The awareness of sulfur dioxide in the dense atmosphere of Venus is more than a million times higher than that found on Earth. On our planet, almost all of this pungent and toxic gas comes from volcanic eruptions.
For this reason, it is thought that the detected sulfur dioxide in the upper atmosphere of Venus, well above its cloud cover, must have been recently pumped from lower bounds.
The surface of Venus is covered by hundreds of volcanoes, but whether still active today remains controversial, constituting an important scientific objective for the Venus Express mission of the ESA.
This mission has discovered evidence pointing to recent volcanic activity on a geological time scale, that is, in the last few hundred thousand or million years.
The analysis of the infrared radiation emitted by the surface of Venus identified a volcano whose summit had a composition different from the other surrounding volcanoes, suggesting that it had erupted in the recent past of the planet.
A new study has analyzed the variation of the concentration of sulfur dioxide in the upper atmosphere over six years, discovering new tracks.
Upon arrival at Venus in 2006, the European satellite recorded a significant increase in the average density of sulfur dioxide in the upper atmosphere, followed by a sharp decline to levels almost ten times lower today.
The probe NASA's Pioneer Venus had also detected a similar decrease during its mission orbiting Venus from 1978 to 1992.
At that time, it was suggested the hypothesis that Pioneer Venus had arrived in time to record the descent of the sulfur dioxide that had been injected into the atmosphere by one or more volcanoes.
"If you see that the concentration of sulfur dioxide in the upper atmosphere increases, you know something has been up there recently, as sunlight kills these molecules in a couple of days," explains Emmanuel Marcq, the French laboratory Latmos Atmospheric Research and lead author of the paper reporting these findings in Nature Geosciences .
"A volcanic eruption could have released sulfur dioxide up to these levels, but this phenomenon could also be the result of the peculiarities of the atmospheric circulation of Venus, we still do not fully understand," says Jean-Loup Bertaux, co-author of this publication and principal investigator of Venus Express instrument with which this study was performed.
Venus has an atmosphere in 'super rotation', it takes only four Earth days to complete one lap on the planet, breakneck speed considering that Venus takes 243 days to complete one rotation on its axis.
This intense atmospheric circulation spread sulfur dioxide across the globe, making it difficult to identify its origin.
Marcq team works on the assumption that if the initial increase in the concentration of sulfur dioxide is due to the volcanic activity could have been caused by a gradual increase in the activity of several volcanoes, not single eruption dramatic proportions.
"On the other hand, given the similar trend detected by Pioneer Venus, it is possible that we are facing a periodic variation of the atmospheric circulation of the planet, which could be even more complex than we have imagined so far," concludes Marcq .
"Following the clues left by trace gases in the atmosphere of Venus, we are beginning to understand the dynamics of the planet, which could lead us to the ultimate test on its volcanic activity," says Hakan Svedhem, Venus Express Project Scientist for the ESA.