New evidence for surface water ice in small-scale cold traps and in three large craters at the north polar region of Mercury from the Mercury Laser Altimeter.

The Mercury Laser Altimeter (MLA) measured surface reflectance, r _s, at 1064 nm. On Mercury, most water-ice deposits have anomalously low r _s values indicative of an insulating layer beneath which ice is buried. Previous detections of surface water ice (without an insulating layer) were limited to seven possible craters. Here we map r _s in three additional permanently shadowed craters that host radar-bright deposits. Each crater has a mean r _s value >0.3, suggesting that water ice is exposed at the surface without an overlying insulating layer. We also identify small-scale cold traps (<5 km in diameter) where r _s >0.3 and permanent shadows have biannual maximum surface temperatures <100 K. We suggest that a substantial amount of Mercury's water ice is not confined to large craters but exists within microcold traps, within rough patches and intercrater terrain. [ABSTRACT FROM AUTHOR]