Planetary Radio • Jun 30, 2021

Finding Life by Looking for Complexity

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Lee Cronin

Regius Chair of Chemistry, University of Glasgow

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Rae Paoletta

Director of Content & Engagement for The Planetary Society

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

University of Glasgow chemist Lee Cronin and his collaborators have developed a new way to detect life. Their "assembly theory" could give us a reliable method for recognizing life or evidence of past life based on the complexity of molecules in any environment. The Planetary Society’s Rae Paoletta shares our favorite images of Saturn’s rings with Mat. Bruce Betts reveals which star takes up more of Earth’s night sky as he resolves another What’s Up space quiz.

Lee Cronin Portrait
Lee Cronin Portrait Lee Cronin is Regius chair of chemistry at the University of Glasgow.
Scratching at the Surface
Scratching at the Surface The sampler arm of the Viking 2 lander digs in the regolith at Utopia Planitia. The cylinder on the right is the ejected shroud that once covered the collector head on the sampler.Image: NASA/JPL/Bill Dunford
Digging for Clues
Digging for Clues The surface sampler arm on the Viking 1 lander digs for samples at Chryse Planitia on Mars.Image: NASA/JPL/Bill Dunford

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Mat Kaplan: Don't look for what life is look for what it does. This week on Planetary Radio. Welcome. I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and beyond. Lee Cronin and his colleagues call it assembly theory, it may be able to recognize life as we know it and as we don't. He'll join me from his lab at the University of Glasgow to explain. I'm simply going to assume that everyone who listens to this show loves Saturn. So does my colleague, Rae Paoletta. She has collected a dozen of the best images of that world's rings. Listen to what she has to say before you turn your gaze to them. And we'll look to the stars when Bruce Betts arrives for this week's What's Up. Well, one star anyway, but it's a doozy. Here's a sample of The Planetary Society's weekly newsletter. You can see the downlink at but you can also subscribe for free, really nothing.

Mat Kaplan: Happy Anniversary LightSail 2. As you heard from Bruce last week, our little solar sail completed its second year in Earth orbit on June 25th. Check out the latest images of Earth and get the current status at Squids in space, cute little leopard skin, baby squids. They're now living on the International Space Station because human and squid immune systems have a lot in common. Who knew, right? What's 21 years old has revolutionized our view of the universe and is showing its age.

Mat Kaplan: Engineers are still trying to figure out what's wrong with the Hubble Space Telescope. Be sure to hear next week's plan rad when I'll visit the follow on to Hubble, the James Webb Space Telescope and a Hawking big comet has been discovered as a side benefit of the dark energy survey. 2014 UN271 could be 200 kilometers wide. Sadly, it won't get closer to the sun than Saturn's orbit. But maybe we'll still get a show in a few years. Rae, great new piece and what a wonderful collection of images you have gathered for this June 29th piece that people will find at the best pictures of Saturn's rings. There's so many to choose from how did you come up with 12?

Rae Paoletta: Saturn is so near and dear to my heart. And I know some people will probably take issue with this because I'm showing preference towards one planet. But Saturn is my favorite. And there's just so many great pictures to choose from that. It was really tough to narrow it down. But I'm really, really thrilled with this collection.

Mat Kaplan: You have lots of company. I think I've read that most polls say that Saturn is everyone's favorite planet or most people's favorite planet. You call this focus on the rings, though, an examination of the phrase you use is fleeting beauty, maybe not in human terms. But yeah, pretty temporary in the great scheme of things.

Rae Paoletta: Yeah. It's kind of amazing. Saturn's rings, we don't know exactly when or even how they formed. Like we have some ideas. They could be essentially shredded comets, asteroids, moons, that could have formed anywhere from maybe 10 million 100 million years ago. That's a really big, big jump in time. In just 100 million years, they could be completely gone. The rings are actually being pulled into Saturn by the planet's gravity, and it's forming this kind of ring rain in Saturn's atmosphere. So it is ephemeral, beautiful, all of those things.

Mat Kaplan: It's another great phrase that I love that's in the piece ring rain. We won't go through all of these. We don't have time, but there are three that I want to call out because they are especially affecting for me beginning with a Daphnis in the Keeler gap, which you call an incredible shot. I could not agree more just describe this surreal image.

Rae Paoletta: It is really incredible, right? We've got a few of these pictures where the moons can be easily seen. And this one to me is just stunning. So we've got Daphnis, this tiny shepherd moon. It's located in this space in Saturn's a ring that's called, as you said the Keeler gap. And to me, it just looks almost like it's framed by the rings. And it's just kind of this small satellite. It's hard to believe it's real looking at this photo.

Mat Kaplan: These little perturbations, though, that it is actually causing, it's shepherding the wings and you can see these gentle curves and there's this one little string like bit that's being drawn along with the moon, I assume. But it is just mind blowing.

Rae Paoletta: Yeah. I think it Daphnis actually has a nickname for that reason, the wave maker moon.

Mat Kaplan: Let me go on to the next one here. I call it out because we talk a lot on this show. And we've talked with some fantastic ring experts, including all those conversations we've had with Linda Spilker and Carolyn Porco as well. Everyone likes to talk about of course, they're incredibly wide, but incredibly thin as well. And this image you've chosen, it's the second from last in the piece, I think gives a real feeling for just how utterly narrow or thin these structures are.

Rae Paoletta: It's incredible, right? When I look at this, I feel like you have to dissect it from almost like an art, the way like you would in art history class or something. There's so many things going on here that are so exciting, right? So you've got like the spooky backdrop, which I love a spooky space pick. I don't about you.

