Lunar Fines Research Articles

Quantitative grain size estimation on airless bodies from the negative polarization branch

This work explores characteristics of the negative polarization branch (NPB), which occurs in scattered light from rough surfaces, with particular focus on the effects of fine particles. Factors such as albedo, compression, roughness, and the refractive index are considered to determine their influence on the NPB. This study compiles experimental data and lunar observations to derive insights from a wide array of literature. Employing our proposed methodology, we estimate the representative grain sizes on the lunar surface to be D ~ 1–2 µm, with D ≲ 2–4 µm, consistent with observed grain size frequency distributions in laboratory settings for lunar fines. Considering Mars, we propose that the finest particles are likely lacking (D ≫ 10 µm), which matches previous estimations. This study highlights the potential of multiwavelength, particularly near-infrared, polarimetry for precisely gauging small particles on airless celestial bodies. The conclusions provided here extend to cross-validation with grain sizes derived from thermal modeling, asteroid taxonomic classification, and regolith evolution studies.

Dust Rotation and Swirl Morphology in Lunar Magnetic Anomalies

The scattering of light off the bright regions of lunar swirls suggests a relatively higher fraction of fine-grained dust compared to dust with similar optical maturity values found elsewhere on the lunar surface when assuming an isotropically oriented dust distribution, without preferred grain orientation. Here we propose a mechanism by which the ferromagnetic lunar fines, lofted by electrostatic effects or by meteoroid impacts, may rotate in a lunar magnetic anomaly and, upon landing, produce patches of organized alignments, generating anisotropic surface structures. We simulate these rotations for Reiner Gamma and provide a proof of concept for such a dust rotation model. While the magnetic forces remain negligibly small to influence the trajectories of the lofted particles, the magnetic torques have a significant effect on the rotation of magnetized dust, and can generate an organized landing pattern for elongated lunar fines, which offers a possible explanation for the lunar albedo patterns.

Physicochemical properties of respirable-size lunar dust

We separated the respirable dust and other size fractions from Apollo 14 bulk sample 14003,96 in a dry nitrogen environment. While our toxicology team performed in vivo and in vitro experiments with the respirable fraction, we studied the size distribution and shape, chemistry, mineralogy, spectroscopy, iron content and magnetic resonance of various size fractions. These represent the finest-grained lunar samples ever measured for either FMR np-Fe0 index or precise bulk chemistry, and are the first instance we know of in which SEM/TEM samples have been obtained without using liquids.The concentration of single-domain, nanophase metallic iron (np-Fe0) increases as particle size diminishes to 2µm, confirming previous extrapolations. Size-distribution studies disclosed that the most frequent particle size was in the 0.1–0.2µm range suggesting a relatively high surface area and therefore higher potential toxicity.Lunar dust particles are insoluble in isopropanol but slightly soluble in distilled water (~0.2wt%/3 days). The interaction between water and lunar fines, which results in both agglomeration and partial dissolution, is observable on a macro scale over time periods of less than an hour.Most of the respirable grains were smooth amorphous glass. This suggests less toxicity than if the grains were irregular, porous, or jagged, and may account for the fact that lunar dust is less toxic than ground quartz.

Apollo 12 Lunar Module exhaust plume impingement on Lunar Surveyor III

Understanding plume impingement by retrorockets on the surface of the Moon is paramount for safe lunar outpost design in NASA’s planned return to the Moon for the Constellation Program. Visual inspection, Scanning Electron Microscopy, and surface scanned topology have been used to investigate the damage to the Lunar Surveyor III spacecraft that was caused by the Apollo 12 Lunar Module’s close proximity landing. Two parts of the Surveyor III craft returned by the Apollo 12 astronauts, Coupons 2050 and 2051, which faced the Apollo 12 landing site, show that a fine layer of lunar regolith coated the materials and was subsequently removed by the Apollo 12 Lunar Module landing rocket. The coupons were also pitted by the impact of larger soil particles with an average of 103 pits/cm 2. The average entry size of the pits was 83.7 μm (major diameter) × 74.5 μm (minor diameter) and the average estimated penetration depth was 88.4 μm. Pitting in the surface of the coupons correlates to removal of lunar fines and is likely a signature of lunar material imparting localized momentum/energy sufficient to cause cracking of the paint. Comparison with the lunar soil particle size distribution and the optical density of blowing soil during lunar landings indicates that the Surveyor III spacecraft was not exposed to the direct spray of the landing Lunar Module, but instead experienced only the fringes of the spray of soil. Had Surveyor III been exposed to the direct spray, the damage would have been orders of magnitude higher.

