Measurement of lunar and planetary magnetic fields by reflection of low energy electrons

A method is described to measure the magnitude, direction and scale size of magnetic fields near the surface of the Moon and other planetary bodies. The method is especially useful when the planetary surface fields are weak and of small scale size. The method to measure magnetic fields by this technique can be described as follows: (1) The moon is situated in an ambient magnetic field (e.g., the interplanetary magnetic field) which is always populated by electrons in the energy range 15 eV to 15 keV. These electrons move along the field lines in helical trajectories. (2) Electrons approaching the Moon's surface are reflected if they encounter magnetic fields there. The fraction of electrons reflected depends on the strength, spatial extent and direction of the lunar magnetic field. (3) By use of well-established theory it is possible to calculate the reflection coefficient for a distribution of magnetic fields on the lunar surface. (4) Comparison of the observed and calculated reflection coefficients is then made in order to determine the actual lunar surface fields. (Auth.)