Georgiana Y. Kramer

M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies

[1] We examined the lunar swirls using data from the Moon Mineralogy Mapper (M 3 ). The improved spectral and spatial resolution of M 3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on‐ and off‐swirl. Fresh, on‐swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well‐preserved mafic absorption features compared with fresh off‐swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on‐swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off‐swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ∼1500 nm. Off‐swirl spectra show very little reddening or change in continuum shape across the entire M 3 spectral range. Off‐swirl spectra are dark, have attenuated absorption features, and the narrow range in off‐swirl albedos suggests off‐swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 mm. For each of the studied regions, the 2.82 mm absorption feature is significantly weaker on‐swirl than off‐swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off‐swirl surfaces. Nanophase iron (npFe 0 ) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe 0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls. Citation: Kramer, G. Y., et al. (2011), M 3 spectral analysis of lunar swirls and the link between optical maturation and surface

The petrogenesis of the Apollo 14 high-Al mare basalts

Abstract In this paper, we report analysis of various basaltic lunar samples including 14053 and 14072, KREEP basalt 15386, thirty basalt clasts from Apollo 14 breccia 14321, as well as impact-generated samples (matrix from breccia 14168, olivine vitrophyres 14321,1180 and 14321,1539, and impact melt 14310) using a combination of solution and laser ablation inductively coupled plasma mass spectrometry (ICP-MS). The basalt clast samples were previously analyzed by instrumental neutron activation. On plots of incompatible trace elements (ITEs) vs. compatible trace elements, the Apollo 14 high-Al basalts form three approximately subparallel trends that, on the basis of current data, are also separated by age. Plots of ITE ratios (i.e., Nb/Ce vs. Zr/Y) can be used to indicate source composition, and also divide the basalts into three groups: Group A (~4.3 Ga); Group B (~4.1 Ga); and Group C (~3.9 Ga). New data for 14072 suggest the sample does not fit with any of the three groups defined here, and may indicate the presence of a fourth group of high-Al basalts in the proximity of the Apollo 14 site. The Apollo 14 high-Al basalts are compositionally distinct from known Apollo 14 impact melts and impact-generated lithologies. The three groups cannot be related by varying degrees of partial melting of a single, KREEP-contaminated source and, therefore, require three separate source regions. The new data indicate that Group A basalts evolved through closed-system crystal fractionation. However, the new data from basalts forming Groups B and C require open-system evolution that involves combined assimilation and fractional crystallization (AFC). Unlike previous AFC modeling of the Apollo 14 high-Al basalts, an assimilant composed of KREEP is not sufficient to generate the compositional ranges of each basalt group. The modeling of both groups requires a mixture of KREEP and granite as the assimilant, which supports the notion of a genetic relationship between these two lunar components.

Peak-Ring Structure and Kinematics from a Multi-disciplinary Study of the Schrödinger Impact Basin

The Schrödinger basin on the lunar farside is ∼320 km in diameter and the best-preserved peak-ring basin of its size in the Earth–Moon system. Here we present spectral and photogeologic analyses of data from the Moon Mineralogy Mapper instrument on the Chandrayaan-1 spacecraft and the Lunar Reconnaissance Orbiter Camera (LROC) on the LRO spacecraft, which indicates the peak ring is composed of anorthositic, noritic and troctolitic lithologies that were juxtaposed by several cross-cutting faults during peak-ring formation. Hydrocode simulations indicate the lithologies were uplifted from depths up to 30 km, representing the crust of the lunar farside. Through combining geological and remote-sensing observations with numerical modelling, we show that a Displaced Structural Uplift model is best for peak rings, including that in the K–T Chicxulub impact crater on Earth. These results may help guide sample selection in lunar sample return missions that are being studied for the multi-agency International Space Exploration Coordination Group.

The basalts of Mare Frigoris

This paper discusses the methodology and results of a detailed investigation of Mare Frigoris using remote sensing data from Clementine, Lunar Prospector, and Lunar Reconnaissance Orbiter, with the objective of mapping and characterizing the compositions and eruptive history of its volcanic units. With the exception of two units in the west, Mare Frigoris and Lacus Mortis are filled with basalts having low-TiO2 to very low TiO2, low-FeO, and high-Al2O3 abundances. These compositions indicate that most of the basalts in Frigoris are high-Al basalts—a potentially undersampled, yet important group in the lunar sample collection for its clues about the heterogeneity of the lunar mantle. Thorium abundances of most of the mare basalts in Frigoris are also low, although much of the mare surface appears elevated due to contamination from impact gardening with the surrounding high-Th Imbrium ejecta. There are, however, a few regional thorium anomalies that are coincident with cryptomare units in the east, the two youngest mare basalt units, and some of the scattered pyroclastic deposits and volcanic constructs. In addition, Mare Frigoris lies directly over the northern extent of the major conduit for a magma plumbing system that fed many of the basalts that filled Oceanus Procellarum, as interpreted by Andrews-Hanna et al. (2014) using data from the Gravity Recovery and Interior Laboratory mission. The relationship between this deep-reaching magma conduit and the largest extent of high-Al basalts on the Moon makes Mare Frigoris an intriguing location for further investigation of the lunar mantle.

Lunar swirls exposed at Workshop Without Walls

Lunar Swirls Workshop Without Walls; Moffett Field, California, 7 September 2011 For 40 years the nature and origin of strange, bright, sinuous markings on the surface of the Moon, known as lunar swirls, have been a topic of intense interest and debate to lunar scientists. Now, with the influx of new data about the lunar surface and its interaction with the space environment, the swirls are attracting a more diverse following. Lunar swirls was the topic of the NASA Lunar Science Institutes first “Workshop Without Walls,” a virtual meeting using the latest technology in interactive video teleconferencing.