Mat Kaplan: Of course.

Rae Paoletta: That to me is the best, right? You've got this kind of eerie glow. It almost looks like the ring from the horror movie, the Rings.

Mat Kaplan: Yeah. It does. You're right.

Rae Paoletta: I'm a big horror movie fan. So I had to see the crossover there. And I think what's so cool about this is not only is the show how thin the actual rays are themselves, it shows just like how massive the moon of Titan is. And Titan is in the backdrop there. Does a really nice job describing the scale, right? Like Titan is the second largest moon in our solar system. It's also bigger than the planet Mercury. So kind of impressive there. And you can also see Enceladus, too. If you look really closely it's there.

Mat Kaplan: Absolutely. I'll call out the last one, not because it's just so visually stunning, although it is gorgeous. But because it has such meaning for me. July 19th, 2013, I was standing outside at JPL with 1000 or more other people talking with Linda Spilker. And at the right moment, we all started waving at the sky. Describe what's going on here. Why were we all out there?

Rae Paoletta: So this photo is called The Day the Earth Smiled. And to me, it's just, I say this in the piece, but it's hard to not get emotional looking at this picture. You can basically see Saturn's rings, you can see Saturn, and you can also see in the same shot the Earth and the moon. To me, it's just kind of like a family picture of all of us. I know I like to wax poetic about Saturn a lot. But for me, this does kind of bring a sense of connectedness in how we really are, all in this cosmic journey together, whatever you want to call it. It's a perspective really, that's just so special.

Mat Kaplan: Great piece. June 29th is when this was published, called the best pictures of Saturn's rings, you'll find it at Thank you for joining us again on the show, Rae. We'll talk again soon.

Rae Paoletta: Always a pleasure. Thank you, Mat.

Mat Kaplan: You know those two big questions Bill Nye likes to ask, "Where do we come from? And are we alone?" Answers to both may require a reliable way to detect the presence or past presence of life. Some of the greatest scientists I know are on this quest. Lee Cronin, his colleagues at the University of Glasgow, and his collaborators at Arizona State University, and the NASA Goddard Space Flight Center, have concentrated on something all life as we know it does, it builds big molecules. Their work has just been published as assembly theory. Lee and I talked a few days ago, I am always on the lookout for great stories that are appropriate for planetary radio.

Mat Kaplan: Some of them are obvious updates from spacecraft around the solar system, and so on. This one was less obvious, although I have to say it immediately grabbed my attention. And the more I have learned about assembly theory, the more excited I have become. So congratulations on this really great work. Let's start with this. I think it has been maybe hundreds, possibly even 1000s of years that humans have been attempting to come up with an acceptable universal definition for life. It really has in all that time has never been terribly successful, has it?

Lee Cronin: No, and I think that's one of the most ironic things about it. It was always in plain sight, but never really tangible because people were arguing about their own biases.

Mat Kaplan: And talking about in a way what life is rather than what life does, which seems to be the approach that you and your collaborators have taken.

Lee Cronin: Yeah. So I've always been interested in complexity theory since I was a child in programming and so on. But in the chemistry lab, when we make molecules, we have to put in a lot of information to make drugs and whatnot. And I got thinking many years ago about, how big does my molecule need to be before it becomes impossible for it to be created by a non living system? And it turns out not very. And that was really the train of thought that we went through, we realized that only that we have a new approach is actually a new theory about how information in the universe works.

Mat Kaplan: Which is quite profound capability, or perception, I guess is a better way to put it. And you have called this assembly theory. Give us an idea of what assembly theory is all about. And of course, we will also put up links to the press releases about the story, but also to the original paper in the May 24 Nature Communications. And I do highly recommend that people read both the abstract and the introduction to the paper, but please give us the thumbnail description.

Lee Cronin: Yeah. So put simply what assembly theory does, it allows you to take a given object that you can find, and so the first thing is you need to find many identical copies of this object, so you can then break them. And when you break them, you break them gently, and you break them into lots of different parts. And then you say, "Okay. How can I then reassemble this object with the minimum number of steps?" This is really assembly theory in a nutshell. So the larger the number of steps you need, and this must be the shortest path. In theory, the more unlikely the object could have made itself. It's a bit like the blind watchmaker argument, or automate light turn on its head. And don't worry, I won't. It's not a creationist argument. We cannot talk about how evolution is able to shape the trajectory that allows these objects to form. But at its core, assembly theory tells you the probability of the object could form without some informational process. Be it a designer or evolution.

Mat Kaplan: And you express this probability as the MA number, the molecular assembly index?

Lee Cronin: Correct. Now, this is actually underlying a much deeper theory that I'm working on the collaborators right now on what's called assembly information theory or causal assembly theory. But for molecules because if we're going to go and look for aliens in the solar system, molecules are good enough, okay. And we simply give the number of steps you need the MA index. And one of the nice things about this theory, I should say is that I invented the theory from an experiment I knew already worked, which is why this was a bit of a slam dunk because I didn't have to have a philosophical argument with people about what life could be. I could say, "Here's my theory. Here's the equation. Here's the experiment, shall we go see if the experiment fits the theory?"

Mat Kaplan: I was struck when you said a few moments ago, that this solution has been right in front of our faces in front of our eyes, perhaps for many, many years. Because I had kind of the same impression. Why do you think has nobody quite taken this approach in the past?

