Gases in Venus atmosphere could be from volcanic activity Artist's impression of an active volcano on Venus. PARIS, Dec. 3 (UPI) -- Six years of observations of Venus by a European space probe have raised the intriguing possibility the planet is volcanically active, scientists say. ESA's Venus Express has shown large changes in the planet's atmosphere with a significant increase in sulphur dioxide, a pungent, toxic gas that on Earth is almost all generated by volcanic activity. While Venus is covered in hundreds of volcanoes, there has been ongoing debate about whether they remain active today, an ESA release said Monday. A search for clues as to whether there has been active volcanism on geologically recent timescales is one of the goals of the Venus Express mission, scientists said. Immediately after arriving at Venus in 2006, the spacecraft recorded a significant increase in the average density of sulphur dioxide in the upper atmosphere. "If you see a sulphur dioxide increase in the upper atmosphere, you know that something has brought it up recently, because individual molecules are destroyed there by sunlight after just a couple of days," researcher Emmanuel Marcq said. An injection of sulphur dioxide from one or more volcanoes is one possibility, researchers said, but not the only one. "A volcanic eruption could act like a piston to blast sulphur dioxide up to these levels, but peculiarities in the circulation of the planet that we don't yet fully understand could also mix the gas to reproduce the same result," said study co-author Jean-Loup Bertaux, principal investigator for the instrument on Venus Express that made the detections.