Bistatic Radar Observations of Near-Earth Asteroid (163899) 2003 SD220 from the Southern Hemisphere

TL;DR

This study presents radar observations of near-Earth asteroid 2003 SD220, revealing its elongated shape, rotation, and surface properties through Doppler radar data collected during its close approach.

Contribution

First radar observations of asteroid 2003 SD220 from the Southern Hemisphere, providing detailed shape, rotation, and surface property analysis.

Findings

Asteroid has an elongated, asymmetric shape with a large concavity.

Radar cross sections ranged from 0.25 to 0.39 km² over three days.

Rotation causes observed variations in limb-to-limb bandwidth.

Abstract

We report results of Canberra-ATCA Doppler-only continuous wave (CW) radar observations of near-Earth asteroid (163899) 2003 SD220 at a receiving frequency of 7159 MHz (4.19 cm) on 2018 December 20, 21, and 22 during its close approach within 0.019 au (7.4 lunar distances). Echo power spectra provide evidence that the shape is significantly elongated, asymmetric, and has at least one relatively large concavity. An average spectrum per track yields an OC (opposite sense of circular polarisation) radar cross section of 0.39, 0.27, and 0.25 km$^{2}$, respectively, with an uncertainty of 35 \%. Variations by roughly a factor of two in the limb-to-limb bandwidth over the three days indicate rotation of an elongated object. We obtain a circular polarization ratio of 0.21 $\pm$ 0.07 that is consistent with, but somewhat lower than, the average among other S-class near-Earth asteroids observed by radar.