Lee Cronin: I don't know. I guess, so I think chemists, and I'm a chemist, are very good at making molecules and they're very biased, and they accept and they think that complex molecules can arise. The fact that chemists have two contradictory views, the first to tell you how hard it is to make a new drug, new molecule, how much work they need to do. And then when you show them a complex molecule, they'll turn around say, "Oh, that can happen by chance." And I think NASA and people working in astrobiology and people thinking about complexity, got this, realize correctly, that you can't just get information for free, but how can we encapsulate it? So for me, a molecule is an information ship in a bottle. If you find a complex molecule, you haven't found the alien, but you found evidence, the alien made the thing. And that is so exciting because it captures that information.

Mat Kaplan: Another extremely exciting factor about this new theory is that it should work, there's no reason why it wouldn't work, not just for life as we know it. But for, as we frequently say on this show, life is we don't know it. So forgive me for putting it this way. But the problem in the past has been that we don't know what we don't know about life is we don't know it.

Lee Cronin: Yeah. Absolutely. You're right. And this is one of the reasons why I had so many arguments with people at NASA when I was developing this. The people that argued with me about this fell into roughly three camps. They still do. First camp, which used to be the biggest camp saying it's ludicrous. You don't even know enough mathematics. You don't know enough chemistry. You don't know enough computer science. It's too hard to use complexity theory because everything is complicated. And then the so is ludicrous. The second group of people just opposed it because they want it to go and look for amino acids or RNA or DNA, their own little pet marker chirality, all of which are valid for life on earth. And now we're getting into the point where everyone said, "Oh, yeah, it's obvious." So I think that it's obvious that this works.

Lee Cronin: And I'm really excited because they're the three stages of a new idea coming to life. Ridicule, suppression, and of course. And so that's kind of nice because I'm not saying we shouldn't go and look for amino acids on Titan, or chirality on Mars, I'm just saying what I'm proposing we'll find life forms that you weren't expecting. And also it captures life as we know it. So why would you use a life form detector that was only Earth centric, when we are going to other planets? And I think that, that is then really the slam dunk, we need to get this on all the missions.

Mat Kaplan: Have you come to the point where you may have found or if you haven't found it yet, do you think that there is a threshold of complexity, a line above which something can be said to be the product of biology? And if it falls below that, probably not?

Lee Cronin: Maybe, but I'm going to hesitate. I think it's always going to be a scale because we don't know the conditions of the planet that we're going to. But I would say on Earth, it's very nice. You can fingerprint life on earth. And it seems to be there is a threshold by which is very unlikely you're going to find identical copies of a molecule by a random process on earth over, I don't know, say 15 steps, whereas on Titan, it may be that the density of the atmosphere, or the way that chemistry is going on might push that out a bit further.

Lee Cronin: But the thing is, when people argue about the fresh idea, I just say, "Look, we can argue about a simple to complex molecule, but is a Tesla complex enough? Is an iPhone complex enough? Is a piece of sound simple enough?" And what I do is I get people to put take their line. And the fact we can draw a line between this, between the simple and complex is the first point. But the beautiful point is the same line that we're using to look for non life to life, also goes to intelligence and techno signatures. It's one continuum.

Mat Kaplan: Which brings us right back to information theory. So I can't wait to see the expansion from special assembly theory to General Assembly theory. If you're part of the reference.

Lee Cronin: Yeah. No, that's exactly what's happening. Because information does not exist in a universe without life. It's a really important thing to say because life needs to generate context for itself. But causation does exist because we had to get to life. And so what assembly theory actually says is, how much causation can we accumulate before we come to life? Now, the reason I hesitated about your comment about the threshold is this, is that I don't think there's a eureka moment where a planet makes a transition from death to living. I think there is an accretion of the ability to process causal structures and turn them into information. So what happens is you have random chemistry doing nothing very much. But then there's a bubble that gets trapped if you like.

Lee Cronin: And when that bubble that gets trapped is able to act on other bubbles being formed later causally, then suddenly, you have life, or you have the trajectory that gives rise to life. And I think it's not hard and fast. It's like the invention of flights. The flying squirrels, they don't flap their wings or they are a dead end for flight, or their very first objects that went into the air, is really thinking about the evolutionary continuum. But yes, when you go to a planet, you should be able to look at the planet and say, "Dead or alive. And where's the threshold?" And that's really exciting.

Mat Kaplan: Absolutely fascinating. And I hope that listeners are beginning to understand why I found this so exciting when I discovered it. Let me throw an example at you, which is one of your own examples. A molecule on earth, an earth bound molecule, one that I recognized, thank goodness, not because of personal experience, but it's called Taxol. That natural plant based chemotherapy drug. It's a very complex molecule, you use it as an example, how likely is it the Taxol would be created in any abundance without being created by a living organism? I suppose you might find a molecule here or there just by chance, right?

Lee Cronin: Yeah. So let's do the math. So the chance of finding Taxol on any abundance is zero. I know that statistical mechanics will say, "Oh, no, can we not say it's like, very, very, very improbable?" But sure, the probability would require a universe larger than our universe by a factor of 10 or 20. So let me say, so Taxol has a number of atoms in it. So it's about 62 atoms, right? Or 63 atoms. I forget a carbon atoms, there's some hydrogen atoms don't count those because they just add on to say there's little causal power of those. If you were to take those 63, 64 atoms and mix them in a bucket, and then pull out molecules of Taxol to do that, would require... And let's just say now we didn't just do it in one bucket, we filled the entire universe with buckets. You would not be able to fill the known universe with enough buckets to even pull out one molecule.

