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New research by NASA suggests that the early oceans on the planet Venus may have been lost due to a runaway greenhouse effect reports Space.com. The existence of oceans on Venus is suggested by the high abundance of deuterium (D) relative to hydrogen (H) in its atmosphere. Because deuterium is the heavier isotope of the element hydrogen it is not as easily lost from the planet. The D/H ratio in Venus' atmosphere is 120 times that of the Earth's and suggests there may have been an early ocean as deep as 100 m covering the planet early in its history. The disappearance of Venus' ocean has been thought to be due to either a runaway greenhouse effect that boiled off the ocean, with water lost from the upper atmosphere, or in the catastrophic giant impact which reversed the rotation of the planet. The latest research, by Maura Rabbette and colleages of NASA's Ames Research Center, suggests that the evaporation of water from the surface of the ocean may have caused a runaway greenhouse effect. Water vapour is a greenhouse gas that allows radiation from the Sun to reach the surface but absorbs the heat radiated from the surface and prevents much of it from escaping into space. The trapped heat increases the temperature the atmosphere and thus more water is evaporated. Computer models performed by Rabbette suggest that this chain-reaction leads to a runaway greenhouse effect which could have boiled away the venusian oceans. The giant impact, which reversed the rotation of Venus, thus probably was not responsible for the loss of Venus' oceans and may have occurred before its oceans had formed.
More info: Space.com
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