The thick atmosphere of Venus is primarily carbon dioxide, with smaller amounts of nitrogen, sulphur dioxide, water vapor and other gases. At high altitudes, sunlight converts CO2, SO2 and H2O into sulphuric acid and carbon monoxide, thus creating a cloud of acid droplets.
Russian and American probes into the atmosphere have revealed three cloud layers. The sulphuric acid mist is not very dense, one could see for a mile or so, but at 20 miles thick even the lower layer is completely obscured from view. The cloud deck ends where heat boils and decomposes the suphuric acid. This is 30 miles above the surface, and even at that altitude the pressure is slightly higher than Earth sea level.
|Venus rotates in a retrograde direction once in 243 days; however its upper atmosphere rotates every 4 days. This 200 mph superrotation of the atmosphere is not fully understood yet. Above, an ultraviolet view of the north pole of Venus was derived from Pioneer Venus images. It shows the polar vortex caused when the spinning atmosphere converges toward the axis of rotation.|
Scientists once speculated that the Venusian surface might be polished smooth by its intense winds, but landers have shown that the atmosphere at the surface moves sluggishly. The terrain of Venus appears untouched by erosion.
Above on the left, raw images from Venera 14 show some dust blown off the lander after about 50 minutes. The Venera 13 images on the right show a change in illumination and shadowing, possibly due to moving clouds.
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