NEW HIGH-RESOLUTION RADAR MAPPING OF THE MOON

Earth-based radar probing offers the opportunity to study the rock population and bulk dielectric properties of the lunar regolith to depths up to a few tens of meters, and to reveal portions of the polar terrain in permanent shadow from the Sun. We are currently mapping the entire near side of the Moon at a spatial resolution of 400-800 m using a 70-cm radar wavelength, and targeted regions at 20-m spatial resolution using a 12.6-cm wavelength. These observations use the Arecibo Observatory to transmit the radar signal, and the Greenbank Telescope to receive the echoes in both senses of circular polarization. Analysis of the new 70-cm radar images shows that: (1) mare basalt deposits extend west from Oceanus Procellarum beneath up to 50 m of ejecta from Orientale basin, (2) melt-rich ejecta from Orientale covers many of the permanently shadowed areas near the south pole, and (3) that virtually all craters of Imbrian or younger age have concentric deposits of rock-poor ejecta, similar to radar-dark crater “haloes” on Venus. New 12.6-cm observations reveal unprecedented detail in the permanently shadowed floors of south polar craters such as Shoemaker and Faustini.