The intriguing question of whether phosphine gas could have biological origin was raised by the alleged detection of it in Venus' atmosphere.
The question was raised because of how hostile Venus seems to life. Scientists have found that Venus could be habitable high above its scorching surface, thanks to the cloud formation.
Particularly, the amount of solar radiation at certain altitudes is similar to that on Earth. This means that microbes capable of photosynthesis could survive at these altitudes. The thick cloud layer could provide some protection from harmful ultraviolet radiation. It is possible that the acidity within those clouds is lower than expected and within acceptable limits for life.
The researchers stated that "Together" in their paper that "these photophysical as well as chemical considerations support the possibility of phototrophy in Venus clouds.
Venus is not likely to be habitable. The conditions on Venus' surface are truly awful. The atmosphere is almost completely made up of carbon dioxide, which rotates 60 times faster than Earth's rotation and produces insane winds.
It is filled with thick clouds full of sulfuric acid and the atmospheric pressure at zero altitude is nearly 100 times higher than Earth's. As if that wasn't enough, the average surface temperature is 471 degrees Celsius (880 Fahrenheit).
When astronomers reported that they had found phosphine gas last year in the planet's atmosphere, there was much controversy. It could also be explained by microorganisms.
There are very few places where phosphate is found on Earth. One of these contexts is the anaerobic (low oxygen) ecosystems. It can be found in swamps, sludges, and in intestinal gas. Anaerobic microorganisms make phosphine and the clouds of Venus are also anaerobic.
Although a biological origin is possible, it is not the only explanation. A volcanic origin can also be possible. However, in order to determine if a biological origin is feasible, an accurate analysis of Venus' habitability is essential.
A team of scientists, led by Rakesh Mogul, California State Polytechnic University Pomona, began to conduct one. They first examined the amount of sunlight that could penetrate Venus's clouds. Data from Russia's Venus Expedition between 1967 and 1983 is available. While none of the probes survived the surface, they did send back measurements of the clouds they observed during their descents.
These and other historical measurements allowed the researchers to calculate the light levels in the clouds. They found that the irradiances at Venus's lower and middle clouds were similar to those at Earth’s surface, which is where photosynthetic activity is abundant.
However, light levels are not enough. An earlier study found that Venus' clouds lack enough water activity to sustain life as it is today. If the composition of Venus’ clouds is different than we think, this might not be true. The current estimates put the sulfuric acid concentration at 75% in the middle clouds, and 98% in the lower clouds.
Mogul and his team reexamined Venus data, and discovered that signatures indicating sulfuric acids could also be caused neutralized forms like ammonium bisulfate. This would mean that Venus' clouds could have significantly higher water activity and less acidity than previously estimated.
However, this does not mean that it is impossible. This research is meant to prove that it is possible. It also opens up avenues for future research to examine the Venusian atmosphere in greater detail to determine habitability.
Mogul stated that "our study provides tangible support to the potential for phototrophy/chemotrophy using microorganisms within Venus's clouds."
"The pH and water activity levels of Venus's cloud could be within acceptable limits for microbial growth on Earth. However, the constant illumination with low UV indicates that Venus's clouds might be suitable for life. Our belief is that Venus's cloud would be a great target for life detection or habitability missions like those for Mars and Europa.
Astrobiology published the research.