Venus is undoubtedly a hell planet. Its atmosphere swirls with toxic clouds of sulfuric acid at temperatures of up to 880 degrees Fahrenheit. If anything lives on the last place in the solar system anything would be expected to survive, it could be kind of like Sea Monkeys that spring to life in water, or at least whatever could pass for a life-sustaining fluid on Venus.
Such hypothetical life could make it if it can withstand going through desiccation and reanimation like a Sea Monkey (or a tardigrade). While there have been alternate theories on how microbes could survive on Venus, this is the first time that anyone has proposed there could be chemotrophic life forms whose life cycle potentially involves spending most of their time in atmospheric liquid droplets before they fall to the scorching lower haze layer after those droplets evaporate. The desiccated microbes or “spores” could then be rehydrated when gravity waves headed upward carry them back into the clouds.
“Venus atmosphere life outside liquid droplets is not possible is that free-floating life outside of droplets would rapidly desiccate (by net loss of liquid to the atmosphere) in the very dry atmosphere of Venus,” said MIT astrobiologist Sara Seager, who led a study recently published in Astrobiology. “Specifically, a free-floating cell will lose water until its internal water activity is the same as the vapor pressure of the atmosphere around it.”
Earth does have microbes in its atmosphere, some of which are sustained by water droplets. Others are free-floating. Whether cell division can actually take place up there is still unknown, and Seager was careful to note that what happens on Earth should not be used as an analog for Venus. Anything that synthesizes a poison like sulfuric acid (H2SO4) is definitely not life as we know it.
Because life as we know it, or at least as far as we know it, does need some sort of liquid, any microbes that may or may not live in the Venusian atmosphere are also believed to require it. Sulfuric acid being that liquid does not necessarily make survival impossible. There are actually microorganisms on Earth that can survive in sulfuric acid. Ferroplasma acidphilum sucks its energy out of iron, which its biochemistry depends on. So if microbes here can synthesize what is otherwise seen as poison, they can possibly be crawling around elsewhere. It’s just that the sulfuric acid on Venus is much more intense.
“The Venusian sulfuric acid clouds are much more acidic than even the most harshly acidic conditions found on Earth,” Seager said, but added that “Preliminary studies suggest that even in such harsh polyextreme hydrothermal conditions, life can survive and possibly even thrive.”
There is also the possibility that life on Venus could be photosynthetic, because neither oxygen nor carbon is necessary for the process. Anoxygenic photosynthesis is a thing. So long as light is coming from somewhere, there are life forms that can synthesize it. Ectothiorhodospira bacteria on Earth metabolize arsenic this way.
So even Earth’s death-defying microbes might not be able to pull off survival on Venus. Nobody knows because we have no samples, but there still is the possibility that something could be living and multiplying even in the seventh circle of hell. Venus still might not be barren. Even with clouds of sulfuric acid strong enough to make the stuff on Earth look refreshing, a microbe living inside a liquid droplet is actually exposed to more water than the parched atmosphere. Venus has a relative humidity of about .07% compared to the driest places on Earth, whose relative humidity is about 2%.
Whether Venus could have sulfur-synthesizing microbes, never mind how it got there if it does exist, remains speculative. Microbes could have been shared by collisions with early Earth and Mars or come from an extraterrestrial source. Only future missions could start probing those clouds full of secrets.