Comparing Worlds: Climate Catastrophes in the Solar System

good evening everyone I'd like to welcome you to this lecture in the eighth annual silicon astronomy Valley a circumvallate astronomy lectures my name is andrew frak noi i'm the astronomy instructor here at foothill college and it's a great pleasure for me to welcome everyone here in the auditorium and everyone listening or viewing on the web to this particularly interesting and very special lecture our speaker tonight is dr. David Grinspoon a curator of astrobiology at the Denver Museum of Nature and Science dr. Grinspoon is an expert on the planet Venus and planets inside the asteroid belt in general the so called terrestrial planets in general in fact he mentioned to me that he is one of the few American scientists working on the Venus Express mission sent up by the European Space Agency which just by coincidence is celebrating its first year anniversary around Venus today so he is as many of you probably know the author of what I think is the very best book on venus called venus revealed and another book an award-winning book called Lonely Planet's the natural philosophy of alien life both of which have been widely praised his non-technical articles have been published in Scientific American Natural History the New York Times and other distinguished publications he is also now an author of a new podcast which he's doing on the astrobiology magazine website but one of the most exciting things I think is that every year the planetary astronomy community in the United States gives a medal to an astronomer who has done an enormous amount of work throughout his or her lifetime to make planetary astronomy come alive for the public this very special award is called the Carl say in metal and I'm delighted to say that our speaker dr. David Grinspoon is the winner of this year's Carl Sagan medal and when you win this medal you actually have a choice of where you give the public lecture that goes with the medal and I am delighted to say that dr. Grinspoon chose Foothill College and the silicon valley astronomy lectures for his metal lecture so I'm going to introduce dr. Grinspoon now by saying that we are extremely pleased to have him presenting a talk on comparing planets climate catastrophes in the solar system but to actually present the medal it's a great pleasure for me to introduce a previous medal winner dr. David Morrison who has senior scientist at the NASA Astrobiology Institute right here at NASA Ames a former speaker in our lecture series and an upcoming speaker next year in our lecture series dr. Morrison is now going to present the Carl Sagan medal thank you Andy good evening everyone it's a real pleasure for me to present this medal to David Grinspoon it actually he already received it once at the division for planetary sciences meeting but the second part of his obligations which I'm sure not too hard are to give this public lecture so it is an honor for me on behalf of the previous winners to present this medal and to say it's a special pleasure because dr. Grinspoon knew Carl Sagan well considered Sagan his mentor Uncle Carl in fact for a part of his life and I think it is something that Carl Sagan would be pleased and proud to see David Grinspoon and other former students of his achieving this great honor thank you very much thank you David thank you Andy thank you DPS and and thank you all for for coming this evening it's it's really a pleasure to be here for a number of reasons and I've heard about this series a lot it's a this is a famous lecture series and many of my friends many people I know have have spoken here before some of my best friends are astronomers believe it or not and and and a lot of them have said hey you know you should you should come and do this sometime and and I'm really pleased to have the opportunity to be here with you this evening so I want to talk about climate tonight and of course we've all been hearing a lot about climate recently and you know there's a good reason for that it's a it's a sorry a hot topic these days and you may not think of it as as a part of planetary sciences as space exploration but that's really how I think about it long before the current cultural debate and before global warming was on the cover of Time magazine and at your local movie theater and all these places and and before this you know the discussion we have going now really got started I first heard actually Carl Sagan was the first person I heard about global warming from and another planetary scientists we're talking about it in the 1970s and in fact the history goes back farther than that because planetary scientists think about climate in this very what we say a first-order way not necessarily thinking of a planet as a detailed system at first because the first thing we know about planets usually you know it starts up they start off as just dots in the sky and then we have just a small amount of data and it's we think about planets a lot usually before we get to see them as close-up objects so the the notion of what should a planet's surface temperature be which is ultimately the the simplest form of the climate problem is something that planetary scientists have been thinking about you know for for at least decades and so what I want to do tonight is present my view of the sort of planetary perspective on climate change now why do we explore the solar system why do we go into space there are a lot of reasons of course and I've actually been thinking about this a lot recently I mean I think about all the time it's partly because it's what I do for a living but there happens to be a meeting this week that it started off this afternoon over at NASA Ames Research Center just down the road here which is about the environmental ethics and and space exploration and so a lot of what we're doing actually is talking about this question of why do we explore space and what are the sort of larger human dimensions of that and it's really fun because there are scientists there but there are also philosophers and historians and sociologists and other people so it's interdisciplinary but when you think about why we explore the solar system of course there are there are a lot of reasons and you know for one thing it's fun for another thing we're for another thing we're curious we want to know it's part of the way we human beings are but there of course are practical reasons to but then we're always confronted in planetary science and I think anybody who does science that seems esoteric but especially something where where you're sort of sending machines off off the earth we're confronted with these questions of you know why should we spend money out there when we have so