Based on analyses of recent high resolution observations of the approximately 1000 km diameter Heng-O ring structure by the Goldstone Solar System Radar, we predict that the structure is a large corona. Calibrated values of radar backscatter coefficient (&sgr;¿) indicate lateral variations of a factor of 4 in Fresnel reflectivity in the vicinity of Heng-O, as well as in other areas of the plains, at scales of tens of km. We predict that areas with very low reflectivity values, which occur in a variety of geological settings, are soil-dominated, with bulk densities as low as 1.5 g/cm3. ¿ American Geophysical Union 1990