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.     

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.     

Lyman continuum observations of solar flares

A study is made of Lyman continuum observations of solar flares, using data obtained by the Harvard College Observatory EUV spectroheliometer on the Apollo Telescope Mount. We find that there are two main types of flare regions: an overall mean flare coincident with the H flare region, and transient Lyman continuum kernels which can be identified with the H and X-ray kernels observed by other authors. It is found that the ground level hydrogen population in flares is closer to LTE than in the quiet Sun and active regions, and that the level of Lyman continuum formation is lowered in the atmosphere from a mass column density m 5/sx 10^–6 g cm^–2 in the quiet Sun to m 3/sx 10^–4 g cm^–2 in the mean flare, and to m 10^–3g cm^–2 in kernels. From these results we derive the amount of chromospheric material evaporated into the high temperature region, which is found to be - 10¹⁵g, in agreement with observations of X-ray emission measures. A comparison is made between kernel observations and the theoretical predictions made by model heating calculations, available in the literature; significant discrepancies are found between observation and current particle-heating models.     

Lunar properties from transient and steady magnetic field measurements

The electrical conductivity of the lunar interior has been determined from magnetic field step transients measured on the lunar dark side. The simplest model which best fits the data is a spherically symmetric three layer model having a nonconducting outer crust of radial thickness 0.03R _moon; an intermediate layer of thicknessR0.37R _moon, with electrical conductivity ₁ 3.5 × 10^–4 mhos/m; and an inner core of radiusR ₂ 0.6R _m with conductivity ₂ 10^–2 mhos/m. Temperatures calculated from these conductivities in the three regions for an example of an olivine Moon are as follows: crust, < 440 K; intermediate layer, 890 K; and core, 1240 K. The whole-moon relative permeability has been calculated from the measurements to be/ ₀ = 1.03 ± 0.13. Remanent magnetic fields at the landing sites are 38 ± 3 at Apollo 12, 43 ± 6 and 103 ± 5 at two Apollo 14 sites separated by 1.1 km, and 6 ± 4 at the Apollo 15 site. Measurements show that the 38 remanent field at the Apollo 12 site is compressed to 54 by a solar wind pressure increase of 7 × 10^–8 dynes/cm².National Research Council Postdoctoral Associate.     

Apollo 12 ropy glasses revisited

Abstract— We analyzed ropy glasses from Apollo 12 soils 12032 and 12033 by a variety of techniques including SEM/EDX, electron microprobe analysis, INAA, and ³⁹Ar-⁴⁰Ar age dating. The ropy glasses have KREEP-like compositions different from those of local Apollo 12 mare soils; it is likely that the ropy glasses are of exotic origin. Mixing calculations indicate that the ropy glasses formed from a liquid enriched in KREEP and that the ropy glass liquid also contained a significant amount of mare material. The presence of solar Ar and a trace of regolith-derived glass within the ropy glasses are evidence that the ropy glasses contain a small regolith component Anorthosite and crystalline breccia (KREEP) clasts occur in some ropy glasses. We also found within these glasses clasts of felsite (fine-grained granitic fragments) very similar in texture and composition to the larger Apollo 12 felsites, which have a ³⁹Ar-⁴⁰Ar degassing age of 800 ± 15 Ma (Bogard et al, 1992). Measurements of ³⁹Ar-⁴⁰Ar in 12032 ropy glass indicate that it was degassed at the same time as the large felsite although the ropy glass was not completely degassed. The ropy glasses and felsites, therefore, probably came from the same source. Most early investigators suggested that the Apollo 12 ropy glasses were part of the ejecta deposited at the Apollo 12 site from the Copernicus impact Our new data reinforce this model. If these ropy glasses are from Copernicus, they provide new clues to the nature of the target material at the Copernicus she, a part of the Moon that has not been sampled directly.     

