All you need to known about the discovery of Phosphine in Venus’ clouds!
EDIT: The findings have since become into doubt after independent review of the data, but the science behind the potential discovery I discuss here is still interesting! I will do a blog post on some other linked discoveries soon, which I will link here once its done!
If you took my Astrobiology course, or read my astrobiology series last year, you’ll know that I – along with the majority of other astronomers- thought that Venus was one of the most least likely places to look for life today. There was always the possibility that Venus could have been home to life in the distant past when it was more earth like, but now? The scientific consensus was that it was too hot, too acidic, too windy for life to survive today! And then BAM Hannahbella Nel DMed me a link to a press conference, and I sat in my climbing gym watching the press release, absolutely screaming with excitement on the inside! But what does it mean, really? I had never heard of phosphines before this week, but after a few hours of research (well quite a few hours… I challenged myself to read and try to understand the paper!), let’s dive in!
First of all, what is this even about?
On the 14th of September, the Royal Astronomical Society held a press conference with the team behind the paper– a team that was slowly put together as they connected over their various projects relating to phosphine. It was lead by Professor Jane Greaves, an astronomer who set up the experiment and telescope use, William Bains, the biochemist who lead the effort to model Venus’ atmosphere and investigate all of the other potential sources, Sara Seager who had worked on the first paper that suggested phosphine as a potential biosignature, and Anita Richards processed the ALMA data… as well as many more scientists from across the world who didn’t take part in the press conference but played a crucial role in the discovery.
What was the discovery?
In 2017, they pointed the James Clerk Maxwell Telescope at Venus, and got a mess of data back, as there was a lot of reflections and distortion, as Venus is much closer and brighter than the distant galaxies JCMT usually observes. After focussing on some other projects, Jane came back to it a year or so later, and saw a dip in the spectrum, right where it was expected! They then followed it up with ALMA, which has a higher resolution and magnification.
What data was collected?
To understand what this dip actually means, we need to know about 2 key physics principles:
- When Venus is heated by the sun, some of that heat is re-emitted at longer wavelengths, for example radio waves. Radio waves are also produced when CO2 absorbs shortwave radiation and re-emits it as long wave radiation. It is these radio waves that are collected by the telescope
- Some of the radio waves are absorbed when they hit a molecule in the atmosphere, which creates a dip in the spectrum obtained. Each element/molecule absorbs a specific wavelength/frequency. For phosphine, one such frequency is 266.9GHz.
This wavelength is in the radio part of the spectrum, so can be observed using telescope arrays here on earth! The other absorption wavelengths are in the IR range and shorter, much of which is blocked by the Earth’s atmosphere, so would have to be measured using a space telescope.
This dip was from the wavelengths absorbed by phosphine! They actually took measurements from different latitudes, which showed that the gas was mainly found at mid latitudes (peaking at 20 parts per billion/ppb), with none being measured above 60°. This coincides with the upper boundary of the hadley cell, a convection cell created by heated air rising at the equator and falling at the poles. They also managed to figure out that the gas was present at roughly 50-60km up. On earth, this altitude has sub zero temperatures and less than 0.05x surface pressure… but on venus, this height is actually quite habitable, with temperatures of roughly 30 degrees and pressure similar to that at sea level on earth!
Could the detection be anything else?
As you can see from this graph, the JCMT data doesn’t have the highest resolution, so there was the possibility that it was some sort of noise/distortion… but the signal wasn’t seen when they looked at other nearby astronomical objects, and also it was observed again, independently, by the ALMA telescope, using different methods of data reduction.
The other possibility would be contamination by another gas with a similar absorption frequency, but again, they knew this, and ruled it out: The only other potential contaminant would be Sulphur Dioxide (all others are not present in high enough concentrations), but it was calculated that the upper atmosphere would have to be 3x as hot as measured for it to have a big enough impact. So they are pretty sure it is phosphine, we just don’t know what is producing it!
What even is phosphine?
