Centauri Dreams

Keith Cooper’s The Contact Paradox is as thoroughgoing a look at the issues involved in SETI as I have seen in any one volume. After I finished it, I wrote to Keith, a Centauri Dreams contributor from way back, and we began a series of dialogues on SETI and other matters, the first of which ran here last February as Exploring the Contact Paradox. Below is a second installment of our exchanges, which were slowed by external factors at my end, but the correspondence continues. What can we infer from human traits about possible contact with an extraterrestrial culture? And how would we evaluate its level of intelligence? Keith is working on a new book involving both the Cosmic Microwave Background and quantum gravity, the research into which will likewise figure into our future musings that will include SETI but go even further afield.

Keith, in our last dialogue I mentioned a factor you singled out in your book The Contact Paradox as hugely significant in our consideration of SETI and possible contact scenarios. Let me quote you again: “Understanding altruism may ultimately be the single most significant factor in our quest to make contact with other intelligent life in the Universe.”

I think this is exactly right, but the reasons may not be apparent unless we take the statement apart. So let’s start today by talking about altruism before we explore the question of ‘deep time’ and how our species sees itself in the cosmos. I think we have ramifications here for how we deal not only with extraterrestrial contact but issues within our own civilization.

I’m puzzled by the seemingly ready acceptance of the notion that any extraterrestrial civilization will be altruistic or it could not have survived. Perhaps it’s true, but it seems anthropocentric given our lack of knowledge of any life beyond Earth. What, then, did you mean with your statement, and why is understanding altruism a key to our perception of contact?

• Keith Cooper

I think so much that is integral to SETI comes down to our assumptions about altruism. How often do we hear that an older extraterrestrial society will be altruistic, as though it’s the end result of some kind of evolutionary trajectory. But there’s several problems with this. One is that the person making such claims – usually an astrophysicist straying into areas outside their field of expertise – is often conflating ‘altruism’ with ‘being nice’.

And sure, maybe aliens are nice. I kind of get the logic, even though it’s faulty. The argument is that if they are still around then they must have abandoned war long ago, otherwise they would have destroyed themselves by now, ergo they must be peaceful.

And it’s entirely possible, I suppose, that a civilisation may have developed in that direction. In The Better Angels of Our Nature, Steven Pinker attempted to argue that our civilization is becoming more peaceable over time, although Pinker’s analysis and conclusions have been called into question by numerous academics.

• Paul Gilster

I hope so. I think the notion is facile at best.

• Keith Cooper

It’s what human societies should always aim for, I truly believe that, but whether we can achieve it or not is another question. When it comes to SETI, we seem to home in on the most simplistic definitions of what an extraterrestrial society might be like – ‘they’ve survived this long, they must be peaceful’. A xenophobic civilization might be at peace with its own species, but malevolent towards life on other planets. A planet could be at peace, but that peace could be implemented by some 1984-style dystopian dictatorship where nobody is free. Neither of which is particularly ‘nice’, and we could think of many other scenarios, too.

Nevertheless, this myth of wise, kindly aliens has grown up around SETI – that was the expectation, 60 years ago, that ET would be pouring resources into powerful beacons to make it easy for us to detect them. To transmit far and wide across the Galaxy, and to maintain those transmissions for centuries, millennia, maybe even millions of years, would require huge amounts of resources. When we consider that the aliens may not even know for sure whether they share the Universe with other life, it’s a huge gamble on their part to sacrifice so much time and energy in trying to communicate with others in the Universe.

If we look at what altruism really is, and how that may play into the likelihood that ET will want to beam messages across the Galaxy given the cost in time and energy, then it poses a big problem for SETI. ET really needs to help us out – to display a remarkable degree of selfless altruism towards us – by plowing all those resources into transmitting signals that we’ll be able to detect.

One of the forms that altruism can take in nature is kin selection. We can see how this has evolved: lifeforms want to ensure that their genes are passed on to later generations, so a parent will act to protect and give the greatest possible advantage to their child, or nieces and nephews. That’s a form of altruism predicated by genes, not ethics. Unless some form of extreme panspermia has been at play, alien life would not be our kin, so they would be unlikely to show us altruistic behaviour of this type.