Cosmic ray exposure ages of features and events at the apollo landing sites

Cosmic ray exposure ages of lunar samples have been used to date surface features related to impact cratering and downslope movement of material. Only when multiple samples related to a feature have the same rare gas exposure age, or when a single sample has the same⁸¹Kr-Kr and track exposure age can a feature be considered reliably dated. Because any single lunar sample is likely to have had a complex exposure history, assignment of ages to features based upon only one determination by any method should be avoided. Based on the above criteria, there are only five well-dated lunar features: Cone Crater (Apollo 14) 26 m.y., North Ray Crater (Apollo 16) 50 m.y., South Ray Crater (Apollo 16) 2 m.y., the emplacement of the Station 6 boulders (Apollo 17) 22 m.y., and the emplacement of the Station 7 boulder (Apollo 17) 28 m.y. Other features are tentatively dated or have limits set on their ages: Bench Crater (Apollo 12) ?99 m.y., Baby Ray Crater (Apollo 16) ?2 m.y., Shorty Crater (Apollo 17) ≈ 30 m.y., Camelot Crater (Apollo 17) ?140 m.y., the emplacement of the Station 2 boulder 1 (Apollo 17) 45–55 m.y., and the slide which generated the light mantle (Apollo 17) ?50 m.y.     

TWO-FLUID MODEL FOR HEATING OF THE SOLAR CORONA AND ACCELERATION OF THE SOLAR WIND BY HIGH-FREQUENCY ALFVÉN WAVES

A model of the solar corona and wind is developed which includes for the first time the heating and acceleration effects of high-frequency Alfvén waves in the frequency range between 1 Hz and 1 kHz. The waves are assumed to be generated by the small-scale magnetic activity in the chromospheric network. The wave dissipation near the gyro-frequency, which decreases with increasing solar distance, leads to strong coronal heating. The resulting heating function is different from other artificial heating functions used in previous model calculations. The associated thermal pressure-gradient force and wave pressure-gradient force together can accelerate the wind to high velocities, such as those observed by Helios and Ulysses. Classical Coulomb heat conduction is also considered and turns out to play a role in shaping the temperature profiles of the heated protons. The time-dependent two-fluid (electrons and protons) model equations and the time-dependent wave-spectrum equation are numerically integrated versus solar distance out to about 0.3 AU. The solutions finally converge and settle on time-stationary profiles which are discussed in detail. The model computations can be made to fit the observed density profiles of a polar coronal hole and polar plume with the sonic point occurring at 2.4 R and 3.2 R , respectively. The solar wind speeds obtained at 63 R are 740 km s^-1 and 540 km s^-1; the mass flux is 2.1 and 2.2 × 10⁸ cm^-2 s^-1 (normalized to 1 AU), respectively. The proton temperature increases from a value of 4 × 10⁵ K at the lower boundary to 2 × 10⁶ K in the corona near 2 R .     

Green spherules from Apollo 15: Inferences about their origin from inert gas measurements

Green spherules from the clod 15426 and from fines 15421 contain about 100 times less trapped inert gases than normal bulk fines from Apollo 15. These spherules have apparently never been directly exposed to the solar wind. Spherules from other fines contain about 10 times more trapped gas than those from the clod. The gas in the former is surface correlated. However, spherules from fines 15401 are exceptionally gas-poor. (He⁴/Ne²⁰) _T in all spherules is commonly less than 10, which implies severe He⁴ losses. (Ne²⁰/Ar³⁶) _T on the other hand is nearly always greater than 10; and ranges up to 20.3.The Ne²¹ _C and Ar³⁸ _C radiation ages vary from 22 to 750 × 10⁶ yr, but most of them lie in the range 200–400 × 10⁶ yr. He³ _C ages are always much younger, owing to He³ _C losses.The trapped gases can be of solar-wind origin, but this origin requires a two-stage model for the spherules from the clods. First, solar wind was trapped in a parent material, from which the spherules were formed, presumably by impact melting. When the spherules were formed, some fraction of the original gas was retained by them. Another possibility is that the gases were absorbed from an ambient gas phase.The trapped gases may also be assumed to represent primordial lunar gas. The composition of this gas is then similar to the solar or unfractionated component of gas-rich meteorites, but unlike that in most of the carbonaceous chondrites.The Ar⁴⁰-Ar³⁶ systematics show two families of spherules: those from 15426 and 15421 which define a line with slope of about 4–5; and those from the fines which fall near a line with slope of about 1.4–1.9. Both lines have similar Ar⁴⁰-intercept-values of about 3–9 × 10^–6 cm³ STP g^–1 of Ar⁴⁰. The corresponding K-Ar⁴⁰ age can be as old as 4300 or as young as 2500 × 10⁶.The gas content of the spherules from fines suggests strongly that all spherules were at one time in clod-like material. This, in turn, seems to imply that a body or layer of cloddy material like 15426 was, and perhaps still is present in the Apollo 15 landing area. Cone Crater impact has tapped this body, but has probably not produced the clods. The green material may have been transported to the Apollo 15 site from elsewhere either as impact-ejecta or by a volcanic eruption. Our results do not permit a choice between the two possibilities.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April, 1973.On leave of absence at the Max-Planck-Institut für Kernphysik, Heidelberg, Germany.     

