Wet Mercury Radar observations of Mercury's poles in the 1990s revealed regions of high backscatter that were interpreted as indicative of thick deposits of water ice; however, other explanations have also been proposed (see the Perspective by Lucey ). MESSENGER neutron data reported by Lawrence et al. (p. 292 , published online 29 November) in conjunction with thermal modeling by Paige et al. (p. 300 , published online 29 November) now confirm that the primary component of radar-reflective material at Mercury's north pole is water ice. Neumann et al. (p. 296 , published online 29 November) analyzed surface reflectance measurements from the Mercury Laser Altimeter onboard MESSENGER and found that while some areas of high radar backscatter coincide with optically bright regions, consistent with water ice exposed at the surface, some radar-reflective areas correlate with optically dark regions, indicative of organic sublimation lag deposits overlying the ice. Dark areas that fall outside regions of high radio backscatter suggest that water ice was once more widespread.