Terraforming of Venus

The terraforming of Venus is the hypothetical process of engineering the global environment of the planet Venus in such a way as to make it suitable for human habitation.Terraforming Venus was first seriously proposed by the astronomer Carl Sagan in 1961, although fictional treatments, such as The Big Rain by Poul Anderson, preceded it. Adjustments to the existing environment of Venus to support human life would require at least three major changes to the planet. These three changes are closely interrelated, because Venus's extreme temperature is due to the greenhouse effect caused by its dense carbon-dioxide atmosphere:

Prior to the early 1960s, the atmosphere of Venus was believed by astronomers to have an Earth-like temperature. When Venus was understood to have a thick carbon dioxide atmosphere with a consequence of a very large greenhouse effect, the idea of altering the atmosphere to make the surface more Earth-like became a possibility. This prospect, known as terraforming, was first seriously proposed by Carl Sagan in 1961, as a final section of his classic article in the journal Science discussing the atmosphere and greenhouse effect of Venus. Sagan proposed injecting photosynthetic bacteria into the Venus atmosphere, which would convert the carbon dioxide into reduced carbon in organic form, thus reducing the carbon dioxide from the atmosphere and reducing the greenhouse effect.

Unfortunately, the knowledge of Venus' atmosphere was still inexact in 1961, when Sagan made his original proposal for terraforming. Thirty-three years after his original proposal, in his 1991 book Pale Blue Dot, Sagan conceded his original proposal for terraforming would not work because the atmosphere of Venus is far denser than was known in 1961:

"Here's the fatal flaw: In 1961, I thought the atmospheric pressure at the surface of Venus was a few bars ... We now know it to be 90 bars, so if the scheme worked, the result would be a surface buried in hundreds of meters of fine graphite, and an atmosphere made of 65 bars of almost pure molecular oxygen. Whether we would first implode under the atmospheric pressure or spontaneously burst into flames in all that oxygen is open to question. However, long before so much oxygen could build up, the graphite would spontaneously burn back into CO2, short-circuiting the process."

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