Lunar MareBroad low plains surrounded by basin-forming mountains, originally thought to be a sea (pl. maria). This term is applied to the basalt-filled impact basins common on the face of the Moon visible from Earth. BasaltBasalt is the most common extrusive igneous rock on the terrestrial planets. For example, more than 90% of all volcanic rock on Earth is basalt. The term basalt is applied to most low viscosity dark silicate lavas, regardless of composition. Basalt is a mafic, extrusive and fine grained igneous rock unbrecciated, low-Ti
Found October 1999 near 30° 22′ N., 5° 3′ W. A small 300 g stone was found by an association of European collectors at a location west of the Kem Kem plateau in Morocco. A second stone weighing 156 g and designated NWA 479 was recovered a year later. It is both chemically and petrographically indistinguishable from NWA 032, and the two stones are obviously paired. Northwest Africa 032 is a previously-unsampled, unbrecciated, interior mare basalt that was not exposed to solar windSupersonic flow of high-speed charged particles continuously blowing off a star (mostly e- and p+). When originating from stars other than the Sun, it is sometimes called a "stellar" wind. The solar wind may be viewed as an extension of the corona into interplanetary space. The solar wind emanates radially implanted gases.
Over the course of several ANSMET seasons, six paired basaltic lunar meteoritesAchondrite meteorites from the surface of the Moon. Most were found in the hot deserts of northern Africa and Oman and others were found in the cold desert of Antarctica, although one, a 19-gram specimen, was recovered in 1990 from Calcalong Creek, Australia. These stones are of great importance because, with a combined weight of ~1.93 kg were recovered from the Antarctic LaPaz Icefield (LAP). Through chemical, mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous, and petrographic comparisons, including CSD measurements, as well as crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. and CRE age determinations, the LAP lunaites have been shown to be almost certainly source craterBowl-like depression ("crater" means "cup" in Latin) on the surface of a planet, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by volcanic activity, though some are due to cryovolcanism. paired with NWA 032/479. However, some differences do exist between the LAP and the NWA samples. There is a disparity in their mineral compositions, considered to be the result of greater fractionationConcentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process. in the LAP samples following lavaHot molten or semifluid rock derived from a volcano or surface fissure from a differentiated and magmatically active parent body. extrusion. In addition, the LAP samples have larger grain sizes than those in the NWA samples, indicative of crystallization in a more slowly-cooled location within a common parental magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava.. Another findMeteorite not seen to fall, but recovered at some later date. For example, many finds from Antarctica fell 10,000 to 700,000 years ago. from Northwest Africa, NWA 4734, has a similar age as well as chemical characteristics that overlap those of NWA 032/479 and the LAP 02205 pairing group (e.g., these meteorites have 3% TiO2; Korotev, 2007), and all of these meteorites are likely source crater paired but derive from distinct parental source lava flows in a common volcanicIgneous rock that forms from cooling magma on the surface of a planet or asteroid. complex (Elardo et al., 2012, 2014).
The mineralogy of NWA 032 consists of phenocrysts of olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion, pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category., and chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. in a very fine-grained matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. of radiating pyroxene and feldsparAn alumino-silicate mineral containing a solid solution of calcium, sodium and potassium. Over half the Earth’s crust is composed of feldspars and due to their abundance, feldspars are used in the classification of igneous rocks. A more complete explanation can be found on the feldspar group page. crystals. The olivine phenocrysts (the larger light-colored crystals seen in the photo above) make up ~8 vol% of the meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and and have measurments of up to 1.3 mm across. The pyroxene phenocrysts constitute ~5 vol% of the rock and constitute a larger range of grain sizes, some appearing as small as ~0.2 mm. The fine- to medium-grained matrix is comprised of pyroxene, primarily in the form of augiteHigh-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, that occurs in many igneous rocks, particularly those of basaltic composition. In order to be considered augite, the clinopyroxene must contain 20 to 45 mol % of calcium (Wo20 - 45). An important and unique Martian meteorite is NWA 8159, that has been classified as an augite basalt. and pigeoniteLow-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, found as a major mineral in eucrites and shergottites. In order to be considered pigeonite, the clinopyroxene must contain 5 to 20 mol % of calcium (Wo5 - 20). Chondrites of petrologic types 4 and below contain significant low-Ca clinopyroxene. During metamorphism to higher temperatures, all existing. Accessory phases include ilmeniteTi-Fe oxide, TiFeO3, found in achondrites, lunar mare basalts, and shergottites. Ilmenite forms as a primary mineral in mafic igneous rocks. It crystallizes relatively early out of a magma before most of the other minerals, and as a result, the heavier crystals of ilmenite precipitate to the bottom of the magma, troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites., and trace metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn. A low abundance of late-stage mesostasisLast material to crystallize/solidify from a melt. Mesostasis can be found in both chondrules, in the matrix around chondrules, and in achondrites as interstitial fine-grained material such as plagioclase, and/or as glass between crystalline minerals. (~0.3 vol%) is present. High-silica glass is found in the abundant shock veins that permeate the stone (~6 vol%).