• Paul Gilster

But we haven’t exhausted all the forms altruism might take. Is there an expectation of mutual benefit that points in that direction?

• Keith Cooper

Okay, so what about quid pro quo? That’s a form of reciprocal altruism. Consider, though, the time and distance separating the stars. It could take centuries or millennia for a message to reach a destination, and there’s no guarantee that anyone is going to hear that message, nor that they will send a reply. That’s a long time to wait for a return on an investment, if there even is a return. Why plow so many resources into transmitting if that’s the case? What’s in it for them?

So if kin selection and reciprocal altruism are not really tailored for interstellar communication, then it seems more unlikely that we will hear from aliens. Of course, there is always the possibility of exceptions to the rule, one-off reasons why a society might wish to broadcast its existence. Maybe ET wants to transmit a religious gospel to the stars to convert us all. Maybe they are about to go extinct and want to send one last hurrah into the Universe. But these would not be global reasons, and we shouldn’t expect alien societies to make it easy for us to discover them.

• Paul Gilster

Good point. Why indeed should they want us to discover them? I can think of reasons a society might decide to broadcast its existence to the stars, though I admit that it’s a bit of a strain. But aliens are alien, right? So let’s assume some may want to do this. I like your mention of reciprocal altruism, as it’s conceivable that an urge to spread knowledge, for example, might result in a SETI beacon of some kind that points to an information resource, the fabled Encyclopedia Galactica. What a gorgeous dream that something like that might be out there.

Curiosity leads where curiosity leads. I wonder if it’s a universal trait of intelligence?

• Keith Cooper

It’s interesting that you describe the Encyclopedia Galactica as a ‘dream’, because I think that’s exactly what it is, a fantasy that we’ve imagined without any strong rationale other than falling back on this outdated idea that aliens are going to act with selfless altruism. As David Brin argues, if you pump all your knowledge into space freely, what do you have left to barter with? And yet it is expectations such as receiving an Encyclopedia Galactica that still drive SETI and influence the kinds of signals that we search for. I really do think SETI needs to move on from this quaint idea. But I digress.

• Paul Gilster

It’s certainly worth keeping up the SETI effort just to see what happens, especially when it’s privately funded. But I want to circle back around. I’ve always had an interest in what the general public’s reaction to the idea of extraterrestrial civilization really is. In the 16 years that I’ve been writing about this and talking to people, I’ve found a truly lopsided percentage that believe as a matter of course that an advanced civilization will be infinitely better than our own. This plays to a perceived disdain for human culture and a faith in a more beneficent alternative, even if it has to come from elsewhere to set right our fallen nature.

Put that way, it does sound a bit religious, but so what — I’m talking about how human beings react to an idea. Humans construct narratives, some of them scientific, some of them not.

I’m also talking about the general public, not people in the interstellar community, or scientists actively working on these matters. As you would imagine with COVID about, I’m not making many talks these days, but when I was fairly active, I’d always ask audiences of lay people what they thought of intelligent aliens. The reaction was almost always along two lines: 1) The idea used to seem crazy, but now we know it’s not. And 2) it would be something like an European Renaissance all over again if we made contact, because they would have so much to teach us.

A golden age, with its Dantes and Shakespeares and Leonardos. Or think of the explosion of Chinese culture and innovation in the Tang Dynasty, or Meiji Japan, all this propelled by the infusion not of recovered ancient literature and teaching, as in the European example, but materials discovered in the evidently limitless databanks of the Encyclopedia Galactica.

I ran into these audience reactions so frequently in both talks to interested audiences and just conversations among neighbors and friends that I had to ask what was propelling the Hollywood tradition of scary movies about alien invasion? What about Independence Day, with its monstrous ships crushing the life out of our planet? So I would ask, if you believe all this altruistic stuff, why do you keep going to these sensational movies of death and destruction?

