SETI Talks: Why is Earth Still Habitable?

the best evidence we have for the first appearance of life on earth are fossilized microorganisms found in the precipitates of hydrothermal vents and dated at nearly 3.8 billion years old it's actually been suggested that the very first such organisms may have actually appeared as much as 4.3 billion years ago and the implications for this are profound given that the formation of earth as a planet was somewhere a little over four and a half billion years ago it seems that life took hold on this planet almost immediately after the planet was formed which further implies that life as we know it may be as natural a byproduct of planet formation as planets are a byproduct of star formation at least when the basic conditions of habitability are met but what is a habitable world and what do we mean when we talk about habitability so there are perhaps somewhere between 10 and 14 million different species of life forms on earth today which ignores the trillions upon trillions of individual viruses that some biologists consider to be life forms as well and yet as a it is estimated that 99 of all life forms that ever existed on earth are now extinct clearly life has been tested on earth countless times since the planet was formed from extreme swings and global temperature to super volcanoes asteroid impacts and coronal mass ejections to pathogens and potentially even human-induced existential threats life seems to hang by a thread and yet here we still are frank drake introduced us to the notion of habitable worlds and planets which under the right conditions go on to see life emerge in his now famous drake equation n sub e is the number of planets in our galaxy that are in the so-called habitable zone of their host star now estimated to number in the tens of billions and f sub l is the fraction of those planets that go on to develop life hey don't take my word for it if you're not familiar with the drake equation you must be new to our seti talks lecture series in which case i urge you to go look it up so today we look to worlds beyond our solar system exoplanets to be more precise to help us better understand life on our own planet and understand why we're even able to be here today to ask such questions is why is the earth still habitable so good morning good day and good evening ladies and gentlemen and welcome to our may 2021 city talks program city talks is the monthly lecture series produced by the seti institute in mountain view california i'm bill diamond president and ceo the city institute is a non-profit research and education institution whose mission is to lead humanity's quest to understand the origins and prevalence of life and intelligence in the universe and to share this knowledge to inspire and guide present and future generations our steady talks lecture series has been running for more than 10 years and if you visit the archive on the institute's youtube channel you'll discover hundreds of lectures debates and panel discussions featuring many of the world's foremost researchers educators and explorers in space science covering an extraordinary range of topics over a year ago the coronavirus compelled us to convert the talks to a virtual online series but that's given us the opportunity to reach a global audience and make new friends and we're delighted to have you with us today so whether you're joining us uh today on zoom or facebook youtube or some other platform we bid you welcome and thank you for coming along as our regular attendees know we love to find out where you're watching from so if you're on zoom use the chat function to give us your coordinates and location and on facebook use the comment section and let's see how far we are reaching across our own planet today and if you happen to be watching from an exoplanet somewhere a very special welcome to you and please let us know your coordinates we also like to poll the audience to find out who's joining us for the first time and who's a habitual fan so if you're with us on zoom you will see a pop-up on your screen where you can let us know select the answer that best fits and hit submit and we'll share the results in just a bit so explore the question of habitability on earth and understand why we even exist we've invited two extraordinary scientists whose research includes investigations into the habitability of exoplanets and the conditions for life on earth we're joined by an astrophysicist from the university of oxford and a professor of earth system science at the university of southampton our guest will be introduced by our moderator for tonight's or today's discussion frank martinez who is a chemist and planetary scientist no that's the wrong person frank is a is an astronomer and senior scientist at the seti institute and he will be moderating today's panel discussion and introducing our guests we will have time for audience questions after the moderated discussion so if you're watching via zoom post your questions using the q a feature you see at the bottom of your screen my colleagues rebecca and simon will be fielding your questions and we'll do our best to answer as many as uh as we can so before we get started i want to make you aware of some uh really terrific upcoming events you might be interested in our next study talk is on june 23rd and we'll explore the definition of life and as a side note you may be surprised to learn that where science is concerned we don't have a good working definition then on july 21st we'll explore rogue planets and the opportunity for life the seti institute is also a sponsor of the silicon valley astronomy lecture series and the next presentation is on may 26th at 7 pm and it's a talk about the search for techno signatures and the new science of life in the universe with adam frank so you join that it should be a lot of fun you can learn more about these and other events on our website at seti.org forward slash talks so hang on for dear life and let's get this conversation as we ask why is earth still habitable and i'll turn it over to you trunk thank you bill uh welcome everybody so yeah why earth is still unbeatable and that's a question you ask and probably often and that's the question that scientists have been asking as well um the reason we decided to do this talk today is because also a lot you can if you open newspapers every month you will see that astronomers may have discovered a new potentially habitable world and so to really kind of understand what it means to have discovered a potentially habitable world i think it was very important to understand what is habitability and to to study the planet that we know which is the most habitable at the moment earth so that's the reason for which we invited uh two scientists two very different scientists uh one is uh earth system scientist and the second one is an astrophysicist and we hope this conversation we kind of put some enlighten us about the role of habitability and how our planet is still habitable so let me introduce them hello sarah so sara rigemer is an astrophysicist at oxford university she's working on the detection of potential possible life on exoplanets by looking for atmospheric biosignatures research is mostly about modeling atmosphere and the climate of exoplanets extrasolar planets so she's going to talk about this in more detail i would like to mention that sarah was selected as a ted fellow this year and a talks will be soon available online she's also has a course on astrobiology that will be published soon has been published recently on amazon audible and let me introduce you toby hi toby hi so toby tyrell is a professor of earth system science in the school of ocean and earth science at the university of southampton in the uk so after degrees in engineering artificial intelligence and computer modelling he decided to use his expertise to to study the climate on our planet um most people know toby for his book on the critical analysis of the gaia hypothesis i knew that i read this book before i met you in fact and i um and to and toby has been working recently on the on the model to simulate the climate history of planets and he will talk about this in more details today so sarah let's uh let's uh toby um let's start with you since uh i mentioned your work tell us a bit about this recent paper and this recent result that was published in nature um a few months ago okay thank you very much frank please tell me if you can't hear me or if you can't see my slides properly so so i hope