many problems down here and you know what are we doing are we gonna go screw up other planets when we you know we have so many problems here and um you know I think these are important questions and and those of us involved in this lucky enough to receive public funding to to study this subject matters we shouldn't duck from these questions and you know in a sort of humorous way the onion magazine I hope I remember what my first slide is yes the the onion you know sort of encapsulated this this viewpoint but with a headline that said NASA announced its plan to launch 700 million dollars into space and then if you read the article they said well they've sent $10 bills up before but now they're gonna see what happens when they send you know $100 bills and you know so is that all we're doing well no of course there are many reasons to explore the solar system and one set of reasons I think are actually and this may sound strange but I think they're they're really um spiritual they're spiritual reasons to explore space and I was in a Venus Express meeting recently in column Germany where of course this our Cologne where this amazing Cathedral is and also just a little over a year ago believe it or not we had the New Horizons lunch to the wrong button I'm getting the blue light and we go they we had a New Horizons launch to towards Buddha which has already made it past past Jupiter and the to me it seems like there's really a lot that comes down to self-knowledge and when I say self-knowledge I'm not just talking about humans knowing about themselves in the narrow context but knowledge of our planet and of our planets larger surroundings is a form of self-knowledge and and to me you know what do I mean by spiritual I'm talking I guess you know I'm a science dammit Jim I'm a scientist not a theologian but I think I'm talking about that are the connection with large things larger than ourselves that's really all I mean but what's neat and interesting about their certain aspects of this that I think we're the spiritual and the pragmatic meat and I think when we're trying to understand the earth as a planet it's really both it's at once spiritual but it's also very practical its knowledge we need to survive and it also feeds our hunger for connection and deeper knowledge of the universe so that's just I think kind of cool now we hear a lot these days about climate modeling and and we make all these projections we hear about all these projections about the of the future how much co2 there's going to be what the temperature is going to be in different years and we have different curves based on different assumptions about various things and we really depend a lot on these climate models now you know we're all in a way banking on them being right and you know but what are they it's kind of a mysterious thing people almost expect it to be a crystal ball but of course we don't have a crystal ball we can't see the future and how do we know our climate models are right one thing we learn about climate when we study other planets and when we think deeply about the earth is that it's very complex it's hard to model there's so many subtleties and feedbacks how can we really know we can't do the experiment we have to wait until the future and then it may be too late if our models are wrong so what can we do well one thing we can do is look to the other planets and if we use the same equations which we do and we can get the climates of other planets right then it's not true that we only have one experiment and we just have to wait to see how it comes out so that it's one way we can get some sort of reality checking on our climate modeling now there's the here's a modern portrait of our solar system and notice that Pluto is just refuses to be excluded so we're not going to exclude Pluto but we're going to focus actually mostly on the inner solar system not completely but mostly on the inner solar system and that's because Venus Earth and Mars make a sort of natural trio for many interesting comparisons that are very relevant for climate and certain other aspects of Earth evolution because we have only three nearby examples of terrestrial or earth-like planets with sizable atmosphere ok Mercury's the terrestrial planet - in the sense of being a small rocky world near the Sun but it doesn't really have much of an atmosphere but Venus Earth and Mars all do and it's very interesting to compare their their current States and try to reconstruct the past states of their atmospheres and and their climates and see what we can learn about climate in general that that can be helpful to us so anyways these this is just some other nice portraits courtesy various space and actually I think this one's not from a spacecraft that's kind of what Mars looks like through a really good telescope but again of our trio of earth-like somewhat earth-like worlds Venus Earth and Mars and here are the sort of landscape photographs a typical place on earth the first landscape we really got to know on Mars the Viking one landing site and one of the Soviet Venera panoramas of the surface of Venus so okay yeah it in astrobiology we also think about comparative climate with the goal of figuring out where in the universe the habitable zones are and when we talk about habitable zones we you know it may be a narrow-minded way because we you know in some sense we're looking for ourselves out there but we think of life that can use liquid water and that gives us a range of distance from the Sun we're within some distance the orbit of Venus perhaps or closer or a little bit farther that you cannot have stable water on a planet surface and beyond some disk because it gets too hot and and beyond some distance you can't have stable water on the surface because it's going to freeze out now this is sort of a simple-minded notion but it turns out to work pretty well and there's a lot of complexities that we figure out that we've learned about this but the other thing that's interesting is for different types of stars this habitable zone is in different places at different distances from the star so this is our type of Sun and this is you know a schematic not to scale of our solar system and then for instance for a lower mass star which is less bright the habitable zone will be closer because it you have to be closer to that started to achieve the same equilibrium temperature and for a higher mass star the habitable zone will be farther out interestingly recently we've been revising our ideas about low mass stars there's a several recent papers about this and it may be that most of the habitable real-estate in our galaxy and in the universe is not around sun-like stars but is in fact around lower mass stars that's