Venus shines down beautifully when prominent in the evening or morning skies. But as students of Venus well know, looks can be very deceptive.

An artist’s view of an active volcano raging on Venus. Credit: ESA/AOES

In reality, Venus is a hellish world that has been dubbed “Earth’s evil twin”. As well as having a surface temperature twice that found inside a domestic oven on full, the atmospheric pressure is so heavy that anyone foolish enough to go there would be instantly crushed.

That air is pretty nasty too, containing more than a million times as much sulphur dioxide as found in Earth’s atmosphere. There has been speculation that this is being fuelled by volcanoes, as on our own planet. Indeed, leading Venus expert Professor Fred Taylor has told Skymania that there could be as many as a million volcanoes all over the surface of our ugly sister.

Now the European Space Agency (ESA) is reporting that six years of study by its Venus Express spacecraft have shown large changes in the levels of sulphur dioxide in Venus’s atmosphere, boosting the possibility that volcanoes are erupting to produce the pungent, toxic gas.

The new findings add to previous evidence of ongoing volcanic activity such as infrared radiation that suggested lava flowing from a volcano that erupted quite recently.

The evidence from Venus begins with the arrival of Venus Express in 2006 when the robotic probe detected a notable increase in the average density of sulphur dioxide in the planet’s upper atmosphere. This rise was soon followed by a sharp drop in levels of the gas to around ten times less today.

This remarkable change mirrored results observed from another probe, NASA’s Pioneer Venus, which orbited the planet from 1978 to 1992 and observed a similar fall in levels of sulphur dioxide. That was also put down to the effects of recent and subsiding volcanic activity.

Changing levels of sulphur dioxide observed by NASA’s Pioneer and ESA’s Venus Express. Credit: E. Marcq/L. Esposito/ESA/AOES

Gases from a volcanic eruption would quickly be spread in the air by the rapid rotation speed of Venus’s atmosphere which whips around the planet in just four Earth days. That is considerably faster that the 243 days Venus itself takes to rotate on its axis.

French scientist Dr Emmanuel Marcq, lead author of a paper on the latest findings Nature Geoscience, said: “If you see a sulphur dioxide increase in the upper atmosphere, you know that something has brought it up recently, because individual molecules are destroyed there by sunlight after just a couple of days.”

Colleague Dr Jean-Loup Bertaux, the principal investigator for the instrument on Venus Express that made the detections, cautioned: “A volcanic eruption could act like a piston to blast sulphur dioxide up to these levels, but peculiarities in the circulation of the planet that we don’t yet fully understand could also mix the gas to reproduce the same result.”

Håkan Svedhem, ESA’s Project Scientist for Venus Express, said: “By following clues left by trace gases in the atmosphere, we are uncovering the way Venus works, which could point us to the smoking gun of active volcanism.”

Related: Venus – our neighbour from hell

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