Density within the moon and implications for lunar composition

Density models for the Moon, including the effects of temperature and pressure, can satisfy the mass and moment of inertia of the Moon and the presence of a low density crust indicated by the seismic refraction results only if the lunar mantle is chemically or mineralogically inhomogeneous. IfC/MR ² exceeds 0.400, the inferred density of the upper mantle must be greater than that of the lower mantle at similar conditions by at least 0.1 g cm^–3 for any of the temperature profiles proposed for the lunar interior. The average mantle density lies between 3.4 and 3.5 g cm^–3, though the density of the upper mantle may be greater. The suggested density inversion is gravitationally unstable, but the implied deviatoric stresses in the mantle need be no larger than those associated with lunar gravity anomalies. UsingC/MR ³=0.400 and the recent seismic evidence suggesting a thin, high density zone beneath the crust and a partially molten core, successful density models can be found for a range of temperature profiles. Temperature distributions as cool as several inferred from the lunar electrical conductivity profile would be excluded. The density and probable seismic velocity for the bulk of the mantle are consistent with a pyroxenite composition and a 100 MgO/(MgO+FeO) molecular ratio of less than 80.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.     

Rotation of the moon and lunar coordinate systems

The need for precise definition of lunar reference systems is stressed and the principles on which systems of lunar coordinates could be based are established. Differences between coordinate systems defined by the dynamical properties of the lunar configuration and the rotational motion of the lunar globe about its centre of gravity are outlined, and rigorous mathematical formulae relating those systems have been developed. The principles of reduction of measurements are outlined and in the Appendix the absolute coordinates obtained for 700 lunar features are presented.Paper presented to the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 1971.     

Effects of the physical libration of the moon on lunar orbiters

Lunar physical libration, which is true oscillation of lunar equator in the space, alters the lunar gravitational field in the space coordinate system and affects the orbiting motion of lunar orbiters (hereafter called as lunar satellites) correspondingly. The effect is very similar to that of the precession and nutation on the earth satellites, and a similar treatment can be used. The variations in the gravitational force and in the orbit perturbation solution are clearly given in this paper together with numerical illustrations.     

Unipolar induction in the moon and a lunar limb shock mechanism

The unipolar induction mechanism is employed to calculate electric field profiles in the interior of a chemically homogeneous Moon possessing a steep radial thermal gradient characteristic of long-term radioactive heating. The thermal models used are those of Fricker, Reynolds, and Summers. From the magnetic field, the magnetic back pressure upon the solar wind is found. The electric field profile is shown to depend only upon the activation energy,E _o, of the geological material and the radial gradient of the reciprocal temperature. The current is additionally dependent upon the coefficient of the electrical conductivity function but only by a scale factor. Since the Moon is experimentally known to correspond to the case of weak interaction with the solar wind, the magnetic back pressure is calculated without the need for an iterative procedure. The results indicate that a hot Moon can yield sufficient current flow so that the magnetic back pressure is observable as a vestigial limb shock wave using an activation energy of about 2/3 eV together with a conductivity coefficient of about 10³ mhos/m. Such matter is approximated by diabase-like composition, although the result that both the activation energy and coefficient enter into the current determination does not rule out the possibility of a match with other similar substances. The calculations are entirely consistent with earlier results which indicated a model where the unipolar current density is dominated by a high impedance surface layer and a strong shock wave is inhibited. In addition to the magnetic back pressure, the integration of the current continuity equation permits current densities and joule heating rates to be calculated, though the magnitude of the latter for present solar wind conditions is not thermally important.On leave from NASA Ames Research Center     

The chemical composition and structure of the moon

Three types of igneous rocks, all ultimately related to basaltic liquids, appear to be common on the lunar surface. They are: (1) iron-rich mare basalts, (2) U-, REE-, and Al-rich basalts (KREEP), and (3) plagioclase-rich or anorthositic rocks. All three rock types are depleted in elements more volatile than sodium and in the siderophile elements when relative element abundances are compared with those of carbonaceous chondrites. The chemistry and age relationships of these rocks suggest that they are derived from a feldspathic, refractory element-rich interior that becomes more pyroxenitic; that is, iron/magnesium-rich; with depth.It is suggested that the deeper parts of the lunar interior tend toward chondritic element abundances. The radial variation in mineralogy and bulk chemical composition inferred from the surface chemistry is probably a primitive feature of the Moon that reflects the accretion of refractory elementenriched materials late in the formation of the body.     

