Starting with the assumption that planetary surfaces are self‐affine (fractal) over the scales applicable to radar scattering, we derive various surface parameters, e.g., rms slopes and autocorrelation functions, and examine the implications for radar scattering models. The results of this work provide several new insights of interest to planetary geologists and others using radar to study surface features. First, the unidirectional slope histograms of self‐affine surfaces are Gaussian, and the adirectional slope histograms are Rayleigh. Normalization of the adirectional histogram by solid angle results in a Gaussian adirectional slope density function and therefore a Gaussian quasi‐specular angular scattering function. Next, the wavelength dependent behavior of surface roughness inferred from lunar radar observations is consistent with self‐affine topography. Finally, surface rms height measurements are functions of profile length. Therefore, when determining the applicability of the small perturbation model to a surface based on those measurements, it is necessary to consider the length of the profile with respect to the sampling wavelength.

A model to explain the low emissivity venusian highlands is proposed utilizing the temperature‐dependent dielectric constant of ferroelectric minerals. Ferroelectric minerals are known to occur in alkaline and carbonatite rocks, both of which are plausible for Venus. Ferroelectric minerals possess extremely high dielectric constants (105) over small temperature intervals and are only required in minor (≪1%) abundances to explain the observed emissivities. The ferroelectric model can account for: (1) the observed reduction in emissivity with increased altitude, (2) the abrupt return to normal emissivities at highest elevations, and (3) the variations in the critical elevation observed from region to region.

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The high vapor pressure of volatile metal halides and chalcogenides (e.g., of Cu, Zn, Sn, Pb, As, Sb, Bi) at typical Venus surface temperatures, coupled with the altitude‐dependent temperature gradient of ∼8.5 K km−1, is calculated to transport volatile metal vapors to the highlands of Venus, where condensation and accumulation will occur. The predicted geochemistry of volatile metals on Venus is supported by observations of Cu, Zn, Sn, Pb, As, Sb, and Bi minerals around terrestrial volcanic vents, spectroscopic observations of CuCl in volcanic gases at Kilauea and Nyiragongo, and large enrichments of these and other volatile elements in terrestrial volcanic aerosols. A one‐dimensional finite difference vapor transport model shows the diffusive migration of a thickness of 0.01 to >10 μm/yr of moderately to highly volatile phases (e.g., metal halides and chalcogenides) from the hot lowlands (740 K) to the cold highlands (660 K) on Venus. The diffusive transport of volatile phases on Venus may explain the observed low emissivity of the Venusian highlands, hazes at 6‐km altitude observed by two Pioneer Venus entry probes, and the Pioneer Venus entry probe anomalies at 12.5 km.

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