Experimental constraints on the solidification of a hydrous lunar magma ocean

The identification of hydrogen in a range of lunar samples and the similarity of its abundance and isotopic composition with terrestrial values suggest that water could have been present in the Moon since its formation. To quantify the effect of water on early lunar differentiation, we present new analyses of a high‐pressure, high‐temperature experimental study designed to model the mineralogical and geochemical evolution of the solidification material equivalent to 700 km deep lunar magma oceans first reported in Lin et al. (2017a). We also performed additional experiments to better quantify water contents in the run products. Water contents in the melt phases in hydrous run products spanning a range of crystallization steps were quantified directly using a secondary ion mass spectrometry (SIMS). Results suggest that a significant but constant proportion (68 ± 5%) of the hydrogen originally added to the experiments was lost from the starting material independent of run conditions and run duration. The volume of plagioclase formed during our crystallization experiments can be combined with the measured water contents and the observed crustal thickness on the Moon to provide an updated lunar interior hygrometer. Our data suggest that at least 45–354 ppm H₂O equivalent was present in the Moon at the time of crust formation. These estimates confirm the inference of Lin et al. (2017a) that the Moon was wet during its magma ocean stage, with corrected absolute water contents now comparable to estimates derived from the water content in a range of lunar samples.     

Mineralogy and petrology of the LaPaz Icefield lunar mare basaltic meteorites

Abstract— Five basaltic meteorites from the LaPaz ice field are paired on the basis of their mineralogy and texture, and represent a unique basalt type distinct from those in the Apollo or Luna sample collections. LaPaz Icefield (LAP) 02205, LAP 02224, LAP 02226, LAP 02436 and LAP 03632 all contain plagioclase, pyroxene, ilmenite, spinel, olivine, and minor troilite, metal, phosphate, baddeleyite and silica (cristobalite). Brown glassy melt veins are ubiquitous and cross the primary igneous texture. Plagioclase, the major mineral and occurring as laths in a subophitic texture, is of narrow compositional range, from An_85–89. Pyroxene, also a major mineral, is strongly zoned, from augite and pigeonite cores to very iron‐rich rims. Ilmenite laths comprise approximately 3–5% of the basalts. Spinels show a large compositional range, comparable to that documented in Apollo 15 basalts, indicating an early chromite‐rich stage followed by an intermediate to late stage with Cr‐rich ulvöspinel. Relatively large, subhedral to skeletal olivine crystals (Fo_46–62) are sparse, and are too Forich to be in equilibrium with the bulk rock, indicating that these are xenocrysts rather than phenocrysts. The presence of melt veins with a similar composition to the bulk rock, maskelynitized plagioclase feldspar, and metastable cristobalite indicate that these rocks underwent significant shock, between 30 and 50 GPa. Calculated oxygen fugacity, using spinel‐ilmenite‐iron metal equilibria, is within the range defined by previous studies of lunar materials. The bulk composition (low MgO) and low calculated temperatures, together with modelling calculations, indicate an origin by fractional crystallization of a more primitive low TiO₂ parent liquid similar to Apollo 12 olivine basalt.     

The Mineralogy,petrology and geochemistry of lunar samples - a review

Crystallization from the molten state has been an important process for the formation of rocks on the Moon; the phenomenon of fractional crystallization is therefore discussed. The principal chemical and mineralogical features of the Apollo 11, 12 and 14 basaltic crystalline rocks are described, and an account is given of other rock types and minerals which are represented among the coarser particles in the lunar soils. A comparison is made between the chemical compositions (major, minor and trace element concentrations) of rocks and soils.Based upon the above data, one possible model for the outer shell of the Moon is presented, which consists of an outer layer of Al-rich rocks underlain by a layer which is more ferromagnesian in character. Partial melting of the latter was probably responsible for the extrusion of lavas at the surface which spread to form the basalts (Apollo 11 and 12) of the non-circular maria. The Apollo 14 (Fra Mauro) basalts are relatively enriched in potassium, rare earth elements, zirconium, phosphorus and certain other elements and may derive from partial melting of the more aluminous upper layer.The separation of the outer Moon into two layers could have occurred through gravity-aided fractional crystallization at an early stage (first few hundred m yr) in lunar history.Paper presented to the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 1971.     

