Lunar Surface Material Research Articles

The lunar regolith: physical characteristics and dynamics

The fine size fraction of the lunar regolith (less than 1 mm mean particle diameter) is composed mostly of particles that owe their origins either directly or indirectly to the impacts of meteoroids on the lunar surface. Comminution of pre-existing rocks and particles is the dominant process affecting the characteristics of the regolith. However, agglutination of pre-existing particles by the glassy, molten spatter and ejecta from small meteoroid impacts is a competing constructive process of low efficiency. Grain size frequency distributions of the less than 1 mm fraction of the regolith tend to be slightly bimodal, with a broad mode in the 1-40 size range (500- 62.5 pm due mostly to agglutination and another mode at approximately 50 (31.3 pm) and finer that appears to be caused by the ballistic influx of fine particles from older (finer) regolith. In general, the size frequency distribution curves are nearly symmetrical and indicate poor to very poor sorting. There is a strong correlation of sample mean grain size (and other size parameters) with the length of time that the regolith has had to accumulate at each landing site. The greater the total length of regolith accumulation time, the greater the comminution by meteoroids, and hence the finer the sample mean grain size and the greater the total agglutinate content. These properties also correlate positively with solar wind implanted carbon and nitrogen contents. Thus, sample mean size, agglutinate content, solar wind nitrogen and carbon, as well as solar particle track densities, can all be used as measures of regolith ‘maturity’. Local sample collection site geology, such as proximity to boulders or recent craters, strongly influences sample modal particle type populations and grain size characteristics. Lunar chondrules of several types have been identified in the regolith and rock samples. Many of these chondrules have textures that are identical with many meteoritic chondrules. The chondrules in lunar surface materials appear to result from lunar impact processes. It may be that chondrules have originated in many meteorites by some of the same processes. If true, this occurrence has important implications for the origin and history of chondritic meteorites.

Irradiation and accretion of solids in space based on observations of lunar rocks and grains

Clues to a wide range of questions relating to the origin and evolution of the solar system and dynamic physical and electromagnetic processes occurring concurrently and in the past in our galaxy have been provided by a study of the lunar samples. This information is deduced from a variety of complementary physical and chemical evidence. In this presentation, greatest emphasis is laid on information based on the cosmogenic effects, i.e. those arising from interactions of low energy cosmic rays with lunar surface materials. This information is generally not obtainable from examinations of meteorite samples, except in the case of certain types termed gas-rich meteorites, due to loss of their surface regions by atmospheric ablation. The present discussions will concern the nature of experimental data to date and implications thereof to the charged particle environment of the Moon, ancient magnetic fields and the nature of, time scales involved in the irradiation and accretion of solids in space, based on lunar regolith dynamics. It becomes clear that there does not yet exist any consensus on the absolute values of charged particle or the meteorite fluxes, and also about the details of the evolution of the lunar regolith. This would be expected also considering that one is dealing with phenomena which range in size/energy scales over many orders of magnitude and that the techniques used for the studies were only recently developed in many cases. The complex history of evolution of lunar material is slowly being understood and it is a hope that a great deal of quantitative information will soon be available which will in turn allow discussion of evolution of solid bodies in the solar system.

The cause and significance of luminescence in lunar plagioclase

Most lunar samples luminesce under proton or electron excitation, and most of the emission comes from the plagioclase present. The cause of this luminescence has been found by investigating the emission and excitation spectra of lunar, terrestrial and synthesized plagioclases. Emission spectra show three broad peaks: a weak one around 450 nm which is common to most silicates; a dominant one around 560 nm for which the activator is found to be Mn 2+ in Ca sites; and a very weak one between 700 and 780 nm for which we conclude the activator to be Fe3+ in A1 sites. However, this near-infrared peak is usually the dominant one for terrestrial plagioclases; its weakness in lunar samples is attributed to reducing conditions when the lunar surface materials were formed causing more of the iron to be present as Fe2+. Luminescence photography of lunar rock chips is found to be a simple method of surveying plagioclase crystal forms in rough samples.

