Mars Science Laboratory Dynamic Albedo of Neutrons passive mode data and results from sols 753 to 1292: Pahrump Hills to Naukluft Plateau

Abstract

The Dynamic Albedo of Neutrons instrument (DAN) onboard the Mars Science Laboratory (MSL) uses 3He proportional counters to detect neutrons escaping the martian surface. This neutron leakage flux can be used to estimate the amount of hydrogen in the shallow martian regolith. During sols 753 through 1292 of the MSL mission, the rover traversed from Pahrump Hills to the Naukluft Plateau and acquired slightly less than 2000 h of neutron count rate data covering ~3 km of traverse and 125 waypoints along that traverse. Here we present an analysis of these data, including new procedures to leverage the oversampling of the instrument within its own spatial footprint, water equivalent hydrogen (WEH) estimates, and DAN passive geochemical index (DPGI) values. The average water equivalent hydrogen estimate for this region of the traverse is 1.6 wt% with a standard deviation of 1.1 wt%. These results show that Curiosity transitioned into a relatively lower WEH-content region as it left the plains of Gale crater and began ascending the hills at the base of Mt. Sharp. We also show that the WEH populations of the geologic units investigated during this time (Murray and Stimson Formations) are statistically different both from each other and the previously studied Aeolis Palus sediments (Smooth Hummocky, Bedded Fractured, Eolian, Rugged, and Striated Light-toned). Additionally, DAN passive WEH estimates agree with measurements from other MSL instruments in this region and are consistent with decreasing phyllosilicate abundance with increasing elevation.