A distinct variant of high-titanium mare basalt from the Van Serg core,Apollo 17 landing site

Abstract— A fragment of basalt picked from the drive tube collected at Van Serg crater at the Apollo 17 landing site has a bulk chemistry more primitive than that of other high-titanium mare basalt groups collected at the site. The sample has a fine-grained olivine phyric, subophitic texture that is distinct from that of other high-titanium basalt samples. The grain size and texture suggest that the sample has a composition close to that of a magma. The crystallization sequence, with appearance of oxide minerals later than in other groups, and other petrographic features such as more-calcic plagioclase and early pigeonite rather than augite, are consistent with this sample representing a distinct variant of Apollo 17 high-titanium basalts. It is not related through closed-system igneous processes to any of the other mare basalt groups identified among Apollo 17 samples. Its characters emphasize the complexity of contemporaneous magma processes on the Moon and the heterogeneity of that part of the mantle that was melted.     

Depositional processes of impactites from the YAX-1 drill core in the Chicxulub impact structure inferred from vertical profiles of PDF orientations and grain size distributions of shocked quartz

Core samples from the Chicxulub impact structure provide insights into the formation processes of a shallow-marine-target, complex crater. Although previous studies investigated the impactites (generally suevitic and polymict breccias) of the Yaxcopoil-1 (YAX-1) drill core in the Chicxulub impact structure, the interpretation of its deposition remains controversial. Here, we analyze planar deformation features (PDFs), grain size, and abundance of shocked quartz throughout the YAX-1 impactite sequence (794–895 m in depth). PDF orientations of most quartz grains in YAX-1 impactites show a distribution of both low angles ({104}, {103}, {102}) and high angles (orientations higher than 55° to c-axis), while the lower part of the impactite sequence contains quartz showing only PDF orientations of low angles. High-abundance, coarse-grained shocked quartz is found from the lower to middle parts of the impactites, whereas it abruptly changes to low-abundance, fine-grained shocked quartz within the upper part. In the uppermost part of the impactites, repeated oscillations in contents of these two components are observed. PDF orientation pattern suggests most of the shocked quartz grains experienced a range of shock pressure, except two samples in the lower part of impactites, which experienced only a high level of shock. We suggest that the base and lower part of the impactite sequence were formed by ejecta curtain and melt surge deposits, respectively. Our results are also consistent with the interpretation that the middle part of the impactite sequence is fallback ejecta from the impact plume. Additionally, we support the contention that massive seawater resurges into the crater occurred during the deposition of the upper and uppermost part of the impactites.     

The early geological history of the Moon inferred from ancient lunar meteorite Miller Range 13317

Miller Range (MIL) 13317 is a heterogeneous basalt‐bearing lunar regolith breccia that provides insights into the early magmatic history of the Moon. MIL 13317 is formed from a mixture of material with clasts having an affinity to Apollo ferroan anorthosites and basaltic volcanic rocks. Noble gas data indicate that MIL 13317 was consolidated into a breccia between 2610 ± 780 Ma and 1570 ± 470 Ma where it experienced a complex near‐surface irradiation history for ~835 ± 84 Myr, at an average depth of ~30 cm. The fusion crust has an intermediate composition (Al₂O₃ 15.9 wt%; FeO 12.3 wt%) with an added incompatible trace element (Th 5.4 ppm) chemical component. Taking the fusion crust to be indicative of the bulk sample composition, this implies that MIL 13317 originated from a regolith that is associated with a mare‐highland boundary that is KREEP‐rich (i.e., K, rare earth elements, and P). A comparison of bulk chemical data from MIL 13317 with remote sensing data from the Lunar Prospector orbiter suggests that MIL 13317 likely originated from the northwest region of Oceanus Procellarum, east of Mare Nubium, or at the eastern edge of Mare Frigoris. All these potential source areas are on the near side of the Moon, indicating a close association with the Procellarum KREEP Terrane. Basalt clasts in MIL 13317 are from a very low‐Ti to low‐Ti (between 0.14 and 0.32 wt%) source region. The similar mineral fractionation trends of the different basalt clasts in the sample suggest they are comagmatic in origin. Zircon‐bearing phases and Ca‐phosphate grains in basalt clasts and matrix grains yield ²⁰⁷Pb/²⁰⁶Pb ages between 4344 ± 4 and 4333 ± 5 Ma. These ancient ²⁰⁷Pb/²⁰⁶Pb ages indicate that the meteorite has sampled a range of Pre‐Nectarian volcanic rocks that are poorly represented in the Apollo, Luna, and lunar meteorite collections. As such, MIL 13317 adds to the growing evidence that basaltic volcanic activity on the Moon started as early as ~4340 Ma, before the main period of lunar mare basalt volcanism at ~3850 Ma.     

