If we didn’t have enough excuses to build floating cloud cities on Venus, here’s another item to add to the list: The planet’s lower atmosphere may be teeming with extraterrestrial microbes.
As detailed in a paper published recently in Astrobiology, studies of organisms capable of withstanding extreme environments on earth—appropriately known as extremophiles—has made the prospect microbial life on Venus more plausible in recent years. In fact, pockets of carbon dioxide-munching microbes adrift in the Venusian atmosphere may explain mysterious dark patches that have been observed in Venus’ clouds for over a century.
At first glance, Venus seems like one of the last places in the solar system you’d expect to find life. Its atmosphere is mostly composed of carbon dioxide and water droplets containing sulfuric acid, both of which are toxic to humans. Moreover, temperatures on the surface of Venus can soar to 900 degrees Fahrenheit during the day and surface pressures are about 92 times greater than the Earth’s atmospheric pressure at sea level.
Nevertheless, planetary scientists consider Venus to be Earth’s twin. Not only is Venus nearly the same size, scientists also think it may have had liquid water on its surface for nearly 2 billion years before succumbing to a runaway greenhouse effect resulting from intense and sustained lava flows on the surface. Moreover, conditions get far more Earth-like in the low-to-mid Venusian atmosphere (around 25 miles up). Here, the atmospheric pressure and gravity are approximately the same as Earth, and temperatures range between 32 and 120 degrees Fahrenheit.
Taken together, these are all conditions that make Venus’ atmosphere a promising candidate for extraterrestrial life in the solar system.
Read More: Why We Should Build Cloud Cities on Venus
On Earth, scientists have found microbes alive at altitudes over 100,000 feet, as well as extremophiles capable of living in environments such as Yellowstone’s hot springs or near hydrothermal vents in the deep ocean.
“We know that life can thrive in very acidic conditions, can feed on carbon dioxide, and produce sulfuric acid,” Rakesh Mogul, a professor of biological chemistry at California State Polytechnic University, Pomona, said in a statement. These conditions are quite similar to those found in Venus’ atmosphere, Mogul and his coauthor Sanjay Limaye, a planetary scientist at the University of Wisconsin-Madsion, point out. Moreover, the presence of extremophile alien microbes on Venus may help to explain a long standing mystery about the planet’s atmospheric composition.
Previous observations of Venus’ atmosphere by spacecraft and telescopes on Earth have found dark patches in the planet’s atmosphere that are mostly composed of concentrated sulfuric acid as well as some other unknown light-absorbing particle.
“Venus shows some episodic dark, sulfuric rich patches, with contrasts up to 30–40 percent in the ultraviolet, and muted in longer wavelengths,” Limaye said. “These patches persist for days, changing their shape and contrasts continuously and appear to be scale dependent.”
While working on Akatsuki, a Japanese spacecraft launched in 2010 and the most recent to visit Venus, Limaye learned that there are bacteria on Earth that have light-absorbing properties similar to the unknown particles observed on Venus. Moreover, these mysterious Venusian particles have the same dimensions as some bacteria on Earth. Limaye and Mogul suggested that these dark spots may be atmospheric microbial blooms, similar to the way algae blooms in pockets of water on Earth.
The problem is that so far, every probe that has entered Venus’ atmosphere has carried scientific instruments that were incapable of distinguishing organic material from inorganic particles. Limaye cited the need for more data about the nature of these spots as a strong reason to support more missions to the Venusian atmosphere. While there are plenty of proposals for blimp-like machines that could be deployed around Venus, many of these projects have stalled out over the last two decades due to funding problems.
“To really know, we need to go there and sample the clouds,” Mogul said. “Venus could be an exciting new chapter in astrobiology exploration.”