Special Topics - Alien Life and the Probability of Life Part 2: Life as We Don’t Know It

okay let's go ahead and get started so to recap a little bit yesterday in this special topics lecture on alien life and the probability of life we looked at life essentially as we think we understand it right i talked a little bit about the somewhat fuzzy definitions of what life is cautioned you that this is a relatively myopic view because we have only ever seen what we consider to be life on this planet one planet in a solar system that's one of trillions of solar systems in the universe we have no idea whether or not there are other things we would consider living out there but if we imagine that when a star forms and if rocky planets form in a zone where it's not too hot not too cold so that liquid solid and gaseous water can essentially co-exist on that surface then maybe based on the history of life on earth independently on a world like that life as we think we understand it could have also emerged but today we're going to explore the possibility of life as we don't know it okay and that's the theme for today it is as i've cautioned a very narrow view of what living things are you know even intelligence and the sense of identity itself these are things that we take for granted from the human experience but a fair question to ask is if you met another intelligent being that didn't think in the way that we did would you know it and would you not consider it intelligent and would it not consider you intelligent okay these are things you have to think about when you start diving into the subject of life and again to reiterate i'm going to have a better reference than this in the sort of star trek universe we've that we've used as a reference point for some things during the semester there are a strange number of humanoid bipedal ten-fingered ten-toed life forms with various skin colors and various ear shapes and eyebrow ridges that all essentially look human and all essentially share similar cultural aspects some might be more peaceful some might be more thoughtful some might be more warlike et cetera et cetera et cetera but they are all strangely similar to humans and of course that's on purpose you know computer graphics only came into sort of a fairly modern form where you could emulate living things in a realistic way in recent decades um obviously you just needed to use actors to do the parts of aliens and it was cheaper just to make them look like humans with paint okay or makeup so that they didn't look that different in fact in the 1990s the tv series star trek the next generation tried to explain why it was that there are so many humanoid life forms in the galaxy as an ancient race far more ancient than the other ones seeding the building blocks of dna on many worlds and then just kind of letting it happen and that somehow from this humanoid forms were inevitable was the idea but even that is not really that believable okay but let's really go into like alien life and what that could look like and there are many ways i'm only going to touch on a handful so again if we knew everything we didn't know then we wouldn't need science science is about establishing reliable information about the natural world it is a methodological process that has to be repeated over and over and over again a body of knowledge that can be memorized only arises as a result of establishing that reliable body of information as reliable in the first place that's what science does and when there's nothing new to know in the universe presumably science will simply stop okay but we are seemingly nowhere near that point right now and again i want to remind you that our conception of life is biased in at least several ways right carbon-based carbon atoms is the scaffold of the kinds of molecules organic molecules and so forth that we take for granted nitrogen as the scaffolding for dna and rna a rocky watery planet which earth definitely qualifies as earth-like temperatures okay in the sort of 20 degrees celsius range typically is what you find across the surface of this planet heavily regulated by the feedback mechanisms built into the atmosphere and surface regions of the planet we take that stability for granted it has allowed life as we understand it to flourish but it is a very narrow range of temperatures we can adapt as can other creatures pretty readily to changes there are extremophiles that live near volcanic vents on this planet that live in extreme cold okay we can adapt to both of those things we're a very adaptable species but it's still a very narrow range i mean we're essentially talking sort of sub freezing to maybe a hundred and fifteen hundred and twenty fahrenheit near near volcanic vents we're getting closer to the temperature of liquid rock and i'll come back to that topic in a bit but it's not a very wide range of temperatures the existence of dna at all for the passing on of traits heredity and for the ability to alter traits through random mutation okay so a sub structure that can be copied but also altered to create variety our definition of intelligence in self as i said before we're highly biased to what we understand as thinking things okay and a sense of self there may be creatures that have no particular sense of of self right that values very specifically the organic community over the individual ants may be one of those for example i would consider ants to be highly intelligent because of the sheer amount of engineering that they're capable of doing uh but they don't seem to value the individual except in very specific ways right that's an alien way of thinking to us okay nonetheless we take advantage of community too humans have thrived and succeeded because of community so these are things to keep in mind as you would grapple with this subject especially if you're thinking about going into it as a career move at some point so let's start with the first possible what we don't know or what we might not have expected although from chemistry we might actually really expect this and that would be rather than carbon-based life life that depends on silicon the chemistry