The Northwest Africa (NWA) 773 clan of lunar meteorite stones are coarse‐grained breccias that provide an opportunity to examine a lunar igneous system that includes inferred intrusive and extrusive ...lithologies, possibly related through a common liquid line of descent from a single source region. Such extensive sampling of a single very low‐Ti (VLT) magmatic system on the Moon is unprecedented among the lunar samples. This study focuses on the olivine gabbro (OG), anorthositic gabbro (AG), and ferroan gabbro (FG) lithologies variably contained in NWA 773, NWA 2727, NWA 3160, NWA 3170, NWA 7007, and NWA 10656. Mineral compositions in the three gabbros indicate the crystallization sequence OG → AG → FG. Petrologic modeling of these three lithologies, and an olivine phyric basalt that also occurs in the NWA 773 clan, however, suggests that the relationship among the lithologies is more complex. The OG and basalt can be modeled as originating from a VLT KREEP‐bearing parental melt similar to the Apollo 14 Green Glass b1 composition through mainly equilibrium crystallization. The AG and FG, however, do not fit this simple model and require either a more complex crystallization sequence involving fractional crystallization, magma chamber recharge, or perhaps heterogeneity in the source region.
The rover Opportunity has investigated the rim of Endeavour Crater, a large ancient impact crater on Mars. Basaltic breccias produced by the impact form the rim deposits, with stratigraphy similar to ...that observed at similar-sized craters on Earth. Highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits. Gypsum-rich veins cut sedimentary rocks adjacent to the crater rim. The gypsum was precipitated from low-temperature aqueous fluids flowing upward from the ancient materials of the rim, leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate-rich sandstones of the Meridiani region.
Outcrop exposures of sedimentary rocks at the Opportunity landing site (Meridiani Planum) form a set of genetically related strata defined here informally as the Burns formation. This formation can ...be subdivided into lower, middle, and upper units which, respectively, represent eolian dune, eolian sand sheet, and mixed eolian sand sheet and interdune facies associations. Collectively, these three units are at least 7 m thick and define a “wetting-upward” succession which records a progressive increase in the influence of groundwater and, ultimately, surface water in controlling primary depositional processes.
The Burns lower unit is interpreted as a dry dune field (though grain composition indicates an evaporitic source), whose preserved record of large-scale cross-bedded sandstones indicates either superimposed bedforms of variable size or reactivation of lee-side slip faces by episodic (possibly seasonal) changes in wind direction. The boundary between the lower and middle units is a significant eolian deflation surface. This surface is interpreted to record eolian erosion down to the capillary fringe of the water table, where increased resistance to wind-induced erosion was promoted by increased sediment cohesiveness in the capillary fringe. The overlying Burns middle unit is characterized by fine-scale planar-laminated to low-angle-stratified sandstones. These sandstones accumulated during lateral migration of eolian impact ripples over the flat to gently undulating sand sheet surface. In terrestrial settings, sand sheets may form an intermediate environment between dune fields and interdune or playa surfaces. The contact between the middle and upper units of the Burns formation is interpreted as a diagenetic front, where recrystallization in the phreatic or capillary zones may have occurred. The upper unit of the Burns formation contains a mixture of sand sheet facies and interdune facies. Interdune facies include wavy bedding, irregular lamination with convolute bedding and possible small tepee or salt-ridge structures, and cm-scale festoon cross-lamination indicative of shallow subaqueous flows marked by current velocities of a few tens of cm/s. Most likely, these currents were gravity-driven, possibly unchannelized flows resulting from the flooding of interdune/playa surfaces. However, evidence for lacustrine sedimentation, including mudstones or in situ bottom-growth evaporites, has not been observed so far at Eagle and Endurance craters.
Mineralogical and elemental data indicate that the eolian sandstones of the lower and middle units, as well as the subaqueous and eolian deposits of the Burns upper unit, were derived from an evaporitic source. This indirectly points to a temporally equivalent playa where lacustrine evaporites or ground-water-generated efflorescent crusts were deflated to provide a source of sand-sized particles that were entrained to form eolian dunes and sand sheets. This process is responsible for the development of sulfate eolianites at White Sands, New Mexico, and could have provided a prolific flux of sulfate sediment at Meridiani. Though evidence for surface water in the Burns formation is mostly limited to the upper unit, the associated sulfate eolianites provide strong evidence for the critical role of groundwater in controlling sediment production and stratigraphic architecture throughout the formation.
Fluorapatite grains from Apollo 15 Mare basalt 15058,128 were analyzed by Raman spectroscopy, Raman spectral imaging, time-of-flight secondary ion mass spectrometry (TOF-SIMS), field emission ...scanning electron microscopy (FE-SEM), and electron probe microanalysis (EPMA) in an attempt to detect structurally bound OH- in the fluorapatite. Although OH- could not be definitively detected by Raman spectroscopy because of REE-induced photoluminescence, hydroxyl was detected in the fluorapatite by TOF-SIMS. The TOF-SIMS technique is qualitative but capable of detecting the presence of hydroxyl even at trace levels. Electron microprobe data indicate that on average, F and Cl (F+Cl) fill the monovalent anion site in these fluorapatite grains within the uncertainties of the analyses (about 0.07±0.01 atoms per formula unit). However, some individual spot analyses have F+Cl deficiencies greater than analytical uncertainties that could represent structural OH-. On the basis of EPMA data, the fluorapatite grain with the largest F+Cl deficiency constrains the upper limit of the OH- content to be no more than 4600±2000 ppm by weight (the equivalent of approximately 2400±1100 ppm water). The TOF-SIMS detection of OH- in fluorapatite from Apollo sample 15058,128 represents the first direct confirmation of structurally bound hydroxyl in a lunar magmatic mineral. This result provides justification for attributing at least some of the missing structural component in the monovalent anion site of other lunar fluorapatite grains to the presence of OH-. Moreover, this finding supports the presence of dissolved water in lunar magmas and the presence of at least some water within the lunar interior.