The answer: Because people think they’re fun. They’re a good diversion, a comic book tale, a late night horror movie where getting scared is the point. Whole film franchises are built around the idea that fear is addictive when experienced within the cocoon of a home or theater. Thus the wave of horror fiction that has been so prominent in recent years. It’s because people like being scared, and the reason for that goes a lot deeper into psychiatry than I would know how to go. I admit I may not believe in Cthulhu, but I love going to Dunwich with H. P. Lovecraft.

Keith, as we both know — and you, as the author of The Contact Paradox would know a lot more about this than I do — there is an active lobby against messaging to the stars: METI. I’ve expressed my own opposition to METI on many an occasion in these pages, and the discussion has always been robust and contentious, with the evidently minority position being that we should hold back on such broadcasts unless we reach international consensus, and the majority position being that it doesn’t matter because sufficiently intelligent aliens already know about us anyway.

I don’t want to re-litigate any of that here. Rather, I just want to note that if the anti-METI position gets loud pushback in the interstellar community, it gets even louder pushback among the general public. In my talks, bringing up the dangers of METI invariably causes people to accuse me of taking films like Independence Day too seriously. From what I can see from my own experience, most people think ETI may be out there but assume that if it ever shows up on our doorstep, it will represent a refined, sophisticated, and peaceful culture.

I don’t buy that idea, but I’m so used to seeing it in print that I was startled to read this in James Trefil and Michael Summers’ recent book Imagined Life. The two first tell a tale:

Two hikers in the mountains encounter an obviously hungry grizzly bear. One of the hikers starts to shed his backpack. The other says, “What are you doing? You can’t run faster than that bear.”

“I don’t have to run faster than the bear — I just have to run faster than you.”

Natural selection doesn’t select for bonhomie or moral hair-splitting. The one whose genes will survive in the above encounter is the faster runner. Trefil and Summers go on:

So what does this tell us about the types of life forms that will develop on Goldilocks worlds? We’re afraid that the answer isn’t very encouraging, for the most likely outcome is that they will probably be no more gentle and kind than Homo Sapiens. Looking at the history of our species and the disappearance of over 20 species of hominids that have been discovered in the fossil record, we cannot assume we will encounter an advanced technological species that is more peaceful than we are. Anyone we find out there will most likely be no more moral or less warlike that we are…

That doesn’t mean any ETI we find will try to destroy us, but it does give me pause when contemplating the platitudes of the original The Day the Earth Stood Still movie, for example. It’s so easy to point to our obvious flaws as humans, but the more likely encounter with ETI, if we ever meet them face to face, will probably be deeply enigmatic and perhaps never truly understood. I also argue that there is no reason to assume that individual members of a given species will not have as much variation between them as do individual humans.

It’s a long way from Francis of Assisi to Joseph Goebbels, but both were human. So what happens, Keith, if we do get a SETI signal one day. And then, a few days later, another one that says, “Disregard that first message. The one you want to talk to is me?”

• Keith Cooper

I’m hesitant to rely too closely on comparisons with ourselves and our own evolution, since ultimately we are just a sample of one, and we could be atypical for all we know. I see what Trefil and Summers are saying, but equally I could imagine a world, perhaps with a hostile environment, where species have to work together to survive. Instead of survival of the fittest, it becomes survival of those who cooperate. And suppose intelligent life evolves to be post-biological. What role do evolutionary hangovers play then?

I think the most we can say is that we don’t know, but that for me is enough of a reason to be cautious both about the assumptions we make in SETI, and about the possible consequences of METI.

But you’re right about our flawed assumption that aliens will exist in a monolithic culture. Unless there’s some kind of hive mind or network, there will likely be variation and dissonance, and different members of their species may have different reactions to us.

If we detected two beacons in the same system, I think that would be great! Why? Because it would give us more information about them than a single signal would. Since we will have no knowledge of their language, their culture, their history or their biology, being able to understand their message in even the most general sense is going to be exceptionally difficult.

So, if we detect a signal, we might not be able to decipher it or learn a great deal. But if we detect two different, competing beacons from the same planet, or planetary system, then we will know something about them that we couldn’t know from just one unintelligible signal, which is that they are not necessarily a monolithic culture, and that their society may contain some dissonance, and this may influence how, and if, we respond to their messages.