Bombardment as a cause of the lunar asymmetry

A comparison of the lunar frontside gravity field with topography indicates that low-density ( 2.9 g cm^–3) types of rock form a surface layer or crust of variable thickness: 40-60 km beneath terrae; 20-40 km beneath non-mascon maria; 0-20 km beneath mascon maria. The observed offset between lunar centers of mass and figure is consistent with farside crustal thicknesses of 40-50 km, similar to frontside terra thicknesses.The Moon is asymmetric in crustal thickness, and also in the distribution of maria and gamma radioactivity. Early bombardment of the Moon by planetesimals, in both heliocentric and geocentric orbits, is examined as a possible cause of the asymmetries. The presence of a massive companion (Earth) causes a spin-orbit coupled Moon to be bombarded non-uniformly. The most pronounced local concentration of impacts would have occurred on the west limb of the Moon, when it orbited close to the Earth, if low-eccentricity heliocentric planetesimals were still abundant in the solar system at that time.A very intense bombardment of this type could have redistributed crustal material on the Moon, thinning the west limb crust appreciably. This would have caused a change in position of the principal axes of inertia, and a reorientation of the spin-orbit coupled Moon such that the thinnest portion of its crust turned toward one of the poles. Erupting lavas would have preferentially flooded such a thin-crusted, low-lying area. This would have caused another readjustment of principal moments, and a reorientation of the Moon such that the mare areas tipped toward the equator. The north-south and nearside-farside asymmetries of mare distribution on the present Moon can be understood in terms of such a history.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

Random processes as a cause of the lunar asymmetry

The offset of the center of mass of the Moon from its center of figure together with moment of inertia differences are explainable by a lunar crust of randomly varying thickness. The necessity of postulating a method of preferential material transport into a particular lunar hemisphere to explain the lunar asymmetry is eliminated.This paper represents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration.     

The lunar mean moment of inertia and the size of the Moon's core

In this paper the relation between the uncertainty of the Moon's mean moment of inertia (I/Ma ²) and that of the core density _c is discussed with a two-layer model of the Moon - a mantle obeying Roche's law of the density distribution and a homogeneous core (Fe-core or Fe-FeS-core). When the uncertainty of I/Ma ² is 0.0023 (that is the accuracy in present observation), a core with radius of 450 km will be appropriate to the limitation of _c about 1 g cm^–3. Considering the accuracy obtained in space explorations, and the compressibility and the quasi-homogeneity of the Moon, we suggest that the parameters C ₂₀, , , a, and GM of the Moon should define as primary constants, but C ₂₂ and C/Ma ² as derived constants. Therefore, the ratio of mass of Moon to that of Earth in the IAU (1976) system of astronomical constants will become a deducible constant.     

Internal rotation of the Sun as inferred from GONG observations

Helioseismology is a direct and most informative method of studying the structure and dynamics of the Sun. Determining the internal differential rotation of the Sun requires that the frequencies of its eigentones be estimated with a high accuracy, which is possible only on the basis of continuous long-term observations. The longest quasi-continuous series of data have been obtained by the Global Oscillation Network Group (GONG). The parameters of each individual mode of solar acoustic oscillations with low spherical degrees l=0, 1, 2, 3, 4, 5, 6 are determined by using 1260-day-long series of GONG observations. The mean frequency splitting by rotation for the modes of each radial order n is calculated by using all possible combinations between the eigenfrequencies in multiplets. As a result, it has become possible to statistically estimate the splitting and its measurement errors for the modes of each radial order. The mean splitting for each given degree l=1–6 is presented under the assumption of its independence of oscillation frequency, which holds for the achieved accuracy. The frequencies and splittings for the modes with low spherical degrees l, together with the MDI group results for higher degrees l, are used to invert the radial profile of solar angular velocity. Using the SOLA method to solve the inverse problem of restoring the rotation profile has yielded solutions sensitive to the deepest stellar interiors. Our results indicate that the solar core rotates faster than the surface, and there may be a local minimum in angular velocity at its boundary.     

