• Dirk Schulze-Makuch

The Idea of Microbial Life in the Venusian Atmosphere is NOT dead

Updated: Dec 3, 2021

Take Aways from the Venera D Cloud Habitability System Workshop

UV image of Venus from the Venus Pioneer probe. The black streaks indicate UV absorption (Credit: NASA).

This week the Venera D Cloud Habitability System Workshop is held at the Space Research Institute in Moscow, Russia. The focus of the workshop, which is still ongoing, is on the upcoming missions, not only the Russian-led Venera D mission but also the American missions Davinci and Veritas, and the European-led EnVision mission. On the first day, however, the question of whether the clouds of Venus are habitable was center-stage.

While the clouds are the most benign Venusian environment today, the low water availability and extreme acidity pose stark challenges to any form of life. Oleg Kotsyurbenko from the Yugra State University in Russia emphasized that any life existing in the Venusian clouds would have to be an extremophilic organism dealing with multiple environmental stressors. Even if there is life that can deal with the stressors, it would be difficult for a biosphere to keep a constant amount of biomass in the Venusian atmosphere to ensure long-term survival. Diana Gentry from the NASA Ames Aerobiology Laboratory agreed and emphasized that the challenge would not only be biomass, but how water availability would be maintained throughout geological time scales to keep a biosphere viable. She also underlined that we have to look at the “small stuff,” meaning at the scale of microbial life. We know from previous work that microenvironments can support life even if the larger environment is hostile to life.

Whether life is possible in the Venusian clouds depends largely on how acidic the clouds are. Jan Spacek from Firebird Biomolecular Sciences in Florida pointed out that no organic carbon is stable at sulfuric acid concentrations of 60% or more (by volume), which most experts think is the case in the Venusian atmosphere. However, Rakesh Mogul from the California State Polytechnic University in Pomona emphasized that we don´t know how acidic the Venusian atmosphere really is. He stated that already a small amount of ammonia in the atmosphere would drop acidities down to levels that microbes on Earth could handle.

In my talk at the workshop, I pointed out that microbial life might have evolved by natural selection from former surface life on Venus (at a time when Venus still had oceans). If that is the case, Venusian life would be expected to be better adapted to Venusian conditions than any Earth life, perhaps by using hygroscopic salts to attract the much needed water.

The next steps in Venus exploration should be the following: try to independently confirm (or refute) the presence of the biomarker phosphine in the Venusian atmosphere, conduct laboratory experiments to test whether microbes could adapt over generations to hyperacidity and the other environmental stressors in the cloud layer, and launch missions to Venus.

The currently planned missions will help gain critical insights into the natural history of the planet, whether Venus is still volcanically active, and constrain environmental conditions in the Venusian atmosphere. However, the most crucial aspect of a mission would be to examine the aerosols, particularly the so-called mode 3 particles in the lower cloud layer. The Venus Cloud Explorer, a proposal for a mission presented by Kevin Baines from JPL intends to do just that by sampling and analyzing the aerosols in the Venusian atmosphere. If there is any life in the Venusian atmosphere, the aerosols may be it, microorganisms coated by elemental sulfur to absorb UV radiation.

While we need to realize that the challenges of the Venusian environment to life are formidable, to say the least, there may be ways for life to persevere. If our previous research of life in extreme environments taught us anything, then it is that life (mostly) finds a way!

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