Possible fossil lunar magnetism inferred from satellite data

Magnetization of selected nonmare areas, principally on the moon's far side, is inferred from positive disturbances in the magnitude of the magnetic field exterior to the magnetic signature of the lunar cavity observed in magnetometer data from the lunar orbiter Explorer 35. A less favored model for the field perturbations involves variations in the thickness of the low-conductivity crustal layer of 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.     

Satellite observations of magnetic fields due to ocean tidal flow

The ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through Earth's main magnetic field. Extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring Earth's magnetic field. Here, we consider the magnetic fields generated by the ocean lunar semidiurnal (M2) tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations.     

Surveyor v: magnet experiment

During the Surveyor V landing, a footpad with an attached permanent magnet assembly slid for about a meter through lunar surface material at a depth of about 10 centimeters. Subsequent pictures showed material adhering to the magnetic pole edges, where the magnetic field strength is greatest. Comparison of these pictures with those made under simulated laboratory conditions permits three conclusions. (i) Iron is present on the lunar surface in one of the forms attracted to a 500-gauss magnet. (ii) A 1-percent addition by volume of powdered free iron to a powdered terrestrial rock represents an upper limit for the lunar results. (iii) The lunar results are most similar to a terrestrial plateau basalt with no addition of free iron.     

Permanent lunar surface magnetism and its deflection of the solar wind

Magnetic compressions intermittently observed outside the lunar wake in the solar wind may be limb shocks caused by the presence of local regions of permanent magnetism on the lunar limb. Observable compression would be due to regions of length scale (radius) at least as great as several tens of kilometers and field strength greater, similar 10 gammas. Thousands of such regions might exist on the lunar surface. The steady magnetic field measured at the Apollo 12 site probably has length scale less, similar 10 kilometers and probably does not produce an observable limb shock.     

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.     

The moon: sources of the crustal magnetic anomalies

Previously unmapped Apollo 16 subsatellite magnetometer data collected at low altitudes over the lunar near side are presented. Medium-amplitude magnetic anomalies exist over the Fra Mauro and Cayley Formations (primary and secondary basin ejecta emplaced 3.8 to 4.0 billion years ago) but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles. The largest observed anomaly (radial component approximately 21 gammas at an altitude of 20 kilometers) is exactly correlated with a conspicuous light-colored deposit on western Oceanus Procellarum known as Reiner gamma. Assuming that the Reiner gamma deposit is the source body and estimating its maximum average thickness as 10 meters, a minimum mean magnetization level of 5.2 +/- 2.4 x 10(-2) electromagnetic units per gram, or approximately 500 times the stable magnetization component of the most magnetic returned sample, is calculated. An age for its emplacement of 相似文献   

Lunar magnetic anomalies and surface optical properties

For typical solar wind conditions, lunar magnetic anomalies with dipole moments m > 5 x 10(13) gauss-cubic centimeters will strongly deflect the solar wind, producing local plasma voids at the lunar surface. The correlation of the largest observed anomalies (m approximately 10(16) gauss-cubic centimeters) with unusual, relatively high albedo surface features may therefore imply that solar wind ion bombardment is an important determinant of the optical properties of the lunar surface.     

Lunar magnetic field: permanent and induced dipole moments

Apollo 15 subsatellite magnetic field observations have been used to measure both the permanent and the induced lunar dipole moments. Although only an upper limit of 1.3 x 10(18) gauss-cubic centimeters has been determined for the permanent dipole moment in the orbital plane, there is a significant induced dipole moment which opposes the applied field, indicating the existence of a weak lunar ionosphere.     

Magnetic dynamo in the moon: a comparison with the Earth

The assumption that the moon had an internal magnetic field produced in the same way as the geomagnetic field requires that the moon rotated faster than the angular velocity at which it would break up. This suggests that a lunar dynamo is not a tenable explanation for the magnetic remanence observed on the moon.     

