What are the prospects for follow-up observations of phosphine on Venus?

What are the prospects for follow-up observations of phosphine on Venus?

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Today, it was officially announced that astronomers have detected phosphine on Venus via the $ ext{PH}_3(0 o1)$ transition (Greaves et al 2020). While the line was found by both the James Clerk Maxwell Telescope and ALMA, and while the team is fairly confident that the detection is robust, follow-up observations would nevertheless be nice, particularly in other bands. Sousa-Silva et al 2020 note that phosphine has strong features in the 2.7-3.6, 4.0-4.8, and 7.8-11.5 micron bands, and while they're pessimistic about detecting phosphine in $ ext{CO}_2$-dominated atmospheres around Sun-like stars using less than ~200 hours of observing time, those numbers are for exoplanets, where we'd expect substantially lower fluxes than we'd receive from Venus.

With all that in mind, what are the most promising bands to search for phosphine on Venus, in addition to to the $1 o0$ transition? Are they the three infrared bands discussed by Sousa-Silva et al, or could other trace components of the Venusian atmosphere block the signal at some wavelengths? I see that $ ext{SO}_2$ was the only remotely feasible possibility for a source mimicking the observed phosphine transition, but that would require temperatures twice as high as observed.

As a side note, it's been announced that BepiColombo will use an onboard spectrometer to try to detect phosphine on Venus during two flybys of the planet en route to Mercury. The first will be on October 15, 2020, and the second will be on August 10, 2021. I haven't been able to find out more details on the planned observations, but the spectrometer (MERTIS) operates in the 7-14 micron band.

This figure is from the paper "Phosphine as a bio signature gas in exoplanet atmospheres". It shows the absorption cross section of Phosphine compared to other molecules. We can see that Phosphine has a distinct enough profile from the others molecules in the 7.8-11.5 microns range, with the exception of NH3. Probing from 2-11.5 microns should then allow to distinguish Phosphine from other molecules. Simulations seem to indicate that current state of the art nIR ground-based spectrometers could detect phosphine to a minimum of a few ppb, so expect a lot of follow-up observations from the ground in the coming months.

Life on Venus? Future space missions could check it out

Scientists say they’ve detected a chemical associated with biological activity within the clouds of Venus, at a height where airborne life forms could theoretically exist.

The chemical, known as PH3 or phosphine, isn’t the first biomarker to be found in Venus’ atmosphere. But the scientists say they can’t come up with a non-biological process that could produce phosphine at the levels they’re seeing.

This isn’t the smoking gun for life on Venus. Nevertheless, the latest findings — which leaked out over the weekend and were published today in Nature Astronomy — give peer-reviewed weight to an idea that once seemed almost ludicrous: the idea that microbes or other life forms may be perpetually floating in Venus’ acidic air, more than 30 miles above the planet’s searingly hot surface.

The findings are also likely to give a push to several proposed space missions that are already targeting the clouds of Venus.

“It may be that Venus , not Mars, is our best hope for a long-inhabited nearby neighbor,” David Grinspoon, a senior scientist at the Planetary Science Instutute, told me in an email.

The possibility of finding life in Venus’ clouds has been under debate for decades. The late astronomer Carl Sagan surveyed the prospects almost 60 years ago. More recently, Grinspoon and other astrobiologists have revived the case for closer study of Venus, in hopes of finding traces of microbial life in the clouds.

Grinspoon told me it’s been a tough sell. “Folks would roll their eyes at my conference talks, but I was tolerated because I did a lot of good work on other aspects of Venus , writing papers on the clouds, the surface evolution, the climate, and so forth,” he said.

It’s not hard to see why Venus has been upstaged by Mars as well as the icy moons of Jupiter and Saturn when it comes to the search for life elsewhere in the solar system. Although Venus is close to Earth’s size and mass, its average surface temperature of 900 degrees Fahrenheit is hot enough to melt lead, due to a runaway greenhouse-gas effect.

Venus’ dense, surface-obscuring atmosphere consists primarily of carbon dioxide, but it’s also laced with droplets of sulfuric acid that makes it inhospitable to most life on Earth.

Even if amped-up versions of our own planet’s acid-loving microbes were to exist on Venus, the only place astrobiologists can imagine them getting a foothold would be within a temperate band of clouds that lie between 30 and 40 miles above the surface.

Just last month, a team of scientists — including some of the co-authors of the newly published study — proposed a spore-based life cycle for aerial microbes within that cloud band.

What kind of evidence might such creatures leave behind? Researchers at the Massachusetts Institute of Technology zeroed in on phosphine — a smelly, toxic gas given off by anaerobic bacteria on Earth. MIT planetary scientist Clara Sousa-Silva thought the spectral fingerprint of phosphine would be a good biosignature to look for when advanced telescopes analyze the light reflected by planets in alien star systems.

“I was thinking really far, many parsecs away, and really not thinking literally the nearest planet to us,” she said in a news release.

The astronomers who focused in on Venus weren’t expecting to find phosphine, either. When they observed the planet using the James Clerk Maxwell Telescope in Hawaii, they expected to rule out some of the claims surrounding life on Venus.

“This was an experiment made out of pure curiosity, really — taking advantage of JCMT’s powerful technology, and thinking about future instruments,” study lead author Jane Greaves, an astronomer at Cardiff University in Wales, said in a news release.

“I thought we’d just be able to rule out extreme scenarios, like the clouds being stuffed with organisms,” she said. “When we got the first hints of phosphine in Venus’ spectrum, it was a shock!”

What’s more, the phosphine was found precisely in the band of the cloud layer that’s most hospitable to life.

The detection was confirmed with follow-up observations from the Atacama Large Millimeter Array, or ALMA, in Chile. Greaves and her team then turned to other scientists to help interpret the findings.

Researchers considered a wide range of non-biological mechanisms for putting phosphine into the Venusian atmosphere — for example, by cooking other molecules with solar radiation or lightning, or having the wind sweep up minerals from the surface, or having the phosphine expelled by volcanoes, or bringing it in from space via meteors.

Phosphine is created non-biologically at Jupiter and Saturn, due to the abundance of hydrogen and the crushing atmospheric pressure at those gas giants, but the researchers noted that such conditions don’t exist on Venus. “That particular chemistry is definitely not happening at Venus,” MIT’s William Bains said today during a news briefing.

None of the mechanisms that the researchers considered could produce the level of phosphine that the astronomers detected, which amounts to 20 molecules per billion. Their most productive non-biological scenario could make, at most, only one-ten-thousandth of the required amount.

That leaves the biological scenario as the favored explanation, unless someone else comes up with a better explanation that the research team missed.

“It’s very hard to prove a negative,” Sousa-Silva said. “Now, astronomers will think of all the ways to justify phosphine without life, and I welcome that. Please do, because we are at the end of our possibilities to show abiotic processes that can make phosphine.”

On Earth, microbes are routinely lofted into upper levels of the atmosphere and eventually drift back down. But on Venus, such organisms would be killed off if they sank too low. Such an exclusively aerial biosphere might have evolved from an earlier age when Venus was far more hospitable to life, Sousa-Silva said.

“A long time ago, Venus is thought to have oceans, and was probably habitable like Earth,” she said. “As Venus because less hospitable, life would have had to adapt, and they could now be in this narrow envelope of the atmosphere where they can still survive.”

So what’s next? Sousa-Silva and MIT’s Jason Dittman are leading an effort to confirm the phosphine findings with data from other telescopes, and map the distribution of phosphine across the Venusian atmosphere over time. If there are daily or seasonal variations, that could provide additional evidence for biological activity.

“The experiment must and will be repeated,” Grinspoon told me. “Laboratory studies will be undertaken to see how PH3 behaves in a Venus-like environment and what else could possibly produce it. But the best test, and the one I’m most excited about, is to go back to Venus and investigate the atmosphere in situ.”

Last month, a panel of scientists presented a 222-page report laying out the possibilities for a flagship mission to Venus, as part of the astronomy community’s 2020 decadal survey of science priorities.

One mission concept, advanced by Northrop Grumman, calls for sending an instrument-laden, solar-powered aircraft called VAMP into the Venusian atmosphere.

Another concept, known as DAVINCI+, is one of four proposals vying for funding through NASA’s Discovery Program. The DAVINCI+ spacecraft would map Venus and its atmosphere from orbit. It’d also drop a spherical probe through the atmosphere, all the way to the surface, to sniff out the molecules making up each layer.

“Our vision for DAVINCI+ is to send a chemistry lab and orbiter to Venus to put the planet into its appropriate context in our solar system,” principal investigator Jim Garvin, who is chief scientist at NASA’s Goddard Space Flight Center, said in a news release.

If DAVINCI+ is selected for full funding next year, Garvin and his teammates propose launching the mission in 2026.

Yet another Discovery Program finalist, the proposed VERITAS mission, would concentrate on creating three-dimensional maps of Venus’ surface features and geology. NASA is also considering a CubeSat mission to study Venus’ atmosphere.

Meanwhile, California-based Rocket Lab is making plans to send a probe to Venus within three years or so.

“I’m working very hard to put together a private mission to go to Venus in 2023,” Rocket Lab CEO Peter Beck said last month during a webcast. “We’re going to learn a lot on the way there, and we’re going to have a crack at seeing if we can discover what’s in that atmospheric zone. And who knows? You may hit the jackpot.”

MIT’s Sara Seager said she and her colleagues have been talking with Rocket Lab about putting together the scientific payload for such a mission. The requirements are challenging: Such a payload would have to weigh no more than 3 kilograms (6.6 pounds), Seager said.

Details about potential funding for Rocket Lab’s mission haven’t yet come to light, but Russian-Israeli tech billionaire Yuri Milner is known to have Venus on his short list for a privately funded mission.

Back in 1985, the twin Soviet Vega probes deployed two balloon explorers in the Venusian atmosphere. Instruments on the balloons sent back data for 46 hours before their batteries ran out. Today, Seager was asked about that mission concept and said “a balloon is certainly the best way” to study what’s in the clouds.

“We have a long list of things we’d like, actually,” she said.

Over the past 30 years, NASA, the European Space Agency and the Japan Aerospace Exploration Agency have sent probes to Venus. In light of the findings published today, Grinspoon thinks it’s high time for the next visit.

“Now that we’ve found a genuine candidate biosignature, we absolutely must go,” he said. “And even if this turns out to be a false alarm, it could be productive, in the way that the ‘Mars rock’ (ALH84001) was. That turned out — probably — to be a false alarm, but it got everyone to think about it in a fresh way and ask, ‘Why not?’ ”

Update for 8:50 a.m. PT Sept. 14: NASA’s associate administrator for science, Thomas Zurbuchen, tweeted that the findings are “intriguing” but added that NASA will defer further comment until the post-publication discussion has run its course:

An intriguing paper about chemistry on Venus was published today. @NASA was not involved in the research & cannot comment directly on the findings however, we trust in the scientific peer review process & look forward to the robust discussion that will follow its publication.

&mdash Thomas Zurbuchen (@Dr_ThomasZ) September 14, 2020

Update for 1:10 p.m. PT Sept. 14: Later in the day, NASA Administrator Jim Bridenstine tweeted that “it’s time to prioritize Venus” — which will probably lift the spirits of the folks working on the aforementioned proposals for missions to Venus:

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.

&mdash Jim Bridenstine (@JimBridenstine) September 14, 2020

In addition to Greaves, Sousa-Silva, Bains and Seager, the authors of the Nature Astronomy paper, “Phosphine Gas in the Cloud Decks of Venus,” include Anita Richards, Paul Rimmer, Hideo Sagawa, David Clements, Janusz Petkowski, Sukrit Ranjan, Emily Drabek-Maunder, Helen Fraser, Annabel Cartwright, Ingo Mueller-Wodarg, Zhuchang Zhan, Per Friberg, Iain Coulson, E’lisa Lee and Jim Hoge.

Did Scientists Just Find Life on Venus? Here's How to Interpret the Phosphine Discovery

In a paper released today in Nature Astronomy, astronomer Jane Greaves at Cardiff University and an international team of scientists announced the presence of phosphine in Venus’s atmosphere. Phosphine is considered a “biosignature”—a molecule strongly associated with the chemistry of life that has few non-life methods of production, particularly on a rocky planet like Venus. The team used two observatories—the James Clerk Maxwell Telescope (JCMT) in Hawaii and the Atacama Large Millimeter Array (ALMA) in Chile—to verify their detection.