Lunar stratigraphy

The lunar scene is a continuous panorama of ancient impact physiography. Multi-ringed circular basins and smaller craters scar the Moon’s highlands and provide evidence of a violent early history. Basin formation, the major material-transporting mechanism on the Moon, produces a deep inner depression, one or more benches, a basin rim, and radially lineated ejecta. Study of lunar photographs indicates that, on a relative age scale, subdued basin and crater features are older representations of younger, well-preserved forms. Absolute age dating of returned samples makes it feasible to calibrate this relative age scale. All the larger basins were formed during pre-Nectarian, Nectarian and Imbrian times, i.e. 4.6- 3.9 Ga ago. Following this major sculpturing episode, and during the Imbrian and Eratosthenian times, mare volcanism became the most important mode of deposition of lunar surface materials. Basaltic lavas from deep-seated sources flowed to partially fill the impact basins and cover their peripheral troughs and surrounding lowlands between 3.8 and 3.2 Ga ago. This occurred more frequently on the near side than on the far side, probably because the farside crust is thicker. During the past 1 Ga, i.e. Copemican time, only a small number of craters were formed in both highland and mare rocks. Successes and failures of photogeologists in studying lunar stratigraphy provide the necessary lessons for understanding the geological history of the terrestrial planets. This is particularly true since both Mars and Mercury display many types of features in common with the Moon.

Cosmic ray interactions with lunar materials: Nature and composition of species formed

The solar and galactic cosmic rays interact directly with lunar surface materials, and the dominant nature of interactions is essentially the complete absorption of corpuscles. These corpuscles damage the lattice structure, and induce a complex set of reactions in the materials producing various species. The cosmic ray damage of the lattice would not produce an amorphous layer, similar to that produced by the solar wind, because the solar wind erosion rate is faster than the cosmic ray-induced amorphous layer formation rate. The species formation rate considered in this paper are those produced by protons, the dominant component of cosmic rays. Protons produce H, H2, OH, H2O, and hydrogenated species of carbon, nitrogen, sulfur, etc. These species, while migrating in the material, encounter oncoming cosmic ray corpuscles, and undergo a complex set of reactions. Although a variety of species are produced by protons, the dominant contributor to the atmosphere is H2. The H2 flux (molecules cm−2 sec−1) is about 1.5 × 105 as compared to the H flux of 8.4 × 101 and the H2O flux of 4.6 × 10−2. These fluxes are about 10−3 smaller than the fluxes of the same species produced by the solar wind protons. Thus the contributions of the cosmic ray-induced species to the atmosphere is very small compared to the solar wind-induced species. Although simulated experiments showed high concentractions of OH and H2O in the terrestrial materials of lunar type, these species concentrations in the lunar materials under the lunar environment is much smaller than those observed in the simulated experiments.

Volatilisation from solid particles of the regolith

WE have previously1 dwelt on the possible volatilisation of some elements from continuous melts of lunar surface material as a result of which it becomes depleted in elements such as Na, K and Rb, and so on. The mechanism of volatilisation proper was not confined to the liquid phase, and so they can also volatilise from the solid phase. Moreover, if solidification is not accompanied by crystallisation, the temperature dependence of the volatilisation time constant τv found in ref. 1 should remain unchanged.

Solar-wind interactions: Nature and composition of lunar atmosphere

The solar wind interacts directly with the lunar surface material resulting in an essentially complete absorption of the corpuscles producing no upstream bowshock but a cavity downstream from the Moon. The main source of most neutral species of the atmosphere, except probably40Ar, is the solar-wind interaction products. The other sources which appear to be minor contributors to the atmosphere are the interaction products of cosmic rays, planetary degassing, effects of meteorite impacts and radioactive decays. Most of the hydrogen atoms derived from the solar-wind protons contribute to the atmosphere as hydrogen molecules rather than atoms. Only on the basis of the solar-wind protons, alpha particles and ions of oxygen and carbon, the atmospheric species concentration (cm−3) near the lunar surface at 300K are as follows: H2 3.3 to 9.9 × 103; He 2.4 to 4.7 × 103; H 3.7; OH 0.25; H2O 0.24; and O2, O, CO, CO2 and CH4 in concentrations smaller than H2. Whatever the source, the OH and H2O concentrations in the atmosphere are about the same. The calculated concentrations are in good agreement with the observations by the Apollo 17 lunar surface mass spectrometer and the Apollo 17 orbital UV spectrometer. At the time of sample collection from the Moon, the hydrogen content in the trapped gas layer of the lunar surface material was partly as hydrogen atoms and partly as hydrogen molecules, but at the time of sample analysis hydrogen was mostly in molecular form. The H2O content at the time of sample analysis was only a few parts per million by weight.

Spectral reflectance systematics for mixtures of powdered hypersthene, labradorite, and ilmenite

Spectral reflectance measurements in the range from 0.4- to 2.5 microns were made for synthetic powder mixtures of a single suite of plagioclase, pyroxene, and ilmenite, which are the principal mineral phase types making up virtually all lunar surface materials studied to date. Binary and ternary data plots of the parameters albedo, band depth, and red to blue ratios versus mixture composition show how variation in the concentration of each mineral phase in a mixture affects changes in the overall reflectance spectrum of the mixture. Principal mixing effects noted are (1) the disproportionate darkening effect of opaque ilmenites and (2) the persistence, the wavelength stability, and the depth versus concentration proportionality of the 1-micron band of pyroxene. These results indicate that by comparing the albedo and band depth of an unknown spectrum with calibration data obtained with laboratory standards, it is possible to determine the ratio of crystalline phases in the material producing spectra such as may be obtained telescopically from small areas on lunar and planetary surfaces.

