Phosphine on Venus; unpacking the Venusian discovery

Let’s get the biggest point out of the way first: No, scientists did not announce proof of life on another planet.

What they did find, however, is tantalizing in its potential meaning – though a great deal of work remains to rule out the possibility that other, unknown processes could be creating the phosphine signature detected in Venus’ atmosphere by a team of international researchers using ground-based telescopes on Earth.

In short, it all comes down to the detection of phosphine in a temperate cloud layer of the Venusian atmosphere. 

Read the paper HERE

The phosphine signature, confirmed via independent observations from two telescopes on Earth, is certainly intriguing because the only natural way we know of for phosphine to form on terrestrial planets is as a byproduct of life.

The trick here is that we don’t actually know what specific lifeform it is on Earth that produces the phosphine found in our swamps and marshes.  It is believed to be microbiotic, potentially E. coli.  But even with in situ research literally in the environment where phosphine is being created naturally on Earth, we still don’t know what causes it.

And that largely complicates the nature of the discovery announced by Professor Jane Greaves and her team. 

While many have been quick to highlight and publicize the possibility of this being life, scientists on the other hand are far more skeptical and cautious, offering microbial life as a potential answer to this question only after all abiotic processes of phosphine production have been ruled out — which they have not.

In fact, life might not even factor into this discovery at all.  But that’s not headline catching.

Now, yes.  This discovery could indicate the presence of microbial life.  But there could be many other reasons why phosphine is in Venus’ atmosphere.

One of the easiest ways to naturally produce phosphine through abiotic means is seen in the atmospheres of Jupiter and Saturn, where the immense pressures deep within those planets’ atmospheres utilize hydrogen — in part — to create phosphine. 

What members of the discovery team have been able to rule out so far is that the same complex processes that create phosphine at Jupiter and Saturn are not possible on Venus due to the lack of hydrogen atoms — let alone hydrogen gas — in the Venusian atmosphere and the planet’s sheer incapability of producing the pressures necessary for abiotic phosphene production.

But the team did not stop there.  In making the announcement, Dr. William Bains explained how his part of the team considered other forms of abiologic phosphine production (photochemical, thermodynamic, and rock chemistry).

While it was found that all of those processes are possible on Venus, they cannot account for the concentration of phosphine observed — which comes in at nearly 20 parts per billion.

In fact, speaking to the discovery, the team emphasized that the naturally occurring phosphine production processes on Venus are millions of times weaker than they would need to be in order to account for the amount of phosphine detected.

That would seemingly leave biological processes as the remaining option — but that is where Venus’ corrosive, sulfuric acid atmosphere adds another problem. 

Venus’ atmosphere is filled with sulfuric acid, is thousands of times more acidic than battery acid, hundreds of times drier than the driest place on Earth, and destroys biological molecules within seconds.

The temperate, habitable layer of Venus’ atmosphere as presented by Professor Sara Seager on 14 September 2020. (Credit: Royal Astronomical Society)

The Venusian atmosphere should destroy all life as we know it — meaning there is essentially no chance this signature could be explained as a life seeding event where an asteroid impact to Earth caused a life-containing rock to spiral through space and deliver that life to Venus.

Nevertheless, with the available information in hand, a team of scientists led by Professor Greaves, conclude in their paper that “the presence of [phosphine — PH3] is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’ atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery.”

“PH3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH3 on Earth, from the presence of life.”

The find:

It all started when Professor Greaves read about a hypothetical scenario of an alien civilization trying to determine if life existed on Earth.  The paper — as others have as well — concluded that phosphine would likely be a definitive biosignature to prove the existence of life on Earth given that the only way phosphine is currently known to form naturally on terrestrial planets is as a byproduct of life.

Phosphine is also a relatively easy substance to detect in the 1.123 millimeter wavelength.

After more study, Professor Greaves and her team put together a model of where — based on current understanding of the Venusian atmosphere — one would expect to find concentrations of phosphine if they existed. 

This modeling led to the conclusion that the phosphine would largely be concentrated in mid-latitude regions and mainly absent from the equatorial and polar areas of the planet.

The phosphine detection from the James Clerk Maxwell Telescope. (Credit: Jane S. Greaves et al.)

Professor Greaves and her team then put together a proposal to use the James Clerk Maxwell Telescope (JCMT) in Hawai’i to search for the signature in Venus’ atmosphere. 

The proposal was outright rejected.  Nevertheless, Professor Greaves and her team persisted and got the decision overturned and secured observation blocks with the telescope.

Over five mornings in June 2017, the James Clerk Maxwell Telescope peered at Venus.  And there it was.  The tell-tale signature of phosphine at the exact locations in Venus’ atmosphere where predicted.

