Sulphur Dioxide Detected On Venus Points To Active Volcanoes

Lawrence LeBlond for – Your Universe Online

The European Space Agency (ESA) has been observing Earth´s sister planet for six years with its polar orbiter Venus Express. During its visit of the second planet from the sun, the orbiter has shown huge changes in sulphur dioxide content in the planet´s atmosphere, leading experts to believe volcanic activity has been increasing on the surface of Venus.

ESA officials explain that Venus´s thick atmosphere contains more than a million times as much sulphur dioxide as Earth´s, and offer that most of the pungent, toxic gas must be generated by volcanic eruptions. And most of the sulphur dioxide remains trapped below the dense upper clouds, where the sunlight cannot penetrate and dissolve the gas.

According to these observations, the Venus Express mission scientists believe that sulphur dioxide found in the upper atmosphere above the upper cloud deck must be supplied from below. But while scientists generally concur that Venus is littered with hundreds of volcanoes, it has remained unclear if any were still active today. The observations should help planetary scientists get a better understanding of what is going on beneath Venus´s thick atmosphere.

The clues indicate that volcanism has been on the rise over the past few hundreds of thousands to millions of years. And a recent analysis of infrared radiation from the surface of Venus pointed to lava flows atop a volcano with composition distinct from those of their surroundings, suggesting that the volcano had erupted in the planet´s recent past.

So now, the recent data gleaned from Venus Express provides another clue that volcanic activity has been occurring on the planet for some time. Even as the orbiter arrived at Venus in 2006 it was picking up significant measurements of sulphur dioxide in the upper atmosphere, but then followed by a sharp decline to values roughly ten times lower today than 6 years ago.

A similar decline was also seen during NASA´s Pioneer Venus mission, which visited the planet from 1978 to 1992. During that time, it was believed volcanic activity had probably been on the decline as well.

Dr. Emmanuel Marcq of Laboratoire Atmosphères, Milieux, Observations Spatiales, France, and lead author of a paper on the findings, said that if you detect an increase in sulphur dioxide 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.”

“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,” co-author Dr Jean-Loup Bertaux, Principal Investigator for the instrument on Venus Express that made the detections, said in statement.

Since Venus´s atmosphere is in constant motion around the planet, whipping around the planet in just four Earth-days, it is extremely difficult to isolate an individual point of origin for any sulphur dioxide found in the atmosphere. And because of the super-rotating atmosphere and the vast distribution of sulphur dioxide, it´s hard to tell exactly how many volcanoes were responsible for the gas´s release.

The research team, however, speculate that if volcanism is in fact responsible for the initial increase in sulphur dioxide, then it´s possible it came from the gentle increased output of several volcanoes, rather a dramatic eruption from just one volcano.

“Alternatively, and taking into account the similar trend observed by Pioneer Venus, it´s possible that we are seeing decadal-scale variability in the circulation of the atmosphere, which is turning out to be even more complex than we could ever have imagined,” noted Marcq.

ESA´s Venus Express Project Scientist, HÃ¥kan Svedhem, said that clues from the orbiter reveal a pretty good picture of how our sister planet works. He added that the data “could point us to the smoking gun of active volcanism.”

The paper is published in the journal Nature Geoscience.