Thermal radiation properties of Apollo 14 fines

The thermal radiation properties as a function of bulk density, angle of illumination and wavelength are presented for lunar fines from the Apollo 14 mission. The density range covered is from 1095 kg/m³ to 1590 kg/m³ and a wavelength range of 0.36–14.5 μm. The solar albedo and total emittance were calculated from spectral values and are compared to Apollo 11 and 12 values.     

Thermophysical properties of lunar material returned by Apollo missions

Data on thermophysical properties measured on lunar material returned by Apollo missions are reviewed. In particular, the effects of temperature and interstitial gaseous pressure on thermal conductivity and diffusivity have been studied. For crystalline rocks, breccias and fines, the thermal conductivity and diffusivity decrease as the interstitial gaseous pressure decreases from 1 atm to 10^–4T. Below 10^–4T, these properties become insensitive to the pressure. At a pressure of 10^–4T or below, the thermal conductivity of fines is more temperature dependent than that of crystalline rocks and breccias. The bulk density also affects the thermal conductivity of the fines. An empirical relationship between thermal conductivity, bulk density and temperature derived from the study of terrestrial material is shown to be consistent with the data on lunar samples. Measurement of specific heat shows that, regardless of the differences in mineral composition, crystalline rocks and fines have almost identical specific heat in the temperature range between 100 and 340K. The thermal parameter calculated from thermal conductivity, density and specific heat shows that the thermal properties estimated by earth-based observations are those characteristic only of lunar fines and not of crystalline rocks and breccias. The rate of radioactive heat generation calculated from the content of K, Th and U in lunar samples indicates that the surface layer of the lunar highland is more heat-producing than the lunar maria. This may suggest fundamental differences between the two regions.Now at Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York, U.S.A.     

The evolution of the moon

The thermal evolution of the Moon as it can be defined by the available data and theoretical calculations is discussed. A wide assortment of geological, geochemical and geophysical data constrain both the present-day temperatures and the thermal history of the lunar interior. On the basis of these data, the Moon is characterized as a differentiated body with a crust, a 1000-km-thick solid mantle (lithosphere) and an interior region (core) which may be partially molten. The presence of a crust indicates extensive melting and differentiation early in the lunar history. The ages of lunar samples define the chronology of igneous activity on the lunar surface. This covers a time span of about 1.5 billion yr, from the origin to about 3.16 billion yr ago. Most theoretical models require extensive melting early in the lunar history, and the outward differentiation of radioactive heat sources.Thermal history calculations, whether based on conductive or convective computation codes define relatively narrow bounds for the present day temperatures in the lunar mantle. In the inner region of the 700 km radius, the temperature limits are wider and are between about 100 and 1600°C at the center of the Moon. This central region could have a partially or totally molten core.The lunar heat flow values (about 30 ergs/cm²s) restrict the present day average uranium abundance to 60 ± 15 ppb (averaged for the whole Moon) with typical ratios of K/U = 2000 and Th/U = 3.5. This is consistent with an achondritic bulk composition for the Moon.The Moon, because of its smaller size, evolved rapidly as compared to the Earth and Mars. The lunar interior is cooling everywhere at the present and the Moon is tectonically inactive while Mars could be and the Earth is definitely active.     

Lightcurves of 1999 Leonid Impact Flashes on the Moon

Optical flashes observed on the night side of the Moon during the 1999 Leonid meteor shower have attracted the interest of astronomers. These flashes are attributed to high-velocity impacts of Leonid meteoroids on the lunar surface. Here, we report five lunar flashes detected over a 5.8-h observation period centered at 11:25 UT on Nov. 18, 1999, in Japan. The flashes are characterized by an abrupt brightening. Three flashes exhibited afterglows that remained visible for at least 50 ms, which is longer than the duration predicted for radiation from an impact-generated plasma cloud. We show that thermal radiation from hot droplets ejected from the lunar surface during high-velocity impacts could be the cause of the afterglows.     

The directional characteristics of lunar infrared radiation

A theory of the directional characteristics of the lunar infrared radiation measured by Saari and Shorthill has been derived. This theory is in excellent agreement with experiment at all angles of observation and at all phase angles. The radiation law used to describe the angular dependence of the infrared radiation emitted by a flat element of the lunar surface is 0.85 cos + 0.22 cos², where is the angle between the surface normal and the direction of observation. This radiation law is subsequently modified by taking into account lunar surface roughness. We assume a surface covered in part with spherical craters of various depth to diameter ratios as a model for the lunar soil. Re-radiation within the craters has been accounted for. Extensive use is made of group theoretical and invariant tensor methods which enable us to show that most of the details of the radiation pattern do not depend on the detailed nature of the surface features assumed, but only on the average surface slope. A best fit to the Saari-Shorthill data has been obtained by assuming 50% of the lunar surface to be covered with craters with a depth to diameter ratio of 1:3, while the remainder of the surface is essentially flat. The mean deviation between theory and experiment is 4K.This work has been supported by the National Aeronautics and Space Administration under Contracts No. NAS8-20 385 and NAS8-25 585, Marshall Space Flight Center, Alabama.Receipt delayed due to postal strike in Great Britain.     