you can see my slides now so yeah i've been interested for a very long time in this question of how earth uh wait a moment do you see this like i don't see your slide over okay let me just how's that now yep now we see it thank you okay great right so yeah i've been interested in this uh question of how earth hung on to its habitability uh for a very long time and i've been to a lot of conferences about it i've spoken to a lot of people about it and obviously i've read a lot of uh books and papers about it um and during that time there's really is there's two main views that i've come across uh that that people hold as to how earth manages to stay habitable and so we're not talking here about earth being habitable at one point for the origin of life but obviously we're talking about it's staying habitable without interrupt interruption for uh as bill just said maybe 3.8 billion years so an enormous duration of time and obviously for life to develop and complexify uh it couldn't stay habitable for most of that time with a short interruption but had to stay habitable for all that time uh yeah two main views that i've come across as to as to how that happened one is the gaia hypothesis which suggests that once life becomes abundant on a planet it sort of like takes over the reins of climate control and ensures that climates stay habitable uh the second main view predominant amongst uh geologists or scientists is that all that a planet needs is silicate weathering um and so the if a planet if silicate weathering this process of eroding silicate rocks if that takes place on a planet then that will make earth have a thermostat which then keeps climate on track so these are the sort of like prevailing views of the during the time that i've been talking to people but hidden away in the literature in really only two or three different places sort of so just hidden away is another view that's uh that really struck my interest which is that rather than it being a surefire thing once you have life or once you have silicate weathering uh perhaps the uh persistence of habitability is much more of a chancy thing much more of a fluky thing that depends upon happenstance and what happens during the history of a planet i thought this was uh a plausible view and very interesting um i was struck by the fact that when you look in the um in the index all the textbooks for instance on this subject you won't see any mention of luck or fortune or happenstance or hazard that sort of thing it's really only talking about the mechanistic explanations but anyway i was very interested in this possibility and um i wanted to investigate if uh indeed it did seem reasonable that chance was involved in habitability habitability outcomes so i managed to find a way to look at this in a computer simulation and this gives you a little bit of an idea of what i did so the y-axis on this plot is the rate of change of temperature of a planet over time this is a very very simple model i should say um so if we're above the x axis on this plot we're talking about warming over time if we're below the x axis we're talking about planet getting cooler over time and then the the x-axis is the planet's temperature so we're showing rate of change of temperature against temperature and uh my approach involved uh randomly generating lots of different planets with different climate systems and the way that this was done was by positioning nodes across the habitable temperature range so these are the black dots that you can see here and then randomly allocating rates of change of temperature to them and just linearly interpolating between them so this gives one example of a planet and you can see there's a zone of runaway cooling towards the lower end of the temperature range a zone of runaway warming to the right-hand end and then as it happens for this planet there's a zone of stabilization of temperature so in that red box there if if the planet happens to be at any of the temperatures in that range it will settle towards the attractor point so the the red uh bullseye in the middle there so uh this is just one planet but this rand using random number generators i came up i just sort of automatically can produce a whole zoo of different planets all with different climate systems in this very simple scheme and you can just see a few of them here so a whole sort of menagerie uh complete diversity of different planets and this is all done using random number generators no human intervention um and also there's no bias in this scheme there's no inbuilt bias towards either stabilization or destabilization so that maybe gives you just an insight into the approach that i took and so i generated a lot of planets and then i ran them forward through in time to see whether they would stay habitable while exposing them importantly while exposing them to perturbations of the planet's temperature so to chance events like super volcano eruptions nearby supernovae flares of the parent star etc different things that could knock the planet's temperature away from its current value and then i just ran them for up to three billion years to see if they managed to manage to stay habitable in terms of temperature for that duration okay so what did the simulation actually show and this slide gives you an idea of the results that were obtained so each of the blue circles on here is the result of running one planet uh 100 times with different chance factors different asteroid impacts etcetera on each of those 100 runs and so the y-axis here is the percentage success or in other words the number of times out of 100 the planet stayed habitable and yeah so each blue circle with a stem is the result for one planet and what you can see is that most of the planets showed no uh propensity at all for staying habitable over three billion years not even one time out of a hundred they managed to stay habitable for that long but if we move towards the right hand side of this plot you'll see that a few of them did exhibit some uh possibility of staying habitable but the most important aspect for um the purposes of my paper was that for those ones that did exhibit some possibility of staying habitable they didn't exist all exhibit 100 so it wasn't an all-or-nothing thing but rather there were different degrees of success and you can see most of those planets that sometimes stayed habitable in fact only stayed habitable rather infrequently and so the main conclusion that i drew from that is unambiguous in the simulation is that chance is involved in the outcomes so it's not just a matter of whether a planet has favorable mechanisms for stabilizing the temperature but it's also what happens in terms of whether for instance you get a particularly serious asteroid impact at a critical period in the planet's history for instance so if we're to try and draw an inference from that from that for earth we would say that probably if you were to have visited earth at the time when life first evolved and tried to make a prediction as to whether earth would remain habitable for the next few billion years long enough for intelligent life to evolve you would uh probably have it would probably be in the case that those odds were really rather poor that there wasn't a high probability of earth staying habitable but yet thanks partly to luck it did remain habitable so that would be the main conclusion and i think that hopefully textbooks will uh refer to this a little bit more in future thank you toby thank you for this interesting presentation and we're gonna go back to this of course uh sarah you want to tell us a bit about exoplanets and habitability of exoplanets all right thank you very much and please let me know if you can see my slides okay yes that good good all right so thank you so much for having me here uh as toby talked about just earth habitability over four billion years i want to look a bit more at earth's bio signatures and how those have evolved over 400 billion years if we were to look at earth as an exoplanet and what i like to point out is that earth we can see as an exoplanet and it's really represented many types of planets its biogeochemical evolution has had many different phases and that could look different for uh if we were to see earth at different times so earth has been you know this hella shadean world the archaean world with tidal pools snowball earth the triassic period and all of these atmospheres and the signs of life would have been different so when we think about earth's atmosphere over 4.5 