The implications are massive: there could be life in Venus’ atmosphere. This may sound implausible, but there are regions of Venus’ upper atmosphere that are remarkably temperate and relatively hospitable. For decades there has been a hypothesis that, against the odds, microbial life forms could be floating around the planet. This detection is one piece of evidence in support of that hypothesis, but we are far from proving the existence of life.

Predictably, the news about this announcement has generated lots of breathless news coverage and claims about confirmed Venusian life on social media. These are inaccurate characterizations of the paper released today. What can we as non-scientists do to responsibly interpret this claim and not contribute to misinformation?

Let’s consider several pieces of context for evaluating the reliability—and implications—of this claim.

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We need independent confirmation

This is the first announcement of a difficult detection that required significant modeling and data analysis to tease the phosphine signal out of the noise. It’s possible the authors’ analysis contains an error or ignored important context that led to a false-positive result. Independent scientific teams must now do the work to confirm this signal.

This situation is not theoretical. In 2014, a group of highly respected cosmologists announced the detection of gravitational waves from the earliest moments of the Big Bang, making headlines across the world. Upon further study, it turned out to be misinterpreted signals from galactic dust. The team ultimately withdrew their claim.

I asked Wladimir Lyra, an astronomer at New Mexico State University who was not involved with this paper, his thoughts on the paper. “The analysis is very thorough they definitely thought hard about the data,” he said. “They did go the extra mile to lend credence to this detection, but they could still be overfitting the spectrum in deriving the abundance of phosphine,” he said, referring to the process by which the scientific team analyzed their results.

Nienke van der Marel, an astronomer from the University of Victoria, Canada, and an expert on ALMA observations of circumstellar disks, agrees that the detection with 2 facilities makes it robust, especially the higher signal-to-noise detection with ALMA. "Even if ALMA had reduction issues that led to a false detection, it would still be a big coincidence to get a JCMT noise peak at that same frequency".

Phosphine detections in Venus's atmosphere The two charts represent the detection of phosphine in Venus’s atmosphere as seen by the JCMT observatory (left) and the ALMA observatory (right). The dotted red line is the team’s analytical model for phosphine abundance. The solid red line shows the same model after processing it using the same spectral fitting used for the data. For a full discussion of these charts, see Greaves et. al. 2020. Image: Greaves et. al. 2020

As Lyra mentioned, the authors of this paper went to great lengths to validate their detection before publishing their results. Not only did they use two separate observatories, but they observed Venus at two different times (the James Maxwell Observatory in 2017 and ALMA in 2019) and detecting it on both occasions. This reduces the likelihood of a false-positive due to observation-specific errors. The team also validated their analytical process by looking for a molecule known to exist in Venus’s atmosphere, and found it. They even looked at Jupiter’s moon Callisto for phosphine and didn’t see it, as expected.

Again, this doesn’t mean the signal is real. It means that the team did solid work to verify that their signal was real, and were confident in the results to publish it. To their credit, they also shared details of their analysis and computational scripts online for the world to scrutinize. There is nothing we can do but wait for the process of science to get to work, but there appears to be no significant reason to doubt this detection at this time.

A home for life? Venus, as seen in this image captured by NASA's Mariner 10 spacecraft in 1974, was not considered a likely habitat for life due to its crushing surface pressures and extreme heat. But a possible biosignature detection in its atmosphere suggests that the search for life should take an expansive view of planetary habitability. Image: NASA / JPL / Mattias Malmer

Biosignatures do not equal life

Assuming the presence of phosphine is confirmed, the detection of a single biosignature does not mean life has been found on Venus.

Planets are complex systems that are not fully understood. Even Mars, which has been explored in greater detail than any other planet beyond Earth, has significant gaps in our understanding of its geologic history, chemistry, atmosphere, and climate. Recall that methane, a possible biosignature, was detected in Mars’s atmosphere in 2004. But follow-up observations by NASA’s Curiosity rover and the European Space Agency’s Trace Gas Orbiter yielded contradictory and inconclusive results.

Venus is far less understood than Mars. Though the planet was the recipient of the first interplanetary probe in 1962 and numerous Soviet missions in the 1970s and 1980s, only 2 missions have orbited in the last 25 years. The current scientific understanding of its surface chemistry, geologic processes, atmospheric behavior, and interaction with the interplanetary medium may lack critical pieces of information that would explain the presence of phosphines through natural processes, rather than life.

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Yet the authors systematically look at all possible methods of natural phosphine creation on Venus, such as the production by lightning, delivery by meteorites, and photochemical reactions in the atmosphere, and find that they would all produce far less phosphine than observed.

Finally, there is an off chance that there is an unknown molecule in Venus’s atmosphere with a chemical signature very similar to that of phosphine just close enough to mimic the phosphine signal at the scale of detection of the JCMT and ALMA observatories. The authors acknowledge this, and propose further observations that could help eliminate this possibility.

Ultimately, work must be done to verify these analyses and to better understand Venus itself. Right now, the best we can say is that the production of phosphine is strongly associated with life on rocky planets, and there is a candidate detection for phosphine in the atmosphere of Venus.

Listen to what the scientists say

The science team is quick to admit that they don’t know the answer to why they detected phosphine in Venus’s atmosphere. From their paper:

“If no known chemical process can explain [phosphine] 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. questions of why hypothetical organisms on Venus might make [phosphine] are also highly speculative.”

Life is just one possible explanation, and an explanation that raises its own set of difficult questions at that. This is perhaps the most critical input for how to calibrate our skepticism: how do the individuals presenting the data talk about their own discovery? Do they assert answers they cannot know, or do they present the data and acknowledge its limitations?

Reading this paper, the team appears to have made good faith efforts to verify their results, limit their own biases, and to acknowledge the range of possible answers to this detection. Their willingness to share their data and analyses openly is also a good indication of intent and desire to engage in the scientific debate that will surely commence.

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Our uncertain future of biosignature detections

If nothing else, this announcement should remind us how little we know about the cosmos. There is so much yet to figure out—no planet is ever fully explored. Even the ones right next door.

This paper makes a strong case for the detection of phosphines in Venus’s atmosphere and that an unknown process is responsible for their generation—biological or otherwise. But this is the start, not the end, of the discovery process. It may end up leading to the confirmation of life many years into the future. It may (perhaps more likely) end up establishing a novel natural pathway for generating phosphine in Venus’s atmosphere. The self-correcting process of science works at the group level—not on that of the individual. We will have a better sense of this claim in the next few years by looking at the community consensus after more data are collected and more debate occurs.

For now, it’s ok to be excited by the possibility of the unknown. Hold your celebration on the likelihood of life, though, until we have the extraordinary evidence we’d need to verify that extraordinary claim. This is not it, though it’s a compelling reason to increase our exploration of Venus.

Venus's surface from radar data This 3D image of Venus’ surface was generated using radar data from NASA’s Magellan spacecraft. The 3-kilometer-tall volcano Gula Mons can be seen on the horizon, along with the 48-kilometer-wide Cunitz crater at near-center. Image: NASA

I venture that, in the not-too-distant future, astronomers will make more detections of biosignatures in our solar system and in solar systems beyond. As the next generation of ground- and space-based telescopes come online, their immense sensitivity, combined with the ever-growing number of confirmed exoplanets, will likely unleash many exciting hints of life.

But consider: Venus is our celestial neighbor, accessible by robotic spacecraft and easily observed by telescopes. We largely know what it’s made of, what its surface looks like, and how its atmosphere behaves. Yet so much remains unexplained in light of this extraordinary new finding. At least a decade will pass before any dedicated robotic mission will arrive at Venus that could help address this question. But at least a robotic mission is a possibility.

The detection of a biosignature in the atmosphere of a distant exoplanet may forever remain ambiguous. It may be hundreds, if not thousands of light-years away far too distant for direct exploration in our lifetime or for many human lifetimes to come. How little will we know about its surface, geology, and climate? How could we possibly discern or constrain the possible types of natural processes that could result in a false signal? Or, conversely, how could we assuredly confirm a biological origin knowing next to nothing about the context from which it arose?

We may find clever solutions to these problems in time. But it’s very likely they will lag behind the discoveries themselves. In that interim, we will find ourselves in a state of excited uncertainty—the very state we find ourselves in right now, with Venus. In the midst of ambiguity, easy answers are seductive, even soothing. But they are likely wrong, or at least incomplete. We must learn to embrace the uncertainty and to resist our desires for a binary answer—life or no life?—while the process of science does its work.

A Great Debate

Some researchers are skeptical of the detection itself perhaps the signal is from another chemical masquerading as phosphine.

The paper was initially rejected by the journal Science by referees who objected to the data analysis, says Seager. But, she adds, the techniques the team used were standard to radio astronomy. (It’s worth noting that a journal rejection in and of itself arguably says little, as the list of papers rejected by prestigious journals that eventually won Nobel Prizes is rather extensive.)

Compounds typically absorb at numerous wavelengths, and together, they create a unique, recognizable chemical fingerprint. However, the team has identified phosphine by absorption at only a single wavelength — one that is also shared by sulfur dioxide.

This gives some researchers pause.

"As a geochemist, I always worry about detection from one peak," says Justin Filiberto, a geochemist at LPI. "A single line is a coincidence, not a detection," adds Kevin Zahnle, an astrobiologist at NASA Ames Research Center in Mountain View, California.

The team behind the new find agrees that more phosphine lines should be sought to confirm its presence. But they also argue they can rule out sulfur dioxide based on their current observations. If it were a signal from sulfur dioxide, they say, other spectral lines should have been present, which they did detect.

This is convincing to some. However, "I'm told there has been much skepticism, including from journal referees, about the detection," tweeted Chris Lintott , an astrophysicist at the University of Oxford and host of the BBC's program The Sky at Night. "JCMT and ALMA were not made to look at things as bright as Venus and this is a difficult observation."

But Greaves and radio astronomers Anita Richards of the University of Manchester "know JCMT and ALMA very well,” Lintott added. “Iɽ bet the detection is real."

What Phosphine Means on Venus

A biosignature is always going to create a rolling discussion that gradually homes in on a consensus. Which is to say that the recent discovery of phosphine in the upper atmosphere of Venus has inspired a major effort to figure out how phosphine could emerge abiotically. After all, the scientists behind the just published paper on the phosphine discovery seem to be saying something to the community like “We can’t come up with a solution other than life to explain this. Maybe you can.”

The ‘maybes’ are out there and they include life, but what a tough spot for life to develop, for obvious reasons, not the least of which is the hyper-acidic nature of its clouds. So let’s dig into the story a bit more. The idea of life in the cloud layers of an atmosphere has a long pedigree, even on Venus, where discussions go back at least to the 1960s. Harold Morowitz and Carl Sagan examined the matter in a paper in Science in 1967, a speculation that led them to conclude “it is by no means difficult to imagine an indigenous biology in the clouds of Venus.”

And while the temperature at Venus’ surface can reach 480° Celsius, the temperatures between 48 and 60 kilometers above the surface are relatively benign, in the range of 1° to 90° C. A team led by Jane Greaves (Cardiff University) detected the spectral signature of phosphine through observations at 1 millimeter wavelength made with the James Clerk Maxwell Telescope (JCMT) in Hawaii, later confirmed with data from the Atacama Large Millimeter Array (ALMA) observatory in Chile. The resulting paper is lengthy and judiciously written, as witness:

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. Hence a possible droplet-phase photochemical source for PH3 must be considered (even though PH3 is oxidized by sulfuric acid). Questions of why hypothetical organisms on Venus might make PH3 are also highly speculative…

And here again, the note that what we are talking about is unusual chemistry:

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. However, we have ruled out many chemical routes to PH3

Image: Artist’s impression of Venus, with an inset showing a representation of the phosphine molecules detected in the high cloud decks. Credit: ESO / M. Kornmesser / L. Calçada & NASA / JPL / Caltech. Licence type Attribution (CC BY 4.0).

