Presentation #207.06 in the session “Radar Observations: Zapping them before they Zap Us!”.
Near-Earth asteroid 2100 Ra-Shalom has been the subject of extensive study for numerous years, but its physical nature is still poorly understood. We are using the shape-based thermophysical model SHERMAN to investigate the thermal properties of Ra-Shalom’s surface. The model is constrained by spectra obtained in August 2019-September 2019 at NASA’s Infrared Telescope Facility (IRTF). We find that a single, consistent set of thermal parameters fits four of the five nights of observations; however, on the fifth night those thermal parameters do not fit with the observations. Because the asteroid was at a different viewing orientation on that night, it is possible that Ra-Shalom has a different composition or a surface feature in the observed hemisphere. A previous study conducted by  utilized a radar-derived shape model assuming a prograde rotation, but they were unable to incorporate any lightcurves. For our thermophysical modeling, we assumed the retrograde rotation and shape model derived by  from extensive lightcurve observations, but we are using radar data taken in 2000 and 2003 from Arecibo to enhance the lightcurve shape model. The radar images indicate surface features and concavities on the shape model which may affect the thermal model calculations. We will present a comparison of the lightcurve shape model and our newly derived lightcurve+radar shape model. We will also compare the thermophysical properties inferred using the new shape model to determine if a single set of homogeneous thermal properties can fit the observed spectra of Ra-Shalom. References:  Shepard M.K., et al. 2008. Icarus, 193(1).  Ďurech, J., et al. 2018. Astronomy and Astrophysics, 609.