Lunar dust charging by photoelectric emissions

The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar ultraviolet (UV) radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function (WF) of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17 and Luna-24 missions as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Chemical markers for bacteria in extraterrestrial samples.

Interplanetary missions to collect pristine Martian surface samples for analysis of organic molecules, and to search for evidence of life, are in the planning phases. The only extraterrestrial samples currently on Earth are lunar dust and rocks, brought back by the Apollo (U.S.) and Luna (Soviet Union) missions to the moon, and meteorites. Meteorites are contaminated when they pass through the Earth's atmosphere, and during environmental exposure on Earth. Lunar fines have been stored on Earth for over 30 years under conditions designed to avoid chemical but not microbiological contamination. It has been extremely difficult to draw firm conclusions about the origin of chemicals (including amino acids) in extraterrestrial samples. Of particular concern has been the possibility of bacterial contamination. Recent work using state-of-the-art gas chromatography tandem mass spectrometry (GC-MS/MS) has dramatically lowered the chemical background, allowing a clear demonstration that lunar fines are remarkably different from terrestrial dust in that they generally lack certain chemical markers (muramic acid and 3-hydroxy fatty acids) characteristic of Earth's bacteria. Thus, lunar dust might be used as a negative control, in conjunction with GC-MS/MS analyses, in future analytical studies of lunar dust and meteorites. Such analyses may also be important in studies designed to search for the presence of life on Mars.

Maximum Visible Polarization of 4179 Toutatis in the Apparition of 1996

Our visible polarimetry of asteroid 4179 Toutatis during the apparition of 1996 has revealed the existence of a maximum polarization Pmax of (7.0 ± 0.2)% at a phase angle (Sun-asteroid-observer angle) αmax of 107°±10α at an effective wavelength of 0.53 μm. This is the second significant report of Pmax and αmax for the asteroids; the first one for 1685 Toro by Kiselev et al. (1990, AAA51.098.084) has large uncertainties. A comparison of our values of Pmax and {αmax with those of laboratory measurements reported by Bowell et al. (1972, Proc. Lunar Sci. Conf.) as well as Shkuratov and Opanasenko (1992, AAA56.094.027) suggests that the Toutatis' surface is covered with a material having similar polarimetric properties to those of lunar fines with a size of less than 80 μm. Furthermore, our multi-channel polarimetry has confirmed a decrease in the polarization with increasing wavelength.

天然原子炉と宇宙化学

A brief historical review of the studies on the natural reactor and the occurrence of 244Pu in the early solar system is presented. Results from recent studies on the occurrence of ‘excess’ heavy isotopes of xenon in carbonaceous chondrites and lunar fines reveal that they formed when the ratio of 244Pu to 238U in the early soalr system was in the range of 0.0153 to 0.262 (atom/atom). While the carbonaceous chondrites seem to have all formed from a parent body (4, 890±8) to (4, 908±8) million years ago, ages of lunar fines varied from (4, 649±7) to (4, 992±8) million years.

Plutonium-244 dating VII. Initial abundances of uranium-235 and plutonium-244 in lunar samples

Re-examination of a vast amount of lead and xenon isotope data that have been accumulated since the Apollo 11 landing on the moon in July 1969 reveals that some of the lunar fines and breccia started to retain their radiogenic lead and fissiogenic xenon isotopes about 5 billion years ago when the ratios of235U and244Pu to238U in the early solar system were approximately 4 and 2 atoms per 10 atoms of238U, respectively.

Plutonium-244 dating

Re-examination of xenon isotope data for lunar fines, breccia and rocks reveals that in situ decay product of the spontaneous fission of 244 Pu is widely distributed in the lunar samples and some of the lunar samples contain in excess of 1000 0 10 −12 ccSTP 136f Xe/g of 244 Pu fission xenon. The 244 Pu ages calculated from the ratios of 136f Xe to 238 U in these samples vary from 3965 to 4909 million years

Helium and neon isotopes in stratospheric particles

Abstract— Helium and neon isotope ratios were determined for 16 interplanetary dust particles (IDPs) collected in the stratosphere. The concentration of helium observed varied greatly from particle to particle, with the highest values approaching those found for lunar surface fines and some gas‐rich meteorites. With the exception of one particle, for which the 3He/4He was (1.45 ± 0.05) × 10−3, the remainder of the particles had ratios falling between 1.4 and 3.1 × 10−4, with an average of (2.4 ± 0.3) × 10−4, substantially less than is associated with the solar wind or observed in average lunar fines or in lunar fines having sizes comparable to those of the IDPs studied. The average 20Ne/22Ne found was 12.0 ± 0.5. Only three reasonably reliable 21Ne/22Ne ratios could be determined, and for these the average was 0.035 ± 0.006. The isotopic ratios appear to preclude the presence of any appreciable amount of cosmic ray‐produced spallogenic products. The high 4He concentrations observed for some of the particles, approaching those observed for lunar surface grains, suggest they were not heated to high temperatures and degassed as they descended in the earth's atmosphere. From Flynn's study of the dynamics of IDPs entering the earth's atmosphere this could mean they entered the atmosphere at relatively low velocities, and hence may be primarily of asteroidal rather than cometary origin.