Phosphine is a rare molecule, one that is made on Earth through industrial methods, although microbes that live in environments without oxygen can likewise produce it when phosphate is drawn from minerals or other sources and coupled with hydrogen. MIT researchers have previously investigated it as a potential biosignature, one of a great many studied by Sara Seager and William Bains that we’ll want to use in our investigations of exoplanet atmospheres. It’s clear, though, that no one expected to find it in the clouds of Venus. Greaves explains:

“This was an experiment made out of pure curiosity, really – taking advantage of JCMT’s powerful technology, and thinking about future instruments. I thought we’d just be able to rule out extreme scenarios, like the clouds being stuffed full of organisms. When we got the first hints of phosphine in Venus’ spectrum, it was a shock!… 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.”

The international team working on the phosphine detection has investigated everything from minerals drawn into the clouds from the surface to volcanes, lightning, even sunlight, but none of the processes examined made enough phosphine to account for the data. In fact, the abiotic methods could produce at best one ten thousandth of the amount found in the telescope data.

But what a tough place for life to persist given an atmosphere where the high clouds are about 90 percent sulphuric acid. The hostility of the Venusian environment doubles down on the question of whether there are abiotic processes we have yet to consider. Following up on the phosphine detection, a new paper from the MIT researchers homes in on the matter:

(Greaves et al. 2020) have reported the candidate spectral signature of phosphine at altitudes >

57 km in the clouds of Venus, corresponding to an abundance of tens of ppb [parts per billion]. It was previously predicted that any detectable abundance of PH3 in the atmosphere of a rocky planet would be an indicator of biological activity (Sousa-Silva et al. 2020). In this paper we show in detail that no abiotic mechanism based on our current understanding of Venus can explain the presence of

20 ppb phosphine in Venus’ clouds. If the detection is correct, then this means that our current understanding of Venus is significantly incomplete.

Image: This artistic impression depicts Venus. Astronomers at MIT, Cardiff University, and elsewhere may have observed signs of life in the atmosphere of Venus. Credit: ESO (European Space Organization)/M. Kornmesser & NASA/JPL/Caltech.

And from MIT co-author Clara Sousa-Silva, who examined phosphine as an exoplanet biosignature in a paper earlier this year, a look at the broader implications:

“A long time ago, Venus is thought to have oceans, and was probably habitable like Earth. As Venus became less hospitable, life would have had to adapt, and they could now be in this narrow envelope of the atmosphere where they can still survive. This could show that even a planet at the edge of the habitable zone could have an atmosphere with a local aerial habitable envelope.”

What a boon this finding will be to those interested in taking our eye off Mars for an astrobiological moment and looking toward the nearest terrestrial planet, for follow-up studies have to include one or more missions to Venus to study its atmosphere, perhaps including some kind of sampling and return to Earth. The MIT paper, Bains et al. as referenced below, includes both Seager and Sousa-Silva as co-authors, along with Cardiff’s Greaves, and bears a title that defines the issue: “Phosphine on Venus Cannot be Explained by Conventional Processes.”

Seager’s work on a wide range of potential biosignatures is definitive and has been examined before in these pages. Anyone interested in the broader question of how we go about defining a biosignature needs to get conversant with her “Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry,” Astrobiology, June 2016, 16(6): 465-485 (abstract).

So perhaps life, or perhaps a yet undiscovered mechanism for producing phosphine on Venus. Either way, the path forward includes an examination of a possible paradigm shift — the authors use this phrase — involving not just Venus but terrestrial planets in general. And I think we can assume that laboratory work on phosphorous chemistry is about to get a major boost.

The paper is Greaves et al., “Phosphine gas in the cloud decks of Venus,” Nature Astronomy 14 September 2020 (abstract). The MIT paper is Bains et al., “Phosphine on Venus Cannot be Explained by Conventional Processes,” submitted to Astrobiology – Special Collection: Venus (preprint). The Sousa-Silva paper on phosphine is “Phosphine as a Biosignature Gas in Exoplanet Atmospheres,” Astrobiology Vol. 20, No. 2 (31 January 2020). Abstract.

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Paul, as soon as I saw the phosphine story break yesterday, I came to Centauri Dreams to REALLY understand it, and to avoid the sensationalism. I read the Nature paper, but a lot of it was beyond my knowledge-level.

Thanks for your work, helping us amateurs make sense of the Cosmos.

What a kind thing to say! Thanks, John. I’m delighted the site is helpful and glad to have you aboard.


New evidence suggests presence of potential biosignature on closest planet to Earth.

San Francisco – September 15, 2020 – Breakthrough Initiatives, the privately-funded space science programs founded by science and technology investor and philanthropist Yuri Milner, are funding a research study into the possibility of primitive life in the clouds of Venus. The study is inspired by the discovery, announced yesterday, of the gas phosphine, considered a potential biosignature, in the planet’s atmosphere.
The science team undertaking the research will comprise world-class physicists, astronomers, astrobiologists, chemists and engineers, led by Dr. Sara Seager, Professor of Planetary Science, Physics and Aerospace Engineering at the Massachusetts Institute of Technology. The group will investigate the scientific case for life and analyze the technical challenges of an exploratory mission in the event that such evidence proves compelling.

1. Venus super impact 700 million years ago causing the
Cambrian explosion.

2. The Snowball Earth from 775 to 717 million years ago may have been caused by the global oceans on Venus being blown into space by the comet or asteroid super impact.

3. Could the Earth have been encircled with rings of material from super impacts on Venus 700 million years ago? This may be why the earth became a snowball because of the shadow of the ring from the Venus debris. This may be made of salt water and mud. the long term effect would be bring material from the impact on Venus to earths surface and atmosphere.

4. Venus panspermia If animal life such as sea worms was embedded in the material from Venus the remains would not be record till later because of the ice and scarring of earth surface by the world wide glaciers.

5. Life on Venus may have returned after the impact and possibly evolved to survive in the upper atmosphere.

6. What would be the effects of such a large impact and how orbital dynamics would transport material from the inner orbit of Venus to the earths orbit. The solar winds, flares and CME may also blast material from Venus to Earth.

It would be remarkable if the Venusian biota had identical biology to terrestrial biota, which it would have to if any fell to Earth and survived. This would imply a panspermia event and likely common origin for the life on both worlds. Given the current acidic nature of Venus atmosphere, could life have evolved a means to survive the very different environment of the oceans and teh clouds? Most likely the ocean to cloud hypothesis is a red herring. If there is life in Venus’ clouds, I would expect it to be more akin to the bacteria in earth’s clouds which have origins on the surface and are swept up. But on Venus, they would have to have evolved some form of protection from the acid. Grinspoon had suggested that the microbes reproduced and died quickly maintaining populations, back in 2018. Greaves notes that the atmosphere on Venus has a circulation model of sinking at the poles and rising at the equator. This implies that life would be drawn down to the hot depths and cooked, but the components needed would be drawn back up at the equator.
While one interpretation is that this is life, it could also be that the equator is where the phosphine is produced, either at depth or by UV sunlight, and then degrated by the acid as it circulates back to the poles, as the data indicates.

Well, I’m glad you lived before 700 million years ago, but put the earth were Venus is and what would end up with, earth panspermia to Venus. The original pre space age view of Venus was a tropical paradise and 700 to 800 years ago it may have well been that. Solar wind may have infected earth with early life and plants from oceans and land areas on Venus. I venture to guess that maybe the land areas were appearing later because of solar erosion of water being so close to the sun. The big question is when the super impact happened and as Nicky said no evidence of it, but resurfacing for 700 to 800 million years have would of wiped it out. What is needed is thousands of chip seismographs powered by diamond radioactive waste cells that land on Venus and last for years. This would give us a complete view of the interior and what may have happened in the past. The Russians have been way ahead of research and landers for Venus and launch opportunities come every 19 months with only a 4 month cruise. Hopefully more probes will be sent.

Soviet Balloon Probes May Have Seen Rain on Venus.

“Looking again at the old data Dorrington noticed that one of the balloons, from Vega 2, seemed to have reduced its leakage rate at some point, as if it had somehow repaired itself. “I thought that was funny,” he said.
An alternative explanation for why the balloons descended would have been that they got heavier, most likely from a buildup of liquid on their outer surface. Sulfuric acid could have precipitated out of Venus’ clouds in a fine mist, coating the balloons and then slowly dripping off. In the case of the Vega 2 balloon, sensors indicated that at one point the probe’s buoyancy changed quickly, on the order of a minute, which could have happened when the balloon ran into a light drizzling shower.”
“This work is credible and interesting, but speculative,” wrote planetary scientist Kevin McGouldrick of the University of Colorado, Boulder, who was not involved in the work, in an email to Wired.

Maybe the Venusian life caught a ride on the balloon “In the case of the Vega 2 balloon, sensors indicated that at one point the probe’s buoyancy changed quickly, on the order of a minute”

Regarding interesting data from the Pioneer Venus drop probes, read the following quote taken from this page:

“Some unexpected problems arose. All the temperature probes failed when sulphuric acid blocked the inlet. When it boiled off its constituents entered the instruments. The sensors did not physically break, acid films on the sensors were indicated from partial shorting of insulation while in the clouds, but this cleared as the probes descended into higher temperatures.

“These anomalous events entered the engineering and science data at the same altitude in all four probes. Anomalies included power variations, changes in the Large Probe’s transponder static phase error and receiver AGC, jumps in internal pressure and temperature readings were probably due to static discharges inside or outside the probe.

“One explanation suggested there was a reaction between the atmospheric sulphur and probe materials. Because each probe was always colder than the atmosphere, sulphur condensed on the outside of the probe pressure vessels and was carried down into the regions of higher temperatures. This generated an electrical charge. Each probe then acted as a large capacitor because parts of the probe had not been electrically bonded to avoid heat transfer. Also, titanium, though a tough material, is a poor conductor, so would act as an insulator and stop electrical charges from dissipating. One conclusion was that most of the anomalies could be explained by these unexpected electrical interactions.”

Now for some other hopefully useful online documents in our quest to see if this phosphine finding leads anywhere…

Venus Atmospheric Composition In Situ Data: A Compilation:

This great NASA book on the PV missions is here in PDF format:

There is also this relevant PV data document:

The Pioneer Venus Orbiter: 11 years of data. A laboratory for atmospheres seminar talk

Don Mitchell’s excellent site on the Soviet exploration of Venus:

Let’s assume that the PH3 has an atmospheric microbial origin. What is your best guess as to whether these little guys would be the descendants of an independent abiogenesis event on Venus as opposed to descendants of Earth-based microbes that somehow hitched a ride to our sister planet? If the hypothetical Venetian microbes were from an independent genesis, then what would this tell us, from a statistical perspective, about how common at least microbial life may be in the Universe?

If there is Venusian life and it is from a unique biogenesis independent from earth, then I would say that this makes the probability that life is common in the universe as very high, as it indicates that life does arise wherever conditions are favorable.

Unless it turns out that we are unlucky and this hypothetical life is hard to disambiguate between single or different biogeneses, then we will have an example of a different biology and double the examples of the biological space life can take. The value to industry is likely to be high, making a sample return worth the cost if there is sufficient evidence that life does exist.

Yes I’m sure the industrial military complex would love a hard shell, molecular acid for blood kind of aliens!

Recent studies have found an increased impact flux since Phanerozoic, which implies that the Venus surface age (calculated from size-frequency) is actually a lot younger than 700 Myr assumed back in the 1990s. More recent calculations place it around 200 Myr when Venus was resurfaced. Also we have no evidence in regard to a huge impact was the cause of resurfacing.

Venus’ Ancient Layered, Folded Rocks Point to Volcanic Origin.
September 17, 2020. (Or maybe sedimentary rocks!)

“Tesserae are tectonically deformed regions on the surface of Venus that are often more elevated than the surrounding landscape. They comprise about 7% of the planet’s surface, and are always the oldest feature in their immediate surroundings, dating to about 750 million years old. In a new study appearing in Geology, the researchers show that a significant portion of the tesserae have striations consistent with layering.”
“While the data we have now point to volcanic origins for the tesserae, if we were one day able to sample them and find that they are sedimentary rocks, then they would have had to have formed when the climate was very different – perhaps even Earth-like.”