of silicon and the chemistry of carbon are for all intents and purposes essentially identical they are in the same column on the periodic table of the elements and so the way in which they bond to other things is extraordinarily similar what differentiates them of course is that silicon is a lot heavier than carbon now like its cousin carbon silicon oxygen carbon these things were forged beginning in the first stars they did not arise in the universe at the beginning of time they arose starting 500 to 1 billion 200 million to 500 million years after the big bang that's when the first stars lived and then died they lived only tens of millions of years and they spewed heavy elements out into the universe in the form of clouds of gas which then under the right conditions gravity pressure and so forth could recompress and form new generations of stars which would then also burn hydrogen and helium and eventually carbon and oxygen all the way up to iron where the fusion process chokes out in stars and they explode and die so silicon was forged right there alongside carbon and oxygen in those first death phases of those young stars and because of all of its similarities to carbon apart from its heavier mass there's been a lot of speculation that maybe somewhere maybe even on this planet but perhaps definitely on other planets that something using silicon which may have been abundant in that world when it formed uh could have evolved in a silicon-based way now this has been a topic for decades of course and there's some recent work that i cite in the bibliography to these slides that suggest that it is possible but maybe not very likely of course you might say the same thing about carbon-based life on a rocky planet around a you know g-type star in the middle of a suburb in the milky way okay so likely in all of this i was talking to where's donnie done i was talking to donny about probabilities after the lecture last time i mean when you get into these like these could be ultra rare or they could be ultra common events they could be inevitable events once these atoms exist in the right places in the right conditions on a planet someplace so i'm not entirely sure how people are basing these probabilistic arguments since again we've been trapped on one planet for a very long time but nonetheless um the likelihood of silicon based life in a water-rich environment from a chemical perspective is not very likely and there's a simple reason for that when you dissolve silicon in water it rapidly forms silicates sio2 for example okay so the silicon will bond to oxygen very quickly and gobble that up and you'll get silicon dioxide and now the silicon becomes chemically inert so it's not really available to form the kind of scaffolding that carbon is able to do for example nevertheless in the right conditions and with the right solvent it's not impossible that this could have occurred so we know on earth for example that diatoms not the only example but they incorporate silicon into their bodily structures so we already know on earth there are organisms that use silicon as part of their their components humans have used directed evolution in the lab to make small living organisms that employ silicon so you take organisms you expose them to a silicon-rich environment where chemically they could use it instead of carbon then you look for organisms that take advantage of it you you get their genetic makeup you re-breed them it's classic directed evolution it's just a breeding program for microorganisms right so if you like dogs with certain fluffy coats right you breed them and then you get more dogs down the line with more fluffy coats right humans have been doing this for thousands of years and in fact it was these uh breeding of say pigeons that led charles darwin to think well if humans can do it nature could do it over much longer periods of time and he was right so we've already demonstrated that we can direct evolution by controlled breeding of microorganisms that utilize silicon and incorporate them into their chemistry so you can make an argument from that that given millions of years and the right temperatures in the right solvent nature could probably do it too so what are the conditions well silicon is heavy and as i said in the last lecture the reason that a lot of um i mean it's a simple physics argument as to why carbon is so useful for things it's it's light and easily manipulated by enzymes that is very you know lower inertia silicon has a much higher inertia than carbon at the temperatures we normally experience here it's not really energetically or from a force perspective very favorable to employ silicon when there's plenty of carbon lying around and it's much easier to move around but at higher temperature where there's a lot of thermal motion and things are moving rapidly anyway the mass of silicon becomes less important all right so for example you have a lot of mass and if you're moving very slowly right then your kinetic energy and your mass are are are roughly they're not in a very healthy ratio in the sense that your mass is probably a whole lot bigger in terms of its energy content than the energy content of your mobility but if you go faster if you take a human being and put them closer and closer to the speed of light that inertia becomes less and less important as time goes on they behave as if they're moving so fast they have so much kinetic energy that they behave as if their mass is negligible okay so in the right high temperature conditions it might be that enzymatic action is perfectly happy moving silicon around because there's so much thermal noise anyway the silicon is getting moved around pretty much for free by the by the environment the other thing that you need is the right solvent and this is where things get kind of interesting so the the science suggests that the right solvent perhaps for forming silicon based life is um sulfuric acid okay now picture of that planet right a sulfuric acid rich world rich and also in silicon where at high temperature maybe because of volcanism volcanic action on the planet where this kind of chemistry