Lee Cronin: So there are more possible configurations of the atoms in Taxol than there are atoms in the universe. So you go, "Oh, gosh, okay. That's a downer. So that can't even happen randomly." So now I found a milligram of Taxol, which is several million molecules. So not only have you found a one in a universe molecule, you've found a million of them. And that then allows, that gets the alarm bells really ringing. And you can then start to say, "Well, of course, Taxol didn't get built in a flash, did it? It was the accretion of information, step by step." Taxol is evidence of four billion years of coin flipping in evolution on earth. And isn't that beautiful? Just in one molecule, there's evidence that process went on, and it's all there.

Mat Kaplan: That is sublimely beautiful. Something else you talk about is something that has come up many times on our show, the Viking landers, those pioneering, still amazing landings on Mars back in the mid 1970s, which attempted to detect life. And of course, there were what a lot of people, most people still say, were ambiguous results from at least one of those experiments on both of the landers. What went wrong there? Yeah. We didn't understand enough about Mars, right? We didn't know that the surface is covered in perchlorates. But would it have been possible to do that experiment in a different way? If not in the mid 1970s, then now, where you could have used assembly theory to help determine whether something was kicking around on Mars?

Lee Cronin: Yeah. So let me answer the question. First of all, I think NASA did it right, actually. They made a really good mistake. It was a really good mistake to make, which is to say, "Look, we're going to look for metabolic evidence, we're going to think about the chemistry of Mars. And we'll go." So the fact we're arguing about whether life is there or not now, is just to do with the technology we sent there at the time. It was always going to be ambiguous. And that's when Martian got up and actually hit the flatlander with the Martian axe, we would still be arguing today. Because we just didn't yet have really the correct framework. Now, what I would do is I take one minute, if I may, to kind of explain the theoretical framework that doesn't exist yet. If we take particle physics, when people are licking the Higgs boson, this is a way the framework, I look at it. So to basically predict the Higgs boson, we need to have a theory of stuff, a theory of matter. So we have a theory in these particles, that's called the standard model.

Lee Cronin: Now with that standard model, we can then make a simulation, if when those particles are likely to be seen. So we've got a theory, then a model, then a simulation. With the simulation, we get an energy range. So we now can build a machine. And what we do is we bombard particles together, and we look for evidence of that energy. So the Higgs is about 128.3 Giga electron volts, smash things together, find something in this range, in your [inaudible 00:23:20], you have found evidence of the Higgs and therefore gravity. So let's apply this to our thing here. What is life? We don't know. Is DNA, is peptides, is lipids, life is me, blue or whatever. And you say, "Okay. If life is about complexity, or generating objects have more degrees of freedom than can be explained by non causal based structures." That's our theory. Then we say, "Okay. Let's make a system and model. Let's randomly mix all the molecules together, we get the rough idea where to search, threshold high up."

Lee Cronin: Now we then make a detection system, a mass spectrometer to weigh the molecules. And then we go to either the lab where we're trying to make life in my lab right now or to Mars. And we simply do that. So that was a very long winded way of saying, if we go back to Mars, with a suitable mass spectrometer that NASA has at Goddard, right now, they could do the experiment in a year, two years, whatever it takes at Mars. And they would be able to at least have a go detecting those molecules. And if they did detect a molecule, that MA greater than 15, we will know that either Mars was alive in the past, or had been contaminated by humans with life, or that some technologies on Mars and making complex molecules, either of those things would be really fascinating.

Lee Cronin: And then if it was thought to be contamination, we could fingerprint that and roll it out. So that's what I think we are going to do in our lifetime, in the next few years. And there's existing kit on Mars and plan to go to Titan, that may indeed be able to do these types of experiments. And so NASA didn't go wrong. They were just naive. They didn't have a framework but now thanks to what we've done together with NASA's help, we now have a framework. We understand what life does, we have a model for it, we have a detection system. Let's go.

Mat Kaplan: Are you saying that the Curiosity rover, the Mars Science Laboratory, that the mass spectrometer or spectrometers that it carries, and perhaps the somewhat more limited one on perseverance, that these could currently have the capability to assess the molecular assembly index?

Lee Cronin: So not directly because they don't have quite the sophistication of the ones that just been developed. Because what you need to be able to do. This is a really delicate point, what the mass spec does, right now that takes lots of molecules in to make my analogy with say porcelain is like taking lots of cups and saucers, and breaking them all apart. And when you break them all apart, you don't know where all the parts are from. But there are very sophisticated mass specs now where you can select an individual cup from an individual saucer because of its molecular weight. And then you trap that in electric field, and you hit that and only that, and that gives what we call intrinsic measure of the complexity.

Lee Cronin: But all is not lost, we are finding a way using machine learning to basically retro fit on these probes hints to get some hints. But if you really want the proper detection, no machine learning, no fake kind of bias because all machine learning is biased in some way by what we put into it, we have to use this approach and go back with a more high resolution mass spectrometer, but we'll be there.

Mat Kaplan: Would you like to see exactly that sort of apparatus headed to Titan on dragon fly in? Or a few years from now?

Lee Cronin: Yes, I would. And I'm not sure the team have made their decisions already about what they're sending there.

Mat Kaplan: True.

Lee Cronin: And I don't think it's vastly incompatible. But of course, when I was trying to convince the dragonfly team that this was a new approach. And they hear this all the time, they must have 100 crazy people saying, "I can detect alien, put this on your probe." So quite properly, they need to go through proper due diligence process. There might be ways before we can add on other parts. And there are other missions in the works right now because NASA is always working up new missions, as is ISA. And I'm talking to both ISA and NASA and others about how we might. But there's actually more to this than just mass spectrometers, we might even be able to detect life in exoplanet atmospheres using assembly theory remotely with JWST and various other new telescopes that can be put up very soon.