For me, the name of the game is information. Learn as much about them as we can before we embark on making contact, because the more we know, then the less likely we are to be surprised, or to make a misunderstanding that could be catastrophic.

• Paul Gilster

Just so. But there, you see, is the reason why I think we have to be a lot more judicious about METI. It’s just conceivable that, to them as well as us, content matters.

But look, I see you’re headed in a direction I wanted to go. If information is the name of the game, then information theory is going to play a mighty role in our investigations. So it’s no surprise that you dwell on the matter in The Contact Paradox. Here we’re in the domain of Claude Shannon at Bell Laboratories in the 1940s, but of course signal content analysis applies across the whole spectrum of information transmittal. Shannon entropy measures disorder in information, which is a way of saying that it lets us analyze communications quantitatively.

Do you know Stephen Baxter’s story “Turing’s Apple?” Here a brief signal is detected by a station on the far side of the Moon, no more than a second-long pulse that repeats roughly once a year. It comes from a source 6500 light years from Earth, and Baxter delightfully presents it as a ‘Benford beacon,’ after the work Jim and Greg Benford have done on the economics of extraterrestrial signaling and the understanding that instead of a strong, continuous signal, we’re more likely to find something more like a lighthouse that sweeps its beam around the galaxy, in this case on the galactic plane where the bulk of the stars are to be found.

Baxter’s story sees the SETI detection as a confirmation rather than a shock, a point I’m glad to see emerging, since I think the idea of extraterrestrial intelligence is widely understood. No great revolution in thought follows, but rather a deepening acceptance of the fact that we’re not alone.

Anyway, in the story, the signal is investigated, six pulses being gathered over six years, with the discovery that this ETI uses something like wavelength division multiplexing, dividing the signal into sections packed with data. Scientists turn to Zipf graphing to tackle the problem of interpretation – as you present this in your book, Keith, this means breaking the message into components and going to work on the relative frequency of appearance of these components. From this they deduce that the signal is packed with information, but what are its elements?

Shannon entropy analysis looks for the relationships between signal elements, so how likely is it that a particular element will follow another particular element? Entropy levels can be deduced – how likely are not just pairs of elements to appear, but triples of elements? In English, for example, how likely is it that we might find a G following an I and an N? Dolphin languages get as high as fourth-order entropy by this analysis, as you know. Humans get up to eighth or ninth. Baxter’s signal analysts come up with a Shannon entropy in the range of 30 for ETI.

Let me quote this bit, because I love the idea:

“The entropy level breaks our assessment routines… It is information, but much more complex than any human language. It might be like English sentences with a fantastically convoluted structure – triple or quadruple negatives, overlapping clauses, tense changes… Or triple entendres, or quadruples.”

We’re in challenging territory here. In the story, ETI is a lot smarter than us, based on Shannon entropy. The presence of this kind of complexity in a signal, in Baxter’s scenario, is evidence that the detected message could not have been meant for us, because if it were, the broadcasting civilization would have ‘dumbed it down’ to make it accessible. Instead, humanity has found a signal that demonstrates the yawning gap between humanity and a culture that may be millions of years old. If we find something like this, it’s likely we would never be able to figure it out.

Would something like this be a message, or perhaps a program? If we did decode it, what would it mean? An ever better question: What might it do? Baxter’s story is so ingenious that I don’t want to give away its ending, but suffice it to say that impersonal forces may fall well outside our conventional ideas of ‘friendly’ vs. ‘hostile’ when it comes to bringing meaning to the cosmos.

But let’s wrap back around to Shannon and Zipf, and the SETI Institute’s Laurance Doyle, to whom you talked as you worked on The Contact Paradox. Doyle told you that communication complexity invariably tells us something about the cultural complexity of the beings that sent the message. And I think the great point that he makes is that the best way to approach a possible signal is by studying how communications systems work right here on Earth. Thus Claude Shannon, who started working out his theories during World War II, gets applied to the question of species intelligence (dolphins vs. humans) and now to hypothetical alien signals.