Largest impact feature in the solar system is on Venus at over 8000 miles (13000 km) across.

Venus: Will private firms win the race to the fiery planet?

“The company’s CEO, Peter Beck, is fascinated by Venus and has already announced his intention to send a mission there in 2023. He’s funding and constructing it in-house.”
“Peter Beck’s message is “give me a call. If anybody wants to join the team, come join us. But, you know, the bus is leaving we’re going!”

“BREAKTHROUGH INITIATIVES” should get together with them!

Potential biosignature discovery could boost prospects of Venus missions.

“Beck said he was assembling a “pretty amazing” science team, but did not disclose with whom he was working. At the RAS briefing, Seager said she had been in discussions with Beck about a Venus mission. The spacecraft, she said, would weigh only about 15 kilograms, of which 3 kilograms would be available for a science payload. “We have to work hard to make sure an instrument that would be useful for the search for life will fit into that payload,” she said. “We’re really looking forward to it.”

So maybe they already have!

Did the Vega aerostats placed in the Venusian atmosphere by the Soviets as part of their Vega-Halley mission in 1985 detect anything that might be interpreted differently now in support of this new announcement?

Maybe I just missed it but I have not seen any mention yet about the only balloon probes sent to Venus. Note how the second link below says the Vega balloons may have detected rain. What else might they have found that we initially missed?

A detailed article on plans to get more probes to Venus. At least now they have no excuse not to be attuned to finding life signs:

As for America’s only attempt so far to directly explore Venus’ atmosphere using the four drop probes from the Pioneer Venus mission in 1978, if I remember correctly all four probes reported an increase in infrared radiation before those sensors were overloaded. Is there any correlation there? Did the PV mission detect anything we might interpret differently now?

I was completely unaware of these earlier missions. Both teh Vega and Pioneer missions had mass spectrometers, yet I don’t see any indication that they detected anything special. Do you have any data on the results to determine if they even detected the phosphine gas as one would expect if they were sensitive enough?

Not that I am aware of, nor will I pretend to you that I did an exhaustive search, either. However, this link that I also provided above has access to most if not all of the atmospheric data from the Pioneer Venus mission:

Most of the Venera landers were also designed to sample the planet’s atmosphere as they descended through it. If anyone knows where a nice one-stop-shopping spot or spots for their data might exist, please let us know.

Venus has lightning in its atmosphere. It also has many active volcanoes. Both are ingredients for supporting life, at least high in the atmosphere or deep underground. Just saying.

Feasibility Analysis and Preliminary Design of ChipSat Entry for In-situ Investigation of the Atmosphere of Venus.

“Recent miniaturization of electronics in very small, low-cost and low-power configurations suitable for use in spacecraft have inspired innovative small-scale satellite concepts, such as ChipSats, centimeter-scale satellites with a mass of a few grams. These extremely small spacecraft have the potential to usher in a new age of space science
accessibility. Due to their low ballistic coefficient, ChipSats can potentially be used in a swarm constellation for extended surveys of planetary atmospheres, providing large amounts of data with high reliability and redundancy. We present a preliminary feasibility analysis of a ChipSat planetary atmospheric entry mission with the purpose of
searching for traces of microscopic lifeforms in the atmosphere of Venus. Indeed, the lower cloud layer of the Venusian atmosphere could be a good target for searching for microbial lifeforms, due to the favourable atmospheric conditions and the presence of micron-sized sulfuric acid aerosols. A numerical model simulating the planetary entry of a spacecraft of specified geometry, applicable to any atmosphere for which sufficient atmospheric data are available, is
implemented and verified. The results are used to create a high-level design of a ChipSat mission cruising in the Venusian atmosphere at altitudes favorable for the existence of life. The paper discusses the ChipSat mission concept and considerations about the spacecraft preliminary design at system level, including the selection of a potential

Hmm, sounds like something is working towards a chip powered probe for Venusian life…

Lots of little smart probes are the future of deep space exploration.

To show just how much the paradigm of crewed versus unmanned space vessels has changed in the past four decades, read the following from this link of an interview with Dr. Sara Seager, an astrophysicist and planetary scientist at the Massachusetts Institute of Technology (MIT), discussing who, what, and how a suitably advanced species would best move through interstellar space:

“My personal opinion about life that could traverse the galaxy, if we are now talking about life that could come to Earth, or in the future, if we’re able to travel to a distant star system, is that it probably has to be nonbiological because space is very harmful for people. We can barely survive on Earth, if you think about it, and Earth is a very safe, well-designed place for us, or rather we are adapted to our environment. So I think for us initially as human beings to find life elsewhere, it’s bound to be biological, since that’s all we can see it’s all we know how to do. But if we ever think of traveling through the galaxy or of alien life coming here, then I believe on a personal level that it will be nonbiological.”

Carl Sagan predicted life on Venus in 1967. We may be close to proving him right.

So it was all the more surprising when Sagan co-authored a paper proposing we might still one day find microbial life above our sister planet. “If small amounts of minerals are stirred up to the clouds from the surface, it is by no means difficult to imagine an indigenous biology in the clouds of Venus,” he wrote in Nature in 1967 — two years before NASA landed on the moon. “While the surface conditions of Venus make the hypothesis of life there implausible, the clouds of Venus are a different story altogether.”

As Sagan pointed out, a high carbon-dioxide atmosphere was no obstacle. Up at the 50km (31-mile) layer, at the top of Venus’ clouds, conditions are actually hospitable and almost Earth-like. Organisms could thrive in the upper reaches the same way bacteria thrives around superheated, CO2-rich vents at Yellowstone. Add sunlight and water vapor to CO2, he said, and you have the recipe for that building block of life, photosynthesis.

“Sagan’s work on Venus was formative, though few today remember his impact,” says Darby Dyar, the chair of NASA’s Venus Exploration Advisory Group. “His idea was prescient, and still makes sense today: between the hellish surface conditions on present-day Venus and the near-vacuum of outer space must be a temperate region where life could live on.”

Just 11 years after Sagan made his prediction, another Venus probe discovered methane in the atmosphere — which could be considered a predictor of the presence of organic material. Scientists like Sagan were cautious about the discovery no one could prove methane meant life beyond a reasonable doubt. (We also found it on Mars in 2018, and have yet to explain that). Still, no one ever gave a reasonable alternative for why the methane might be hanging around on Venus.

Here is another paper by Sagan from 1971 titled The Trouble with Venus:

Can you repost the link to the Sagan paper? It seems truncated.

Hopefully this link works. If not, simply go to Google and type in Sagan The Trouble with Venus 1971:

I also found this other relevant paper from 1971 where Sagan was a consultant:

I also recommend the BBC’s “Sky at Night” episode that was a a prepublication exclusive interview with Greaves and Bains. Bains was particularly informative about the issues of life surviving in a sulfuric acid atmosphere and showed that terrestrial plants with waxy cuticles can withstand the extremely corrosive effect of the acid.

The question however is that this sort of protection must be available for bacterial organisms that can float in the clouds (unless there is some complex plant or animal that has gas bags to do the same).

The first issue is experimental – is teh signal and artifact or some sort of algorithm error? I think the team have done a lot of work to eliminate both, but follow up is necessary.
Is the identification in error? So far they seem to have eliminated other compounds, but this is where I might be concerned – a misidentification. But again, so far no one has indicated this is a likely error.
Bains was careful to not rule out some form of abiotic chemistry, but maybe there is a route that they missed. What is important is that phosphine is rapidly degraded by sulfuric acid, so it must be produced copiously. The assumption is biotic production, but this is a Sherlock Holmes deduction “After eliminating the impossible….”.

If it is life, the atmosphere must be preventing and sinks for key biological elements. Carbon is not a problem, nor sulfur. But what about other needed elements? A sink could slowly wind down the resource. On Earth, phosphorus is one such element that is limiting. Would it be the same on Venus, requiring some sort of injection of new material to ensure that phosphine can be produced by hypothetical organisms?

If nothing else, this finding should invigorate studies of the Venusian atmosphere and chemisty, as well as possibly prioritizing a mission to the atmosphere to do some sampling of the material, including looking for other biosignatures.

The Venusian atmosphere has oxidized forms of sulfur (sulfur dioxide SO2 and sulfur trioxide SO3) as well as a reduced form (hydrogen sulfide H2S). Now phospine (PH3) has been found.

I have read that no abiotic process has been found such as from lightning or sunlight, but what about hydrogen from the solar wind? That could provide a continuous effect of reducing both sulfur oxides and phosphorus oxides.

The extended figure 7 of the paper include the reduction of phosphorus oxides with hydrogen. Unless the solar wind is increasing production by 4 orders of magnitude over their assumed production rates, then this route seems unlikely. Any mechanism also has to account for the change in PH3 signal strength from the equator (high) to the poles (not measurable) – wouldn’t the solar wind generate reactions at the poles too, albeit lower?

Well, they do mention the solar wind once, but dismiss its possible effects because they assume it’s impossible for the solar wind hydrogen to move down to the cloud height.

Measurements taken over a number of years would be nice. If the phosphine level changes with the solar cycle, that would be interesting.

And the phosphine level being undetectable at the poles doesn’t disprove the solar wind hypothesis. The collection of the solar wind *should* decrease with latitude. And if there’s a rate limited oxidation reaction, the amount of solar wind collection would have to be higher than the rate limit to become detectable.

You are saying that since venus has no protective magnetic field, that solar protons might penetrate sufficiently to drive up the rates of PH3 production to mimic the levels claimed to be observed? Would other species in the upper atmosphere or clouds reacting with the protons also be present that are detectable by spectroscopy also be present to confirm or falsify this hypothesis?

@Randy Chung I think you’re on one possible right track there.
The detected presence of small amounts of methane on Venus could also be created via such hydrogen as you suggest.

Phosphine can also be created from volcanic sources, the process require a temperature of over 200C which indeed is found on Venus.

Anyway I’d like to see the detection of Phosphine by a second science team, it’s a rule of thumb that any unusual detection should been done by more than one research group before it’s treated as fact.

The reason they haven’t found any abiotic means for Venus is probably because… they didn’t look very hard and they didn’t talk to people who have studied these things for years. Note that there is not a single Venus person on these papers. Today David Catling mentioned some abiotic routes they did not consider, and I’m sure others will come about. Then there are problem with the data analysis, claiming 15 sigma detections in the abstract and showing 1 sigma in the plots of the main paper, the way they deal with the line broadening, the wings, etc. More than one person has pointed out that one normally obtains lines at two different frequencies to try to confirm your candidate since there are so many overlapping lines. They didn’t wait for that observation. I think this may be a great motivator for future Venus in-situ exploration, but I’m not convinced by these papers that this is life or even a detection of PH3. But now people are busy thinking harder about this, and we can hope for some follow up results in the coming year or years.

Do you have a link for the Catling critique? I cannot find one on Google.

Thank you for trying. Those are the same references I found. However only the Forbes article may be relevant but I refuse to whitelist a business magazine for science opinions.

My initial criticisms were mostly misplaced. It came from only reading the main Nature Astronomy paper. To fully understand their approach one MUST also read the Supplementary Materials and the recently submitted Astrobiology paper ( Note that the title of the latter may seem a bit provocative, but reading it through the word “Conventional” takes on an important meaning.
There are a number of supporting papers to consider as well before criticizing fully:

This in some ways points to the poor formatting of journals like Nature Astronomy. We are past the days of print editions. Let’s go to a normal journal format so that we can get away from hiding much of the relevant information in the Supplementary Materials, while also putting many of the important figures in odd places (often at the end) rather than embedded with the text.

Recent papers have suggested that Venus could have habitable until 2 billion years ago. If this is the case, then Venus could quite easily had life on it–even if only through bolide transfer from Earth.

As Venus entered its full greenhouse phase, it would have snuffed out its lifeforms with the remainder having to adapt to more and more extreme environments until now the last species cling on in the sulphuric acid clouds.

So the idea seems quite probable.

That’s a good point, and it suggests an interesting experiment. With most missions to search for life, we have to assume it has a completely unknown biochemistry. But if Venus life descends from Earth, even billions of years ago, it should have ribosomes and ribosomal RNA and be amenable to a simple environmental PCR survey.

