Using Precision Astrometry to Recover Near-Earth Object Candidates

The Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) telescopes, located on Haleakala, Hawaii, spend much of their time searching the sky for Near-Earth Objects (NEOs) that may represent a hazard to Earth. The cameras on each telescope have small pixels and therefore deliver excellent astrometry. Some Near-Earth Object candidates that Pan-STARRS discovers are lost, because they are not recovered on subsequent nights. Over the course of the approximately 1 hour of observations when NEOs are initially discovered, many of the NEOs seen by Pan-STARRS display a small amount of non-linear motion (or curvature) in their path through the sky. This curvature arises due to the motion of the observer, and is a helpful diagnostic tool for establishing the approximate distance to the NEO and its size. At the present time, this curvature is not being fully used to tightly constrain the predicted position of the NEO one night later, and as a result, some NEOs are not recovered. A detailed study of the astrometric precision of Pan-STARRS was undertaken, using objects for which very precise orbits are known. The precision astrometry for NEOs from Pan-STARRS from a single night, and the curvature that it displays, was then used to better constrain the likely position of NEOs one night later. The predicted positions were compared to the real positions for these objects. For some objects, there was little change in the predicted position, but for four of the sample of eleven Near-Earth Objects evaluated, there was a major improvement in the predicted position. This technique will likely improve the discovery rate of all NEOs from Pan-STARRS, but with particular benefit to the smaller (nearby) NEOs.