Physical Characterization of 2015 JD₁: A Possibly Inhomogeneous Near-Earth Asteroid

The surfaces of airless bodies such as asteroids are exposed to many phenomena that can alter their physical properties. Bennu, the target of the OSIRIS-REx mission, has demonstrated how complex the surface of a small body can be. In 2019 November, the potentially hazardous asteroid 2015 JD₁ experienced a close approach of 0.033 1 au from the Earth. We present results of the physical characterization of 2015 JD₁ based on ground-based radar, spectroscopy, and photometric observations acquired during 2019 November. Radar polarimetry measurements from the Arecibo Observatory indicate a morphologically complex surface. The delay-Doppler images reveal a contact binary asteroid with an estimated visible extent of ∼150 m. Our observations suggest that 2015 JD₁ is an E-type asteroid with a surface composition similar to aubrites, a class of differentiated enstatite meteorites. The dynamical properties of 2015 JD₁ suggest that it came from the ν₆ resonance with Jupiter, and spectral comparison with major E-type bodies suggests that it may have been derived from a parental body similar to the progenitor of the E-type (64) Angelina. Significantly, we find rotational spectral variation across the surface of 2015 JD₁ from the red to blue spectral slope. Our compositional analysis suggests that the spectral slope variation could be due to the lack of iron and sulfides in one area of the surface of 2015 JD₁ and/or differences in grain sizes.