Crystallization of the olivine and pyroxene phenocrysts that would eventually compose the NWA and LAP samples occurred over a temperature range of ~200°C and over a time interval from a few days up to a month under slow-cooling conditions (<2°C/hour), probably within a shallow dyke or sill (Day and Taylor, 2007). Initially, the olivine and chromite phenocrysts crystallized slowly under low pressure conditions, producing the more typical steep zoning profiles reflected in decreasing Mg# from coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. to rim, with a surrounding FeO-rich rim. Burger et al. (2009) ascertained that the pyroxene phenocrysts show evidence of an additional stage of crystallization from a melt with a fluctuating Ca composition, alternating between pigeonite and augite. Oscillatory zoning occurs in both olivine and pyroxene; in olivine this banding is thought to be caused by rapid crystal growth accompanied by slower P diffusionMovement of particles from higher chemical potential to lower chemical potential (chemical potential can in most cases of diffusion be represented by a change in concentration). Diffusion, the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. Because diffusion is thermally activated, coefficients for diffusion, known as ‘solute trapping’, while in pyroxene the development of a coarser oscillatory banding profile is considered to be the result of convectionTransfer of heat energy by moving material. Temperatures increases with depth in planetary objects. Deep hot less-dense material physically rises and cools, releasing heat and becoming denser. The now cooler denser material sinks back into deeper regions, where it will be reheated and rise again. Convection is an important mechanism cycling associated with variable temperature regimes within the magma chamber (Elardo and Shearer, 2013). Some phenocrysts contain cores with a primitive composition consistent with that predicted for the parental source magma (Fagan et al., 2002).
It has been inferred that this low viscosityThe degree to which a liquid resists flow. High-viscosity liquids (e.g., "molasses in winter") resist flow to a great degree. More formally, viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress. Water has a low kinetic viscosity of 0.6959 magma was then emplaced upon the surface, perhaps 10–20 m thick, where the LAP samples experienced uniformly slow cooling at rates of ~0.2°C/hour within the middle of the flow and crystallized within ~40 days. At the same time, the slowly-cooled phenocrysts that would become the NWA samples were incorporated within the less insulated magma layers, perhaps the upper margin, where they experienced rapid cooling at rates of 20–60°C/hour. This rock solidified rapidly at up to ~60°C/hour, producing the characteristic plumose matrix textures in <10 hours (Fagan et al., 2002; Zeigler et al., 2005; Anand et al., 2006; Joy et al., 2006; Day and Taylor, 2007).
This petrogenetic model was expounded upon by Day and Taylor (2007) to account for other lunar meteorites and to explore the possibility that they also formed within the same differentiated stratigraphic unit as the NWA and LAP samples. Based on chemical compositions, mineralogies, textures, cooling rates, and crystallization and CRE ages, it was initially considered that the lunar pairing group of NWA 773 might represent the more rapidly cooled cumulate-rich base of this magma unit, with the more rapidly cooled basaltic component, as represented by NWA 3160, deriving from the lowermost layer adjacent to local pre-existing rock. However, the finding that NWA 773 was formed from a KREEPy reservoir in contrast to the non-KREEPy source for the NWA 032/LAP/NWA 4734 mare basalt suite rules out such a relationship (Elardo et al., 2014).
