Low-frequency electromagnetic methods for planetary subsurface exploration

Electromagnetic (EM) sounding of the Earth has been used for decades for science and resource exploration, but has seen limited planetary application. The inductive foundation of low-frequency electromagnetics has much greater investigation depth than surface-penetrating radar, at the expense of poorer resolution. Ambient EM energy from the solar wind, ionosphere, magnetosphere, or lightning provides natural sources for deep sounding, and can be measured using simple magnetometers and/or electrometers. Artificial sources (transmitters) yield higher SNR in shallower investigations. Planetary applications include crust and mantle structure, temperature, and composition, characterization of groundwater or interior oceans, mapping of shallow ice deposits, and potentially even detection of extant biosignatures.