Thermal and Optical Characterization of Near-Earth Objects: Science Commissioning of the Recently Upgraded Mid-Infrared Camera MIRSI on the NASA Infrared Telescope Facility

Abstract: Mid-infrared (mid-IR) observations of Near-Earth Objects (NEOs) have historically been a valuable tool for understanding their physical properties. However, the current state of mid-IR instruments on ground-based telescopes places several limitations on performing thermal characterization of NEOs. The complexity of maintaining these instruments in operational conditions on telescopes has led to their decommissioning. Here, we present the first science commissioning observations out to 12.5 microns from the upgraded Mid-Infrared Spectrograph and Imager (MIRSI) at the NASA-IRTF. We obtained 42 observations of 31 NEOs and derived their diameters and albedos. Since MIRSI allows simultaneous optical observations with its MIRSI Optical Camera (MOC), we were able to determine the absolute magnitude for most of the targets at the time of the thermal acquisition. We present ejecta characterization for the Didymos system from observations made 11 hours and 9 days after the Double Asteroid Redirection Test (DART) impact. We present albedo and size measurements for (98943) Torifune 2001 CC21, the fly-by target of the Japanese Extended Hayabusa2 Mission. We also highlight several applications that the MIRSI system will provide for future airless body characterization, such as constraining thermal inertia from simultaneous optical and thermal lightcurves. This work also demonstrates the importance of having MIRSI as an available rapid-response instrument for planetary defense purposes.