Optical constants for terrestrial analogs of lunar materials

view Abstract Citations (9) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical constants for terrestrial analogs of lunar materials Egan, W. G. ; Hilgeman, T. Abstract Representative terrestrial analogs of the dominant lunar constituents plagioclase feldspar and pyroxene were selected, and the refractive, absorption, and scattering components were determined separately in the range from 0.33 to 2.3 m. A newly developed theory was employed to separate the absorption from the scattering based on thin section total reflectance and transmission measurements. The selected minerals were bytownite (Minnesota) and augite (Ontario, Canada); a comparison of their absorption peaks with those inferred from reflectance measurements on lunar samples reveal comparable bands at 2.0, 1.3, 1.0 to 0.9, 0. and the UV. The similarities indicate that the optical constants resonably characterize the lunar-surface material. Another result is the introduction of plagioclase as a possible candidate material causing the 0. feature in asteroids and in the interstellar medium. Publication: The Astronomical Journal Pub Date: October 1973 DOI: 10.1086/111486 Bibcode: 1973AJ.....78..799E full text sources ADS |

Vitrification darkening of rock powders: implications for optical properties of the lunar surface

Laboratory experiments show that albedoes as low as those on the Moon can be produced by vacuum vitrification and associated chemical fractionation of ordinary terrestrial basaltic material. Vitrification is established as an unequivocal process that can account for the low albedo and apparent local darkening with age of the lunar surface. The spectral reflectance curves of glass powders are significantly different than those of the parent rock mineralogy; thus, the presence of ubiquitous glass in lunar surface material complicates compositional determinations by interpretation of spectral reflectance curves. Vitrification of rocks on the Moon may highly modify the chemical composition of the resulting glass; thus, glass fragments found in lunar fines cannot be assumed to represent bulk parent rock material. Progressive impact vitrification of lunar surface material throughout the Moon's history may have led to a fine-grain, opaque, refractory-rich material we call ‘ultimate glass’. This unidentified and, at this point, hypothetical component may exist in dark regolith material; if found, it may be a useful indicator of regolith maturity.

Average chemical composition of the lunar surface

The available data on the chemical composition of the lunar surface at eleven sites (3 Surveyor, 5 Apollo and 3 Luna) are used to estimate the amounts of principal chemical elements (those present in more than about 0.5% by atom) in average lunar surface material. The terrae of the Moon differ from the maria in having much less iron and titanium and appreciably more aluminum and calcium.

Production of lunar fragmental material by meteoroid impact

The rate of production of new fragmental lunar surface material is derived theoretically on the hypothesis that such material is excavated from a bedrock layer by meteoroid impacts. An overlaying regolith effectively shields the bedrock layer from small impacts, reducing the production rate of centimeter-sized and smaller blocks by a large factor. Logarithmic production rate curves for centimeter to meter-sized blocks are nonlinear for any regolith from centimeters to tens of meters in thickness, with small blocks relatively much less frequent for thicker (older) regoliths, suggesting the possibility of a statistical reverse bedding. Modest variations in the exponents of scaling laws for crater depth-diameter ratio and maximum block-diameter to crater diameter ratio are shown to have significant effects on the production rates. The production rate increases slowly with increasing size of the largest crater affecting the region.

Boulder tracks and nature of lunar soil

Boulder tracks from 19 different locations on the Moon, observable in Lunar Orbiter photographs, have been examined. Measurements of the track width indicate that some of the boulders sank considerably deeper than others. It is suggested that lunar surface materials vary from place to place; the state of compaction (density of lunar soil) is probably one of the significant variables. Using bearing capacity theory, modified to be applicable to the rolling boulder problem by theoretical studies and extensive testing, the friction angle of the lunar soil was estimated. Most of the results were between 24 and 47 degrees with an arithmetic average of 37 degrees. These values suggest corresponding density variations of 1.25 to 2.00 g/cm3.

