Curtis Willard Parkin

Apollo 12 magnetometer: measurement of a steady magnetic field on the surface of the moon.

The Apollo 12 magnetometer has measured a steady magnetic field of 36 � 5 gammas on the lunar surface. Surface gradient measurements and data from a lunar orbiting satellite indicate that this steady field is localized rather than global in its extent. These data suggest that the source is a large, magnetized body which acquired a field during an epoch in which the inducing field was much stronger than any that presently exists at the moon.

Whole body response of the moon to electromagnetic induction by the solar wind

A comparison has been made of the interplanetary magnetic field as measured both by Apollo 12 on the lunar surface and by Explorer 35 in orbit around the moon. Two examples are given, one of a step change in the field vector and another of a sinusoidally varying field. A large response measured on the surface is attributed to confinement of the induced field lines between the streaming solar plasma and the high-conductivity interior. A steep bulk electrical conductivity gradient in the lunar crust is implied, with a confining layer roughly 100 kilometers deep.

Global electromagnetic induction in the Moon and planets

Abstract A summary of experiments and analyses concerning electromagnetic induction in the Moon and other extraterrestrial bodies is presented. Magnetic step-transient measurements made on the lunar dark side show the eddy current response to be the dominant induction mode of the Moon. Analysis of the poloidal field decay of the eddy currents has yielded a range of monotonic conductivity profiles for the lunar interior: the conductivity rises from 3·10 −4 mho/m at a depth of 170 km to 10 −2 mho/m at 1000 km depth. The static magnetization field induction has been measured and the whole-Moon relative magnetic permeability has been calculated to be μ μ 0 = 1.01 ± 0.06 . The remanent magnetic fields, measured at Apollo landing sites, range from 3 to 327 γ. Simultaneous magnetometer and solar wind spectrometer measurements show that the 38-γ remanent field at the Apollo 12 site is compressed to 54 γ by a solar wind pressure increase of 7·10 −8 dyn/cm 2 . The solar wind confines the induced lunar poloidal field; the field is compressed to the surface on the lunar subsolar side and extends out into a cylindrical cavity on the lunar antisolar side. This solar wind confinement is modeled in the laboratory by a magnetic dipole enclosed in a superconducting lead cylinder; results show that the induced poloidal field geometry is modified in a manner similar to that measured on the Moon. Induction concepts developed for the Moon are extended to estimate the electromagnetic response of other bodies in the solar system.

Lunar Surface Magnetometer

The lunar surface magnetometer is one of five instruments in the Apollo lunar surface experiments package (ALSEP). It measures three components of the vector magnetic field in the range 0 to 400? with a resolution of 0.2? and a frequency response from dc to 3 Hz. This instrument also has a gradient measuring capability, making it an automatic magnetic observatory on the lunar surface. The magnetometer experiment deployed by Astronauts Conrad and Bean on Apollo 12 has measured a steady magnetic field of approximately 36? on the lunar surface. During each lunar day-night period the magnetic fields in the geomagnetic tail, transition zone, and interplanetary region are superimposed upon this steady field. Measurements of the induced lunar magnetic field will permit the interior electrical conductivity and temperature to be calculated.

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 ≈ 0.03Rmoon; an intermediate layer of thicknessΔR≈0.37Rmoon, with electrical conductivityσ1 ≈ 3.5 × 10−4 mhos/m; and an inner core of radiusR2 ≈ 0.6Rm with conductivityσ2 ≈ 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 beμ/μ0 = 1.03 ± 0.13. Remanent magnetic fields at the landing sites are 38 ± 3γ at Apollo 12, 43 ± 6 and 103 ± 5γ at two Apollo 14 sites separated by 1.1 km, and 6 ± 4γ at the Apollo 15 site. Measurements show that the 38γ remanent field at the Apollo 12 site is compressed to 54γ by a solar wind pressure increase of 7 × 10−8 dynes/cm2.

Electromagnetic sounding of the moon using Apollo 16 and Lunokhod 2 surface magnetometer observations /preliminary results/

A new technique of deep electromagnetic sounding of the Moon using simultaneous magnetic field measurements at two lunar surface sites is described. The method, used with the assumption that deep electrical conductivity is a function only of lunar radius, has the advantage of allowing calculation of the external driving field from two surface site measurements only, and therefore does not require data from a lunar orbiting satellite. A transient response calculation is presented for the example of a magnetic field discontinuity of February 13, 1973, measured simultaneously by Apollo 16 and Lunokhod 2 surface magnetometers.