Venus is the planet closest to Earth's orbit in its orbit. Image: NASA
Reading On Venus, there could be active volcanoes that blow large amounts of the gas sulfur dioxide into the atmosphere. This is indicated by measurements of the space probe Venus Express. As the European space agency Esa announced, the probe registered strongly fluctuating sulfur dioxide concentrations in the upper atmosphere of the planet. Within a few days, the amount of sulfur dioxide fell 70 to 90 kilometers in height by two-thirds. "We do not understand why values ​​vary so wildly and why so much sulfur dioxide is up there, " says Jean-Loup Bertaux of French research institute CNRS in Verrières-le-Buisson. The sunlight would actually destroy the gas at high altitudes quickly. In a deeper atmosphere 35 kilometers up, the total only fluctuated by 40 percent within two years.

The measurements have fueled an old discussion: for some time now, some planetary scientists have argued that the high sulfur dioxide levels are an indication of active volcanism. Others believe that the responsible volcanic eruptions were already ten million years ago. Because sulfur dioxide can last up to twenty million years in the Venus atmosphere before it is destroyed by chemical reactions with the crustal rock. In the earth's atmosphere, another chemistry rules, where the gas disappears from the air within a few years.

Jean-Loup Bertaux is therefore skeptical whether the values ​​are really an indication of currently active volcanoes. "But we can not explain the fluctuations, " he admits. He and his colleagues now want to look for more clues. For example, if high levels of sulfur dioxide are concentrated in an area of ​​the planet, it may indicate the eruption cloud of an outbreak. An instrument of Venus Express that measures heat radiation could also record the heat of freshly emitted lava. Pierre Drossart of the Observatoire de Paris, who evaluates the heat measurements, reports: "So far, however, no heat anomaly has been found."

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