than 0.5. This may be a result of light-curve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. For a sample of 23 high-albedo NEOs we do not find that their shapes are significantly different from the McNeill et al. NEO shape distribution. We performed a Monte Carlo analysis on 1505 NEOs observed by Spitzer, sampling the visible and thermal fluxes of all targets to determine the likelihood of obtaining a high albedo erroneously. Implementing the McNeill shape distribution for NEOs, we provide an upper limit on the geometric albedo of 0.5 ± 0.1 for the near-Earth population.