Phosphine consists of 3 hydrogens and a phosphorus bound by covalent bonds. Like most of Venus’ atmosphere, it is very toxic, and has been used in chemical warfare, as a fumigant, and in the semiconductor industry, and is generally regarded as an incredibly dangerous substance. And yet it is produced in our intestines, and in the deep sea! Why is this? Well the one thing the environments where phosphine is biologically produced have in common is that they have low oxygen concentrations.
Oxygen is a vital part in some stages of respiration, but the most important role it plays is in the electron transport chain, which produces most of the energy (in the form of ATP) that we need to survive. Strap in, coz this paragraph – a whistle stop tour of the biochemistry of respiration- is into A Level Biology territory! (If this isn’t your vibe, and you just want to know how it relates to astrobiology and venus, skip to here… but try give it a read, as its fascinating!)
Here’s how it works: Hydrogen ions are pumped into the outer compartment of the mitochondria (where respiration takes place- in single celled organisms like bacteria, it occurs around the cell membrane), which creates a high concentration of H+ there, which then try to diffuse back into the main part (matrix) of the mitochondria. However, the membrane is impermeable to them, and the protein channels they were pumped out of are a one way system. Instead, they are funnelled through a different kind of protein channel called ATP synthase. This has a special shape reminiscent of a turbine or windmill! The hydrogen ions are charged, so they cause the inner ‘axle’ of the protein to rotate as they flow past. This axle is also charged in places, which can then push together ADP (a product of a different stage of respiration and the precursor to ATP) and a phosphate group… producing ATP! What does this have to do with oxygen? Well pumping the hydrogen ions into the outer compartment requires energy as it goes against the concentration gradient, so it requires energy to start with! This comes from something called the electron transport chain, which is a series of reactions where electrons move from a high energy state in NADH (also a product of an earlier stage of respiration) to a low energy state (thus releasing energy) in… water! The transport chain not only provides energy to pump the H+ ions out, but the water produced by it uses some of the H+ to add to electrons and oxygen, preventing the H ions from ‘clogging up’ the mechanism! So to keep the hydrogen ions flowing, and the ATP synthase turning, oxygen is necessary.
But in hypoxic conditions, a different process occurs: a series of reactions removes hydrogen from the glucose (the original source/reactant in respiration) and is taken to the mitochondria by a molecule called NAD, where it is split into electrons and hydrogen ions to be used in the process above. However, the NAD molecules can only drop off the hydrogen when there is oxygen present to maintain the flow of hydrogens.
If there is no oxygen to react with, the process grinds to a halt and no ATP is produced… which is very bad news for the organism. But not all is lost! Instead of oxygen, organisms in extreme environments, like on Venus, another molecule must be substituted: this might be carbon (producing methane) or sulphur (producing hydrogen sulphide), but phosphorus could also be used, creating phosphine!
Big shout out to my biology teacher for helping me with this biochem paragraph!
Why not look for oxygen/methane then?
To prove the existence of life, you need to mount enough evidence for there to be no other option… 2 quotes come to mind:
Extraordinary Claims require Extraordinary Evidence.Carl Sagan
When you have eliminated the impossible, whatever remains, no matter how improbable, must be the truth.Sherlock
So for a biosignature to show us life exists, there must be no other potential sources- that crosses methane and most other compounds off the list, even if life here on earth needs/produces it, as there are often non-biological sources too. So is phosphine the biosignature we’ve been waiting for?
Well on earth, phosphine is only produced industrially/anthropogenically or biologically. But on the gas giants, phosphine is produced biologically, from the intense heat and pressure. That’s not thought possible for a small rocky world. But Venus is a very strange world, probably the most gas-giant-like of any inner planet.
So what chemistry is there that could produce phosphines?