Ultrathin amorphous coatings on lunar dust grains

UItrathin amorphous coatings have been observed by high-voltage electron microscopy on micrometer-sized dust grains from the Apollo 11, Apollo 12, Apollo 14, and Luna 16 missions. Calibration experiments show that these coatings result from an "ancient" implantation of solar wind ions in the grains. This phenomenon has interdisciplinary applications concerning the past activity of the sun, the lunar albedo, the ancient lunar atmosphere and magnetic field, the carbon content of lunar soils, and lunar dynamic processes.     

Lunar-modulated geomagnetic orientation by a marine mollusk

Behavioral experiments indicated that the marine opisthobranch mollusk Tritonia diomedea can derive directional cues from the magnetic field of the earth. The magnetic direction toward which nudibranchs spontaneously oriented in the geomagnetic field showed recurring patterns of variation correlated with lunar phase, suggesting that the behavioral response to magnetism is modulated by a circa-lunar rhythm. The discovery of a magnetic sense in a mollusk with giant, reidentifiable neurons provides a unique opportunity to study the cellular mechanisms underlying magnetic field detection.     

Lunar surface magnetic fields and their interaction with the solar wind: results from lunar prospector

The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30 degreesS to 80 degreesS) and low ( approximately 100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80 degreesS latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system.     

Mariner 10 mercury encounter

Mariner 10's closet approach to Mercury on 29 March 1974 occurred on the dark side of the planet at a range of approximately 700 kilometers. The spacecraft trajectory passed through the shadows of both the sun and Earth. Experiments conducted included magnetic fields, plasma and charged particle studies of the solar wind interaction region, television photography, extreme ultraviolet spectroscopy of the atmosphere, the detection of infrared thermal radiation from the surface, and a dual-frequency radio occultation in search of an ionosphere.     

Lunar impact basins and crustal heterogeneity: new Western limb and far side data from galileo

Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole-Aitken basin (>2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.     

A new theory of lunar magnetism

In the hypothesis advanced here it is supposed that the field, in which rocks at the lunar surface acquired the remanent magnetization found through the Apollo project, arose from permanent magnetization of the deep interior of the moon. This theory involves the assumption that the moon, apart from a surface shell, accreted cold and remained below the Curie point of iron until sometime later than 3 x 10(9) years ago. The magnetization was acquired as the moon formed in a gas sphere in the strong magnetic field of the early sun.     

Magnetic reconnection in the near Venusian magnetotail

Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.     

Lunar surface: changes in 31 months and micrometeoroid flux

Comparison of pictures of the lunar surface taken 31 months apart by Surveyor 3 and Apollo 12 show only one change in the areas disturbed by Surveyor: a 2-millimeter particle, in a footpad imprint, that may have fallen in from the rim or been kicked in by an approaching astronaut. Vertical walls 6 centimeters high did not collapse and dark ejecta remained dark. No meteorite craters as large as 1.5 millimeters in diameter were seen on a smooth soil surface 20 centimeters in diameter; this indicates a micrometeoroid flux lower than 4 x 10(-7) micrometeoroids per square meter-second at an energy equivalent to about 3 x 10(-8) gram at 20 kilometers per second. This flux is near the lower limit of previous determinations.     

An impactor origin for lunar magnetic anomalies

The Moon possesses strong magnetic anomalies that are enigmatic given the weak magnetism of lunar rocks. We show that the most prominent grouping of anomalies can be explained by highly magnetic extralunar materials from the projectile that formed the largest and oldest impact crater on the Moon: the South Pole-Aitken basin. The distribution of projectile materials from a model oblique impact coincides with the distribution of magnetic anomalies surrounding this basin, and the magnetic properties of these materials can account for the intensity of the observed anomalies if they were magnetized in a core dynamo field. Distal ejecta from this event can explain the origin of isolated magnetic anomalies far from this basin.     

The ancient lunar core dynamo

Lunar paleomagnetism provides evidence for the existence of an ancient lunar magnetic field generated in an iron core. Paleointensity experiments give a surface field of 1.3 gauss, 4.0 x 10(9) years ago, subsequently decreasing exponentially. Thermodynamic arguments give a minimum value of the heat source in the core at that time: known sources, radioactive and other, are quantitatively implausible, and it is suggested that superheavy elements were present in the early moon.