One of the major recent successes in the field of planetary radar astronomy was the discovery and mapping of deposits of volatiles on the shadowed floors of impact craters at the poles of Mercury. Because of the similarity of their radar scattering properties to those of icy surfaces in the solar system, the deposits are thought to be water ice. The figure shows the most recent Arecibo 12.6 cm wavelength radar image of the north polar region of Mercury made at a resolution of 1.5 km by J. Harmon (NAIC), P.Perrilat (NAIC) and M. Slade (JPL). It was published in the January, 2001 issue of Icarus. The donut shape of the deposits close to the pole are due to the presence of central peaks in the craters while the bright arcs away from the poles coincide with the shadowed areas for these craters. A detection of the "ice" at the north pole was also obtained with the Arecibo 70 cm wavelength radar indicating that the deposits may be at least several meters thick.ˆà

Arecibo S-band radar image of the north polar region of Mercury by J. Harmon, P. Perrilat, and M. Slade. The resolution is 1.5 km and the image measures 450 km on a side. The bright features are thought to be ice deposits on permanently shadowed crater floors.ˆà