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EXPERT REACTION: Phosphine gas discovery has us wondering - Is there life on Venus?

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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.

Journal/conference: Nature Astronomy

Link to research (DOI): 10.1038/s41550-020-1174-4

Organisation/s: Cardiff University, Cardiff, UK

Funder: Additional funding support is provided by the Science and Technology Facilities Council of the United Kingdom and participating universities in the United Kingdom (including Cardiff, Imperial College and the Open University) and Canada. Starlink software is currently supported by the East Asian Observatory. ALMA is a partnership of ESO (representing its member states), NSF (United States) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Funding for the authors was provided by STFC (grant ST/N000838/1, D.L.C.); Radionet/MARCUs through ESO (J.S.G.); the Japan Society for the Promotion of Science KAKENHI (grant no. 16H02231, H.S.); the Heising-Simons Foundation, the Change Happens Foundation, the Simons Foundation (495062, S.R.); the Simons Foundation (SCOL award 59963, P.B.R.). RadioNet has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 730562. J.S.G. is a Visitor at the Institute of Astronomy, University of Cambridge. S.R. is a SCOL Postdoctoral Fellow.

Media release

From: Springer Nature

Nature Media Release: Phosphine detected in the clouds of Venus 

Phosphine gas has been detected in the atmosphere of Venus, according to a paper published in Nature Astronomy. This finding suggests that Venus could host unknown photochemical or geochemical processes.

On Earth, phosphine is a gas that is produced predominantly by anaerobic biological sources. The conditions at the surface of Venus are hostile to life, but the environment of its upper cloud deck — around 53–62 km above the surface — is temperate. However, the make-up of the clouds is highly acidic, and in such conditions phosphine would be destroyed very quickly.

Jane Greaves and colleagues observed Venus with the James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array in 2017 and 2019, respectively. They detected a spectral signature that is unique to phosphine, and estimated an abundance of 20 parts-per-billion of phosphine in Venus’s clouds. The authors investigated different ways the phosphine may have been produced, including from sources on the surface of the planet, micrometeorites, lightning, or chemical processes happening within the clouds. Ultimately, they were unable to determine the source of the trace quantities of phosphine.

The authors argue that the detection of phosphine is not robust evidence for microbial life and only indicates potentially unknown geological or chemical processes occurring on Venus. Further observations and modelling are needed to explore the origin of phosphine in Venus’s atmosphere.

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James Clerk Maxwell Telescope Media Release: JCMT finds hints of life on Venus

MAUNAKEA HAWAI`I - An international team of astronomers, led by Professor Jane Greaves of Cardiff University, UK, today announced the discovery of a rare molecule – phosphine – in the clouds of Venus. On Earth, this gas is only made industrially, or by microbes that thrive in oxygen-free environments. The detection of phosphine could point to such extra-terrestrial “aerial” life. “When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”, said Jane, who first spotted signs of phosphine in observations from the James Clerk Maxwell Telescope (JCMT) in Hawai`i.

Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes – floating free of the scorching surface, with access to water and sunlight, but needing to tolerate very high acidity. The detection of phosphine, which consists of hydrogen and phosphorus, could point to this extra-terrestrial ‘aerial’ life. The new discovery is described in a paper published today in Nature Astronomy.

The first detection of phosphine in the clouds of Venus was made using the JCMT in Hawai`i. The team were then awarded time to follow up their discovery with 45 telescopes of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Both facilities observed Venus at a wavelength of about 1 millimetre, much longer than the human eye can see – only telescopes at high altitude can detect it effectively. “In the end, we found that both observatories had seen the same thing — faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below” said Jane.

The astronomers then ran calculations to see if the phosphine could come from natural processes on Venus. Massachusetts Institute of Technology scientist Dr William Bains led the work on assessing natural ways to make phosphine. Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning, but none of these could make anywhere near enough of it. Natural sources were found to make at most one ten thousandth of the amount of phosphine that the telescopes saw. In contrast the team found that in order to create the observed quantity of phosphine on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity. Any microbes on Venus will though likely be very different to their Earth cousins. Earth bacteria can absorb phosphate minerals, add hydrogen extracted from water, and ultimately expel phosphine gas.

