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Chris Tinney & Martin Van Kranendonk: Life Among the Stars

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As scientists, when we don’t have facts, we’re not required to have an opinion… we can just say ‘I don’t know’?

Chris Tinney

Water starts to become a problem when you start to think, how did we make life....Not only are oceans too wet, they're too salty and they can't concentrate the important elements required for life, like carbon, phosphorus, manganese, boron ...the oceans may not have been the setting for the origin of life.

Martin Van Kranendonk

Less than two decades ago, wondering whether other stars really did host planets was a matter for science fiction writers rather than scientists. Today, we’ve gone from complete ignorance, to a treasure trove of ‘exoplanets’– different sized planets that orbit around other stars – thanks to innovation, persistence, and meticulous measurement. But what does this mean for the search for life beyond Earth? Adding this diversity of exoplanets spread across our galaxy, to the planets and moons in our very own solar system, only makes the search for alien life more complicated. 

To find out where we should look for life, we need to ask whether a planet or moon is habitable and if it has the conditions necessary to get life started. Although we can (mostly) answer the first question, the second is harder to determine. Not only would we need to delve into a distant planet’s past, but also settle the hotly contested debate on the origin of life here on Earth? Did life on Earth start in deep sea vents as previously thought or in hot springs on land as more recent evidence seems to show? 

Join us to hear from exoplanet expert Chris Tinney and origin of life researcher Martin Van Kranendonk as they share the latest findings on these fascinating questions. 

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This event was chaired by Katrin Juliane Meissner, Professor of Climate Science at UNSW Sydney and the Director of the Climate Change Research Centre. 

Presented by the UNSW Centre for Ideas and the Australian Institute of Physics. Supported by UNSW Science. This event was part of the UNSW x National Science Week program.


Katrin Meissner: Welcome to the 2020 Einstein lecture with a very exciting topic tonight, Life Among The Stars. Or, where would we actually go if we want to look for life in outer space? We're very fortunate tonight to have two excellent speakers and panellists, Professor Chris Tinney, who is an expert on exoplanets or planets outside of our solar system. And Professor Martin Van Kranendonk who is an expert on the very beginning of life on Earth billions of years ago. This brings us to the first speaker tonight, Professor Chris Tinny. Chris is a professor in astronomy here at UNSW. He was born in Queensland, he grew up in Sydney, and then he left the country for a few years to work in California, and in Germany. But we're very fortunate to have him back here at UNSW Science, where his group has been involved in the discovery of over 50 exoplanets. He is Chris Tinney, the man who boldly goes where no man has gone before.

Chris Tinney: Tonight, Martin and myself are going to be doing a sort of a tag team act, me talking about the astronomy and the physics of the possibility of life amongst the stars, and Martin talking about the geology and the biology. That gives us a chance to both bring something different to this subject. And when I was invited to do this, I was told, now Chris, you've got to try and be positive, don't, don't try and be too negative, because amongst my colleagues, it's possible that if people are classified into glass half full, and glass half empty, I'm the category that gets classified is glass half empty. Now personally, I think that this is a shame, not just for me, but also for my scientific colleagues. Because if I'm given a glass that's half full, and asked, what is it? My answer is going to be, it's half a bloody glass. I'm a scientist, I spend my life measuring things. And so if I can't measure the contents of the glass to better than a factor of two, I'm doing a pretty bad job. Science is all about measurement. And most of the progress that we make in science, over the last two centuries, has been about the relentless improvement in our ability to measure things, both at cosmological scales and tiny little quantum scales. It's almost invariably through improved measurement of things that we either challenge prevailing theories, so for example, improved measurements showed that classical physics didn't work, and that we needed to invent quantum physics, or to confirm that new theories that have been come up with, are actually the truth, like general relativity. Or, to make astounding new discoveries. And exoplanets certainly fall into the category of astounding new discoveries. 25 years ago, we knew of precisely zero planets outside our solar system. So tonight, when we talk about life out there amongst the stars, and what we've measured, and how it's been done, and what it means, and looking for biology elsewhere in the universe, what I'll try to tell you about is what we know about the life out there amongst the stars. 

And the first thing I should say is, what life amongst the stars do we know about? Well, it's that one, it's our Earth, this is the only life that we currently know of anywhere else in the universe. It's the only example we've got. And so consequently, in the absence of any other examples, if we want to try and predict what life amongst the stars might look like or where it is, we're going to be talking about life like we know it, Jim. Life is we don't know it, Jim, is great fun, lots of fun down the pub, writes nice science fiction, but at the moment, we can't say anything about it. So what we want to do then is think about what is it that makes the earth habitable, what makes it just right for the life that we currently see? So there are lots and lots of things you can think of, we've got a nice solid surface, we've got the right temperature, we've got some liquid water on the planet, but not too much. We've got an atmosphere that's not too thick, and not too thin. The fact that we've got oxygen is actually not a big deal because life actually made its own oxygen, or at least made it free in the atmosphere. We've got plate tectonics going on on the surface of the planet. We've got that driving a carbonate cycle. There's a lot of things that have led to life developing and becoming the way we know it now. And that's a lot of stuff, and frankly, astronomers are not in a position to be able to answer most of those questions. 

So the two things we do tend to focus on when we think about whether a planet is going to be habitable are, is it solid, and can it host liquid water? The solid part, sorry, the liquid water part is important because we believe that liquid water is the key solvent that makes life work, that got life started. And that leads to a concept of a habitable zone for a planet orbiting its star. If a planet orbits much closer to its star than the Earth does, it will be too hot. If it orbits much further away, it will be too cold. And so this leads to the idea of the, sort of, Goldilocks zone in which our Earth happens to sit. Now, it's actually a little bit more complicated than that. And I'm not going to be able to go into too much detail on that. Because if you calculate a habitable zone for our solar system, you actually find that Venus lies in it, you find that Mars probably lies in it. But Venus is a hellhole with a thick atmosphere and a surface that will melt lead, and Mars is an icy desert that's got almost no atmosphere left. But you can still basically say, there are some parts of an extrasolar planetary system that should be habitable. And some parts that aren't. 

