D. W. Strangway

Dielectric properties of the first 100 meters of the Moon

Reviewing 92 measurements of lunar sample dielectric constant versus density at frequencies above 100 kHz, gives the relationK′ = (1.93 ± 0.17)p by regression analysis, where K′ is the dielectric constant of a soil or solid at a density ofpg/cm3. This formula is the geometric mean between the dielectric constant of vacuum (1) and the zero porosity dielectric constant of lunar material. Similarly, the loss tangent (D) can be described byD = [(0.00053 ± 0.00056) + (0.00025 ± 0.00009)C]p whereD is the loss tangent at densitypg/cm3 withC percent of total FeO + TiO2 (approximately proportional to ilmenite content). Using the density versus depth relations derived from lunar surface core tubes, and from laboratory studies of lunar soil compression gives a model of the dielectric properties as a function of depth in the lunar regolith. The dielectric constant increases smoothly with depth, as a function of the soil compaction only. The loss tangent, however, is more sensitive to the ilmenite content than it is to density. Neither dielectric constant nor loss tangent varies significantly with the temperature observed in a lunar day.

The electromagnetic response of a low-loss, 2-layer, dielectric earth for horizontal electric dipole excitation

The use of the radio interferometry method requires a detailed understanding of the nature of electromagnetic wave propagation in structures composed of materials with low electrical loss. This paper contains the results of a detailed experimental and theoretical study into the response of a 2-layer, plane‐stratified, low‐ loss dielectric earth. The technique used to construct a scale model with microwave equipment to experimentally simulate the 2-layer structure response is discussed. The wave nature of the response derived from the theoretical investigations is used to interpret the features of the experimental results. The experimental results are useful in turn in demonstrating the reliability of approximate theoretical solutions for the electromagnetic fields about the dipole obtained by normal mode and geometrical optics methods. Such features as (1) the modification of the dipole radiation pattern seen when the antenna is placed at the interface between media of differing electrical properties, and...

A determination of the intensity of the ancient lunar magnetic field.

Thermal demagnetization of lunar breccia 15498,36 shows that the natural remanent magnetization is a simple thermoremanence carried by metallic iron. Using the classical Thellier-Thellier method the strength of the magnetizing field at the time of sample formation was found to be 2100 ±80 gammas.

Intermediate‐scale magnetic anomalies of the Earth

Four separate magnetic anomaly maps of the earth are derived from magnetometer satellite data acquired at dawn and at dusk using two different altitude ranges. The magnetic anomalies on the two dawn maps (or dusk maps) are well correlated for spherical harmonics of degree less than 51, suggesting that the time varying external magnetic field and leveling noise have negligible effects on these harmonics. Dawn and dusk maps have an appreciable asymmetric component for harmonics of degree n ⩽ 5 and n = 15 and 17, arising from the quasi‐stable external magnetic field. Dawn‐dusk covariant harmonics of degree 18⩽n⩽60 with signal‐to‐noise ratios greater than 1.5 correlate well. Correlation coefficients are higher than 0.75, implying that these harmonics can be repeatably derived. A global scalar magnetic anomaly map is derived based on these harmonics. The map is then converted to a magnetic susceptibility anomaly map by an inversion technique. The susceptibility anomalies delineate the ocean‐continent differenc...

Magnetic properties of lunar samples.

A breccia sample (10023) from the moon was found to have a strong and fairly stable remanent magnetization. If this sample was not magnetized by local fields in the spacecraft or in the lunar receiving laboratory, it must have been magnetized on the moon. This could have happened in a variety of ways, such as cooling through the Curie temperature, by comitinuous thermal cycling, or by impact, but all of these require the presence ofr a magnetic field. Such a field could have been of internal origin in the moon, or it could have been a residual effect from the earths magnetic field at a time when the moon and the earth were much closer together. Thermomagnetic studies identify the presence of iron with about 1 percent nickel (igneous). iron with abiout 5 to 10 percent nickel (meteoritic), iron with about 33 percent or more nickel (meteoritic), and ilmenite.

