European scientists said on Monday they had found tantalising clues to back theories that Venus -- Earth\'s cursed sister -- has active volcanoes. Mapping of the desolate surface of Venus shows the second planet from the Sun to be studded with more than a thousand volcanoes. Many astrophysicists believe these have been dead for possibly millions of years, but others say that, like volcanoes on Earth, they may still burst into life, given signs of what could be recent lava flows. New evidence in the debate has been thrown up by Venus Express, a European Space Agency (ESA) probe that has encircled Venus since 2006, according to a study published in the journal Nature Geoscience. Patiently monitoring Venus, the unmanned scout recorded a sharp rise in levels of sulphur dioxide (SO2) -- a gas that on Earth is a telltale of volcanism -- shortly after its arrival six years ago. Concentrations of SO2 then fell, and today are 10 times lower than in 2006. \"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,\" said French atmospheric physicist Emmanuel Marcq in an ESA press release. A NASA probe, Pioneer Venus, also snared a strange SO2 signature in the 1980s during its 1978-1992 mission that, at the time, briefly raised suggestions that Venus was not volcanically dead. But another explanation for the rise-and-fall SO2 levels seen by Venus Express may lie with the planet\'s notoriously complex atmosphere -- a devil\'s brew of toxic gases whipped by hurricane-force winds. A Venusian \"day,\" meaning the time it takes the planet to rotate fully on its axis, is 243 Earth days. But its atmosphere rotates at such a speed that gas molecules take just four days to be blown all the way around. \"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 Marcq\'s colleague, Jean-Loup Bertaux, in charge of the SPICAV spectrometer which noted the SO2 fluctuations. Venus, slightly smaller than the Earth, was once touted as a sister planet to ours and, in early science fiction, as a potential home from home. But in 1970, it was found to host an atmosphere of carbon dioxide with a pressure 90 times that on Earth and a surface cooked to 457 degrees Celsius (855 degrees Fahrenheit), possibly the result of runaway global warming.