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.

The Mars Science Laboratory (Curiosity rover) Dynamic Albedo of Neutrons (DAN) experiment detects neutrons for the purpose of searching for hydrogen in the shallow subsurface of Mars. DAN has two modes of operation, active and passive. In passive mode, the instrument detects neutrons produced by Galactic Cosmic Ray interactions in the atmosphere and regolith and by the rover's Multi-Mission Radioisotope Thermoelectric Generator. DAN passive data from Yellowknife Bay to Amargosa Valley (sols 201 through 753) are presented and analyzed here. Water equivalent hydrogen (WEH) estimates from this portion of Curiosity's traverse range from 0.0 wt. % up to 15.3 wt. %. Typical uncertainties on these WEH estimates are 0.5 wt. % but in some cases can be as high as similar to 4.0 wt. % depending on the specific circumstances of a given measurement. Here we also present a new way of reporting results from the passive mode of the experiment, the DAN passive geochemical index (DPGI). This index is sensitive to some key geochemical variations, but it does not require assumptions about the abundances of high thermal neutron absorption cross section elements, which are needed to estimate WEH. DPGI variations in this section of the traverse indicate that the shallow regolith composition is changing on both the local ( meters) and regional (-100 s of meters) scales. This variability is thought to be representative of the diverse composition of source regions for sediments within the crater floor. Kolmogorov-Smirnov Tests on the populations of WEH estimates and DPGI values demonstrate there are statistically significant differences between nearly all of the geologic units investigated along the rover's traverse. We also present updated previous DAN passive results from Bradbury Landing to John Klein that make use of revised DAN active mode results for calibration, however, no qualitative changes in the interpretations made in Tate et al. (2015b) are incurred. (C) 2017 Elsevier Inc. All rights reserved.

The Mars Science Laboratory Dynamic Albedo of Neutrons (DAN) experiment measures the martian neutron leakage flux in order to estimate the amount of water equivalent hydrogen present in the shallow regolith. When DAN is operating in passive mode, it is sensitive to neutrons produced through the interactions of galactic cosmic rays (GCR) with the regolith and atmosphere and neutrons produced by the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). During the mission, DAN passive mode data were collected over the full diurnal cycle at the locations known as Rocknest (sols 60–100) and John Klein (sols 166–272). A weak, but unexpected, diurnal variation was observed in the neutron count rates reported at these locations. We investigate different hypotheses that could be causing these observed variations. These hypotheses are variations in subsurface temperature, atmospheric pressure, the exchange of water vapor between the atmosphere and regolith, and instrumental effects on the neutron count rates. Our investigation suggests the most likely factors contributing to the observed diurnal variations in DAN passive data are instrumental effects and time-variable preferential shielding of alpha particles, with other environmental effects only having small contributions.

The Mars Science Laboratory (MSL) Curiosity rover recently traversed over plateaus of mafic aeolian sandstones (the 'Stimson' formation) that overlie mudstones (the 'Murray' formation). Within the Stimson formation we observed many lighter-toned, halo-forming features, that are potentially indicative of fluid alteration (see Fig. 1). These halo features extend for tens of meters laterally and are approx.1 meter wide. The halo features were characterized by Curiosity's geochemical instruments: Alpha Proton X-Ray Spectrometer (APXS), Chemin, Chemcam and Sample Analysis at Mars (SAM). With respect to the host (unaltered) Stimson rocks, fracture halos were significantly enriched in silicon and low in iron [1]. Changes in hydrogen abundance (due to its large neutron scattering cross section) greatly influence the magnitude of the thermal neutron response from the Dynamic Albedo of Neutrons (DAN) instrument [2]. There are also some elemental species, e.g. chlorine, iron, and nickel, that have significant microscopic neutron absorption cross sections. These elements can be abundant and variable results provide a useful estimate of the lower bound for bulk hydrogen content (assuming a homogeneous distribution).

