Signs of life on Venus? – Expert Reaction from the AusSMC

David Bowie may have got his planets mixed up, it seems, after international researchers say they’ve discovered a tantalising hint that Venus may harbour life – phosphine gas.

On Earth, this gas is predominantly produced by living creatures that call oxygen-free environments home, so could the same be true on Venus? The planet’s surface is very hostile, but the upper cloud deck – around 53-62 km above the surface – is a contender for life, the scientists say. The clouds themselves are very acidic and destroy phosphine very quickly, which might mean something up there is creating it anew, they add. But they also point out that the gas alone doesn’t prove there’s life, because it may be being generated by geological or chemical processes unknown to us.

Australian experts discuss the research. This is a republished Expert Reaction from the Australian Science Media Centre.

Dr Brendan Burns is a Senior Lecturer at the School of Biotechnology and Biomolecular Sciences at The University of New South Wales, as well as Deputy Director, Australian Centre for Astrobiology

“In this study, using a combination of a telescope in Hawai`i and the Atacama Array in Chile, astronomers detected trace levels of phosphine gas in the atmosphere of Venus. The team conducted exhaustive calculations and modelling and could not come up with plausible natural ways for these levels of phosphine to occur. What is obviously intriguing is that phosphine is a potential biosignature of life, as this molecule is a by-product of some microbial metabolism on Earth.

“However, this finding comes with a huge caveat: the atmosphere of Venus is 96% carbon dioxide, with a surface temperature of up to 460 C making it the hottest planet in our solar system. So hot it would melt lead on the surface. While it is true the atmosphere is not as hot as the surface, in addition to the high CO2 there are also clouds of sulfuric acid (up to 90%), so these are conditions not exactly welcoming to life – as we know it.

“As the authors admit themselves the phosphine could simply originate from some unknown geochemical or photochemical reactions. Thus, far more work is needed to follow up these observations, but even a slim possibility of a biosignature of life existing outside Earth has the profound potential to alter our understanding of our very place in the universe.”

Brendan has not declared any conflicts of interest.

Professor Fred Watson, AM is an astronomer from the Department of Industry, Science, Energy and Resources

“The quest for life-signatures in planetary atmospheres has taken a dramatic new turn. While the well-observed methane plumes in the atmosphere of Mars seem just as likely to come from ancient volcanism as methane-emitting microbes, the detection of phosphine gas in Venus’ upper cloud layers is much more suggestive of biological processes. The astronomers who found this rare chemical say they have ruled out other sources such as reactions involving sunlight, surface minerals, volcanoes, lightning or meteorites, leaving only unknown geological or chemical processes. Or life.

“Could there really be living organisms in the upper atmosphere of Venus? Often described as Earth’s ugly sister, the planet is about the same size, but has an average surface temperature well above the melting point of lead, and an atmosphere laced with corrosive acid. Despite these hostile conditions, scientists have long wondered whether the atmosphere’s temperate upper layers could provide a habitat for alien life forms. The answer is still probably no, but until the possibility is ruled out by further observations, this new discovery will intrigue researchers everywhere.”

Fred has not declared any conflicts of interest.

Associate Professor Alice Gorman is from the College of the Arts, Humanities and Social Sciences at Flinders University and an internationally recognised leader in the emerging field of space archaeology

“Before the Mariner 2 flyby of Venus in 1962, it was thought that Venus’ thick clouds might hide signs of life on the surface. The USSR Venera landing missions through the 1970s and 1980s put an end to theories about Venus as a lush ocean world. The surface was shown to be dry and hot, and the clouds largely made of sulphuric acid – the most corrosive environment in the solar system. It looks like Venus’ oceans were lost about 700 million years ago.

“With the surface ruled out, there was speculation that the more temperate clouds might have aerial life forms. The discovery of phosphine gas, which on Earth is produced by microbes, is the first concrete evidence to support this theory.

“While we can’t be certain yet of the source of the phosphine, the possibility that it might be related to microbial life is exciting. Did life evolve on Venus, or is it related to the transportation of pre-biotic materials around the solar system on comets and asteroids? This will shed light on the emergence of life on Earth.

“There’s a lot of attention on Mars these days, but these results build an even stronger case for return to Venus. The phosphine was observed by ground-based telescopes and we need space-based observations too. Currently, there’s only the Japanese orbiter Akatsuki gathering data directly from Venus. The European Space Agency’s BepiColumbo is due to fly past in October, on its way to Mercury.

“On Earth, phosphine is a poisonous and explosive gas sometimes used as a pesticide. Pure phosphine is odourless, but mixed with other compounds it can smell like rotting fish or garlicky feet. The ‘planet of love’ might turn out to be the stinky planet too.”

Alice has not declared any conflicts of interest.

