This view of the clouds of Venus at full phase was taken by the Pioneer Venus spacecraft through an ultraviolet filter to enhance the visibility of the formations. Pioneer Venus returned over 1000 such cloud pictures within two years and was still operating after 10 years in orbit. Although similar in size and internal structure to Earth, Venus is a very different world. It has a thick atmosphere of mainly carbon dioxide with clouds of sulphuric acid, creating a runaway greenhouse effect with surface temperatures of 485 degrees Celsius and atmospheric presure 90 times that at sea level on Earth. The impenetrable clouds meant that nothing was known about the planet's surface until the Soviet Venera probe landed and was briefly able to transmit images in 1975.
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