Basaltic magmatism and the bulk composition of the moon

The lunar interior is comprised of two major petrological provinces: (1) an outer zone several hundred km thick which experienced partial melting and crystallization differentiation 4.4–4.6 b.y. ago to form the lunar crust together with an underlying complementary zone of ultramafic cumulates and residua, and (2) the primordial deep interior which was the source region for mare basalts (3.2–3.8 b.y.) and had previously been contaminated to varying degrees with highly fractionated material derived from the 4.4–4.6 b.y. differentiation event. In both major petrologic provinces, basaltic magmas have been produced by partial melting. The chemical characteristics and high-pressure phase relationships of these magmas can be used to constrain the bulk compositions of their respective source regions.Primitive low-Ti mare basalts (e.g., 12009, 12002, 15555 and Green Glass) possessing high normative olivine and high Mg and Cr contents, provide the most direct evidence upon the composition of the primordial deep lunar interior. This composition, as estimated on the basis of high pressure equilibria displayed by the above basalts, combined with other geochemical criteria, is found to consist of orthopyroxene + clinopyroxene + olivine with total pyroxenes > olivine, 100 MgO/(MgO + FeO) = 75–80, about 4% of CaO and Al₂O₃ and 2× chondritic abundances of REE, U and Th. This composition is similar to that of the earth's mantle except for a higher pyroxene/olivine ratio and lower 100 MgO/(MgO + FeO).The lunar crust is believed to have formed by plagioclase elutriation within a vast ocean of parental basaltic magma. The composition of the latter is found experimentally by removing liquidus plagioclase from the observed mean upper crust (gabbroic anorthosite) composition, until the resulting composition becomes multiply saturated with plagioclase and a ferromagnesian phase (olivine). This parental basaltic composition is almost identical with terrestrial oceanic tholeiites, except for partial depletion in the two most volatile components, Na₂ and SiO₂. Similarity between these two most abundant classes of lunar and terrestrial basaltic magmas strongly implies corresponding similarities between their source regions. The bulk composition of the outer 400 km of the Moon as constrained by the 4.6-4.4 b.y. parental basaltic magma is found to be peridotitic, with olivine > pyroxene, 100 MgO/ (MgO + FeO) 86, and about 2× chondritic abundances of Ca, Al and REE. The Moon thus appears to have a zoned structure, with the deep interior (below 400 km) possessing somewhat higher contents of FeO and SiO₂ than the outer 400 km. This zoned model, derived exclusively on petrological grounds, provides a quantitative explanation of the Moon's mean density, moment of inertia and seismic velocity profile.The bulk composition of the entire Moon, thus obtained, is very similar to the pyrolite model composition for the Earth's mantle, except that the Moon is depleted in Na (and other volatile elements) and somewhat enriched in iron. The similarity in major element composition extends also to the abundances of REE, U and Th. These compositional similarities, combined with the identity in oxygen isotope ratios between the Moon and the Earth's mantle, are strongly suggestive of a common genetic relationship.     

Solar-wind interactions with the moon: Nature and composition of nitrogen compounds

The lunar atmosphere and magnetic field are very tenuous. The solar wind, therefore, interacts directly with the lunar surface material and the dominant nature of interaction is essentially complete absorption of solar-wind particles by the surface material resulting in no upstream bowshock, but a cavity downstream. The solar-wind nitrogen ion species induce and undergo a complex set of reactions with the elements of lunar material and the solar-wind-derived trapped elements. The nitrogen concentration indigeneous to the lunar surface material is practically nil. Therefore any nitrogen and nitrogen compounds found in the lunar surface material are due to the solar-wind implantation of nitrogen ions. The flux of the solar-wind nitrogen ion species is about 6×10³ cm^–2 s^–1. Since there is no evidence for accumulation of nitrogen species in the lunar surface material, the outflux of nitrogen species from the lunar material to the atmosphere is the same as the solar-wind nitrogen ion flux. The species of the outflux are primarily NO and NH₃, and their respective concentrations in the near surface lunar atmosphere are found by calculation to be 327 and 295 cm^–3. The calculated concentration of NH₃ seems to be consistent with the sunrise concentration results of the mass spectrometer implanted on the lunar surface. This is not the case for the concentration of NO. According to the presently calculated concentration value of NO, the mass spectrometer should have detected NO at sunrise, but no report was made for its detection. There is also discrepancy about the concentration of N₂ which is explained in this paper. The concentrations of nitrogen species in the lunar material at the time of sample collection on the Moon remained about the same when the samples were analyzed on the Earth. However, no specific experiment was planned to detect the nitrogen species in the lunar material samples.     

On the accuracy of lunar ephemerides using the data provided by the future Russian lunar laser ranging system

The potential effect of the future Russian lunar laser ranging system (LLRS) on the accuracy of lunar ephemerides is discussed. In addition to the LLRS in Altai, several other observatories suitable for the LLRS installation are considered. The variation of accuracy of lunar ephemerides in the process of commissioning of new LLRS stations is estimated by mathematical modeling. It is demonstrated that the error in the determination of certain lunar ephemeris parameters may be reduced by up to 16% after seven years of operation of the Altai LLRS with a nearly optimal observational program.     

The significance of the magnetism observed in lunar rocks

Partial thermal remanence experiments on lunar igneous rocks indicate that the magnetization of lunar rocks is not a normal single component thermoremanent magnetization. The magnetization therefore may not have been acquired at the time of initial cooling of the rock and thus should be used cautiously in making estimates of the intensity of the ancient lunar magnetic field.Contribution No. 201, Geosciences Division, The University of Texas at Dallas.     