The spatial and temporal distribution of lunar mare basalts as deduced from analysis of data for lunar meteorites

In this work we analyze data for lunar meteorites with emphasis on the spatial and temporal distribution of lunar mare basalts. The data are mostly from the Lunar Meteorite Compendium (http://www-curator.jsc.nasa.gov/antmet/lmc/contents.cfm cited hereafter as Compendium) compiled by Kevin Righter, NASA Johnson Space Center, and from the associated literature. Analysis of the data showed that (i) a significant part of the lunar meteorite source craters are not larger than hundreds of meters in diameter; (ii) cryptomaria seem to be rather abundant in lunar highlands; (iii) the ratios of lunar meteorites belonging to three broad petrologic groups (mare basalt/gabbro, feldspatic highland breccias, and mingled breccias which are a mixture of mare and highland components) seem to be roughly proportional to the areal distribution of these rocks on the lunar surface; and (iv) the meteorite mare basalt ages show a range from ～2.5 to 4.3 Ga and fill the gaps in the Apollo/Luna basalt age distribution. The ages of mare basalt clasts from mingled breccias seem to be systematically higher than those of “normal” mare basalts, which supports the suggestion that mingled breccias originated mostly from cryptomaria.     

The origin of young mare basalts inferred from lunar meteorites Northwest Africa 4734, 032, and LaPaz Icefield 02205

Northwest Africa (NWA) 4734 is an unbrecciated basaltic lunar meteorite that is nearly identical in chemical composition to basaltic lunar meteorites NWA 032 and LaPaz Icefield (LAP) 02205. We have conducted a geochemical, petrologic, mineralogic, and Sm‐Nd, Rb‐Sr, and Ar‐Ar isotopic study of these meteorites to constrain their petrologic relationships and the origin of young mare basalts. NWA 4734 is a low‐Ti mare basalt with a low Mg* (36.5) and elevated abundances of incompatible trace elements (e.g., 2.00 ppm Th). The Sm‐Nd isotope system dates NWA 4734 with an isochron age of 3024 ± 27 Ma, an initial ε_Nd of +0.88 ± 0.20, and a source region ¹⁴⁷Sm/¹⁴⁴Nd of 0.201 ± 0.001. The crystallization age of NWA 4734 is concordant with those of LAP 02205 and NWA 032. NWA 4734 and LAP 02205 have very similar bulk compositions, mineral compositions, textures, and ages. Their source region ¹⁴⁷Sm/¹⁴⁴Nd values indicate that they are derived from similar, but distinct, source materials. They probably do not sample the same lava flow, but rather are similarly sourced, but isotopically distinct, lavas that probably originate from the same volcanic complex. They may have experienced slightly different assimilation histories in route to eruption, but can be source‐crater paired. NWA 032 remains enigmatic, as its source region ¹⁴⁷Sm/¹⁴⁴Nd definitively precludes a simple relationship with NWA 4734 and LAP 02205, despite a similar bulk composition. Their high Ti/Sm, low (La/Yb)_N, and Cl‐poor apatite compositions rule out the direct involvement of KREEP. Rather, they are consistent with low‐degree partial melting of late‐formed LMO cumulates, and indicate that the geochemical characteristics attributed to urKREEP are not unique to that reservoir. These and other basaltic meteorites indicate that the youngest mare basalts originate from multiple sources, and suggest that KREEP is not a prerequisite for the most recent known melting in the Moon.     