billion years it has also changed and here you can see just a kind of a quick schematic cartoon of how these gases might have changed we might have had more methane when we had methanogenesis and before the rise of oxygen and then broadly speaking though there's a lot of nuance in this oxygen rose in two relative distinct phases over its 4.5 billion your lifetime and so we can think about how might that have looked like could we have seen that oxygen at what point for different uh planets around other stars and so we can take these different time intervals and this is work that i did a few years ago where i look at earth around different stars at these different phases of when earth has a different combination of gases and i want to also bring out the fact that the stars that we are observing and will observe for exoplanets are very different we have stars that are hotter than the sun we have stars that are cooler than the sun and so we don't expect to see only earth analog systems with a sun-like star so we want to take into account the type of radiation environment from those different stars and so this is a figure from that paper where i look at the biosignature detection through geological time with if we take earth from these different time points and put it around different types of stars so in this first column here this is the spectra of a pre-life planet so a planet without any biology mainly just carbon dioxide water and some methane from volcanoes in the atmosphere and the different lines represent the red lines would be cooler stars and the black lines are going to be hotter stars and the sun is a blue line in the middle of that and then if we go down then we have what the ir the infrared spectra looks like after that first rise of oxygen after the great oxidation event and we start building some oxygen in the atmosphere and ozone and then the uh the second rise of oxygen and finally the modern atmosphere i want to highlight a few key features which i think are interesting namely the first one is the ozone feature so if we look at in the first case it actually overlaps a co2 feature so if there's a lot of co2 in an exoplanet atmosphere it might be harder for us to see that ozone feature if we look in the second row we actually see the ozone feature quite strong even with only one percent of current concentrations so that's one percent of our 21 oxygen for the hottest stars and that's because these hotter stars have more near uv and that creates more ozone and then as we get a further rise of oxygen we see more stellar types have a stronger ozone feature and then for the modern earth we see ozone in most stellar cases what we really would like to see is the combination of say oxygen or ozone in combination with methane that would be a really strong biosignature detection and so you can then look at where will we see the both the methane and the ozone together and and that varies that strength of signal varies for the different star types and for the different geological evolutional periods so i just kind of want to summarize when when we think about finding biosignatures on exoplanets we tend to think that we'll see this whole biosphere and bioluminescent vegetation and and tall people with blue tails and theorists like myself we we claim that we're going to find this very easy to interpret spectra it's going to be a nice clean line with signs of vegetation oxygen ozone methane it's going to be very easy to interpret and the reality is going to be a lot more complicated we're going to be looking at a pale blue pixel uh there's going to be multiple models that will fit the data there's going to be error in those models and it's going to be difficult so i like to think of this as we have two hurdles to overcome first we have this technological hurdle which we're first our first chance of doing this detection is going to be in the 2020s which is exciting with telescopes like the james webb space telescope and the large gray ground-based observatories these extremely large telescopes might be able to detect some of these biosignature gases but really it is also this 25-year horizon where we're not just going to be able to detect a few planets but dozens and and maybe even a hundred or a thousand planets and try to actually see what we can find in a more statistical sample but then we're still going to be left with this interpretation hurdle we might detect many molecules in the atmosphere of exoplanets but we're looking from light years away and so how are we going to distinguish this when we're not on the planet and we can't look and take pictures of you know alien life on the surface and so that's what i want you to think about as as mentioned i have a few astrobiology resources one is already out i have a course called searching for extraterrestrial life you can find it on amazon audible and it's a 10 part series that covers the exoplanets what we're finding there origins of life and also things like the fermi paradox and drake equation and then also as mentioned my ted talk is going to go up online this coming monday on ted.com which is also again about these nuances of detecting microbial life on exoplanets so thank you very much for having me here today thank you sarah thank you to both of you very interesting conversation so i have a lot of questions and i prepare a document we have these like 20 of them but we are not going to be able to go through the 20 questions so let's first a very interest very important question for you toby um so it was my understanding that earth was habitable and will remain a beatable forever before i read your paper basically that was where the vision i had so can you give us more more details about the problem of habitability what exactly what's the indication that suggests that earth is not a stable system basically and what can disturb the system sure so in terms of uh uh understanding that earth isn't sort of wouldn't just stay habitable be stable and that there is a question to answer there um one thing that we that addresses that is what's known as the faint young sun paradox which probably some of the people listening will have will have heard of before so this is the understanding that um due to the the way that stars change over time as they burn hydrogen and it converts into helium stars like the sun get hotter over time or rather they get more luminous over time they send more radiation out to space and what that means for earth is that the rate at which earth has been heated by the sun has increased over the time that life has been present on earth by as much as 30 or 40 percent so a very large change in the heat input received from the sun and uh carl sagan was actually one of the first people to realize the implications of this for habitability and together with george mullen he noted that um because of this faint young sun on the early earth the ocean should have been completely frozen over if everything else has been the same as it is today under the faint young sun uh or conversely you can look at another way given that uh there was for most of the time liquid water present on earth at that time as the sun has got hotter up to the present day the ocean should have boiled away so something must have counteracted that changing heat input from the sun and helped the earth stay stable which it wouldn't have done obviously if it was only if nothing had counteracted the change in the solar input but also we can look at the amount of carbon dioxide in the surface system of the earth so in the oceans and in the atmosphere and then the soils for instance at all interchange and we can compare that to the the rate at which carbon is exchanged with the rock reservoir which is extremely large and the calculation has been done that if there was only a 25 imbalance between the rate at which carbon dioxide or carbon is coming in from the rocks to the surface system and the rate which is leading again then within within only a million or a few million years we would either run down the carbon dioxide concentration in the atmosphere completely and the earth would freeze over or we would increase the carbon dioxide sufficiently that the oceans would boil away so rather than climate being stable is actually rather precarious which leads us to this habitability problem that uh this work addressed and you know we can even see this today sort of with global warming that we're changing the carbon dioxide concentrations and having quite a big impact on temperature already we can also