We have only had the briefest of glimpses of a barren landscape from the two Russian landers that made it down to the ground back in the 1980s. So it’s no wonder that a report published in Nature Astronomy claiming that the upper levels of Venus’ atmosphere contain a molecule that is a potential signature of life comes as something of a shock.
The molecule in question is PH₃ (phosphine). It is a highly reactive and flammable extremely smelly toxic gas, found (among other places) in heaps of penguin dung and the bowels of badgers and fish.
It is present in Earth’s atmosphere in only trace quantities—less than around a few parts per trillion—because it is rapidly destroyed by the process of oxidation. The fact that this molecule is nevertheless present in our oxidizing atmosphere is because it is continuously produced by microbes.
Phosphine is present in Venus’ atmosphere at concentrations way above the level that can be explained by non-biological processes. Does that mean there are microbes present in Venus’ atmosphere, sailing through the clouds in aerosol droplets—a Venus fly-trap at the micro-scale?
The authors do not claim to have found evidence for life, only for “anomalous and unexplained chemistry.” But, as Sherlock Holmes said to Dr. Watson, “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”