then becomes inevitable now it's interesting okay here's the more direct star trek reference there was an episode in the original star trek series where they encounter a silicon-based life form it's killing off people on a planet the enterprise crew investigates it turns out there's a silicon based life form there that essentially looks like a a moving like meatball sub it's sort of a magma creature and what's interesting about that is that that's actually not entirely wrong in the sense that it's very likely that an organism that depends on silicon would have evolved in a rather extreme scenario i mean sulfuric acid and probably very close to volcanic vents because that's the kind of temperature you would need to make this easy for nature to lower the barrier for this happening in the first place now it can't be too hot like liquid rock is too hot because that dissolves all the chemical bonds so it doesn't matter what you make if you get the magma temperature all the chemical bonds are dissolved anyway all right so you've got to be near magma temperature but not exactly magma temperature so near a thermal vent maybe this could have all happened but the truth is is we really have no evidence for this in the world around us not on earth at least and the chance of it happening is really not well understood okay so i would argue that the most likely outcome on this planet for silicon life is what we're doing we're making thinking machines we're making artificially intelligent computers those are all based on silicon and germanium chemistry now they're not silicon based in the sense of using silicon for the you know metabolic processes of life but it's replacing the wet wear in in say our head with hardware in the form of silicon based microchips okay that's interesting for a couple of reasons one we're attempting to emulate in machines the way that we think so we're literally creating in our image a kind of thinking machine the most obvious example of those are the robots that deliver food on this campus they can cross a road they're better than all of us because they wait for the damn pedestrian crossing at the corner of daniel an airline curse all of you i just want to turn right stop crossing when you're not supposed to your damn kids get off my campus all right the robots stop wait look right if it's not safe they stay there so they're smarter than us right i've i've you know darted across crosswalks when i'm not supposed to thousands of times in my life the robots don't do that we programmed them not to do that okay does anybody know what kind of brain inspired modern driving cars driving robots things like that anybody know it was the cat brain house cat specifically a part of the cat brain it's visual cortex so there are some very famous experiments conducted by two researchers huble and weasel about 40 or 50 years ago where they wired up the cat's visual cortex to electrical wiring and then they moved patterns in front of its eyeballs and they notice that certain clusters of neurons fire when vertical lines go by and when horizontal lines go by and when certain diagonal orientations and corners the different parts of the cortex fired for different shapes and from that they inferred that what's going on in the cat's visual cortex is there are little substructures that are trained on features and then they're wired into larger substructures that collect the features together and go oh a corner a vertical line a horizontal line that's a table i want to jump on that okay they've learned to assemble features into high-level abstract concepts all through these neural networks that are built into their wet wear so computer scientists these days starting in the 1980s but definitely ramping up when the advent of graphical processing units came into play have been emulating the cat visual cortex in convolut convoluted cnns convolution neural networks and recurrent neural networks that do time series analysis so they can actually do predictive text and things like that all that image recognition all that text prediction all that you know automatic translation from one language to another it's all based on the huble and weasel experiments that inspire the computer uh programming generation of the 80s and 90s and aus okay we have never emulated a full brain of a living organism and we've certainly never fully emulated a human brain but we're getting there so i would argue that the most likely outcome for silicon-based life on this planet is we build it eventually it does become self-aware either in a way we understand or in a way it understands and well we all know how that movie ends okay so you know just keep that in mind so let's move on from silicon-based life and let's look around in our neighborhood and see if there are other places where interesting chemistry and physics could have occurred that might lead to an alternate chain of life that we wouldn't fully understand but could expect to be there and then go looking for it so we're going to look nearby for unexpected things in our solar system we can't travel to other stars we don't know how to crack that walnut yet so we've got to stick to our own solar system we definitely know how to planet hop in our solar system um a typical journey from earth to another planet in the solar system you know for fuel efficient considerations and and taking you know taking advantage of the timing of orbits and when planets align in various ways is that it takes months to years to make a journey into the solar system either the inner solar system from earth to venus or mercury or to the uh to mars and then to the outer solar system jupiter saturn uranus neptune and beyond okay the dwarf planets that litter the space beyond neptune are almost completely unexplored we only recently got an image of pluto right that was a very recent development so we could imagine hunting around for places in the solar system where there are rocky worlds okay well venus and mars are obvious mercury is another one uh and where there may be the right ingredients for organic life as we understand it or a form of organic life that could be similar to