Asteroid Diameters and Albedos from NEOWISE Reactivation Mission Years Six and Seven

Abstract

We present diameters and albedos computed for the near-Earth and main belt asteroids (MBAs) observed by the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft during the sixth and seventh years of its Reactivation mission. These diameters and albedos are calculated from fitting thermal models to NEOWISE observations of 199 near-Earth objects (NEOs) and 5851 MBAs detected during the sixth year of the survey and 175 NEOs and 5861 MBAs from the seventh year. Comparisons of the NEO diameters derived from Reactivation data with those derived from the WISE cryogenic mission data show a ~30% relative uncertainty. This larger uncertainty compared to data from the cryogenic mission is due to the need to assume a beaming parameter for the fits to the shorter-wavelength data that the Reactivation mission is limited to. We also present an analysis of the orbital parameters of the MBAs that have been discovered by NEOWISE during Reactivation, finding that these objects tend to be on orbits that result in their perihelia being far from the ecliptic, and thus missed by other surveys. To date, the NEOWISE Reactivation survey has provided thermal fits of 1415 unique NEOs. Including the mission phases before spacecraft hibernation increases the count of unique NEOs characterized to 1845 from WISE's launch to the present.