If a larger body of genetic sequence could be read and the data transmitted back to Earth, this information could likely be used right away to synthesize new enzymes – of immense and immediate value to industry.

I just had another thought on this matter. The environment of this postulated Venus lifeform is an anoxic, CO2 saturated, sulphuric solution, which is similar to certain volcanic springs here on earth. A search of such springs might turn up an analog.

The fact that many scientists act so much more aggressive (“teach astrobiologists chemistry”, “phosphine shitstorm”) towards PH3-life association on Venus than seasonal CH4-life association on Mars is probably that it is so much more conceivable if life had existed on Mars than on Venus.

Despite 20ppb PH3 is making a much stronger case than seasonal methane, the conceivability of life is so much lower on Venus that possibly a taboo is forming around this topic now.

I’m trying to dig through some of the findings from the Venus missions, especially the Vega ballons. It seems that phosphorus was detected, but assumed to be H2PO3. None reported PH3 as expected as this is a novel detection.

But given the instruments used, why has PH3 not been detected previously? Both spectra and mass spectrometry have been used, yet neither resulted in a reported detection of PH3. Is this due to better instruments or simply looking for the nonobvious?

Previous missions have detected an unspecified absorbtion of UV light, attributed to particles if undetermined composition. If organic, that would be interesting.

What interests me is what instruments would we deploy on a probe that would confirm the detection of PH3 in the atmosphere given apparent past failures, and extend the data to try to detect other biosignature molecules or even organisms, much like the plume experiments for Europa that are planned.

One aspect I’m curious about is the equilibrium with PH4+ … my understanding is that phosphine is remarkably resistant to protonation, such that PH4+ might have a pH of -14 or so. But Venus’ atmosphere is something akin to fuming sulfuric acid … I haven’t tracked down what its effective pH might be estimated to be. I have no idea how it would be reaching this environment as a salt, but can we rule it out?

abiotic process generating phosphine :

Preparation and occurrence
Phosphine may be prepared in a variety of ways.[10] Industrially it can be made by the reaction of white phosphorus with sodium or potassium hydroxide, producing potassium or sodium hypophosphite as a by-product.

3 KOH + P4 + 3 H2O → 3 KH2PO2 + PH3
Alternatively, the acid-catalyzed disproportioning of white phosphorus yields phosphoric acid and phosphine. Both routes have industrial significance the acid route is the preferred method if further reaction of the phosphine to substituted phosphines is needed. The acid route requires purification and pressurizing. It can also be made (as described above) by the hydrolysis of a metal phosphide, such as aluminium phosphide or calcium phosphide. Pure samples of phosphine, free from P2H4, may be prepared using the action of potassium hydroxide on phosphonium iodide (PH4I).

Laboratory routes
It is prepared in the laboratory by disproportionation of phosphorous acid[11]

4 H3PO3 → PH3 + 3 H3PO4
Phosphine evolution occurs at around 200 °C. Alternative methods involve the hydrolysis of aluminium phosphide, calcium phosphide, and tris(trimethylsilyl)phosphine.

Here’s a related New Scientist article from 2002 discussing the observation of other chemicals in disequilibrium in Venus’ atmosphere (carbon monoxide, hydrogen sulphide and carbonyl sulphide) which are also difficult to explain:

Good catch. Also, I think that André Brack quoted in the article is wrong:

“For life, you need a volume of water, not just tiny droplets.”

We know that bacteria are alive in terrestrial clouds and even into teh stratosphere. They are important as seeds to start droplet formation. Whatever the objections to Schulze-Makuch’s hypothesis may be, I don’t believe Brack’s objection is valid any longer.

The phosphine may have come from an ocean and water over two billion years ago when Venus was still in the life belt since the Sun was a considerable percent less bright in the distant past. There could be phosphine deep inside the crust which is rereleased through volcanism.

The phosphine in Venus atmosphere can’t be made today by life because there is no place life could exist for long there. Life would not stay at the same altitude in Venus atmosphere with the right temperature because of the Hadley type convention cells which would cause the air to move up too high drop back down lower into a too hot area, but that does not matter anyway because there is very little water vapor in Venus atmosphere which makes it impossible for life to live there or phosphine to be made. I have to conclude that the phosphine was made long ago when Venus had water and oceans which have long since evaporated from the increased brightness of the Sun over time. Phosphine on Earth has to be dissolved with water first to be released from the rocks before it can be used by life or plants in the water and “phosphine cycles.”

The Hadley cell was a nagging question in my mind — looking at it appears that unlike Earth which has three, Venus has just one set of convection cells going all the way from equator to pole. I would have thought that life swept to the poles would be checkmated, since it has to return at lower altitude … but according to the graphic on page 4 (I ought to track down Goldstein, 1989) the return from pole to equator is still above 70 km — if anything, still a little chilly! On the other hand Wikipedia’s article adds some material about a lower Hadley cell, cold polar collars at 60-70 degrees latitude with (continual?) upwelling of adiabatically cooled air, clouds at 72 km, also the polar vortex … it turns out the science of another planet’s atmosphere isn’t that easy for a non-meteorologist to work out. :) But the scientists at the press conference thought life could survive in the planet’s circulation, and from a first glance at what’s known it seems more plausible than I’d have imagined.

Well, if my goal was to suggest I had more to learn about the meteorology the above accomplished it… the first cell I was looking at was between day and night sides of the planet and shouldn’t be confused with a Hadley cell. Nonetheless, there are routes by which suspended organisms could escape searing heat, perhaps often enough to allow their propagation.

Great article, Paul!
It will be good to see some more interest in Venus, going forward, if only to honor and finally catch up with the heroic efforts of Soviet scientists and engineers of the Venera and Vega projects in the seventies and eighties.
I believe it is unlikely that we will see a sample return, though, as that would require bringing a full sized rocket to Venus. The much lower escape velocities of the moon and even Mars make a return plausible, but Venus is well beyond reach in my opinion.

Would a balloon delivery system to the edge of space carrying some Venusian surface samples make the difference between needing a powerful rocket for escape velocity or a much smaller one that can be carried by said balloon? Get the balloon high enough so it can reach a return vehicle in a very low orbit around Venus.

Either that or place a biolab on the planet and perform the analysis right there. Certainly we have improved since the Viking biolab days, as impressive as those instruments were.

Venus sample return mission revisited

Edition 4 dated: July 9, 2019

An abiotic source of phosphine would likely be as exotic as exolife, something like the way LGM-1 turned out to be the first neutron star.

I’m always bothered by the adjectives that describe life as surviving, even thriving, in unimaginably “tough” environments. Those critters know nothing other than their environment which, akin to our 1atm,

70°F habitant is often a pleasant, sometimes not, always variable, survivable ecotone. In fact, I think they are geniuses in their environment. Venusian microbes — or life anywhere if it exists — are no doubt sturdy enough to survive the pH levels, pressure, radiation levels, chemistry etc. they evolved in a “tough environment” is relative. As either Wainwright or LL Bean said “there’s no such thing as bad weather, only unsuitable clothing.” In astrobiology, this might be recast as “there’s no such thing as a tough environment, only unsuitable genes.” And not to beat a dead microbe, but if you drag a Snailfish up from 26,000 feet below the surface of the ocean where it is in equilibrium, it will find our environment “tough.”

The Cool Worlds video by David Kipping on the subject, and the Event Horizon video by John Michael Godier.

It migth seem that one or more of the Three Chinese Curses are operative:
May you live in interesting times
May you be recognized by people in high places
May you find what you’re looking for

Isn’t the real problem on Venus the extreme lack of water, also in its atmosphere (as G. Hillend also remarks)? Hence, making a biotic cycle unlikely.
But ‘fossil’ phosphine remaining from very early Venusian life would be almost as great a discovery.
The question is: can phosphine of early biotic origin stay in the Venusian atmosphere this long>

We should do a sample return from the Venusian atmosphere. It’s time to stop using indirect means and just go for the jugular. And that also applies to the Europan and Enceladus atmospheres.

But are any of these starting compounds and the reaction conditions present on Venus, even at or below the surface. For example, your first reaction requires pure, white phosphorus. On Earth, this has to be extracted from phosphorus containing compounds. Perhaps the hot conditions on Venus will allow phosphorus to be separated.

What your argument does suggest is that the PH3 probably originated below the clouds. As with Geoffrey Hillend’s suggestion of fossil PH3, the origin of the gas could be distinguished from biotic processes in the clouds by a sampling at various depths in the atmosphere. This might falsify the hypotheses of the various origin sources – cloud biotic or abiotic UV production vs production or fossil emissions at or below the surface. If atmosphere production was falsified, that would falsify the biotic hypothesis too.

Apparently the Russians are now all worked up again to start exploring Venus, with some even claiming it is a “Russian planet”:

Already they seem to be forgetting this joint mission plan with the US from just over one year ago:

“Can life survive a star’s death? Webb telescope can reveal the answer”
When stars like our sun die, all that remains is an exposed core—a white dwarf. A planet orbiting a white dwarf presents a promising opportunity to determine if life can survive the death of its star, according to Cornell University researchers.
In a study published in the Astrophysical Journal Letters, they show how NASA’s upcoming James Webb Space Telescope could find signatures of life on Earth-like planets orbiting white dwarfs.

A planet orbiting a small star produces strong atmospheric signals when it passes in front, or “transits,” its host star. White dwarfs push this to the extreme: They are 100 times smaller than our sun, almost as small as Earth, affording astronomers a rare opportunity to characterize rocky planets.

In A Complete Fluke, A European Spacecraft Is About To Fly Past Venus – And Could Look For Signs Of Life

September 16, 2020, 10:49 am EDT

Earlier this week, scientists announced the discovery of phosphine on Venus, a potential signature of life. Now, in an amazing coincidence, a European and Japanese spacecraft is about to fly past the planet – and could confirm the discovery.

On Monday, September 14, a team of scientists said they had found evidence for phosphine in the atmosphere of Venus. The region in which it was found, about 50 kilometers above the surface, is outside the harsh conditions on the Venusian surface, and could be a habitat for airborne microbes.

To find out for sure, we will need to send a mission into the Venusian atmosphere to look for such life. Several proposals are on the table, with the closest being a spacecraft from the U.S. company Rocket Lab that could send a probe into the atmosphere as soon as 2023.

BepiColombo, launched in 2018, is on its way to enter orbit around Mercury, the innermost planet of the Solar System. But to achieve that it plans to use two flybys of Venus to slow itself down, one on October 15, 2020, and another on August 10, 2021.

The teams running the spacecraft already had plans to observe Venus during the flyby. But now, based on this detection of phosphine from telescopes on Earth, they are now planning to use both of these flybys to look for phosphine using an instrument on the spacecraft.

“We possibly could detect phosphine,” says ESA’s Johannes Benkhoff, BepiColombo’s Project Scientist. “But we do not know if our instrument is sensitive enough.”

The instrument on the European side of the mission, called MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer), is designed to study the composition of the surface of Mercury. However, the team believe they can also use it to study the atmospheric composition of Venus during both flybys.

On this first flyby, the spacecraft will get no closer than 10,000 kilometers from Venus. That’s very far, but potentially still close enough to make a detection.

“There actually is something in the spectral range of MERTIS,” says Jörn Helbert from the German Aerospace Center, co-lead on the MERTIS instrument. “So we are now seeing if our sensitivity is good enough to do observations.”

As this first flyby is only weeks away, however, the observation campaign of the spacecraft is already set in stone, making the chance of a discovery slim. More promising is the second flyby next year, which will not only give the team more time to prepare, but also approach just 550 kilometers from Venus.

“[On the first flyby] we have to get very, very lucky,” says Helbert . “On the second one, we only have to get very lucky. But it’s really at the limit of what we can do.”

If a detection can be made, it would provide independent verification of the presence of phosphine in the atmosphere of Venus. And for future missions planning to visit the planet, which alongside Rocket Lab’s mission includes potential spacecraft from NASA, India, Russia, and Europe, that could be vital information.

Even if the first flyby is unsuccessful in detecting phosphine, the team plan to use lessons learned to revise their observations for the second flyby. And it just might be that this mission, in a happy coincedence, could contribute to a major scientific discovery before it even reaches its intended target.