Infrared and Raman spectra of lunar samples from Apollo 11, 12 and 14

We report the room temperature infrared reflectance spectra of several lunar surface rocks in the form of polished slices or butt ends. The spectra were obtained over the frequency range 20-2000 cm^–1 throughout the mid and far infrared (5-500µ) region of the electromagnetic spectrum where the fundamental internal and lattice vibrational modes of all minerals and rocks occur.Some fines samples were examined as pressed pellets and their reflectivities compared with the bulk samples. Several terrestrial minerals and rocks were also investigated. Kramers-Kronig analyses of these reflectance spectra were undertaken and the dispersion of the dielectric response ( and ) and the optical constants (n andk) have been determined over this frequency range. The low frequency and high frequency (infrared) dielectric constants were also calculated from the reflectance data.Raman light scattering measurements were made on all the samples supplied from the first three Apollo missions. Large background scattering proved to be the greatest experimental problem. Successful spectra in nearly all cases were obtained from small crystalline inclusions imbedded in the main ground mass. Some crystalline bulk rocks containing many very fine inclusions gave identifiable spectra and at least three different types were obtained.Supported by NASA Grant NGR 22-011-069 and by a Northeastern University Grant for Basic Research.     

Line intensity ratios of transitions within the 1s 22s 22p 2 ground configuration of Mgvii

Using theR-matrix approach new calculations have been made for the electron impact excitation of the fine structure transitions within the 1s ²2s ²2p ² ground configuration of Mgvii. The computations have been made at a large number of energies in order to account for the contribution of resonances. All partial waves withL 9 are included in the calculations which are considered to be sufficient for the convergence of collision strengths in the energy range below 65 Ry. From this collision strength data, excitation rate coefficients have been calculated at a series of electron temperatures which are employed in the computation of population of the five lowest levels of Mgvii. The line intensity ratios for the transitions³ P ₁ ¹ D ₂ and³ P ₂ ¹ D ₂ to³ P ₁ ¹ S ₀ are then calculated in the temperature range of 10⁵ to 10⁷ K at electron densities in the range 10⁶ to 10¹⁰ cm^–3. The calculated values are in good agreement with the earlier available results.     

The velocity structure of the lunar crust

Seismic refraction data, obtained at the Apollo 14 and 16 sites, when combined with other lunar seismic data, allow a compressional wave velocity profile of the lunar near-surface and crust to be derived. The regolith, although variable in thickness over the lunar surface, possesses surprisingly similar seismic properties. Underlying the regolith at both the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is low-velocity brecciated material or impact derived debris. Key features of the lunar seismic velocity profile are: (i) velocity increases from 100–300 m s^–1 in the upper 100 m to 4 km s^–1 at 5 km depth, (ii) a more gradual increase from 4 km s^–1 to 6 km s^–1 at 25 km depth, (iii) a discontinuity at a depth of 25 km and (iv) a constant value of 7 km s^–1 at depths from 25 km to about 60 km. The exact details of the velocity variation in the upper 5 to 10 km of the Moon cannot yet be resolved but self-compression of rock powders cannot duplicate the observed magnitude of the velocity change and the steep velocity-depth gradient. Other textural or compositional changes must be important in the upper 5 km of the Moon. The only serious candidates for the lower lunar crust are anorthositic or gabbroic rocks.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April, 1973.     

