Abstract— We present new compositional data for 30 lunar stones representing about 19 meteorites. Most have iron concentrations intermediate to those of the numerous feldspathic lunar meteorites (3–7% FeO) and the basaltic lunar meteorites (17–23% FeO). All but one are polymict breccias. Some, as implied by their intermediate composition, are mainly mixtures of brecciated anorthosite and mare basalt, with low concentrations of incompatible elements such as Sm (1–3 μg/g). These breccias likely originate from points on the Moon where mare basalt has mixed with material of the FHT (Feldspathic Highlands Terrane). Others, however, are not anorthosite‐basalt mixtures. Three (17–75 μ/g Sm) consist mainly of nonmare mafic material from the nearside PKT (Procellarum KREEP Terrane) and a few are ternary mixtures of material from the FHT, PKT, and maria. Some contain mafic, nonmare lithologies like anorthositic norites, norites, gabbronorites, and troctolite. These breccias are largely unlike breccias of the Apollo collection in that they are poor in Sm as well as highly feldspathic anorthosite such as that common at the Apollo 16 site. Several have high Th/Sm compared to Apollo breccias. Dhofar 961, which is olivine gabbronoritic and moderately rich in Sm, has lower Eu/Sm than Apollo samples of similar Sm concentration. This difference indicates that the carrier of rare earth elements is not KREEP, as known from the Apollo missions. On the basis of our present knowledge from remote sensing, among lunar meteorites Dhofar 961 is the one most likely to have originated from South Pole‐Aitken basin on the lunar far side.
Abstract Chlorine is one of the highly mobile elements that participated in early aqueous chemistry and later alteration in Mars history. Our new experimental results suggest that chlorine could cycle on present‐day Mars between the atmosphere and surface, driven by multiphase redox plasma chemistry induced by current Martian dust activity (dust storms, dust devils, and grain saltation). We present two sets of experimental results that demonstrate the instantaneous release of chlorine from seven common chlorides during a medium strength electrostatic discharge (ESD) process that induced plasma chemistry in a Mars environmental chamber. Results include (1) the direct detection of a plasma emission line at 837.8 nm of the first excited state of the Cl atom ( Cl‐I ) by in situ plasma spectroscopy during the ESD process for MgCl 2 , FeCl 2 , and AlCl 3 and (2) the characterization of Cl‐bearing phases in the films deposited on the upper electrode after 7 hr of ESD exposure on each of seven chlorides (NaCl, KCl, CaCl 2 , MgCl 2 , FeCl 2 , AlCl 3 , and FeCl 3 ), using Raman spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive X‐ray (EDX) spectroscopy, and X‐ray photoelectron spectroscopy (XPS). This study is part of a series of laboratory investigations on the Martian atmosphere and surface interaction induced by electrochemistry.
In light of global remotely sensed data, the igneous crust of the Moon can no longer be viewed as a simple, globally stratified cumulus structure, composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual‐melt (KREEP) sandwich horizon near the base of the lower crust. Instead, global geochemical information derived from Clementine multispectral data and Lunar Prospector gamma‐ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique: (1) the Procellarum KREEP Terrane (PKT), (2) the Feldspathic High‐lands Terrane (FHT), and (3) the South Pole‐Aitken Terrane (SPAT). The PKT is a mafic province, coincident with the largely resurfaced area in the Procellarum‐Imbrium region whose petrogenesis relates to the early differentiation of the Moon. Here, some 40% of the Th in the Moon's crust is concentrated into a region that constitutes only about 10% of the crustal volume. This concentration of Th (average ∼5 ppm), and by implication the other heat producing elements, U and K, led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust. Lower‐crustal materials within the PKT likely interacted with underlying mantle materials to produce hybrid magmatism, leading to the magnesian suite of lunar rocks and possibly KREEP basalt. Although rare in the Apollo sample collection, widespread mare volcanic rocks having substantial Th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources. The FHT is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation. Basin impacts into this region do not excavate significantly more mafic material, suggesting a thickness of tens of kilometers of anorthositic crust. The feldspathic lunar meteorites may represent samples from the anorthositic central region of the FHT. Ejecta from deep‐penetrating basin impacts outside of the central anorthositic region, however, indicate an increasingly mafic composition with depth. The SPAT, a mafic anomaly of great magnitude, may include material of the upper mantle as well as lower crust; thus it is designated a separate terrane. Whether the SPA basin impact simply uncovered lower crust such as we infer for the FHT remains to be determined.
