Could life exist in Venus’ atmosphere?

Venus is an extremely inhospitable world on the surface, but high up in its atmosphere, life may be able to survive. Credit: NASA / JPL
Venus is an extremely inhospitable world on the surface, but high up in its atmosphere, life may be able to survive. Credit: NASA / JPL

Venus has a reputation for being one of the most inhospitable places in the solar system, and deservedly so. Its thick carbon dioxide (and acidic) atmosphere has a crushing pressure similar to that in the deepest oceans on Earth and the scorching temperature on the surface is hot enough to melt lead. It’s like that everywhere on the planet, all the time. It has therefore been considered an extremely unlikely environment to support any kind of life. Even the toughest microbes here would find survival next to impossible. There is however a possibility, even if remote, that the upper atmosphere of this hellish world could be habitable, according to some scientists.

Dirk Schulze-Makuch, an astrobiologist at Washington State University, has been studying this idea with his colleagues, and thinks it is plausible and may even explain some interesting observations about Venus’ atmosphere.

The conditions in the upper atmosphere are much more hospitable than those farther down. At an altitude of about 50-60 kilometres (30-40 miles), the pressure and temperature are similar to those on Earth. There is also water vapour and traces of oxygen.

On Earth, bacteria thrive in clouds, making it more conceivable that the same thing could, just maybe, happen on Venus as well. Some earthly bacteria also thrive in acidic conditions similar to those found in Venus’ cloud layers.

Floating microbes could also conceivably explain a three-part puzzle about the Venusian atmosphere. First, the clouds appear to absorb more UV light than scientists think they should. According to theory, microbes could use sulfur, which is also abundant in Venus’ atmosphere, as a kind of sunblock since it absorbs harmful UV. Also, there are particles in the atmosphere which haven’t been identified yet. Known as “mode 3” particles, they are larger than other droplets or crystals in the atmosphere (and about the same size as bacteria) and are non-spherical in shape. They also contain a lot of sulfur. Lastly, there is another chemical in Venus’ atmosphere which took scientists by surprise. Carbonyl sulfide (OCS) is very difficult to produce inorganically, as in without life. On Earth, it would be considered an unambiguous indicator of biological activity. So what is it doing in Venus’ clouds?

Understandably, the search for other life elsewhere in the solar system has been focused on Mars, Europa, Enceladus and Titan. Could such evidence have been on our closest planetary neighbour, Venus, all along? As unlikely as it may seem, the findings are intriguing, but will require much more follow-up and observation to figure out.

It is also now thought that Venus likely had oceans early in its history and was generally more Earth-like before succumbing to a runaway greenhouse effect. Is it possible that life started there and then later retreated to and adapted to the upper atmosphere as conditions on the ground became inhospitable? Maybe, just maybe…

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