There is not enough water in the upper atmosphere of Venus to support life of the terrestrial type.
Astronomers have determined that the activity of water in Venus’s clouds at altitudes where temperatures allow microbiological life forms to exist is two orders of magnitude below the limit for known extremophiles. This means that even in the upper layers of the atmosphere of Venus, the life of the terrestrial type could hardly survive.
The conditions near the surface of Venus cannot be called favorable for the development of life – the average temperature of the planet’s surface is 467 degrees Celsius, and the atmospheric pressure is several tens of times higher than that of the Earth.
However, the recent discovery of phosphine at altitudes of about 53-61 kilometers, which is considered a potential biomarker, has revived interest in the idea of the existence of microbiological life forms (for example, extremophiles) in its atmosphere.
There is not enough water in the upper atmosphere of Venus for life to exist
1. From the point of view of the physiological activity of organisms of the terrestrial type, the abundance of water is important for them, which can be quantified using the parameter of water activity.
2. Even if the temperature in the atmospheres of other planets allows the formation of droplets containing various substances and water, for a more complete assessment of habitability, it is necessary to determine the activity of water, which depends not only on temperature and pressure but also on the composition of the atmosphere.
3. Scientists suggest that the permissible temperature range for the metabolism and growth of microbiological organisms is from -40 to 130 degrees Celsius, and cell activity can occur up to a water activity value of 0.585.
4. A group of astronomers led by John E. Hallsworth of Queens University in Belfast decided to determine the water activity in the clouds of Venus, Jupiter, and Mars by calculations based on observations of temperature and water vapor content in the atmosphere.
5. The authors believe that there is no reason to assume that hypothetical Venusian organisms will have the same biochemical basis as on Earth, however, due to the lack of any alternative biochemical theories, they considered the question of whether organisms similar to terrestrial, survive on Venus, for example, in drops of sulfuric acid clouds.
6. Scientists have determined that the value of water activity for sulfuric acid droplets, which make up the bulk of Venus’s clouds, is less than 0.004, which is two orders of magnitude below the limit for known extremophiles.
7. For droplets in clouds to be habitable, water activity must be highly disequilibrium, which means that it is not determined by the relative humidity of the environment.
8. According to the researchers, the previously published theory that Venusian organisms could store water somewhat expands the habitability of Venus’s clouds, but it still cannot get around the need for an acceptable level of water activity.
9. From this point of view, Jupiter’s clouds (although their composition is poorly suited for the development of life), where the activity of water is estimated at more than 0.585, could be more suitable for the life of the terrestrial type than the atmosphere of Venus.
10. As for Mars, strong ultraviolet radiation and low temperatures, allowing only icy clouds to form, give water activity values much lower than the limits allowed for terrestrial life forms.
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• Hallsworth, J. E., Koop, T., Dallas, T. D., Zorzano, M.-P., Burkhardt, J., Golyshina, O. V., Martín-Torres, J., Dymond, M. K., Ball, P., & McKay, C. P. (2021, June 28). Water activity in Venus’s uninhabitable clouds and other planetary atmospheres. Nature News.
• Patel, N. V. (2021, June 28). Venus doesn’t have enough water in its clouds to sustain life. MIT Technology Review.
• Phys.org. (2021, June 28). Lack of water rules out life on Venus: study. Phys.org.
• Pultarova, T. (2021, June 28). No hope for life in Venus clouds, but maybe on Jupiter, study suggests. Space.com.