During the time period 1961–1972, 11 magnetometers were sent to the moon. The primary purpose of this paper is to review the results of lunar magnetometer data analysis, with emphasis on the lunar interior. Magnetic fields have been measured on the lunar surface at the Apollo 12, 14, 15, and 16 landing sites. The remanent field values at these sites are 38, 103 (maximum), 3, and 327 γ (maximum), respectively. Simultaneous magnetic field and solar plasma pressure measurements show that the Apollo 12 and 16 remanent fields are compressed during times of high plasma dynamic pressure. Apollo 15 and 16 sub‐satellite magnetometers have mapped in detail the fields above portions of the lunar surface and have placed an upper limit of 4.4 × 1013 G cm³ on the global permanent dipole moment. Satellite and surface measurements show strong evidence that the lunar crust is magnetized over much of the lunar globe. Magnetic fields are stronger in highland regions than in mare regions and stronger on the lunar far side than on the near side. The largest magnetic anomaly measured to date is between the craters Van de Graaff and Aitken on the lunar far side. The origin of the lunar remanent field is not yet satisfactorily understood; several source models are presented. Simultaneous data from the Apollo 12 lunar surface magnetometer and the Explorer 35 Ames magnetometer are used to construct a whole moon hysteresis curve from which the global lunar permeability is determined to be µ=1.012±0.006. The corresponding global induced dipole moment is ∼2 × 1018 G cm³ for typical inducing fields of 10−4 G in the lunar environment. From the permeability measurement, lunar free iron abundance is determined to be 2.5±2.0 wt%. Total iron abundance (sum of iron in the ferromagnetic and paramagnetic states) is calculated for two assumed compositional models of the lunar interior. For a free iron/orthopyroxene lunar composition the total iron content is 12.8±1.0 wt%; for a free iron/olivine composition, total iron content is 5.5±1.2 wt%. Other lunar models with a small iron core and with a shallow iron‐rich layer are also discussed in light of the measured global permeability. Global eddy current fields, induced by changes in the magnetic field external to the moon, have been analyzed to calculate lunar electrical conductivity profiles by using several different analytical techniques. From night side transient data, ranges of conductivity profiles have been calculated. At a depth of 250 km into the moon, the conductivity ranges between 1 × 10−4 and 2 × 10−3 mhos/m. Thereafter, conductivity rises with depth and ranges between 2 × 10−3 and 8 × 10−2 mhos/m at 1000 km depth. Harmonic analyses of day side data are similar to night side results except at the greater lunar depths, where harmonic day side profiles show lower conductivities than the night side results do. Transient response analysis has recently been applied to data measured in the lobes of the geomagnetic tail, and thus calculation is allowed of a conductivity profile that increases with...

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.

The response of the moon to magnetic‐field step transients in the solar wind has been investigated for over 100 events, by using simultaneous data from the Apollo‐12 lunar surface magnetometer and the lunar‐orbiting Explorer‐35 magnetometer. These transient events were all selected at times when the moon was in the free‐streaming solar wind and the Apollo‐12 magnetometer was on the lunar dark side. The lunar‐nighttime Apollo‐12 magnetometer data consistently show a distinct difference between radial and tangential surface magnetic‐field components for all step transients; this property strongly implies that the surface magnetometer is measuring a global rather than a local effect. The simplest model, although not unique, which qualitatively explains all the general aspects of the dark‐side transient‐response data is a spherically symmetric three‐layer model having a thin outer crust of very low electrical conductivity. The intermediate layer, of radial thickness R1–R2, where 0.95 RM≤R1

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During the 4‐day period when the moon is in the geomagnetic tail, the principal constituents of the lunar atmosphere are neon and argon. The surface concentrations of neon and argon are calculated from a theoretical model to be 3.9×103 and 1.7×103, respectively. The lunar atmosphere is ionized by solar ultraviolet radiation, resulting in electrons at a temperature of about 1.5×105 °K and ions at about 370°K. We investigated dynamic properties of the lunar ionosphere in the high‐latitude tail lobes during quiescent times when plasma energy density from external sources is below the sensitivity threshold of the suprathermal ion detector at the lunar surface. We found that a hydrostatic model of the ionospheric plasma is inadequate because the gravitational potential energy of the plasma is considerably smaller than its thermal energy. A hydrodynamic model, comparable to that used to describe the solar wind, is developed to obtain plasma densities and flow velocities as functions of altitude. The hydrodynamic flow of the ionospheric particles is away from the sunlit hemisphere, in a direction parallel to the magnetic field, and forms a cylinder whose base is the lunar diameter. At 100‐km altitude the calculated ionospheric density is 1.2×10−2 cm−3, with a flow velocity of 4–7 km/s. The corresponding energy density is 2.5×10−13 erg/cm3. Flow under these quiescent conditions exists approximately one third of the time in the geotail. During other times when cross‐tail electric fields are present, the steady flow away from the moon is disrupted by drift velocity components perpendicular to the geomagnetic field lines; also, sporadic occurrences of plasma sheet or lobe plasma temporarily dominate the plasma environment during nonquiescent times. The electromagnetic properties of the quiescent ionosphere are investigated, and it is concluded that plasma effects on lunar induction studies can be neglected for quiescent conditions in the geomagnetic tail lobes.