Electrical properties of planetary surfaces

Abstract

The electrical properties of the lunar surface are those of very good dielectric insulators. The results of the Apollo programme and laboratory studies on lunar samples have confirmed the predictions of Earth-based and spacecraft measurements of the dielectric properties of the lunar surface, and helped to increase the reliability of such studies of the surfaces of other planetary bodies. It appears that the electrical properties of the surfaces of Mercury, Venus and Mars are all very similar to those found for the Moon. Mercury has no atmosphere and in this sense is very similar to the Moon; Mars has a mean atmospheric pressure and temperature at the surface that is far below the triple point of water; while Venus has surface temperatures and pressures that are far above the critical point of water. This means that water is unlikely to contribute to the dielectric properties of either planet. The dielectric constant of the surface of the Moon is determined largely by the bulk density and is related to the density by the formula = (1.93 ± 0.17) for dielectric constant, k,at density p g/cm3. Thus, most soils have k about 3, while solid rocks have k about 7.5. Loss tangents appear to be dependent upon density, frequency, temperature, and possibly ilmenite content, and thus are more difficult to predict than the dielectric constant. Typical loss tangents are likely about 0.005 for the Moon, Mars and Mercury, and about 0.01 to 0.2 for Venus.