On its traverse to Columbia Hills, the Mars Exploration Rover Spirit investigated an outcrop designated “Wooly Patch” that exhibited morphological, mineralogical, and geochemical characteristics at the extreme ends of ranges observed among rocks studied at West Spur, a westward projecting salient near the foot of the Columbia Hills, Gusev crater. The major‐element composition and Fe‐mineralogy, as determined by the Alpha‐Particle X‐ray Spectrometer and Mössbauer Spectrometer, are inconsistent with any reasonable assemblage of basaltic minerals in that there is an excess of Si and Al. The combined data are best explained by the presence of 14–17% phyllosilicate minerals. Phyllosilicates that account for the composition and cation ratios include members of the kaolinite, serpentine, chlorite, and septechlorite groups. The potential existence of kaolinite‐type Al‐rich phyllosilicates within the Wooly Patch outcrop suggests a mildly acidic environment (pH 4–6) in the past and an open hydrologic system with good drainage conditions in the environment where these rocks were altered.
The sharp, nonoverlapping Raman bands for plagioclase, pyroxene, and olivine would be advantageous for on‐surface, active mineralogical analysis of lunar materials. A robust, light‐weight, low‐power, rover‐based Raman spectrometer with a laser exciting source, entirely transmission‐mode holographic optics, and a charge‐coupled device (CCD) detector could fit within a <20 cm cube. A sensor head on the end of an optical fiber bundle that carried the laser beam and returned the scattered radiation could be placed against surfaces at any desired angle by a deployment mechanism; otherwise, the instrument would need no moving parts. A modern micro‐Raman spectrometer with its beam broadened (to expand the spot to 50‐μm diameter) and set for low resolution (7 cm −1 in the 100–1400 cm −1 region relative to 514.5‐nm excitation), was used to simulate the spectra anticipated from a rover instrument. We present spectra for lunar mineral grains, <1 mm soil fines, breccia fragments, and glasses. From frequencies of olivine peaks, we derived sufficiently precise forsterite contents to correlate the analyzed grains to known rock types and we obtained appropriate forsterite contents from weak signals above background in soil fines and breccias. Peak positions of pyroxenes were sufficiently well determined to distinguish among orthorhombic, monoclinic, and triclinic (pyroxenoid) structures; additional information can be obtained from pyroxene spectra, but requires further laboratory calibration. Plagioclase provided sharp peaks in soil fines and most breccias even when the glass content was high.
Caption: View looking over the Moon's south pole from the far side, with 20 km diameter Shackleton crater in the foreground, generated in Lunar QuickMap, with the Diviner Lunar Radiometer Experiment (DLRE) polar summer maximum temperature data overlain on Lunar Reconnaissance Orbiter Cameras (LROC) Wide Angle Camera (WAC) morphologic basemap with the DLRE layer opacity set to 50% (see https://bit.ly/3s9qKVH).The colors represented in the DLRE overlay correspond to surface temperatures ranging from an astoundingly cold < 50 K (dark blue) to a toasty 350 K or more in sunlight (red to yellow).† The Earth would be visible on the lunar horizon from this perspective.This image of the Earth was taken by the LROC Narrow Angle Cameras (NAC) and colorized using visible bands from the Wide Angle Camera (see http://lroc.sese.asu.edu/posts/231).In this image of Earth one can see the western hemisphere as it would appear from the south pole of the Moon, with North America in the lower right and South America in the upper left.The Earth images were taken on August 9,
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