Thanks to the Vega probes, we know the amount of phosphorus in Venus’ atmosphere, and we can expect that most of that will be oxidised into phosphates (__PO-3), or phosphoric acid (H3PO4). This can then be reduced by adding hydrogen/taking away the oxygen, turning it into phosphine! Often there is a step in between where phosphorous acid (H3PO3) is created. But why does the reaction take place? Well reactions that are exothermic (release energy) can happen whenever molecules happen to be moving fast enough (have enough energy) to react when they collide. This is determined by thermodynamics, and can be fairly confidently modelled. William Bains lead the atmospheric chemistry team, during which they modelled 75 potential reactions. None of them (individually nor collectively) produced enough to explain the 20 ppb levels. The other process causing reactions is from ~photochemical interaction~ which is a fancy way of saying molecules are ionised and given energy by UV radiation from the sun, allowing them to be more reactive. They then moved on to production via volcanoes, lightning or delivery by meteorites, all of which only contributed a few parts per quadrillion. Putting these (every possible thing they could think of/is known to science) together, you get a rate that’s ~105x too small! Currently, this leaves either some unknown chemical process, or an unknown biochemical process… aka life!
So if there really is life on Venus, how did it get there?
With life, there are 2 options:
a) it independently arose (abiogenesis), separate from life on earth.
b) it was transported (panspermia) from earth to venus by asteroids, for example when an asteroid hits earth and the rock thrown into the air has enough acceleration to escape earth’s gravity, and impacts on another planet, with organisms embedded inside.
Panspermia is mainly theoretical, but we do know that rocks can travel between planets- we found a bit of mars on antarctica and elsewhere on earth (about 0.038% of meteorites found seem to originate from mars, and just a few more -0.043%- from the moon). None have been found to be from venus, as it would be very difficult for rock to be ejected through its thick atmosphere, and any rock launched from earth would probably burn up in
What about abiogenesis? Is it plausible? Well back at the start of the solar system, it’s thought that *all* three of the large inner planets were habitable for a few million years: Mars hadn’t yet cooled so it had a magnetic field, and the sun wasn’t yet hot enough for Venus to reach the tipping point of its climate change. Life could have developed in this stage, but could this just be a fossil? A signature of past life? Probably not, as its lifetime varies from a few minutes at the top of the atmosphere, to a few years at the base, and a few millennia at mid altitudes (although as the time for mixing between the base and top is shorter than this so the actual lifetime would be cut short). So we are pretty certain that it is being produced today, whether that is consistently or periodically, at a rate unexplained by known chemical reactions.
To prove it was biogenesis, the life would have to be entirely different to any found on earth, such as using different amino acids, or having a fundamentally different genetic structure or mechanism. And that would be SO cool, as it would prove that life is capable of starting under different conditions, raising the likelihood of life existing in the wider universe too! If it was panspermia, and it appeared to be related to life on earth, that would raise a LOT of philosophical questions about where we come from.
The main thing that’s keeping scientists even more skeptical is: you know that nice temperate layer I wrote about earlier where the phosphine seems to be concentrated? Well that’s also the layer with the highest concentrations of sulphuric acid (up to 98%– that’s 18.4M concentration… for reference we usually used 1M max in GCSE). These form the droplets that create the clouds that make Venus’ atmosphere opaque. They can have pHs as low as -1.26 (for reference, the lowest pH survivable by acidophilic bacteria is only -0.06)! So to survive, they would have to be highly adapted, and probably have a resistant outer ‘shell’ for protection. But as the famous Jurassic Park goes…
Even if it turns out not to be life, but an unknown reaction, sending more spacecraft to study venus will still be worth it, as it’s kind of been neglected since we found out how much easier it was to get on to Mars (comparatively.. getting to Mars is still a huge feat). Venus could reveal a lot about the future of our planet, giving an insight into climate change, both now and in the future, and more about the solar system and our beginnings as a whole!
This whole discovery is just so exciting, and although we need to hold a healthy dose of scepticism (may I repeat, we have not found evidence of life, we’ve found evidence of a chemical that on earth seems to be associated with life), it’s just such a crazy concept! Aliens have been part of popular culture for decades, and to have potentially found it on Venus of all places, requires a paradigm shift in not just science, but society.
Thanks for reading, I really enjoyed researching and writing this post, sorry it was a bit long.. if you got this far, you’re amazing!
Also, huge shout out to my biology teacher for helping me with the specifics of respiration!