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The MAG/ER experiment relies on a Magnetometer for measurements of the Moon's global magnetic field in space and an Electron Reflectometer for measurements of localized magnetic fields on the surface of the Moon. The ER derives information on the Moon's surface magnetic fields by analyzing electrons that emanate from the Moon. For the most part, however, such electrons can only be detected a few days each months (around full Moon periods) when the Earth passes between the Sun and Moon, thereby shielding the Moon from the constant stream of electrons generated by the Sun. Yet with only close to half of the surface magnetic field data expected over its one year nominal mission collected to date, already the following results have been observed:

  • Although it was previously believed that the Moonís magnetic field was too weak to repel the charged particles of the solar wind, an intriguing magnetic anomaly on the Moonís surface has been found that can stand off the solar wind, thus creating the smallest known magnetosphere, magnetosheath and bow shock system in the Solar System. While most planetsí global fields create a large encompassing magnetosphere around the entire body, the Moon contains magnetized rocks on its upper layers, some of which are magnetized strongly enough to form small dipole magnetic fields scattered on the lunar surface. These mini-magnetospheres, around 100 km in diameter (the Moon is approximately 3500 km in diameter), can stand off the solar wind locally.

  • The presence of strong magnetic fields located diametrically opposite young large impact basins on the lunar surface have been detected. This discovery supports the theory that lunar crustal magnetization is associated with the formation of young impact basins. Two components of this model illustrate how such peculiar fields may have formed. A first component is that of an impactsí physical effects at the antipodes (or, opposite side). When large objects strike the Moon, seismic and surface waves are sent through the lunar material. This results in unusual looking terrain at the antipodes, where the rocks appear to have been temporarily fluidized and then resolidified. In addition, when ejecta from the original impacts are sent flying, secondary impacts occur where they land. Most of this ejecta lands near the periphery of the basin, but there is an increased amount found at the antipodes. The combination of the primary and secondary impactsí physical effects cause a shock, or pressure pulse, to be sent through the material of the lunar crust. Microscopic metallic iron particles in the soil carry this magnetization induced by this shock to the antipodal regions causing an increased magnetic field. A second component of the lunar impact model involves the build up of ionized gas. Impacts at velocities greater than 10 km/s will vaporize rock into hot gas, and this hot gas is partly ionized into electrons and positive ions. The ionized gas from the impact will expand around the Moon and exclude any ambient magnetic field from the ionized gas, forcing it around until it converges at the antipodes, thus compressing and amplifying the magnetic field at the antipodes.


    This diagram shows the how the Earth's magnetic field is affected by solar radiation-solar wind. The Earth's magnetic field is strong enough to "stand off" the radiation, that is divert it around the Earth much like a boulder in a running stream diverts water around it. LP's Magnetometer/Electron reflectometer experiment has revealed a tiny magnetic field on the Moon which is strong enough to accomplish the same feat.

  • The solar wind has been found to have non-uniformly (due to localized magnetic anomalies) implanted hydrogen in the lunar crust. Strong anomalies deflect the solar wind around local magnetic field, so we find concentrations of hydrogen around the peripheries of magnetic aberrations, but very little solar wind hydrogen is located directly at the center of these regions. Around the edges, where hydrogen exists in local concentrations, may be practical locations for possible future lunar bases.


    This diagram shows the magnetic anomaly on the Moon which is powerful enough to "stand off" the solar wind. This is the smallest such magnetic shock front ever identified.

Of course, the process of completely mapping the lunar magnetic fields is still in progress, and many more questions can be addressed once the complete data set is analyzed. At that point, scientists will be able to investigate the existence of a core and more accurately determine its upper size limit. They can also determine the electrical conductivity and postulate about the composition of the core. In addition, mapping the direction of the magnetization, and therefore determining the orientation of the field lines at the time of magnetization, will help elucidate the origin of the lunar magnetic field. Another enigma waiting to be solved is the unexpected correlation between individual magnetic anomalies with unusual albedos markings in the antipodal zones -- the markings are lighter in color, and therefore higher in albedo. Answers to these and many other questions are anticipated as the mission develops.

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