Sverdrup-Henson crater: A candidate location for the first lunar South Pole settlement

Robotic and manned exploration of the Moon is the next target in Solar System exploration. The availability of in situ resources such as water ice, iron oxides, helium-3, and rare earth elements, combined with permanently sunlit areas, provides the opportunity for the first settlement, either human or robotic, on the Moon. We used several selection criteria (abundance of water ice, the slope of terrain, usable energy sources, communications, and base expandability) to identify a suitable area for a future base in the southern polar crater Sverdrup-Henson. Due to the higher abundance of water ice, we found that the Sverdrup-Henson site is better suited to host a base than the nearby craters de Gerlache and Shackleton. The crater floor is partly in permanent shadow and exhibits numerous signatures of water ice. Since water ice is essential for rocket fuel production and human survival, its presence is necessary for a first settlement. Sverdrup-Henson has a flat floor ideal for building and safe traversing, is accessible from the surrounding intercrater plains, and has nearby locations suitable for communications and solar power production. Thus, the Sverdrup-Henson site holds great potential for future missions. We propose further exploration of this area through in situ measurements to better constrain available resources.

Precise Detections of Solar Particle Events and a New View of the Moon

We have invented a new method for detecting solar particle events using data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO). Using a simple function of the total particle detection rates from four of CRaTER's six detectors, we can precisely identify solar energetic particle event periods in the CRaTER data archive. During solar-quiet periods we map the distribution of a mare-associated mixture of elements in the lunar regolith using this new method. The new map of the moon probably reflects an as-yet unknown combination of lunar albedo protons, neutrons, and gamma rays, and most closely resembles Lunar Prospector maps of gamma rays characteristic of thorium and iron. This result will lead to multiple follow-up studies of lunar albedo particles and may also contribute to the study of diurnally-varying hydrogenation of the lunar regolith.

Geochemistry of the lunar highlands as revealed by measurements of thermal neutrons

Thermal neutron emissions from the lunar surface provide a direct measure of bulk elemental composition that can be used to constrain the chemical properties of near-surface (depth <1 m) lunar materials. We present a new calibration of the Lunar Prospector thermal neutron map, providing a direct link between measured count rates and bulk elemental composition. The data are used to examine the chemical and mineralogical composition of the lunar surface, with an emphasis on constraining the plagioclase concentration across the highlands. We observe that the regions of lowest neutron absorption, which correspond to estimated plagioclase concentrations of >85%, are generally associated with large impact basins and are colocated with clusters of nearly pure plagioclase identified with spectral reflectance data.

Petrologic Characteristics of the Lunar Surface

Petrologic analysis of the lunar surface is critical for determining lunar formation and evolution. Here, we report the first global petrologic map that includes the five most important lunar lithological units: the Ferroan Anorthositic (FAN) Unit, the Magnesian Suite (MS) Unit, the Alkali Suite (AS) Unit, the KREEP Basalt (KB) Unit and the Mare Basalt (MB) Unit. Based on the petrologic map and focusing on four long-debated and important issues related to lunar formation and evolution, we draw the following conclusions from the new insights into the global distribution of the five petrologic units: (1) there may be no petrogenetic relationship between MS rocks and KB; (2) there may be no petrogenetic link between MS and AS rocks; (3) the exposure of the KREEP component on the lunar surface is likely not a result of MB volcanism but is instead mainly associated with the combined action of plutonic intrusion, KREEP volcanism and celestial collision; (4) the impact size of the South Pole-Aitken basin is constrained, i.e., the basin has been excavated through the whole crust to exhume a vast majority of lower-crustal material and a very limited mantle components to the lunar surface.

Elemental mapping by Dawn reveals exogenic H in Vesta's regolith

Using Dawn's Gamma Ray and Neutron Detector, we tested models of Vesta's evolution based on studies of howardite, eucrite, and diogenite (HED) meteorites. Global Fe/O and Fe/Si ratios are consistent with HED compositions. Neutron measurements confirm that a thick, diogenitic lower crust is exposed in the Rheasilvia basin, which is consistent with global magmatic differentiation. Vesta's regolith contains substantial amounts of hydrogen. The highest hydrogen concentrations coincide with older, low-albedo regions near the equator, where water ice is unstable. The young, Rheasilvia basin contains the lowest concentrations. These observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites--observed as clasts in some howardites--and subsequent removal or burial of this material by large impacts.

Performance of orbital neutron instruments for spatially resolved hydrogen measurements of airless planetary bodies

Orbital neutron spectroscopy has become a standard technique for measuring planetary surface compositions from orbit. While this technique has led to important discoveries, such as the deposits of hydrogen at the Moon and Mars, a limitation is its poor spatial resolution. For omni-directional neutron sensors, spatial resolutions are 1-1.5 times the spacecraft's altitude above the planetary surface (or 40-600 km for typical orbital altitudes). Neutron sensors with enhanced spatial resolution have been proposed, and one with a collimated field of view is scheduled to fly on a mission to measure lunar polar hydrogen. No quantitative studies or analyses have been published that evaluate in detail the detection and sensitivity limits of spatially resolved neutron measurements. Here, we describe two complementary techniques for evaluating the hydrogen sensitivity of spatially resolved neutron sensors: an analytic, closed-form expression that has been validated with Lunar Prospector neutron data, and a three-dimensional modeling technique. The analytic technique, called the Spatially resolved Neutron Analytic Sensitivity Approximation (SNASA), provides a straightforward method to evaluate spatially resolved neutron data from existing instruments as well as to plan for future mission scenarios. We conclude that the existing detector--the Lunar Exploration Neutron Detector (LEND)--scheduled to launch on the Lunar Reconnaissance Orbiter will have hydrogen sensitivities that are over an order of magnitude poorer than previously estimated. We further conclude that a sensor with a geometric factor of approximately 100 cm(2) Sr (compared to the LEND geometric factor of approximately 10.9 cm(2) Sr) could make substantially improved measurements of the lunar polar hydrogen spatial distribution.