Phosphine in the atmosphere of Venus — what does it mean?

On 12 September 2020 the discovery of the compound phosphine in the atmosphere of Venus was leaked, hinting at the existence of microbial life on Venus! The EarthSky.org article violated a press embargo and was quickly pulled, but not before Google cached it.

UPDATE: the Nature paper is now freely available post press conference: https://www.nature.com/articles/s41550-020-1174-4

This got me thinking about the possibilities of this announcement, and where this path might lead. At the very least we will have learnt something new about the universe — namely how phosphene is produced on Venus — and we may just have opened the door to some bewildering possibilities. The reason that this could be incredible profound is that phosphine is known to astrobiologists as a “biosignature” for terrestrial planets — meaning detection of it is a very strong clue that life exists there. To be clear this is not proof of life, but is a very intriguing clue! More on phosphine as a biosignature:

Phosphine (PH3)only exists on Earth through biological processes (specific microbes in oxygen-free environments can generate it) or through industrial processes where it is made by people. In the astronomy/astrobiology community there are no other known sources for phosphine except in conditions of very extreme temperatures like that in the hot dense inner atmospheres of Jupiter and Saturn (where phosphine is seen) or stars. Phosphine, once created, is destroyed over time by various processes, such as reactions with oxygen and hydrogen or by ultraviolet radiation reactions. What this means is that without a source generating phosphine, it should slowly disappear over time and not be detectable. Seeing phosphine in a temperate rocky planet’s atmosphere is therefore considered a very probably biosignature (see this paper, which makes the case for phosphine as a biosignature, but for exoplanets in other solar systems).

By Pablo Carlos Budassi — Own work, CC BY-SA 4.0

What does this mean?

Assuming the measurements are real and accurate and phosphine exists in Venus’s atmosphere in significant quantities, then there are only two possible explanations and either one is a very exciting step forward:

1. The source of phosphine is some sort of physical or chemical process that is not expected on rocky planets like Venus. We humans are boundlessly ignorant, so this is honestly a more likely outcome than actually finding life — we first need to investigate and rule out other sources!!!
2. It is being created by life (likely microbes that float in the “habitable zone” of the atmosphere) at least as fast as it can be destroyed by natural processes.

Assuming that it is indeed life that is creating this gas, what does that mean? Venus is a stone’s throw away from Earth in celestial terms, but it’s still really far away — on average 40 million kilometers. Finding life on another planet in our solar system is very significant, and leads to two more titillating possibilities:

A. Life evolved independently on multiple planets

This is freaking profound! If life independently evolved right under our noses on the nearest planet to us, one that we thought was inhospitable due to its hot acidic atmosphere, then it’s very possible that life is just about everywhere in the universe!!! Life is abundant. We’ll probably soon find it on other solar system planets and see similar biosignatures in the atmospheres of planets around other stars. If life is abundant, then it is very likely that life has existed for millions of years on millions of planets, and it becomes almost a statistical certainty that life should have evolved into more complex organisms and then into intelligent life. We are not alone! That we see nothing is the so-called Fermi paradox. So… where are they??

1. Advanced civilizations are unstable: they evolve and then destroy themselves via some kind of “Great Filter” — something like a nuclear war, climate disasters, biological weapon pandemics, etc. On celestial time scales civilizations briefly, gloriously flash and then they disappear — so far we’ve never got lucky enough to spot one. This also quite likely means our days are numbered…
2. Advanced civilizations, as we know them, are transient. Instead of dying out after flashing, they transcend. They’re out there, everywhere, but we cannot see them. We’re like ants dumbly probing around ourselves with our primitive antennae, incapable of seeing them right in front of us.
3. Intelligent life is so so so so so rare that it basically never evolves to that point and we’re the chosen ones/part of God’s plan.
4. UFOs are real. The little green men are here. The truth is out there.
5. They’re hiding from us and each other (and we should probably start hiding too). Read The Three-Body Problem by Cixin Liu.

B. Life on Venus and Earth have the same source

This is intriguing, because this means life first evolved somewhere, and then somehow jumped to other planets. This is not too crazy as we know from meteorites that bits of other planets like Mars end up on Earth. A big asteroid impact might eject some particularly hardy microscopic lifeforms out into space, or maybe they travel by other more speculative means. This opens up some more possibilities:

1. Life evolved on Earth, and jumped to Venus. Maybe we’re alone in this universe besides some brethren on Venus, or perhaps it also made it to other places like Mars.
2. Life evolved on Venus or somewhere else in the solar system like Mars, and jumped to Earth and the rest is history, although we’re now technically venusians!
3. Life originated outside the solar system and then ended up on Earth and Venus. This panspermia hypothesis is wild too! Maybe primitive life (from god knows where) is floating around the universe like aimless dandelion seeds, waiting millenia until a nice fertile planet like Earth happens to fly by and catch them. Maybe life was seeded here on purpose… Maybe early precursor life was sent out by an advanced civilization to populate other solar systems (like the protomolecule in The Expanse)? But why? Was it a means of galactic exploration to seed life that eventually would evolve to be curious and “phone home”? Was it to terraform the atmospheres of other planets for future colonization? Was it the last desperate breath of a dying civilization? As a communications method that could last for aeons — is there a message buried deep in our DNA that might be retrievable? The possibilities are endless…

So, in summary?

Mind boggling possibilities! (lucidchart)

HOLY SHIT!!! Maybe the analysis is wrong, or the data is compromised in some way. I’m sure follow up studies will agree or refute this soon, and perhaps this story ends there with a sad fizzle. If, however, the data is right then it becomes super important that we go to Venus for proof of life and/or to discover what this exotic new source of phosphine is. A number of atmospheric balloon missions have been proposed that would allow us to fly around in the atmosphere looking for life. Time to accelerate these missions!!!

Finally, if we do find proof of life, then it opens up some bewildering possibilities about our place in the universe. Imagine the technology and societies possibe If life is everywhere then we better start thinking hard about why we’re not seeing it…