Relationship between positive cerium anomaly and adsorbed water in Antarctic lunar meteorites

Abstract— Concentrations of adsorbed water in single mineral grains of Antarctic lunar meteorites were determined with micro infrared (IR) spectroscopy. A relationship was found between the mineral's ability to adsorb water and the extent of Ce anomaly in rare earth element (REE) patterns precisely determined by the isotope dilution method using a thermal ionization mass spectrometer. Asuka (A) 881757, a lunar meteorite from the mare basalt without Ce anomaly, showed no trace of IR absorption due to adsorbed water. On the contrary, Yamato (Y) 791197-109, Y-86032-98, Y-86032-95, Y-791197-115 and Y-82192-55A from the lunar highland exhibiting positive Ce anomaly showed IR absorption due to adsorbed water in some of their minerals. The detected water would be of terrestrial origin, because it was not structurally bound and easy to exchange judging from the spectral band shape. The contrast in concentration of adsorbed water between the lunar highland and the mare basalt is derived from a difference in the density of microfractures in mineral grains. Average concentrations of adsorbed water in the lunar highland meteorites were 3.8 mg/cm³ for pyroxene and olivine, and 1.7 mg/cm³ for plagioclase. This contrast between minerals is noteworthy because it has been known that Ce anomaly of pyroxene and olivine is larger than that of plagioclase both for Antarctic lunar meteorites and some lunar rocks. Furthermore, more adsorbed water was detected for minerals in meteorites that exhibit larger Ce anomaly. The present observations demonstrate that the extent of Ce anomaly correlated with the concentration of adsorbed water, which suggests that active mineral surface resulting in adsorption of water could be a trace of interaction forming Ce anomaly. Terrestrial weathering on Antarctica and REE fractionation on the Moon are discussed for possible origins of the Ce anomaly.     

Preliminary results of the Apollo 17 infrared scanning radiometer

The thermal emission of the lunar surface has been mapped by an infrared scanner from lunar orbit. Samples from approximately 2.5 × 10⁵ scans reveal the full range of lunar temperatures from 80 K to 400 K. The temperature resolution was 1 K with about ± 2 K absolute precision. Spatial resolution was approximately 2 km over most of the horizon-to-horizon scan. The total mapped area amounted to approximately 30% of the lunar surface. The data currently available confirms the large population of nighttime thermal anomalies in western Oceanus Procellarum predicted by Earthbased observations. Most of these ‘hot spots’ are associated with fresh impact features or boulder fields. Also seen in the data are ‘cold spots’ where     

Latitude effects in lunar thermal evolution

A simple analytical model is developed from which we have calculated the temperature throughout the lunar interior resulting from internal heat sources and the imposition of surface temperature boundary conditions. The surface temperature is determined almost entirely by the balance of solar heating and surface reradiation; as a consequence this temperature is latitude dependent, decreasing towards the lunar poles. The internal solution shows that the latitude effect exists almost undiminished to great depths within the Moon. It is suggested that this dependence on latitude may have a significant effect on the Moon’s thermal evolution. Using the liquefaction model the high concentration of lunar maria at low latitudes may be explained.     

Thermal study of the unilluminated surface of the waning moon

A program of lunar infrared radiometry which uses large area scanning is described. Procedures for atmospheric attenuation correction and data reduction to temperature by relative radiometry are outlined. The scan data of the waning Moon taken during ten evenings in the 10- to 12-µm window are presented as isothermal contour maps of the lunar disc. More than 160 areas of anomalous thermal emission have been found in the lunar darkside data. These are tabulated and are also shown on an accompanying map. An error analysis, derived from accuracy estimates of the independent parameters, is included.     

Lunar and terrestrial tidal effects on the Moon's rotational motion

An accurate model of the rotation of the Moon, constructed by numerical integration, has been presented in a previous paper. All direct perturbations capable of producing at least 10^–4 seconds of arc on the Moon's rotational motion have been included, and the physical librations resulting from planetary effects and Earth-Moon figure-figure interactions have been presented. The present study deals with the Moon's physical librations resulting from the non-rigidities of the Moon and the Earth. The effects of the Moon's elasticity and of a lunar phase lag are analyzed. Physical librations due to lunar tides and those due to terrestrial tides are presented and described.     