a tangent I could go off on the other interesting thing is that as I'll talk about a little bit later on this habitable zone slowly moves out as a star ages because most stars and our Sun apparently included get hotter as they go through most of their lifetimes or get they get brighter they put out more sunlight and therefore you have to move a little bit farther away if you're gonna have that same temperature all other things being equal so the habitable zones move out over time away from the stars now just a little bit about Earth Venus and Mars I don't want to overwhelm you with numbers and facts but I want to point out a couple of things one thing is that the atmospheres of these three planets are pretty different in some fundamental ways first of all just the amount of atmosphere the surface pressure on earth almost by definition it's it's about one bar or one atmosphere it's like a slightly different definition venus has a much denser much more atmosphere almost 100 times the surface pressure of Earth and Mars has a very thin atmosphere just you know to first order as we say about one percent of Earth's or or six millibars on average and it fluctuates for interesting reasons so that that's just the total amount of atmosphere if you look at the composition what the atmospheres are made out of of course on earth we have our familiar nitrogen oxygen atmosphere mostly nitrogen trace amounts of co2 and this number is unfortunately changing compare that to Venus and Mars which are almost all co2 both of them over 95 percent co2 carbon dioxide and that is going to be that's going to play a lot in in our subject matter that we're here to discuss this evening one interesting thing just looking at this is that notice these molecules that make up most of Earth's atmosphere are diatomic that is each molecule has two atoms into an o2 whereas these molecules co2 and co2 that make up most of these atmospheres are try on ik it turns out that diatom diatomic molecules are not greenhouse gases they don't absorb infrared if you just think about a nitrogen molecule the two nitrogen sort of vibrating in place for reasons I won't really go into now but we could come back and discuss it does it doesn't interact with infrared light whereas a floppy or bigger molecule like co2 or h2o or methane ch4 has these larger and more numerous vibrational modes there's sort of bigger floppier molecules and they do a much better job at capturing that infrared radiation and turning it into vibrations of those floppy molecules and as a result those are greenhouse gases they have absorbed infrared but these diatomic molecules are not what else do I want to point out before we go on oh well obviously the surface temperatures are important and related to these other numbers here's good old Earth average about 60 degrees Fahrenheit Venus is outrageously hot and you know there's a connection there between the amount and composition of the atmosphere and the surface temperature Mars even though it's mostly co2 is quite called it's there's not very much atmosphere there there's not much of a greenhouse and of course distance from the Sun will play into this as well note there's something called equilibrium temperature which is colder than surface temperature and the difference between these two on each planet is basically the greenhouse effect and so notice on Venus it's huge the equilibrium temperature on Venus is called it's even colder than Earth but it's got this massive greenhouse and so the surface temperature is quite huge I'm gonna explain a little bit more what I mean by equilibrium temperature right now but I just wanted to sort of give you an overall sense of what these numbers look like Oh before I explain equilibrium temperature so just overall the sort of question we're trying to address here why are the atmosphere so different and here are some sort of I'm sort of jumping to the answers and then we're going to come back and and think about these things but one thing is that Earth has life and that actually over time has greatly affected the atmosphere in particular life of course the green plants the life has made oxygen and altered the composition of earth and given it an atmosphere and a climate very different from that which it would have if it was a lifeless world in terms of these overall variables of size position and in this case the the existence of life Mars what jumps out at us is its size it turns out Mars is very small and that makes it vulnerable to atmospheric loss through these various processes I'll get back to Venus its position in terms of the difference between Venus and Earth it seems to largely come down to the fact that Venus is closer to the Sun and even if Venus and the earth started out very very similar we think we understand now why it would have evolved to being so different oh and the other thing well no I don't have to go back because I'll point that out again in the future but the other thing I meant to point out an overall graph of the planets that the plot that show you the difference is that Venus is incredibly dry compared to earth even though it's very similar in some other ways and we'll talk about why that is but first what do I mean by equilibrium temperature well think of a bunch of people around a campfire if you are called you can move in closer and if you're warm you can back off well it's the same way with planets and a star not that they can decide to move in closer although occasionally they do but but that the the temperature has a very simple relationship to the radiation coming from the center of the system and and the distance and we can actually do a calculation if we if we know one other variable and that's something we call albedo which is sort of the portion of sunlight reflected from something so if something reflects all the light hitting it we say it has an albedo of 1 if it has reflux no light we say it as an albedo of zero and in terms of real materials dirt is generally pretty low albedo and ice and snow are very high and clouds I don't have them on here but clouds can also be very high basic roughly the same as snow and then all of these other things water is actually pretty low albedo and so the overall reflectivity of a planet is a result of whatever the surface is made of in whatever combination and oh I do have clouds down here and if we if we know the albedo of of an object a planet or anything else in space and we know its distance from a star we can actually calculate its temperature and I won't go into these equations but if you like equations you can see that this is there's actually something quite beautiful about this but that would be a whole other lecture but the point the point is that the