Arecibo's bright pixels fall in permanently shadowed craters
The highest-resolution radar image of Mercury's north polar region made from the Arecibo Observatory (Harmon et al., Icarus, 211, 37-50, 2011) is shown in yellow on a mosaic of MESSENGER orbital images. Radar-bright features in the Arecibo image all lie in areas mapped as in shadow in MESSENGER images to date, consistent with the proposal that radar-bright materials contain water ice.
This image is shown in a polar stereographic projection with every 5° of latitude and 30° of longitude indicated and with 0° longitude at the bottom. On Mercury, 5° of latitude is approximately 213 km.