“It’s kind of perfect timing,” says Helbert . “Now [the flyby] is even more exciting.”

We need to go to Venus as soon as possible

Answering questions about the possibility of life there will require not one but several new missions that can directly study the planet.

There is also the idea of exotic photo chemistry, the abiotic phosphine produced by photo dissociation of molecules like hydrogen sulfide and chemical recombination which would need some phosphorus high in the atmosphere.

I like Allex Tolley’s idea about measuring the chemistry at different altitudes. Another probe to Venus with a good mass spectrometer would work. We could land it in a deep crater and then use an x ray spectrometer to look at the rocks in the crater if it is possible to make an x ray spectrometer that won’t break in the high temperature and pressure on the surface of Venus. I don’t think a laser spectrometer like the one in Curiosity rover will be effective in such a thick atmosphere. Maybe we could increase the power or use a high frequency, ultra violet laser to burn rock and take the spectra of the sparks or light coming from the rock. The goal would be to get the spectra of a deep excavation with the hope that we could see any water bearing geology that proves there was running water or oceans in the past like calcite and hematite etc or sandstone. We also might find phosphine and phosphorus. It might also help us to know if the all of crust has been completely recycled so landing several probes in different locations, the craters and highlands to help us confirm our theories about the geology of Venus.

A scientific paper offered the conjecture that Venus had a habitable surface environment as recently as 200 million years ago (can’t find the link at the moment). As pure speculation, if life was present and evolved on Venus at a similar rate as on Earth, a complex ecological system, presumably with advanced plant and animal life, would have been present. Presumably some sort of fossil record may not be extant that could be discovered with suitable surface rovers.

Said rovers could maintain a relatively cool internal environment through a combination of super insulation and mechanical refrigeration. Such refrigeration, working against a huge thermal gradient, would need a great deal of power. Where could that power come from? One possibility is via microwave power from several orbiting satellites or, if the winds permit, cables hung from balloons-born solar panels. Admittedly highly speculative but visually interesting.

As a last bit of speculation, there would be a non-zero possibility that intelligent life may have evolved. That intelligent life may have visited Earth at a time when only single cell life forms existed. Having found it all rather boring, the Venusians decided to mix thing up a little and triggered the Cambrian explosion of life forms! Should be good enough for a sci-fi story.

Sadly, I expect that the phosphine gas brouhaha to go the way of those martian meteorites but I want to believe…

Forgot to mention that upon learning of the discovery of phosphine gas in the Venusian atmosphere that may be a biosignature, my first thought was to check Centuri Dreams for the real lowdown. Was not disappointed!

Thank you, Patient Observer!

In 2003, Geoffrey Landis suggested that H2S in the atmosphere of Venus could be of biological origin ( ) because H2S should react with SO2. Here we are next door on the periodic table, same conundrum, same explanation.

If life *were* generally hoarding hydrogen, might there be considerably more of the element hidden in the atmosphere of Venus than we imagine?

What about the transits of Venus across the Sun? On June 8, 2004 and again on June 6, 2012 Venus transited the Sun and according to Wikipedia spectrographic studies where done of the atmosphere of Venus.

Observation of the atmosphere of Venus simultaneously from Earth-based telescopes and from the Venus Express spacecraft. This gave a better opportunity to understand the intermediate level of Venus’s atmosphere than is possible from either viewpoint alone, and should provide new information about the climate of the planet.

Spectrographic study of the atmosphere of Venus. The results of analysis of the well-understood atmosphere of Venus will be compared with studies of exoplanets with atmospheres that are unknown.

The Hubble Space Telescope used the Moon as a mirror to study the light reflected from Venus to determine the makeup of its atmosphere. This may provide another technique to study exoplanets.

So has has anyone looked for Phosphine in the results?

The current conditions in the cloud cover of Venus would indeed be a very “tough place” for life to evolve. However, if the hypothetical lifeforms living in these clouds had descended from life that evolved on a much younger, and much more hospitable (from our perspective) Venus, then it would not be without precedent to suggest that this life could have evolved adaptive traits over the millions/billions of years since then that could allow such life to survive in the hellish conditions of the contemporary Venusian climate. We have seen on our own planet that life, once evolved, is incredibly robust. There are entire ecosystems sustained by sulfide vents in the abysmal depths of Earth’s oceans, a place where they must endure conditions not so terribly different from those in the Venusian cloud habitat, such as temperatures above the boiling point of water, extremely high pressure, and very high acidity (pH < 3 in some cases), to name a few. So, I personally do not find it to be such a far-fetched notion that some particularly hardy microbes could live quite comfortably in the Venusian cloudscape. Looking forward to watching this discovery unfold!

If terrestrial creatures can live around geothermal vents in the deep ocean, or boiling hot sulfur springs, or under miles of solid rock, or in the water tanks of nuclear reactors, then I think the high clouds of Venus could be their version of the Bahamas in comparison.

I want to join praising Paul Gilster in such exquisite work over the years turning Centauri Dreams to the site for no-nonsense information about space and interstellar matter that such breaking news like phosphine in the Venusian atmosphere make people check what is the opinion of other closely knowledgeable in the subject matter. Despite I’m no longer actively here I tend to turn back for good reading and checking the comments.

Although I’m in believe this is result of living organisms I remind myself all such news in the past have turned out to be explained by natural processes that we weren’t aware of. Take the discovery of pulsars and the notion it’s Little Green Men, thus LGM-1 designation to very first such discovery.

On lighter tone I would like to greet our Venusian overlords, microbial or not.

Yes, it would be an interesting meeting! Thank you, Dmitri, for the kind words. I’m glad you’ve found the site useful and I’ll try to keep it that way.

I think the phosphine could come from a phosphine telluride reaction, tellerium is suspected of building up around volcanoes due to the tempeture been about right forming the gas phosphine.

If there is life on Venus, how could it have got there? Origin of life experts explain

September 20, 2020 3.42pm EDT

Bacteria on the ISS survive the perils of space for three years

Three years in space wasn’t enough to kill a hardy radiation-resistant bacterium, suggesting bacteria may be able to travel between planets.

Again, we humans may think of Venus as a form of hell for life, but for some organisms it may contain enough of the ingredients to maintain certain creatures in relative comfort long enough to keep reproducing. We are only just starting to figure this out.

EPSC2020: Parker Solar Probe, Akatsuki and Earth-bound observers give rare top-to surface glimpse of Venus

Akatsuki observations of Venus at the time of the Parker Solar Probe flyby. These observations sampled the upper atmosphere at roughly 70 km altitude above the surface. Credit: JAXA, Planet-C

Observations of Venus by NASA’s Parker Solar Probe, JAXA’s Akatsuki mission and astronomers around the world have given a rare cloud-top-to-surface glimpse of the Earth’s neighbouring planet. The results are being presented this week at the Europlanet Science Congress (EPSC) 2020, which is taking place as a virtual meeting from 21 September – 9 October.

On 11 July 2020, the Parker Solar Probe, which is travelling to the inner Solar System to catch particles of the outer atmosphere of the Sun, completed the third of a series of flybys of Venus. From 19 June to 18 July, astronomers and members of the Akatsuki science team joined forces to support the probe’s encounter through a coordinated campaign of observations. The ground-based observations were contributed largely by amateur astronomers.

A similar campaign will be carried out to support the flyby of Venus by ESA’s BepiColombo mission on 15 October 2020.

“The campaign has resulted in multiple, multi-level observations right from the surface to the cloud-tops and airglow phenomena, which have given us unique insights into Venus’s atmosphere,” said Ricardo Hueso, a former member of ESA’s Venus Express mission and coordinator of the amateur participation. “The opportunity to observe Venus with so many instruments and with such a large collaboration means that we can enhance the scientific value of these short visits by the Parker Solar Probe and BepiColombo to Venus.”

A Precursor Balloon Mission for Venusian Astrobiology [IMA]

A Precursor Balloon Mission for Venusian Astrobiology

Andreas M. Hein, Manasvi Lingam, T. Marshall Eubanks, Adam Hibberd, Dan Fries, William Paul Blase

The recent detection of phosphine in the atmosphere of Venus has reignited interest in the possibility of life aloft in this environment. If the cloud decks of Venus are indeed an abode of life, it should reside in the “habitable zone” between

60 km altitude, roughly coincident with the middle cloud deck, where the temperature and pressure (but not the atmospheric composition) are similar to conditions at the Earth’s surface.

We outline a precursor astrobiological mission to search for such putative lifeforms in situ with instrument balloons, which could be delivered to Venus via launch opportunities in 2022-2023. This mission would collect aerosol and dust samples on small balloons floating in the Venusian cloud deck and directly scrutinize whether they include any apparent biological materials and, if so, their shapes, sizes and motility.

Our balloon mission would also be equipped with a miniature mass spectrometer that ought to permit the detection of complex organic molecules. The mission is augmented by contextual cameras that will be used to search for macroscopic signs of life in the Venusian atmospheric habitable zone.

Finally, mass and power constraints permitting, radio interferometric determinations of the motion of the balloons in Venusian winds, together with in situ temperature and pressure measurements, will provide valuable insight into the poorly understood meteorology of the middle cloud region.

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM) Earth and Planetary Astrophysics (astro-ph.EP) Space Physics (

Cite as: arXiv:2009.11826 [astro-ph.IM]
(or arXiv:2009.11826v1 [astro-ph.IM] for this version)

From: Andreas M. Hein [view email]

[v1] Thu, 24 Sep 2020 17:18:27 UTC (3,579 KB)

Is Phosphine in the Mass Spectra from Venus’ Clouds?

Rakesh Mogul, Sanjay S. Limaye, M. J. Way, Jamie A. Cordova Jr
Considering the implications of the reported single spectral line detection of phosphine (PH3) by Greaves et al., we were inspired to re-examine data obtained from the Pioneer-Venus Large Probe Neutral Mass Spectrometer (LNMS) to search for evidence of phosphorus compounds. The LNMS obtained masses of neutral gases (and their fragments) at different altitudes within Venus’ clouds.

Published mass spectral data correspond to gases at altitudes of 50-60 km, or within the lower and middle clouds of Venus – which has been identified as a potential habitable. We find that LMNS data support the presence of phosphine although, the origins of phosphine remain unknown.

Comments: <1200 words, 1 figure

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:2009.12758 [astro-ph.EP]
(or arXiv:2009.12758v1 [astro-ph.EP] for this version)

From: Rakesh Mogul [view email]

[v1] Sun, 27 Sep 2020 06:18:01 UTC (478 KB)

Translation: The Pioneer Venus Large drop probe detected phosphine in the atmosphere of Venus back in December of 1978. Its origin is still unknown, however.

Yes this is super interesting and your updates are enjoyable reading.

Here are a few links that may be of interest, I need to catch up on them too (wasn’t too well for a week when this news broke)

Phosphine on Venus Cannot be Explained by Conventional Processes

A Precursor Balloon Mission for Venusian Astrobiology

Might active volcanisms today contribute to the presence of phosphine in Venus’s atmosphere?

On The Biomass Required To Produce Phosphine Detected In The Cloud Decks Of Venus

Feasibility Analysis and Preliminary Design of ChipSat Entry for In-situ Investigation of the Atmosphere of Venus

Transfer of Life Between Earth and Venus with Planet-Grazing Asteroids

Detection of simplest amino acid glycine in the atmosphere of the Venus

Arijit Manna, Sabyasachi Pal, Mangal Hazra

Amino acids are considered to be prime ingredients in chemistry, leading to life. Glycine is the simplest amino acid and most commonly found in animal proteins. It is a glucogenic and non-essential amino acid that is produced naturally by the living body and plays a key role in the creation of several other important bio-compounds and proteins.

We report the spectroscopic detection of the presence of the simplest amino acid glycine (NH2CH2COOH) with transition J=13(13,1)󈝸(12,0) at ν=261.87 GHz (16.7σ statistical significance) with column density N(glycine)=7.8×1012 cm−2, in the atmosphere of the solar planet Venus using the Atacama Large Millimeter/submillimeter Array (ALMA).

