Astrobiology and the Search for Extraterrestrial Life - with Ian Crawford

I'm going to talk about something that's interested me for a long time and that is the search for light from the universe and I have on the uses of the picture is the picture of the the only known inhabited planet in the whole in that in the whole universe so it's beautiful planet that we live on with its seas and clouds and its atmosphere that life has changed to suit itself but the point is this is the only place in the universe that we know is has has life upon it and and so obviously it's begs the question are there other inhabited planets out there but it's also the more you think about it it's a little bit strange that this is the only place that we know life exists upon and the more we've explored the solar system the stranger it gets because we keep finding places in the in the solar system that we know either are or in the past would have been habitable places so don't have time to do a thorough survey of this but if we just look a few places in our own solar system we start with Mars so so Mars has been at that's a place where we people have been interested in life for a long time since since HTT Wells wrote War of the Worlds in 1899 or whenever it was and we've been searching for life on Mars for a long time we still haven't found any that that in itself may say something I mean clearly if there is life on Mars it's not at all abundant and it's hiding below the surface or something it hasn't changed Mars into a Bluegreen planet in the way that a life has changed the earth into such a place service for the food for thought there on the other hand we as we've explored Mars with our Rovers this is the Curiosity rover that's been crawling around Mars for four years now that's an artist's drawing of course but at one of many what one of them one of 43 actually robotic Rovers which have been exploring the surface of Mars and on our spacecraft which have been looking at Mars from orbit have started turning up evidence that early Mars at least Mars in the first quarter of its history Mars in the first thousand million years of solar system history was a much more habitable place than it is now and I'll illustrate this with just what the wrong picture the picture at the upper left here with the greens and blues on it this is a high photograph from an orbiting spacecraft it shows a large well it shows part of the rim of a large 60 who are 450 kilometer diameter impact crater so this is the rim of the impact crater but it shows multiple evidences that liquid water flowed on Mars in the past in fact there is one picture there are three pieces of independent evidence of early Mars having liquid water on its surface the most obvious is this river valley and dried-up river valley now that's me and around here burst through the rim of jezero crater so this is evidence for liquid water at least liquid something but come to the fact we know it's water shortly then then there's in the crater floor there's this structure and now this is a delta it's that dried-up Delta and it's one of us now as I've started to turn up on Mars rivers produce Delta's wherein rivers carrying sediment flow into standing bodies of water and then the river carrying the sediment slows down and the sediment drops Delta is formed so this implies that not only was the water in this river the whole of Desiree crater there which is 50 kilometers across when this was all going on was once full of water Tom's a crater lake and it's very large one and it's one of hundreds that have now been found on Mars so there was a lot of liquid water on early Mars but then the clinching argument of these colors these are false colors but they're assigned to the spectral properties of the surface rocks and the Blues that the Blues here correspond to minerals that igneous minerals that basaltic lavas are made out of and you expect for the trust of Mars but the greens and turquoisey colors these are indicate the presence of clay minerals and clay minerals are what you get when you erode volcanic rocks with liquid water and so the fact that clay minerals are cropping out in this Delta implies that it was water it wasn't liquid lava it wasn't liquid carbon dioxide it wasn't liquid anything else because in order to make clay minerals you require liquid water so all of this was going on about three thousand three and a half thousand million years ago in the earliest part of Mars history you would have planet for with rivers and crater lakes must have had a thicker atmosphere must have had a higher temperature for water to be stable by any stretch of the imagination would have been a habitable environment for microorganisms at least what we do not know is whether it was ever inhabited and that's what's driving a lot of Mars research but if it was then life was that got going in that environment either became extinct or it's migrated underground it hasn't flourished and taken over the whole planet in the way that it did on on the earth and of course it may not have evolved there at all just because the environments habitable doesn't mean that it was inhabited because there may be things in the origin of life which make forming a lot originating life from non-life very much much harder than merely having a habitable environment with liquid water so I'll return to that then there are places in the outer solar system this is this shows of the southern hemisphere of Saturn's moon Enceladus which is actually seen venting water into space these are plumes of water emanating from the South Pole of Enceladus and so this is a small moon 500 kilometer diameter moon with an icy crust but underneath the icy crust there is an ocean of liquid water because we can see the water venting into space and it's now becoming clear that many of the outsi icy moons in the outer solar system Ganymede Callisto Titan and solidus beneath their icy