Mat Kaplan: IZ was afraid to ask you about that. I should not have assumed that this kind of work could not be done so remotely from space based telescopes that are millions of kilometers away from what they're looking at. You're saying that there might be a pathway?

Lee Cronin: Yeah. Now, it's slightly more complicated. And we don't want to go down the lines of phosphene on Venus and I'm not saying, and it's probably a debate we don't want to get into because I have great respect for the teams involved. But there's also a very good... How can I put it? Story there and how to get people excited, and maybe how to think about this in the more agnostic way. But let's park there. Now what I've said is that molecules are really good ships in the bottle catalyst, ship in a bottle information, they are an absolute pristine artifact of evidence of complexity. However, if you now think of every object in the molecule as a discrete piece of information that's locked together, what you could also now think about discrete pieces of information that control the gases in an atmosphere, in terms of the amount of oxygen or methane, or ammonia that you can see spectroscopically.

Lee Cronin: Now what you can do is almost build a meteorological model of what's going on the planetary atmosphere. Once you start to see differences in concentrations between the gases that are connected, you can start to use assembly theory to say, "This planet looks to be really acting rather oddly." There's too much information in the atmosphere. That's what you could do with one of the worst case scenarios. And one of the best case scenarios, in the future, we might be have developed techniques where we can do remote infrared, and we can pull out infrared signatures from high concentrations, has to be high concentrations of complex molecules. But I have to say that's a very science fiction... Well, it's not science fiction because it's possible. It's just technologically harder than detecting gravity waves 50 years ago.

Mat Kaplan: It's a fascinating option perhaps for the future and it had already occurred to me that there are probably several good sides fiction stories hidden away here in assembly theory. How did you test assembly theory here on earth? You didn't have life as we don't know what to test. But you did extensive work with biological and non biological samples, didn't you?

Lee Cronin: Yeah. So what we did first of all, it was assembly theory, once I got an idea there was a connection, a mathematical connection between the complexity of the molecule and the number of features, we could measure what we call spectroscopically. So we can measure this using mass spectrometry, weighing the molecule and breaking it. There's a technical nuclear magnetic resonance, which would tell you literally the number of different types of atoms and infrared which gives you a lovely signature of number of absorbance is associated with how a molecule moves. So briefly speaking, infrared tells you how many dance moves a given molecule has. The more complex... I'm sorry if I'm patronizing some of the audience or infrared spectroscopy, but it is a nice analogy, even if you are infrared spectroscopy. But basically, if you're a complex molecule, and you have more different bonds, you've got more dance moves, you've got more dance moves, you've got more absorptions in the infrared.

Lee Cronin: So we went to the lab, and we got complex molecules. And we measured the number of absorbances in the infrared NMR and mass spec. And to our surprise, they all correlate it very well. In fact, infrared and NMR was like almost one to one. Mass spec was harder because molecules fall apart, not always on demand because some bonds are weak, weaker than others, but that doesn't matter. So we did that with a test set. And then what we then did is said, "Okay. Works with these molecules. What about mixtures?" And we got a whole load of mixtures from Earth. We generated some prebiotic soups in the laboratory, we took some Ecoli, we took yeast, we took loads of dev stuff, inorganic stuff, granite, coal, and also NASA, bless their cotton socks. They gave us some samples that they blinded because they didn't believe us. So they gave us a lot of the samples, which were like, we were quite stressed. And I must say, this is not as rigorous as a vaccine trial because we only gave us a four or five samples.

Lee Cronin: But nevertheless, had we have failed, it would be and they gave us the Murchison meteorite, which was one of the most analytically complex objects ever collected from out of space. They gave us, which was dead. We all know that Murchison is dead, but was it always dead? That's the question. They gave us a fossil, which was a few million years old. And then we got some seawater from Antarctica and various other samples. So to our surprise, we got the Murchison. We said there's something really weird going on Murchison, but it's most certainly dead. And this fossil, which really freaked us out, they kept passing the tests. So we had no choice but to go to NASA and say, "This looks alive." And they said, "Oh, yeah. That's the fossil, that's several million years old." I see all the work. And we also did for fun because we're in Scotland, we did some scotch whisky.

Lee Cronin: And the reason why we did Scotch whisky is I love peated Scotch whisky. Peated Scotch whisky is the barrels are left, they're heavily peated in the water. So the water has lots of tannins and natural products. There's also a distillery not far from my house called Glengoyne. It is the most severely whiskey distillery, which isn't peated, but it's still lovely. And I got some Glengoyne. And so 10 year Glengoyne, 10 year [inaudible 00:33:22], which one is the most complicated? It's the peated one because the beaded one has more natural products in there and the assembly theory, which I thought was kind of cool. So that's how we did it.

Mat Kaplan: Oh, and so assembly theory, perhaps will be adopted by the distillery industry before too long. It's absolutely fascinating. I'll apologize again to the scientists out there, and ask you to take us into science 101 and talk about why it is so important that assembly theory allows us to make falsifiable tests, and the importance of falsifiability in all of science.

Lee Cronin: Yeah. That's a really important point. That what you want to be able to do is if you've got a test, you want to be able to show that how the test fails and when the test succeeds. And under what conditions can the test be falsified? Because if you can't ultimately falsify something, then you're never going to be sure that your thesis is correct. So what I wanted to do with NASA in particular, is prevent false positives. And we don't know that they're necessarily false, but they're at least ambiguous. So Viking number one, the Allen Hill meteorite, where we found a nano fossil, the phosphine on Venus, these all could be evidence of life. But the problem is that we don't have enough evidence and a scientific framework that allows us to falsify, it all rests on assumptions that can't be tested. So what we tried to do with assembly theory is to say, well, look, people will say, "Well, but you're breathing out CO2. That CO2 went through you. And that CO2 is evidence of life, it will fail assembly theory tests." Correct, it will.

