Exploring the Surface of Mars with the Curiosity Rover Neutron Detector*

The Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory Curiosity rover has acquired thousands of measurements at the surface of Mars over the past six years. DAN measures thermal and epithermal neutron counts between pulses of a 14.1 MeV D-T pulsed neutron generator. The resulting neutron die-away curves can be used to interpret the bulk hydration, subsurface geology, and layering structure of the shallow subsurface of Curiosity’s landing site in Gale Crater. Analyses of DAN data have characterized the hydration and extent of high-silica materials at several locations along the rover's traverse. DAN data have also been used to characterize the bulk hydration of active sand dunes, which were determined to be some of the least hydrated features Curiosity has investigated. The hydration state of the dunes can then be used to constrain the abundance of amorphous phases within the dune sand, which is an important indicator for environmental conditions during sediment transport as well as providing information about the composition of the source material. DAN is the first neutron measurements made on the surface of another planet, and interpretations of these highly localized neutron data requires a careful approach to simulations, geochemical modeling, and geologic settings in order to test hypotheses at the site. DAN active observations across the rover traverse provide planetary scientists with a rich nuclear dataset that will help unravel the geologic history of Gale Crater. The success of the DAN instrument demonstrates the value of nuclear instrumentation in planetary science investigations.