Water and Chlorine in the Martian Subsurface Along the 27 km Traverse of NASA's Curiosity Rover According to DAN Measurements: 2. Results for Distinct Geological Regions

This paper is Part II of a double-paper series that presents the abundance of water and chlorine along with other neutron-absorbing elements in the shallow subsurface of Gale crater based on measurements by the Dynamic Albedo of Neutron (DAN) instrument onboard NASA's Curiosity rover. Initial results were represented as pixels on map data products from both DAN active and passive measurements made along the 27-km traverse of the rover, corresponding to the mission period from landing on the martian surface in August 2012 through December 2021. In Part II, the contents of water and chlorine along with other neutron absorbers are studied separately for distinct geological regions along the traverse. Mean values and sample variances of these values are presented for each region. Water-equivalent hydrogen (WEH) measurements show variability within the Jura member of the Murray formation and increase within the Carolyn Shoemaker formation. A large fraction of stratigraphic units (e.g., Bradbury, Sheepbed, Pahrump Hills and others) have mean WEH values between 2 and 3 wt.%, while units in the second part of the traverse (Jura, Knockfarrill Hill, Glasgow, Pontours) have mean values of WEH above 3 wt.%. The mean absorption-equivalent chlorine value has no large variations for all tested geologic units; it is equal to around 1% for all of them. The Dynamic Albedo of Neutrons instrument installed on NASA's Curiosity rover provides measurements of hydrogen (as an indicator of water) and other neutron-absorbing elements (primarily chlorine) in the shallow subsurface of Gale crater on Mars. The initial data set for this study consists of pixel data products obtained from the instrument measurements taken over the rover's traverse of 27 km from August 2012 to December 2021. The data has been analyzed for distinct geological members defined by the Mars Science Laboratory team, allowing independent examination of various geological locations. The Jura, Knockfarrill Hill, and Pontours members exhibit mean water estimation values above 3 wt.%, while the majority of stratigraphic units, such as Bradbury and Sheepbed, have mean water values ranging between 2 and 3 wt.%. Measurements of water reveal differentiation in the Jura member of the Murray formation. The highest water values, reaching up to 4 wt.%, are observed in locations of the Carolyn Shoemaker formation. For other neutron-absorbing elements, the mean value is roughly 1 wt.% for all geological units tested and does not vary significantly. The Dynamic Albedo of Neutron (DAN) data was analyzed for the period of time from August 2012 to December 2021, for almost 27 km of the MSL traverse 15 distinct MSL geological regions were examined using the DAN data The DAN data recognized the presence of two subregions within the Jura member of the Murray formation based on Water-equivalent hydrogen concentration