ESAs Venus Express has measured a highly variable quantity of the volcanic gas sulphur dioxide in the atmosphere of Venus. Scientists must now decide whether this is evidence for active volcanoes on Venus, or linked to a hitherto unknown mechanism affecting the upper atmosphere.
The search for volcanoes is a long-running thread in the exploration of Venus. Volcanoes are a key part of a climate system, says Fred Taylor, a Venus Express Interdisciplinary Scientist from Oxford University. Thats because they release gases such as sulphur dioxide into the planets atmosphere.
On Earth, sulphur compounds do not stay in the atmosphere for long. Instead, they react with the surface of the planet. The same is thought to be true at Venus, although the reactions are much slower, with a time scale of 20 million years.
Some scientists have argued that the large proportion of sulphur dioxide found by previous space missions at Venus is the smoking gun of recent volcanic eruptions. However, others maintain that the eruptions could have happened around 10 million years ago and that the sulphur dioxide remains in the atmosphere because it takes such a long time to react with the surface rocks.
New observations from Venus Express showing rapid variations of sulphur dioxide in the upper atmosphere have revived this debate.
The SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) instrument analyses the way starlight or sunlight is absorbed by Venuss atmosphere. The absorbed light tells scientists the identity of the atoms and molecules found in the planets atmosphere. This technique works only in the more tenuous upper atmosphere, above the clouds at an altitude of 7090 km. In the space of a few days, the quantity of sulphur dioxide in the upper atmosphere dropped by two-thirds.
Jean-Loup Bertaux, Service dAeronomie du CNRS, Verrires-le-Buisson, is the Principal Investigator for SPICAV. I
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European Space Agency