Faculty Feature: Why astronomers went gaga over phosphine on Venus

By Dr. Jim Chisholm

     On September 14th, a group of scientists published a paper in Nature on the discovery of the gas phosphine (PH3) in the clouds of the planet Venus.

     It’s kind of a big deal.

     From time immemorial, humanity has pondered whether there was life elsewhere in the universe. Science fiction about green-skinned aliens has given way to the actual search for extraterrestrial life. As in all pursuits, planetary scientists have started small: searching for microbes. On Earth, the total mass of all microscopic life is about that of all plants and animals – counting by individual creature instead, the average Earthling is a bacterium, so we expect this to be the case on other planets if they have life.

     Not only that, but life is present on Earth in the places you’d least expect it: hypersaline lakes, underwater superheated thermal vents and, yes, even high up in the atmosphere – these extremophiles are capable of existing in environments that would be toxic for most other forms of life.

     But back to phosphine.

     To date: scientists have found no direct evidence of life on other planets. Not for lack of trying – the NASA Viking landers of the 1970s made the first searches for subsurface life in the Martian soil, searches that current Mars rovers continue to this day.

     But you can also do an indirect search for life – looking for an effect in an environment that wouldn’t be present if life isn’t there. Like coming across a crude wooden dam on a creek and deducing there are beavers nearby (if you’re keen on beavers). It’s often easier to search for these “tracers” of life than to search for the actual creatures.

     On Earth, phosphine is a by-product of decaying organic matter – essentially bacteria farts, and chemists have catalogued and studied the various ways in which phosphine can be produced. While other, non-life-associated, reactions can give rise to phosphine, the dominant method of production involves living creatures producing it – making it an idea tracer for searching for life outside the Earth.

     While the surface of Venus, with its 800 degree Fahrenheit and 92 times Earth’s atmospheric pressure, is unsurvivable for even the hardiest hyperthermophiles (bacteria that enjoy really hot temperatures), high up in Venus’s thick cloud cover, conditions are much more pleasant. Further, you can easily observe the clouds of Venus from Earth and, as of two weeks ago, can also observe the presence of phosphine there too.

     This is not proof there is life on Venus. There could be some other process in the Cytherian atmosphere that is producing phosphine that has nothing to do with life. Or it could be the first evidence of life outside of the Earth. Either way – scientists have learned something new about the universe.