| Summary: | The Mercury Laser Altimeter (MLA) measured surface reflectance, r(sub s), at 1064 nm. On Mercury, most water-ice deposits have anomalously low r(sub 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 craters. Here we map r(sub s) in three additional permanently shadowed craters that host radar-bright deposits. Each crater has a mean r(sub s) value greater than 0.3, suggesting that water ice is exposed at the surface without an overlying insulating layer, bringing the total to ten large craters that host exposed water ice at Mercurys north pole. We also identify small-scale cold traps (less than 5 km in diameter) where r(sub s) greater than 0.3 and permanent shadows have biannual maximum surface temperatures less than 100 K. We suggest that a substantial amount of Mercury's water ice is not confined to large craters, but exists within micro-cold traps, within rough patches and inter-crater terrain.
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