Lee Cronin: Assembly theory will fail to detect simple molecules produced by life. But what we all really care about, rather than detecting molecules that could be produced by life, we only want to make sure we capture those molecules that are complex enough that they could not be produced any other way. That was why we really carefully constructed this argument to say, "Here is our probabilistic model. Our assumptions are the following. Atoms and bonds and molecules are the same all over the universe. And chemistry, complicated chemistry cannot just happen by randomly because we don't have enough chance in the universe." Those are the only two assumptions we have to make. Even those assumptions, we can then falsify the experiment and say, "Right, if we detect no complex molecules on Titan, if we send the right kit, or Mars, or Venus or Enceladus, does that mean there is no life?" No. Because we could be a false negative.

Lee Cronin: But if we go to these places, and we detect molecules, and we roll out contamination from the craft, that's the only confounder, we might be able to say, "Oh, hang on," then we will know, for sure that we have detected alien life elsewhere in the universe. And that, for me is so exciting because then you really are... The explanation for the complexity has to be even more outrageous than the detection of the alien life.

Mat Kaplan: I am so glad that you're now with this work are reaching this level of acceptance, or at least attracting the attention that it seems to deserve. I want to note some of the funding sources for the work and your collaborators. It was because of the press release put out by Arizona State University that I discovered this story. Although, the University of Glasgow, your own institution did the same. I note that you got support from DARPA here in the United States, and very significantly, the John Templeton Foundation, which is such an interesting organization, and is so interested in the origins of life on Earth, and perhaps elsewhere.

Lee Cronin: I could correct for the record, DARPA did not pay for any of this work. It was a mistake in the air of the press release, which I've tried to correct. But DARPA do give me money to make complex molecules as part of the programs for the important for the US, particularly in trying to make molecules on demand for medicine and so on. So there is actually some kind of intellectual overlap, but I think I should correct that. But yes, Templeton did fund in fact, Templeton is for me, it's been a really open minded organization. I should say, for the record, actually, some of my colleagues in the UK have questioned me taking the funding from Templeton for reasons that they say, "Well, Templeton funds, religious thought and so on," and that I'm somehow being trapped in some kind of conspiracy. But I reject that utterly for a number of reasons.

Lee Cronin: Number one, the UK funds are taxpayer funds theology, and in the US, as well. So I don't have any problem with an organization that funds theological and philosophical thoughts. And the other thing is that when I went to Templeton, they realized I had an idea that was not mainstream in my field, and there was no one going to fund me, and to do this. And if it wasn't for their funding, and then I got some more funding on the back of that from the UK Funding Council, and then from breakthrough, but if it wasn't for that sequence of events, I wouldn't have got the work done. And so I'm very grateful to the Templeton and they've been nothing but generous and open minded, and demanded that I am the same and I think is a really good organization. But it does raise some arguments, but I think they're misplaced.

Lee Cronin: Basically, I will not take money from organizations I think don't have the right ethical or kind of scientific approach. And the thing I really liked about the John Templeton Foundation is that they are questioning things and really asking hardcore scientists to question their own nature of reality. That is not the same thing as believing in earlier of creationism and things like that. I'm really happy they funded me and my collaborators of course, the ASU, they've also been funded by Templeton, they have NASA money. Sadly, NASA can't fund me in the UK. Maybe one day they'll fund me in the US if I ever have a footprint in the US. But actually, it wasn't the NASA... Well, NASA funding is important for my collaborator. What's more important than funding was the fact that NASA could be persuaded that this was a useful avenue to go down. Science isn't all about money. We need that to basically make the wheels go round.

Lee Cronin: But NASA are spending the money where it counts and going to the solar system, and potentially the outer solar system. So that's a really great thing that they're doing the fact that Jim Green, the Chief Scientist at NASA, I've talked to him about this result, he's super excited. He wants to get this on all the missions within reason. And I think NASA are behind it because it gives them an objective measure to go and look for life. But wouldn't be brilliant if you found weird life on Earth? Or we started to understand how dead chemistry transitions to life because one of the things that I should mention is that it's kind of an atheroma, right? We're saying, if you find a complex molecule, that it must be life. And then people will say, "But gee, does that mean no life make complex molecule?" But then how do the molecules get complex enough for life? And I'll say, "Yes, this is the question now, how did the origin of life happen?" So we should see this threshold focusing in on this question to be a much deeper question we're trying to answer and we'll be revising it.

Lee Cronin: Certainly, I think there's three thresholds, a low threshold where we've got a dead planet, an upper threshold where we have a technological planet, and there's a threshold in the middle where the planets transitioning to biology, and wouldn't be brilliant if we actually were able to go out and how many types of exoplanets are there out there? Well, if you think about it, there are dead exoplanets. There are technological ones with intelligent life on them. There are living ones, we hope. Yeah. And ones that have died. There's only four types of exoplanet dead ones, living ones, technological ones, or ones that once were alive, put in that frame. We should get astronomers and scientists to look up in the sky, countless exoplanets and say, "Which one are you? Are you alive, dead, technological, or you haven't made it yet?"