The ultraviolet extinction by hollow spherical particles of graphite

Using the discrete dipole approximation, we have calculated the extinction efficiency of hollow spherical particles of graphite as a possible constituent of interstellar grains. The particles had a shell structure with the basal plane perpendicular to the radius. The calculations were made on the particles having the outer radiusR ₀=10 and 5nm in the wave number region from 0.8 to 8.0 m^–1 using the anisotropic optical constants. It was found that the hollow particles with the inner radiusR ₁0.65R ₀ yield an extinction feature at 4.6 m^–1, which fits fairly well to one observed in the interstellar extinction.     

Fission Track Age of the Brahin Pallasite

The results of the determination of the fission track age of the Brahin pallasite are presented. Crystals of phosphates (stanfieldites), with an enhanced uranium concentration, were found directly in the investigated samples. Fossil tracks in them are represented by two generations. The distribution and partial annealing of first-generation track lengths point to a shock/thermal event at an early stage in the cosmic history of the pallasite. The value of the fission track age, registering the time of its passage, was computed from second-generation tracks. It was shown that the second generation is represented mainly by tracks of the spontaneous fission of ²³⁸U and ²⁴⁴Pu nuclei (_Pu/_U 4). The calculations performed made it possible to establish that the last intensive thermal event in the cosmic history of the Brahin pallasite occurred 4.26–4.20 billion years ago. The temperature of the reheating of its parent body did not rise above 500°C. The excellently preserved character of the second-generation tracks provides evidence that the pallasite underwent subsequent cosmic evolution in mild conditions.     

Positrons and low energy cosmic rays from supernovae

Burgeret al. (1970) calculated the positron flux from the decay of⁵⁶Co⁵⁶Fe from cosmic rays injected from supernovae. The plasma properties of the ejected matter are determined in the present calculation in order to include the ionization loss of the positrons as the matter expands. It is found that using the matter velocity distribution of previous supernova model calculations that roughly 10% of the positrons escape. The average lifetime in the galaxy due to ionization loss is found to be relatively small, 1.5×10⁵ yr, and with the above injection results in ×3, the observed flux. The same matter velocity distribution is subjected to ionization loss in the galaxy and a steady state low energy, 10E200 MeV, differential flux spectrum is found,J(E)E ^–1.2. This removes the difficulty of the high galactic energy density resulting from a steeper spectrum.     

Production of a short-lived filament by a surge

A large surge was observed on September 17, 1971, part of which, after travelling 200 000 km through the corona, returned to the surface to form a filament. The filament lasted about 30 min, then rose up and returned to the source of the surge. We interpret this as the filling of a semi-stable magnetic trap.The energetics of radio, X-ray, and surge expulsion are estimated. The radio spectrum and flux correspond to a thermal source of area 4 (arcmin)², T 190 000 K, N _e ² V 7 × 10⁴⁸, which is optically deep at 8800 MHz.The soft X-ray source has T 12 × 10⁶ K, N _e ² V 3 × 10⁴⁸; and if an equal mass is expelled in the surge, the kinetic energy of the surge is similar to the thermal energy of the X-ray source.     