MSL DYNAMIC ALBEDO OF NEUTRONS EXPERIMENT: Sols 0 753. C. G. Tate 1 , J. Moersch 1,2 , B. Ehresmann 3 , I. Jun 4 , C. Hardgrove 2 , M. Litvak 5 , I. Mitrofanov 5 , P. Bellutta 4 , W.V. Boynton 6 , F. Fedosov 5 , D. Golovin 5 , K. Harshman 6 , D. Hassler 3 , A.S. Kozyrev 5 , A. Malakhov 5 , M. Mokrousov 5 , S. Nikiforov 5 , A.B. Sanin 5 , and A. Vostrukhin 5 . 1 Dept. of Physics and Astronomy, University of Tennessee, Knoxville, TN, USA, ctate10@utk.edu, 2 Dept. of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, USA, 3 Southwest Research Institute, Boulder, CO, USA, 4 Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA, 5 Space Research Institute, RAS, Moscow, Russia, 6 University of Arizona, Tucson, AZ, USA.

The recent availability of large volume cerium bromide crystals raises the possibility of substantially improving gamma-ray spectrometer limiting flux sensitivities over current systems based on the lanthanum tri-halides, e.g., lanthanum bromide and lanthanum chloride, especially for remote sensing, low-level counting applications or any type of measurement characterized by poor signal to noise ratios. The Russian Space Research Institute has developed and manufactured a highly sensitive gamma-ray spectrometer for remote sensing observations of the planet Mercury from the Mercury Polar Orbiter (MPO), which forms part of ESA’s BepiColombo mission. The Flight Model (FM) gamma-ray spectrometer is based on a 3-in. single crystal of LaBr3(Ce3+) produced in a separate crystal development programme specifically for this mission. During the spectrometers development, manufacturing, and qualification phases, large crystals of CeBr3 became available in a subsequent phase of the same crystal development programme. Consequently, the Flight Spare Model (FSM) gamma-ray spectrometer was retrofitted with a 3-in. CeBr3 crystal and qualified for space. Except for the crystals, the two systems are essentially identical. In this paper, we report on a comparative assessment of the two systems, in terms of their respective spectral properties, as well as their suitability for use in planetary mission with respect to radiation tolerance and their propensity for activation. We also contrast their performance with a Ge detector representative of that flown on MESSENGER and show that: (a) both LaBr3(Ce3+) and CeBr3 provide superior detection systems over HPGe in the context of minimally resourced spacecraft and (b) CeBr3 is a more attractive system than LaBr3(Ce3+) in terms of sensitivities at lower gamma fluxes. Based on the tests, the FM has now been replaced by the FSM on the BepiColombo spacecraft. Thus, CeBr3 now forms the central gamma-ray detection element on the MPO spacecraft.

We present a method of conversion of the lunar neutron counting rate measured by the Lunar Reconnaissance Orbiter (LRO) Lunar Exploration Neutron Detector (LEND) instrument collimated neutron detectors, to water equivalent hydrogen (WEH) in the top 1 m layer of lunar regolith. Polar maps of the Moon's inferred hydrogen abundance are presented and discussed. (C) 2016 Elsevier Inc. All rights reserved.

The Dynamic Albedo of Neutron (DAN) instrument on board the Mars Science Laboratory Curiosity rover acquired a series of measurements as part of an observational campaign of the Kimberley area in Gale crater. These observations were planned to assess the variability of bulk hydrogen and neutron-absorbing elements, characterized as chlorine-equivalent concentration, in the geologic members of the Kimberley formation and in surface materials exposed throughout the area. During the traverse of the Kimberley area, Curiosity drove primarily over the "Smooth Hummocky" unit, a unit composed primarily of sand and loose rocks, with occasional stops at bedrock of the Kimberley formation. During the Kimberley campaign, DAN detected ranges of water equivalent hydrogen (WEH) and chlorine-equivalent concentrations of 1.5-2.5wt % and 0.6-2wt%, respectively. Results show that as the traverse progressed, DAN observed an overall decrease in both WEH and chlorine-equivalent concentrationmeasured over the sand and loose rocks of the Smooth Hummocky unit. DAN measurements of WEH and chlorine-equivalent concentrations in the well-exposed sedimentary bedrock of the Kimberley formation show fluctuations with stratigraphic position. The Kimberley campaign also provided an opportunity to compare measurements from DAN with those from the Sample Analysis at Mars (SAM) and the Alpha-Particle X-ray Spectrometer (APXS) instruments. DAN measurements obtained near the Windjana drill location show a WEH concentration of similar to 1.5 wt %, consistent with the concentration of low-temperature absorbed water measured by SAM for the Windjana drill sample. A comparison between DAN chlorine-equivalent concentrations measured throughout the Kimberley area and APXS observations of corresponding local surface targets and drill fines shows general agreement between the two instruments.

