Jessica M. Sunshine

Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1

Lunar Water The Moon has been thought to be primarily anhydrous, although there has been some evidence for accumulated ice in permanently shadowed craters near its poles (see the Perspective by Lucey, published online 24 September). By analyzing recent infrared mapping by Chandrayaan-1 and Deep Impact, and reexamining Cassini data obtained during its early flyby of the Moon, Pieters et al. (p. 568, published online 24 September), Sunshine et al. (p. 565, published online 24 September), and Clark et al. (p. 562, published online 24 September) reveal a noticeable absorption signal for H2O and OH across much of the surface. Some variability in water abundance is seen over the course of the lunar day. The data imply that solar wind is depositing and/or somehow forming water and OH in minerals near the lunar surface, and that this trapped water is dynamic. Space-based spectroscopic measurements provide evidence for water or hydroxyl (OH) on the surface of the Moon The search for water on the surface of the anhydrous Moon had remained an unfulfilled quest for 40 years. However, the Moon Mineralogy Mapper (M3) on Chandrayaan-1 has recently detected absorption features near 2.8 to 3.0 micrometers on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M3 data with neutron spectrometer hydrogen abundance data suggests that the formation and retention of hydroxyl and water are ongoing surficial processes. Hydroxyl/water production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.

Estimating modal abundances from the spectra of natural and laboratory pyroxene mixtures using the modified Gaussian model

Spectra of samples containing multiple pyroxene components are explored as a function of modal abundance using the modified Gaussian model (MGM). The MGM, unlike other approaches, allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great potential for remote applications. Quantitative understanding of the spectral characteristics of lithologies which include mixtures of two or more pyroxenes is fundamental to analyzing remotely acquired spectra of terrestrial and extra-terrestrial targets. A series of mass fraction mixtures created from several different particle size fractions were analyzed with the MGM to quantify the properties of pyroxene mixtures as a function of both modal abundance and grain size. Results of this MGM analysis indicate that band centers, band widths, and relative band strengths of absorptions from individual pyroxenes in mixture spectra are largely independent of particle size. In addition, systematic changes in relative band strength as a function of modal abundance are observed, which yield particle size independent relationships that can be used to estimate modal abundances from the spectra of unknown samples. Spectra of natural samples exhibiting both zoned and exsolved pyroxenes are evaluated as examples of spectra likely to be measured from actual lithologies. Spectral properties of both pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5-10% without predetermined knowledge of the end-member spectra. In contrast, the spectra of samples exhibiting zoned compositions are consistent with one dominant pyroxene component. This single pyroxene component has anomalously wide absorption bands and appears to represent an average composition.

Seeing through the dust: martian crustal heterogeneity and links to the SNC meteorites

Through the application of new analytical techniques to high spatial resolution imaging spectrometer data, the ferrous mineralogy of major volcanic terrains on Mars is shown to consist of significant fractions of both low- and high-calcium pyroxene. Changes in the relative abundances of these pyroxenes are observed for units of different age and morphology, even in regions with higher degrees of alteration and contamination from dust. Volcanic rocks with these characteristics are uncommon on Earth but are typical of the basaltic SNC meteorites (shergottites, nakhlites, and chassignites) thought to be from Mars. Thus, it is possible to infer, even through the veil of dust, that the SNC meteorites have mineralogic affinities to major volcanic provinces on Mars and are therefore truly representative of the heterogeneity observed on the surface of the red planet.

Crustal diversity of the moon: Compositional analyses of Galileo solid state imaging data

The multispectral images of the lunar limb and farside obtained by the solid state imaging (SSI) system on board the Galileo spacecraft provide the first new pulse of compositional data of the Moon by a spacecraft in well over a decade. The wavelength range covered by SSI filters (0.4-1.0 }x7fm) is particularly sensitive to the composition of mare basalts, the abundance of mafic (ferrous) minerals, and the maturity of the regolith. To a first order, the limb and farside material is consistent with previous characterization of nearside lunar spectral types for mare and highland soils and craters. Most basalts are of an intermediate TiO 2 composition and most of the highland crust is feldspathic with local variations in mafic content identified principally at impact craters. Dark manfling material on the farside can be interpreted in terms of known properties of lunar pyroclastic glass. Regions of cryptornate are shown to have spectral properties intermediate between those of highland and mare soils, as would be expected from a mixture of the two. There are several important exceptions and surprises, however. Unlike the basalt types identified on the nearside, limb and farside basalts exhibit an exceptionally weak 1 [xm ferrous absorption band. This may indicate a compositionally distinct lunar basalt group that, for example, is more Mg-rich than most basalts of the nearside. Some of the most notable compositional anomalies are associated with South Pole-Aitken Basin. This large region has a much lower albedo than surrounding highlands. The inner, darkest, portion of the basin exhibits optical properties indistinguishable low-Ti basalts. Deposits to the south exhibit unique properties with a strong and broad ferrous 1 [xrn absorption, most consistent with abundant olivine. The unusual compositions associated with South Pole-Aitken and their spatial e3tent suggests the impact creating this huge lunar basin excavated mafic-rich lower crust or perhaps mantle material. 1. INTRO OUCrIION

Overview of Primitive Object Volatile Explorer (PrOVE) CubeSat or Smallsat concept

Here we describe the Primitive Object Volatile Explorer (PrOVE), a smallsat mission concept to study the surface structure and volatile inventory of comets in their perihelion passage phase when volatile activity is near peak. CubeSat infrastructure imposes limits on propulsion systems, which are compounded by sensitivity to the spacecraft disposal state from the launch platform and potential launch delays. We propose circumventing launch platform complications by using waypoints in space to park a deep space SmallSat or CubeSat while awaiting the opportunity to enter a trajectory to flyby a suitable target. In our Planetary Science Deep Space SmallSat Studies (PSDS3) project, we investigated scientific goals, waypoint options, potential concept of operations (ConOps) for periodic and new comets, spacecraft bus infrastructure requirements, launch platforms, and mission operations and phases. Our payload would include two low-risk instruments: a visible image (VisCAM) for 5-10 m resolution surface maps; and a highly versatile multispectral Comet CAMera (ComCAM) will measure 1) H2O, CO2, CO, and organics non-thermal fluorescence signatures in the 2-5 μm MWIR, and 2) 7-10 and 8-14 μm thermal (LWIR) emission. This payload would return unique data not obtainable from ground-based telescopes and complement data from Earth-orbiting observatories. Thus, the PrOVE mission would (1) acquire visible surface maps, (2) investigate chemical heterogeneity of a comet nucleus by quantifying volatile species abundance and changes with solar insolation, (3) map the spatial distribution of volatiles and determine any variations, and (4) determine the frequency and distribution of outbursts.