Mat Kaplan: You are safe with me because I have the greatest of admiration for the Templeton Foundation. In fact, the great Paul Davies at Arizona State University, as it happens, was heard on our show, and I know that he has also been recognized by the Templeton Foundation. Speaking of transitions to biology, before I let you go, you slid something into one of your earlier statements, which I almost had to interrupt you regarding I decided to save it. You said that your lab there at the University of Glasgow, the Cronin group, that you are working on the genesis of life, creating life in the laboratory. Did I hear you right?

Lee Cronin: Yep. So two weeks ago, we published another paper in Nature Comms on the other one, which was the robotic prebiotic chemist that is looking for complexity. And what I'm trying to do in my lab is, I wonder if I've bitten off more than I can chew sometimes it's like, we're building a theory for life. We're building the detection system for life. And we're also building the robotic engine to explore chemical space, to look for the emergence of life, and then say, "How did that happen?" And to do that I couldn't get money directly. I actually had to do it by building digitizing chemistry and making a drug project. So we've got robots that build drugs. And I use that technology to basically start this prebiotic project. So we now have three engines that are working right now, 24/7, searching chemical space, and looking for life.

Mat Kaplan: I hardly know what to say, except to say that I hope that you are able to continue this great science for many, many years to come. This is exciting stuff. You sound like someone who is quite passionate, and very much enjoys his work.

Lee Cronin: Yeah. I have a lot of fun. I think the pandemic has been a challenge for my team and me and trying to making sure things get going. But I think it's been so exciting that the theories are working, and we're making progress. And it's the great people in my team and the collaborators. And also one of the people that I got to help me read through the paper was in Africa was, in fact, an astronaut at the last astronauts to touch the Hubble Space Telescope. Guy called John Grunsfeld, and getting all those people together and convincing those and really us all sharing the question like, "Are we alone in the universe? How did life start?" These are not just esoteric questions, but they're vital for understanding what is going to happen to life on Earth, in the future, how humanity goes, what happens with technology. And so I'm really excited. I suppose it's my little mission for finding purpose. But also it's good fun because we get to do science in new ways and talk across disciplines. And don't be in any one pigeonhole. I really like to do science in any shape, or form.

Mat Kaplan: Lee, thank you for more than satisfying all my expectations for this conversation. It has been absolutely delightful to talk with you. And I do wish you the greatest of continued success. I suspect from the sound of it, we may have more to talk about in the future. Thank you.

Lee Cronin: I very much hope so. Thanks for having me on.

Mat Kaplan: Lee Cronin is Regius Professor of chemistry at the University of Glasgow, where he leads the Cronin group. You'll find the paper about assembly theory and much more, including this week space trivia contest on this week's episode page at More about that contest when I return with Bruce for What's Up?

Bill Nye: Bill Nye, the planetary guy here. The threat of a deadly asteroid impact is real. The answer to preventing it, science and you as a Planetary Society supporter, you're part of our mission to save humankind from the only large scale natural disaster that could one day be prevented. I'm talking about potentially dangerous asteroids and comets. We call them Near Earth Objects or NEOs. The Planetary Society supports dedicated NEO finders and trackers through our Shoemaker Near Earth Objects grant program. We're getting ready to award our next round of grants, we anticipate a stack of worthy requests from talented astronomers around the world. You can become part of this mission with a gift in any amount, visit And when you give today, your contribution will be matched up to $25,000. Thanks to a society member who cares deeply about planetary defense. Together, we can defend Earth. Join the search at today. We're just trying to save the world.

Mat Kaplan: Time for What's Up on planetary radio here is the chief scientist of The Planetary Society, Bruce Betts, also the guy who runs our Shoemaker NEO grant program, and I don't know how many of you out there caught it. But we had a great live webinar on Saturday, last Saturday to update everybody on our planetary defense activities, including Shoemaker Neo, Casey Dreier and Tim Spahr, the former head of the Minor Planet Center joined us. So you are marvelous.

Bruce Betts: Well, thank you. You always are marvelous. Yeah. It was good reviewing what we do in planetary defense for protecting the world from asteroid impact, along with a whole lot of other people in the world. Talked about all sorts of things thanks to you, Mat, including our Shoemaker Neo grants, which go to avid amateurs and professionals who upgrade their telescope facilities using our grants typically. Anyway, there's a new round of grants out there proposals due July 28th

Mat Kaplan: A lot of you probably heard Alessandro Nastasi and Russ Durkee, you want to see them and the other four winners of grants awardees in the last round of the 2019 ground. They are also, they have little videos that they produce that we put in the webinar, and they came up pretty well. It was fun to watch.

Bruce Betts: Yeah. It first time we had done that inviting videos, all six of the winners give us videos from their respective observatories, and it was neat.

Mat Kaplan: So what's up there other than 1000s of New Earth objects we need to watch out for?

Bruce Betts: Most of what you can't see, but what you can see are some nice bright planets. I'm excited about Venus coming up in the evening west shortly after sunset looking super bright, but what I'm excited about is Mars that's been hanging out in the west for a while, and Venus will be snuggling on July 12th. Closer than a full moon. And speaking of the moon, they'll also have a crescent moon there July 12th. But in the meantime, Mars is headed down Venus is headed up. Venus is over 100 times brighter than Mars right now. Middle of the night Saturn and Jupiter rising, Jupiter much brighter, Saturn yellowish rising in the east in the middle of the night up high in the south in the pre dawn.

Mat Kaplan: Hey, before you go on, let me tell everybody that even if you missed that webinar, you can watch it anybody can watch it at

Bruce Betts: To move on to this weekend space history. A lot of stuff happened this week. For example, 1997 Mars Pathfinder landed successfully on Mars. 2005 Deep Impacts slammed its big 800 kilogram copper impactor into a comment. Five years, ago 2016 Juno started orbiting Jupiter and given us great data from Jupiter. All right. We move on to.