Shock pressures greater than 25 GPa are revealed by the melt pockets and veins, maskelynized feldspar, and mosaisicm in olivine. High-pressure polymorphs of olivine are present in impact melts, including ringwooditeHigh-pressure olivine polymorph with a spinel structure that is found in highly shocked meteorites (above ~50 GPa, shock level > S5) and the Earth's transition zone mantle (~13 GPa). Under even higher pressure in the lower mantle (~24 GPa), ringwoodite decomposes into perovskite (Mg,Fe)SiO3, and magnesiowüstite (Mg,Fe)O, whose properties are and wadsleyiteHigh pressure polymorph of olivine, β-Mg2SiO4, found on Earth and in some meteorites. It is thought to make up 50% or more of Earth's mantle between depths of 400 and 525 km. Wadsleyite transforms into ringwoodite at high pressure, but the exact pressure depends strongly on composition. At lower pressures,. Northwest Africa 032 has a low-Ti composition often associated with an earlier-formed basaltic unit. It represents a unique crystalline mare basalt source containing high olivine phenocryst abundances. A relatively short terrestrial age of ~5 t.y. has produced only very minor terrestrial weathering (W0), evidenced by a thin calcite covering on the exterior with some calcite veining, but with most of the interior remaining virtually free of alteration. Typical for many hot-desert meteorite finds, the trace elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of Ba is enriched in NWA 032 compared to Apollo basalts.
Subsequent to the finding of NWA 032, a 154 g mare basalt meteorite, Dhofar 287A, was found in the desert of Oman. These two mare basalt lithologies exhibit some close similarities as well as some important differences (Anand et al., 2003). They are both low-Ti mare basalts similar to Apollo 12 and 15 basalts. However, Dhofar 287A contains a higher abundance of olivine phenocrysts (~20 vol% vs. ~8 vol%) in a larger size range (>2 mm vs. 0.4 mm), and which are more highly zoned compared to those in NWA 032. It also contains a larger vol% of late-stage mesostasis (~3 vs. 0.3), some of which is surrounded by highly Fe-enriched pyroxferroite. Moreover, Dhofar 287A has a coarser-grained texture than NWA 032 (50–100 µm vs. <20 µm, respectively), inferring a faster cooling rate for the latter. Compared to NWA 032, Dhofar 287A has a REEOften abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. pattern consistent with the assimilation of a KREEPLunar igneous rock rich in potassium (K), rare-earth elements (REE), phosphorus (P), thorium, and other incompatible elements. These elements are not incorporated into common rock-forming minerals during magma crystallization, and become enriched in the residual magma and the rocks that ultimately crystallize from it. component, although a limited association of NWA 032 with a KREEP component (similar to the La Paz basalt) has been proposed by Barrat et al. (2005) to explain certain anomalous trace element ratios. As a further distinction between the two, NWA 032 has a much greater abundance of impact melt veins. There is ample evidence to indicate that these two mare lithologies were derived from distinct source regions, and have experienced different petrogenetic histories.
The International Union of Geological Sciences—Subcommission on the Systematics of Igneous Rocks, having established a Working Party on the classification of lunar rocks, has adopted a Classification System for Lunar Rocks. The terms ‘highland’ and ‘mare’, which were originally established as geographical terms based on the surface morphology of the Moon and its resulting albedoRatio of the amount of light reflected by an object and the amount of incident light. Albedo is used as a measure of the reflectivity or intrinsic brightness of an object. A white, perfectly reflecting surface has an albedo of 1.0 while a black perfectly absorbing surface would have an, are now utilized on a geochemical basis composing two subdivisions of the broader igneous group.
Mare basalts cover ~17% of the lunar surface but account for only ~1% of the total volume of the crustOutermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the. They are largely the result of eruptions within basins located asymmetrically on the nearside of the Moon, and predominantly in the western region including the Oceanus Procellarum and Mare Imbrium basins. It has been argued that this asymmetry is the result of a complex sequence of events that began within the first 50 m.y. of Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. history. In the upper levels of the fully enveloping magma oceanCompletely molten surfaces of terrestrial planets or moons that formed soon after accretion. Samples returned by the Apollo missions provide evidence of a lunar magma ocean, crystallization of which produced a stratified Moon with a low-density crust formed by accumulation of the mineral plagioclase overlying a higher density mantle of, which extended to a depth of at least 500 km, crystallization proceeded until reaching a point of 82–94% completion. At this time the cumulateIgneous rock composed of crystals that have grown and accumulated (often by gravitational settling) in a cooling magma chamber. precursor to the low-Ti basalts was formed. Finally, a low-degree partial melt from this precursor material underwent fractionation to form the low-Ti mare basalts. The low-Ti NWA 032 is similar to basalts collected by Apollo 12 and Apollo 15 with respect to Ti content, but not with respect to major element, REE, and LREE compositions (e.g., REE abundances are enriched compared to that of Apollo basalts). The parent melt is thought to have had a bulk composition similar to that of the Apollo 15 low-Ti yellow picritic glasses, representing the residue that remained after ~20% olivine had crystallized at low pressure (Zeigler et al., 2005). Despite the finding of elevated incompatible element abundances in the bulk rock, isotopic compositions indicate that the parental source of NWA 032 was highly depleted in incompatible elements; this discrepancy is not yet completely understood.