crusts have oceans of liquid water these may also be habitable environments but of course proving wet searching them to see whether there's anything alive within these oceans be a much very significant challenge but the point is in our own solar system we see all of these all of these habitable places and then the most exciting thing that's happened in astronomy in the last 20 years is the realization that planet solar systems like our own are not at all rare I mean the first planets found orbiting solar type self-type star occurred in in 1995 and in the last 20 years we've now found four thousand planets orbiting other stars and we've now we've this efficient statistical base now for us to be confident that almost all stars will have planets I mean already we can say that 70% of stars have planets and we but we also know our statistics are not complete and that 70% can only go up so by the time the statistics are all in it's going to turn out that 90% or more of stars her accompanied by planetary systems you may recognize this photograph it's part of the southern Milky Way I thought inch beautiful brights stars this is the Southern Cross this is the nearest star Alpha Centauri four light-years away this is this is the southern coalsack which is a foreground dust cloud kind of tower that collapses on the gravity to make new stars and planets and then in the background you've got millions and millions of stars well the thing is we now know that all of these stars will have planetary systems and then we look at our own solar system and we see that the range diversity of planets and many of them are there are habitable or have been inhabited the have to be there's no getting away from it have to be a an enormous number millions and billions of habitable planets in the galaxy the question is is that enough but I think we do just because a habitable doesn't mean they're inhabited right so all we can say is that if life is not common in the universe it's not because as a shortage of planets there'll be millions and billions of planets so we searched been searching our own solar system for evidence of life either present in the current extent life in the solar system or life in the past we haven't found evidence for either yet but it's important it's important that we keep it's important that we keep looking and eventually once we've explored Mars and the the icy moons sufficiently we will have an answer to this question it may take many decades but it's already clear that if life arose elsewhere in our solar system not only is it not flourished anywhere else apart from the power part from the earth if it's if it's it's never can have certainly to the present time even if it exists it can only be at a microbial stage of existence because otherwise we would we would know and even that isn't certain so the only other thing that we can do until we can build starships to actually go to the stars and explore planets around Alpha Centauri with Rovers like the Curiosity raiveer that's that's obviously a long way in the future the only other thing we can do is look at the stars with telescopes from from the earth we can start studying these planets that we found and look to see whether their atmospheric compositions indicate atmospheres that have been changed by biology so astrobiologists call these molecules biomarkers things in planetary atmospheres that would indicate life exists on the planet to do that on these newly found planets is a tremendous observational challenge it is something that will develop over the coming 20 years it requires large telescopes ideally large telescopes in space like the the the James Webb Space Telescope which is to be launched soon we hope and other other large space-based telescopes and so we will start to get statistic eventually but it will take several decades given the size of the instruments that we need we'll be able to start analyzing planets orbiting nearby star studying their bio signatures looking for bio signatures in their atmospheres and we'll get some sort of statistical answer as to whether bio signatures are common in extrasolar planets or not the other thing we can do the other end of the observational spectrum is we can say that if life had had arisen on any of these other planetary systems and evolution had gone through a kind of sequence of stages analogous to what it did do here some fraction of these planets with life may have given rise to intelligent beings capable of producing technologies and we might be able to observe the technologies and in particular we might be able to observe artificial radio transmissions or artificial laser beams or artificial signals of some kind this is called a search for extraterrestrial intelligence SETI it's usually been before it is usually performed within the radio spectrum this is the Parkes radio telescope in New South Wales scanning the heavens for signs of artificial radio signals this has been going on for 50 years an hour actually longer so started in 1960 the first ever SETI search and he hasn't found anything either 50 50 years the galaxy seems very quiet now again it's too early to draw too much from this conclusion one could out lots for reasons why aliens might be present they might not be transmitting radio waves they might be deliberately not doing so they might they might be transmitting at frequencies that we're not listening in to maybe we're looking at radios and they're using lasers or something although we've now started to look for a party official laser signals and haven't found any of those so it's too soon to draw a conclusion but the fact is we've been looking for 50 years if this carries on and the techniques for SETI are getting more and more sophisticated more and more sensitive this carries on for another 50 years and we haven't found any signals then we're gonna you know maybe start to think that intelligent life that transmits