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Investigating Water Ice in Persistently Shadowed Craters in Mercury's North Polar Region
Deutsch, Ariel N Heather Macdonald, Eugene Tracy
Deutsch, Ariel N
Heather Macdonald, Eugene Tracy
Abstract
Through a combination of Earth-based radar observations, available spacecraft neutron spectrometer and laser altimeter data, and thermal modeling, it has previously been suggested that the planet Mercury hosts extensive water ice deposits in its polar regions. This study concentrates on observations of the permanently shadowed craters of Mercury’s north polar region, where water ice is expected. To examine the interior of craters that host radar-bright material, images from the Wide Angle Camera (WAC) aboard the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft were processed using Integrated Software for Imagers and Spectrometers (ISIS) and stretched on a grayscale to expose reflectivity differences and surface features. This process revealed intriguing dark material within 53.2% of the individual craters studied in the region 75º N and northward, which is interpreted to be sublimation lags. The relationships between visible reflectivity material, radar-bright deposits, and regions of persistent shadow were mapped for these craters. Reflectivity-light material was revealed in the Prokofiev and Kandinsky craters (4.2%), indicating exposed water ice deposits. The remaining craters either did not reveal dark or light material (29.8%) or did not return images of high enough quality for analysis (12.8%). Additionally, the area of 84º N and northward was analyzed on a regional scale. Areas of persistent shadow were mapped and then compared to radar data to both qualify and quantify the relationship between shadowed areas and radar-bright features. In the study area, ~82% of the Harmon et al. (2011) radar-bright features aligned with the mapped areas of persistent shadow. The results of this study indicate that water ice stably resides in the persistently shadowed craters on Mercury’s north polar region and is typically insulated by a reflectivity-dark lag deposit.
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2014-05-01
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Geology