Could the Discovery of Phosphine and Glycine Hint at the Existence of Life in Venus's Upper Atmosphere? *Please read the note at the beginning of the text.

Venus in true color - Via Wikimedia Commons

Note: the phosphine ‘discovery’ on Venus has since been disproven; scientists confirmed in 2021 that the phosphine reported to be prevalent in Venus’s atmosphere was probably sulfur dioxide, not phosphine. This effectively closes the article to the changes of time, but nevertheless serves as a testament to the unending pursuit of knowledge, which continues to lead us past the blind hypotheses and to the solid facts. It is a lesson that no science, whether rock solid or unproven, should be taken to be an insoluble fact (it does not mean, however, that we should push science aside or disregard it).

Since we ‘discovered’ Venus, we have looked up at the brightest planet in our night sky and wondered, “could someone be looking back at us?” Venus has always been considered Earth’s twin sister: the two planets both have similar orbits, occupy the general habitable zone of the Sun, and are similarly massive. Would it not make sense that under those vibrant orange clouds there could be some extraterrestrial species, some perhaps advanced enough to detect Earth? Could they look toward their planetary brother and wonder the same about earth? Our wonders continued until the 1960s, when planetary astronomer Carl Sagan discovered the runaway greenhouse effect on Venus, even before the early Soviet probes landed – and melted – there. 

Upon first visiting the planet, we were stunned to learn that our planetary sister’s atmosphere was 96.5% carbon dioxide (Earth, for context, is .04177% CO2), an efficient greenhouse gas. The greenhouse effect led to Venus's presently scorching surface temperatures of 880 degrees Fahrenheit – hot enough to melt lead. Venus’s dense atmosphere also results in its atmospheric pressure that is over one hundred times that of earth’s surface – equivalent to the pressure you experience when 3,000 feet underwater. 

Instantly, our dreams of a planetary partner brimming with extraterrestrial life were diminished. Nevertheless, recent findings hint that even Venus, the hottest and arguably the most hellish planet in the solar system, could have some of the ingredients necessary for life.

Extraterrestrial life on Venus? Maybe, but probably not.

On September 14th, 2020, a landmark study was published, which presented a mysterious discovery of a biomacromolecule known as “phosphine” in Venus’s temperate upper atmosphere. 

The study presented findings of an unnaturally high abundance of phosphine the researchers discovered while measuring certain aspects of Venus’s atmosphere at the Atacama Large Millimeter Array and the James Clerk Maxwell Telescope.

The macromolecule was most evident at around 56 kilometers above the surface of Venus. According to the study, however, neither the upper nor the lower limits of the phosphine occurrence had been measured.

Another group of researchers discovered, also using the Atacama Large Millimeter Telescope (ALMA), an abundance of the amino acid glycine, in the equatorial and mid-latitude regions of Venus. The altitude at which they saw the strongest absorption line (this indicates the presence of certain molecules – in this case, glycine) was around 50 kilometers.

Why is this important (even though it probably does not mean life)?

Phosphine is a biomolecule that, as we know of, almost never forms without biological processes; the rocky, inner planets of the solar system do not have suitable pressures, temperatures, and abundances of hydrogen gas to produce substantial amounts of phosphine – especially not enough to explain its peculiar abundance on Venus. Unlike on the rocky planets, most phosphorus on the Jovian planets are bonded to phosphine molecules. 

Phosphine is exceedingly rare on earth. A very small amount of phosphine exists in our atmosphere, but most of it is produced by living organisms: extremophile bacteria eat up phosphate and process it, resulting in phosphine – which the bacteria eventually excretes. The phosphate the bacteria consume often comes from minerals or biological decay – it is one of the few known earthly processes that involves phosphine. 

Artificial production of phosphine requires a 200-degree Celsius environment to produce in a laboratory (this is the temperature at which phosphorus acid is decomposed, or broken up into multiple separate products).

There are also no natural processes that could produce such a significant amount of phosphine on Venus. That leaves us with the only two explanations we know of: the experiment may have been a fluke, or some biological process has produced this significant amount of phosphine.

The most spectacular part of the latter experiment was that the researchers found glycine in the same regions that the researchers of the former study found phosphine, which at least somewhat supports the phosphine hypothesis. The exceptional nature of this discovery is underscored by the discussion in the latter paper itself, “Distribution of glycine is stronger in mid latitude (22.5◦–67.5◦) compared to the equator. Near the pole, there is no evidence of the presence of glycine (< 3σ). Recently, the presence of PH3 in Venus was also found to be stronger near mid latitude and it was not detected by ALMA beyond 60◦ latitude (7). The mid-latitude Hadley circulation may give the most stable life supporting condition with circulation times of 70–90 days being sufficient for (Earth-like) microbial life reproduction (4, 7). At height 65–70 km, zonal wind blow at a nearly constant velocity ∼100 m s−1 between latitude range 50◦N to 50◦S and then air speed gradually decrease towards pole (16). The latitude dependent distribution of glycine roughly matches (within ∼10◦) with the detection limit of recently detected phosphine (7) and with the proposed upper Hadley-cell boundary (16) where gas circulates between upper and lower altitudes.” Isn’t that something? The astrobiology community may have reason to be excited.

So, what is the controversy?

There is much contest over the results, however. Three separate papers, one of which was written by the lead researcher in the phosphine study, challenged the discovery.

In the paper Jain Greaves, the lead researcher, wrote in response to her own discovery, she presented observations made by the Texas Echelon Cross Echelle Spectrograph (TEXES) in Mauna Kea, Hawaii. The observations there indicated, remarkably, a very limited amount of phosphine at similar altitudes of Venus’s atmosphere, a strong conflict with the data obtained at ALMA and JCMT.

The observations at TEXES that found a very small amount of phosphine in Venus’s atmosphere were conducted in 2015, which could mean that one of the observations were incorrect, or that there is extreme variation in the abundance of phosphine in Venus’s atmosphere. 

This piece is the first of a two-part entry on Venusian life and the groundbreaking studies, which was released in October 2020. Take care and, as always, stay curious.

If you have any questions, comments, or corrections, please comment on this post or email with your concerns. Thank you.


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