If we look at the one example we know about the planets in our solar system, or if we look at the planets of our solar system, and we look at the various categories of them, we can see that they divide up into a couple of different groups, this diagram is showing you the planets all to the same scale. So their diameters, their radii, are all actually equivalent in this diagram. And you can see that the biggest thing out there in our solar system is Jupiter, it's around about 1/10 of the diameter, or the radius, of the sun, and it's around about one eight hundredths of the mass of the sun. If we go down to the earth, we find something that is 1/11th of the radius of Jupiter, and around about one three hundredth of Jupiter's mass. The fact that it is smaller, a little bit smaller, and a lot less massive, leads you to calculate that the density of the Earth is actually much much higher than for the other giant planets in our solar system. So we call Jupiter and Saturn, gas giants, because they're largely composed of hydrogen and helium, they don't have a solid surface. Similarly, if you go out to Uranus, and Neptune, they're slightly denser than Jupiter and Saturn, but also don't have a solid surface. So if I want to find a planet that’s solid, that's got a surface, I want to be looking for a small planet, a rocky planet. It’s going to have to be something like the size of the Earth, within a couple of factors, then it's going to have to have a mass roughly like the size of the Earth. If I now look at a diagram in which all of the things in our solar system are scaled by their distance from the sun, you can see that those rocky, small planets sit right down there in the interior of our solar system. The gas giant planets are much much further out. And so while the Earth has an orbital period of just one year, if I go five times further out than the Earth out to Jupiter planets have orbital periods of 12 years, they're also much much further from the sun, and therefore they're much colder. 

What does that tell us about how other solar systems should look? Well, scientists tend, ever since Copernicus, to assume that humans don't live somewhere special in the universe, we assume that we're not living in a special God ordained location. And therefore, that if I've got one model to look at, I should probably expect to find that the universe will look more or less like that almost everywhere. And in order to come up with models for how planetary systems like our own formed, they developed a very complex model to try and say how our planetary system got to look like it is, and then extrapolated from that to how other extrasolar planetary systems should look. And this model basically says that planets are not a divine product of anything at all. They are just the building site rubble that is leftover from making stars. As gas and dust is being accreted onto stars, it is forced to form into a thin pancake like disk. And within that pancake-like disk, dust will start to agglomerate together to form what we call planetesimals, those planetesimals aggregate together to form larger and larger planet cores. And if those planet cores are far enough away from the slightly warm young star, beyond what we call the frost line, they can start to collect icy materials and they become rocky plus icy, they grow very rapidly, then they can start to collect gas, and they grow very, very rapidly indeed, and that would predict that in the outer regions, you've very rapidly formed large, gassy, icy planets, and in the inner regions close to the Sun inside the frost line where ices can't exist, because the young sun makes it too hot, you start to get solar, you start to get terrestrial planets, like we see in the inner regions of the solar system. 

Unfortunately, when we then went to find planets around other stars, we expected to find things that looked just like that. And the number of those that we found that looked just like our solar system, even today, is pretty much none, plus or minus a few. Almost none of the planetary systems that we have found around other stars actually look anything like our own solar system. What we have found is a whole menagerie of weird ass planets that look nothing like what we expected based on the model predicted from our own solar system. So we found gas giant planets. In fact, the very first extrasolar planets around normal sunlight stars we found were a gas giant planets, not orbiting out in 12 year orbits where Jupiter is in our solar system, but orbiting in four day orbits, way, way inside where Mercury orbits in our own solar system. Absolutely nobody predicted that, and it caused a furore. The idea that planets could possibly be in that location was contentious for a number of years, until we just kept finding too many examples for it not to be true. And the answer to that is, it turns out that planets don't just stay where they form, they migrate. Gas giant planets in particular, form out in the outer regions of extrasolar planetary systems and move into the inner regions. We found eccentric planets, now almost all the planets in our solar system move in nice circular orbits, they're all pretty much coplanar with each other. Whereas what we found in extrasolar planetary systems is that eccentric planets, planets that move on highly elliptical orbits are quite common. And now a planet on the eccentric orbit is hard to be habitable, because when it's far away from its host star, it is much much colder than when it is close in to the host star. And so you cannot really make eccentric planets, very habitable. We have found closely packed planetary systems like nobody predicted. Five, six planets all sitting inside where the orbit of Mercury is around our sun. Things that nobody predicted. We have found planets that are actually rotating, not nice and coplanar with their host star, but actually completely orthogonally to the rotation axis of their host star.

And what we've also found is that when we look at the statistics of planetary systems, the most common planets that we find are things that are slightly smaller than Neptune, things that don't actually exist in our solar system at all. There are no things in our solar system in between the mass of Neptune, and the mass of the terrestrial planets. So almost everything we've found out about extrasolar planetary systems is that they are different from our own. So is that the death knell? Should we expect that our solar system is unique, that every other planetary system will look completely different? Well, to understand that, we need to understand a little bit about how we actually find planets around other stars. And the real problem, it's a very difficult observation to do, it’s why we only did it 25 years ago for the first time. And the real problem with doing this is because stars are really, really bright. So the sun is burning nuclear fuel at the rate of something like 2,000,000,050 megaton nuclear explosions every second. So solar energy truly is nuclear energy, just at a safe distance. Planets, on the other hand, are really, really dark. He is an example of that. This is an image of Venus transiting across our sun. And if you look at Venus, compared to the sun, it's just black. Planets are mostly inert, they emit almost no light of their own. The other problem is that planets sit on the sky, very, very close to stars. That means that it is almost impossible to disentangle the very faint light from the bright glare of the star that they are sitting next to on the sky. And that means that only a handful of planets that we have discovered, have actually been discovered orbiting… have been directly imaged, that we've seen light from the planet. Mostly, what we do is just infer the existence of the planet, from the existence… from the effect it has on the star. So, the most obvious way to do that is to basically just do the experiment I've just shown you with the transit of Venus. And you can imagine that if a planet transits across its host star, and you measure the brightness of the host star very closely, it'll get a little bit dimmer. If a bigger planet goes across the same sized star, it'll get dimmer and it'll get more dim, it will basically dim proportionally with the square of the radius of the planet compared to the radius of the star. So if you go and do very careful observations of stars, you can see this dimming, if the orbital plane of the planetary system that you're looking at happens to be exactly aligned with our line of sight to the star. It turns out those observations are incredibly hard to do from the ground, the Earth's atmosphere means that the precision of measurement that you need to do is almost impossible. 

