Considering what we know about the key ingredients for the formation of life on Earth, here are three explanations for how this process may have occurred on our sister planet.
The recent discovery of phosphine in Venus̵
The researchers, who published their findings in Nature Astronomy, I can’t really explain how the phosphine got there.
They explored every conceivable possibility, including lightning, volcanoes, and even meteor delivery. But each source they modeled could not produce the amount of phosphine they detected.
Most of the phosphine in Earth’s atmosphere is produced by living microbes. Hence the possibility of living Venus phosphine production cannot be ignored.
But the researchers, led by British astronomer Jane Greaves, say their discovery “isn’t solid proof for life” on Venus. Rather, it is evidence of “anomalous and inexplicable chemistry”, of which biological processes are only one possible origin.
If life had existed on Venus, how could it have happened? Exploring the origins of life on Earth could shed some light.
The ingredients for life (as we know it)
Understanding how life on Earth was formed not only helps us understand our origins, it could also provide insight into the key ingredients needed for life, as we know it, to form.
Details of the origins of life on Earth are still shrouded in mystery, with multiple competing scientific theories. But most theories include a common set of environmental conditions considered vital for life. These are:
Water is needed to dissolve the molecules necessary for life, to facilitate their chemical reactions. Although it has been suggested that other solvents (such as methane) may support life, water is very likely. This is because it can dissolve a wide range of different molecules and is found throughout the universe.
Temperatures above 122 ° C destroy the most complex organic molecules. This would make the formation of carbon-based life almost impossible in very hot environments.
A process to concentrate the molecules
Since the origin of life would have required a large amount of organic molecules, a process would be required to concentrate organic substances from the diluted surrounding environment, through absorption on mineral surfaces, evaporation or floating on water in oily patches .
A complex natural environment
For life to have originated, there would have to be a complex natural environment in which a wide range of conditions (temperature, pH and salt concentrations) could create chemical complexity. Life itself is incredibly complex, so even the most primitive versions would need a complex environment to originate.
A series of metal traces, accumulated through water-rock interactions, would be needed to promote the formation of organic molecules.
So, if these are the conditions required for life, what does it tell us about the likelihood of life forming on Venus?
It’s unlikely today …
The chance of life as we know it forming on the surface of present-day Venus is incredibly low. An average surface temperature above 400 ℃ means that the surface cannot have liquid water and this heat would also destroy most of the organic molecules.
Venus’s milder upper atmosphere, however, has temperatures low enough to allow water droplets to form and therefore could potentially be suitable for life to form.
That said, this environment has its limits, like sulfuric clouds acid which would destroy organic molecules unprotected by a cell. For example, on Earth, molecules like DNA they are quickly destroyed by acidic conditions, although some bacteria can survive in extremely acidic environments.
Furthermore, the constant fall of water droplets from the atmosphere of Venus to its extremely hot surface would destroy all unprotected organic molecules in the droplets.
In addition to this, with no mineral surfaces or grains in the Venusian atmosphere that organic molecules could concentrate on, any chemical elements for life would be dispersed in a diluted atmosphere, making life incredibly difficult to form.
… but perhaps less unlikely in the past
With all this in mind, if atmospheric phosphine is indeed a sign of life on Venus, there are three main explanations for how it could have formed.
Life may have formed on the surface of the planet when its conditions were very different from now.
Models suggest that the surface of the primitive Venus was very similar to the early Earth, with lakes (or even oceans) of water and mild conditions. This was before a runaway greenhouse effect transformed the planet into the hellish landscape it is today.
If life had formed then, it may have adapted to spread through the clouds. Then, when intense climate change churned the oceans, killing all life on the surface, the microbes in the clouds would become the last outpost for life on Venus.
Another possibility is that life in Venus’ atmosphere (if any) comes from Earth.
It has been documented that the planets of our inner solar system exchange materials in the past. When meteorites crash into a planet, they can precipitate that planet’s rocks into space where they occasionally intersect with the orbits of other planets.
If this happened between Earth and Venus at some point, the Earth’s rocks may have contained microbial life that may have adapted to Venus’s highly acidic clouds (similar to Earth’s acid-resistant bacteria).
A truly alien explanation
The third explanation to consider is that a truly alien life form (life like us do not do it I know) may have formed on the surface of Venus at 400 ° C and survive there to this day.
Such a foreign life would likely not be carbon-based, as nearly all complex carbon molecules decompose at extreme temperatures.
Although carbon-based life produces phosphine on Earth, it is impossible to tell only carbon-based life can produce phosphine. Therefore, even if there is totally alien life on Venus, it can produce molecules that are still recognizable as a potential sign of life.
It is only through further missions and research that we can find out if there is, or was, life on Venus. As the famous scientist Carl Sagan once said: “Extraordinary claims require extraordinary evidence”.
Fortunately, two of the four finalist proposals for NASA’s next round of funding for planetary exploration focus on Venus.
These include VERITAS, a proposed orbiter to map the surface of Venus, and DAVINCI +, proposed to fall across the planet’s skies and sample different atmospheric layers as they descend.
Written by Luke Steller, a doctoral student at UNSW and Martin Van Kranendonk, professor and head of the school at UNSW.
Reference: “Phosphine gas in the cloud deck of Venus” by Jane S. Greaves, Anita MS Richards, William Bains, Paul B. Rimmer, Hideo Sagawa, David L. Clements, Sara Seager, Janusz J. Petkowski, Clara Sousa-Silva , Sukrit Ranjan, Emily Drabek-Maunder, Helen J. Fraser, Annabel Cartwright, Ingo Mueller-Wodarg, Zhuchang Zhan, Per Friberg, Iain Coulson, E’lisa Lee and Jim Hoge, 14 September 2020, Nature Astronomy.
DOI: 10.1038 / s41550-020-1174-4
Originally published in The Conversation.