Quantitative estimation of helium-3 spatial distribution in the lunar regolith layer

³He (helium-3) in the lunar regolith implanted by the solar wind is one of the most valuable resources because of its potential as a fusion fuel. The abundance of ³He in the lunar regolith is related to solar wind flux, lunar surface maturity and TiO₂ content, etc. A model of solar wind flux, which takes account of variations due to shielding of the nearside when the Moon is in the Earth's magnetotail, is used to present a global distribution of relative solar wind flux over the lunar surface. Using Clementine UV/VIS multispectral data, the global distribution of lunar surface optical maturity (OMAT) and the TiO₂ content in the lunar regolith are calculated. Based on Apollo regolith samples, a linear relation between ³He abundance and normalized solar wind flux, optical maturity, and TiO₂ content is presented. To simulate the brightness temperature of the lunar surface, which is the mission of the Chinese Chang-E project's multichannel radiometers, a global distribution of regolith layer thickness is first empirically constructed from lunar digital elevation mapping (DEM). Then an inversion approach is presented to retrieve the global regolith layer thickness. It finally yields the total amount of ³He per unit area in the lunar regolith layer, which is related to the regolith layer thickness, solar wind flux, optical maturity and TiO₂ content, etc. The global inventory of ³He is estimated as 6.50×¹⁰⁸ kg, where 3.72×¹⁰⁸ kg is for the lunar nearside and 2.78×¹⁰⁸ kg is for the lunar farside.     

Lunar velocity structure and compositional and thermal inferences

Seismic data from the Apollo Passive Seismic Network stations are analyzed to determine the velocity structure and to infer the composition and physical properties of the lunar interior. Data from artificial impacts (S-IVB booster and LM ascent stage) cover a distance range of 70–1100 km. Travel times and amplitudes, as well as theoretical seismograms, are used to derive a velocity model for the outer 150 km of the Moon. TheP wave velocity model confirms our earlier report of a lunar crust in the eastern part of Oceanus Procellarum.The crust is about 60 km thick and may consist of two layers in the mare regions. Possible values for theP-wave velocity in the uppermost mantle are between 7.7 km s^–1 and 9.0 km s^–1. The 9 km s^–1 velocity cannot extend below a depth of about 100 km and must decrease below this depth. The elastic properties of the deep interior as inferred from the seismograms of natural events (meteoroid impacts and moonquakes) occurring at great distance indicate that there is an increase in attenuation and a possible decrease of velocity at depths below about 1000 km. This verifies the high temperatures calculated for the deep lunar interior by thermal history models.Paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.     

INSTRUMENTATION FOR GEOLOGICAL FIELD WORK ON THE MOON

A human return to the Moon will require that astronauts are well equipped with instrumentation to aid their investigations during geological field work. Two instruments are described in detail. The first is a portable X-ray Spectrometer, which can provide rapid geochemical analyses of rocks and soils, identify lunar resources and aid selection of samples for return to Earth. The second instrument is the Geological and Radiation environment package (GEORAD). This is an instrument package, mounted on a rover, to perform in-situ measurements on the lunar surface. It can be used for bulk geochemical measurements of rocks and soils (particularly identifying KREEP-enriched rocks), prospect for ice in shadowed areas of craters at the poles and characterise the lunar radiation environment.     

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.     

Electrical conductivity of lunar surface rocks and chondritic meteorites

The electrical conductivities of several samples from returned Apollo 11 and 12 lunar rocks and from chondritic meteorites were measured from 300 to 1100K. Collectively the lunar samples represent all three of the major NASA classifications of lunar surface rocks. Of general interest is the observation that the conductivities of the lunar samples are much larger than the values which have previously been used in theoretical discussions of lunar phenomena. It is also found that the conductivity at 300K, (300), is extremely sensitive to the thermal history of the sample for both lunar and meteoritic material. Magnetic measurements are presented to help characterize the changes which occur upon heating.Principal Investigator - Apollo Lunar Science Program, Geophysics Research Laboratory, University of Tokyo, Japan.     