to us in some way but by a completely independent evolutionary chain now venus is too hot as far as we know what's interesting about venus going back to silicon-based life is it rains sulfuric acid on venus okay the atmospheric pressure there is something like 90 times the atmospheric pressure on the surface of earth nearly all missions that have been sent to venus as an attempt to land have failed the soviets were the only ones that successfully landed on venus and their missions lasted less than about an hour before they were destroyed by the conditions on the surface they did manage to take some pictures so you can take a look at photos of of one part of the surface of venus it is a hellscape it was very similar to earth at the beginning of the solar system earth and venus are fairly close in their orbits and they're essentially twin worlds they're about the same size but why is venus so different from earth it's believed that it had an ocean at the beginning life may have even separately evolved there but runaway volcanism on venus eventually led to overproduction of carbon dioxide in its atmosphere the oceans boiled off into space and this then created a vicious feedback cycle where now the atmosphere of venus is 90 something percent carbon dioxide you can't even see through it with visible light it's shrouded you have to use other forms of light radar and other things like that to peer through the cloud layers and the clouds are rich in sulfuric acid so it literally rains sulfuric acid in the atmosphere of venus all right so maybe maybe in the atmosphere of venus with that kind of high temperature it's got a runaway greenhouse effect high temperature sulfuric acid maybe silicon got together and did something on the clouds on venus we don't know mars is a little sibling of venus in earth it's smaller than the two but it had its atmosphere stripped away and it no longer has a geomagnetic shield its core doesn't seem to be spinning like ours anymore it has no discernible magnetic field it's unprotected from the solar wind and in addition to its small mass its atmosphere has essentially been stripped away so its atmosphere is 90 carbon dioxide just like venus but it's very thin okay and gravity is far lower on mars but there is evidence that it once had water on its surface and it's entirely possible that billions of years ago life separately evolved on mars as well and that the only planet that won out in the long term was earth somehow we were just right okay but what about beyond there are places out in the outer solar system where interesting things are happening so for example this is europa it is a moon of the planet jupiter and it is my favorite thing in the solar system the chemist some of the chemists at smu will be like titan around saturn that's the place to go and i don't disagree with them but i really like the idea of europa so europa is an icy world you can see it's got dust gathered on its surface a great deal of that dust is due to its fellow moon io which is a huge amount of volcanic action on it this spews sulfur into the region around jupiter sulfur ions get trapped in the magnetic field of jupiter and and there's a big sulfur conveyor belt in the magnetic field of jupiter and some of that sulfur winds up peppering dusting other worlds so some of that that dust you see there is accumulated from sulfur that comes from io nearby not even the same moon but the rest of that is ice and you can see it's it's got structure on it right the ice has gorges and canyons and so forth um what's going on here is that while it doesn't have plate tectonics like the earth does as we understand it because uh europa goes around jupiter and jupiter has such an extremely strong gravitational field it's a huge it's a failed star jupiter with not a little more mass but an appreciable amount more mass not as much as you'd think could have ignited into a second star in our solar system but it didn't um failed stars are called brown dwarfs jew or hot jupiters uh jupiter is still cooler than brown dwarfs or hot jupiters okay so it's it's still pretty small by gas giant standards but it's the biggest planet in our solar system and it has this whole mini solar system of moons going around it europa is one of them and because it has an elliptical orbit around jupiter sometimes the gravitational force is stronger on the surface or across the surface of the europa sometimes it's weaker and just like play-doh it stretches and squashes the moon just from gravity and if you've ever taken clay or play-doh and and stretched and squashed and stretched in squash what happens to it it gets hot okay this is known as tidal heating so stretching and squashing a material made that constant stretching and squashing action will heat the material and we think that's what's happening inside of europa so not only is the surface cracking under these tidal forces okay but we think there's also heat trapped below the surface from this tidal heating this uh tidal force difference on on europa as it orbits so that's interesting and what does this mean well the surface is quite dynamic so it has those those uh great canyons and everything you saw but there are also cryovolcanoes these are volcanoes on the surface that spew water not lava but water and we don't know for sure we would like to eventually to send a mission to try to burrow down below the ice sheet of europa and see what's going on in the in the ocean it's a liquid water ocean underneath that ice surface we'd like to see what's going on down there look for evidence direct evidence of thermal vents from all that tidal stretching and squashing but we know already that there are plumes of material shooting out of what looked like cryovolcanoes on the surface and so of course the natural question is to say oh well if life evolved down here all these organic molecules would be spewing out from microorganisms or possibly bigger things that litter the subsurface ocean of europa it could be that life evolved down by these thermal vents and it's been building an ecosystem in this ocean ever since we don't know we would expect to see maybe some