Abstract
THE remarkable photographs of the surface of Venus returned by the Venera 9 and 10 spacecraft have revealed the presence, in two different sites, of a variety of rocklike forms, some angular and some smooth. Press reports1 express surprise at the absence of very efficient erosional mechanisms. It may be useful to point out instead that it is the presence, not the absence, of erosional mechanisms on Venus which is surprising. The degree of erosion of surface rocks on Venus is determined by an equilibrium between the rate of production and the rate of destruction of surface rocks. The principal causes of erosion of terrestrial rocks—running water, diurnal and seasonal temperature changes, particularly in deserts, and aeolian abrasion—are all absent on Venus. The surface temperature of 750 K is above the critical point temperature of water. Ground based radio-astronomical measurements, a comparison of the temperatures measured by Venera spacecraft at a variety of solar zenith angles, together with the high heat capacity of the massive Venus atmosphere, all clearly demonstrate that the diurnal temperature differences are a few degrees K at most2,3. The obliquity of the rotation axis of Venus is so small that there are effectively no seasons on the planet. The efficiency of aeolian abrasion depends on the velocity to a power ≥3; since both theory and observation show the velocities in the lower atmosphere of Venus to be about an order of magnitude less than at comparable regions in the Earth's atmosphere, it follows that sandblasting on Venus is at most 10−3 as efficient as on Earth4.
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SAGAN, C. Erosion and the rocks of Venus. Nature 261, 31 (1976). https://doi.org/10.1038/261031a0
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DOI: https://doi.org/10.1038/261031a0
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