And so what's happened is that we have sent up a number of space missions. Two in particular, I'm going to talk about. One, the Kepler Mission that finished in 2018. And the second, the TESS Mission, which started in 2018. These are looking at patches of the sky looking at hundreds of 1000s of stars, at the one time looking for the tiny regular blips as transits go across them. And they have told us about 1000s of extrasolar planets. The animation you're looking at is what's known as the Kepler Orrery. It is a animation of 1000s of Kepler planets all sitting there rotating around, squiggling around their stars, as discovered by the transits detected by Kepler. Now, the key thing about the transit measurement is that it only tells you the planets size, it doesn't tell you anything else about the planet, it tells you the period, because if you've looked closely, you've seen a dip, and then you've seen another dip, and then you've seen another dip, if you see three dips, you can be confident you've measured the period correctly, and you've measured it size. But we want to know more than just the size of the planets, so what we would really like to know is, what are the nature of the planets in there? Are they rocky? Or are they gas giants? Or are they ice giants? The size alone doesn't tell me that, I need to know the mass of the planet as well. How can I measure the mass of the planet? Well, I can do that by relying on gravitational physics. So in this animation, if you look closely near the centre of the star, you'll see a little x that's not moving. planets don't orbit stars, sorry, planets and stars both orbit, the barycentre, the centre of mass of the system. So planets have big orbits, stars have little orbits. Those orbits are quite small, but if that orbital alignment is not in the plane of the sky, like I'm showing you there, but if I'm looking at a system that's tilted over, I will see the star move backwards and forwards. And I can see the star move backwards and forwards, if I can measure its velocity, we measure the velocity this is 1000 using the Doppler effect. Listen to this ambulance going past, you should have noticed that the pitch changed, the wavelength of the sound that we detect coming from the ambulance changes differently from when it's coming towards me than when it's going away from me, we can do the same thing with the light from stars, we can take the light from stars, and we can stretch that light out and measure it with a lot of precision and look at the dark lines that are superimposed on the big broadband spectrum of the star. And if I do that, very, very carefully over a number of years, I can measure a plot of dots like this with time, and I can fit a curve to it. The amplitude will tell me about the mass of the planet, the length there, the period, will tell me about the period of the planet, and once I've done that for long enough, I can write a paper, and issue a press release, and commission somebody to draw me some surfboard art so that the newspapers might actually cover my story. We've been doing this up at the Anglo-Australian telescope near Coonabarabran now for many years. And we've found many planets up there. One of the other things I can measure from this technique, if you look at that yellow curve there, you'll see it has a different shape from the other curves on that plot, and that shape tells me about the eccentricity, it tells me about the deviation from the circularity of the orbit.

If I combine both of those two things together, I can start to answer the question, is a planet that I found solid? If a planet is going to be terrestrial, like the Earth, it'll have a density of about five and a half grams per cubic centimetre. Something like Mars is a little bit lower, around about four grams per cubic centimetre, and Neptune, Jupiter and Saturn are much lower, again, more closer to one gram per cubic centimetre. If I can measure the densities of extrasolar planets by measuring both the size from a transit and the mass from a Doppler observation, which we have to do from the ground, then I could combine those together and make a plot of dots that tells me about the distribution of planet densities. And what this plot here is showing you, the white one with the plots of dots, is that small planets have a tendency to be higher in density, but it's not a one to one relationship. So, it's not enough for me to just say, to observe a planet transiting and say, ooh, that's a small planet, it must have a solid surface, it should be rocky, I actually need to go and measure masses. And that's what we go and do all the time with our big ground based telescopes. 

Now, the next question, is it so…. that's something about how we address the question of are there solid planets out there? Are those solid planets sitting in the habitable zones? There are like a handful of systems that we have currently found, that are, what we think are small, rocky planets sitting near their star's habitable zones. Here is a selection of those for you to look at with all of them having one or two, or even three planets that might be potentially habitable. But there's a little bit of a difference here, there's a tweak in all of these three systems, and indeed, all of the systems we found that are remotely habitable, which is that all of the host stars here are not stars like the sun, they are all smaller than the sun. And that is because currently the technology for detecting both the transits from small planets in one year orbits, and then measuring the Doppler follow up measuring the masses from small planets around sun like stars in one year orbit is just too hard. If you've looked at all of those plots before, we were measuring velocities at levels of metre per second, to one metre per second, to see the velocities of these tiny little planets, Earth like planets, in earth like orbits around the sun like stars, they need to be down at point one metre per second. But fortunately, not all stars are created equal. There are small stars out there called M-dwarfs, for purely historical reasons, that are lower in luminosity than the sun. And because they're lower in luminosity, the habitable zone shrinks in closer to the host star. And I can then actually find that both the Doppler signature and the transits become easier to measure and the periods become shorter. So I don't have to spend an entire career just looking at the one system. That then means that these M-dwarf planets are the best places for us to go and do searches for bio signatures. Now, Martin will probably talk a little bit more about this later on. Currently, as I've said, we're just inferring the existence of planets, what we'd really like to do is be able to see something about the light from those planets or the atmospheres of those planets. So that we can take the vast array of models that people have got out there for planetary systems, and constrain them down with some data. We're not able to do that at the moment, sadly. Our telescopes are just not big enough. Whether they're on the ground, or in space. On the other hand, over the next decade or two new giant telescopes, like the 25 metre Giant Magellan Telescope will be becoming available in Chile, the James Webb Space Telescope will launch at some point in the future, whenever NASA gets around to it. This is an eight metre space based telescope. These are telescopes that will give us the grasp, to be able to try and look at actual bio signatures, to try and work out whether the atmospheres of these planets really are habitable, whether they have the signatures for life. In the meantime, what we need to do is find the best places to point those giant telescopes when we come around. And that's what we're doing here in Australia at the moment. The UNSW lead Voloce facility, which is currently working away up at the Anglo-Australian telescope near Coonabarabran, is looking at new planets being discovered as we speak, because TESS is still up there, orbiting around the Earth and the Moon finding new planets all the time. And that will then give us the places where we want to go and look to understand whether life really is out there. And having run over time. I will now hand over.

