What new insights into Venus’s sulfurous chemistry say about its hellish climate

·3 min read
The clouds of Venus as seen by the Hubble Space Telescope (Nasa)
The clouds of Venus as seen by the Hubble Space Telescope (Nasa)

Scientists may be a step closer to discovering the identity of a mystery ingredient in the opaque yellow clouds of Venus, after new computational techniques revealed new chemical reactions in the hot house planet’s atmosphere.

Similar to Earth in size and mass, Venus is something like an evil twin, its thick, predominantly carbon dioxide atmosphere trapping heat in an extreme greenhouse effect that keeps the second planet from the Sun’s surface hot enough to melt lead. The Venusian skies are wrapped in opaque clouds of sulfuric acid that block visible light from reaching the surface.

But as far back as the late 1970s, scientists observed that something in Venus’s atmosphere readily absorbs some ultraviolet light. They just couldn’t figure out what this mysterious ingredient was, but always suspected it had to do with the sulfur chemistry of the Venusian clouds.

A new study published in Nature Communications now expands on the ways in which sulfurous clouds can form in the Venusian atmosphere, which could bring scientists closer to identifying the mystery ingredient. And the computational techniques used in the research could also bear further fruit in future studies, especially given they do not require expensive missions to Venus or dangerous laboratory experiments.

Scientists have long known of the presence of sulfur and related compounds such as sulfuric acid on Venus, but just how the many different forms of sulfur compounds develop in the atmosphere has remained fuzzy.

“We know that the atmosphere of Venus has abundant SO2 [sulfur dioxide] and sulfuric acid particles,” senior scientist at the Planetary Science Institute and author on the new study James Lyons said in a statement. “We expect that ultraviolet destruction of SO2 produces sulfur particles. They are built up from atomic S (sulfur) to S2, then S4 and finally S8. But how is this process initiated, that is, how does S2 form?”

One way to get S2, or disulfur, is to combine two sulfur atoms. But Dr Lyons and his colleagues have found another way.

“We found a new pathway for S2 formation, the reaction of sulfur monoxide (SO) and disulfur monoxide (S2O), which is much faster than combining two S atoms to make S2,” he said.

Importantly, the researchers discovered this pathway using computational chemistry techniques known as ab initio calculations.

“For the first time, we are using computational chemistry techniques to determine which reactions are most important, rather than waiting for laboratory measurements,” Dr Lyons said. “People are reluctant to go in the lab to measure rate constants for molecules made up of S, chlorine (Cl), and oxygen (O) — these are difficult and sometimes dangerous compounds to work with. Computational methods are the best — and really only — alternative.”

While the results of the new study do not solve the mystery of the ultraviolet absorbing ingredient in the Venusian atmosphere, Dr Lyons and his colleagues note in the study that the results will help inform future studies that could solve that mystery — and possibly go further.

The new understanding of sulfur chemistry will inform upcoming missions to Venus, such as Nasa’s Deep Atmosphere Venus Investigation of Noble gasses, Chemistry, and Imaging, or Davinci+ mission, and a self-funded mission by rocket launch provider Rocket Lab that will send a probe into Venus’s sulfurous clouds to search for signs of alien life.

And back on Earth, the new sulfur chemistry will help scientists better understand terrestrial volcanic activity, assess the potential for geoengineering proposals to tackle climate change, and help scientists better understand the atmosphere of the early Earth before oxygen rose to become a major ingredient of our air.