In a broader sense, we’re exploring what intelligence is. Does intelligence mean technology, or are technological societies a subset of all the intelligent but non-tool making cultures out there? SETI specifically targets technology, which may itself be a rarity even in a universe awash with forms of life with high Shannon entropy in communications they make only among themselves.

A great benefit of SETI is that it is teaching us just how much we don’t know. Thus the recent Breakthrough Listen breakdown of their findings, which extends the data analysis to a much wider catalog of stars by a factor of 220, all at various distances and all within the ‘field of view,’ so to speak, of the antennae at Green Bank and Parkes. Still more recent work at the Murchison Widefield Array tackles an even vaster starfield. Still no detections, but we’re getting a sense of what is not there in terms of Arecibo-like signals aimed intentionally at us.

So how do you react to the idea that, in the absence of information to analyze from an actual technological signal, we will always be doing no more than collecting data about a continually frustrating ‘great silence?’ Because SETI can’t ever claim to have proven there is no one there.

• Keith Cooper

That’s one of my unspoken worries about SETI; how long do we give it before we start to suspect that we’re alone? People might say, well, we’ve been searching for 60 years now – surely that’s long enough? Of course, modern SETI may be 60 years old, but we’ve certainly not accrued 60 years’ worth of detailed SETI searches. We’ve barely scratched the tip of the iceberg bobbing up above the cosmic waters.

So how long until we can safely say we’ve not only seen the tip of the iceberg, but that we’ve also taken a deep dive to the bottom of it as well? Maybe our limited human attention spans will come into play long before then, and we’ll get bored and give up. I think we can also be too quick to assume that there’s no one out there. Take the recent re-analysis of Breakthrough Listen data, which prompted one of the researchers, Bart Wlodarczyk-Sroka of the University of Manchester, to declare:

“We now know that fewer than one in 1600 stars closer than about 330 light years host transmitters just a few times more powerful than the strongest radar we have here on Earth. Inhabited worlds with much more powerful transmitters than we can currently produce must be rarer still.”

Except that we don’t know that at all. All we can say was that there was no one transmitting a radio signal during the brief time that Breakthrough was listening. We could have easily missed a Benford Beacon, for instance. It’s a problem of expectation versus reality – we expect these powerful, omnipresent beacons, and when we don’t find them we jump to the conclusion that ET must not exist, rather than the possibility that our expectation is flawed.

The Encyclopedia Galactic is a similar kind of expectation that isn’t just a fanciful notion, but is a concept that actively influences SETI – we expect ET to be blasting out this guide to the cosmos, so we tailor SETI to look for that kind of signal, rather than something like a Benford Beacon. It also biases our thinking as to what we might gain from first contact – all this knowledge given to us by peaceful, selflessly altruistic beings. It would be lovely if true, but I think it’s dangerous to expect it.

Case in point: Brian McConnell recently wrote on Centauri Dreams about his concept for an Interstellar Communication Relay – basically a way of disseminating the data detected within a received signal, giving everybody the chance to try and decipher it [see What If SETI Finds Something, Then What?]. He rightly points out that we need to start thinking about what happens after we detect a signal, and the relay is a nifty way of organising that, so that should we detect a signal tomorrow, we will already have procedures in hand.

I won’t comment too much on the technical aspects, other than to say that if a message contains a Shannon entropy of 30, then it probably won’t matter how many people try and make sense of the message, we won’t get close (A.I., on the other hand, may have a bit more luck).

The Interstellar Communication Relay is an effort to democratize SETI. My cynical side worries, however, about safeguards. The relay relies on people acting in good faith, and not concealing or misusing any information gleaned from a signal. McConnell proposes a ‘copyleft license’, a bit like a creative commons license, that will put the data in the public domain while preventing people commercialising it for their own gain. I can see how this makes sense in the Encyclopedia Galactica paradigm – McConnell refers to entrepreneurs being allowed to make “games and educational software” from what we may learn from the alien signal.

I worry about this. In The Contact Paradox, I wrote about how even something as innocent as the tulip, when introduced into seventeenth-century Dutch society, proved disruptive (https://en.wikipedia.org/wiki/Tulip_mania). The Internet, motor cars, nuclear power – they’ve all been disruptive, sometimes positively, other times negatively.