Katrin Meissner: Thank you, Chris, for this voyage into outer space. Our next speaker is Professor Martin Van Kranendonk. Martin is a professor of geology and astrobiology here at UNSW Sydney. He's also the director of the Australian Centre for Astrobiology, and the Big Questions Institute. Martin was born and trained in Canada. And he moved to Australia in 1992. So he claims that he moved to Australia to follow his passion for ancient geology. But I wonder if the climate maybe had a small role to play in this decision. He joined UNSW in 2012. And we're very lucky to have him here. His team investigates the earliest signs of life on Earth. And that happened more than 3 billion years ago, long, long time before dinosaurs, of course. And his research is also used by NASA, and by the European Space Agency, and the search for life on Mars. Martin, the floor is yours.

Martin Van Kranendonk: Thank you very much Katrin. And good evening, everyone. It's my great pleasure to be able to speak to you tonight about something I'm extremely passionate about. And that's been alive. And the question of course, on everyone's lips is, is there life elsewhere? Is there life out amongst the stars? Could there have been life in our very solar system? And so Chris gave us a really nice introduction that painted a really lovely picture about how diverse our solar system is, and how diverse planetary systems are around other stars. And I want to then explore that if you had a chance, you know, to get a rocket and go explore for signs of life in the universe, where exactly would you go? And that's a really difficult question. Of course, in our own solar system, that technology allows us to go and explore the worlds that are in our relatively nearby neighbourhood. And we have a wonderful smorgasbord of worlds to explore. We heard about Jupiter, Saturn and Neptune. But of course there are also moons of some of those giant planets, which are worlds right unto themselves. So you can see the sulphur volcanoes of Io on the right, and the water ice worlds of Enceladus down in the bottom. And of course, there's Mars, which has been a siren for thoughts about life outside of Earth for a long, long time. 

To get life, the ancient Greeks 2500 years ago, just about, identified the four basic elements for life as they knew it, earth, water, air and fire. And that was the world as they saw it. And that almost absolutely applies to thinking about life, you need to have a rocky planet nucleus, so that's the earth. You need to have water, as we all know, everywhere that there's life on Earth, there's water. And, you need to have some heat and fire to keep things warm, and to keep life moving. But where it's different, in terms of getting life started, is you need to have organic molecules coming from space. The meteorites that have bombarded earth and all the planets early in their system contain organic molecules, the building blocks of life. And this, of course, is the key element for making life. Because all of life on Earth is carbon based. When I say organic molecules, I mean, these complex molecules that have carbon. Carbon is very common in the solar system. In fact, in the universe, just like water is, it's a very common molecule. So to have these as the building blocks of life is not so unexpected. And so if you have those four elements, somehow, miraculously, you get life. Simple. Well, of course, it's not so simple. There are so many steps that we still don't understand about how to make life. And so part of the question when you're searching for life elsewhere, is, does a planetary body, does a moon have the basic ingredients for life?

So those basic elements that we talked about about, water, earth, heat, were combined back in the 1970s into the model for the origin of life, as occurring in the deep oceans, well below any penetrating sunlight, at these sites called black smokers, where hot water has been circulating through the crust, and comes back to the surface mineral rich and very hot. And that's exciting for chemistry because then you can make things happen. You can make carbon combined with other elements and make some complexity and stuff. So when you have steep gradients of heat and temperature, and this interaction between rock and hot water, not cold water, then you can get some things happening. And it was believed, and it still is, that the earliest forms of life just lived on chemical energy, nothing to do with sunlight, like we know and love here in Australia, and of course, all around the world. And so, as Chris had pointed out, that idea of having water as a basic ingredient for life, means that finding the habitable zone, and in space exploration, to follow the water, find places where there's water. So earth you can see at the top sits right in that habitable zone of blue, the right distance from the stars. But there are also moons around some of the larger planets that get heated by tidal forcing. So on the right, we can see Enceladus and Europa, two moons of Jupiter and Saturn, that have water ice crusts, and actually liquid oceans as well. And so one of the most exciting avenues for space exploration to look for signs of life now is going to the moon Enceladus. Because it's been observed by spacecraft flying by, that there are jets of water coming out of the planet. And that points to an ocean world. And so there are missions being designed to go to Enceladus with a little submarine that can drill through the ice, and then poke around through the oceans and explore for any life that might be deep down. The other idea that people have had is that you could actually send a spacecraft through those jets of water, with this beautiful little piece of technology called nanopore that can identify DNA, our building blocks, the stuff of our own genetics, they can identify that just by getting a sample of water. And so it's been suggested that we could just have a mission to fly a probe through the jets of Enceladus, and see if there's any life there by looking for DNA. 