radio waves and builds radio telescopes might be might might be rare which would be consistent with life itself being rare of course but in between those two there are a wide range of other possibilities so this shows our Frank Drake Frank Drake who conducted the first SETI search in 1960 he called it project Ozma he looked at the two nearest single solar-type stars for a few hours with with a radio telescope and detected nothing and since then the searches have got bigger and bigger and more sophisticated and they're still detecting nothing but Drake tried in 1961 he tried to quantify this he tried to try to think how many supposing life exists elsewhere in the universe how many technological civilizations do I expect to find this would give up this would give astronomers a clue as to how many stars they should be looking at how much it is very expensive telescope time should be devoted to SETI rather than to mapping hydrogen clouds in the galaxies or rather more prosaic Astrophysical tasks so Drake came up with his famous equation which he first codified in 1961 in which he reasoned that the number the number of technological civilizations extent in the galaxies at any time that's the begin at the front of the equation would equal the all these things multiplied together so R and I'll explain why I did it this way in a minute but let me just define the terms our subscript star is the rate of of star formation in the galaxies which astronomers do know it's of the order of one per year except in recent years it's been creeping out up it might be several per year actually it might be seven per year so but anyway a few per year when Drake wrote his equation it was it was about one per year so one or a bit more then if subscript P is the fraction of star of those stars which form planetary systems now in 1961 there was no one had any idea what that was but now we do thanks to the last 20 years of astrophysics research we know that that fraction is about one I mean I told you it's at least point seven it's probably going to be 0.9 or more when all the statistics come in so in round numbers all stars have planets which means the fraction would be one the fraction of stars with some fraction of stars with planets would be one that would be F subscript P then he realized that planets don't just stars typically don't just form one planet I mean our solar system's got so when I was at school it was it was nine planets but only eight planets as Pluto is being demoted but nevertheless Pluto is still there is an astronomical object so obviously and we've got all these moons right the moons of Jupiter and Saturn like Enceladus so n subscript T is the number of planets within each solar systems that have habitable environments so for the solar system that is at least one because the earth is habitable but you could justify a number like a three or four for that early Mars was habitable Enceladus is habitable so anyway a few I don't thing is we have good we've got this part of the drakes equation we've got could could reasonably good estimates of what these numbers might be but then the latter half of the equation there are things that we know nothing about and that we desperately need to find out and which is driving most of astrobiology research today F subscript L is the fraction of planets with habitable environments on which life actually evolves or originates we don't know what that is it could be very common it might be that on nearly all habitable environments life originates but if that were true life should have originated in jezero traitor when my crater was full of water and everything if that were true when we explore bars we'll find evidence for at least past life so there's a way of constraining this number by exploring our solar system obviously if this if this fraction is a lot less than one then we we might find habitable environments in the solar system like early Mars or Enceladus but they won't be inhabited because fraction they difficult to evolve life from non-life anyway we don't know what that is it's important for us to find out F subscript eyes and the fraction of such life that becomes intelligent eventually over evolutionary time scales we don't know that either F subscript C is the fraction of such intelligent life that can communicate across interstellar space now here Drake's really sort of showing his he's his sort of bias in inherent bias because he's written n here strictly n is not the number intelligent civilizations in the galaxy that's what you've got to forget have you stopped here it's the number that can communicate across interstellar space because he really wanted an equation to inform the SETI searches and to to a radio astronomer your communicative if you can build radio telescopes essentially and then then have you take this the rate of star formation that multiplied by all these fractions is the rate of formation of communicative interstellar civilizations per year if you've taken the star formation to be per year and multiply it by all these fractions this is the rate of the formation of communicative technological civilizations in the galaxy per year and then if you want to know how many there are at any given time take that formation rate and multiply it by the lifetime of these civilizations and that's the L at the end and we don't know what that means either so in a sense the Drake Equation sums up a lot of ignorance it's not very predictive because you can put in you can put in what you want and to some extent get out what you want on the other hand it is it has been a very useful tool because it does break down the problem into easily manageable chunks I mean space exploration and astronomy have already start given started giving us answers to these which we didn't have you know fifty years ago a future exploration can start may start to put some constraints on these frictions and that's um that's