look at mars for instance and see that mars was did once have a habitable temperature and doesn't anymore so that's a rather stark example that just because a planet has a habitable temperature once doesn't mean it will stay that way all right thank you you cover a lot of uh interesting ideas here uh sarah you're the astronomer of the group so tell us a bit um about the stability of stars um i was i didn't know about the the sun the the faint uh young sun paradox and is that something that has been studied in in the field of astrophysics and do we see the same effect for other type of stars that's a great question uh so the faint young sun paradox especially as it's supposed for our planet is for our sun but most stars 75 percent of the stars in the universe are these um dwarf stars they're much cooler and the problem for mdor stars is very different for habitability so m dwarf stars evolve very slowly they don't have this increase of 30 percent luminosity over 4 billion years it takes them you know they're gonna be around for trillions of years and stars are that they use their fuel very very slowly and so that but they do have a different problem which is that early in their life cycle when they're forming they have a lot of energy that's coming out they have a lot of radiation and so so what's interesting is that the habitable zone of where a planet would be habitable for an m star in its early life before it really is fully formed as a star that's different than where it'll be the planet would be habitable for its duration of lifetime so a lot of the research right now is looking at can m stars remain habitable through that phase transition can you develop a secondary atmosphere that recovers and you know maybe you get volatile delivery from asteroids for example because in that pre main sequence lifetime of m stars you would probably boil away all of your water uh and so this is one of the questions i think we'll be able to answer with james webb uh is actually do m star uh planets like planets orbiting m stars do they have atmospheres at all that would be a super interesting question because if they are able to have atmospheres and those aren't completely ablated in their early uh life cycle that'll be a great win for habitability i'd say and if we find a bunch of airless rock balls then then that would that would be a bit more depressing and that's certainly a question i think we can answer in the next few years with james webb yeah because earth is is a lucky planet in a way that we are around a g-type star which is relatively stable but the work that toby mentioned here is that this this my view of a stable star was completely wrong in fact it's not the case because the start of evolve of a billion of years and this will have changed the habitability because of change of temperature so toby just to go back to something you mentioned this gaia hypothesis i know you like this topic so why why this hypothesis came out why do we need it well we thought we needed it and uh why do you think it's um is not the perfect hypothesis to explain the reason for which earth is still habitable the hypothesis was originally uh proposed by james lovelock and also lynne margulis a famous biologist um and the the the reason that james lovelock first thought about it was that he was examining i think the atmosphere of mars for biosignatures and then he compared it to the atmosphere of the earth and he noticed the very high levels of methane and oxygen in earth's atmosphere they shouldn't coexist in the sense that um if you have an oxygenated atmosphere it will remove the methane so the the reason they do coexist is that they're continually being produced by life and also being continually removed so you get a dynamic balance so that coexistence of oxygen and methane was showing that earth's atmosphere is strongly perturbed by life and we know now that i think no scientists these days would dispute the fact that life is a tremendous force for ins in terms of shaping earth's environment uh lovelocker mughalis took a stage further than that they said that not only is it a tremendously strong force but it actually acts in a certain direction if you like towards uh uh improving or stabilizing or keeping the planet suitable for life and it's that it's that second step that uh causes problems for a lot of scientists that they would struggle to accept that second step so that's uh uh in essence what the gaia hypothesis is um i'm trying to remember the rest of your question now oh so why why do i think that maybe it's not it's not a credible hypothesis so i i wrote this book as you said and i uh tried to compare the the modern day evidence against the suggestions for the gaia hypothesis and it doesn't really stack up against the evidence so i i without going to all the details i concluded that it is a very very interesting idea but it but it's not the way that the earth works as far as as i judged it for sure okay so i'm gonna go to questions with both of you we'll talk about we will be able to talk about the view of each other work but um i want to first test put the stage here and i have a question for sarah about habitability so people our audience understand what what astronomers meant when they talk about habitability uh is that only related to temperature on the surface of the planet and if not give us some maybe some examples yes so i think i think this is actually a common misunderstood term uh even within the astronomer community because there's the there are places where life could exist even in our own solar system say in the oceans of europa that's a habitable environment however as an astronomer that is not a habitable zone moon because we would not be able to detect that life we need a biosphere a full biosphere that's interacting with the atmosphere and then we need to be able to see that light from you know earth with our telescopes and so when we talk about habitable zone planets we're really it's a shorthand for a remotely detectable planet that has a potential for having stable liquid water on the surface that could interact and have a biosphere and then we're going to be able to detect it that's not to say that life couldn't exist in a myriad of other environments you know life could exist in the subsurface of mars for example but as an exoplanet we're not going to be able to see that uh since subsurface life would be very uh difficult for us to detect because again we're relying on detecting atmospheric signatures so habitability i think there's two ways we can frame it one is in the solar system and we can look for different habitable environments and where extremophiles might live where the limits of life are and that's a very different usage of the term than when we think about it in an exoplanet context where we're thinking about where can we actually see if there's life on that planet and then that's looking at where could liquid water be and is there an atmosphere and can we see that atmosphere hey so toby correct me if i'm wrong but basically yours the article you you wrote recently is the view of astronomers applied to earth because you focus mostly on the temperature is that correct yes i focus only on the temperature in in the paper there's one sensitivity analysis one uh exploration with a with a variant of the model where we had multiple environmental variables and we looked to see whether we got the same sort of result and we did but um on the whole the paper is only focused on temperature um yeah so if we can imagine that the reason for which earth is still habitable it's because earth has not been fully habitable at some moment it was not habitable you can give us some example sarah and you you both have been working on the same on some of the cases where loss earth lost is habitability but maybe extremophiles survive for the short amount of time and those extreme muscles are the one that then bring back earth to uh to bring back life to our planet is that a view that we can basically consider to be the just true it could be basically an explanation for the fact that our planet is inevitable so i can maybe start on that so uh yeah i i accept that view and it's certainly the case that uh you know from what we know extremophiles at the moment that for instance deep in the ocean crust we have uh organisms that can survive and presumably they're rather resistant to you know temporary uh changes at the uh the other surface so survival in refuges only to emerge after some event and recolonize the surface of the