Broadband submillimeter measurements of the full Moon center brightness temperature and application to a lunar eclipse

We report on observations of the full Moon brightness temperature covering the frequency range of 300-950 GHz, and also on observations of the lunar eclipse of July 16, 2000, though only covering the frequency range of 165-365 GHz due to poor atmospheric transmission at higher frequencies. All observations were performed from the summit of Mauna Kea (HI) using a Fourier Transform Spectrometer mounted on the Caltech Submillimeter Observatory and supplemented by measurements of the atmospheric opacity using a 183 GHz Water Vapor Monitor. The telescope was pointed to the center of the lunar disk (with a footprint of ∼45-15 km on the Moon at 300 through 900 GHz). In order to obtain the correct values of the Moon brightness temperatures at all frequencies we carefully corrected for the atmospheric absorption, which varies across the submillimeter domain. This correction is fully described. The measured pre-eclipse brightness temperature is around 337 K in the 165-365 GHz range. This temperature slightly increases with frequency to reach ∼353 K at 950 GHz, according to previous broader band data. The magnitude of the temperature drop observed during the eclipse at 265 GHz (central frequency of the band covered) was about ∼70 K, in very good agreement with previous millimeter-wave measurements of other lunar eclipses. We detected, in addition, a clear frequency trend in the temperature drop that has been compared to a thermal and microwave emission model of the lunar regolith, with the result of a good match of the relative flux drop at different frequencies between model and measurements.     

Hypervelocity Impact Experiments in the Laboratory Relating to Lunar Astrobiology

The results of a set of laboratory impact experiments (speeds in the range 1–5 km s⁻¹) are reviewed. They are discussed in the context of terrestrial impact ejecta impacting the Moon and hence lunar astrobiology through using the Moon to learn about the history of life on Earth. A review of recent results indicates that survival of quite complex organic molecules can be expected in terrestrial meteorites impacting the lunar surface, but they may have undergone selective thermal processing both during ejection from the Earth and during lunar impact. Depending on the conditions of the lunar impact (speed, angle of impact etc.) the shock pressures generated can cause significant but not complete sterilisation of any microbial load on a meteorite (e.g. at a few GPa 1–0.1% of the microbial load can survive, but at 20 GPa this falls to typically 0.01–0.001%). For more sophisticated biological products such as seeds (trapped in rocks) the lunar impact speeds generate shock pressures that disrupt the seeds (experiments show this occurs at approximately 1 GPa or semi-equivalently 1 km s⁻¹). Overall, the delivery of terrestrial material of astrobiological interest to the Moon is supported by these experiments, although its long term survival on the Moon is a separate issue not discussed here.     

Lunar microcraters: Implications for the micrometeoroid complex

The contributions of lunar microcrater studies to understand the overall micrometeoroid environment are summarized and compared to satellite data.In comparison with small-scale laboratory studies, most lunar crater morphologies are compatible only with impact velocities > 3·5 km/sec and projectile densities between 1–8 g/cm³; a mean value is most likely 2–4 g/cm³. The particles arenon-porous and fairly equi-dimensional; needles, platelets, rods, whiskers and other highly asymmetric particle shapes can be excluded. Data on projectile chemistry is sparse and non-diagnostic at present.The crater diameters are converted into projectile masses via small scale laboratory impact experiments. Accordingly, the observed span of crater pit diameters (0·1 μm–1 cm) corresponds to a particle mass range of ≈ 10^?15–10^?3 g. This large, dynamic detection range is a unique feature of the lunar rock detector. Absolute crater densities on different rocks vary from “production” to “equilibrium” conditions. After normalization of such densities, relative microcrater size frequencies are obtained to deduce a mass frequency distribution for particles 10^?15–10^?3 g. There is evidence that this distribution is bimodal. A radiation pressure cutoff at 10^?12 g particle mass does not exist. The micrometeoroid flux obtained from lunar rocks is compatible with satellite data. There is indication that the micrometeoroid flux may have been lower in the past. Some speculative astronomical consequences concerning the origin of micrometeoroids are discussed.     

A new theory for the formation of the maria and cayley type lunar regions

A new liquefaction theory for the origin of the flat marial and Cayley areas on the lunar surface is described. It is supposed that the flat terrain in these areas resulted from periods in the development of the Moon when these regions, although not liquid, had a sufficiently low viscosity for the surfaces to relax more or less completely to a level form. To account for this low viscosity a model is developed in which, within these regions and for relatively short periods in the early history of the Moon, preferentially high temperatures were maintained close to the lunar surface. The paper examines in some detail the possibility that these high temperatures may have resulted from instabilities in the lunar heat flow pattern caused by the presence of a surface layer of very low thermal conductivity produced by the debris of early meteorite impacts.A comparison is made between current models for the formation of the lunar surface and the theory here proposed: the advantages of the latter are enumerated and discussed.Normally at Queen Mary College, University of London, England.