kind of what we want in order to get a realistic estimate anyway there art there are two obviously you can get what you want from the Drake Equation you can go home and put in your own numbers but but there are clearly two extreme possibilities Drake is an optimist Drake is still alive and he's still an optimist and and Drake despite you know despite having not discovered anything for 50 years he's still an optimist but but and he's got some some reason to be in a way so but an optimist says that we already know there's one star but been man it might be bigger now that makes it even more optimistic but then an optimist would set all these fractions to one all stars have planets we now know that's true a real optimist might make this number a bit bigger than one but anyway and then you can't get any optimistic than having these fractions bigger than one so an optimist would say given the habitable and planet life inevitably evolves natural selection we never to believe will lead to intelligence they subscript high intelligence will inevitably discover how to communicate across interstellar space that's f subscript C put those equal to one one one one one one and then your estimate for the number of civilizations communicative civilizations strictly in the galaxy today B 1 times 1 times 1 times 1 times 1 times L if you've measured the star formation rate in stars per year you have to measure the lifetime in years so if you thought of technological civilization with only last 400 years you're expecting a hundred in the galaxy at the present time and so there'd be pretty thin on the ground given that the galaxy is a hundred thousand light years across and contains a hundred thousand million stars if you thought Carl Sagan used to argue this was a million civilizations might last for a million years or longer once they discover their technology so that's an optimistic view of technology technology can go either way can either make you immortal or it can kill you after 10 years if you start dropping nuclear bombs on each other and this is so this is in the realm of extraterrestrial sociology extraterrestrial Paula we know nothing about that a figure the city optimists like drag like he's a thousand years and the reason they like a thousand years is it seems not unreasonable that a technological civilization might last for a thousand years that's comparable to civilization all durations that we're familiar with in our own very limited history although that is a very anthropomorphic view there's another reason why they like a thousand years though if L was a thousand the years it means as a thousand civilized you mean that mean implies to be a thousand technological civilizations in the galaxy today that means there actually be about a thousand light years away apart from each other on average and city people kind of like this because they know they haven't detected anything yet in that in fifty years but they also know their distance limit to which these searches are sensitive is a few hundred to a thousand light years if there were civilizations a thousand light years away from us and it was transmitting to us it wouldn't be surprising that we haven't detected it yet on the other hand that we might wake up tomorrow morning and detect it so this can keep the SETI people going right it this is a reason for them it's not an extreme number like a million civilizations in the galaxy that's Sagan and others like to argue but it's not a very pessimistic one and it means that a signal might be detected within our lifetimes if the wearer of the order of a thousand technological civilizations in the galaxy at the present time so that's that so that says that so if you can't get more optimistic you can't get more optimistic than that because we've set all these fractions to one but you don't have to be optimistic there are reasons I think if you look at the evolutionary history of life on Earth not to be optimistic and the fact that we haven't found any life on Mars despite the fact we know Mars was once habitable so if we just look this this little diagram shows my potted history of life on Earth the planet is our four-and-a-half thousand million years old so these are timescales in thousands and millions of years planet formed here we're at the top things have happened in this huge length of time that have resulted in us being here in this room in 2017 obviously in order for that happened life had to evolve on this planet well there is evidence that it did say our earliest fossil evidence for life on Earth you sort of back here 3.5 3.8 billion years ago this is this is this this is some reasons to be optimistic for life on Earth because it implies that although we don't know how life originates from non-life it did happen on this planet very early after the planet formed that might imply that we don't know how life is life originates from non-life but nature knows how to do it and nature knows how to do it quickly on planets that were like what the earth was it's a very different place but planets that were like the earth was back here planets with liquid water on their surfaces a lot of volcanic rock and probably thick carbon dioxide atmospheres on such a planet life did arise on the earth and it did so relatively quickly so you might space on that our view that life gets forming on planets quickly once on habitable planets quickly therefore life will be common of course we're talking about microbial life only and we're talking about an example of one that strictly you cannot generalize into the whole universe but but if looking for example of one that's a message you could take from it but then look at this we've got one to three thousand million years I also have to skip all this I mean a lot of very interesting biology was happening in this prime time scale but destroy your attention to the first fossil evidence we have for multi-celled animals to