In a paper published March 30 in the journal Astrobiology, an international team of researchers suggests that the thick and acidic atmosphere of Venus may actually serve as a potential safe haven for microbial life. In the hypothesis paper, they not only present multiple lines of evidence showing the venusian clouds could harbor extreme forms of life, but also show that airborne life on Venus would help explain the fluctuating appearance of the planet’s clouds — a mystery that has plagued astronomers for nearly a century.
Although scientists have debated the habitability of Venus’ atmosphere for many decades — Carl Sagan co-authored a paper on the topic in 1963 — our sister world is often still ignored as a target for astrobiological research. This is primarily because the surface of Venus is now almost undoubtedly inhospitable to life, sporting temperatures of over 860 degrees Fahrenheit (450 Celsius) and surface pressures about 90 times greater than those found on Earth. However, despite the fact that Venus is now a hellish landscape (largely due to a run-away greenhouse effect), at one point, the planet looked a lot more like Earth does today.
“Venus had plenty of time to evolve life on its own,” said lead author Sanjay Limaye, a planetary scientist at the University of Wisconsin-Madison’s Space Science and Engineering Center, in a press release. In fact, previous research suggests that Venus could have once maintained a habitable climate with liquid water on its surface for as long as 2 billion years. “That’s much longer than is believed to have occurred on Mars,” he said.
This would have allowed life to initially form on the surface of Venus (when the toxic planet looked more like present-day Earth) before eventually migrating up into the venusian clouds. Although this scenario may seem unlikely, on Earth, microorganisms such as bacteria can (and do) get swept high up into the atmosphere. According to co-author David Smith of NASA’s Ames Research Center, by using specialized research balloons, scientists have even found such high-altitude microorganisms surviving up to 25 miles (41 kilometers) above the Earth’s surface.
Furthermore, as the new paper points out, a series of space probes sent to Venus between 1962 and 1978 showed that, though the surface of Venus is not conducive to life, the venusian atmosphere very well could be. At altitudes between 25 and 37 miles (40 and 60 kilometers), the atmospheric temperature of Venus ranges between about 90°F and 160°F (30°C to 70°C), and the pressure is almost the same as you would find at sea level on our own planet. On the other hand, the acidic, sulfur-laden venusian air is rather toxic — that is, at least to most forms of life.
Over the years, though, scientists have compiled a large catalog of microbes that are known to survive and thrive in incredibly harsh environments here on Earth. One such organism is the humble tardigrade — a microscopic animal (often called a “water bear”) that can survive even the most extreme conditions. These hardy critters have been found almost everywhere on the planet, ranging from the driest deserts to the tallest mountaintops. In 2007, researchers even found that Tardigrades could survive up to 10 days in the irradiated vacuum of space.
“On Earth, we know that life can thrive in very acidic conditions, can feed on carbon dioxide, and produce sulfuric acid,” said co-author Rakesh Mogul, a professor of biological chemistry at California State Polytechnic University, Pomono, in a press release. Considering this, Mogul says it’s worth noting that the atmosphere of Venus is primarily made of carbon dioxide and water containing lots of sulfuric acid, meaning the toxic clouds do not necessarily rule out venusian life.
Perhaps most importantly, according to the paper, the physical and chemical conditions within Venus’ atmosphere allow for microorganisms to not only exist, but also contribute to the persistently changing appearance of the planet’s clouds. “Venus shows some episodic dark, sulfuric rich patches, with contrasts up to 30-40 percent in the ultraviolet, and muted in longer wavelengths,” said Limaye. “These patches persist for days, changing their shape and contrasts continuously, and appear to be scale dependent.”
The researchers also point out that, based on previous spectroscopic observations, the dark patches are made up of particles that are almost the same size and shape as some light-absorbing bacteria found here on Earth. According to Limaye and Mogul, this means that the atmospheric patches could be living colonies of microorganisms, similar to algae blooms commonly found in large bodies of water on Earth. However, every instrument used to sample Venus’ atmosphere so far has been incapable of distinguishing between inorganic and organic compounds.
So for now, it seems, the question of whether extraterrestrial life floats above the surface of Venus remains a mystery. “To really know, we need to go there and sample the clouds,” said Mogul. “Venus could be an exciting new chapter in astrobiology exploration.”