... The latest contribution to the investigation into active Venusian volcanism comes from the SPICAV-UV spectrometer on board Venus Express, which has been in orbit around the planet since 2006.
By studying the SPICAV data, a team of scientists from France and Russia has discovered an unusual change in the amount of sulphur dioxide (SO2) gas in the upper atmosphere.
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.
Since Venus does not experience any seasons, the authors of the paper in Nature Geoscience suggest two possible explanations: periods of active volcanism, or long-term variability in the general circulation of the atmosphere ...