Resent radar observations of asteroid 1566 Icarus

We report Doppler-only radar observations of Icarus at Goldstone at a trans mitter frequency of 8510 MHz (3.5 cm wavelength) during 8-10 June 1996, the first radar detection of the object since 1968. Optimally filtered and fol ded spectra achieve a maximum opposite-circular (OC) polarization signal-to -noise ratio of about 10 and help to constrain Icarus' physical properties. We obtain an OC radar cross section of 0.05 km(2) (with a 35% uncertainty) , which is less than values estimated by Goldstein (1969) and by Pettengill et al. (1969), and a circular polarization (SC/OC) ratio of 0.5+/-0.2. We analyze the echo power spectrum with a model incorporating the echo bandwid th B and a spectral shape parameter it, yielding a coupled constraint betwe en B and n. We adopt 25 Hz as the lower bound on B, which gives a lower bou nd on the maximum pole-on breadth of about 0.6 km and upper bounds on the r adar and optical albedos that are consistent with Icarus' tentative QS clas sification. The observed circular polarization ratio indicates a very rough near-surface at spatial scales of the order of the radar wavelength. (C) 1 999 Elsevier Science Ltd. All rights reserved.