Compositional diversity of ordinary chondrites inferred from petrology,bulk chemical,and oxygen isotopic compositions of the lowest FeO ordinary chondrite,Yamato 982717

We performed a petrologic, geochemical, and oxygen isotopic study of the lowest FeO ordinary chondrite (OC), Yamato (Y) 982717. Y 982717 shows a chondritic texture composed of chondrules and chondrule fragments, and mineral fragments set in a finer grained, clastic matrix, similar to H4 chondrites. The composition of olivine (Fa_{11.17 ± 0.48 (1σ)}) and low‐Ca pyroxene (Fs_{11.07 ± 0.98 (1σ)}Wo_{0.90 ± 0.71(1σ)}) is significantly more magnesian than those of typical H chondrites (Fa_16.0‐20, Fs_14.5‐18.0), as well as other known low‐FeO OCs (Fa_12.8‐16.7; Fs_13‐16). However, the bulk chemical composition of Y 982717, in particular lithophile and moderately volatile elements, is within the range of OCs. The bulk siderophile element composition (Ni, Co) is within the range of H chondrites and distinguishable from L chondrites. The O‐isotopic composition is also within the range of H chondrites. The lack of reduction textures indicates that the low olivine Fa content and low‐Ca pyroxene Fs content are characteristics of the precursor materials, rather than the result of reduction during thermal metamorphism. We suggest that the H chondrites are more compositionally diverse than has been previously recognized.     

Geochemical studies of the SUBO 18 (Enkingen) drill core and other impact breccias from the Ries crater,Germany

Suevite and melt breccia compositions in the boreholes Enkingen and Polsingen are compared with compositions of suevites from other Ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis. No significant differences in average chemical compositions for the various drill cores or surface samples are noted. Compositions of suevite and melt breccia from southern and northeastern sectors of the Ries crater do not significantly differ. This is in stark contrast to the published variations between within‐crater and out‐of‐crater suevites from northern and southern sectors of the Bosumtwi impact structure, Ghana. Locally occurring alteration overprint on drill cores—especially strong on the carbonate‐impregnated suevite specimens of the Enkingen borehole—does affect the average compositions. Overall, the composition of the analyzed impact breccias from Ries are characterized by very little macroscopically or microscopically recognized sediment‐clast component; the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components. The Polsingen breccia is significantly enriched in a dioritic clast component. Overall, chemical compositions are of intermediate composition as well, with dioritic‐granodioritic silica contents, and relatively small contributions from mafic target components. Selected suevite samples from the Enkingen core have elevated Ni, Co, Cr, and Ir contents compared with previously analyzed suevites from the Ries crater, which suggest a small meteoritic component. Platinum‐group element (PGE) concentrations for some of the enriched samples indicate somewhat elevated concentrations and near‐chondritic ratios of the most immobile PGE, consistent with an extraterrestrial contribution of 0.1–0.2% chondrite‐equivalent.     

Chronology,geochemistry, and petrology of a ferroan noritic anorthosite clast from Descartes breccia 67215: Clues to the age,origin, structure,and impact history of the lunar crust

Abstract— The petrology, major and trace element geochemistry, and Nd‐Ar‐Sr isotopic compositions of a ferroan noritic anorthosite clast from lunar breccia 67215 have been studied in order to improve our understanding of the composition, age, structure, and impact history of the lunar crust. The clast (designated 67215c) has an unusually well preserved igneous texture. Mineral compositions are consistent with classification of 67215c as a member of the ferroan anorthositic suite of lunar highlands rocks, but the texture and mineralogy show that it cooled more rapidly and at shallower depths than did more typical ferroan anorthosites (FANs). Incompatible trace element concentrations are enriched in 67215c relative to typical FANs, but diagnostic signatures such as Ti/Sm, Sc/Sm, plagiophile element ratios, and the lack of Zr/Hf and Nb/Ta fractionation show that this cannot be due to the addition of KREEP. Alternatively, 67215c may contain a greater fraction of trapped liquid than is commonly present in lunar FANs. ¹⁴⁷Sm‐¹⁴³Nd isotopic compositions of mineral separates from 67215c define an isochron age of 4.40 ± 0.11 Gyr with a near‐chondritic initial ε¹⁴³_Nd of +0.85 ± 0.53. The ⁴⁰Ar‐³⁹Ar composition of plagioclase from this clast records a post‐crystallization thermal event at 3.93 ± 0.08 Gyr, with the greatest contribution to the uncertainty in this age deriving from a poorly constrained correction for lunar atmosphere ⁴⁰Ar. Rb‐Sr isotopic compositions are disturbed, probably by the same event recorded by the Ar isotopic compositions. Trace element compositions of FANs are consistent with crystallization from a moderately evolved magma ocean and do not support a highly depleted source composition such as that implied by the positive initial ε¹⁴³_Nd of the ferroan noritic anorthosite 62236. Alternatively, the Nd isotopic systematics of lunar FANs may have been subject to variable degrees of modification by impact metamorphism, with the plagioclase fraction being more strongly affected than the mafic phases. ¹⁴⁷Sm‐¹⁴³Nd isotopic compositions of mafic fractions from the 4 ferroan noritic anorthosites for which isotopic data exist (60025, 62236, 67016c, 67215c) define an age of 4.46 ± 0.04 Gyr, which may provide a robust estimate for the crystallization age of lunar ferroan anorthosites.     