Its detection in the atmosphere of Venus might be one of the keys to understand the formation mechanisms of prebiotic molecules in the atmosphere of Venus. The upper atmosphere of Venus may be going through nearly the same biological method as Earth billions of years ago.

Comments: 14 pages, 4 figures, submitted in Science

Subjects: Earth and Planetary Astrophysics (astro-ph.EP) Biological Physics (

Cite as: arXiv:2010.06211 [astro-ph.EP]
(or arXiv:2010.06211v1 [astro-ph.EP] for this version)

From: Sabyasachi Pal Dr. [view email]

[v1] Tue, 13 Oct 2020 07:35:56 UTC (879 KB)

A stringent upper limit of the PH3 abundance at the cloud top of Venus

T. Encrenaz (1), T. K. Greathouse (2), E. Marcq (3), T. Widemann (1), B. Bézard (1), T. Fouchet (1), R. Giles (2), H. Sagawa (4), J. Greaves (5), C. Sousa-Silva (6) ((1) LESIA, Observatoire de Paris, PSL Université, CNRS, Sorbonne Université, Université de Paris, (2) SwRI, (3) LATMOS/IPSL, UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, (4) Kyoto Sanyo University, (5) School of Physics and Astronomy, Cardiff University, (6) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology)

Following the announcement of the detection of phosphine (PH3) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the infrared range.

Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO2 and H2O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm−1 where a PH3 transition is present.

From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-σ upper limit of 5 ppbv for the PH3 mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths.

Our result brings a strong constraint on the maximum PH3 abundance at the cloud top and in the lower mesosphere of Venus.

Comments: Astronomy & Astrophysics, in press

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:2010.07817 [astro-ph.EP]
(or arXiv:2010.07817v1 [astro-ph.EP] for this version)

From: Bruno Bézard [view email]

[v1] Thu, 15 Oct 2020 15:11:37 UTC (805 KB)

Portuguese astrophysicist Clara Sousa-Silva involved in possible discovery of life on Venus

By Lurdes C. da Silva / O Jornal editor

Posted Sep 24, 2020 at 5:19 PM

“Understanding the heavens without having to go there… it’s like a super-power.”

BOSTON – Clara Sousa-Silva was only 12 years old when she decided to become an astrophysicist, while watching a solar eclipse with her parents, who explained step-by-step what she was about to see and precisely at what time.

“I could not believe that we, as a species, could predict the movement of the heavens like that,” she says. “I have always liked the idea of understanding the heavens without having to go there. It’s like a super-power… and I wanted it.”

Today, the 33-year-old Porto native is a molecular astrophysicist at Massachusetts Institute of Technology (MIT) and a member of the international team of astronomers who recently discovered with powerful telescopes signs of what might be life in the clouds of the planet Venus.

According to a study published last week in the journal Nature Astronomy, scientists at MIT, Cardiff University in Wales and other prestigious institutions detected the chemical phosphine near the top of the acidic clouds that blanket Venus. This rare molecule could be produced by living organisms.

“I think discovering any potential bio signature on a habitable planet is very exciting. Discovering a biosignature on our nearest planet is even more exciting,” Sousa-Silva told O Jornal. “Finally, discovering phosphine on Venus, when phosphine has no known non-biological production pathways on rocky planets, is really, really significant.”

In fact, her goal has been to find a habitable or inhabited planet by identifying every relevant molecule contributing to its biosphere. She uses quantum physics and computer calculations to create molecular “fingerprints” that allow scientists to detect remote gases on extrasolar planet atmospheres — particularly gases that are associated with life.

“I have dedicated my career to phosphine and it is wonderful to see that work be useful for such a grand discovery,” Sousa-Silva said. “I like understanding how the molecules that life produces interact with light, and I love that we can detect that behavior from thousands and thousands of miles away.”

Sousa-Silva arrived in the United States in 2016 to join MIT as a postdoc researcher. Last year, she became the co-director of the Harvard-MIT Science Research Mentoring Program. In this capacity, she organizes and manages an outreach program where high school students do a year-long independent research project under the guidance of astrophysics.

She also enjoys being a science communicator, giving numerous lectures and presentations.

“Science is only as good as the audience it reaches,” Sousa-Silva said. “I like feeling like I am contributing to making the scientific community more inclusive, and more interesting, and that’s why I enjoy science communication.”

Sousa-Silva left Portugal at age 18 to pursue an integrated Bachelor’s and Master’s Degree in Physics and Astronomy at the Scotland University of Edinburgh.

In 2015, she received a Ph.D. in Molecular Astrophysics from the University College London in the United Kingdom.

“If we ever want to understand worlds beyond our own, we need to have access to a complex toolkit of data and models,” Sousa-Silva said. “It’s my goal to be able to unambiguously detect an alien biosphere from Earth, and without quantum chemistry that would be impossible.”

But she will not jump to any conclusions when asked if someday we will be able to communicate with alien life forms.

“Hah. No. Not in any relevant way,” Sousa-Silva said. “I believe life is inevitable and, if it happens on Earth, it likely happened elsewhere, but I don’t necessarily believe that intelligent alien life exists.”

“Until we understand how we develop an advanced consciousness on Earth, I will not be attempting to figure out how common such life is in the universe,” she concluded.

This group from the Netherlands is out to trash Dr. Clara Sousa-Silva quantum physics and computer calculations to create molecular “fingerprints” for phosphine in the clouds of Venus. Hmm…

Re-analysis of the 267-GHz ALMA observations of Venus: No statistically significant detection of phosphine.

Astrochemist brings search for extraterrestrial life to Center for Astrophysics

Clara Sousa-Silva explores telltale biosignature gases on other planets

n September, a team of astronomers announced a breathtaking finding: They had detected a molecule called phosphine high in the clouds of Venus, possibly indicating evidence of life.

That discovery shook the scientific establishment. Once thought of as Earth’s twin, Venus — though nearby and rocky — is now known to have a hellish environment, with a thick atmosphere that traps solar radiation, cranking surface temperatures high enough to melt metal, and accompanied by surface pressure akin to that thousands of feet below Earth’s ocean surface.

But the detection, led by researchers from Cardiff University in Wales, the Massachusetts Institute of Technology, and the University of Manchester in England, was high in the atmosphere, where conditions are far more hospitable and the idea of microbial life more plausible. It was accomplished using spectroscopy, a method of determining the presence of different molecules in a planet’s atmosphere by analyzing how those molecules alter the light reflected from the planet.

A key member of the team was fellow Clara Sousa-Silva, who had spent years studying the molecule’s spectroscopic signature and who believes that phosphine is a promising way to track the presence of extraterrestrial life.

Sousa-Silva shifted her fellowship from MIT to the Center for Astrophysics | Harvard & Smithsonian and will spend the next two years advancing her work on biosignatures and life on other planets. She spoke with the Gazette about the recent discovery and what the future of the search for life may hold.

GAZETTE: Folks like you will be helping answer an interesting question in the decades to come: whether life is something rare or whether it’s not really that rare after all. It seems the thinking on that has been shifting in recent decades.

SOUSA-SILVA: I do like that the shift is happening and that people are thinking that life is more common. I’m hoping that shift will go so far as thinking that life is not that special. It’s just an inevitable occurrence in a variety of contexts. If it can appear in places as different as Earth and Venus, which are at first glance similar because of their size and location but otherwise very different, then it must be extremely common because it would be the height of hubris to think that only the solar system can have life, but it has arisen twice in totally different environments.

That seems really implausible. The sun is average, rocky planets are extremely common, the molecular cloud that formed the solar system was not special. Life on Earth came to be in a huge diversity of forms, and life changed Earth’s atmosphere many times. We only have one planet where we know life existed, but Earth has been many planets, which is something an astronomer colleague of mine, Sarah Rugheimer, likes to say. We have quite a lot of data points that basically show that life is pretty good at making itself happen in many ways throughout history.

Complications In The ALMA Detection Of Phosphine At Venus

Posted January 26, 2021 12:23 AM

Recently published ALMA observations suggest the presence of 20 ppb PH3 in the upper clouds of Venus. This is an unexpected result, as PH3 does not have a readily apparent source and should be rapidly photochemically destroyed according to our current understanding of Venus atmospheric chemistry.

While the reported PH3 spectral line at 266.94 GHz is nearly co-located with an SO2 spectral line, the non-detection of stronger SO2 lines in the wideband ALMA data is used to rule out SO2 as the origin of the feature. We present a reassessment of wideband and narrowband datasets derived from these ALMA observations.

The ALMA observations are re-reduced following both the initial and revised calibration procedures discussed by the authors of the original study. We also investigate the phenomenon of apparent spectral line dilution over varying spatial scales resulting from the ALMA antenna configuration. A 266.94 GHz spectral feature is apparent in the narrowband data using the initial calibration procedures, but this same feature can not be identified following calibration revisions.

The feature is also not reproduced in the wideband data. While the SO2 spectral line is not observed at 257.54 GHz in the ALMA wideband data, our dilution simulations suggest that SO2 abundances greater than the previously suggested 10 ppb limit would also not be detected by ALMA. Additional millimeter, sub-millimeter, and infrared observations of Venus should be undertaken to further investigate the possibility of PH3 in the Venus atmosphere.

What Is Phosphine and Why Does It Point to Extra-Terrestrial Life Floating in the Clouds of Venus?

This artistic impression depicts our Solar System neighbour Venus, where scientists have confirmed the detection of phosphine molecules. The molecules were detected in the Venusian high clouds in data from the James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array, in which ESO is a partner.
Astronomers have speculated for decades that life could exist in Venus’s high clouds. The detection of phosphine could point to such extra-terrestrial “aerial” life. Credit: ESO/M. Kornmesser & NASA/JPL/Caltech

An international team of astronomers recently 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. Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes — floating free of the scorching surface but needing to tolerate very high acidity. 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!” says team leader Jane Greaves of Cardiff University in the UK, who first spotted signs of phosphine in observations from the James Clerk Maxwell Telescope (JCMT), operated by the East Asian Observatory, in Hawaii. Confirming their discovery required using 45 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, a more sensitive telescope in which the European Southern Observatory (ESO) is a partner. Both facilities observed Venus at a wavelength of about 1 millimeter, much longer than the human eye can see — only telescopes at high altitude can detect it effectively.

On September 14, 2020, an international team of astronomers announced the discovery of a rare molecule — phosphine — in the clouds of Venus. This detection could point to extra-terrestrial “aerial” life in the Venusian atmosphere. Watch our summary of the discovery. Credit: ESO

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.

This new image from ALMA, the Atacama Large Millimeter/submillimeter Array in which ESO is a partner, shows planet Venus. Rather than a real feature on the planet, the patchiness of the disc may be due to the response of the interferometer to the very bright emission from Venus, which makes it hard to sample the largest scales accurately. Credit: ALMA (ESO/NAOJ/NRAO), Greaves et al.

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.

This artistic illustration depicts the Venusian surface and atmosphere, as well as phosphine molecules. These molecules float in the windblown clouds of Venus at altitudes of 55 to 80km, absorbing some of the millimeter waves that are produced at lower altitudes. They were detected in Venus’s high clouds in data from the James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array, in which ESO is a partner. Credit: ESO/M. Kornmesser/L. Calçada

While the discovery of phosphine in Venus’s clouds came as a surprise, the researchers are confident in their detection. “To our great relief, the conditions were good at ALMA for follow-up observations while Venus was at a suitable angle to Earth. Processing the data was tricky, though, as ALMA isn’t usually looking for very subtle effects in very bright objects like Venus,” says team member Anita Richards of the UK ALMA Regional Centre and the University of Manchester. “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,” adds Greaves, who led the study published today in Nature Astronomy.

Another team member, Clara Sousa Silva of the Massachusetts Institute of Technology in the US, has investigated 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.”

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. As molecules of phosphine float in the high clouds of Venus, they absorb some of the millimeter waves that are produced at lower altitudes. When observing the planet in the millimeter wavelength range, astronomers can pick up this phosphine absorption signature in their data, as a dip in the light from the planet. Credit: ALMA (ESO/NAOJ/NRAO), Greaves et al. & JCMT (East Asian Observatory)

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. Although the high clouds of Venus have temperatures up to a pleasant 30 degrees Celsius, they are incredibly acidic — around 90% sulphuric acid — posing major issues for any microbes trying to survive there.