The Dynamic Albedo of Neutrons (DAN) experiment on the Mars Science Laboratory (MSL) rover Curiosity is designed to detect neutrons to determine hydrogen abundance within the subsurface of Mars (Mitrofanov, I.G. et al. [2012]. Space Sci. Rev. 170, 559-582. http://dx.doi.org/10.10071s11214-012-9924-y; Litvak, M.L. et al. [2008]. Astrobiology 8, 605-613. http://dx.doLorg/10.1089/ast.2007.0157). While DAN has a pulsed neutron generator for active measurements, in passive mode it only measures the leakage spectrum of neutrons produced by the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) and Galactic Cosmic Rays (GCR). DAN passive measurements provide better spatial coverage than the active measurements because they can be acquired while the rover is moving. Here we compare DAN passive-mode data to models of the instrument's response to compositional differences in a homogeneous regolith in order to estimate the water equivalent hydrogen (WEH) content along the first 200 sols of Curiosity's traverse in Gale Crater, Mars. WEH content is shown to vary greatly along the traverse. These estimates range from 0.5 +/- 0.1 wt.% to 3.9 +/- 0.2 wt.% for fixed locations (usually overnight stops) investigated by the rover and 0.6 +/- 0.2 wt.% to 7.6 +/- 1.3 wt.% for areas that the rover has traversed while continuously acquiring DAN passive data between fixed locations. Estimates of WEH abundances at fixed locations based on passive mode data are in broad agreement with those estimated at the same locations using active mode data. Localized (meter-scale) anomalies in estimated WEH values from traverse measurements have no particular surface expression observable in co-located images. However at a much larger scale, the hummocky plains and bedded fractured units are shown to be distinct compositional units based on the hydrogen content derived from DAN passive measurements. DAN passive WEH estimates are also shown to be consistent with geologic models inferred from other MSL instruments, which indicate that fluvial/lacustrine activity occurred at certain locations (e.g., Yellowknife Bay). (C) 2015 Elsevier Inc. All rights reserved.

Deep space manned missions are already a near future of astronautics. Radiation risk on such a long-duration journey appears to be one of the basic factors in planning and designing the mission. The paper relates to the scientific objectives and experiments for investigation of the radiation environment to be carried out during the ExoMars 2016 and 2018 joint missions of the European Space Agency (ESA) and the Federal Space Agency of Russia (Roscosmos) to Mars. The following topics are described: 1) The charged particle telescope and the experiment Liulin-MO for measuring the radiation environment on board the ExoMars 2016 Trace Gas Orbiter satellite as a part of the Fine Resolution Epithermal Neutron Detector (FREND) and 2) Liulin-ML experiment and instrument for investigating the radiation environment on Mars as a part of the active detector of neutrons and gamma rays (ADRON) on the Russian surface platform for ExoMars 2018 mission. Liulin detectors will be used in combination with the neutron detectors to study the radiation conditions both from charged particles and neutrons during the cruise phase, in Mars orbit and on the surface of Mars.

Thermal conductivity of the near-surface Martian regolith derived from variations in MSL passive neutron counts and ground temperature measurements

Searching for water in the soil of Gale Crater is one of the primary tasks for the NASA Mars Science Laboratory rover named Curiosity. The primary task of the Dynamic Albedo of Neutrons (DAN) experiment on board the rover is to investigate and qualitatively characterize the presence of water along the rover’s traverse across Gale Crater. The water depth distribution may be found from measurements of neutrons generated by the Pulsing Neutron Generator (PNG) included in the DAN instrument, scattered by the regolith and returned back to the detectors. This paper provides a description of the data processing of such measurements and data products of DAN investigation.