But all of this is predicted on the idea of water, which is good for life that already exists. Now, I say that because you have to remember that even the simplest form of life, a tiny little microbe that you can't even see with your eye, is an unbelievably complicated machine. It has a little motor, a flagellum, it's got a set of pumps and a membrane and all kinds of organelles that create this activity. That's an extremely sophisticated system. And so we know that that works in a water medium, fantastic. But how did we get to life? And what were the conditions necessary to make life? So I showed you before this meteorite, famous one, fell here in Australia and a little town called Murchison, just over 50 years ago. It has all kinds of organic molecules. And in fact, people who still have samples of that meteorite in a jar, if you open the jar, you can smell space in that Murchison meteorite, because those organic molecules are partly volatile. But to take those simple molecules and make them more complicated for something like DNA, there's so many steps. It's a big complicated process. And then how do you put DNA inside those membranes and make it work with other organelles and make it move and reproduce, and all that sort of thing. There are big gaps in our knowledge. And it turns out, though, that some of those early steps, the conditions for making complex organic molecules means you have to have dry conditions. And so this is known now as the water problem. That conditions to make life, not when you already have life, but conditions to make life, may not need water all the time. And so the water problem is this complicated idea of some organic geochemistry here, but basically to take the simple building blocks from the meteorites into very complex molecules that are the building blocks then for complex life, the way to get them to bond together is to kick out a water molecule. You can see those h2o and the arrows going out, the energy of binding molecules together is caused by water leaving the system. And so if you want to make RNA or DNA, if you create that in a watery environment, they'll just break down, they'll just dissolve. 

And so water becomes a problem when you start to think about, how did we make life? So in this quote from David Deamer, a colleague of ours from the University of California at Santa Cruz, you can heat a solution of amino acids, so simple building blocks, and water forever, but none of the complex molecules, here called polymers, will be produced. On the other hand, polymer synthesis can occur if the amino acids are in a dry state. And this has led a whole group of researchers all around the world to rethink the origin of life. Because the oceans, not only are they too wet, they're too salty. And they can't concentrate the important elements required for life like carbon, phosphorus, manganese, boron, the oceans may not have been the setting for the origin of life. Instead, there's a whole group and we're just one, that had the cover of Scientific American a few years ago, considering now that life may have started in hot springs on land. And it's primarily because hot springs are freshwater. And they can undergo the wet dry cycles required to make those complex molecules. And here's an image of a geyser erupting in Iceland actually at the place where the name came from, Geysir. And geysers can erupt every hour, the ground gets wet when it erupts and dries out. Organic molecules get more complex. They're interesting chemical environments, that water rock interaction, hot water rock interaction that we saw on the deep sea vents. They've really got a lot going for them. And so there's quite a lot of excitement now about this idea of life on land. The other thing that hot springs we know can do, is that if you take those simple organic molecules, with some fatty molecules, they can self assemble into spherical structures shown in the bottom right, called vesicles, that are the same composition as the membranes of the simple cells. And so we're making proto cells. And in fact, those proto cells can concentrate organic matter that gets more complicated on the road towards RNA, and DNA. And so hot springs are wonderful for a variety of reasons that oceans can't do. They're also the most complex geological environment on Earth, much more so than the deep oceans. Here's a lovely example from around Rotorua and New Zealand, of two different springs, very close to each other. One like, normal sort of water, neutral, but quite hot, and it's precipitating arsenic and gold, so there's element concentrations. And the one in the foreground, that greenish pool, is very acidic, if you dip your finger in it, you will lose your skin. But that has a different chemistry. And you can see the gleaming water in between, those fluids are mixing. And to make life, something as complicated as life, you'd need complexity. And hotspring fields are complex. So people are now very excited about investigating hot springs and their complexity. So model is now being developed, that we've been part of, that starts to think about organic molecules coming in from meteorites in space, early in Earth's history, getting concentrated in pools on land, and then undergoing this wet dry cycling, of making organic molecules more complex, getting caught up in these proto cells, and then undergoing sort of an early Darwinian evolution to make more and more complex systems on the road to life. And then it had to adapt to the oceans, later. So that's a pretty fundamental rethinking of our own origins, because of course, we all come from this process. 

But could this model apply to the early Earth? We see hot springs today, the Earth is 4.5 billion years old. What about when our planet was very young, when it was hotter? When the sun was cooler, when all kinds of things had changed? How can we understand whether this could have applied back in early Earth? Chris showed this wonderful picture earlier, I think it's one of the best images of planet Earth from a satellite, of course, because Australia is in it. My field is up in the northwest of the country, and there are rocks preserved there that are three and a half billion years old. And when we go back that far in time, we have to get rid of our thought of our planet as a blue planet with green continents and blue oceans and white clouds. If I was able to sip a pina colada on a pier, looking out over the ocean three and a half billion years ago, the oceans would be bright green because they're full of iron. There's no oxygen around, the sky would be orange because it's full of carbon dioxide. And the landmasses would be black volcanic rocks. No green covering, no plants, no fungi, no dinosaurs, no elephants, nothing. And so if I was looking at Earth from afar, I would see a green world with black continents and orange puffy clouds. And so our early Earth was an exoplanet. It was a very different place to what we have today. 

Our group does research on the oldest evidence of life in the world, from those rocks in Northwest Australia. And we've been able to prove that structures left behind in rocks were actually made by communities of living microorganisms. And work that Raphael Baumgartner did, while he was here as a postdoc for a couple of years, definitively proved that these structures and rock were made by life, because by peering deep into the insides of those rocky structures, we can find the remains of organic matter, of the microbes that made them. So just like Chris would look far out into the solar system and well beyond into the universe, by increasing magnification. Our studies go down to the opposite direction, we go finer and finer and finer, to seek these little kernels of scientific truth. The other part of the research that we've been able to contribute to the story is, we found that the oldest convincing evidence of life, three and a half billion years ago, occupied land. And this rock that my PhD student, now graduated, Dr Tara Djokic, found in these ancient hills is very unique and formed from a geyser erupting onto an exposed land surface. The splashing makes those black and white layers that you found, so we can prove that there were wet dry cycles on land three and a half billion years ago. And what's more, these hotspring environments are occupied by those microbial communities. So we've been able to confirm an image that was actually drawn many years ago now, from the Smithsonian Institution here, that the first foothold of life on a very young earth would have looked like this, splashing geysers, hot springs, and adapting to the oceans and a volcanic world. 