Mat Kaplan: Sorry about your ears everybody wearing headphones.

Bruce Betts: The first spacewalk Of course done by cosmonaut Alexei Leonov, the Soviet Union, other Eastern Bloc countries put out stamps to commemorate this. But at the time, the Soviet Union did not publish details of what the Voskhod spacecraft looked like. So the stamps are actually mildly hilarious. They just made up spacecraft images, you can check out Leonov's stamps, and you'll find them. They look like some kind of sci fi thing, but not like the Bossgard. So there's a thing.

Mat Kaplan: So if I wanted to see that those stamps, you have a suggestion on what to Google?

Bruce Betts: Yeah. Something like Leonov USSR stamp 1965, or I believe it's linked from his Wikipedia page, the Soviet Union one that I find most amusing. And I'm assuming you can also put a link from our show page.

Mat Kaplan: We'll do that. We'll definitely do that. Go to if you want to catch the link there. I'm going to check that out. That just sounds wonderful. We're ready to go on to the contest.

Bruce Betts: I asked you after the sun, what star has the largest angular diameter as seen from Earth? How did we do, Mat?

Mat Kaplan: Here is the reigning response from Jean Lewin in the state of Washington. We know as far as angles go triangles all have three. And to determine a star's diameter we use interferometry measured at two different points along Earth's elliptic path, R Doradus at about 57 mas is the largest when you do the math. Is that interferometry? I love the poem.

Bruce Betts: I was just taken away by the rhyme.

Mat Kaplan: And mas, what are we talking about there?

Bruce Betts: Milliarcseconds. So 360 degrees across the sky and the full circle and then break that into arc minutes, 60 minutes per degree, 60 arc seconds per arc minute and this is a whopping... I've got it in arc seconds which is .57 arc seconds.

Mat Kaplan: That would do it 57 milliarcsecond.

Bruce Betts: Yeah. It's still not very wide. You're not going to go out and go, "Whoa, look at that wide star up in the sky." But maybe some when people mentioned it, but what blows my mind is the star is so big, it's 178 light years away. And it's still the biggest angle on the sky have a star besides the sun of course.

Mat Kaplan: Here's a comment along those lines from Darren Richie also in Washington surprised to learn both he's talking about Betelgeuse as well here which we heard from a lot of people was for a long time thought to be the widest apparent in our sky. Surprised to learn both appear only slightly smaller than Pluto and larger than Eris. Despite being light years away.

Bruce Betts: I believe the term is ginormous. There's big as our orbits of things like Mars, and just the star so they're rather mind blowing even in the mind blowing land of size of things in space.

Mat Kaplan: We heard exactly that from Norman [Cosoon 00:52:46] about the orbit of Mars even at the para helium. Jerry Robinette from Ohio, R Doradus not to be confused with Eldorado which was quite large by automobile standards but not really stellar. I beg to differ Jerry, that was that the Eldorado, the automobile Eldorado, first front wheel drive car. I guess, they didn't work all the kinks out, but it was a pioneer.

Bruce Betts: Random car facts.

Mat Kaplan: Marcel Yun Krigsman in the Netherlands fun fact. The constellation Doradus was introduced based on observations by two Dutch sailors one of them Frederik de Hutman, was born here in my hometown Gouda. There's a park here named after him and his brother Cornelius. I know we haven't said the winner yet. But finally, Robert Klain in Arizona another piece of trivia, there are two constellations named for dolphins Doradus, the dolphin fish and Delphinus the dolphin.

Bruce Betts: Delphinus.

Mat Kaplan: Delphinus, he left out the I.

Bruce Betts: I least find it more fun to pronounce that way. I don't know. Delphinus the dolphin. See? It's fun.

Mat Kaplan: So Robert adds, do you think they did that... Wait for it, on porpoise? So bad.

Bruce Betts: Are we fin-ished?

Mat Kaplan: Not quite because our winner is Robert [Laporta 00:54:12], who is a past winner. But it has been going on three years since he got chosen by Thank you very much, Robert. We're going to be sending you a hardcover copy of Carbon, the first winner of that great book Carbon: One Atom's Odyssey by John Barnett.

Bruce Betts: Here's your question, who was the first married couple to fly in space together? To fly to space together and in space. I think they're the only married couple that's flown in space together. People can correct me if I'm wrong, but I do want the first married couple to fly in space together. Go to

Mat Kaplan: I cannot remember the names but I do remember a random space fact about them. Well, we'll find out in two weeks everybody because you have until July 7th, 2021. That'd be Wednesday, July 7th at 8:00 AM Pacific Time, to get us this answer and maybe win yourself a Planetary Radio t-shirt, which you will look stunning in. We can state this as a matter of fact.

Bruce Betts: This is so true. All right. Everybody go out there, look up the night sky and think about dolphins because they're just so darn cute. We're talking of the marine mammal, not the fish. Thank you. And good night.

Mat Kaplan: I always wanted one. When I was growing up, I wanted one in the pool because I just thought that it'd be the greatest thing in the world. And we'd just go out and swim around and play ball. And when he got tired of me, he'd just poke me and I'd get out.

Bruce Betts: That is a beautiful vision. I'd like to think that happening for you.

Mat Kaplan: He's Bruce Betts having that vision right now. He's the chief scientist of The Planetary Society, and he joins us every week here for What's Up. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by its lively members. Help them assemble something grand at Mark Hilverda and Jason Davis, associate producers Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. Ad astra.