temperature is a simple relationship based on simple physics of the s is just the solar flux the amount of radiation coming from the Sun this alpha is that albedo the reflectivity and and and this solar flux folds in also the distance from the star so if we know how bright the star is we know the distance and we know the reflectivity you can calculate exactly the temperature of that object if it has no atmosphere now that temperature without an atmosphere just based on the overall reflectivity that's what I mean by equilibrium temperature but what about real interesting planets like Earth and other ones with atmospheres well in order to understand what's happening there I have to think about a little bit more physics at which is simply that in terms of the heat radiation coming off of something the thermal radiation coming off of any object all objects are radiating you're putting out infrared right now being an object of approximately 96 Fahrenheit or however you're feeling tonight the the is about 6,000 and sorry to jump systems but 6000 Kelvin or absolute temperature and an object that hot radiates in the visible at about what we call half a micron and this is you know basically visible light this is you know the color of sunlight but an object the temperature of the earth which is much colder it also has thermal radiation but it's it's shifted way out into the red it's it's in the infrared okay so the Sun puts out visible radiation the earth puts out infrared radiation and remember what I said about diatomic and tri atomic gases the more of these tri atomic gases like co2 and h2o and even bigger molecules like methane you have an atmosphere the more of this incoming radiation which heats the surface and get sri radiated as infrared the more that infrared gets trapped by the atmosphere and re-radiated to the ground and of course you've heard this you've heard about this before that's the basis of the greenhouse effect and that's why in a planet with an atmosphere depending on what it's made out of and how thick it is the surface temperature is always warmer than that equilibrium temperature now there's another factor which is the factor of time and the evolution of the Sun as I mentioned at the beginning stars get brighter as they age and this sorry about the complexity of this graph but if you look over here it's a solar luminosity relative to present value and this curve that says s over s o this is the brightness of the Sun over time starting off about four-and-a-half billion years ago the beginning of the solar system and ending up now you can see the sun's gotten about thirty percent brighter since the earth has been here and from that using that equation I showed you earlier you can calculate the equilibrium temperature over time and this is equilibrium temperature this curve this Pervis surface temperature assuming that the greenhouse effect hasn't changed so there's the equilibrium temperature now it's about 250 degrees Kelvin there's the surface temperature now about 285 degrees Kelvin and this difference between the two is due to the greenhouse effect now if we go back in time because the Sun was fainter the surface temperature was cooler and if we assume that greenhouse effect have stayed the same then the surface temperature gets cooler and then there's a problem a paradox because you go back in time and for much of the history of the earth it looks like the surface temperature was below the freezing point of water earth should have been an ice planet but we know it wasn't because we see a lot of geological evidence and actually biological evidence that the earth doesn't seem to have been frozen over all this time so why wasn't the early Earth frozen over and by the way I have to mention now that the person who really figured this out first and applied it to the earth and to the solar system was Carl Sagan it's one of his big contributions to planetary science was this faint young Sun problem as he called it and Carl actually worked a lot with another amazing planetary scientists over here at NASA Ames named Jim Pollock who was Carl's first graduate student at Harvard and then set up shop and was here at NASA Ames for many many years and until he unfortunately died about a decade ago or more now Jim Pollock has been gone that's it's hard for me to believe because Jim was also another of my mentors when I finished graduate school I did a postdoc here at NASA Ames and worked for Jim Pollock learning climate modeling which to some degree he had learned to do from Carl Sagan and again we were doing climate modeling but not mostly not of the earth but of other planets so just a little lineage there so what why wasn't the early Earth frozen over given this seemingly solid chain of argument what was different well the greenhouse effect we strongly suspect was stronger so the atmosphere must have evolved that must have changed it was different what was different well a lot of people think there was probably a huge amount of co2 on the early earth and there's some good reasons to think this like look at the neighbor planets what are they made out of but another interesting possibilities that could have been biogenic methane we know there were methanogens that or simple organisms that that make methane there still are on earth and we have reason to believe that they were common on the early earth and that there was some amount of biogenic methane and the interesting idea is that if you were making enough biogenic methane you have to be putting it in the atmosphere at a high rate because it gets destroyed rapidly by a lot of chemistry and photo chemistry and other other things but if there was a high enough rate you could have had a methane greenhouse methane is a very powerful greenhouse gas so the early Earth could have been warmed by biogenic methane we don't know at this point I'm gonna actually skip ahead a little bit because I feel like I'm being slow but I want to talk about a little bit about feedbacks why is it so hard to predict climate in the future of Earth and on other planets in general it comes down to feedbacks which lead to nonlinearities in the equations because you have components of the system that depends sensitively on other components of the system and then come back and control in some way those components that they also depend upon that's what a feedback basically is and it leads to these equations that are much more complex than the ones I've showed you so far and a simple example of we have positive and negative feedback okay and the terminology can be a little misleading because it's not sure that positive feedback is good and negative feedback is bad in fact it's often the other way around because negative feedback