Shock melting and vaporization of lunar rocks and minerals

The entropy associated with the thermodynamic states produced by hypervelocity meteoroid impacts at various velocities are calculated for a series of lunar rocks and minerals and compared with the entropy values required for melting and vaporization.Taking into account shock-induced phase changes in the silicates, we calculate that iron meteorites impacting at speeds varying from 4 to 6 km/s will produce shock melting in quartz, plagioclase, olivine, and pyroxene. Although calculated with less certainty, impact speeds required for incipient vaporization vary from ~ 7 to 11 km/s for the range of minerals going from quartz to periclase for aluminum (silicate-like) projectiles. The impact velocities which are required to induce melting in a soil, are calculated to be in the range of 3 to 4 km/s, provided thermal equilibrium is achieved in the shock state.Contribution number 210, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, Calif. 91109, U.S.A.     

Report of the Working Party on the classification of the lunar igneous rocks

Abstract— A report is presented for a possible revised classification of lunar igneous rocks that still uses the division of Moon rocks into mare and highland types. It subdivides the mare rocks into basalts depending on TiO₂ content and glasses depending on colour, and subdivides the highland rocks principally into KREEP basalts and into coarse‐grained igneous rocks comparable to and using terrestrial igneous rock terminology.     

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.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

On244Pu in lunar rocks from Fra Mauro and implications regarding their origin

The evidence forin situ produced fission xenon from²⁴⁴Pu in rock 14321 is presented. The inferred abundance ratio²⁴⁴Pu/²³⁸U is found to be consistent with values observed in a meteorite. Data from a stepwise release of the xenon permits a characterization of the trapped component, which can be shown to be distinct from solar xenon. We discuss the evidence for the presence of fission gases and of uncorrelated radiogenic argon in this and in other Apollo 14 rocks and some implications regarding their origin.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

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.     

On the accretion of the earth and moon

The bodies which produced the premare impact craters on the moon contained a much higher proportion of smaller bodies in the earliest observable times than subsequently. This suggests that the earth and moon accreted from small objects with only an occasional large planetoid.If the earliest observable lunar craters are 4.3 × 10⁹ yr old, the half-life of the primitive planetesimals which produced the giant lunar craters larger than 161 km in diameter, was 143 × 10⁶ yr, while the half-life of the primitive planetesimals which produced lunar craters larger than 1 km in diameter was only 88 × 10⁶ yr. The half-life of the bodies which produced 1 km craters was still shorter, about 75 × 10⁶ yr.     

Minerals mapping of the lunar surface with Clementine UVVIS/NIR data based on spectra unmixing method and Hapke model

The distribution of minerals on the lunar surface is information which could contribute to studying lunar origin and evolution. In this paper, the distribution of clinopyroxene, orthopyroxene, olivine, ilmenite, and plagioclase on the lunar surface has been mapped based on Hapke radiative transfer model and linear unmixing of spectra with Clementine UVVIS/NIR data. The results have been validated on the basis of minerals modal abundance data of the Apollo samples, and problems in the minerals abundance mapping have been analyzed. The validation based on analysis data of Apollo samples indicates that plagioclase mapped in this paper represents the total abundance of plagioclase and agglutinitic glass. The minerals mapping results show that the lunar surface is mainly composed of pyroxene, plagioclase, agglutinitic glass, and ilmenite. Basalt in the lunar mare is mainly composed of clinopyroxene and ilmenite, and lunar highland is mainly composed of plagioclase and agglutinitic glass. Orthopyroxene is mainly distributed on the north of Mare Imbrium, on the south of Maria and Aitken Basin. According to our results, there is probably no large area of olivine distribution on the lunar surface which is different from earlier published results. Therefore, emphasis should be put on the olivine distribution in the minerals mapping using hyperspectral data such as M³ of Chandrayaan-1 and IIM of ChangE-1.     

On periodic flybys of the moon

This paper considers the plane circular restricted three-body problem for small . Symmetric periodic solutions of the second species (passing near the body of mass ) and their distance from the center of the body of mass are studied by constructing perturbations of arc-solutions (solutions with consecutive collisions) existing for =0. Orbits which also pass near the body of mass 1- are studied in detail. The results are applied to finding periodic orbits in the Earth-Moon system and in the Sun-Jupiter system.Russian version: Preprint No. 91 (1978) of Inst. Appl. Math.; present English translation was made by L. M. Perko and W. C. Schulz (February 1979).     

Improvement of the numerical lunar ephemeris with laser ranging data

Analysis of lunar laser ranging data is underway at several institutions. We describe here our efforts at improving the numerical ephemeris of Moon, based on over three years' span of data. Orbit generation and correction procedures are discussed briefly. Comparisons of the new ephemeris with observations and with a widely available ephemeris are illustrated. The standard deviation of the observation residuals is 7 m.Communication presented at the conference on Lunar Dynamics and Observational Coordinate Systems held January 15–17, 1973 at the Lunar Science Institute, Houston, Tex., U.S.A.