Earth’s sister planet, Venus, has not been considered a priority when searching for extraterrestrial life. Its surface temperature, around 450 ° C, is believed to be hostile to even the most resistant microorganisms, and its dense, sulfurous and acidic atmosphere has kept the surface almost completely free of visiting spacecraft.
We have only been able to catch a brief glimpse of its arid landscape since the two Russian landers that reached the surface of Venus in the 1980s. Therefore, it is not surprising that a report published in Nature Astronomy that the upper levels of Venus’s atmosphere contain a molecule that is a possible sign of life has been something of a shock.
The molecule in question is PH₃ (phosphine). It is a highly reactive, flammable and extremely smelly toxic gas, which is found, among other places, in penguin manure and in the guts of badgers and fish.
It is present in Earth’s atmosphere only in small amounts, less than a few parts per trillion, because it is rapidly destroyed by the oxidation process. However, the fact that this molecule is present in our oxidizing atmosphere is due to the fact that it is produced continuously by microbes. Therefore, it is proposed that phosphine in the atmosphere of a rocky planet is a solid signal for life.
It should not be stable in the atmosphere of a planet like Venus, where it would rust rapidly unless, as on Earth, there is a constant fresh supply. So why were the study authors looking for phosphine in such an unpromising environment? Are you sure you have found it?
Reading between the lines of the report, it seems that the team did not expect to find phosphine. In fact, they seemed to be actively seeking his absence. Venus was to supply the “base atmosphere” of a rocky planet, free of a phosphine biosignature. Scientists researching rocky exoplanets could compare the atmospheres of these bodies with those of Venus, to identify any possible biological signatures of phosphine.