After decades of looking to the outer solar system and beyond for signs of extraterrestrial life, an international team of scientists is suggesting that humanity take another look at a planet a little closer to home: Venus.
Although the surface of Venus is much too hot and inhospitable for life as we know it, scientists have long thought that microbes could be comfortably reproducing in the clouds of the Venusian atmosphere. Now, a new study in the journal Astrobiology suggests that dark patches in the atmosphere of Venus could, just possibly, be caused by light-absorbing bacteria. To find out, the study authors want to send a floating aircraft to comb the skies of Venus.
Earth’s sister Venus, the second rock from the sun, is similar in size, mass, and composition to our home planet-but that is generally where the comparisons end. The planet’s atmosphere is 96.5 percent carbon dioxide and almost 3.5 percent nitrogen. The runaway greenhouse climate keeps surface temperatures hovering around 864 degrees Fahrenheit (462 degrees Celsius), while atmospheric pressures on Venus can be as high as pressures a kilometer deep in the oceans of Earth.
But for all the planet’s seemingly inhospitable traits, “Venus has had plenty of time to evolve life on its own,” said University of Wisconsin-Madison scientist Sanjay Limaye, who led the new study, in a press release. Limaye points to models that suggest Venus could have sustained 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,” says Limaye.
American and Soviet probes studying Venus in the 1960s and 70s revealed that the temperature and pressure conditions in the lower and middle portions of the Venusian atmosphere-around 25–27 miles up from the surface-do not necessarily preclude life. In 1967, Carl Sagan co-authored a paper with noted biophysicist Harold Morowitz suggesting that life could exist in the clouds. “While the surface conditions of Venus make the hypothesis of life there implausible, the clouds of Venus are a different story altogether,” Sagan and Morowitz wrote.
A chance encounter convinced Limaye to give the planet another look. Talking with co-author of the new paper Grzegorz Słowik of Poland’s University of Zielona Góra, Limaye learned about bacteria on Earth with light-absorbing properties. With a group of researchers, they noted similarities between the bacteria and a mystery within the atmosphere of Venus: dark spots in the atmosphere.
NASA has studied “an unknown UV absorber” embedded within the Venusian clouds. In presentation slides, the agency says that “the unknown UV absorber has been a subject of intense scrutiny since the dawn of the space age.” At the moment, the only probes which have observed this phenomenon have lacked the technical capability to distinguish between materials of an organic or inorganic nature. This unknown absorber, Limaye’s team suggests, could be alien bacteria in the clouds of Venus.
“On Earth, we know that life can thrive in very acidic conditions, can feed on carbon dioxide, and produce sulfuric acid,” says Rakesh Mogul, a professor of biological chemistry at California State Polytechnic University, Pomona, and a co-author on the new paper. Similarly harsh conditions might be able to sustain life amongst the clouds of Venus, something the team suggests could be similar to algae in lakes on Earth-except floating in the clouds.
There are many unknowns surrounding the new hypothesis, including when exactly Venus’s water supply evaporated. Limaye and his colleagues have an idea for how to get find the answers: the Venus Atmospheric Maneuverable Platform, better known as VAMP. A hypothetical aircraft proposed by Northrop Grumman, the VAMP would steer like a plane and float like a blimp through the skies of Venus, taking samples of the Venusian atmosphere. This craft would carry instruments capable of identifying living microorganisms.
“To really know, we need to go there and sample the clouds,” says Mogul. “Venus could be an exciting new chapter in astrobiology exploration.”