Venus' atmosphere bears no signs of microbes eating or pooping, suggesting that the odd chemical composition of the planet's clouds cannot be explained by extraterrestrial life.
In a new study, researchers analyzed the biochemistry of the thick, sulfur-rich Venusian clouds, which have fascinated scientists for decades. They looked for "fingerprints" that any potential cloud-dwelling organisms would leave there as a result of their feeding and excretion.
"We've spent the past two years trying to explain the weird sulfur chemistry we see in the clouds of Venus," Paul Rimmer, an atmospheric scientist at the University of Cambridge in the U.K. and a co-author of the study, said in a statement (opens in new tab). "Life is pretty good at weird chemistry, so we've been studying whether there's a way to make life a potential explanation for what we see."
The researchers modeled chemical reactions expected in Venus' atmosphere, which is rich in sulfur dioxide. Concentrations of sulfur dioxide are high in the clouds closer to the planet's surface but diminish with altitude. Scientists thought the sulfur dioxide might be disappearing as it got eaten by cloud-dwelling critters. When the researchers ran the models, however, they found that chemically, that hypothesis didn't work.
"If life was responsible for the sulfur dioxide levels we see on Venus, it would also break everything we know about Venus's atmospheric chemistry," Sean Jordan, an astronomer at the University of Cambridge and first author of the paper, said in the statement. "We wanted life to be a potential explanation, but when we ran the models, it wasn't a viable solution."
The models simulated metabolic reactions that the atmospheric microbes would use to produce energy from food sources and generate waste. The results suggested that although such microbes could suck out some sulfur dioxide from the clouds, that process would produce large molecules that have not been detected.
"We looked at the sulfur-based 'food' available in the Venusian atmosphere — it's not anything you or I would want to eat, but it is the main available energy source," Jordan said. "If that food is being consumed by life, we should see evidence of that through specific chemicals being lost and gained in the atmosphere."
The researchers said that although the study failed to produce the results they had hoped for, it provides valuable insight into the atmospheric chemistry of alien planets, and the methodology developed for this study could be used to look for life outside the solar system.
"Even if 'our' Venus is dead, it's possible that Venus-like planets in other systems could host life," said Rimmer. "We can take what we've learned here and apply it to exoplanetary systems — this is just the beginning."
In particular, the researchers said, the results might guide the observations of the James Webb Space Telescope, which is set to reveal its first scientific images next month, as the telescope is capable of detecting such chemical fingerprints in the atmospheres of distant exoplanets.
Now that life doesn't seem to be the answer to Venus' odd atmospheric chemistry, scientists still have a lot of work to do to explain what's actually going on in those thick, sulfur-rich clouds.
The study was published June 14 in the journal Nature Communications (opens in new tab).