The more evolved material that was the precursor of the high-Ti basalts was not produced until after 95% crystallization had occurred; consequently, trapped residual melt occurs only in high-Ti basalts. The most widely accepted formation scenario suggests that following the crystallization of the lunar magma ocean, a gravitationally unstable, Ti-rich, cumulate ilmenite layer was crystallized beneath the crust. Having a greater densityMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much than the peridotite mantleMain silicate-rich zone within a planet between the crust and metallic core. The mantle accounts for 82% of Earth's volume and is composed of silicate minerals rich in Mg. The temperature of the mantle can be as high as 3,700 °C. Heat generated in the core causes convection currents in below it, this ilmenite began to founder and sink to the deep interior, bringing with it the heat-producing elements U and Th. Situated above a small metallic core, this ilmenite layer experienced thermal expansion. Coupled with a lack of convection in the overlying peridotite mantle preventing the removal of heat, an eventual instability occurred leading to the migration of this molten plume to one hemisphere of the Moon and to the formation of a stable, cumulus stratigraphy. The melting, and eventual convective mixing, of this Ti-rich ilmenite with the peridotite mantle, resulted in the olivine-bearing, Ti-rich basalt that was eventually carried to the surface through volcanism. An alternative scenario argues that a negatively-buoyant, high-Ti cumulate could not have formed, but instead, the Ti-rich ilmenite cumulate layer became gravitationally unstable to the point of sinking due to assimilation of 10–20% olivine prior to crystallization.
The lunar mare basalts can help constrain the origin and formation history of the Moon and reveal information about the magma ocean phase. The magma ocean is consistent with the theory in which the Moon formed as a result of an impact on the proto-Earth by a differentiated Mars-sized projectile, which was given the name ‘Theia’ after the mythological Greek Titan who gave birth to the Moon goddess ‘Selene’. During this collision, which occurred 30–110 m.y. after the start of the solar systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with (Yin et al., 2002; Kleine et al., 2005), the metallic core accreted to Earth while the silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the mantle eventually became stabilized in orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around. Alternatively, a modified fissionBreaking apart of a body into smaller fragments. In nuclear physics, fission refers to splitting of a heavy atomic nucleus into two or more lighter nuclei with an associated release of energy. The mass of the nucleus before fission is greater than the combined masses of the resulting fragments; the model involving a rapidly rotating proto-Earth and a nuclear explosion is propounded by Westrenen et al. (2012).
Abundances of platinum group elementsElements with geochemical properties similar to Pt (platinum) including Ru, Rh, Pd, Os, Ir, and sometimes Au. These occur in nature in close association with one another and with Ni and Cu. They are among the least abundant of the Earth’s naturally occurring elements. (PGEs: Ru, Rh, Pd, Ir, Pt) are unique relative to terrestrial and martian basalts. One particular lunar signature is the depletion of Pd due to its partitioningThe tendency of elements to prefer one mineral phase relative to another or to preferentially enter the solid or remain in the liquid during crystallization. into Fe-metal during the magma ocean phase under conditions of low oxygen fugacityUsed to express the idealized partial pressure of a gas, in this case oxygen, in a nonideal mixture. Oxygen fugacity (ƒO2) is a measure of the partial pressure of gaseous oxygen that is available to react in a particular environment (e.g. protoplanetary disk, Earth's magma, an asteroid's regolith, etc.) and (related to the partial pressure of available oxygenElement that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only). The correlation between high-PGE abundances and the high-Ti basalts suggests that the PGEs were concentrated in the same residue from which the high-Ti basalts were derived.
A study of Li abundances and isotopic compositions in NWA 479 phenocrysts, conducted by Barrat et al (2005), led to their consideration that the Moon may be enriched in 7Li, possibly the result of volatilization and loss of 6Li during the Moon’s impact-generated formation. The strong variability of Li isotopic compositions between phenocryst core and rim in NWA 479 is thought to have been established through diffusion processes.
