The amount of water in Venus' atmosphere is so low that even Earth's most drought-tolerant microbes wouldn't stand a chance, study suggests . On the other hand, there is still a (thin) hope for Jupiter.
Last year, a team of astronomers made headlines by suggesting the presence of phosphine, a chemical proposed as a potential indicator of life, in the atmosphere of Venus. If the surface conditions exclude the existence of life on this planet, we know that the Venusian clouds, at an altitude between 35 and 50 km, offer a much milder environment (pressure and temperatures similar to Earth). Thus, the prospect that this chemical which could betray the presence of life could not be immediately ruled out.
Finally, a study published a few months ago suggested that the possible phosphine discovered in the atmosphere of Venus was probably just ordinary sulfur dioxide. Today, a new article published in a Nature goes in the same direction, pointing out that the conditions in the clouds of Venus are in no way compatible with life as we know it . If the Venusian clouds are indeed showing milder temperatures, they don't have not enough water to support it .
As part of this work, microbiologist John Hallsworth and his team at Queen's University in Belfast (Northern Ireland) collected measurements from probes that had flown through the atmosphere from Venus to analyze data on temperature, humidity and pressure in the thick clouds of sulfuric acid encasing the planet.
From these values, scientists were able to calculate "Water Activity", or the water vapor pressure inside individual molecules in clouds, which is one of the limiting factors for the existence of life on Earth. For this activity, which is measured on a scale of 0 to 1, the lowest survival value is 0.585. However, the level recorded in the molecules of Venusian clouds is only 0.004.
“When we looked at the actual concentration of water molecules in these clouds, we found that it was more than a hundred times too low for even the Earth's toughest organisms survive" , confirms John Hallsworth. “It’s an impassable distance” .
According to astronomer Chris McKay, one of the co-authors of the study, the new missions being prepared to probe the environment of Venus do not won't change much. “Our conclusion is based directly on measurements” , did he declare. "It's not a model, it's not a hypothesis. The missions that NASA and ESA have just selected will again make the same measurements – temperature, pressure – and they will arrive at roughly the same conclusions because Venus does not change on this time scale.
During this work, the researchers also examined the same types of data collected on other planets.
For Mars, the Water Activity was measured at 0.537. This value, comparable to what is observed in the Earth's stratosphere, is therefore again "below bearable". Additionally, Martian clouds “are not biologically permissive due to low temperatures which are incompatible with cellular function” , not to mention the "high ultraviolet radiation that can be deadly to airborne microbes" , point out the researchers in the study.
In contrast, the Water Activity recorded in Jupiter's clouds, in regions where temperatures vary between 10 degrees Celsius and -40 degrees Celsius, would be at the minimum threshold of 0.585.
"What we found, and what was unexpected, is that Jupiter's clouds actually provide the right combination of temperature and water activity to support active life" , notes Dr. John Hallsworth. "Now I'm not suggesting that life exists on Jupiter because it would need the right nutrients and we can't be sure. But as for water, it's ok" .
