No signs of life on Venus (yet)

Newswise – The unusual behavior of sulfur in Venus’ atmosphere cannot be explained by an “airborne” form of alien life, according to a new study.

Researchers at the University of Cambridge used a combination of biochemistry and atmospheric chemistry to test the “life in the clouds” hypothesis, which astronomers have speculated about for decades, and found that life cannot explain the makeup of Venus’ atmosphere.

Any life form in sufficient abundance is expected to leave chemical fingerprints on a planet’s atmosphere as it consumes food and expels waste. However, the Cambridge researchers found no evidence of these fingerprints on Venus.

Even if Venus is devoid of life, the researchers say their Resultsreported in the magazine nature communicationcould be useful for studying the atmospheres of similar planets in the galaxy, and the eventual detection of life outside our solar system.

“We’ve spent the past two years trying to explain the strange sulfur chemistry we see in the clouds of Venus,” said co-author dr. Paul Rimmer from Cambridge’s Department of Earth Sciences. “Life is pretty good at weird chemistry, so we explored whether there’s a way to make life a possible explanation for what we’re seeing.”

The researchers used a combination of atmospheric and biochemical models to study the chemical reactions expected to occur, given the known sources of chemical energy in Venus’ atmosphere.

“We looked at the sulfur-based ‘food’ available in Venus’ atmosphere — it’s not something you or I would want to eat, but it’s the main source of energy available,” said Sean Jordan from Cambridge’s Institute of Astronomy, the first author of the article. “If that food is being consumed by life, we should see evidence of it by specific chemicals being lost and gained into the atmosphere.”

The models looked at a special feature of Venus’ atmosphere: the abundance of sulfur dioxide (SO2† On Earth, most SO2 into the atmosphere from volcanic emissions. On Venus there are high levels of SO2 lower in the clouds, but somehow it gets ‘sucked’ out of the atmosphere at higher altitudes.

“If life is present, it must influence atmospheric chemistry,” said co-author dr. Oliver Shorttle from Cambridge’s Department of Earth Sciences and Institute of Astronomy. “Could life be the reason SO2 are the levels on Venus lowered like that?”

The models, developed by Jordan, contain a list of the metabolic reactions that the life forms would carry out to obtain their ‘food’, and the waste by-products. The researchers ran the model to see whether the reduction in SO2 levels can be explained by these metabolic reactions.

They found that the metabolic reactions can result in a drop in SO2 levels, but only by producing other molecules in very large quantities that are not seen. The results suggested a hard limit to how much life could exist on Venus without blowing apart our understanding of how chemical reactions work in planetary atmospheres.

“If life were responsible for the SO2 levels we see on Venus, it would also break everything we know about Venus’ atmospheric chemistry,” Jordan said. “We wanted life to be a possible explanation, but when we ran the models, it wasn’t a viable solution. But if life isn’t responsible for what we see on Venus, it’s still a problem to be solved — there’s a lot of strange chemistry to follow up on.

While there’s no evidence of sulphur-eating life hiding in Venus’ clouds, the researchers say their method of analyzing atmospheric features will be valuable when JWST, the successor to the Hubble telescope, will begin returning images from other planetary systems later this year. Some of the sulfur molecules in the current study are easy to spot with JWST, so learning more about our neighbor’s chemical behavior could help scientists find similar planets in the galaxy.

“To understand why some planets are alive, we need to understand why other planets are dead,” Shorttle said. “If life could somehow sneak into the Venusian clouds, that would totally change the way we look for chemical signs of life on other planets.”

“Even if ‘our’ Venus is dead, it’s possible that Venus-like planets in other systems contain life,” said Rimmer, who also works at Cambridge’s Cavendish Laboratory. “We can apply what we’ve learned here to exoplanetary systems — this is just the beginning.”

The research was funded by the Simons Foundation and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).


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