Decades-long search for alien life has given momentum to biologists unearth the pre-requisites of life, hoping to find life form sooner or later. Mars probe has revealed that water was there on its surface once and now present in its sub-surface layers. Even Saturn’s moons Titan and Enceladus and Jupiter’s moons Europa, Ganymede and Callisto are standing up as possible havens for life under their icy crusts.

Venus, which was almost ruled out has become a candidate now and Indian-origin scientist planetary scientist Sanjay Limaye of the University of Wisconsin–Madison’s Space Science and Engineering Center and his team of researchers have begun dusting off an old idea that the atmosphere of Venus could be a possible niche for extraterrestrial microbial life.

Ever since the habitability of Venus’ clouds was first raised in 1967 by biophysicist Harold Morowitz and astronomer Carl Sagan, the idea has been expanding among the researchers. Planetary scientists David Grinspoon, Mark Bullock and their colleagues have supported the notion that Venus’ atmosphere could be a plausible niche for life.

A series of space probes to Venus launched between 1962 and 1978 by NASA and other space agencies showed that the temperature and pressure conditions in the lower and middle portions of the Venusian atmosphere, between 40 and 60 km altitude, would not preclude microbial life. But the immediate surface is known to be inhospitable, with temperatures soaring above 450 degrees Celsius.

Some models have suggested that Venus once had a habitable climate with liquid water on its surface for more than 2 billion years, much longer than what is believed to have occurred on Mars. “Venus has had plenty of time to evolve life on its own,” explains Limaye.

Since Earth’s surface has supported microorganisms or bacteria, which are found to be capable of being alive even at altitudes of 41 kilometers above the surface, the study co-author David J. Smith of NASA’s Ames Research Center, is confident that the microbial life could be found in the mid-atmosphere of Venus, if not on the surface.

Microbes can inhabit even in incredibly harsh environments such as the hot springs of Yellowstone, deep ocean hydrothermal vents, the toxic sludge of polluted areas, and in acidic lakes worldwide on the Earth, he said.

"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. He notes that the cloudy, highly reflective and acidic atmosphere of Venus is composed mostly of carbon dioxide and water droplets containing sulfuric acid.

Limaye, who is a NASA participating scientist at the Japan Aerospace Exploration Agency’s Akatsuki mission to Venus, quoting a co-author Grzegorz Słowik of Poland’s University of Zielona Góra on light-absorbing properties of bacteria, said the famous dark patches on Venus atmosphere could be composed of concentrated sulfuric acid and other unknown light-absorbing particles.

“Venus shows some episodic dark, sulfuric rich patches, with contrasts up to 30–40 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,” said Limaye.

Limaye said he was inspired when he visited Tso Kar, a high-altitude salt lake in northern India where he observed the powdery residue of sulfur-fixing bacteria on decaying grass at the edge of the lake being wafted into the atmosphere.
“To really know, we need to go there and sample the clouds,” echoed Mogul. “Venus could be an exciting new chapter in astrobiology exploration.”

A Venus Atmospheric Maneuverable Platform, or VAMP, which is an aircraft being sent to Venus to explore its atmosphere and Russia’s Roscosmos Venera-D mission will undertake missions to Venus, sometime in the late 2020s. Venera-D is likely to include an orbiter, a lander and a NASA-contributed surface station and maneuverable aerial platform.

The findings, supported by NASA, have been published in the journal Astrobiology.

A Venus Atmospheric Maneuverable Platform, or VAMP aircraft, would fly like a plane and float like a blimp, to explore the atmosphere of Venus, which has temperature and pressure conditions that do not preclude the possibility of microbial life. [Photo: NORTHROP GRUMMAN]