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Mössbauer spectroscopy of Apollo 11 samples
Abstract
Apollo 11 lunar dust, breccia and igneous rocks, using Mossbauer spectroscopy and petrographic techniques
... The lack of atmosphere on the Moon allows solar wind (most of which is H) to reach the lunar surface and be implanted into the top tens to hundreds of nanometers of layer of surface grains, which would reduce any ferric iron to lower valence or even metallic iron during impact events (2). Iron in Apollo samples is dominantly ferrous (Fe 2+ ) or metallic, and the upper limit of ferric iron-bearing materials is less than 1 weight % (wt %) [e.g., (3)], which reflects the highly reduced state of the Moon. ...
... However, the detection of ferric iron-bearing species on the Moon has remained elusive in sample analyses and remote observations. Ferric iron-bearing minerals FeOOH (goethite, lepidocrocite, and akaganeite), Fe 2 O 3 (hematite and maghemite), and Fe 3 O 4 (magnetite) were found in some Apollo samples [e.g., (3,10,11,12)], but some of these studies argued that those alteration phases were products of possible terrestrial contamination [e.g., (10)]. The Solid State Imager (SSI) onboard the Galileo mission detected a possible ferric absorption near 0.7 m at high latitudes of the Moon (>58°S) during its flyby, but that study could not determine whether that absorption was caused by phyllosilicates, ilmenite, ferric iron-bearing clinopyroxene, or other species (13). ...
Hematite (Fe 2 O 3 ) is a common oxidization product on Earth, Mars, and some asteroids. Although oxidizing processes have been speculated to operate on the lunar surface and form ferric iron–bearing minerals, unambiguous detections of ferric minerals forming under highly reducing conditions on the Moon have remained elusive. Our analyses of the Moon Mineralogy Mapper data show that hematite, a ferric mineral, is present at high latitudes on the Moon, mostly associated with east- and equator-facing sides of topographic highs, and is more prevalent on the nearside than the farside. Oxygen delivered from Earth’s upper atmosphere could be the major oxidant that forms lunar hematite. Hematite at craters of different ages may have preserved the oxygen isotopes of Earth’s atmosphere in the past billions of years. Future oxygen isotope measurements can test our hypothesis and may help reveal the evolution of Earth’s atmosphere.
... The bombardment of solar wind particles makes the lunar surface a highly reducing environment [10]. Previous studies have shown that minerals containing ferric iron (Fe 3+ ) are rare in lunar samples (less than 1%, and may be contaminants from the Earth) and the vast majority of iron on the Moon exists in the form of ferrous iron (Fe 2+ )-bearing minerals and metallic iron (Fe 0 ) due to the highly reducing environment [11]. In addition, several studies indicated that the solar wind also plays an important role in space weathering [12][13][14][15], which is a collection of complex physical and chemical processes [16]. ...
Hematite, a ferric mineral with diagnostic features in the visible and infrared spectral range, has recently been discovered in the polar regions of the Moon by the Chandrayaan-1 Moon Mineralogy Mapper (M3). The oxygen involving the oxidization process producing lunar hematite is supposed to originate from the Earth’s upper atmosphere, and hematite with different ages may have preserved information on the oxygen evolution of the Earth’s atmosphere in the past billions of years. The discovery of lunar hematite may provide insight into the understanding of the oxidation products on the Moon and other airless bodies. In this work, we analyze hematite abundance distribution in the lunar polar regions, showing that the content of hematite on the lunar surface increases with latitude, and is positively correlated with surface water abundance. We suggest that the latitude dependence of hematite is derived from the latitude dependence of water, which indicates that water may play an essential role in the formation of hematite. The correlation between hematite and the optical maturity parameter (OMAT) was analyzed and a significant positive correlation was observed, which suggests that the hematite in the polar regions is the result of gradual and persistent oxidation reactions. In addition, based on the analysis of oxygen particles in the Earth wind, it was found that O+ and O2+ are much more abundant, suggesting that low-energy O+ or O2+ ions escaping from the upper atmosphere of the Earth may play a crucial role in the formation of hematite in the lunar polar regions.
... Iron is a critical element that records the oxygen potentials of solar system materials [1][2][3] . The lunar surface and interior are identified as highly reducing because Apollo samples mainly contained ferrous (Fe 2+ ) or metallic iron (Fe 0 ), and only small amounts of ferric iron ions (Fe 3+ ) (<1 wt%) were detected 4,5 . Despite the highly reduced state of the Moon, a higher Fe 3+ concentration (for example, 0-25% Fe 3+ /∑Fe (∑Fe = Fe 2+ + Fe 3+ ) in lunar picritic glass beads) in Apollo samples has recently been revealed 1,6-8 . ...
Although ferric iron indisputably exists on the highly reducing surface of the Moon, its formation mechanism and evolution are still under debate. Here we show that micrometeorite impact-induced charge disproportionation of iron could have produced the large amounts of ferric iron (average Fe3+/∑Fe > 0.4) in agglutinate melts returned by China’s Chang’e-5 mission. The charge disproportionation reaction synchronously generated nanophase metallic iron (npFe0), and quantitative analyses of iron valence indicate that it is a dominant pathway for formation of npFe0 within the lunar agglutinate glass. The discovery of the charge disproportionation reaction in the agglutinates suggests that much more Fe3+ could be present on the Moon than previously thought, and that its abundance is progressively increasing with micrometeoroid impacts. Lunar high-concentration ferric ion (Fe3+/∑Fe > 40%) and ~63% of nanophase metallic iron (npFe0) are produced via charge disproportionation of ferrous iron from micrometeoroid impacts, as observed in the Chang’e-5 sample. This ongoing process would lead to a continuously increasing abundance of Fe3+ in the lunar regolith.
