Phosphine Discovery in Venus’ Atmosphere Raises the Big Question of Life

A close-up view of our “morning star” neighbor: reprocessed image of Venus captured February 7-8, 1974, by NASA’s Mariner 10 spacecraft. (Credit: NASA/JPL-Caltech)

Today an international team of scientists led by Jane Greaves of Cardiff University in the UK announced the discovery of phosphine (PH3) in the atmosphere of our neighboring planet Venus — a detection made using data from ground-based telescopes located in Hawaii and Chile. On Earth, phosphine is created for industrial uses in labs and by certain bacteria that thrive in harsh environments lacking oxygen and, since there are no labs or factories on Venus, the question of what’s producing phosphine could have a biological answer.

“If no known chemical process can explain PH3 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.”
— Greaves, J.S., Richards, A.M.S., Bains, W. et al. Phosphine gas in the cloud decks of Venus. Nat Astron (2020).

This artistic representation shows a real image of Venus, taken with ALMA, in which ESO is a partner, with two superimposed spectra taken with ALMA (in white) and the James Clerk Maxwell Telescope (JCMT; in grey). The dip in Venus’s JCMT spectrum provided the first hint of the presence of phosphine on the planet, while the more detailed spectrum from ALMA confirmed that this possible marker of life really is present in the Venusian atmosphere. Credit: ALMA (ESO/NAOJ/NRAO), Greaves et al. & JCMT (East Asian Observatory)

From a news release from ESO, which operates the ALMA observatory which acquired some of the relevant data:

The international team, which includes researchers from the UK, US and Japan, estimates that phosphine exists in Venus’s clouds at a small concentration, only about twenty molecules in every billion. Following their observations, they ran calculations to see whether these amounts could come from natural non-biological processes on the planet. Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning, but none of these could make anywhere near enough of it. These non-biological sources were found to make at most one ten thousandth of the amount of phosphine that the telescopes saw.

To create the observed quantity of phosphine (which consists of hydrogen and phosphorus) on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity, according to the team. Earth bacteria are known to make phosphine: they take up phosphate from minerals or biological material, add hydrogen, and ultimately expel phosphine.

Any organisms on Venus will probably be very different to their Earth cousins, but they too could be the source of phosphine in the atmosphere.

“The discovery raises many questions, such as how any organisms could survive. On Earth, some microbes can cope with up to about 5% of acid in their environment — but the clouds of Venus are almost entirely made of acid.”
— Clara Sousa Silva, MIT research team member

The team believes their discovery is significant because they can rule out many alternative ways to make phosphine, but they acknowledge that confirming the presence of “life” needs a lot more work. [Editor’s note: bold mine.] Although the high clouds of Venus have temperatures up to a pleasant 30 degrees Celsius (86ºF) they are incredibly acidic — around 90% sulphuric acid — posing major issues for any microbes trying to survive there. (Source: ESO)

The research paper was published September 14, 2020 in Nature Astronomy.

What Venus’ 880ºF landscape looks like. Approximate (colorized) natural color view of Venus’ surface, captured by the Soviet Venera 14 lander in March 1982 and processed by Don P. Mitchell and myself.

While these findings are exciting and tantalizing, they are far from a confirmation or even direct detection of life. Still, while Venus’ surface is an incredibly harsh environment unsuitable for any type of known terrestrial organisms, there are places higher up in its cloudy atmosphere where some forms of life could potentially thrive. Could phosphine be a telltale sign of its presence? Only further research — and hopefully future in situ science — can determine that.

The team are now eagerly awaiting more telescope time, for example to establish whether the phosphine is in a relatively temperate part of the clouds, and to look for other gases associated with life. New space missions could also travel to our neighbouring planet, and sample the clouds in situ to further search for signs of life. Source: Cardiff University

Watch an explainer video from the Royal Astronomical Society below, featuring research team leader and professor Jane Greaves, and read more about these findings here from the Royal Astronomical Society and here from MIT.