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A Venus Atmospheric Maneuverable Platform, or VAMP. The aircraft, which would fly like a plane and float like a blimp, could help explore the atmosphere of Venus, which has temperature and pressure conditions that do not preclude the possibility of microbial life. Credit: Northrop Grumman<\/p><\/div>\n
\u201cOn Earth, we know that life can thrive in very acidic conditions, can feed on carbon dioxide, and produce sulfuric acid,\u201d says Rakesh Mogul, a professor of biological chemistry at California State Polytechnic University in Pomona and a co-author on the new paper. He notes that the cloudy, highly reflective and acidic atmosphere of Venus is composed mostly of carbon dioxide and water droplets containing sulfuric acid.<\/p>\n
The habitability of Venus\u2019 cloudswas first raised in 1967 by noted biophysicist Harold Morowitz and famed astronomer Carl Sagan. Decades later, the planetary scientists David Grinspoon, Mark Bullock and their colleagues expanded on the idea.<\/p>\n
Supporting the notion that Venus\u2019s atmosphere could be a plausible niche for life, a series of space probes to the planet launched between 1962 and 1978 showed that the temperature and pressure conditions in the lower and middle portions of the Venusian atmosphere \u2013 altitudes between 40 and 60 kilometers (25 \u2013 27 miles) \u2013 would not preclude microbial life. The surface conditions on the planet, however, are known to be inhospitable, with temperatures soaring above 450 degrees Celsius (860 degrees Fahrenheit).<\/p>\n
Limaye, who conducts his research as a NASA participating scientist in the Japan Aerospace Exploration Agency\u2019s Akatsuki mission to Venus, was eager to revisit the idea of exploring the planet\u2019s atmosphere after a chance meeting at a teachers\u2019 workshop with paper co-author Grzegorz S\u0142owik of Poland\u2019s University of Zielona G\u00f3ra. Slowik made him aware of bacteria on Earth with light-absorbing properties similar to those of unidentified particles that make up unexplained dark patches observed in the clouds of Venus. Spectroscopic observations, particularly in the ultraviolet, show that the dark patches are composed of concentrated sulfuric acid and other unknown light-absorbing particles.<\/p>\n
Those dark patches have been a mystery since they were first observed by ground-based telescopes nearly a century ago, says Limaye. They were studied in more detail by subsequent probes to the planet.<\/p>\n
\u201cVenus shows some episodic dark, sulfuric rich patches, with contrasts up to 30 \u2013 40 percent in the ultraviolet, and muted in longer wavelengths. These patches persist for days, changing their shape and contrasts continuously and appear to be scale dependent,\u201d says Limaye.<\/p>\n
The particles that make up the dark patches have almost the same dimensions as some bacteria on Earth, although the instruments that have sampled Venus\u2019 atmosphere to date are incapable of distinguishing between materials of an organic or inorganic nature.<\/p>\n
The patches could be something akin to the algae blooms that occur routinely in the lakes and oceans of Earth, according to Limaye and Mogul, only these would need to be sustained in the Venusian atmosphere.<\/p>\n
Limaye, who has spent his career studying planetary atmospheres, was further inspired to revisit the idea of microbial life in the clouds of Venus by a visit to Tso Kar, a high-altitude salt lake in northernIndia where he observed the powdery residue of sulfur-fixing bacteria concentrated on decaying grass at the edge of the lake being wafted into the atmosphere.<\/p>\n
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A composite image of the planet Venus as seen by the Japanese probe Akatsuki. The clouds of Venus could have environmental conditions conducive to microbial life. Credit: Image from the Akatsuki Orbiter, built by Institute of Space and Astronautical Science\/Japan Aerospace Exploration Agency<\/p><\/div>\n
Limaye notes, however, that a part of the equation that isn\u2019t known is when Venus\u2019 liquid water evaporated \u2013 extensive lava flows in the last billion years likely have either destroyed or covered up the planet\u2019s earlier terrestrial history.<\/p>\n
In the hunt for extraterrestrial life, planetary atmospheres other than Earth\u2019s remain largely unexplored.<\/p>\n