Hydration of a Clay-Rich Unit on Mars, Comparison of Orbital Data to Rover Data

Glen Torridon (GT) is a geomorphic feature of Aeolis Mons (informally Mt. Sharp) in Gale crater, Mars, variably covered by local regolith and wind-blown basaltic sands. The Mars Reconnaissance Orbiter's Compact Imaging Spectrometer for Mars (CRISM) detected clay minerals in GT, making GT a target of investigation by the Mars Science Laboratory (MSL) rover, Curiosity, which confirmed a large abundance of clays. The MSL Dynamic Albedo of Neutrons (DAN) instrument observed enrichments in bulk subsurface (<50 cm) hydration along the rover traverse compared to lower stratigraphic sections of Mt. Sharp. Here, we investigate the relationship between the CRISM 3 µm hydration index and DAN results, taking into consideration the different spatial scales and effective depths of these two instruments. We show that the elevated hydration observed by CRISM in one area of GT corresponds to elevated DAN-derived hydration, while the lower CRISM hydration in another area of GT does not correspond to a significantly lower DAN-derived hydration. We find that CRISM measured lower hydration in areas with good bedrock exposure or sand cover, while DAN bulk hydration is relatively insensitive to these characteristics. DAN active neutron results also show that the stratigraphically higher section of GT has significantly higher neutron absorption, which could be due to Fe- and Mn-rich diagenetic features. Additionally, DAN results show that GT is enriched in hydrogen with respect to other, less clay-rich units observed throughout the traverse, suggesting that subsurface clay minerals could be a significant reservoir for the hydration measured by DAN in GT.