evidence of that here but there's so much charged particle radiation raining down on this moon channeled to europa by the massive magnetic field of jupiter that it essentially rips the chemistry apart so if there are organic molecules they're completely destroyed by radiation in the belts around europa the only way to really know for sure is to get into that ocean and dig around and do some chemistry and do some exploration okay enceladus a different moon this one around saturn also an icy world as you can see it's pock marked with craters it has had some kind of recent uh bombardment activity from asteroids or comets that have been channeled into this moon but there are parts of it that are very smooth where if there was bombardment the evidence is long gone and we can also see evidence again of moving shifting of the surface of this moon this ice sheath over the moon and again near the poles it looks like there's cryovolcanic activity this is a photograph taken i believe but yeah the cassini probe which explored this the saturnian system and we can see evidence of things being ejected from the surface now people thought because of the angle of this photo that these might just be single cryo volcanoes in the same way that we think of volcanic action like so you know upwellings of ice shooting uh in this case salty water the chemical analysis of those plumes suggested salt-rich water okay that's exciting because we've got a lot of that on the surface of our planet but some modeling suggests that given the angle and you can see here there's some ribbons of light here and here also ejected material it could be that these are fissures that are spewing ribbons of material out of them so there's even a debate about whether or not these are cryovolcanoes or something else pushing water hot salt water up through the surface to make these plumes this is an active area of inquiry and we would require another mission to the saturnian system to know more about this so it's possible that in that subsurface ocean there's heat from the tidal forces that saturn also exerts on its moons heating its core it's possible that life evolved down by the thermal vents and it could be there's a whole ecosystem under there again we would need to send a mission there's a leg and a lot of radiation in this part of the solar system channeled there by saturn so it's likely we would have the same problem detecting biomolecules in these plumes as we would say around jupiter these are extreme systems now this is the one that if you talk to a few of the chemists here at smu and rightly so they're really excited about and i'm excited about it too just not as much as europa i have a soft spot for europa i like ice worlds i'm a fan of hof from the empire strikes back so europa just that just works for me okay now why is titan interesting titan is the only moon in the solar system with an atmosphere that's already interesting because that means it's got air of some kind and as you'll see in a bit it's got liquid on its surface and it's got a hard surface that sounds familiar that sounds like earth okay or venus right so already that's interesting and its atmosphere is really fascinating it's mostly nitrogen ah so is earth's right ours is about 70 it's 97 okay and remember nitrogen super important for rna and dna it's the backbone of rna and dna hydrogen does the bonding nitrogen is the scaffold for that stuff oh look hydrogen 0.2 percent in the atmosphere not a lot okay but not zero now this is where it gets really interesting methane two point seven percent of the atmosphere is methane that's a lot of methane methane's a heat trapping gas okay that's a lot of methane for an atmosphere we do not have that much methane in our atmosphere and we're worried about more methane going in and causing more heat trapping we don't have anywhere near as much as titan does that's you're not seeing its surface there that's its hazy atmosphere you can see you can see we're sort of looking through the edges the thin parts of the atmosphere there but you can't see the surface features on titan that methane nitrogen atmosphere is impenetrable to visible light all right which is also interesting because you want to see what's under those clouds all right and in addition to this analysis of the atmosphere suggests it's rich with all kinds of interesting compounds ethane diacetylene acetylene propane cyanoacetylene hydrogen cyanide carbon dioxide carbon monoxide cyanogen argon and helium lots of good stuff there lots of good chemistry is going on in that atmosphere this is an early early area of inquiry but there's enough radiation raining down on the atmosphere that it's very likely that a lot of chemicals are being formed in the upper atmosphere through the injection of ultraviolet light and other forms of radiation it's you know causing reactions to occur you know ionizing things and then they bond after they're ionized and then those molecules forming in the upper atmosphere then get pulled down to the surface by gravity so they're kind of raining down on the surface so it's it's very possible and there's some evidence for this that this atmosphere is just pouring uh all kinds of interesting compounds including highly nitrogen-rich ones down onto the surface of titan let's take a look at the surface of titan this is an image of the surface of titan taken using infrared light infrared light has long enough wavelengths that it can penetrate the atmosphere radar will work as well and there are radar images of the surface of titan as well so when um cassini orbited titan to do these studies this was the first time we'd ever seen through the cloud layer the first time we ever found out that titan had an atmosphere was during the voyager missions and it was a very grainy hazy photo that suggested that titan was an interesting place to go back to that was in the 1970s early 1980s we got back to saturn in the arts that was a long time but cassini was a far superior mission although by modern standards its cameras were poor back then its cameras were state of the art and so this kind of image was just breathtaking and you can