leads to stability and positive feedback causes things usually to go crazy so a simple example of a negative feedback is a thermostat it gets hot enough in the room and the heater turns off it cools it starts to cool down and it goes below some setpoint and the heater turns on again you can draw a diagram of that system and there's pluses and minuses and it leads to a negative feedback a refrigerator is sort of the opposite but again it's a simple mechanical negative feedback system some examples from a planet let's think about the greenhouse effect what happens on a planet here's a negative feedback where you heat up a planet for any reason and more water evaporates when more water evaporates so that's the plus here he makes temperature go up water evaporates and that leads to cloudiness which blocks sunlight and that is the minus here in the system and causes things to cool down so something that causes it to heat up causes some other factor to cause it to cool down and they sort of modulate each other and it leads to stability that's a negative feedback the temperature well it's like a thermostat it will not go on wild excursions a positive feedback there there are several of examples of negative and positive feedbacks but I'm just giving you some good simple examples is what we call it this is ice albedo feedback where ice as I mentioned before has a high albedo it's very reflective if you heat up a planet for some reason you'll tend to melt ice and that means that the the albedo will go down because water is much less reflective than ice so that means that the planet will absorb more radiation which heats things up so this you heat the planet and it causes a change which heats things up even more so there's two pluses here and there's nothing that's sort of damping it and if nothing else was happening it would just get hotter and hotter until all the ice was melted and the same thing applies in the other direction by the way if if something cools the planet down and you have more ice then it's going to reflect more radiation which is going to cool it even more and the planet can end up all iced over we actually think that this has happened a few times in Earth history you may have heard of the snowball earth it's a little bit controversial but there's a lot of good evidence now we think that a few times in Earth's history it has become completely frozen over due to the fact that if something cools it enough that the ice starts to reflect more Sun and that cools the planet more and it kind of runs away until you have a nice ball we actually think this happened about 600 about 700 million years ago and then there was there have been a couple other times and there was one we believe about 2.3 billion years ago and interestingly that snowball earth probably the first one 2.3 billion years ago it might have been caused by life so so we may not be the first species causing a climate catastrophe on earth this is a still a little bit controversial and sorry about the complexity of this graph but the basic idea is that as I mentioned earlier there might have been a methane greenhouse on the young earth caused by bacteria putting out methane which is the potent greenhouse gas but then of course oxygen photosynthesis came along we had green plants they started putting out oxygen and one theory is that when you started having enough of an oxygenation of the atmosphere that it collapsed the methane greenhouse oxygen destroys methane they're just not stable together and it may have been life that collapsed the methane greenhouse and it may have sent the earth into this first snowball now why doesn't it just stay a snowball once the snowball always a snowball because after all it's reflecting all that sunlight and isn't that stable it's it's a positive feedback it's it's it's not it's it's a runaway system but fortunately there's another negative feedback that eventually pulls it back from the snowball we believe now this is something I'm going to tell you about called the carbonate silicate cycle it's a very important climate thermostat on the earth and probably some other planets as well this is the thermostat that probably explains why Earth's climate has ultimately been so stable over its long history of course we know there's been ice ages there's been hothouse conditions but Earth Earth's climate if you look at the long-term history has been remarkably stable within the range of liquid water on the surface through most of its history and why is that well like I said a thermostat or any negative feedback has two components that sort of act concert to each other and on earth it's this is a system that regulates the amount of co2 which regulates the greenhouse effect volcanoes put co2 into the atmosphere that's part of the cycle that's the source and then co2 gets sucked out of the atmosphere by what we call weathering reactions chemical reactions in the presence of water where co2 basically gets dissolved make something called carbonic acid and then in the oceans it gets deposited as carbonate rocks like calcium carbonate which is basically chalk you know that the White Cliffs of Dover are these carbonates they get deposited on the ocean floor as sediments so that's the source of co2 that's the sink but then over the long term what happens is these carbonate rocks gets abducted they get sucked back into the earth by plate tectonics the recycling of Earth's solid rock surface over time the crust the these carbonate rocks gets abducted underneath and at high pressure and temperature in the earth they get broken down and the co2 eventually finds its way into the atmosphere again as the carbon finds its way into the atmosphere again is co2 so in a time scale on average of roughly half a million years earth recycles its co2 and this keeps the climate stable because like a good thermostat these two components well.ok the co2 the volcanoes do not respond to climate basically the volcanoes are always pumping out co2 sometimes more sometimes less but not really caring about climate conditions but this part of the cycle is very sensitive to climate when it's hot this will go much faster both because chemical reactions speed up when it's hot and because there's there's more water and as I said this depends on water when the earth freezes over when you have a snowball earth this part of the cycle stops if it's all ice you don't have weathering reactions it depends on liquid water and that's how we pull out of the snowball because if Earth is completely frozen over and this stops and the volcanoes keep going then after a few million years the co2 builds up and that is what probably has saved the earth from the fate of snowball so this is of a long-term negative