Mini-RF S- and X-Band Bistatic Radar Observations of South Polar Craters on the Moon and their Implications for the Presence of Water Ice

Mini-RF aboard NASA's Lunar Reconnaissance Orbiter (LRO) is a hybrid dual-polarized synthetic aperture radar (SAR) and operates in concert with the Arecibo Observatory (AO) and the Goldstone deep space communications complex 34 meter antenna DSS-13 to collect S- and X-band bistatic radar data of the Moon. Bistatic radar data provide a means to probe the near subsurface for the presence of water ice, which exhibits a strong response in the form of a Coherent Backscatter Opposition Effect (CBOE). This effect has been observed in radar data for the icy surfaces of the Galilean satellites, the polar caps of Mars, polar craters on Mercury, and terrestrial ice sheets in Greenland. Here we present S- and X-band bistatic radar observations for the floors of the south-polar craters Cabeus and Amundsen and discuss their potential for harboring water ice. The first Mini-RF bistatic campaign (2012-2015) included AO S-band observations of the floor of the crater Cabeus that indicated the presence of a CBOE consistent with presence of water ice. In the current LRO extended mission, Mini-RF has acquired DSS-13 X-band observations of the floors of the craters Cabeus and Amundsen. Initial analysis of these data suggest a CBOE is not present. This would indicate that, if water ice is present in Cabeus crater floor materials, it is buried beneath 0.5 m of regolith that does not include radar-detectible deposits of water ice.