Abstract EANA2024-10

In recent years, the interest of astrobiologists to Venus drastically increased due to an active discussion of the habitability of its cloud layer where the existence of the photo- and/or lithotrophic microbial community using sulfur and iron compounds in their energy metabolism is hypothesized.

An important feature of the cloud layer of Venus compared to that of Earth is its absolute spatial isolation as a possible habitat for organisms. If the microbial biomass in clouds on Earth is constantly replenished as a result of the entry of microorganisms from the surface with air convection flows, then such a mechanism is impossible on Venus due to the apparent absence of any terrestrial-type organisms on its super-hot surface.

Despite the extremely low concentration of water vapor in the modern clouds of Venus, it is assumed that living organisms can exist in aerosols, in which the sulfuric acid - water phase can be concentrated in a small volume and contain a certain number of microorganisms capable of active life. Such a community must be characterized by a high survivability potential under severe environmental conditions, the most extreme of which are very low pH levels and water activity.

To date, there are various concepts of the geological past of Venus, in which the availability of water on its ancient surface is discussed. The absence or presence of water reservoirs on the ancient surface of Venus can directly support one or another hypothesis of the possible origin of life on Venus. These hypotheses include the surface/subsurface or cloud scenarios, in which life emerges in the process of increasing complexity of molecular systems. An alternative concept is panspermia, which transforms the problem of the origin of life into that of its delivery to Venus from the outer space and further adaptation of alien organisms to conditions in the Venusian clouds with their subsequent evolution.

A number of terrestrial extremophilic microorganisms living in systems such as acidic fumaroles are, in their physiological properties, closest to organisms capable of surviving in the conditions of Venusian clouds. However, given the combination of extreme factors, it is difficult to find any terrestrial organism that could successfully develop in such environment. Various concepts have been proposed that allow for the existence a form of life there different from that on Earth. Such a life form, for example, may use aqueous sulfuric acid as a solvent instead of water and other acid-resistant biomolecules as the basis of their cellular structures.

Several missions to Venus are planned in the next decade. Some of them aim to detect biomarkers in clouds that can be associated with biological activity. However, direct evidence of life will only be possible by delivery of cloud samples to Earth, which is a more difficult task.

In general, Venus is a unique cosmic body, on the example of which it is possible to model various concepts of the origin of life and scenarios for its further evolution.