basically animals a sort of jellyfish level of multicellular complexity they appear in the fossil record here point six billion years ago so for the vast length of the history of this planet the planets been inhabited but it's been inhabited only by microorganisms so that could imply 3000 million years is a long time I mean not only to three-quarters of the age of the earth it's a significant fraction of the age of the universe that it's taken life on this planet to evolve from a unicellular level of complexity still very complicated to a multicellular blood grade of complexity that their natural selection can work on to produce many multi-multi various animals and plants eventually ourselves or intelligent creatures at the top but it took a long time so if you were to extrapolate this out into the wider universe you might argue that microbial life may be common in the universe it gets going quickly on suitable planets but then evolving multicellular life and animal life and everything that can develop a technology this is probably really hard because it took a very long time and therefore technological life might not be common in the in the universe because it's so many steps have to be gone through to evolve it now just as a quick aside if this story I've told you is on the right lines it makes some predictions if it's true that life always gets going early on planets like what the earth was three-and-a-half to four thousand million years ago then that the prediction that life should have started on Mars because four and a half when jezero crater was full of water three and a half billion years ago it was very similar to what the early Earth was like at the same time planets have diverged a lot since but at that time they were similar so if we go to Mars and we find there was life we find fossil microbes in that Delta in jezero crater yeah it would support this view life look is quick to get going on warm wet rocky planets and there are billions of those in the galaxy we already know that if on the other hand we get to Jethro crater and we find that despite being a perfectly habitable environment life never started we'd have to start thinking you know maybe the something something in the biology that means life doesn't automatically get going just because you've got a nice warm wet habitable environment and life would not be common arguably in the in the in the in the universe in that case the point is we can explore that we can test that hypothesis by exploring our own solar system whether intelligent life eventually evolves we have to go to this we have to go to the stars because it's obviously not happened elsewhere in our own solar system so we after we have to start and this would be where the SETI comes in because then if you start detecting even one other extraterrestrial radio signal from a from another solar system then that tells you to other technologies have arisen elsewhere in the galaxy and it may be rare and it may take a long time but you know it would be it would be experimental evidence intelligence exists but anyway the thing is I said we don't have to be optimistic and one of the earliest people to intuitively see this was was Alfred Russel Wallace can I just ask who has heard of Alfred Russel Wallace oh good because Alfred Russel Wallace deserves to be much better known than so so Wallace as as many of you will know was the co-discoverer of the principle of natural selection with Charles Darwin and it was it was it was Wallace's letter from that was then the what is now Indonesia - Darwin in about 1850 suddenly Darwin realized other people were thinking along these lines and he had to get the Origin of Species out pretty quickly before other people sort of scooped his idea anyway Wallace was a very interesting person and the other an interest in life in the universe so he wrote what could be arguably the world's first just area biology book in 1904 and it was called man's place in the universe but it's interesting because here is a man who was at the very birth of evolutionary biology and he was trying to apply some of the principles of evolutionary biology to the question of will there be other civilizations acting in the universe now here's a quote from his book now it's written quite flatly long-winded a Victorian prose but let me still it's still worth reading it what he says is given the evidence as to the number of very very complex and in and improbable conditions which are absolutely essential for the development of the higher forms of he's here looking at it through the lens of someone who understands natural selection you can have simple life in inverted commas because no life is simple but then if you know to evolve that into a creature which can build a civilization and a technology so many steps right if you look at our own evolutionary history not not all of which would look like they would need at all have been inevitable many of them were contingent on chance events like meteorite impacts extinct dinosaurs and things anyway many many chance events hurdles that the biology has to go through before it really produced us so he realized in his whole sequence of probably of events that evolutionary events that life had to go through each one of which may have had a low probability and then you multiply these low probabilities by each other and you end up with something that could be very improbable by the end so he has a here's a stab he says we've got all these um these improbable conditions that need to be met so he has a go the total chances are get so it seems to him that the total chances against the evolution of man or an equivalent moral and intellectual being these would be the intelligent aliens will be represented by a hundred million of millions to one right now he's just guessed this a hundred millions - millions to one he thinks it's very unlikely intuitively he's got maybe one chance in a