Though ferric iron indisputably exists on the highly reduced Moon, its formation mechanism and evolution have yet to be disclosed. Here we show that micrometeorite impact-induced ferrous disproportionation could produce a large amount of ferric iron (average Fe ³⁺ /∑Fe > 0.4) in agglutinate melts returned by Chang’e-5 mission. The disproportionation reaction synchronously generated nanophase metallic iron (npFe ⁰ ), a dominant formation pathway of npFe ⁰ within the lunar agglutinate glass. The discovery of the disproportionation reaction in the agglutinates suggests that much more Fe ³⁺ could be ubiquitously present on the Moon than previously thought, and its abundance is progressively increasing with micrometeoroid impacts.
Water (ice, liquid, or vapor) is a critical driver of future exploration, and methods of its detection and characterization are a high priority for upcoming lunar missions. Thus, we assess the potential for alteration products resulting from water-ice liberated during various impact events in the lunar polar regions. In this work, we estimate the maximum amount and duration of melted, vaporized, or sublimed water-ice during representative post-impact environments using a model of bulk heat transfer. Our model is sensitive to heat loss by radiation, initial and final near-surface temperatures, and pre-existing water-ice abundance and distribution. Mineral dissolution rates in aqueous solution are used as a metric for potential chemical alteration in the presence of liberated water-ice following an impact. We find that the modeled timescales and potential for water liberation and reactivity are compatible with near-surface chemical alteration in some lunar post-impact environments. While initial surface temperatures less than ∼110 K are adequate to maintain near-surface ice reservoirs at the lunar poles, when heated, pore pressures below a depth of ∼35 cm are potentially adequate to sustain liquid water. Mild near-surface environments (e.g., ∼5 °C) lasting a few decades, allow for aqueous alteration of sensitive minerals such as olivine, apatite, and glassy materials. Higher temperatures favor degassing of H2O, but vapor-phase interactions may occur. The limited amounts of available water will likely result in reactions with only the most sensitive minerals such as glasses and Fe-metal. Over time, secondary mineralization would be mixed into the upper few meters of the lunar regolith through subsequent bombardment, assuming it escapes later intense heating events; however, surface exposures would be subjected to space weathering. Nonetheless, based on our modeling, future explorers should consider instrumentation capable of detecting minor to trace amounts of impact-induced chemical alteration in the upper few meters of the lunar surface.
A nucleus, like an atom, has discreet (quantized) ground and excited levels, the transition from the upper to the lower level being accompanied by gamma-ray emission. Nuclear gamma emission line spectrum is similar in this respect to atomic optical emission spectrum occurring as a result of the transition from the upper to the lower electronic level.
On the basis of heat capacity data in the liquid He temperature range, Morrison and Norton [1970] have suggested that lunar rocks 10017 and 10046 contain an anomalous density of low-frequency vibrational modes. More recently, they have made the same suggestion to account for similar data on a terrestrial diabase [Morrison and Norton, 1971]. In neither paper do they suggest any model that would make such a density of low-frequency modes plausible. This note points out that their data can be explained in a perfectly natural way by spinordering of Fe in pyroxenes and that, if the postulated low-frequency modes do exist, available MSssbauer data place strong constraints on their nature.
On July 24, 1969, the first extraterrestrial samples, with the exception
of meteorites, were returned to earth by Apollo 11. Since then these
samples and the samples returned by Apollo 12 have been subjected to
scientific investigations by hundreds of scientists from many countries.
Drawing on advances from the last 25 years of study of meteorites and
terrestrial rocks the variety and sophistication of the techniques used
on these samples is truly impressive. It can truthfully be said that 10
years ago we could not have made the measurements, and that, even if we
had had the data, we could not have interpreted it. The electron
microprobe, the scanning electron microscope, and the mass spectrometer,
as well as other instruments and techniques, have joined the microscope
as routine tools with which to attack a petrologic problem.
Recoilless resonance spectra taken at 80°K and 300°K were used to identify oxidation products present in meteorites. Wolf Creek (a completely oxidized iron meteorite) contains (in order of decreasing abundance) αFeOOH, βFeOOH, γFe2O3, Fe3O4, and γFeOOH. The dark chondrite fragments in the Cumberland Falls achondrite have spectra containing mainly βFeOOH. The unequilibrated ordinary chondrite Clovis (no. 1) has γFeOOH as the chief oxidation product. Absorption spectra should be recorded at several temperatures in order to avoid ambiguities arising from the presence of superparamagnetic ultrafine particles of iron oxides. A comparison of the Mössbauer spectra of the dark portion of Cumberland Falls with two recent chemical analyses demonstrates that it is not possible to correctly apportion iron among the metal, sulfide, and silicate phases without knowledge of the ferric iron content, which can be determined only by resonance spectroscopy.
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