feedback interestingly the same processes probably occurred early on Venus and Mars when we believe at one point they both had liquid water oceans on the surface but something went wrong on both those planets something different on each one and now what I want to talk about is what happened to Venus and Mars on Venus basically the punchline is that now there's no liquid water and so you don't have this part this part of the cycle broke without liquid water you don't have this weathering the co2 doesn't get sucked out of the atmosphere the volcanic co2 builds up in the atmosphere just all ends up there and that's why you have this thick carbon dioxide rich hot environment on Venus on Mars it was this part of the cycle that broke most of the volcanism died out early Mars is a small planet it didn't retain its internal heat as well as a big planet like Earth does and the volcanoes shut down and the atmosphere did not sustain a thick greenhouse to make matters worse because Mars is a tiny planet the atmosphere also largely escaped into space just because the gravity doesn't hold on to much of an atmosphere so Mars is sort of doubly damned by its small size to not have a warm climate although it may once have had so a little bit of comparative planetology here now if look at Venus and Earth remarkably they're very similar in size and in mass and therefore an escape velocity which depends on mass but very different in terms of their atmospheres Venus has this huge crushing atmosphere and it's very hot on the surface and the most amazing difference in some ways is the amount of water where I'm using scientific notation here so Venus has something like 6 times 10 to the 16th kilograms of water total and Earth has something like 10 to the 21st kilograms so they there's a difference of about a factor of 100,000 between these two numbers so two planets that seem to have started out very similarly from a lot of lines of evidence have this remarkable difference in that earth is a water planet and Venus has only won 100 thousands the water that earth has so what happened how did Venus get so dry well basically we think they started out more or less as identical twins so where did Venus go wrong well basically it was born on the wrong side of the tracks the tracks here being the edge of the habitable zone Venus you know was left out in the Sun too long and there was a runaway greenhouse which is a powerful positive feedback and I've got Jimmy Hendricks here to represent a powerful feedback but the way this works basically is you have a high surface temperature that leads to evaporation more water vapor in the atmosphere and water vapor is a greenhouse gas and so that leads to more of a greenhouse it's a more infrared opacity as we say which heats up the surface more and this thing can run away and basically we think that's what happened to Venus the atmosphere basically ends up as steam the hydrogen escapes into space the oxygen reacts with surface roughest rocks oxidizes the surface rocks and the result is that today Venus has only a tiny tiny fraction of Earth's water inventory which also seems to have had dire climate effects now Venus turns out to be a very complex place and a lot of what I've worked on over the last decade or so is trying to understand all the different interactions controlling the climate of Venus because not only does water come out of volcanoes but sulfur dioxide is another green another greenhouse gas that comes out of volcanoes but on Venus there's a very complex sulfur cycle where so2 comes out of volcanoes it is a greenhouse gas but it also makes the sulfuric acid clouds by reacting with water and with sunlight those clouds are highly reflective so the sulfur is both heating the planet as a greenhouse gas and cooling the planet by making clouds but to make matters worse the sulfur is reacting with surface rocks and those chemical reactions depend on the temperature and the rates of those chemical reactions depend on the temperature so imagine the equations you have to put together to try to capture all of those different temperature dependent processes which are in turn changing the temperature and changing chemistry it's horribly complicated but that also makes it horribly interesting which is why we're working on it and my colleagues and I have a name for the study of this we call it Venus system science trying to understand the interactions between all these different parts of the planet and how they determine the climate and how in turn the climate affects these other parts of the planet and Venus system science is sort of a play on the great popularity of the phrase Earth System science these days where people are trying to understand the earth not as isolated parts but as a system that in some ways behaves in ways that you could only understand by looking at the whole system and we're finding that in some ways venus is the same so it's an interesting comparison and in the introduction and you mentioned that I'm working on a mission now it's very exciting to have an active mission at Venus and it's thanks to the european space agency this orbiter called venus express oh and there it is and we're just starting to really understand what venus express is telling us it's been in orbit as was mentioned one year today but it's only been functioning and it's its scientific mission for for less than a year because it would for a while he just were just in the orbit to get into the the mode where we could take data and this talk I won't really talk too much about Venus Express results for a few reasons and one of them is kind of silly which is that there's a special issue of nature coming out soon and that means that the results are embargoed which means that if you talk about them in public nature will get mad and not publish your paper which may sound really stupid I think it is really stupid but it is the way it is and you know I would get horribly spanked if I told you the truth you know that we had discovered life on Venus or something like that so you're just going to have to wait but in the meantime these are the pretty pictures and Venus Express is telling us a lot that informs this question I can certainly tell you what it's telling us it's telling us what the sulfur abundance really is in the atmosphere how the atmosphere is moving around and how that reflects and and traces the deposition of solar energy and the climate of Venus we're learning all of things and you know invite me back in a year and I'll tell you tell you the answer and then I'm not being cagey here a lot most of its because we haven't actually figured out the answers yet if there's a lot of steps from getting the information down from the spacecraft which is