New analysis of the Apollo 17 surface electrical properties experiment

Numerical modeling was used to compare predicted vs. observed waveforms and to invert for vertically varying dielectric structure. The dielectric constant is readily converted to density and porosity for lunar rocks. The preferred model shows a sharp decrease in porosity in the top 20 − 30 m, with little change below 300 m. This likely tracks the transition from fully gardened regolith, to impact-fractured rock, to largely intact 3.7-Ga basalt. The bottom of the basalt was not detected by the SEP to a depth of ∼2 km or more, which is consistent with reanalysis of Apollo 17 seismic and gravity data.