The other part of our research has a group that's exploring more than the hotspring systems. And we're doing experiments in the natural world instead of in just a glass test tube in our labs, to actually try and start to make some of these complex polymers. So we're looking at trying to make RNA in natural systems. And we have a group in the School of Chemistry that's looking more into how to make these proto cells and how they can develop. Now, this idea about an origin of life on land has profound implications for astrobiology, the search for life in the stars. So if life started in the deep oceans and was always in water, then yeah, the moons of Enceladus and Europa would be interesting targets. But if life started on land, as it now seems more likely, it's perhaps that those water worlds never had the conditions to get life started. It's true, they might be habitable now for life that exists, but without a rocky surface, without hot springs and geysers, maybe life never could have got started there. And then what about Mars? Originally, I was not very excited about Mars, because it doesn't look to have ever had an ocean. But now as I get to learn more about it, and our ideas are changing, it actually looks like a very good target to search for life. Although really, if you look at it, from some of the first landings, you think, really? Would I go look for life in the middle of a desert? Well, this is what Mars looks like today. But way back in the ancient past, in fact, about the same age as the rocks that we study in the Pilbara, three and a half billion years ago, there's very good evidence for extensive water on Mars. In fact, it had a hydrological cycle, there were running rivers, there were dammed up lakes, and there were widespread glaciers as well. There's tiny little remnants of water left at the surface of Mars. On the top left, you can see a little crater that's got a little frozen pond of water ice. We know there's a lot of water ice in the subsurface of Mars, it's frozen, locked into the soil. But most excitingly for our work, and I think for astrobiology in general, is the discovery that Mars had hot springs. It had volcanic heat, ,we know it had water, and so it has those basic ingredients for making life. And the picture in the bottom right is a little volcano called Nili Patera, and the arrows are pointing to two bright white little features there. Those are opaline silica deposited from hot springs, about three billion, or three and a half billion years ago. And when we found this out, combining our research from deep time, Earth, with our knowledge now about this prebiotic chemistry and the origin of life, oh my goodness, all of a sudden, there's this really exciting target on Mars. At the moment, you would have all heard that there are a number of missions that have launched to Mars, the Chinese have launched a mission to Mars, NASA's Perseverance rover just left a few weeks ago. And the Europeans were due to launch this year, but have been delayed and will send their rover in a couple of years time. All of those missions are using that idea of follow the water. And they're going to areas where there was running water, deltas, rivers, lakes, and looking for the traces of life and these organic remnants. But we think that there's an opportunity for another mission to target a type of rock that's already been found by the Spirit rover, about 10 or 20 years ago now. There are outcrops of this opaline silica shown on the right, very unusual texture, little nodules with bumpy kind of fingerlike textures, those are very unusual rocks to find, they've been able to determine that they're made of opaline silica, the same stuff we know is on earth. Hot springs, and textures in those rocks, the red image is from Mars, the grey and white image is from Earth, match 100% deposits from hot springs here on Earth. And if you take one of those little fingers from the earth sample from this place in Chile, and you take a very close look, there's that broken off finger in the upper left, when you use a really high magnification microscope, the silica actually entombs the micro fossils that were living on its surface when the waters were warm. And those finger-like structures are actually made by biology. So some people have started to suggest that there may even be a biosignature already on Mars that we've seen. And we're starting to develop a mission concept with a group of colleagues in Japan, including the Japanese Space Agency, to develop a mission to Mars to go get those samples and bring them back to Earth. We don't think of a fancy rover with lots of scientific instruments, we just want to go get a few grams, and bring it back, and see if there are signs of life. So any future aspiring astrobiologists, there's still lots of research to be done. There's lots of exciting exploration to become involved with. And it's a great discipline that we're still learning so much about. So I want to thank my extraordinary colleagues and students who have been on this journey with me. And I look forward to being able to update you in the years to come. Thank you very much.

Katrin Meissner: Thank you, Martin. For this voyage, back in time and also all the way to Mars. We will now move on to our q&a session. And we will start with a pre-recorded question from Alex Park Community School, I believe. 

First Question: Hi, I’m Maisie and this is Ivy and we are from Alex Park Community School, our question is, how will we withstand the extreme temperatures on Mars?

Katrin Meissner: Thank you, that's a wonderful question. And I think it's probably a question for Martin. How will we withstand extreme temperatures on Mars? 

Martin Van Kranendonk: Thanks for that. Yeah. So that's a very good question. It does get extremely, extremely cold on Mars. I'm Canadian originally. So it wouldn't be a problem for me. But most others would probably find it a bit challenging to survive when the temperatures can get down to as cold as minus 200 degrees. And so of course, nobody can survive those temperatures, even machines struggle under that kind of extreme temperature. So to survive there as a human, you need to have a suit that will not only protect you from the ionising radiation from space, but have a heating element that can keep a thin layer of air warm around your entire body. So you don't literally freeze to death.

Chris Tinney: And of course, then there's the whole issue of no atmosphere, and what atmosphere there is being mostly carbon dioxide. So you pretty much want to take your environmental system with you. You're not going out for a hike in just a nice warm pair of socks.

Martin Van Kranendonk: Absolutely. You need a whole survival pack every time you go outside on Mars.

Katrin Meissner: Not a very friendly place to live.

Martin Van Kranendonk: It's a very tough place to live.