after all just a bunch of numbers and actually interpreting and figuring out what it's telling you and we're kind of in the process of doing that now I want to move on and talk a little bit about Mars now as you I'm sure heard there's a lot of evidence on Mars for ancient surface water we know Mars was once a lot wetter than it is today early spacecraft revealed these enticing river channels and different kinds of channels have different patterns on Mars some some of them are these sort of more branching channels that seem to indicate signs of actual rainfall where some of them are these more catastrophic outflow channels which seems to maybe just be water that's gushed from the ground as our spacecraft have gotten better and our resolution our detail of our images has gotten better we've started to see that Mars is also covered with these layered terrains which seem to be sedimentary I mean this could be a picture of somewhere in Utah where you've hiked where there are these all these ancient sand stones and and sedimentary layers of sedimentary rock and Mars turns out to be full of this stuff once you have good enough cameras to see it and even we even see features like this River riverbeds that seem to have meandered and things that look like river deltas here's a close up of these meanders this takes some amount of sustained flow you don't get this in one mighty flood you don't get this kind of meandering River pattern so there's a lot of evidence that Mars had water in the past and we've confirmed that recently with the sort of ground truth from the Mars rovers because we've actually been able to go up to rocks and ask them what their stories are the rocks have things to say to us they say go home no they they they amazingly the opportunity lander landed right by the opportunity Rover landed right next to these rocks which turn out to be layered sedimentary sulfur rich rocks these are basically fade iron sulfate rocks which seemed to have been deposited in sort of briny acidic surface waters so this then becomes the ground truth that Mars really did have surface water we're still trying to figure out for how long and how extensively but it seems to be quite extensive and it seems to be a long history of at least intermittent water on the surface of Mars now this is very exciting from an astrobiology point of view because maybe from our parochial viewpoint but for actually some pretty good reasoning we believe that if not the only way to make life a watery environment certainly is a good way and there probably is water-based life elsewhere in the universe it may in fact be the only or the dominant form of life we're not sure about that but we certainly have reason to believe that where there's water it's a good candidate to look for life so when we find evidence of water on the surface of Mars we're excited about what that could mean for the past of for Mars is past and the possibility of biological evolution there so it seems that Mars was wetter and warmer in the past but the question is what was different you know what it's another one of these mysteries we know the atmosphere was thicker and we know Mars lost a lot of atmosphere and we think we know why there's something called impact erosion where basically all these craters Mars has a lot of craters and we know how these craters are made things from space hit the surface at high velocity that makes big explosion they make a crater and the big ones also blow a lot of atmosphere off the planet and we have some pretty good models of how this works and so what's interesting about Mars is because you can see so much of the surface history on the planet you can actually count the craters and tell something about you can look at the crater density over time and tell something about the rate at which things were hitting the planet based on what we see in the crater distribution and then you can take that with a model and the big assume that the big crater making impacts will off a certain amount of atmosphere and you can actually model how the atmosphere changed so Burt and the answer is that in the early part of solar system history when the bombardment rate was really high because there was a lot of junk basically left over from the formation of the planets hitting all the planets that was just a lot of bombardment well that's why the ancient surfaces of the solar system are all heavily cratered in that early part of solar system history Mars should have lost most of its atmosphere and then we have good evidence that even since that time Mars has lost more than 90% of the rest of its atmosphere through interaction with the solar wind hitting the top of the atmosphere and other things the fact is Mars is very vulnerable to losing atmosphere because it has a low gravity so any process that strips gas from a planet and there are many of these processes there's this kind of impact erosion there's just thermal escape atoms moving just through the thermal energy of the air in the top of the atmosphere and if a planet doesn't have strong gravity some of those upward moving molecules are just going fast enough they stream off into space there's solar winds stripping gas and all of these things that can remove gas from an atmosphere do it more easily on a small planet like Mars so so Mars was sort of doomed by its small size to lose its atmosphere so does that explain why it was warm and wet early you need a strong greenhouse early - - to make the surface temperature of Mars above the freezing point of water especially we've given that faint young Sun that I mentioned the early Sun was dim dimmer so how was Mars warm enough so the logical obvious choice is a co2 greenhouse and I don't want to go into detail here because I want to move along but the the punchline is a co2 greenhouse from Mars doesn't work you pump up the amount of co2 in the Martian atmosphere and basically it freezes out and you get co2 snow which is reflective and or co2 clouds which are reflective and it's co2 greenhouse sort of eats itself on Mars people have tried modeling this a lot and it doesn't work so how could Mars have been warm well another idea and this is actually again people over here at NASA Ames have worked a lot on this is that an alternative to the co2 greenhouse is that could have been the impacts themselves that were warming the planet a big impact heats up an area of Mars and a big enough one heats up the whole planet for a while and this is a graph that Teresa Segura and Tony Koloff read over at Ames and some other people made showing for instance if you have a you know a say a 300 kilometer impact or hit the surface of Mars it will for about a thousand years be above freezing and a larger impactor will have