Northwest Africa 032 has the highest Th:REE ratio of any other mare basalt, with probable source areas considered to be (in decreasing order of probability) Mare Humorum, Mare Fecunditatis, western Mare Serenitatis, Mare Crisium, and far western Oceanus Procellarum. Spacecraft have found that basalts are not present in all topographic low areas, but instead, reservoirs of basaltic magma are confined at great depth with eruptions being contingent on a combination of factors including the crustal thickness, the concentration of heat-producing elements (K–U–Th), and the extent of the underlying magma columns. Based on spectral data, it was determined that many different basalt units exist within individual mariaBroad low plains surrounded by basin-forming mountains, originally thought to be a sea (pl. maria). This term is applied to the basalt-filled impact basins common on the face of the Moon visible from Earth. , these representing a wide range of crystallization ages, ranging from ~4.35 b.y. (components of the lunar brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Kalahari 009) to as young as ~1.3 b.y. Crater counting methods indicate some maria could be as young as 1 b.y. old (G. T. Taylor, 2007).
Northwest Africa 032 has a mid-range crystallization age of 2.779 (±0.014) b.y. (K–Ar; Fernandes et al., 2003), making it one of the youngest mare basalts in our collections and identical within error margins of the unpaired lunar basalt NWA 8632 (Fagan et al., 2018). This age has been interpreted by some as reflecting the shock event that produced the impact-melt veins rather than its crystallization age. However, a concordant Rb–Sr age of 2.852 (±0.065) b.y. and Sm–Nd age of 2.931 (±0.92) b.y. was obtained for NWA 032 by Borg et al. (2007, 2009), which dispute the association of the K–Ar age with a late shock event. K–Ar dating of basaltic lithologies in Kalahari 009 conducted by Fernandes et al. (2007) revealed the youngest age for any lunar basalt measured thus far, indicating an age of <1.70 (±0.04) b.y. However, utilizing more precise U–Pb systematics within phosphate grains, a chronometer which is not prone to shock resetting effects, an age of 4.35 (± 0.15) b.y. was obtained for this meteorite (Terada et al., 2007).
A look at the ages of the various lunar meteorites reveals that none have a bulk rock age older than ~3.85 b.y., upholding the lunar cataclysm hypothesis. This hypothesis suggests that a large number of impacts occurring over a brief time interval (beginning ~3.9 b.y. ago and lasting 200 m.y.) initiated a metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. phase over much of the Moon’s surface. Noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. studies indicate that NWA 032 resided within the lunar regolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles). for 207 (±43) m.y., and was subsequently buried to an appropriate shielding depth. After its ejection from the Moon, the NWA 032 meteoroidSmall rocky or metallic object in orbit around the Sun (or another star). spent 42 (±5) t.y. in transitWhen a small celestial body moves in front of a much larger one (as when Mercury or Venus appears in silhouette against the solar disk or when a satellite passes in front of Jupiter or Saturn). The shadow of a satellite may also transit the disk of its primary. to Earth (Lorenzetti et al., 2005). According to Nishiizumi and Caffee (2010), this relatively short Moon–Earth transit time would be consistent with a launch from a depth of <1–4.7 m. The meteorite then resided for another ~5 t.y. on Earth (Nishiizumi, 2003). This was a small meteoroid, having a pre-atmospheric size of less than 10 cm in diameter. The presence of solar cosmic ray produced 26Al is indicative of a very low ablationGradual removal of the successive surface layers of a material through various processes. • The gradual removal and loss of meteoritic material by heating and vaporization as the meteoroid experiences frictional melting during its passage through the atmosphere. The resulting plasma ablates the meteor and, in cases where a meteor rate, consistent with a low entry velocity and/or a low entry angle.
The specimen pictured above is a sub-gram partial slice of Northwest Africa 032. Shown in the top photo below is a high-resolution close-up photo showing the large olivine phenocrysts surrounded by the feathery feldspathic crystals within the matrix of this meteorite. Photo by Walt Radomsky Courtesy of R. A. Langheinrich Meteorites For more information on the lunar basalt NWA 032, read the PSRD article by G. Jeffrey Taylor—’The Growing Diversity of Lunar Basalts’, Sept. 2009, from this link. In addition, extensive information can be found on the lunar meteorite website of the Department of Earth Sciences, Washington University. Additional details about the linkage of NWA 032, NWA 4734, and the LAP pairing group mare basalts can be found on the NWA 4734 page.