This artistic impression depicts our Solar System neighbour Venus, where scientists have confirmed the detection of phosphine molecules, a representation of which is shown in the inset. The molecules were detected in the Venusian high clouds in data from the James Clerk Maxwell Telescope and the Atacama Large Millimeter/submillimeter Array, in which ESO is a partner. Astronomers have speculated for decades that life could exist in Venus’s high clouds. The detection of phosphine could point to such extra-terrestrial “aerial” life. Credit: ESO/M. Kornmesser/L. Calçada & NASA/JPL/Caltech

ESO astronomer and ALMA European Operations Manager Leonardo Testi, who did not participate in the new study, says: “The non-biological production of phosphine on Venus is excluded by our current understanding of phosphine chemistry in rocky planets’ atmospheres. Confirming the existence of life on Venus’s atmosphere would be a major breakthrough for astrobiology thus, it is essential to follow-up on this exciting result with theoretical and observational studies to exclude the possibility that phosphine on rocky planets may also have a chemical origin different than on Earth.”

More observations of Venus and of rocky planets outside our Solar System, including with ESO’s forthcoming Extremely Large Telescope, may help gather clues on how phosphine can originate on them and contribute to the search for signs of life beyond Earth.

For more on this discovery on SciTechDaily, see:

More information
This research was presented in the paper “Phosphine Gas in the Cloud Decks of Venus” published in Nature Astronomy.

The team is composed of Jane S. Greaves (School of Physics & Astronomy, Cardiff University, UK [Cardiff]), Anita M. S. Richards (Jodrell Bank Centre for Astrophysics, The University of Manchester, UK), William Bains (Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, USA [MIT]), Paul Rimmer (Department of Earth Sciences and Cavendish Astrophysics, University of Cambridge and MRC Laboratory of Molecular Biology, Cambridge, UK), Hideo Sagawa (Department of Astrophysics and Atmospheric Science, Kyoto Sangyo University, Japan), David L. Clements (Department of Physics, Imperial College London, UK [Imperial]), Sara Seager (MIT), Janusz J. Petkowski (MIT), Clara Sousa-Silva (MIT), Sukrit Ranjan (MIT), Emily Drabek-Maunder (Cardiff and Royal Observatory Greenwich, London, UK), Helen J. Fraser (School of Physical Sciences, The Open University, Milton Keynes, UK), Annabel Cartwright (Cardiff), Ingo Mueller-Wodarg (Imperial), Zhuchang Zhan (MIT), Per Friberg (EAO/JCMT), Iain Coulson (EAO/JCMT), E’lisa Lee (EAO/JCMT) and Jim Hoge (EAO/JCMT).

An accompanying paper by some of team members, titled “The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere,” was published in Astrobiology in August 2020. Another related study by some of the same authors, “Phosphine as a Biosignature Gas in Exoplanet Atmospheres,” was published in Astrobiology in January 2020.

“Phosphine gas in the cloud decks of Venus” by Jane S. Greaves, Anita M. S. Richards, William Bains, Paul B. Rimmer, Hideo Sagawa, David L. Clements, Sara Seager, Janusz J. Petkowski, Clara Sousa-Silva, Sukrit Ranjan, Emily Drabek-Maunder, Helen J. Fraser, Annabel Cartwright, Ingo Mueller-Wodarg, Zhuchang Zhan, Per Friberg, Iain Coulson, E’lisa Lee and Jim Hoge, 14 September 2020, Nature Astronomy.
DOI: 10.1038/s41550-020-1174-4

“The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere” by Sara Seager, Janusz J. Petkowski, Peter Gao, William Bains, Noelle C. Bryan, Sukrit Ranjan and Jane Greaves, 13 August 2020, Astrobiology.
DOI: 10.1089/ast.2020.2244
“Phosphine as a Biosignature Gas in Exoplanet Atmospheres” by Clara Sousa-Silva, Sara Seager, Sukrit Ranjan, Janusz Jurand Petkowski, Zhuchang Zhan, Renyu Hu and William Bains, 22 November 2019, Astrobiology.
DOI: 10.1089/ast.2018.1954

The European Southern Observatory (ESO) is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-meter Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky.”

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

With a diameter of 15m (50 feet) the James Clerk Maxwell Telescope (JCMT) is the largest single dish astronomical telescope in the world designed specifically to operate in the submillimeter wavelength region of the electromagnetic spectrum. The JCMT is used to study our Solar System, interstellar and circumstellar dust and gas, evolved stars, and distant galaxies. It is situated in the science reserve of Maunakea, Hawai?i, at an altitude of 4092m (13 425 feet). The JCMT is operated by the East Asian Observatory on behalf of NAOJ ASIAA KASI CAMS as well as the National Key R&D Program of China. Additional funding support is provided by the STFC and participating universities in the UK and Canada.

Gaseous signs of life on Venus aren't seen in follow-up observations

By Matthew Rozsa
Published October 28, 2020 7:08PM (EDT)

Computer illustration of a view across the rocky surface of the planet Venus, showing clouds of sulphuric acid obscuring the Sun. (Getty Images)


Last month, the science world was stunned and excited when Nature Astronomy published a paper indicating that the atmosphere of Venus appeared to contain trace amounts of phosphine, a gas associated with anaerobic bacteria on Earth that would be near-impossible to produce in any other fashion on Venus. If other scientific studies continued to confirm the report's findings, that could mean that there is life in Venus' clouds.

Now, two subsequent scientific investigations question the evidence on whether phosphine — and perhaps life — resides in the Venusian atmosphere.

Scientists study the Venusian atmosphere by analyzing spectra, or plots of light emanating from the planet, and analyzing the wavelengths. Because different molecules produce different wavelengths when light shines through them, scientists can ascertain chemical compositions of various substances using this method. Whenever looking at spectral data, there is the risk that "noise" — meaning, any variable that could alter the wavelengths for reasons unrelated to the composition of the chemical compounds studied — can cause inaccurate results. Notably, the phosphine spectrum from Venus was faint to begin with.

According to one paper in the scientific journal Astronomy & Astrophysics, written by Thérèse Encrenaz of the Paris Observatory and her colleagues, archived data from an infrared spectrograph in Hawaii called TEXES did not find any indication of phosphine in their data collected between 2012 and 2015. However, the TEXES spectrographic data looked at the cloud tops of Venus, while the original paper claiming phosphine appears in the upper atmosphere analyzed a lower part of the atmosphere, below the cloud tops.

While this does not automatically disprove that phosphine exists in the atmosphere, it opens up logistical questions about how it would move around Venus' atmosphere.

Another paper submitted to Astronomy & Astrophysics that calls into question the evidence for Venusian phosphine was posted online just last week. Authored by astrophysicist Ignas Snellen from Leiden University in the Netherlands and his colleagues, the paper analyzed the same data from the ALMA telescope array in Chile that scientists initially used to find evidence of phosphine on Venus. After reducing the noise, they too concluded that "the presented analysis does not provide a solid basis to infer the presence of PH3 in the Venus atmosphere."

Though the phosphine discovery is not disproven, these findings certainly put a damper on the exciting prospect of life on the second planet from the sun. Likewise, such scientific call-and-responses epitomize how good research is done.

"It's exactly how science should work," Paul Byrne, a planetary scientist at North Carolina State University in Raleigh, told Science News. "It's too early to say one way or the other what this detection means for Venus."

Clara Sousa-Silva, an astrochemist at the Harvard-Smithsonian Center for Astrophysics, expressed a similar view to Science News, telling the publication that having the findings challenged "is completely normal and what I expected (nay, hoped) would happen. This is usually a phase of a project that I enjoy, and I am hoping people will realize this is just what science looks like."

When Salon spoke last month with a planetary scientist who studies Venus, he also observed that the news about possible phosphine was auspicious regardless of whether it would be later verified.

"Personally I find it exciting," Noam Izenberg, a planetary scientist at Johns Hopkins Applied Physics Laboratory and deputy chair of NASA's Venus Exploration Analysis Group, wrote to Salon. "The Venus science community is about as energized as I've seen it in well over a decade. Whether or not this specific finding is verified or falsified by follow up investigations, it drives us to learn and know more. It highlights how much we don't know about Venus, and that fundamental new discoveries, possibly relevant to and reflective of the history of our own planet, await us next door."

Matthew Rozsa

Matthew Rozsa is a staff writer for Salon. He holds an MA in History from Rutgers University-Newark and is ABD in his PhD program in History at Lehigh University. His work has appeared in Mic, Quartz and MSNBC.

Scientists spot potential sign of life in Venus atmosphere

An international team of astronomers has detected a rare molecule in the atmosphere of Venus that could be produced by living organisms, according to a study published Monday. The discovery instantly puts the brightest planet in the night sky back into the conversation about where to search for extraterrestrial life.

The researchers made clear this is not a direct detection of life on Venus. But the astronomical observations confirmed the highly intriguing presence of the chemical phosphine near the top of the acidic clouds that blanket the planet.

Phosphine is a simple molecule produced on Earth by bacteria and through industrial processes. As a result, it is on the list of molecules — oxygen being another — considered by scientists to be potential “biosignatures” of life on Earth-sized planets whose atmospheres can be viewed through telescopes.

The researchers said they know of no non-biological explanation for the relatively high abundance of the molecule in the Venusian atmosphere.

“We did our very best to show what else would be causing phosphine in the abundance we found on Venus. And we found nothing. We found nothing close,” said Clara Sousa-Silva, a molecular astrophysicist at the Massachusetts Institute of Technology and a co-author of the paper published Monday in the journal Nature Astronomy.

Venus is broiling at the surface, but there are layers of the atmosphere where temperatures and pressures are moderate and where solar radiation isn’t too intense. For decades, some planetary scientists have speculated that microbes could be circulating in the atmosphere, which is dominated by sulfuric acid and carbon dioxide and has only small traces of water vapor.

Venus has long been overshadowed by Mars as a potential abode of life, because the planet’s dense atmosphere and proximity to the sun has led to a runaway greenhouse effect, resulting in hellish surface temperatures and crushing atmospheric pressures. Robotic probes have revealed a landscape that appears inhospitable to any imaginable life form.

Mars has always appeared more congenial to life and potential human exploration, and has been targeted by multiple robotic missions, including most recently NASA’s Mars 2020 rover, Perseverance. NASA is pondering proposals for two relatively low-cost robotic missions to Venus, but they have not been approved. Monday’s announcement could push NASA and other space agencies to take a closer look at Venus.

“For something this big, we need follow-up confirmations, we need to have strong scientific debate,” said Casey Dreier, senior space policy adviser at the Planetary Society, a nonprofit pro-space organization that was not involved in the new research. “Ultimately, we’re going to need missions to Venus, and maybe even bringing samples back to Earth.”

Sarah Stewart Johnson, a planetary scientist at Georgetown University who also was not involved with the new study, echoed that sentiment in an email: “This is exactly the kind of anomalous finding we should be following up on. There may be things we’re missing photochemically — that we simply don’t understand — but it’s possible that the phosphine is the result of a biotic process, and its detection surely increases the chances for life.”

A new dawn for Venus exploration?

Thirty-one years have elapsed since the United States last sent a dedicated mission to Venus. That could soon change as NASA considers two of four missions in the late 2020s targeting Venus. One, called VERITAS, would carry a powerful radar to peer through the thick clouds and return unprecedented high-resolution images of the surface. The other, DAVINCI+, would plunge through the atmosphere, sampling the air as it descended, perhaps even able to sniff any phosphine present. NASA plans to pick at least one mission in April 2021.

I have argued before for a return to Venus, and will continue to do so. Even without this latest scientific discovery, Venus is a compelling exploration target, with tantalizing evidence that the planet once had oceans and perhaps even suffered a hellish fate at the hands of its own volcanic eruptions.

But with the detection of a potential biomarker in Venus’ atmosphere, we now have yet another major reason to return to the world ancient Greek astronomers called Phosphorus — a name for Venus that, it turns out, is wonderfully prescient.

This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts.

Paul K. Byrne does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.