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

Abstract

The Mercury Laser Altimeter (MLA) measured surface reflectance, rs, at 1064 nm. On Mercury, most water‐ice deposits have anomalously low rs 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 rs in three additional permanently shadowed craters that host radar‐bright deposits. Each crater has a mean rs 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 rs >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.

Direct evidence of surface exposed water ice in the lunar polar regions

“…As a consequence, surface temperatures in these regions are extremely low (i.e., less than 110 K) ( 1 – 3 ) and are limited only by heat flow from the interior and sunlight reflected from adjacent topography ( 4 – 6 ). These areas are predicted to act as cold traps that are capable of accumulating volatile compounds over time, supported by observations of water ice at the optical surface of polar shadowed locations on Mercury ( 7 – 9 ) and Ceres ( 10 , 11 ). There are a number of strong indications of the presence of water ice in similar cold traps at the lunar poles ( 12 – 14 ), but none are unambiguously diagnostic of surface-exposed water ice, and inferred locations of water ice from different methods are not always correlated.…”

Examining the Potential Contribution of the Hokusai Impact to Water Ice on Mercury

“…Estimates of Mercury's water‐ice inventory range from ~10 16 to 10 18 g (Deutsch et al, ; Eke et al, ; Lawrence et al, ; Moses et al, ; Susorney et al, ). Recent studies have suggested that additional water‐ice reserves may exist in small‐scale cold traps distributed across rough, intercrater terrain in the polar regions (Deutsch et al, ; Neumann et al, ; Rubanenko et al, ).…”

The Chaotic Terrains of Mercury Reveal a History of Planetary Volatile Retention and Loss in the Innermost Solar System

“…The measured global high abundances of S 1 , Cl 2 , and K 5 reveal a significant surface record of volatile-bearing materials. Also, local polar H 2 O ice form deposits within numerous permanently shadowed crater interiors in the planet's polar regions [8][9][10] . Currently documented evidence of surface modifications due to the removal of volatiles includes Mercury's hollows, which are shallow, flat-floored, irregular, rimless depressions with bright interiors, and halos [11][12][13][14] .…”