Isotopic composition of xenon in the solar system.

Xenon in the solar system can be divided into two groups: (a) primordial xenon, whose isotopic composition can be approximated by that of the atmospheric xenon and (b) xenon, whose isotopic composition was severely altered by high energy proton and neutron reactions which took place during the T-Tauri phase of our Sun. The isotopic compositions of the SUCOR (surface correlated) xenon found in lunar fines and the CCFX xenon, corrected for mass fractionation and spallation effects, belong to the group (a) and the AVCC xenon and the so-called s-type xenon found in the Murchison meteorite belong to the group (b). Some of the xenon fractions recently isolated from the Allende and Belgica meteorites appear to be more ‘primordial’ than the atmospheric xenon.

Trapped noble gases indicate lunar origin for Antarctic Meteorite

The isotopic abundances of the noble gases (He, Ne, Ar, Kr, Xe) are reported for Antarctic meteorite ALHA81005. It contains solar wind‐implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites. ALHA81005 also contains a large excess 40Ar component which is identical to the component in lunar fines implanted from the lunar atmosphere. Large concentrations of cosmogenic 21Ne, 82Kr and 126Xe in ALHA81005 indicate a total cosmic ray exposure age of ≥ 2×108 years. The noble gas data alone are strong evidence for a lunar origin of this meteorite.

Synthesis of molecules by irradiation in silicates

We have studied the molecular synthesis induced by the implantation of C and H ions in SiO2 by in situ infrared spectroscopy. We have observed the infrared CO and CO2 bands; the relative concentrations of CO and CO2 depend on the C and H fluences; the bands have characteristics different from those of the corresponding gaseous species. This enables us to identify unambiguously CO2 synthesized by solar wind irradiation in lunar fines.

Vacuum balance studies of milled material and mechanochemical reactions

The types of change in surface properties and porosity of milled materials having widely different hardness and crystal structure are reviewed. For more intensive milling, the use of vacuum balance techniques in conjunction with X-ray diffraction, optical- and electron-microscopy enables changes in microstructure and phase composition to be determined during mechanochemical reactions. Metallic or non-metallic harder materials (Mohs scale 8–9), such as transition metal nitrides or silicon nitride and boron carbide, increase their surface on milling largely due to brittle fracture, so that the surface area tends towards an upper limiting value with comparatively little development of porosity. Softer materials (Mohs scale 1–2), such as gypsum, china clay(Kaolinite) and hydrated lime and magnesia undergo plastic deformation and strain hardening on longer milling, so that the surface area passes through a maximum before decreasing to an equilibrium value. This is applicable also to materials of intermediate hardness (Mohs scale 3–5), such as calcite, magnesite and dolomite, provided that the milling is sufficiently intensive; the flow and welding processes during the plastic deformation leave the grains non-porous to nitrogen gas, but adsorption of water vapour causes development of porosity, a phenomenon also observed with lunar fines (mainly silicate minerals) which are of somewhat greater hardness but contain amorphous surface layers (cf. Beilby layer) and nuclear particle damage tracks having tubular pores with narrow constrictions forming micropores. More intensive milling can result in crystal transformation and mechanochemical reactions. Thus gypsum is converted to anhydrite, viz., CaSO 4.2H 2O → CaSO 4.2H 2O → γ—CaSO 4 → β—CaSO 4. Calcite, CaCO 3, is converted to aragonite, while calcitic CaCO 3 and magnesite, MgCO 3, form dolomite CaCO 3.MgCO 3.

On the possibility of using lunar fines to determine the intensity of the ancient lunar magnetic field

The remanent magnetization of iron grains in lunar fines can be studied by allowing a sample of fines to acquire a depositional remanent magnetization (NRM) in the Thellier determination of an ancient lunar field intensity. Although a natural remanent magnetization (NRM) in the Thellier determination of an ancient lunar field intensity. Although a palaeointensity of ca. 1.0 Oe was determined by this method, several factors complicate the interpretation of the result. These include the origin and nature of the iron metal in lunar fines, and the time and acquisition process of its magnetization.