Paleomagnetism of a miocene transition zone in southeastern Oregon

Abstract A transition in the Earths magnetic field, recorded in a sequence of basaltic lavas in southeastern Oregon (15.1 ± 0.3m.y.) , has been investigated. The reversal pattern is similar at the various sample sites (up to 55 miles apart) and the apparent paleo-intensity ranges from 0.5 Oe outside the transition to a minimum of 0.025 Oe inside the transition. This range is somewhat greater than that reported in other studies of transition zones. The similarity in transition pattern at the widely separated locations indicates that crustal magnetic anomalies could not have given rise to the recorded field. It is probable that the main dipole field and/or non-dipole centers were the primary features influencing the acquisition of TRM during the transition.

A paleomagnetic conglomerate test using the Abee E4 meteorite

Abstract The meteorite Abee is a type 4 enstatite chondrite with many centimeter-size clasts. The paleomagnetic conglomerate test was applied to these clasts, to study the thermal and magnetic history of the meteorite. The directions of magnetization in mutually oriented clasts are significantly different, suggesting the meteorite was not reheated to temperatures much above 100°C during or after accretion. Paleointensity estimates were made using Thelliers method. Interior samples which were probably not reheated during entry into the earths atmosphere show paleointensities of several oersteds. The fusion crust is also strongly magnetized, showing paleointensities up to 60 Oe.

Induced polarization in disseminated sulfide ores containing elongated mineralization

A disseminated sulfide ore is represented by a two‐component system in which metallically conducting prolate spheroidal particles (simulating elongated mineralization) are randomly scattered throughout an electrolytic host. The Helmholtz equations describing the spatial and frequency dependence of anions and cations in the electrolyte near the surface of a particle are solved in prolate spheroidal coordinates. Expressions for the frequency‐dependent dipole moment induced on the particle by external electric fields transverse or parallel to the long axis of the particle are found by examining boundary conditions related to electrochemical charge transfer between the metallic particle and the electrolyte. The dipole moments of individual particles can be used to determine the effective conductivity spectrum of the mixture as a whole via the simple Maxwell formula or a novel recursive calculation which is accurate for large‐volume fractions of particles. Examples of conductivity spectra from this electrochem...

Temperature dependence of electrical conductivity and lunar temperatures

Numerous investigations of the electrical conductivity of lunar and terrestrial materials as a function of temperature have been performed to date in an attempt to provide data on which to base lunar interior temperatures from magnetometer-derived lunar conductivity profiles (Schwereret al., 1971, 1972, 1973; Dubaet al., 1972 and others). There are several pitfalls inherent in the extrapolation of lunar temperatures from laboratory measurements of electrical conductivity. These include the choice of representative material for the lunar interior, appropriate environmental conditions (pressure, fugacity, etc.) and the various measurement difficulties.

Remanent magnetization of lunar samples.

The remanent magnetization of samples returned from the moon by the Apollo 11 and 12 missions consists, in most cases, of two distinct components. An unstable component is readily removed upon alternating field (AF) demagnetization in fields less than 100 Oe and is considered to be an isothermal remanence acquired during or after return to earth. The second component, which has an intensity of about 1 to 2 × 10−6 emu/g, is unaltered by demagnetization in fields up to 400 Oe. It is probably a thermoremanent magnetization due to cooling from above 800°C in the presence of a field of a few thousand gammas. Chips from individual rocks have the same direction of magnetization after demagnetization, while the directions of different samples are random. This again demonstrates the high stability. Our data imply that the moon experienced a magnetic field that lasted at least from about 3.0 by to 3.8 by, which is the age range of Apollo 11 and 12 samples. One explanation of the origin of this field is that the moon had a liquid core and a self-exciting dynamo early in its history. The breccias studied behave very much like the igneous rocks, and it is probable that they acquired their magnetization during cooling. If this is the case, breccias can be used to extend the history to the field, provided suitable age dates can be obtained.