Comparison of the analytical results from the surveyor, Apollo, and Luna missions

The principal chemical element composition and inferred mineralogy of the powdered lunar surface material at seven mare and one terra sites on the Moon are compared. The mare compositions are all similar to one another and comparable to those of terrestrial ocean ridge basalts except in having higher titanium and much lower sodium contents than the latter. These analyses suggest that most, if not all, lunar maria have this chemical composition and are derived from rocks with an average density of 3.19 g cm−3. Mare Tranquillitatis differs from the other maria in having twice the titanium content of the others.

Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material: Reply

Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material: Reply

Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material: Discussion

Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material: Discussion

Geologic interpretation of lunar data

The application of geologic concepts such as uniformitarianism and erosion cycles to lunar problems is illustrated by comparing terrestrial features and experiments with lunar features. Such comparisons include boulder tracks, blocky craters, volcanoes, and an experimental simulation of meteor bombardment. Lunar rock-stratigraphic units, lateral continuity, and superposition are illustrated using the crater Aristarchus. Reflection-emission data collected from the earth prior to unmanned and manned lunar exploration were remarkably good and captured the essence of the lunar surface at the fine scale. These data showed that the roughness of the lunar surface increased at the finer scale and that the lunar surface materials were porous and probably fragmental. Unmanned explorations significantly refined our knowledge of the lunar surface and its materials. In particular, unmanned soft-landing spacecraft obtained information on lunar topography and the physical properties and the chemical composition of the near-surface materials.

A limit on the radiation erosion in lunar surface material

Evidence from Apollo 11 and Apollo 12 lunar samples indicates that particle radiation is not important for the production of grains in the lunar soil greater than 22 microns in size even though sufficiently prolonged irradiations by protons, heavy ions and electrons fracture minerals and glasses like those found on the lunar surface.

Penetration resistance of lunar soils

Penetration resistance, in terms of the slope G of the stress penetration curve, has been correlated with density for a basaltic lunar soil simulant. The values were measured with the standard WES 30° cone penetrometer. This lunar soil simulant has been found to possess the same penetration resistance characteristics as the Apollo lunar soil. Bearing capacity equations have been used to determine G-values for the lunar soil simulant and the predicted values were found to agree very well with measured G-values. Using the same bearing capacity equations the computations were repeated for the lunar gravity field by reducing the material unit weight by a factor of six. These G-values represent a predicted correlation between G and density for lunar soil. This correlation has been entered with density estimates obtained from Apolli core tube studies as well as independent density estimates obtained from astronaut foot-print depth analysis. The probable range in G-values obtained for lunar surface material is expected to be useful in the evaluation of the performance of lunar roving vehicles.

Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material

Research Article| September 01, 1971 Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material CURTIS C MASON CURTIS C MASON National Aeronautics and Space Administration, Manned Spacecraft Center, Houston, Texas 77058 Search for other works by this author on: GSW Google Scholar Author and Article Information CURTIS C MASON National Aeronautics and Space Administration, Manned Spacecraft Center, Houston, Texas 77058 Publisher: Geological Society of America Received: 22 Mar 1971 Revision Received: 21 Apr 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (9): 2625–2630. https://doi.org/10.1130/0016-7606(1971)82[2625:NOTMSA]2.0.CO;2 Article history Received: 22 Mar 1971 Revision Received: 21 Apr 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation CURTIS C MASON; Nature of the Martian Surface as Inferred from the Particle-Size Distribution of Lunar-Surface Material. GSA Bulletin 1971;; 82 (9): 2625–2630. doi: https://doi.org/10.1130/0016-7606(1971)82[2625:NOTMSA]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Apollo 11 and 12 core-sample tubes were 2 cm in diameter; therefore, particles of larger diameter were excluded from the samples. The percentage of 2-cm and larger particles from the Surveyor I particle-count data was combined with the Apollo 11 data, then the data were normalized and plotted as a logarithmic normal distribution. The Surveyor I curve smoothly joins the Apollo 11 averaged core 1 and core 2 curves. The percentage of 8 mm and greater particles from Surveyor I data was combined with the Apollo 12 size-distribution data and the data were normalized. A sharp break in both curves occurs at approximately the 30-percentile point, a fact that can be explained by the theory that the material actually is composed of two populations: one population caused by comminution from the impact of the larger-sized meteorites and the other population caused by the melting of fine material by the impact of smaller-sized meteorites. The Martian atmosphere would vaporize the smaller incoming meteorites and would retard incoming meteorites of intermediate and large size, causing comminution and stirring of the particulate layer. The combination of comminution and stirring of material would result in fine material being sorted out by the prevailing circulationof the Martian atmosphere and the material being transported to regions where it would be deposited. As a result, the Martian surface in the regions of prevailing upward circulation probably is covered either by a rubble layer or by desert pavement; regions of prevailing downward circulation probably are covered by sand dunes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.