hundred million million that will evolve something like human beings anyway the thing is that is a probability if you were to just take this guess because clearly at first sight a probability of a hundred million to millions to one is a probability of 10 to the power of minus 14 for F subscript I in the Drake Equation so you can put that in we can be optimistic about all the other numbers and again you don't have to be well you do have to be for these because we now have Astrophysical constraints on these but it doesn't it doesn't follow for example we don't know they we don't know the subscript L is one we don't know that you know that's what we need to test on Mars that might be a very low number as well but let's just assume you can evolve simple life out of non with a high probability arguing that it happened quickly here but that would be your sole justification the more we explore Mars we will be able to constrain that but then take Wallace's number for the probability of involving intelligence from life as 10 to the minus 14 and then if everything else is 1 the number of technological civilizations you expecting the galaxy at any given time would be 10 to the power of minus 14 times L suppose you take the lifetime of each civilization still to be a thousand years that will be 10 to the power of M minus 11 times L so what does it mean to say there are 10 to the power of minus 11 civilizations in the galaxy at the present time well all it would mean is statistically you'd have to search 10 to the power of 11 galaxies and you'd find one there are about 10 to the power of 11 hundred thousand million galaxies in the observable universe so if Wallace's intuition for the difficulty of evolving intelligent life from life was in the right ballpark we would be it not not only in the galaxy but in the entire observable universe between these two extremes of course there are other possibilities and it's putting constraints on these other numbers that's what these other probabilities that is what's right in what's driving a lot of astrobiology research so this is my my last slide here is a quote from other great Victorian scientist William Huell who also wrote a book in about 18 in the 1850s once it's 1853 searching for life elsewhere in the universe and he he has this statement in it where he says that the discussion and notice this is before natural selection before Darwin and Wallace had had their key inside anyway well Darwin it had is he inside but he'd kept it to himself anyway so he will Huell Huell writes that the discussions in which we are engaged looking for life elsewhere in the universe are at the very boundaries of science at the frontier where knowledge ends when ignorance begins and the thing is 150 years later we're still there at that boundary despite all the advances in astronomy and biology and geology and planetary science ever lost hundra we still do not have an answer to this question planet Earth is still the only known inhabited planet in the universe and we really do not know whether we should be expecting to find others or not we're still at this border between knowledge and ignorance so the only way to get become less ignorant is to get out there into the universe and explore it and eventually we explore it deeply enough we will find the answers so there are several things that we can do we should be continuing our exploration of Mars for the reasons I've outlined the early history of Mars contains a lot of answers even a negative answer that life never evolved on early Mars despite it being habitable would constrain our top fraction for F subscript L in the Drake Equation we should continue to an and the discovery of life on Mars were given out as an answer it would tell us f subscript L is about one the fact that life's evolved independently on two adjacent planets within you know at the same time we should continue searching other stars and searching for by habit planets orbiting other stars and making astronomical measurements of the spectral spectral measurements of the compositions of exoplanet atmospheres to look for biomarkers within the next 20 or 30 years we'll start I think just be able to at least begin that to be able to address this question statistically if we find the hundred planets orbiting other stars in the so-called habitable zone where they ought to be warm and wet and habitable and half of them have strange atmosphere is with oxygen and methane coexisting and things that look out of chemical equilibrium this wouldn't be a proof but it'd be strong evidence that they have life on their surfaces something strange going on if on the other hand we look at these hundred nearest planets and we find that yeah they're all like Venus and Mars they all have caused carbon dioxide atmospheres in chemical equilibrium no evidence for anything going on at all and we've searched a hundred of them we'll start to think yeah maybe life you know life isn't quick to get going on planets habitable anyway we're start to get answers to that question I think statistically within the coming fuse well several decades and of course we we should continue with the the SETI searches because Drake and sagan Attell they may be right we may switch on the news tomorrow morning and a discovery a discovery may have been made the point is unless we continue to look we'll we'll never know so I think really the argument is one that we've continued to search the universe and eventually we will a transition across this boundary from from ignorance into into knowledge now in there thanks thanks very much [Applause]

Channel: The Royal Institution

Views: 326,491

Rating: 4.6642532 out of 5

Keywords: Ri, Royal Institution, astrobiology, lecture, ian crawford, SETI, aliens, extraterrestrials, space, physics, biology, cosmology, drake equation, fermi problem

Id: AJt2mhwUlq4

Length: 35min 56sec (2156 seconds)

Published: Wed Apr 11 2018