Longitude variations of solar magnetic fields of different intensity in cycle 23 as inferred from the SOHO/MDI data

SOHO/MDI magnetograms have been used to analyze the longitude distribution of the squared solar magnetic field 〈B ²〉 in the activity cycle no. 23. The energy of the magnetic field (〈B ²〉) is shown to change with longitude. However, these variations hardly fit the concept of active longitudes. In the epochs of high solar activity, one can readily see a relationship between longitude variations of the medium-strong ((|B| > 50 G or |B| > 100 G) and relatively weak (|B| ≤ 50 G or |B| ≤ 100 G) fields at all latitudes. In other periods, this relationship is revealed mainly at the latitudes not higher than 30°. The background fields (|B| ≤ 25 G) also display longitude variations, which are, however, not related to those of the strong fields. This makes us think that the fields of solar activity are rather inclusions to the general field than the source of the latter.     

The petrology,geochemistry, and age of lunar regolith breccias Miller Range 090036 and 090070: Insights into the crustal history of the Moon

Meteorites ejected from the surface of the Moon as a result of impact events are an important source of lunar material in addition to Apollo and Luna samples. Here, we report bulk element composition, mineral chemistry, age, and petrography of Miller Range (MIL) 090036 and 090070 lunar meteorites. MIL 090036 and 090070 are both anorthositic regolith breccias consisting of mineral fragments and lithic clasts in a glassy matrix. They are not paired and represent sampling of two distinct regions of the lunar crust that have protoliths similar to ferroan anorthosites. ⁴⁰Ar‐³⁹Ar chronology performed on two subsplits of MIL 090070,33 (a pale clast impact melt and a dark glassy melt component) shows that the sample underwent two main degassing events, one at ~3.88 Ga and another at ~3.65 Ga. The cosmic ray exposure data obtained from MIL 090070 are consistent with a short (~8–9 Ma) exposure close to the lunar surface. Bulk‐rock FeO, TiO₂, and Th concentrations in both samples were compared with 2‐degree Lunar Prospector Gamma Ray Spectrometer (LP‐GRS) data sets to determine areas of the lunar surface where the regolith matches the abundances observed on the sample. We find that MIL 090036 bulk rock is compositionally most similar to regolith surrounding the Procellarum KREEP Terrane, whereas MIL 090070 best matches regolith in the feldspathic highlands terrane on the lunar farside. Our results suggest that some areas of the lunar farside crust are composed of ferroan anorthosite, and that the samples shed light on the evolution and impact bombardment history of the ancient lunar highlands.     

