Radar mapping of Mercury's polar anomalies

GROUND-based radar observations of Mercury have revealed unusually strong, highly depolarized echoes from the north1,2 and south2 poles. These anomalous echoes have been cited as evidence of polar ice deposits1–5. Thermal studies3–5 suggest that the permanently shaded floors of large polar craters are cold enough to preserve water ice in a stable state over aeons, in spite of Mercury's proximity to the Sun. Here we present high-resolution radar maps of Mercury's polar regions, derived from delay-Doppler measurements. We have resolved the north and south polar anomalies into numerous crater-sized features, and we have been able to identify the source craters for many of these features after making small corrections to the pole positions on the Mariner-10 images. The coincidence with crater locations, together with other properties of the radar features, are consistent with the polar-ice hypothesis.