Abstract
Magnetic sounding is a powerful tool to explore the interior of
planetary bodies through the electrical conductivity structure. The
electrical conductivity structure of the lunar mantle has previously
been derived from surface magnetic field measurements as part of the
Apollo 12 mission and concurrent magnetometer data acquired from orbit
through the Explorer 35 satellite. Here, we derive the first global
conductivity structure using only satellite magnetometer data collected
by the recent Lunar Prospector and Kaguya Selene satellite missions. We
show that the field in the geomagnetic tail exhibits a simple
geometrical structure and can be well described by a single spherical
harmonic of degree and order one. Employing this information about the
inducing field geometry and assuming a potential representation of the
field in the geomagnetic tail, we derive a frequency-dependent transfer
function and invert it for a global one-dimensional (1-D) electrical
conductivity profile. Our global transfer function shows striking
similarity with the local one obtained from joint analysis of Apollo 12
and Explorer 35 magnetometer data. This indicates the lack of local
variations at the Apollo 12 landing site compared to the
globally-averaged upper to mid-mantle electrical conductivity structure.