Geochemistry and petrology of lunar meteorite Queen Alexandra Range 94281, a mixed mare and highland regolith breccia,with special emphasis on very-low-titanium mafic components

Abstract— Queen Alexandra Range (QUE) 94281, a lunar meteorite recently discovered in Antarctica, is a glassy-matrix, clast-rich regolith breccia containing a mixture of mafic, volcanic-glass and gabbroic constituents and a diverse set of highland constituents. In thin section, the clast assemblage is dominated by coarse mineral debris from a shallow intrusive or hypabyssal setting, or from deep within a thick mare flow. Abundant coarse-grained pyroxene clasts have fine-scale exsolution lamellae and compositions similar to pyroxenes of known lunar very-low-Ti (VLT) basalts and other lunar meteorites of basaltic composition. Pyroxene compositions follow Fe-enrichment extending to hedenbergite, which is associated with fayalite and cristobalite, indicating slow cooling. We refer to the protolith of the crystalline VLT component as VLT gabbro. Fragments of pyroclastic glasses that have high Fe and low Ti concentrations, similar to the pyroclastic green glasses known from Apollo samples, are common. Lithic clasts include abundant subrounded, glassy to cryptocrystalline, aluminous (～17–30 wt% Al₂O₃) KREEP-poor melt breccias of highland origin and a variety of other feldspathic impactites. On the basis of composition of our subsamples, QUE 94281 consists of ～54 wt% mafic or “mare” components and 46 wt% feldspathic or “highland” components. The bulk composition of QUE 94281 is similar to that of Yamato (Y) 793274, but QUE 94281 has slightly greater concentrations of some siderophile elements and slightly lower concentrations of those elements contributed mainly by mafic constituents. Differences in siderophile element concentrations are consistent with longer surface exposure of QUE 94281. Minor differences in trace element variations of subsamples of the two meteorites suggest subtle differences in the composition of their highland constituents. Nonetheless, the overall similarity of compositions supports the possibility that they were ejected from the same source region on the Moon. The crystalline VLT component of QUE 94281 differs from those known from Apollo 17 and Luna 24 VLT lithologies and from that of basaltic breccia Elephant Moraine (EET) 87521. The VLT-gabbro component and the ferroan VLT volcanic glasses in QUE 94281 have compositions that may be petrogenetically related by derivation from a common picritic parent composition, represented by an ultramafic glass found in QUE 94281.     

Interplanetary magnetic field structure and solar wind parameters as inferred from solar magnetic field observations and by using a numerical 2-D MHD model

An attempt is made to infer parameters of the solar corona and the solar wind by means of a numerical, self-consistent MHD simulation. Boundary conditions for the magnetic field are given from the observations of the large-scale magnetic field at the Sun. A two-region, planar (the ecliptic plane is assumed) model for the solar wind flow is considered. Region I of transonic flow is assumed to cover the distances from the solar surface up to 10R _S (R _S is the radius of the Sun). Region II of supersonic, super-Alfvénic flow extends between 10R _S and the Earth's orbit. Treatment for region I is that for a mixed initial-boundary value problem. The solution procedure is similar to that discussed by Endler (1971) and Steinolfson, Suess, and Wu (1982): a steady-state solution is sought as a relaxation to the dynamic equilibrium of an initial state. To obtain a solution to the initial value problem in region II with the initial distribution of dependent variables at 10R _S (deduced from the solution for region I), a numerical scheme similar to that used by Pizzo (1978, 1982) is applied. Solar rotation is taken into account for region II; hence, the interaction between fast and slow solar wind streams is self-consistently treated. As a test example for the proposed formulation and numerical technique, a solution for the problem similar to that discussed by Steinolfson, Suess, and Wu (1982) is obtained. To demonstrate the applicability of our scheme to experimental data, solar magnetic field observations at Stanford University for Carrington rotation 1682 are used to prescribe boundary conditions for the magnetic field at the solar surface. The steady-state solution appropriate for the given boundary conditions was obtained for region I and then traced to the Earth's orbit through region II. We compare the calculated and spacecraft-observed solar wind velocity, radial magnetic field, and number density and find that general trends during the solar rotation are reproduced fairly well although the magnitudes of the density in comparison are vastly different.     

Compositional anomaly of Ganymede and Callisto among the ice satellites as inferred from impact crater morphology

Differences in crater morphology between the Jovian and Saturnian-Uranian ice satellites implies a weaker surface strength for Ganymede and Callisto and thus a more concentrated composition of water. This compositional anomaly among the ice satellites is apparently due to a more complete migration of heavy material toward the inner part of the pre-planetary disc of the Jovian system than occurred in the discs of the Saturnian and Uranian systems.