earth is certainly a possibility a possibility in terms of whether that's actually what happened on earth it's a little bit um certainly when you look at the phanerozoic it doesn't seem that that's what's happened to the last uh half a billion years but even when we go back before the before that to the neoproterozoic ice ages there's evidence that eukaryotic algae so you know reasonably advanced forms and photosynthetic organisms survived through these snowball earth events so um i think that um there's certainly the possibility that survival in refuges is is one way and that perhaps there were temporary events that did um knock surface habitability off track but that's not what seems to have happened over the last um you know nearly a billion years i would i would say yeah i'd agree with that and then say also like first when we consider earth's oldest life form luca the last universal common ancestor it looks to be a hypothermophile but is that because there was a sterilizing surface event say an asteroid impact and it wiped out earlier life that was maybe more surface and not a hypothermophile and we wouldn't be able to see that then because that life is wiped out so so i think it's an interesting question because there are you know as you said refugees where these uh microbes or other life forms could exist thrive and then get through a dark period so to speak um and and i think we can also consider this uh for exoplanets because there's stars that flare uh so then could life exist on say the dark side and then recolonize things like that we even have signs of life now thriving in a chernobyl a radiotrophic fungi which i find it just incredible that life can then use and thrive and still exist in such high radiation environments so i think we don't yet know really what the limits of life are and how adaptable it is especially once it's gotten going so there's one paper that talks about how the limits of the origin of life might be more constrained than where life can eventually evolve to live and then survive through billions of years of history and traumatic events thank you yes so toby i when i look at your figure where you showed the all those planets that lost their habitability as an astronomer working at the city institute it makes me sad frankly it does make me very sad and but then i thought about it and realistically when you look around us in our own solar system those planets that lost their abitability we see them venus and mars are basically those right so do you see a new model something like something very close to venus like do you see any planets that really become venus and planet have really become mars and can you tell us what exactly happened in this case so um there are lots and lots of planets that leave that leave the habit you know all of the planets that i simulated i started them off in at a habitable temperature the large majority of them depart the habitable temperature range rather rapidly um i don't the simulation didn't follow them after that so um i was actually asked by one reviewer of the paper to include simulations where they could come back after departing the habitable zone and i did do that for one um uh one set of experiments but on the whole i didn't follow them after they'd left the habitable temperature range so getting back to your your main point about what does it mean for the the chances of finding intelligent life i think that it does uh seem to make it a little bit less frequent probably in the sense that um it was only about something like one percent of the planets that were simulated uh did stay habitable so it's suggesting that a lot of planets will not maintain their habitability but at the same time i suppose i was a little bit surprised by the fact that without building in any sort of special propensity for keeping climate on track just by really having randomness in there in terms of climate systems there's still you know still temperatures stayed on track for really quite a significant proportion of the planet so that's uh giving a slightly more optimistic view in terms of um you know the the chances of intelligent life being out there in the sense that it doesn't seem extraordinarily hard to uh maintain habitability just just by assuming randomness in terms of the way the climate systems are set up yeah ma the planetary astronomer in me will would have loved to see you and publish in the paper the number of venus and the number of mars you got so because i know mars is important of the topic of the paper but for me mars and venus are equally interesting because they lost their habitability and sarah does bring me perfectly to the transition of my question with so you work will consist basically in studying exoplanets so we can anticipate to that you will provide some uh constraints some inputs to the study of habitability right maybe see some very exotic words can you can you develop a little bit what we astronomers are working on at the moment and what you could expect to see i know it's speculative but maybe you have some ideas already right well yeah so it's an excellent question because i think we can test some of these hypotheses that toby has put forward so i certainly agree that chance has played a role uh that that is that seems to be clear now at what level is it you know only one percent of planets remain habitable or is it 10 or is it 50 i think that's less clear because we don't yet know how if these feedbacks exist we haven't run full climate models which take you know a lot of computational power we haven't used uh and we don't understand all the feedback mechanisms which might keep the planet habitable and so then we can think well okay let's look at this as an astrophysicist let's actually look at planets multiplanetary systems where you're around the same star and and find where you have terrestrial planets in the habitable zone maybe the optimistic capital zone and see if you see something like a carbon cycle where you have a build-up of carbon dioxide on the outside of the habitable zone and less carbon dioxide on the inside of the habitazone is that something you see or do you just see a random assortment of atmospheres and so i think what we can do as exoplaneteers is actually start to look for this in the data and start to see if we can see habitability not just as this theoretical construct can i make my planet habitable which is what you know we do as astronomers right now and measure it and see if we can actually detect that and hopefully provide input as to the robustness of some of the negative feedbacks which could have kept earth habitable over its geological time yeah maybe toby you can tell us what how the research of sarah and other astronomers will be useful for future simulation or maybe refining your modelling do you have some ideas sure yes just before before that i would definitely echo sarah's point that the the the model is not it's robust in terms of chance always playing a role in habitability outcomes but it's not robust in terms of the number of times that occurs so sarah's quite right about we don't the simulation doesn't say too much about that um in terms of how astronomers can provide useful information for the modeling um uh it's it's going to be difficult for the reasons that sarah mentioned in their presentation that they're just so far away and we're looking at the you know the the light coming from the star through the planet's atmosphere and you know it's quite difficult but uh there are definite ways in which uh you know for instance something that that struck my attention recently was reading about uh observations of uh flares on different stars and how frequently they occur and how um without the magnitude of those flares and that's something which is readily observable and can certainly help constrain the magnitude and frequency of the random events that are put into the simulation yeah we could uh i was i was also thinking that maybe in the future let's assume we launched a luvoir or some kind of experiment like this and we observe 300 exoplanets and and then we see kind of different compositions on those exoplanets in the atmosphere but also different maybe structures or features around like a gigantic impact creator etc that will allow you to kind of quantify the frequency of those events of a super volcano gigantic impact crater or flare of a star as you mentioned the that's a very um i mean it's i'm thinking out loud here i think that is combining those two research would be an amazing result