The detection of phosphine gas in the atmosphere of Venus raised the fascinating question whether it could be of biological origin.
Given how inaccessible Venus appears to be to life as we know it, the question caused an uproar. But scientists have now determined that the planet Hell may indeed be habitable – high in clouds, above the scorching surface.
In particular, the level of solar radiation at specific altitudes is comparable to the solar radiation on Earth, meaning that microbes that perform aerial photosynthesis can survive at those altitudes. In addition, the dense cloud layer would provide some protection against harmful ultraviolet radiation, and it is possible that the acidity in those clouds is lower than predicted and within acceptable standards for life.
“Together,” the researchers wrote in their paper, “these photophysical and chemical considerations support the possibility of phototrophy in the clouds of Venus.”
When it comes to habit, Venus has little chance. The conditions on the surface are truly hellish. The planet is completely covered in a dense atmosphere made of carbon dioxide that spins 60 times faster than the planet itself, creating crazy winds.
The sky is filled with thick clouds of sulfuric acid, and its atmospheric pressure at 0 altitude is about 100 times greater than that of Earth. If that weren’t bad enough, this lander is melting hot, with an average surface temperature of 471 °C (880 °F).
So when astronomers announced they had detected phosphine gas in the planet’s atmosphere last year, controversy ensued. This is because one of the reasons for its presence can be microorganisms.
Phosphine can be found here on Earth in a very limited number of contexts, one of which is in anaerobic, or low-oxygen, ecosystems. It is found in swamps and mud, where anaerobic microbes thrive; It is found in the intestines and intestinal gas. Somehow, anaerobic microorganisms produce phosphine, and the clouds of Venus are anaerobic.
A biological origin is not the only explanation – a volcanic origin is also possible – but in order to assess the feasibility of a biological origin in the first place, a proper analysis of Venus’ habitability certainly won’t go astray.
So, led by biochemist Rakesh Mogul of California State Polytechnic University, Pomona, a team of scientists set about conducting one. First, they examined the level of sunlight that can penetrate Venus’s clouds. We have data from Russia’s Venus campaign between 1967 and 1983; None of their probes lasted long on the surface, but they did send back measurements of clouds during their descents.
From these and other historical measurements, the researchers were able to calculate the level of light within the clouds, and determined that the radiation in the middle and lower clouds of Venus is similar to that at Earth’s surface, where photosynthetic life is abundant.
But the light levels alone are insufficient. A study earlier this year found that Venus’s clouds do not have enough water activity to support life as we know it. But this may not happen if the composition of the clouds of Venus is not what we think. Current estimates put the concentration of sulfuric acid at 75 percent for medium clouds and 98 percent for low clouds.
Mogul and his team revisited the Venus data and determined that the signature indicating sulfuric acid could also be due to neutralized forms of sulfuric acid such as ammonium bisulfate. If so, there may be significantly more water activity – and significantly less acidity – in the clouds of Venus than previous estimates.
That is not to say that this is the case. The research aims to establish that this is simply possible – which, in turn, opens the way for future research, including more detailed analysis of the Venusian atmosphere, to determine habitability.
“Our study provides solid support for the potential for phototrophy and/or chemotrophy by microorganisms in the clouds of Venus,” Mogul said.
“Levels of acidity and water activity potentially fall within an acceptable range for microbial growth on Earth, while continuous illumination with limited UV suggests that Venus’s clouds may be hospitable to life. We believe that Venus clouds would make a great target for habitation or life. Detection missions, such as those currently planned for Mars and Europa.”
research has been published in astronomy.