see there's even some very high resolution patches that were taken by certain instruments here and this was all stitched together this revealed a really complex set of surface features including both solid and liquid structures so here's an example of some of the solid and liquid structures the brown areas are what we would think of as surface the blue areas are colored to indicate that these are liquid regions of the surface and these are close to one of the poles there's one of the poles okay so we're kind of at the top or the bottom of titan and then these lakes there are seas or great lakes okay they're equivalent to the seas and great lakes on earth they're there liquid solid gas that's exciting now here's where things get interesting titan's way out in the solar system solar radiation not that prominent out there and even though there are tidal forces that are heating titan from the gravitational attraction of saturn it's just not like earth its surface temperature is negative 179 and a half celsius zero is freezing for water right so just calibrate yourself on that for a second but these are hydrocarbon lakes they're likely methane and ethane there even appear to be seasonal weathering patterns where methane and ethane rain from the atmosphere like rain here on earth but not with water with liquid hydrocarbon because it's so cold there and then they form rivers and deltas they fill the seas they fill the lakes it's a dynamic surface just like earth so we have this beautiful hydrocarbon rainfall and all of this dynamic surface structure again it feels earth-like but freaking cold also methane also really heavy well the atmosphere is one and a half atmospheres at the surface compared to earth not too bad you could take that that's easy okay but the surface is where things get interesting so a probe was sent down through the cloud layer by the cassini satellite the probe was called huygens it was a lander it was designed to land but not return and it was designed to take pictures and measure surface properties by attempting to penetrate the surface with a force probe and using the force profile of that impact tell us what the surface kind of looked like like what would it feel like if we could go there and go with our foot okay the surface is like creme brulee it has a crust but then it's soft underneath maybe methane rich sands underneath it so the penetrometer had to break through the surface so there was a lot of force of resistance at the beginning but then once it got through this crust it was it was sort of sandy and soft underneath liquidy sandy soft like beach sand okay now of course we can't know for sure what that would actually feel like we'd have to go there and you know do the human things like picking it up and let it run through our hands but that's not gonna happen anytime soon so we have to rely on robots and landers to do this for us um this is a photo of the surface of titan okay this is the this looks like it could have been taken in this american southwest the only difference is that you have this hazy orange from the nitrogen-rich atmosphere and that is not rock as we think of it it is rock but it is not made from minerals it's made from water that is water ice in various crystalline stages it's so cold there that water behaves like mineral rock on earth so sand grains are ice those pebbles ice the dirt ice with with these nitrogen and hydrocarbon compounds that have laying a dust layer down on top of them okay so the mountains the hills the valleys the surfaces that's all water ice if you've stood on it and and you had too much thermal heat coming off your boots you'd start to sink through it because you would melt the water ice okay so standing on the surface of titan carries some risks but the good news is if we sent something there and like went into one of the methane lakes or had to punch through the surface a little bit that wouldn't be too hard we just need to heat it a little bit okay so this is really an incredible landscape and you can see why people are excited about this uh tom ranchevsky here in smu department of chemistry elfie kraka who heads the computational chemistry part of the chemistry department they have done extensive work in the bench and in computation in understanding what's going on in this upper atmosphere atmosphere surface layer in terms of carbon nitrogen bonded compounds cyanogen and its many relatives crystal structures what would these compounds actually look like how would they rain down what chemistry is possible in this high-pressure low-temperature methane and nitrogen-rich environment also exposed to lots of radiation from space this is not your typical bench chemistry situation so if you take a look on google for smu you can look for titan in a jar smu the runchevsky's group is attempting to recreate titan in miniature in a jar to understand the chemistry of what it would be like if you went into surface measurements on titan and there is a proposed mission to tighten dragonfly it's moving forward and as its name implies it will fly so we've been testing this kind of technology with a double rotor helicopter on mars that's been wildly successful way more successful than they expected which is great because mars is usually the graveyard of missions 50 of all missions that go to mars fail but that one succeeded spectacularly and so that's given a lot of excitement to the community that we could build in a much thicker atmosphere than you have on mars a flying machine that's semi-autonomous there's no way titan is too far away it would take something like 45 minutes to send and then receive a command acknowledgement so it's in like a 90 minute round trip at light speed you can't send real-time commands this thing has to be able to make decisions essentially on its own with a basic menu of information about what to do and where to go so we need surveys of where it's going to land right and many of those came from cassini but it's going to have to think on its feet you know if it lands in a valley that it didn't mean to and it needs to get out it's got to get out and it's going to have to map its