if we we of course have the potential to observe those exoplanets in the future uh i just can't say to the pub to our audience that they can start sending us questions by clicking on the q a we are going to take a few of them rebecca and simon will basically put those pop up on the screen and ask you questions so please start asking questions now and i have one question i want uh two and pessimistic questions but uh i think it's important we address this this converse in the conversation so one for you first toby um this uh entropy and topic principle so what does that mean and uh what's the final conclusion if if that's if that's the reason for which we see uh that earth is not could not have stay habitable for long periods of time go ahead explain to us this so the the weekend week anthropic principle which is also referred to as observer selection is a philosophical idea which is really quite interesting it's a little bit hard to get your head around if you're not familiar with it but it's based around the fact that you that it's logically impossible for you to observe anything that's incompatible with your own existence so to give a slightly strange example if you were to um be presented with a death certificate for your grandfather at age six you know there must be something wrong you know that it's either not uh it's either an incorrect death certificate or that person was not your grandfather so we can't observe anything that's incompatible with our own existence that does mean that there's a bias towards what we're going to find when we look back on earth's history it's obviously impossible for us to observe um a history of earth where a massive asteroid hit earth and all life was wiped out a few million years ago that's not something we could ever observe because we wouldn't be here to observe it and speculate on it if that happened so um because of this bias it does mean that um because this observer selection bias it does mean that life that the chances of earth having stayed habitable could have been extremely small and if that had been the case if most planets on which life develops don't actually maintain their temperatures for for billions of years and so intelligent life doesn't develop on those then um we would have to be on one of those lucky planets that made it through and just because we must be on one of those lucky planets but just because we are make it doesn't mean that we can get any idea from looking at earth as to just how um likely that was to to to stay habitable so um yeah i think it's really i find it really interesting but also slightly uh it took me a little while to really get my head around i felt thank you i think another another way of framing is like it's the survivorship bias like we've survived you know but but we we're only here because of that so that's another way of terming it that i find useful to to wrap my head around it so sarah's a good transition since you are you the astronomer was looking for life so when you read this when you read this paper i know you read it because we talked about it beforehand and the results so is that the bad news for your research um what's uh what do you think yeah like i said as i as i mentioned i think for for astronomers we we need to test this hypothesis and so i think absolutely we need to bring into the the dialogue that maybe the carbon cycle doesn't uniformly happen all the time maybe it isn't hasn't even happened on earth the whole time and and looking at our assumptions of feedbacks and so that's where i think the strength of toby's work is is that it causes us to question and and then uh and then as i mentioned before uh because the model doesn't have these feedbacks in a more robust climate model i don't think we can actually pull a number out a statistical number which toby also mentioned so it doesn't really change my my philosophical view of that i hope that life is actually quite common and and when we talk to prebiotic chemists people like jack soshak john sutherland who are doing work trying to understand how did life go from a molecule to a living system a simple cell they often think it's actually pretty easy and we see that the first life on earth happened very quickly after earth cooled and had habitable conditions and so that to me indicates that life at least microbial life is relatively easy even though we only have the one example and and what i would love to see is if we find life in our solar system say if we find past evidence of life on mars or current evidence of life on mars in the subsurface or if we find life in europe or on titan you know if we see that that would definitely increase our odds of then looking for microbial life especially in the universe now the question of are we going to find uh you know intelligent life and and you know aliens and these sorts of things as we tend to think of them in science fiction that's that's a different question to me interested in microbial life like do you think we can find life of any sort whether it's microbes plants animals uh or or more advanced uh creatures and then once life gets that gets that hold on the planet the question is how easy is it to eliminate and then it really does depend on a lot of factors and i think we also have to consider what is physically likely you know we know that in an early star system you're going to have more asteroid impacts but then as it kind of quiets down you probably have less would you still you know maintain that habitability so i think there's a lot of questions and for the research that we can do so yeah this now we have a poll when will we detect signs of life beyond earth you have a few options and i'm really curious to hear what the audience thinks okay thank you while we uh we are ready for today question from the audience so don't forget to tell us where you are watching us from please so we have an idea of how far you are and uh and um who is uh which country is the most interesting in the habitability of earth okay let's go so simon you're here go ahead yeah good evening everyone i just want to run down the list of some of these these places where people are uh tuning in from we have um cyprus which they emphasize is on earth um yorkshire bristol in the uk uh virginia we've got coordinates which i'm not going to translate just now because i haven't got a map with me um tennessee india barcelona baltimore um lots more from india as well so uh colombia and mexico so a wonderful selection of locations uh around the globe um this first question is uh going out to to sarah and this is a question on um exoplanet atmospheres and uh what um what have we discovered from from exoplanets uh transits uh as far as their atmospheres are concerned that may may shed some light onto the habitability of those planets all right so first off with our current generation of telescopes we're not really able to see earth-like earth-sized habitable planets we can see bigger planets maybe the mini neptunes uh and and jupiter-sized planets especially hot jupiters and and those are the ones that have been mainly discovered and with this transiting technique of looking at the planet cross in front and seeing the light through the atmosphere we have detected some molecules in in the atmospheres of exoplanets as well as using some high-resolution ground-based techniques we've also detected some molecules including hcn water and some other interesting molecules so we're really waiting for that next generation of telescopes to be able to do this for earth-like planets for habitable zone planets and and what we are finding is that clouds are a problem clouds and hazes are a problem i think that's the number one thing that we've learned so far and that's especially important for the transiting technique because that'll block a lot of what you see and so this means that we might need to look for direct detection missions where we actually block out the starlight we directly take photons from that planet itself and say a planet is partially covered in clouds like earth is you'll still be able to get signal from the surface as well and so transit has a bit of a you know it's only able to probe more or less the upper layers of the atmosphere and with direct detection we'll be able to get deeper into the atmosphere so that would be future telescopes would give us more answers but what we're seeing right now is a lot of flat spectra and that indicates clouds and hazes which will make our challenge a lot harder to actually see what's in the atmospheres of