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Changes in the levels of sulphur dioxide (SO2) since Venus Express arrived in orbit around Venus in 2006 now suggest strongly that the spacecraft has detected volcanic activity on the planet.
The SPICAV data show that the concentration of SO2 above the main cloud deck increased slightly to about 1000 parts per billion by volume (ppbv) between 2006 and 2007, but then steadily decreased over the next five years, reaching only 100 ppbv by 2012. This is very reminiscent of a pattern observed by Pioneer Venus during the 1980s, the only other multi-year dataset of SO2 measurements.
One of best explanations for these changes is a volcanic eruption back in 2006, which would have inserted a great deal of SO2 into the upper atmosphere. Since then, ultraviolet radiation from the sun has steadily destroyed it.