Arecibo Planetary Radar Observations of Near-Earth Asteroids: 2017 December–2019 December

Abstract We successfully observed 191 near-Earth asteroids using the Arecibo Observatory’s S-band planetary radar system from 2017 December through 2019 December. present cross sections for 167 asteroids; circular-polarization ratios 112 based on Doppler-echo-power spectra measurements; and albedos, constraints size spin periods, surface-feature shape evaluation 37 selected delay-Doppler images with a range resolution of 75 m or finer. Out 33 an estimated effective diameter at least 200 sufficient image quality to give clues shape, 4 (?12%) are binary asteroids, including 1 equal-mass asteroid, YE5, 10 (?30%) contact-binary asteroids. For 5 out reliable measurements in both circular polarizations, we measured greater than 1.0, which could indicate that they E-type while mean ? standard deviation were 0.37 ± 0.23. Further, find opposite-sense albedo 0.21 0.11 41 (0.19 0.06 11 S-complex asteroids). identified two 2011 WN15 (505657) 2014 SR339, as possible metal-rich objects their unusually high discuss evidence water ice YE5.