Venus’ clouds have a UV secret. Scientists might have cracked it

Venus still has plenty of secrets under its thick sulphuric clouds.

How much oxygen is really there? Could there be extreme organisms hiding in the clouds? We don’t know everything even about the very tops of the clouds that we can see.

We know that it is made up of sulphuric acid, water, chlorine and iron. But there has to be something else to form patches and streaks in the clouds, visible in ultraviolet (UV) light.  

New research suggests that two iron-bearing sulphate materials called rhomboclase and acid ferric sulphate could be the missing link. The research has been published in Science Advances.

“When examined under UV light, the Venusian clouds featured a specific UV absorption pattern. What elements, compounds, or minerals are responsible for such observations?” says Dr Paul Rimmer from the Cavendish Laboratory at the University of Cambridge, UK, and co-author of the study.

“The only available data for the composition of the clouds were collected by probes and revealed strange properties of the clouds that so far we have been unable to fully explain.”

Luckily, the researchers didn’t have to go all the way to Venus to work out what was going on. Instead, they ran experiments looking at UV absorbance patterns under extremely acidic conditions to mimic what the clouds of Venus would be like.

This happened at an aqueous geochemistry laboratory at the University of Cambridge, and a photochemistry lab at Harvard University, US.

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There were a few options for what the chemical could be – such as ferric chloride, amorphous sulphur, and sulphur monoxide dimer. The researchers went through them one by one to determine whether it matched what we see in Venus’ atmosphere.

“The patterns and level of absorption shown by the combination of these two mineral phases are consistent with the dark UV-patches observed in Venusian clouds,” says co-author Clancy Zhijian Jiang, from the Department of Earth Sciences, Cambridge.

“These targeted experiments revealed the intricate chemical network within the atmosphere, and shed light on the elemental cycling on the Venusian surface.”

This likely isn’t going to be the end of the matter. Although the team looked deeply into these compounds, there could be another reason for the UV absorption pattern.

The authors note that depletion of sulphur dioxide and water in the clouds, a cloud layer where phosphorus is more abundant, or an unknown UV absorber could also be an option.

However, this is a fun step forward, and hopefully it won’t be too long before we can put some of these hypotheses to the test.

“Venus is our nearest neighbour, but it remains a mystery,” says Rimmer.

“We will have a chance to learn much more about this planet in the coming years with future NASA and ESA missions set to explore its atmosphere, clouds and surface. This study prepares the grounds for these future explorations.”

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