Katrin Meissner: Wonderful. And I think we have a second pre-recorded question. 

Second Question: I’ve got a question for Chris Tinney: is there a planet which can sustain life, human or alien, in our solar system?

Chris Tinney: Ok, so another good question there, well, there’s one. There's one that we know of, and that's the one that we're currently on. So that's a pretty good reason not to screw this one up. As Martin has mentioned there, there's the possibility that there may be habitable environments on some of the moons of the gas giants like Enceladus. And Mars probably may once have been habitable, even if it isn't, even if it isn't nowadays. I mean, it once had water, it once had a thicker atmosphere. And it was once warmer because the sun was warmer when the solar system was very young. It's just difficult to see how life survives there now. In fact, having listened to Martin talk, my question was, which do you think will come first, the sort of fossil evidence for extinct life on Mars, like, you know, ancient stromatolites, or the sorts of features you were talking about, or the measurement of active biology that somehow managed to carry on?

Martin Van Kranendonk: And that's a good point, I actually forgot to mention that in my talk, but all of the missions are looking for past life. And it's partly because of that aspect that Mars was warm and wet three and a half billion years ago. So more likely that there was life then. But they're also very concerned about looking for active life, because they're fearful that we might contaminate the planet, when we go to search. So the missions, and certainly I know from NASA, I've been and seen the rover being built, they're incredibly careful about being as sterilised as they can, they clean it, and they take everything apart, and it's just as clean as possible. But bacteria are everywhere. And so there's always some microbial component that goes to a new planet. So they've purposely avoided going anywhere where there's possibility of water or ice on Mars, for fear of contamination. So they're looking for past life, very ancient life.

Katrin Meissner: Interesting. Thank you. And I see there's lots of questions coming in from our audience. Thank you for submitting questions. The first one is from Rita Fatima, and it reads, is it possible that somewhere, there's a new kind of life that doesn't require the conditions that the life is, we know, needs for survival,

Martin Van Kranendonk: I mean, that's, of course, a very exciting possibility that there are types of life that aren't like us that aren't built on carbon or DNA. And, you know, chemically, it's possible. But when you look at it in detail, every time you substitute a different element for carbon, or oxygen, it's harder, it's less efficient, and it's less able to be variable. So one of the amazing things about carbon is that it can form molecules, but in all kinds of different shapes. You know, I talked earlier about complexity. Carbon is a molecule that is able to be very complex in the way it structures with other elements. And that allows, if you think about it, a very diverse scaffold to be made. Everybody knows DNA, that beautiful spiral, that's organic matter, that's carbon. But something like silicone that bonds with oxygen, it can only do it in one way. So you're limited every time you go away from carbon, and the basic building blocks of life as we know it, it gets harder. And the other thing to keep in mind, and Chris would be able to tell better than this, but the molecules that life is made of are actually some of the most common elements in the universe. And so it's not a surprise that they come together in this kind of way. 

Chris Tinney: Simple organic molecules are incredibly common. Yes, that's certainly true. The more complex ones, the more complex they are, then the rarer they are out in interstellar space. But I would actually, my answer to this question would be that this definitely falls into the category of unknown unknowns as Donald Rumsfeld famously said, this is one of these areas where it's great to be a scientist, not a politician or a religious leader, because when we don't have facts, we're not required to have an opinion. We're just allowed to say, I don't know. 

Martin Van Kranendonk: I don’t know. 

Chris Tinney: So this is one where I think we say, we don't know. It'll be great to find out.

Katrin Meissner: Okay, we have another question from Tommy Hartono. Asking why a countries resisting to work together in search of life outside Earth? And how can we make the countries work together? We are scientists, right? Not politicians. But, who would like to take that one?

Chris Tinney: Well, I would say that actually, most scientists are actually incredibly collaborative across international boundaries. So I work regularly, you know, with European scientists, with American scientists, with Chinese scientists. Frankly, we spend most of our time trying to get around the various barriers that are put in our way. I don't, I mean, I think that there are national political issues around things like space exploration. But even there, there aren't very many missions that go up nowadays that don't involve collaboration, that don't involve this widget being built in this country, and that widget being built in another country and then being put together. Most satellite missions, most telescopes that go up are international collaboration. So we do actually work together rather a lot.

Martin Van Kranendonk: Yeah, that's absolutely true. So the Perseverance mission that's just launched, that's, you know, headed by NASA, but they have an instrument on board made in Norway, they have scientists from all around the world who are part of the mission team and have helped design the rover. And so yeah, it's called the NASA mission, or it's called the Chinese mission, or it's called the UAE mission, because they're the ones who have the idea and the concept, but those people work together, and they share technologies. Because, really, I mean, one of the beautiful things about science is that we're doing it for ourselves, for the planet. And space exploration is one of those endeavours that I think is widely regarded as something that's a benefit to all of humanity. So these projects do work in harmony across many different countries. And, in fact, it's actually a beautiful example of collaboration.

Katrin Meissner: Science has no borders, or boundaries. Adrian is asking, if the abnormally large moon around Earth might be a factor in the chance of development of life?

Chris Tinney: So I think Adrian is making the point there that the size and the mass of the moon compared to the Earth is quite unusual in our solar system. None of the other planets, except maybe the Pluto Charon, are anywhere near close to be similar sorts of sizes. Most satellites are actually much, much smaller. And I'm afraid, Adrian, the answer to that one, again, is we don't know. What role the moon would have had in the first start of early life is really completely unclear. It's just, it's guesswork, what impact it would have had on the environment four and a half billion years ago.