exoplanets next question hi everyone there are a lot of questions by the way i apologize that we are not going to be able to get to all of them but um we'll try and we'll try and get to as many as we can um this question has to do with whether life itself controls habitability on a planet we know that life certainly can impact uh habitat and climate but does it actually impact or control habitability so i could maybe start on that um so for sure it definitely impacts habitability so we know on earth for instance that um life makes a difference to the rate at which rocks are weathered so if you have you know roots penetrating into soil and you know penetrating right down to the rock for instance and releasing acids that affects the rate of weathering which releases carbon for instance from the rocks so there are lots of different ways we can talk about the albedo of the planet and how that's affected by whether you have forests instead of snow for instance there's lots of different ways so i think the short answer to that is for definite life does affect habitability the big question uh and i have a very definite opinion on it the big question is whether it affects it in a in always in a beneficial way and i think is much more controversial okay question um about how the sun obviously affects life on earth uh but more specifically about solar winds and and um uh coronal mass ejections and so on uh what's the long-term effect of this that's probably for toby as well i think maybe sarah would be a better place to answer that one yeah the solar wind uh so we have a magnetic field which does help protect and divert a lot of the solar particles from our atmosphere however it's uh you know we do have some atmospheric stripping and certainly on mars say we mars has lost its atmosphere from the solar wind and so and we also do have some uh like these coronal mass ejections and other things but relatively speaking our star is pretty quiet and boring if we look at stars in the universe they're a lot more chaotic especially these m stars that i mentioned which are 75 of the stars out there they're having flares you know every day every and big flares every 100 days is life able to cope with that is life living under rock surfaces is it on the dark side of the planet because these are often tidally locked systems like our moon so it's a single like the same day side and a permanent night side so these are questions that we're just going to have to answer by looking for the atmospheres around these planets and that's what i mentioned earlier on is do planets orbiting m stars that have even bigger flares do they even have atmospheres and then we'll learn a lot more about atmospheric loss and the ability of a planet to retain or to build an atmosphere after formation in such a system next question um i think this one is again for sarah everybody's sort of obsessed with tardigrades because they're so cute and this person would like to ask if you're prepared to speculate on the possibility of exo tardigrades yeah i mean tardigrades are the best uh so exo-tardigrades yeah tardigrades are amazing because they're poly extremophile and complex which is an unusual combination they're actually for people who don't know what tardigrades are definitely go down that youtube rabbit hole it is an amazing one and there's also a great little clip called captain tardigrade which is a little animated uh two minute video but yeah i have tardigrades sitting in my uh kitchen actually on my little shelf because they're so cute and i bring them into classrooms um exo tardigrades yeah i mean i think that life has proven on earth to once it started maybe not the conditions of the origins of life those might be more fragile but once it started it's been able to just go into all sorts of niches where we wouldn't have necessarily expected life to be able to thrive and it's been able to persist uh for through these very catastrophic events in earth's history so i'm optimistic that you would get something that evolution that the selection for these extreme survivors would happen on other planets where life has taken hold and so i don't know what those tardigrades would look like but they i'm sure it would also capture the attention of the uh the people on that planet or people used in a very loose way the beings on that planet this is a next question is from suresh about the the building blocks of life is there a possibility of life uh with elements other than those uh which are made you know used to make life on earth um like alternatives to carbon-based life forms i suppose or variations on that i'm not really sure about the answer to that question i don't know sarah whether you've got any views yeah i mean i have some views whether they're accurate or not is another question and this is also um you know things that we can talk about more but yeah i think this is where solar system exploration is really key because if we see life and say titan the liquid methane ethane lakes on titan that is a whole new type of biochemistry and there's also work done to try to create synthetic biology or see what you can do with different molecules on earth in the lab and those are two avenues i think which are really important to answering this question uh and so so we don't know the answer we don't know if the phase space of life is so regimented that it has to be this carbon-based biochemistry we don't know what i do say is that carbon is very abundant it's more abundant than say silicon and water is very abundant co2 is very abundant so from a sort of chemistry perspective it wouldn't be surprising if we find life that's carbon-based because of just the abundance of these molecules as they're formed in the universe okay this question is a little more speculative about our solar system and the question is if mars was in venus's orbit and venus was in mars's orbit would we have three habitable planets in our solar system instead of just one or potentially just one i can comment on that which is that i think that that assumes that the only thing that really matters is your size and your distance from the sun and from the simulations that i've done i think that uh that those are not the only factors that you know you need factor you need stabilizing feedbacks and you need a degree of luck so sarah i think it certainly would increase the chance you know so if because uh mars lost its atmosphere in part because it is small and it's further away if it was closer maybe it would have had a better time and if venus was further having more mass would have been able to maybe retain the atmosphere whether they would actually be all three habitual or not again probably some chance probably some feedbacks and i wish we could run that solar system and that uh that universe and see the answer but we'll be able to do that with some exoplanet systems for example uh kepler-62 enf are two planets in the same habitable zone around the same star you have the trappist system so uh as an astronomer i think we should go and look for those types of systems okay last right uh one more or we can stop there if you want to take over frank okay uh because i have a question i have two more questions in fact so because while this question was popping about ideas of questions so um one question for toby first of all um two in fact but let's do let's do the first one uh climate change is that the parameters that we should kind of consider um and i'm gonna make climate change is like entrepreneurs human climate change is that something you are working on and is that something that we could give us some answer in the future about habitability or the change of habitability of a planet due to the the effect of uh technology no the model the model that i used is very simple it's a conceptual type model so it doesn't have even an explicit greenhouse in it so it can't really uh include human human impacts okay uh and then two final questions one for sarah so sarah um now you have heard about the abitability of our planet and the fact that uh we may have been lucky um what you wish you could do uh to help toby in his modeling in the future what let's assume you have an infinite budget and you can build gigantic instrument wherever you want okay let's not let's forget about the reality of our planet okay um i guess there's short-term and long-term goals i think one of the things toby is already doing is pursuing a collaboration to link this with a climate model actually that i use one of the these more where you can