Dr Brad Tucker is a Research Fellow and Outreach Manager at Mt. Stromlo Observatory at the Australian National University

“This discovery is super exciting for the exploration and study of Venus. Studies of Mars have found unexplained processes, such as the varying methane in its atmosphere, which has hinted at either unknown geochemistry processes or from that of life.  This discovery on Venus is similar – either there is a new part of Venus we have not understood, or it is from a biological process. Venus is often called Earth’s twin, and this gives us a huge reason to go and explore Venus. The fact that our two neighbour planets, Venus and Mars, now have strong signs that could be from life, is super exciting!”

Brad has not declared any conflicts of interest.

Dr Laura McKemmish is a Lecturer in the School of Chemistry at the University of New South Wales

“This piece of research marks the start of a new era in the search for extra-terrestrial life. While we need to be cautious, scientists don’t yet know how to explain the observed abundance of the phosphine molecule under the conditions in Venus’ clouds without life.

“Biological processes can produce essentially any molecule, but without biology, this number is very limited.

“The authors essentially say: We think we’ve found life on Venus: prove us wrong! This challenges chemists to find natural atmospheric or geological processes that could create phosphine in such abundance. Failing this, biologists must answer how life could exist in the highly acidic environment of Venus’ clouds, far more acidic than any conditions found on Earth (though extremophiles have been found in pH 0 environments on Earth). And I expect probes to be sent quickly to Venus to discover answers as the world asks the question: is there life on Venus?

“To find phosphine, astronomers relied on the predictions of molecular spectroscopy: when a rainbow of light passes through the atmosphere, each molecule absorbs certain colours of light, forming a barcode – or spectrum – that is unique for every molecule. In 2015, Sousa-Silva and collaborators calculated the phosphine spectrum through detailed computational quantum chemistry calculations tuned to experimental observations. These calculations enabled astronomers to look for and detect one specific line of phosphine’s barcode in Venus’s cloud at a very precise invisible microwave ‘colour’. Regardless of what scientists find next, this will be a milestone in the search for extra-terrestrial life.”

Laura has not declared any conflicts of interest.

Dr Nick Tothill is a Senior Lecturer for Computational Imaging, Visual Science & Computational Astrophysics at Western Sydney University

“We usually associate discoveries on other planets with spacecraft, but scientists have been using telescopes on Earth to deduce the nature of other planets ever since Galileo.

“In this work, ground-based radio telescopes have not only been able to detect phosphine as a trace constituent of Venus’ atmosphere, but have shown that the phosphine they’re seeing is in the upper atmosphere of Venus, in the sulphuric acid cloud deck, where chemical reactions should rapidly destroy it.

“The phosphine must come from somewhere, and this could be some chemistry we don’t understand. But chemicals in a planet’s atmosphere that are out of place can also be a sign of life at work – maybe we need to be looking at the clouds on Venus as hard as we’re looking at the rocks on Mars to understand life in our Solar System.”

Nick has not declared any conflicts of interest.

Dr Danny Price is an Australian Project Scientist for Breakthrough Listen as well as a Senior Postdoctoral Fellow at the Curtin Institute of Radio Astronomy (CIRA)

“This is huge: it could be the first detection of life beyond Earth. If life can arise in hyperacidic clouds on Venus, it may be that life is widespread across the Galaxy.

“But before we get too excited, we need to take a deep breath of that Venusian air and rule out less exciting ways that phosphine could be sneaking in.

“There could be some complex mechanisms replenishing phosphine in the atmosphere of Venus, that we haven’t seen happen here on Earth. We need to do intense follow-up observations to provide further evidence.”

Danny has not declared any conflicts of interest.

Swinburne University’s Professor Alan Duffy, Lead Scientist of The Royal Institution of Australia

“This is one of the most exciting signs of the possible presence of life beyond Earth I have ever seen, and certainly from the most surprising location I could imagine! Our twin planet Venus is a hellish world.

“While the surface is hot enough to melt lead, the temperature drops as you go higher into the clouds, becoming Earth-like in both temperature and pressure by an altitude of 50 km exactly where the phosphine was found.

“While the temperature is benign the clouds contain sulfuric acid which should break down the phosphine, so something is forming it anew, and as phosphine is associated with life on Earth it is tempting to think it could be life on Venus but before we can become more confident about that we have to rule out all possible other non-biological means of producing it.

“This paper was exhaustive in ruling out the possibilities, but there may yet be non-living chemical pathways in the extreme environment on Venus that we haven’t yet discovered so we have to learn more about geochemistry on Earth’s twin.

“Any detection of life beyond Earth will only be confirmed if that life is measured in lab, and that means we might yet see NASA’s long-dreamed of mission to Venus finally come true with gigantic balloons floating in this 50 km temperature layer and directly sampling the Venusian air for microbial life.”