environment to do that ah we're back to self-driving cars and robots again right so humans are going to imbue these kinds of systems with some level of artificial intelligence we will control the basic input parameters it will make decisions in real time and it will send back information when it can okay so could there be hydrocarbon based life on titan this is highly speculative because much as i've implied by the work that the chemists here at smu are doing is really unknown about the chemistry of organic compounds on titan's upper and lower atmospheres chemists know a ton about the chemistry in the range of conditions at the surface of this planet okay but we've been conditioned by our environment to care about those things titan is a totally different range of conditions and just the phase diagram of these compounds on titan is wildly poorly understood it's only better understood because people like ranchevsky and collaborators at other institutions have been trying to map this out ever since the data dumps came back from cassini and huygens this is a very exciting frontier of the field chemistry in extreme environments where biochemistry may have evolved in its separate path okay but we know something we know that on earth there is methenogenic life that's organisms that metabolize by ingesting hydrogen and excreting methane ah that's interesting they take in h2 and they spit out methane so it's possible that there's methanogenic life on titan and it's possible that some of that methane in its atmosphere comes from this process that it's depleted the atmospheric hydrogen by breathing it or otherwise processing it in some way and is excreted or exhaled methane and ethane and other hydrocarbons so you could actually for instance attempt to detect life indirectly on a planet like titan by predicting what you'd expect the h2 and methane ratio to be in the absence of life like this and then look at how it changes when life like this is there in the same way that when plants emerged on this planet they went nuts and feasted on the atmospheric carbon dioxide and produced a ton of oxygen which then led to some of the largest non-dinosaur animals on earth ever coming into existence dragonflies the size of a small car why because they had unlimited access to a ridiculous amount of oxygen and they could get bigger and bigger and bigger because those larger bodies could take in lots of oxygen but once that era ended once microbes learned to digest lignin which was the undigestible molecule that trees came up with to keep themselves from getting eaten once the ecosystem adapted and those trees could be digested of course the oxygen levels eventually went down trees started to die off that could be processed and then other life could take over so you can see even in the history of gases in the atmosphere of earth evidence of different kinds of life coming into existence at different times so the catch here of course is that they have to do this at negative 180 celsius that may be a challenge they've got to use liquid methane or ethane as a solvent instead of water because water is not liquid on titan it is rock solid literally and figuratively water is generally recognized in chemistry to be a much better solvent for this kind of chemistry than the you know these the hydrocarbons methane or ethane but again that doesn't mean that an improbable event given enough time couldn't become 100 possible right so you just needed to establish some foothold on that self-sustaining chemical reaction and then as long as there's some kind of selection pressure on the system changes in temperature changes in the radiation changes in the chemical environment that alter the abundance of hydrogen things like that that put pressure on the system and as long as it has a means to adapt to that in our case through the passing on of genes and big picture over a century or more being able to alter the population to handle the new conditions it's possible that that this could have happened and again as i said methodogenic life might simply be detectable by how it affects hydrogen molecular hydrogen in the atmosphere of titan observed versus predicted but again these are extremely early days for this kind of work okay humans are just really beginning to scratch the surface of this kind of possibility this is the kind of stuff that your nobel prizes will be based on let me put it that way okay so let's close out here with the probability of alien life at all in the universe and this is given by something known as the drake equation right we've looked at life as we know it we've started to think a little bit about life as we might not know it but in general what's the probability of life existing in the cosmos and and this was originally codified in a pure dimensional analysis equation you could write this equation down all right think about our our civilization we have a civilization it took some time to emerge when it emerged it took took some time to invent a form of communication that could leave the surface of the planet light raid radio okay it takes time for radio to travel through the universe at light speed so there's only a finite volume since we invented radio where those radio waves could have gotten from earth okay so in principle radio came into existence as a technology in the late 1800s so we're talking about a little over a century so 100 light years give or take let's say 20 light years is is as far as any civilization could have heard us by now but of course civilizations could be much older than us and have invented radio communication long before we did so we might be within the sphere of communication of one of those civilizations but in order for a civilization to emerge you need life to emerge on a planet the planet to come into existence you need a star to have first formed that the planet could be around to provide heat and other things okay so you just take all these numbers the rate of star formation in our galaxy the fraction of those stars with planets the number of uh the average number of planets that can potentially support life given that there are stars with planets