Venus: Surface electromagnetic properties

Abstract

Using Pioneer Venus high‐angle radar imaging data, we have attempted to correct values of the specular power reflection coefficient, previously reported by the Pioneer Venus radar altimetry experiment, for the effects of diffusely scattering small‐scale surface roughness. We have compared these results with values of surface radio emissivity obtained both from the Pioneer Venus radar altimetry experiment and from thermal radioemission observations of Venus made at the Very Large Array. The combined measurements provide credible estimates of the relative dielectric permittivity (ε) at 17‐cm wavelength for the majority of the Venus surface. The lowland regions are characterized by ε = 5.0 ±0.9, a value commonly associated with many types of compact dry basaltic or granitic rocks. Most highland areas, however, display very much larger values, rising to as high as ε = 39 ± 15 over Maxwell Montes. If the high values of permittivity derive from the loading of a host rock matrix with small embedded fragments of an electrically conducting mineral, as we believe, the required volume fraction of this material for Maxwell is about 14%, with many other highland regions containing as much as 10%. Suitable candidates for the conducting mineral are pyrite, other iron sulfides, or, depending on the oxidation state of the surface, possibly magnetite, hematite, or ilmenite.