Apollo 12 sample 12032,366-19 is a 21.3 mg granite fragment that is distinct from any other lunar granite or felsite. It is composed of barian K-feldspar, quartz, sodic plagioclase, hedenbergite, ...fayalite, and ilmenite, with trace amounts of zirconolite, baddeleyite, apatite, and merrillite. The texture of 12032,366-19 is largely a micrographic intergrowth predominantly of K-feldspar and quartz and, to a lesser extent, plagioclase and quartz. Hedenbergite, fayalite, and ilmenite are present in minor but significant quantities--6.0, 3.1, and 1.7 wt%, respectively--and are scattered throughout the feldspar-quartz intergrowths. Trace amounts of Zr-bearing phases are found including zirconolite (0.6 wt%) and baddeleyite (0.04 wt%). Incompatible trace-element concentrations are high in 12032,366-19, particularly the high-field-strength elements, e.g., Zr, Sm, and Th (1500, 25, and 61 µg/g, respectively). The chondrite-normalized, rare-earth-element concentrations form a "V-pattern" that is characteristic of other lunar granitic material. By modeling 12032,366-19 as a derivative from a KREEP-like parent melt, the composition and mineral assemblage can be obtained by extended fractional crystallization combined with separation of the low-density minerals plus trapped melt components prior to final solidification. However, this model cannot quantitatively account for the relatively sodic composition of the plagioclase (An34-50) and requires that the starting melt has Na2O of 1.2-1.4 wt%, which is higher than most KREEP compositions. Formation of this assemblage by silicate-liquid immiscibility is neither required nor indicated by petrogenetic modeling.
•Future lunar rovers will gather ground truth for remotely sensed polar observations.•We identify optimal rover traverses using a wheel–soil interaction model.•We locate traverses using topography ...and multi-temporal lighting simulations.•We examine a traverse that allows a rover to remain sunlit for over 94.4% of the year.
To fully understand the extensive collection of remotely sensed polar observations by the Lunar Reconnaissance Orbiter and other recent lunar missions, we must acquire an array of ground-truth measurements. A polar rover can sample and assay potential polar resources both laterally and at shallow depths. To identify ideal, least-energy traverses for such a polar prospecting mission, we developed a traverse planning tool, called R-Traverse, using a fundamental wheel–regolith interaction model and datasets from the Lunar Reconnaissance Orbiter Camera, Lunar Orbiter Laser Altimeter, and Diviner Lunar Radiometer Experiment. Using the terramechanics model, we identified least-energy traverses at the 20 m scale around Shackleton crater and located one traverse plan that enables the rover to remain illuminated for 94.4% of the lunar year. By incorporating this path planning tool during mission planning, the feasibility of such a mission can be quantified.
Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe(+3)-rich smectites. The ...signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.
The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) and Narrow Angle Cameras (NACs) are on the NASA Lunar Reconnaissance Orbiter (LRO). The WAC is a 7-color push-frame camera (100 ...and 400 m/pixel visible and UV, respectively), while the two NACs are monochrome narrow-angle linescan imagers (0.5 m/pixel). The primary mission of LRO is to obtain measurements of the Moon that will enable future lunar human exploration. The overarching goals of the LROC investigation include landing site identification and certification, mapping of permanently polar shadowed and sunlit regions, meter-scale mapping of polar regions, global multispectral imaging, a global morphology base map, characterization of regolith properties, and determination of current impact hazards.
Excavating into the shallow Martian subsurface has the potential to expose stratigraphic layers and mature regolith, which may hold a record of more ancient aqueous interactions than those expected ...under current Martian surface conditions. During the Spirit rover's exploration of Gusev crater, rover wheels were used to dig three trenches into the subsurface regolith down to 6–11 cm depth: Road Cut, the Big Hole, and The Boroughs. A high oxidation state of Fe and high concentrations of Mg, S, Cl, and Br were found in the subsurface regolith within the two trenches on the plains, between the Bonneville crater and the foot of Columbia Hills. Data analyses on the basis of geochemistry and mineralogy observations suggest the deposition of sulfate minerals within the subsurface regolith, mainly Mg‐sulfates accompanied by minor Ca‐sulfates and perhaps Fe‐sulfates. An increase of Fe2O3, an excess of SiO2, and a minor decrease in the olivine proportion relative to surface materials are also inferred. Three hypotheses are proposed to explain the geochemical trends observed in trenches: (1) multiple episodes of acidic fluid infiltration, accompanied by in situ interaction with igneous minerals and salt deposition; (2) an open hydrologic system characterized by ion transportation in the fluid, subsequent evaporation of the fluid, and salt deposition; and (3) emplacement and mixing of impact ejecta of variable composition. While all three may have plausibly contributed to the current state of the subsurface regolith, the geochemical data are most consistent with ion transportation by fluids and salt deposition as a result of open‐system hydrologic behavior. Although sulfates make up >20 wt.% of the regolith in the wall of The Boroughs trench, a higher hydrated sulfate than kieserite within The Boroughs or a greater abundance of sulfates elsewhere than is seen in The Boroughs wall regolith would be needed to hold the structural water indicated by the water‐equivalent hydrogen concentration observed by the Gamma‐Ray Spectrometer on Odyssey in the Gusev region.
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