British scientists have discovered phosphine gas on the planet Venus, which is evidence of the existence of certain life forms on the planet. The research results are published in the scientific journal Nature Astronomy.
Nature Astronomy reports that measurements of trace gases in planetary atmospheres help to explore chemical conditions different to those on Earth.
"Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine (PH3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH3 at ~20 ppb abundance is inferred," a team of scientists from Cardiff University, led by Jane Greaves wrote. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic.
The presence of PH3 is unexplained after an exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery.
Studying rocky-planet atmospheres gives clues to how they interact with surfaces and subsurfaces, and whether any non-equilibrium compounds could reflect the presence of life. The Solar System offers important testbeds for exploring planetary geology, climate and habitability. Proximity makes signals of trace gases much stronger than those from extrasolar planets, but issues remain in interpretation.
Thus far, Solar System exploration has found compounds of interest, but often in locations where the gas sources are inaccessible. Water, simple organics and larger unidentified carbon-bearing species are known.
An ideal biosignature gas would be unambiguous. Living organisms should be its sole source, and it should have intrinsically strong, precisely characterized spectral transitions unblended with contaminant lines—criteria that are not usually all achievable. It was recently proposed that any phosphine (PH3) detected in a rocky planet’s atmosphere is a promising sign of life. Trace PH3 in Earth’s atmosphere (parts per trillion abundance globally) is uniquely associated with the anthropogenic activity or microbial presence—life produces this highly reducing gas even in an overall oxidizing environment. PH3 is found elsewhere in the Solar System only in the reducing atmospheres of giant planets, where it is produced in deep atmospheric layers at high temperatures and pressures, and dredged upwards by convection. Solid surfaces of rocky planets present a barrier to their interiors, and PH3 would be rapidly destroyed in their highly oxidized crusts and atmospheres. Thus PH3 meets most criteria for a biosignature-gas search but is challenging as many of its spectral features are strongly absorbed by Earth’s atmosphere.
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. Information is lacking—as an example, the photochemistry of Venusian cloud droplets is almost completely unknown.
Unknown chemical species would need to have a transition at an extremely nearby wavelength. However, confirmation is always important for a single-transition detection. Other PH3 transitions should be sought, although observing higher-frequency spectral features may require a future large air- or a space-borne telescope.
Even if confirmed, we emphasize that the detection of PH3 is not robust evidence for life, only for anomalous and unexplained chemistry. There are substantial conceptual problems for the idea of life in Venus’s clouds—the environment is extremely dehydrating as well as hyperacidic. To further discriminate between unknown photochemical and/or geological processes as the source of Venusian PH3, or to determine whether there is life in the clouds of Venus, substantial modelling and experimentation will be important. Ultimately, a solution could come from revisiting Venus for in situ measurements or aerosol return.
"Life on Venus? The discovery of phosphine, a byproduct of anaerobic biology, is the most significant development yet in building the case for life off Earth. About 10 years ago NASA discovered microbial life at 120,000ft in Earth’s upper atmosphere. It’s time to prioritize Venus," Bridenstine said.
Life on Venus? The discovery of phosphine, a byproduct of anaerobic biology, is the most significant development yet in building the case for life off Earth. About 10 years ago NASA discovered microbial life at 120,000ft in Earth’s upper atmosphere. It’s time to prioritize Venus. https://t.co/hm8TOEQ9es— Jim Bridenstine (@JimBridenstine) September 14, 2020
Any detectable PH3 found in the atmosphere of a rocky planet is a promising sign of life and showed that biological production of PH3 is favoured by cool, acid conditions. Initial modelling based on terrestrial biochemistry suggests that biochemical reduction of phosphate to PH3 is thermodynamically feasible under Venus cloud conditions.