Mysterious missing component in Venus’ clouds revealed

What are the clouds of Venus made of? Scientists know that it is mainly made up of droplets of sulfuric acid, with some water, chlorine and iron. Their concentrations vary according to altitude in the thick and hostile Venusian atmosphere. But so far, they have failed to identify the missing element that would explain the cloud spots and streaks, visible only in the UV range.

In a new study published in Scientists progress, researchers at the University of Cambridge have synthesized ferrous sulfate minerals that are stable in the harsh chemical conditions of Venusian clouds. Spectroscopic analysis revealed that a combination of two minerals, rhomboclase and ferric acid sulfate, can explain the mysterious UV absorption function on our neighboring planet.

“The only available data on cloud composition were collected by probes and revealed strange properties of clouds that we have not been able to fully explain until now,” said the lab’s Paul Rimmer. Cavendish and co-author of the study. “In particular, when examined under UV light, the Venusian clouds exhibited a specific UV absorption pattern. What elements, compounds, or minerals are responsible for such an observation?”

Formulated based on Venusian atmospheric chemistry, the team synthesized several ferrous sulfate minerals in an aqueous geochemistry laboratory in the Department of Earth Sciences.

By suspending the synthesized materials in varying concentrations of sulfuric acid and monitoring chemical and mineralogical changes, the team reduced candidate minerals to rhomboclase and ferric sulfate acid, whose spectroscopic characteristics were examined under specially designed light sources to imitate the spectrum of solar flares (FlareLab of Paul Rimmer and Samantha Thompson at the Cavendish Laboratory).

A Harvard photochemistry lab collaborated on the research by providing measurements of the UV absorbance patterns of ferric iron under extreme acidic conditions, with the aim of mimicking the even more extreme Venusian clouds. The scientists are part of the new Origins Federation, which promotes such collaborative projects.

“The patterns and absorption level shown by the combination of these two mineral phases are consistent with the dark UV spots observed in Venusian clouds,” said co-author Clancy Zhijian Jiang, of the Department of Science of Cambridge Earth. “These focused experiments revealed the complex chemical network within the atmosphere and shed light on the cycling of elements on the Venusian surface.”

“Venus is our closest neighbor, but it remains a mystery,” Rimmer said. “We will have the opportunity to learn much more about this planet in the years to come thanks to future NASA and ESA missions designed to explore its atmosphere, clouds and surface. This study prepares the ground for these future explorations.”