How do we manage the disruptive consequences of information from an extraterrestrial signal? Even if ET has the best of intentions for us, they can’t foresee what the effects will be when facets of their culture or technology are introduced into human society, in which case the expectation that ET will be wise and ‘altruistic’ is almost irrelevant. Heaven forbid they send us technology that could be turned into a weapon, and we can’t guarantee that bad actors – after being freely given that information – won’t run off with it and use it for their own nefarious ends. A copyleft license surely isn’t going to put them off.

My feeling is that fully deciphering a signal will take a long, long time, if ever, in which case we shouldn’t worry quite so much. But suppose we are able to decipher it quickly, and it’s more than just a simple ‘greetings’. Yes, we have to think about what happens after we detect a signal, but it’s not just the mechanics of processing that data that we have to think about; we also have to plan how we manage the dissemination of potentially disruptive information into society in a safe way. It’s a dilemma that the whole of SETI should be grappling with I think, and nobody – certainly not me – has yet come up with a solution. But, I think that revising our assumptions, recasting our expectations, and casting aside the idea that ET will be selflessly altruistic and wise, would be a good start.

• Paul Gilster

Well said. As I look back through our exchanges, I see I didn’t get around to the Deep Time concept I wanted to explore, but maybe we can talk about that in our next dialogue, given your interest in the Cosmic Microwave Background, which is the very boundary of Deep Time. Let’s plan on discussing how ideas of time and space have, in relatively short order, gone from a small, Earth-centered universe defined in mere thousands of years to today’s awareness of a cosmos beyond measure that undergoes continuous accelerated expansion. All Fermi solutions emerge within this sense of the infinite and challenge previous human perspectives.

James Gunn may have been the first science fiction author to anticipate the ‘new Venus,’ i.e., the one we later discovered thanks to observations and Soviet landings on the planet that revealed what its surface was really like. His 1955 tale “The Naked Sky” described “unbearable pressures and burning temperatures” when it ran in Startling Stories for the fall of that year. Gunn was guessing, but we soon learned Venus really did live up to that depiction.

I think Larry Niven came up with the best title among SF stories set on the Venus we found in our data. “Becalmed in Hell” is a 1965 tale in Niven’s ‘Known Space’ sequence that deals with clouds of carbon dioxide, hydrochloric and hydrofluoric acids. No more a tropical paradise, this Venus was a serious do-over of Venus as a story environment, and the more we learned about the planet, the worse the scenario got.

But when it comes to life in the Venusian clouds — human, no less — I always think of Geoffray Landis, not only because of his wonderful novella “The Sultan of the Clouds,” but also because of his earlier work on how the planet might be terraformed, and what might be possible within its atmosphere. For a taste of his ideas on terraforming, a formidable task to say the least, see his “Terraforming Venus: A Challenging Project for Future Colonization,” from the AIAA SPACE 2011 Conference & Exposition, available here. But really, read “The Sultan of the Clouds,” where human cities float atop the maelstrom:

“A hundred and fifty million square kilometers of clouds, a billion cubic kilometers of clouds. In the ocean of clouds the floating cities of Venus are not limited, like terrestrial cities, to two dimensions only, but can float up and down at the whim of the city masters, higher into the bright cold sunlight, downward to the edges of the hot murky depths… The barque sailed over cloud-cathedrals and over cloud-mountains, edges recomplicated with cauliflower fractals. We sailed past lairs filled with cloud-monsters a kilometer tall, with arched necks of cloud stretching forward, threatening and blustering with cloud-teeth, cloud-muscled bodies with clawed feet of flickering lightning.”

Published originally in Asimov’s (September 2010) and reprinted in the Dozois Year’s Best Science Fiction: Twenty-Eighth Annual Collection, the story depicts a vast human presence in aerostats floating at the temperate levels. Landis has explored a variety of Venus exploration technologies including balloons, aircraft and land devices, all of which might eventually be used in building a Venusian infrastructure that would support humans.

