Paris, April 5 : European Space Agency's (ESA) Venus Express has measured a highly variable quantity of the volcanic gas sulphur dioxide in the atmosphere of Venus, thus rebooting the search for active volcanoes on the planet.
According to Fred Taylor, a Venus Express Interdisciplinary Scientist from Oxford University, volcanoes are a key part of a climate system because they release gases such as sulphur dioxide into the planet's 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.
Such facts have lead scientists to speculate that the large proportion of sulphur dioxide found by previous space missions at Venus is the 'smoking gun' of recent volcanic eruptions.
However, other scientists 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.
An instrument on Venus Express, VIRTIS (Visible and Infrared Thermal Imaging Spectrometer), can see below the clouds at infrared wavelengths. It detects the signature of sulphur dioxide by the amount of infrared radiation that the molecule absorbs, the stronger the signature, the more abundant the molecule.
The variation appears to be smaller in the lower atmosphere.
"With VIRTIS, we monitor sulphur dioxide at an altitude of 35-40 km, and we have seen no change larger than 40% on a global scale over the last two years," said Giuseppe Piccioni, VIRTIS co-Principal Investigator, IASF-INAF in Rome.
The only way to be absolutely certain that active volcanism is taking place on Venus is to see a volcano in action.
This is not easy when you are trying to look through 100 km of thick, cloudy atmosphere. But the Venus Express team are working on two ways of doing this.
The first is to look for localised increases in sulphur dioxide that would indicate a large plume of the gas issuing from a volcano. The other way is to look for hot spots on the surface that can be shown to be fresh lava flows.
In both cases, the instrument that will be used is VIRTIS.