Venus, the second planet out from the Sun and roughly the same size of Earth, is well known for being the prime example of a runaway greenhouse effect. Shrouded in dense, toxic clouds that hide its barren surface from view, the planet has an average surface temperature 464°C, its dense, carbon-dioxide dominant (96%) atmosphere places an average pressure on that surface around 92 times the mean pressure at sea level here on Earth – or roughly the same pressure as exerted by the sea at a depth of 900 metres (3,000 ft).
Yet, as I’ve recently reported (see: Space Sunday: Venus’ transformation, SLS and an asteroid), there is evidence to suggest that Venus started life as a warm, wet planet with liquid water seas of its own, only to be started on the road to becoming the hothouse we know today thanks to Jupiter’s wandering influence.
However, if this theory is correct, and Venus was once warm and wet, the question of whether it was sufficiently so to give rise to the earliest forms of basic life becomes a very real one – as does what might have happened to that life as the planet started its long transformation in the superheated, super pressurised world we see today.
Did the changing conditions simply wipe out any microbes that may have arisen there, or did those microbes themselves have been transformed, moving to the upper reaches of the Venusian atmosphere where they could survive on the heat from both the Sun and rising from through the planet’s atmosphere without necessarily being dry roasted, while drawing on the minerals and chemicals also floating within the high-altitude clouds?
The idea of entirely atmosphere-borne forms of life on planets like Venus and Jupiter is not new, but this past week, the potential for some form of organic activity on Venus became a lot more real with the detection of a compound this is usually the off-shoot of organic processes within the mid-levels of the Venusian cloud layers.
Phosphine is a colourless, flammable, very toxic gas compound made up of one phosphorus and three hydrogen atoms (PH₃). It is most commonly produced by organic life forms, although it can be created artificially. Thus its presence within the atmosphere of Venus raises the tantalizing possibility that something is alive in that atmosphere.
The detection of phosphine in Venus’ atmosphere was made by an international team using two different telescopes in different parts of the world. The team, led by astronomers working out of Cardiff University in the UK, first identified the compound using the James Clark Maxwell Telescope (JMCT), located in Hawaii. They then turned to the Atacama Large Millimetre/sub millimetre Array (ALMA) in Chile, equipped with more sensitive detectors than JCMT, to confirm their findings.
It’s important to note that while the phosphine has been identified, the team responsible for identifying it are not jumping to the conclusion it means there is life within the Venusian atmosphere. While – in our experience – it is generally the result of organic interactions, it can be produced in the laboratory, as noted, through chemical interactions – and Venus is a veritable chemical hothouse.
What is surprising is the amount of phosphine calculated to be in the cloud layer: roughly 20 parts per billion. While a comparatively tiny amount, it is astonishing to planetary astronomers because it’s long been assumed that if any phosphorus existed in Venus’ atmosphere, it would long ago have bonded with oxygen atoms, of which there are a lot around Venus, albeit the majority being bound within the dominant carbon dioxide.
Following their discovery the team, led by Jane Greaves of Cardiff University and ideo Sagawa at Kyoto Sangyo University, Japan, sought potentially natural means for the formation of phosphine around Venus. These included things such as chemical reactions in the atmosphere driven by strong sunlight or lightning, or the interaction of chemicals coming from volcanic activity, or delivered by meteorites. However, none of these mechanisms could account for the volume of phosphine Venus appears to have.
Even so, this doesn’t necessarily mean that the phosphine is the result of tiny Venuisan organisms; as the team note, it could be the result of as yet unknown photochemistry or geochemistry mechanisms within the planet’s atmosphere or the planet itself.
Although we concluded that known chemical processes cannot produce enough phosphine, there remains the possibility that some hitherto unknown abiotic process exists on Venus. We have a lot of homework to do before reaching an exotic conclusion, including re-observation of Venus to verify the present result itself.
– Study member ideo Sagawa
Obviously, to determine whether or not biotic or abiotic processes are responsible for the phosphine, further study – preferably close-up – of Venus’ atmosphere is required. Although further Earth-based observations from Earth can help confirm the volume of phosphine within the planet’s atmosphere, satellites orbiting Venus will offer a far more complete picture, simply because they can study the planet in detail over the course of years, building up a complete picture of its composition using spectrographic analysis.
Two Venus missions – VERITAS, the Venus Emissivity, Radio Science, InSAR, Topography, And Spectroscopy orbit and DAVINCI+, an atmospheric penetrator, are already being considered by NASA as planetary missions among missions to other destinations, with one of this group of proposals due to be selected in April 2021. Either could help sniff out the phosphine and potentially help identify its cause. Japan’s Akatsuki orbiter may also help in further studies of phosphine around Venus.
The private company Rocket Lab has been developing plans to mount its own mission to Venus for some time, using their Electron rocket, which has been operating since 2018, and their new Photon upper stage, which made its début in august 2020. Rocket Lab founder and CEO Peter Beck believes that Venus has been undervalued as a place for stud (although there have been some 30 fly, orbital and lander missions since 1962).