In a paper just published in the magazine Astrobiology, Sara Seager from MIT and colleagues suggest a way for microbial life to live permanently in the lower atmosphere of Venus. The idea that microbes can exist in Venusian clouds, at an altitude of 50 to 65 kilometers above ground level, was proposed more than 50 years ago by the late Carl Sagan, and has since been advanced by many other authors, including myself.
The possibility of living in such an exotic place may seem foreign at first. But remember that Venus was once in the buildable zone of our solar system, and that “habit” must consider the entire life span of a planet. In fact, one hypothesis is that three of the four inner planets – Venus, Earth and Mars – held early in the history of the solar system. Venus later became too hot, so that life can now only remain in the atmosphere. Mars became too cold, so life today exists only underground. Earth alone is hospitable enough to sustain a diverse and vibrant biosphere.
Given that this idea has been around for years, what’s new about Seager’s work? For one thing, previous papers have not elaborated on what life in the clouds means, and how it can interact with the atmosphere. The only exception was a 2004 paper by myself and colleagues, in which we pointed out that sulfur (specifically a compound called cyclooctasulfur) could be used by microbes as a UV sunscreen and a means of converting ultraviolet light to other wavelengths of light that could have been used for photosynthesis. We speculate that this may be the basis for an ecosystem at Venus, where certain chemotrophic organisms feed on the nutrients.
One problem with this scenario was that many of these microbes fall through the clouds into the lower haze layer and meet a foul end. That we estimated that they would only sit in the clouds for a month, and that their reproduction figures in the atmosphere would balance the loss of microbes from the clouds. Seager and her colleagues came up with a much more elegant solution. They suggest that the drip habitat in which the microbes live would grow inexorably, and would be forced by gravity to settle in the hotter, uninhabitable layer beneath the Venusian clouds. As the droplets evaporate during settlement, the microbes would dry out, and the lower rabbit layer would become a depot for desiccated, dormant life. But emerging pregnancies would regularly lift the dormant microbes back into the clouds, where they would re-hydrate and become active again.
Gravity waves (not to be confused with gravity waves) are an atmospheric phenomenon that can form air wrinkles over bumpy surfaces. The waves then propagate vertically upward, growing larger and larger in amplitude until they break just below the cloud-top. That way, desiccated microbes would fall to the surface and make it back into the clouds.
(ESA)
Some of these microbes would still be lost. But that kind of life cycle would increase the chances that an aerial photo biosphere could last for many millions of years, and still exist today.
Supposedly, the idea of life in the Venusian sphere remains highly speculative. Seager even points out how extreme that environment really is, more than any known environment on Earth. But the door of opportunity has cracked a little wider. And if there’s a chance of life on our twin planet, we need to investigate. There are some fun ideas for doing it, including with airships. Let’s hope some space agency will make it happen.
Like this article?
SIGN UP for our newsletter
.