Martin Van Kranendonk: And one of the interesting things is we get as Chris described, with his Doppler effect of the mass, we can measure the rotation of the moon, and we know it's actually getting further away from the Earth. There’s actually a slingshot effect from the earth’s tides that actually are pushing the moon a little bit further away. So early in Earth history is probably closer, and probably the tides were larger. And so there could have been an influence in terms of how landscapes developed, how interaction of water and rock could have acted back at that time. But that's very difficult to know. And it's not clear that it would have an effect than at the sort of molecular level. It clearly has an effect on life now. We know all about the full moon and the effect that it has and spawning as a coral and the seasons, all those sorts of things are tied to it, absolutely it's got an effect on complex, macroscopic life. But at that smaller level, it's not clear how there could have been a relationship.

Katrin Meissner: The next question is interesting. How will we fight the aliens if they are hostile?

Martin Van Kranendonk: I think there have been a lot of books written about that, that probably have better ideas than us meagre scientists. 

Chris Tinney: No idea. 

Martin Van Kranendonk: Have to outsmart them, I guess.

Katrin Meissner: Right. And there's a wonderful question here from Ted who is in third grade in primary school, and Ted is out asking, do aliens need DNA or RNA or even ATP? That one is for Martin.

Martin Van Kranendonk: Very nice, very nice. So one of the extraordinary things in the world that I work in, is, if you and I see something that's alive, we know it's alive. But again, when you get down to the really fine details, proving the divide between alive and not alive, is incredibly difficult. There are mineral systems, for example, that can grow and become larger, and often make new systems. They're extremely primitive organisms, slime moulds, for example, that can think and solve problems, but they're actually only protists. So does something that's alive need DNA? It actually depends on how you define what is alive. And that is still a challenge for us, believe it or not. I know I'm alive, or I think I am. I'm pretty sure Katrin’s alive. But there's one floor for example, we wouldn't say it's alive, even though it's made from previously living materials. So there's certainly a way of thinking about life, if you can reproduce, grow bigger, that has been found in systems that don't have DNA, or RNA or ATP. Could they build a rocket ship and come and take over our planet? That's not so clear.

Chris Tinney: I suppose the other option is, the other question is, are they just one, you know, if the first forms of life came up with something that worked, you're not going to… evolution builds on what you've already got, and so you build, you build a better form of DNA or a better form… you build a better form of what you've currently got, you don't scrap everything, and go back and start anew. I would have thought it's entirely possible that you might have another incredibly complex organic molecule developed that serves the same function if you started completely again, anew and in an entirely new system. It's so obvious that DNA and RNA are predetermined, they’re a logical end result of evolution. They're just the thing that works for us.

Katrin Meissner: And here is a question from Luke Barnes, who would like to know what exactly the future telescopes like the James Webb will see, whether on exoplanets, clouds, atmosphere?

Chris Tinney: So look, Luke, there are enormous numbers of people across the globe, and  in the United States, especially who are building JWST, thinking about exactly that problem. Our usual experience of building giant telescopes at exorbitant cost is that, you have to say, I'm going to do X with that telescope, I'm going to see this biosignature, I'm going to make that discovery. And so you spend 10, or 20, or 30 years building it, and lots and lots of money. And then you make it freely available to the whole astronomical community via a peer review process. And by that point, the whole subject matter of the field has invariably moved on. And the actual experiments that this expensive telescope gets used for are completely different from the ones that you thought of when you first started planning it 30 years ago, usually, you make much better and more interesting discoveries than you were actually planning on. So exactly what we're going to find with JWST, I'm afraid Luke, I don't know, it's been designed to try and see atmospheres in other planets to see what the compositions of those atmospheres are, they won't have the resolution to take pictures of the surface of the planets, but it'll tell us something about what other planets look like. But I would guess that the things we find will actually be far more interesting than the things we currently plan.

Katrin Meissner: Thank you. And this brings us to the end for tonight. Thank you again for tuning into Life Among The Stars. And thank you for our fantastic panel for a very interesting evening. If you like this event, please subscribe to the newsletter of UNSW Centre for Ideas, and you will learn about other events like this. And enjoy the rest of your evening, stay healthy and to finish in the spirit of the night, live long and prosper.

Chris Tinney Headshot

Chris Tinney

Chris Tinney is a Professor of Astronomy at UNSW Sydney. Born in Australia and raised in Sydney, he moved to Pasadena, California, to do his PhD in Astronomy at Caltech in 1987. After a brief stint in Munich, Germany, he returned to Australia to work for 12 years at the Anglo-Australian Observatory, before moving to UNSW in 2007 to found Australia’s first research group focussed on the planets of other stars. His Exoplanetary Science at UNSW group has been involved in the discovery of over 50 exoplanets to date, and is actively engaged in pursuing studies of new, and potentially habitable planets, being discovered now by NASA’s TESS mission using his 5.4 million Veloce facility at the Anglo-Australian Telescope.

Martin Van Kranendonk Headshot

Martin Van Kranendonk

Martin Van Kranendonk is a Professor of Geology and Astrobiology at UNSW Sydney, and is the Director of the Australian Centre for Astrobiology and the Big Questions Institute. Born and trained in Canada, Martin moved to Australia in 1992 to follow his passion for ancient geology, and joined UNSW in 2012. His team investigates the earliest signs of life on Earth, and the environments it inhabited more than three billion years ago. This research is used by NASA and the European Space Agency in the search for life on Mars, and for understanding the origin of life on Earth. Martin has appeared on numerous television documentaries and films around the world and is passionate about engaging people of all ages with the big questions of science.

Katrin Meissner Headshot

Katrin Meissner (Chairperson)

Katrin Juliane Meissner is a Professor of Climate Science at UNSW Sydney, and the Director of the Climate Change Research Centre. Born in Germany, she completed her undergraduate degrees in engineering and physics in France and was awarded a PhD in Germany in 1999. She then moved to Canada, where she worked as an Assistant Professor at the University of Victoria. In 2009, she moved to UNSW Sydney. Meissner researches climate change, variability and transitions. Her team investigates abrupt climate change events in the Earth’ history, and thresholds and feedbacks in the climate system. 

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