Silicon carbide in circumstellar environment

The presence of small clusters of silicon carbide (SiC) in circumstellar dust shells surrounding late-type stars is inferred from a broad emission feature peaking at around 11µm in infrared spectra [1]. These clusters are expected to condense from molecular arrangements composed of a few carbon and silicium atoms which are present in stellar winds surrounding carbon-rich late-type stars. We have searched for the possible geometric structures of SiC _n ⁺ radicals (n 5) on the basis ofab initio calculations. It is predicted that the linear structures are energetically favored compared to the other planar and 3D ones, except for SiC ₂ ⁺ where a doubt subsists and for SiC ₃ ⁺ where the rhombic structure is clearly more stable than the linear one. In the same way, a conspicuous even-odd alternation of the stability with the number of carbon atoms along the subset of linear species is shown. Vibrational frequencies of all the structures under consideration have then been determined. The possible destabilizing influence of a finite temperature effect on these structures has also been analyzed by using general considerations of thermal statistics.     

Properties and mixing of soil components in Apollo 17 double-drive tube 79001/2

Abstract— Previous studies of Apollo 17 double-drive tube 79001/2 showed that portions of this lunar regolith segment have some unusual properties, such as very high I_s/FeO values (Monis et al., 1989) and N contents (Stone and Clayton, 1989). To understand the geologic significance of these features in this core, we determined the grain-size distribution and modal abundance of the petrographic constituents for samples from 12 different depths of the core. Also, we measured the elemental and isotopic compositions of noble gases in the coarse-grained (150–250 μm) and fine-grained (<20 μm) sample fractions from four depths of this core. The agglutinate abundance and ³⁶Ar contents show depth-related variations similar to those observed for I_s/FeO and N in this core. Samples from the top (～0.5 cm depth) and the bottom (～45 cm depth) of the drive tube are related to Apollo 17 submature soils with about 250–300 Ma galactic cosmic-ray (GCR) exposure age. But the soil at the top of the drive tube received additional surface irradiation for ～2 Ma after deposition at Van Serg. The samples at intermediate depths (i.e., ～7 cm (upper zone) and ～20 cm (lower zone) of the 79001/2 core) show features characteristic of mixtures of Apollo 17 mature soils and finely comminuted regolith breccias having about 600–800 Ma GCR exposure age. The mixing ratios between the coarse and fine fractions of the intermediate-depth samples are similar to each other. Though the mixing ratios for the samples from the top and the bottom of the core are also similar to each other, they differ significantly from the ratios at intermediate depths. The results presented here are consistent with the two-component Van Serg core model proposed by Stone and Clayton (1989) and McKay et al. (1988).     

Charge state distributions of iron in gradual solar energetic particle events

The energy and charge spectra of Fe ions accelerated in gradual events are calculated numerically. Our results are compared with the available observations. Stripping of Fe ions by thermal electrons and protons during ion acceleration in the solar corona results in the dependence of mean charge barq _Feon energy. We consider the influence of varying plasma parameters (temperature T, number density N, and spectral index of turbulence S) on the charge distribution of iron. Our calculations indicate T10⁶ K and N(0.5–1)×10¹⁰ cm^–3at the accelerating site, provided the characteristic acceleration time is about 1 s. The calculated charge spectra for S>2 and S<2 turn out to be different, but some theoretical and experimental uncertainties do not yet allow this parameter to be extracted from observational data. The theoretically obtained charge distributions of Fe could be important in the light of ACE spacecraft data which are currently available for analysis.     

Cylindrical oscillations of force-free electromagnetic fields

This paper is devoted to Force-Free Electromagnetic Oscillations in a constant magnetic field. A correction is made in the derivation of the basic equation. The paper confirms the predicted spectrum of frequencies, namely _n = _o (n + 1)^1/2;n = 0, 1, 2, .... In addition it is suggested that hybrid frequency _n = ( _n ² + _H ² )^1/2 should be found in observational data.     

Thermophysical properties of Apollo 12 fines

The vacuum thermal conductivity of the Apollo 12 fines is presented as a function of temperature for densities of 1300, 1640 and 1970kg/m³. It is found to vary from about 10^?3W/m-°K at 100°K to about 3 x 10^?3W/m-°K at 400°K. The conductivity of the fines is found to be close to that of terrestrial basalt both under vacuum and at higher pressures. The thermal diffusivity is calculated from conductivity and specific heat data. Average values of the thermal conductivity, thermal diffusivity and thermal parameter are also presented.