Six years of observations by ESA’s Venus Express have shown large changes in the sulphur dioxide content of the planet’s atmosphere, and one intriguing possible explanation is volcanic eruptions.
Most of the sulphur dioxide on Venus is hidden below the planet’s dense upper cloud deck, because the gas is readily destroyed by sunlight.
That means any sulphur dioxide detected in Venus’ upper atmosphere above the cloud deck must have been recently supplied from below.
Venus is covered in hundreds of volcanoes, but whether they remain active today is much debated, providing an important scientific goal for Venus Express.
The mission has already found clues pointing to volcanism on geologically recent timescales, within the last few hundreds of thousands to millions of years.
A previous analysis of infrared radiation from the surface pointed to lava flowsatop a volcano with a composition distinct from those of their surroundings, suggesting that the volcano had erupted in the planet’s recent past.
Now, an analysis of sulphur dioxide concentration in the upper atmosphere over six years provides another clue.
Immediately after arriving at Venus in 2006, the spacecraft recorded a significant increase in the average density of sulphur dioxide in the upper atmosphere, followed by a sharp decrease to values roughly ten times lower by today.
A similar fall was also seen during NASA‘s Pioneer Venus mission, which orbited the planet from 1978 to 1992.
At that time, the preferred explanation was an earlier injection of sulphur dioxide from one or more volcanoes, with Pioneer Venus arriving in time for the decline.
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