Now the hard work began not only trying to determine where the phosphine came from based on its concentration levels but also in securing additional time on a more powerful and capable telescope to independently confirm the observation and collect improved data.

The team eventually secured time on the Atacama Large Millimeter/submillimeter Array (ALMA) in March 2019.

“The ALMA data confirm the detection of absorption at the PH3 1–0 wavelength,” notes the team in their paper: independent verification of phosphine’s likely presence.

“The JCMT and ALMA whole-planet spectra agree in line velocity and width, and are consistent in line depth after taking into account ALMA’s spatial filtering,” the team states in their paper — a fancy way of saying “ALMA saw the same thing JCMT saw two years earlier.”

The possibility of a double false positive from the two observation platforms was considered and investigated but ultimately ruled out based on the spectral data returned from the two telescopes. 

The phosphine confirmation detection from ALMA. (Credit: Jane S. Greaves et al.)

After an exhaustive investigation of the known abiotic processes that can lead to the formation of phosphine, Professor Greaves and her team were drawn to the conclusion that “If no known chemical process can explain phosphine within the upper atmosphere of Venus, then it must be produced by a process not previously considered plausible for Venusian conditions.”

“This could be unknown photochemistry or geochemistry, or possibly life.”

But just because the scientists themselves offered life as one possible explanation does not mean that that is the leading candidate or hypothesis.   In fact, the team as a whole were quick to point out that they don’t understand what is causing the presence of phosphine in the atmosphere, and other planetary scientists were also cautious that the explanation is actual life. 

Part of what drives that overall cautiousness is the fact that much of the processes governing how the Venusian atmosphere works are completely foreign and not understood based on the data collected from prior and ongoing missions at the second planet in the solar system. 

In fact, one of the primary things pointed to in the discussion portion of the paper revolves around the fact that Venusian cloud droplets, and the photochemistry thereof, is almost completely unknown.  Those unknown processes governing Venusian cloud droplets could be a possible source of the detected phosphine.

The paper also bluntly points out that any question of hypothetical organisms on Venus that might be making phosphine is “highly speculative.”

Nevertheless, while making that assertion, the team also recognizes that they cannot rule out the possibility that microorganisms are indeed responsible for the phosphine detection.

And that in and of itself is groundbreaking.

The fact that scientists are coming forward to say ‘we have found something that might indicate the presence of life and we cannot rule out life as a possibility’ is in many ways shattering to our philosophical approach to life which deems Earth as “special” and “unique.”

What’s more, the team also points out that the mid-latitude circulation of Venus might provide a very stable environment for life, with circulations of roughly 70 to 90 days adequate enough for the reproduction of Earth-analog microbes.

Moreso, the team’s initial research indicates that the cool acidic conditions in the temperate layer of the mid-latitudes of Venus’ atmosphere are favorable to the biological production of phosphine and that “initial modeling based on terrestrial biochemistry suggests that biochemical reduction of phosphate to phosphine is thermodynamically feasible under Venus cloud conditions.”

Basically, if it does turn out to be life producing the phosphine, conditions within certain parts of Venus’ atmosphere are conducive to such a process.  But that absolutely should not be read as any confirmation that life has been detected.

The team also notes that the observation time thus far has been “modest” at best and that many more observations are needed to understand and better characterize the phosphine detection and what is generating it. 

That could – in some ways – be accomplished through ground-based observations.  But the best and most effective way to answer the question is to send a spacecraft with dedicated instruments – ideally a spacecraft that could descend into the Venusian cloud layer and remain there for weeks or months. 

No such missions are currently planned or announced, though a few missions to Venus are currently either under development or consideration – including an often talked about mission to Venus from Rocket Lab.

When asked, the team stated it was far too early in their process for them to have talked to mission planners, but that they are very eager to do so given the potential importance of this discovery.

With all that said, while this certainly is not conclusive proof of life somewhere else, it does crack open — once again — the door of understanding that life, as Jurassic Park popularized, finds a way.

As previously discussed, if this is life, there is almost a 0% chance it was seeded to Venus by Earth.  Far more probable is that this would be life that developed naturally on Venus (again — huge caveat — if it is indeed life).

But that is the Holy Grail of space exploration – finding life that hasn’t been transported from Earth to another planet but that actually developed and evolved on its own.

To that end, it is possible the scientific community took a gigantic leap in that direction with the detection of phosphine in Venus’ atmosphere. 

Only time will now tell us if it is life or an abiologic process at work on Venus.

Nevertheless, one thing is likely certain from today’s announcement: Venus just catapulted to the near — if not the — top of the list of places to actively seek current life somewhere other than Earth.

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