The Challenges of Performing Electromagnetic Sounding on the Moon

Here we review the electromagnetic geophysical methods used to probe the lunar interior and highlight key challenges including contamination from plasma and crustal magnetic fields. Within conducting layers of the Moon, changing electric and magnetic fields produce induced fields in proportion to the electrical conductivity at depth. The electromagnetic sounding transfer function requires two observations: a reference measurement capturing the driving field change, and a surface or near surface measurement which captures the total field (induction, external, and any local noise sources). Isolation of induction allows for the extrapolation of interior electrical conductivity. Lunar electromagnetic sounding was performed during the Apollo program with surface magnetometers, Apollo 12, 15 and 16, and orbiters including Explorer 35, Apollo 15 and 16 subsatellites. Following, the Kaguya and Lunar Prospector missions have also been used to study the lunar interior using fields measured in orbit. Modeling results suggest plasma and induce magnetic fields couple within the nightside wake cavity. Crustal magnetic fields are known to generate mini magnetospheres suggesting a dynamic interaction between the local plasma and fields at the surface. Recently, Firefly’s Blue Ghost 1 mission contained the Lunar Magnetotelluric Sounder experiment measuring magnetic and electric fields in the Mare Crisium basin. We will discuss the challenges this mission will face in interrupting their data.