Study finds that Venus’ clouds are too dry for life as we know it

Venus, photographed by NASA's Mariner 10 probe in 1974.

Venus, photographed by NASA’s Mariner 10 probe in 1974.
picture: NASA/JPL-Caltech

Venus is now the focus of the space science community because of Three missions It recently announced its exploration, while debate continues over whether there is a biological signature within its clouds. As new research shows, Venus has an atmosphere too dry to support even the toughest of microorganisms, a discovery that could restore the planet’s reputation as Earth’s most ruthless neighbor.

“The water in Venus’ clouds is simply not at the levels needed to support life, which is unfortunate,” Chris McKay, an astrobiologist at NASA’s Ames Research Center and co-author of the new study, said at a press conference. . It actually took place on June 25th.

It’s unfortunate, McKay continued, because “I’m interested in searching for life on other worlds and would like to think Venus is habitable.” Evidence presented in his team’s new study published in natural astronomysuggest otherwise. The finding is also unfortunate, Mackay said, because “our conclusion is directly based on measurements” rather than “a model based on assumptions,” so “it’s hard to imagine that the results will change as we continue to explore.”

The seemingly far-fetched idea that Venus could support life received renewed attention last year when scientists introduced it Guide which showed traces of phosphine in its atmosphere. Since living organisms are one of the only known sources of this gas, it has been considered as possible evidence of life. Suddenly astrobiologists became interested in Venus, a scorching planet usually considered an exceptionally poor candidate for habitability. Since then, other scholars have disposed of Water the cold About this result, a new study of nature has raised doubts.

John Halsworth, a microbiologist at Queen’s University in Belfast who led the new research, specializes in understanding how much stress organisms can withstand, including the minimal amount of water that can sustain extreme organisms on Earth. Warning that life might be detected in the clouds of Venus, he wondered if there would be enough water in the planet’s atmosphere to allow it. As the scientists wrote in the new study, some previous analyzes “tend to neglect the role of water activity, a measure of water’s relative availability, in habitability.”

“It is well known, of course, that life needs water,” Hallsworth said during the press conference. “Living systems, including microorganisms, consist mainly of water, and without hydration they cannot be active and cannot reproduce.”

Some microorganisms can survive with limited access to water, even within water droplets in the clouds of Earth’s atmosphere. Some of these microorganisms “where temperatures permit,” Halsworth said, are metabolically active and capable of cell division. Thus, astrobiologists and planetary scientists naturally focus on regions where water is, or at least where it once was.

For the new study, scientists calculated the amount of water activity in the atmosphere of Venus and on other planets in our solar system. Water activity can be measured on a scale of 0 to 1, which is similar to how relative humidity is measured in our atmosphere. As indicated by scientists, life on Earth requires a water activity of at least 0.585 to maintain metabolism and reproduction. The researchers used this as a baseline for their analysis, in a form derived from the study of extremophiles able to tolerate low-water conditions and microorganisms able to resist exposure to acids. In fact, the clouds of Venus contain generous amounts of sulfuric acid mixed with small amounts of water.

To record the water’s activity, scientists analyzed previously recorded measurements of air temperature, air pressure, and the availability of water vapor on Venus. The team decided to use the same approach to study the other planets, Jupiter, Mars and Earth.

On Venus, water activity has been measured along a range between 42 and 68 kilometers above the surface, since the temperature within this layer is within the limits of habitability. Water activity on Venus has been estimated at 0.004, which is more than 100 times less than the known limit for life and “an insurmountable distance from what it takes for life to be active,” Halsworth explained. He added that water activity within this layer was not uniform, but that even larger amounts were “too far from scale” for any active life form.

This severe drought is bad news for habitability. According to researchers, sulfuric acid in the sky of Venus is largely responsible for reducing the availability of water on the planet. Therefore, for microbes to reside within the clouds of Venus, they must be of a completely unknown type that challenges our understanding of biology.

In the case of Mars, the water activity was recorded at 0.537, which is similar to what is observed in Earth’s stratosphere (a thin layer in our upper atmosphere). Again, this value is below the acceptable life limit but much higher than the value obtained for the flower. In the study, the scientists wrote that clouds on Mars “are not biologically permissive due to low temperatures that are incompatible with cell function” not to mention “high ultraviolet radiation that can be fatal to atmospheric microbes.”

Surprisingly, water activity within Jupiter’s clouds, in regions where temperatures range from 10°C to -40°C, was recorded at levels above the low 0.585 threshold. Adorable.

“One thing we found, which was unexpected, is that Jupiter’s clouds actually have the right mix of temperature and water activity to keep life active; we weren’t expecting that at all,” Hallsworth said. on Jupiter, and I’m not even suggesting that life could be in the clouds, because it would need the right nutrients to be there, and we can’t be sure of that. “

Life, he pointed out, “not only needs a good temperature and availability of water to be active,” but this consequence, that water activity in the depths of Jupiter’s cloud layer is likely to be susceptible to life,” is deep and exciting, Halsworth said. He added that there would be a need to An “entirely new study” to further evaluate and investigate the types of microbes that could theoretically survive in Jovian clouds.

The new document is likely to overshadow three upcoming missions to Venus NASA’s VERITAS, DAVINCI+, and ESA’s EnVision Orbiter Missions. But the authors of the new paper don’t see it that way, as these probes are likely to collect data that further supports the new discovery. Mackay expects similar results, saying that our new understanding of water activity on Venus is unlikely to change.

Interestingly, the scientists said their new approach could also be used to study the atmospheres of exoplanets, and the worlds surrounding other stars. The new James Webb Telescope was developed as an instrument capable of taking the necessary measurements. The ability to detect water activity on near and far planets represents a powerful new skill for astrobiologists, who continue to study the limits of life.

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