We’ve already seen that Carl Sagan had written about possible life in the Venusian atmosphere, and an even more ambitious Paul Burch considered using huge mirrors in space to deflect sunlight, generate power, and cool down the planet. Closer to our time, an internal NASA study called HAVOC, a High Altitude Venus Operational Concept based on balloons, was active, though my understanding is that the project, in the hands of Dale Arney and Chris Jones at NASA Langley, has been abandoned. Maybe the phosphine news will give it impetus for renewal. The Landis aerostats would be far larger, of course, carrying huge populations. I have to wonder what ideas might emerge or be reexamined given the recent developments.

Image: Artist’s rendering of a NASA crewed floating outpost on Venus

With Venus so suddenly in the news, I see that Breakthrough Initiatives has moved swiftly to fund a research study looking into the possibility of primitive life in the Venusian clouds. The funding goes to Sara Seager (MIT) and a group that includes Janusz Petkowski (MIT), Chris Carr (Georgia Tech), Bethany Ehlmann (Caltech), David Grinspoon (Planetary Science Institute) and Pete Klupar (Breakthrough Initiatives). The group will go to work with the phosphine findings definitely in mind. Pete Worden is executive director of Breakthrough Initiatives:

“The discovery of phosphine is an exciting development. We have what could be a biosignature, and a plausible story about how it got there. The next step is to do the basic science needed to thoroughly investigate the evidence and consider how best to confirm and expand on the possibility of life.”

Phosphine has been detected elsewhere in the Solar System in the atmospheres of Jupiter and Saturn, with formation deep below the cloud tops and later transport to the upper atmosphere by the strong circulation on those worlds. Given the rocky nature of Venus, we’re presumably looking at far different chemistry as we try to sort out what the ALMA and JCMT findings portend, with exotic and hitherto natural processes still possible. On that matter, I’ll quote Hideo Sagawa (Kyoto Sangyo University, Japan), who was a member of the science team led by Jane Greaves that produced the recent paper:

“Although we concluded that known chemical processes cannot produce enough phosphine, there remains the possibility that some hitherto unknown abiotic process exists on Venus. We have a lot of homework to do before reaching an exotic conclusion, including re-observation of Venus to verify the present result itself.”

Image: ALMA image of Venus, superimposed with spectra of phosphine observed with ALMA (in white) and JCMT (in grey). 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).

I’ll close with the interesting note that the BepiColombo mission, carrying the Mercury Planetary Orbiter (MPO) and Mio (Mercury Magnetospheric Orbiter, MMO), will be using Venus flybys to brake for destination, one on October 15, the other next year on August 10. It has yet to be determined whether the onboard MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) could detect phosphine at the distance of the first flyby — about 10,000 kilometers — but the second is to close to 550 kilometers, a far more promising prospect. You never know when a spacecraft asset is going to suddenly find a secondary purpose.

Image: A sequence taken by one of the MCAM selfie cameras on board of the European-Japanese Mercury mission BepiColombo as the spacecraft zoomed past the planet during its first and only Earth flyby. Images in the sequence were taken in intervals of a few minutes from 03:03 UTC until 04:15 UTC on 10 April 2020, shortly before the closest approach. The distance to Earth diminished from around 26,700 km to 12,800 km during the time the sequence was captured. In these images, Earth appears in the upper right corner, behind the spacecraft structure and its magnetometer boom, and moves slowly towards the upper left of the image, where the medium-gain antenna is also visible. Credit: ESA/BepiColombo/MTM, CC BY-SA IGO 3.0.

And keep your eye on the possibility of a Venus mission from Rocket Lab, a privately owned aerospace manufacturer and launch service, which could involve a Venus atmospheric entry probe using its Electron rocket and Photon spacecraft platform. According to this lengthy article in Spaceflight Now, Rocket Lab founder Peter Beck has already been talking with MIT’s Sara Seager about the possibility. Launch could be as early as 2023, a prospect we’ll obviously follow with interest.

A final interesting reference re life in the clouds, one I haven’t had time to get to yet, is Limaye et al., “Venus’ Spectral Signatures and the Potential for Life in the Clouds,” Astrobiology Vol. 18, No. 9 (2 September 2018). Full text.

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.