Magnetic Imaging Technology Of Lunar Interior

As the unique satellite of the earth, the moon is the foothold for the first step of human exploration to the universe. The moon does not have the global intrinsic dipole magnetic field similar to the earth which can form a large-scale magnetosphere and its radius and internal conductivity(especially cr ust conductivity) is far less than that of the earth, thus it will be entirely penetrated when variations of the interplanetary magnetic field(IMF) sweep over it with in a n extremely short time. This feature provides a n effective method to study the interaction between IMF and the moon.The deep magnetic imaging technology is a new method we proposed to detect the inner structure of the moon. Based on the magnetotelluric sounding theory, high-precision magnetic field vector detection can be carried out on lunar surface, especially lunar magnetic field induced by step transient IMF; afterwards, deep geological structure could be inversed. It will be conducive for us to cognize the characteristics of lunar crust conductivity distribution, inner structure and asymmetry.In 1969, dozens of step transient IMF disturbance events were observed by Apollo 12 and Explorer 35 magnetometer respectively on lunar surface and in orbit at the same time, and variations of three magnetic field components were recorded; subsequently, the intrinsic magnetic field were detected in by Apollo 14, 15, 16 and Lunokhod 2 magnetometers from USSR in different single site on lunar surface, and then one-dimensional structure inside the moon was inferred from data inversion.Further, one or more magnetometer arrays can be deployed on lunar surface in future exploration, and then the vertical thickness difference and the lunar inner structure in higher accuracy at different sites could be inversed from field data of multi-site joint measurement. Technically supported by lunar rover and carried instruments, these scientific experiments can be completed by operation of the astronauts. Affected and restricted by special lunar electromagnetic environment, the measuring region deployed on lunar surface will not be too large, and the interval of adjacent sites may be only one percent or even thousandth of the lunar radius, which makes the curvature of the measuring region can almost be neglected.It is important to select appropriate positions of magnetometer arrays to ensure the quality and reliability of field data. The magnetic field of several selected sites on lunar surface induced by step transient IMF were calculated by spherical electromagnetic induction theory for two homogeneous models in different parameters; even more, the quantitative relationship of the difference of field components of adjacent sites with the difference of vertical crust thickness and site interval were given for a two-dimensional eccentric model. All are hoped to give certain references for the deployment of magnetometer arrays.