Effect of sample quantity on the results of ferromagnetic resonance studies of lunar samples

Quantitative ferromagnetic resonance (FMR) measurements at 9.5 and 35 GHz were made on lunar fines in order to determine the amount of single domain Fe0 and to ascertain the effect of sample quantity on the results of these experiments. Samples containing more than 10 μg of Fe0 in an X‐band TE104 cavity, or more than 0.11 μg in a Kα‐band TE011 cavity can cause errors greater than 1% in the quantitative determination of Fe0, as well as cause anomalous broadening of the FMR line. Theoretical calculations were derived to show this effect which results from a nonlinear response of the FMR experiment with the sample quantity. Using samples of nominal weights, the amount of Fe0 determined at 35 GHz was 1.2–1.8 times greater than at 9.5 GHz, while the linewidths increased by a factor of 1.2. As the particle size increases, the ratio of Fe0 determined at 35 GHz to that determined at 9.5 GHz increases, suggesting that the additional iron is due to larger spheroidal particles which change from multidomain to single domain at the larger fields.

Diffusion of rare gases of solar wind origin from lunar fines as bubbles

A diffusion mechanism is proposed which takes into account phenomena observed in ion-implanted solids, in particular the precipitation of rare gas in the form of bubbles and their migration. The composition of rare gases in the bubbles is inferred from the calculated distribution of solar wind rare gas ions as a function of depth in the grains. These calculations are made for the location and average composition of Apollo 11 samples. It is shown by analogy with experimental observations in ion-implanted solids that the bubbles would migrate towards the surface and that the diffusion constant for this migration would be strongly depth dependent. Relative abundances of rare gas nuclides remaining behind due to the resultant degassing are estimated for one Apollo 11 soil sample and are compared with observed relative abundances for this sample. A qualitative explanation of some of the experimental observations of Ducati et al. on individual lunar grains is also offered.

Solar wind nitrogen and indigenous nitrogen in lunar material

There is ample evidence that the main source of the abundant light elements in lunar, fine-grained regolith samples in the solar wind. The extra-lunar contribution is easy to detect, because lunar igneous rocks are, in general, strongly depleted in light volatile elements, such as H, He, C, N and Ne. We report on chemically bound nitrogen contents in various lunar samples from the Apollo 11 through Apollo 17 landing sites by using the Kjeldahl method. This technique detects only nitrogen in a bound state and discriminates against molecular nitrogen N 2 of atmospheric origin. We have found by the analysis of grain-size fractions, by leach-experiments, by comparison with trapped noble gases and with agglutinate contents that the main amount of the nitrogen in the fines is derived from the solar wind by ion implantation and is present primarily in a bound state. Leach-experiments on Apollo 15 and Apollo 17 fines indicate two chemical forms of nitrogen: ammonium- and nitride-nitrogen. Nitrogen and carbon chemistry in lunar fines appear to be analogous in respect to the hydrogen compounds ammonia and methane, and the presence of nitrides and carbides. Hot atom chemistry probably causes the synthesis of those compounds on the surface area of fine grains. Implanted nitrogen is better retained in fine-grained material than carbon and the light noble gases and is, therefore, a useful reference in terms of solar elemental abundances. Carbon to nitrogen ratios of lunar fines are interpreted as lower limits for the abundance ratio of these elements in the sun. Bound nitrogen contents have also been determined in several lunar igneous rocks and U.S.G.S. standard rocks using an optimized, program-controlled Kjeldahl method. This technique is superior to the previously applied conventional Kjeldahl method with respect to sensitivity and reproducibility for nitrogen analysis. Most of the lunar igneous rocks analyzed in this work are quite uniform and low in bound nitrogen contents; the range is only about 3 to 8 ppm N for samples of various types. Lunar fines and soil breccias contain, however, a factor of 10 to 20 more nitrogen than igneous rocks. The small nitrogen contents of the rocks imply that indigenous nitrogen and/or ammonia were at very low concentrations at the time of mineral and rock formation in the early history of the moon. This indicates either severa a priori nitrogen depletion of the moon's parent material or rigorous loss of nitrogen and other volatile elements in the early history of the moon.

A lunar terminator configuration

Although introduced more than two decades ago, electrostatic soil transport on the lunar surface remains a controversial subject due, primarily, to insufficiently high surface fields and particle charges to initiate and sustain the phenomenon. This paper introduces a realistic geometrical configuration for the terminators which plausibly provides adequate fields and charges. Myriads of miniature sunlit islands and dark valleys are formed in the vicinity of a zig-zag terminator line as it moves. The islands and valleys are surrounded by areas of opposite electrical polarity, providing local field regions up to thousands of volts per centimeter. The result is random directional movement of electrostatically charged lunar fines. It is shown that the mechanism can readily account for the denuding of certain asteroids while others exhibit a layer of dust on their surface.