kind of march it through time and see these feedbacks and see how robust the system is to changes and i think that'll be really interesting and i'm really excited to read that future paper then there's like the long-term plan uh i would love to fly a mission something like the life mission concept where you have a nulling interferometer and you can actually measure the atmospheres of hundreds of planets habitable planets in the infrared because that's where you get more molecules absorbing and also luboir and i would like those both to go so if you give me i don't know say tens of billions of dollars i will get this done and and then we can fly them both and we'll have the uv as we know is really important that's what my research actually focuses on uv into the optical and near infrared and then we'll have the infrared those two wavelengths combined we can get a lot of amazing data about the habitability and potentially signs of life on exoplanets so that's what i would want to do okay so we have a pole toby you want to introduce the pole can you um do it lee please so i think this poll uh i'm trying i'm trying to remember what the poll is about but i think the poll is um it's here okay yeah so so given that luck has played a role uh or at least i would say that luck has played a role in staying habitable so far um and given human influences what do you think the chances are of earth remaining habitable over the next few million years let's say 10 million years that's the poll while people think about this um i'm curious to know about the goals and motivation of this research for yourself maybe you can give us some kind of personal point of view on that and what's the next step for you are you going to continue to work on this topic specifically or yeah so my motivation was uh because i i found the idea uh that you know the observer selection and the fact that it could there could have been a strong role for chance i found that really compelling but yet it's hardly mentioned anywhere in the literature so i suppose what i hope that my work can contribute to is that it will become more mentioned in the literature and will become accepted as part of the story of how earth happened to stay habitable in terms of next steps uh sarah stole my line there so uh i'm uh yeah very interested to start working with slightly more complex models so uh simple energy balance models it's not gonna be possible to use very sophisticated climate models for this because the computational demands of doing billions of years on complex climate climate models are completely impossible but yeah i'd like to step up in terms of complexity and and see how that works out in terms of whether the same results produced okay could we surely the results for um for um yes for this one so i'm gonna read it down loud now go ahead toby well 31 percent think that there's 100 chance that earth will stay habitable in the next 10 million years and the same uh proportion for 75 percent and 25 and uh there's a few pessimists there saying zero chance of it staying habitable for 10 million years yeah so we had a very optimistic audience in fact that's great well it's a good way to hand this and bill is going to give us the last word but thank you very much to both of you for participating to this interesting conversation bill you are well that was wonderful thank you so much um and yes we do all love tardigrades until we find them in our bed or in our salad of course they're probably already there we just don't know um anyway furthering what what simon mentioned in terms of our global reach today so indeed we had around the u.s folks lots of folks of course from california we had many joining us from virginia and illinois maryland georgia tennessee oregon louisiana new york new mexico washington i think simon the coordinates if i got them right were uh the football stadium in baltimore um so somebody is there um and internationally we had people joining us from cypress and the uk lots from india as you mentioned spain colombia mexico canada and serbia so it was great to have all of you with us today in any event uh toby's shown us that certain elements of habitability and sustained habitability may indeed have quite a lot to do with chance so if earth's long-term habitability through more than 80 percent of its existence is in part based on a roll of the dice what are the implications for billions for the billions of habitable habitable worlds we believe exist in our own galaxy and if there is life beyond earth what are the odds of detecting it and as sarah pointed out bio signatures and planetary atmospheres may give us fascinating clues as to the presence of life on exoplanets and the james webb telescope will hopefully soon give us access to these atmospheres for spectroscopic analysis as she noted however even positive signatures will be indicative and really interesting for sure but not necessarily definitive this of course is one of the compelling motivations for the search for techno signatures including seti research because our confirmed discovery of a technology beyond earth as a proxy for life and intelligence would of course be definitive and thus i think represent a clearly profound discovery in any event our guest today will be receiving a mission patch from the seti talk series and the highly coveted seti talks mug in fact there's only one of these mugs for every speaker who's ever been a lecturer or panelist on seti talks so if you have one you're part of a very special and unique community in fact they're so rare i don't even have one here to show you i wish i did but uh anyway those will be sent on their way to our wonderful speakers today so in closing i want to remind you that the seti institute is a non-profit research education and outreach organization we're supported in part by donations from the public from people like you we bring these lectures and other events to you at no cost but we're very grateful for any and all donations that allow us to continue bringing the stories of extraordinary science to all of you we invite you to join our quest and become part of our community you can visit seti.org for more information make a donation if you're so inclined and also sign up for our monthly science newsletter we call journey which is very cool um and a big thanks to all of you for being with us today and to our guest speakers sarah and toby and to frank for his great moderation i also want to thank rebecca and simon lee beth jasmine and the rest of the team at the seti institute who make this whole wonderful series possible and don't forget to visit our youtube channel and tour the amazing array of lectures including this one which should be posted in a matter of days and most importantly don't just come along for the ride join us at seti.org become part of our team the search for life beyond earth is a journey of ultimate discovery and it's one we invite you to join so thanks very much for being with us have a great rest of your day hey bill do we want to look at sarah's poll results real quick oh yeah absolutely sorry let's do that pull them up okay so it looks like uh when will we detect life beyond earth we've already found it well about uh looks like 13 believe we've already found it fascinating uh 33 of you um think it'll be within 10 years and the majority of you almost 50 percent of you think within the next 10 to 50 years for what it's worth which isn't much that was also my answer i think that's my answer as well is that yes sarah's yeah where were you on this poll where were you on this poll toby you're still muted that was actually my answer as well huh okay and frank how about you within 10 years oh all right fantastic i have some very good bottles of wine resting on that 10 to 50 year i'm slightly older than you sarah that's right and let's see more than 50 years 8 and 1 percent of you said never all right so wonderful so thank you again very much everybody for joining us today thanks for participating in the polls and telling us where you're watching from and don't forget to come back and see us again in uh june for the city talks and you'll find all the information about our upcoming talks events and lectures on our website at seti.org go to seti.org talks to learn more about upcoming lecture series thanks again everyone have a great day we'll see

Channel: SETI Institute

Views: 8,519

Rating: 4.847826 out of 5

Keywords: planetary science, dps, AAS

Id: 816BACdveK4

Length: 70min 22sec (4222 seconds)

Published: Wed May 19 2021