SPACEWATCH Astrometry of Near-Earth Asteroids for Planetary Defense

Abstract The SPACEWATCH ® project at the University of Arizona makes astrometric and photometric observations of asteroids and comets to improve orbital knowledge for the purpose of planetary defense. We are ready to follow up asteroids detected by the upcoming Legacy Survey in Space and Time (LSST) and the Near-Earth Object Surveyor Mission (NEOSM). SPACEWATCH ® ’s highest priority targets are asteroids categorized as Virtual Impactors (VIs), recently discovered Near-Earth Objects (NEOs), the subset of Potentially Hazardous Asteroids (PHAs) capable of making close approaches to Earth in the next few decades, NEO candidates for detecting the Yarkovsky Effect, and asteroids of otherwise declared scientific interest. SPACEWATCH ® leads the USA’s NEO community in astrometric observations of the following priority objects while they are fainter than a V magnitude of 22.5: VIs while distant, asteroids being studied for the Yarkovsky effect, PHAs that will make close approaches to Earth, NEAs measured in the infrared by the WISE/NEOWISE spacecraft mission, and small NEOs that will make close approaches to Earth. By detecting such moving objects while they are faint (and therefore distant), we can increase the accuracy of the orbital elements more. On the dates of the observations, eighty percent of SPACEWATCH ® ’s NEO observations were not duplicated by other surveys. In addition to astrometry, SPACEWATCH ® collects high signal-to-noise photometry of NEOs to create lightcurves and provide rotation periods and rough shape information through their amplitudes of modulation. SPACEWATCH ® ’s target selections for lightcurve observations are set by the needs of radar observers and by the above priorities.