Physical properties of near-Earth asteroids manually recovered from NEOWISE data

The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft was reactivated in December 2013 and since then has been conducting an all-sky survey at 3.4 and 4.6 microns to discover and characterize asteroids and comets that come close to the Earth.  NEOWISE employs an automated pipeline for the detection of moving objects, recording their astrometry and photometry and reporting positions to the Minor Planet Center for archiving.  However, there are a subset of near-Earth objects that are not found by the automated system due to rates of motion or acceleration outside the pipeline limits, an insufficient number of detections, or confusion with background sources.  Because NEOWISE archives every full-frame image obtained during the survey, detections of these objects can be recovered by manually searching the expected positions for coincident sources.

We have performed searches for near-Earth objects in the NEOWISE archives from 2013 to 2019, recovering detections for over 400 objects and enabling fitting of their diameters and albedos (Masiero et al. 2018, Masiero et al. 2020).  This builds on earlier work that searched the data from the cryogenic phase of the original WISE mission (Mainzer et al. 2014).  Objects found through this technique tend to be smaller than those detected by the automated processing. The distribution of albedos for these objects is skewed to high reflectivities, as is expected for a population that is optically-selected.

Here we present the results of our searches along with the physical properties of the recovered objects.  We also will discuss the reasons these objects were missed by the automated processing, and what the observed physical property distribution implies about any remaining objects still waiting to be found in the data.