Before the new study, team member and MIT researcher, Dr Clara Sousa Silva, had thought about searching for phosphine as a ‘biosignature’ gas of non-oxygen-using life on planets around other stars, because normal chemistry makes so little of it. She comments “Finding phosphine on Venus was an unexpected bonus! 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.

The team believes this 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. Although the high clouds of Venus have temperatures up to a pleasant 30 degrees centigrade, they are incredibly acidic – around 90% sulphuric acid – posing major issues for microbes to survive there. Prof Sara Seager and Dr Janusz Petkowski, both at MIT, are investigating how microbes could shield themselves inside scarce water droplets.

The team are now eagerly awaiting more telescope time to establish whether the phosphine is in a relatively temperate part of the clouds, and to look for other gases associated with life. This result also has implications in the search for life outside our Solar system.

On hearing the results of the JCMT study, the JCMT’s Deputy Director Dr Jessica Dempsey said “These results are incredible” and went on to say “this discovery made in Hawai`i, by the JCMT, was made with a single pixel instrument. This is the very same instrument that also captured the first image of a Black Hole, Pōwehi. The discovery of phosphine in the atmosphere of Venus really showcases the breadth of cutting-edge research undertaken by astronomers using the JCMT. I am so pleased of the efforts from all our staff here in Hawai`i

Former UH Hilo astronomy student, E’Lisa Lee who took some of the JCMT data during her time working as a part-time JCMT telescope operator summed up her feelings “An observed biochemical process occurring on anything other than Earth has the greatest and most profound implications for our understanding of life on Earth, and life as a concept.” Adding “Being able to participate in the scientific process, as an operator at JCMT was an incredible and humbling experience. It is my sincerest hope that further observations will allow for greater exploration of Venusian clouds and everything beyond.” E’lisa currently studying for her Master’s degree in physics at Fresno State University.

The JCMT instrument that captured this phosphine discovery has since retired and been replaced by a new and more sensitive instrument known as Nāmakanui. On the potential of this new instrument, Jessica commented “Like it’s namesake, the big-eyed fish hunting food in the dark waters, we will turn the far more sensitive Nāmakanui back to Venus in this hunt for life in our universe.  This is just the beginning, and I’ve never been more excited to be a part of our boundary-pushing JCMT team.”

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr Aditya Chopra is from the Research School of Astronomy and Astrophysics at the Australian National University (ANU)

The result by Greaves et al. is an important step towards improving our understanding of the present-day atmosphere of Earth’s twin. It offers an exciting example of how science-fiction has the power to inspire new and ground-breaking science!

As cutting-edge research often does, this study has given rise to more new questions than answers; and gives us reason to launch bold missions to study the Venusian atmosphere and surface. We think, a few billion years ago, Venus was very much Earth-like and thus Venusian life may have thrived in the past. However, it's hard to imagine how such life could have persisted long after Venus experienced run-away heating.

The paper reminds me of the detection of Methane in the atmosphere of Mars in 2004. Since then, many hypotheses have been proposed and tested to explain Martian methane, but we are still trying to figure out its biotic or abiotic source more than a decade later. The detection of Venusian phosphine will undoubtedly be reanalysed using some of the world's best telescopes, in particular, to study the seasonality of the signature.

As we continue to study the chemistry of Venus, I suspect that geochemical processes may yield a more straightforward explanation. Despite how romantic the idea of alien life might seem, we should remain cautious… Attributing the phosphine to Venusian life, whether aloft in the sulfuric acidic clouds, or living closer to the hellish surface remains improbable at best.

Last updated: 15 Sep 2020 10:06am
Declared conflicts of interest:
None declared.
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.

Last updated: 14 Sep 2020 12:42pm
Declared conflicts of interest:
None declared.
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.

Last updated: 14 Sep 2020 12:39pm
Declared conflicts of interest:
None declared.
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.

Last updated: 14 Sep 2020 12:37pm
Declared conflicts of interest:
None declared.
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!

Last updated: 14 Sep 2020 12:37pm
Declared conflicts of interest:
None declared.
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.

Last updated: 14 Sep 2020 12:36pm
Declared conflicts of interest:
None declared.
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.

Last updated: 14 Sep 2020 12:36pm
Declared conflicts of interest:
None declared.
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.

Last updated: 14 Sep 2020 12:34pm
Declared conflicts of interest:
None declared.
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.

Last updated: 11 Sep 2020 12:07pm
Declared conflicts of interest:
None declared.

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