the fraction of planets that could support life that actually develop life the fraction of planets that go on to also then develop intelligent life ah there's that word intelligent what does that mean okay so we have to be careful with this then the fraction of those civilizations that develop a technology that releases detectable signs of their existence into space and finally the length of time for which such such civilizations actually release those signals into space there's a chance if we don't get our act together in the next hundred years or so and if we can't adapt to the conditions we're creating on the surface of the planet that our radio emitting species may not be around for more than a few hundred more years so it's possible that civilizations come and go all the time in the milky way and there's even some you know scholarly work on when a civilization emerges and then need that has energy demands and it meets those demands in certain ways and then it doesn't change those demands that alters the planet's surface this then creates an inhospitable situation for their civilization their civilization collapses and dies possibly also extincting their species in the process that may only be a hundred or a thousand or ten thousand or a hundred thousand years okay to get to the center of our galaxy takes 26 000 years so if there's a civilization at the center of the galaxy um it has to have invented radio communication sometime in the last 26 thousand years and if it's made itself go extinct by now it ain't there anymore so even if we hear from it it may not exist anymore so you can start to ask do we how well do we know these numbers we actually know the rate of star formation in the milky way galaxy pretty well there's one and a half to three stars made per year in the milky way galaxy the probability of the star having any planets that used to be quite speculative but thanks to things like the kepler satellite we're pretty sure this is a hundred percent a hundred percent of stars have at least one planet going around them now not all of those planets are in the goldilocks zone so you need to know the average number of habitable worlds okay optimistically based on scholarly work this could be something like three to five at a minimum the trappist solar system as like four or five worlds that are all in principle habitable as we understand it in certain parts of those worlds what about the fraction that go on to develop life highly speculative could be a hundred percent on this planet it happened seemingly as soon as the conditions were right for life as we know it boom carbon chemistry boom dna and rna okay amino acids enzymes all that stuff just boom within a few hundred million years of the planet forming so maybe it's 100 what about the fraction that developed intelligent life let's not get started on the definition of intelligent um somebody some people have speculated this could be 0.02 but again i think that's highly biased i think that's a highly subjective number uh what about the number that develop light speed communication radio and the the length of time that they can communicate also highly speculative highly based on a bias toward humanity so let's look at an optimistic and a pessimistic scenario the rare earth hypothesis is one of the very pessimistic scenarios it sort of puts the the fraction of uh planets that are habitable that develop life at around 10 to the negative five so that's the product of those three numbers the probability of intelligent life one in a billion okay that's a big fu to nature right there you know you're not going to do it again says said the humans uh what about the pro the fraction that then develop some ability to communicate off planet 20 the length of time that they would have been communicating on average maybe about 304 years ago this is all based on human existence we have no idea really um but that the number of such species in the milky way besides us would be 10 to the negative 14. that's a 100th of a trillionth of a chance that there's one other species out there basically not only would we be alone in this galaxy that's so low that if you took all the galaxies in the observable universe we might still be alone aw a more optimistic view uh put some of these numbers the fraction of planets at 100 percent that have habitable conditions 20 that develop life 13 this is just another scenario some scholars have cooked up on this based on other numbers fraction of intel the probability of intelligent life 100 super optimistic you're gonna get intelligent life as we understand it that then do uh some kind of off-world communication 20 and the length of time they do it a billion years that's pretty optimistic that we'll be around for a billion years that would mean there are 16 million such communicable civilizations right now in the milky way that we could have contact with now we might not be able to get there but we could at least listen to their radio broadcast and check out their television okay i'm sure they all have a version of the mast singer i'm sure if douglas adams the science fiction writer were alive today it would be reality tv from alien worlds okay this is again really early days for this kind of work so let me close out um defining life is hard finding life is challenging um i think the revelation of the number of stars that have planets has been a really positive revelation the number of planets capable of nurturing or sustaining life we're going to get better at knowing that and in our own solar system as i've hinted today maybe there are even other places where life separately evolved okay so i i hope you've all enjoyed this i've certainly enjoyed this semester we have a final exam left but you'll be fine make sure you check out the announcements that i put on canvas about the final and how i'm going to do grade replacement on one of your earlier macro exams based on performance on the final go read all of that so in case you have questions next week when i'm back for my travels you can ask them quickly okay thanks to all of you and have a good reading day okay bye i'm gonna head to an airport