a longer thermal effect and a smaller one a shorter one but you add this all up and you get some temporary warm periods on Mars whether or not it had a overall thick greenhouse so maybe you had these sulfate-rich brines on a cool early Mars maybe it really wasn't all that warm maybe this was these were temporary periods of warming and cumulatively we see the evidence because nothing is really erasing those rivers are those sediments that fast because Mars is such a geologically dead world now another interesting alternative idea that's a little bit wacky but quite possible given what we know is that there was actually abundant life on early Mars and that Mars had a CH 4 greenhouse a methane greenhouse it's it's certainly a intriguing possibility so the surface may not have been habitable but if there was an origin of life on Mars then where is it now well it probably would have retreated into the subsurface because there's a lot of ice on Mars today there's not liquid water on the surface maybe there is occasionally we see some evidence that's controversial for that but if there is liquid water on Mars there surely is liquid water on Mars somewhere in the interior planets get warmer as you go down into the interior for basic thermal physics and we know there's ice so if you get to some depth there's going to be liquid water so an intriguing possibility is that there may be life at some depth on Mars today now okay I want to talk about one more place in the solar system that is not in the inner solar system so I sort of fibbed earlier when I said I was going up only focused on this system but Titan is a moon of Saturn which turns out to have a lot of interesting comparisons with the earth and particularly in in the field of climate so even though it's an icy moon on a on a giant ringed planet of a giant ringed planet a billion miles from Earth there are some intriguing similarities both Titan and Earth have relatively thick nitrogen atmosphere the surface pressure on Titan believe it or not is actually somewhat higher than that on earth Titan is rich with organic molecules which is of course interesting to us since that's what we're made out of and it's may it has a major constituent of the atmosphere in three phases as does earth earth has water in existing as ice liquid and gas Titan has methane playing in many ways sort of the same role as water on earth and you can see even in this that this Cassini image Cassini is the the Saturn orbiter that that is at Saturn now and making multiple close passes of Titan which is how we know so much about what we've learned about Titan recently you can see these methane clouds near the South Pole of Titan and it seems to have a liquid cycle clouds rain and even legs now which is very intriguing because we don't know anywhere else we don't know of anywhere else where that's true now other than Earth and Titan but there are some important differences of course Titan actually has a larger a thicker atmosphere it's very cold there 94 Kelvin or about minus 90 Celsius no that's not right about almost minus 200 and it's well that's that's all I really want to point out is that it's very called and it's it's got an even thicker atmosphere than Earth now even though it sounds cold this is actually warm for an object at Saturn's distance from the Sun if you did that same equilibrium temperature calculation I talked about earlier you would get a much colder temperature for Titan the reason why Titan has this thick atmosphere and is actually relatively warm for an object at that distance turns out to be methane there's a methane greenhouse that's really important on Titan and that is fascinating because the climate of Titan turns out to be very complicated when you look at Titan from orbit or from on a telescope from Earth you see this orange hazy ball you don't see that surface with rivers and intriguing ice volcanoes and all the things we've discovered recently you see this haze and it's because Titan basically has a photochemical smog you know just like Los Angeles and Denver have and it's actually chemically rather similar to the brown cloud in Denver and it starts with methane but then methane gets destroyed by ultraviolet light and it makes these more complex organics and that makes a haze which is important in the climate so again you have these feedbacks you have methane helping to keep the planet warm but then you have an anti greenhouse effect where the methane is making these organic molecules which cool it to some degree but without this methane the climate would probably collapse and without the methane not only with the methane go away but it would get so called that the nitrogen would start to freeze out on the surface so without the methane you wouldn't just have oh you've got a nitrogen atmosphere but you're just removing the methane the nitrogen would go away too so methane helps maintain the whole atmosphere but the weird thing is that methane is destroyed on a short timescale by that ultraviolet light from the Sun which is making those organics and breaking up the methane so if nothing was adding methane to Titan it would just the atmosphere would would wouldn't be there something must be replenishing that meth untighten Oh so here's just a schematic of the photochemistry so this is a methane molecule carbon with four hydrogen's it gets broken up by sunlight these hydrogen's go streaming off and the the CH threes that are left over recombine into things like ethane and acetylene and and molecules with more and more carbon molecules these organics you also interestingly have nitrogen on Titan which is broken up by mostly by energetic particles from Saturn's magnetosphere and then you get nitrogen combining with these organic molecules and that's really interesting because that's how you make things like amino acids I mean what life on Earth really is you know in its simplest expression is nitrogen containing organic molecules that's what an amino acid is that's what proteins are that's what we are and this and they are being made at least the precursors to that kind of molecule are being made on Titan so that's pretty cool but how is the methane being replenished I don't want to go into a lot of detail here I'm going to skip a little bit but that the fact is it seems as though there's a complex photochemical meteorological hydro geochemical what we call what has been nicknamed a methodological cycle on Titan in analogy to the hydrological cycle of Earth and this is part of which is what's so fascinating not only do well the Huygens Lander the european-made Huygens Lander which which was carried by Cassini to Titan discovered what very much appeared to be river valleys on Titan branching river valleys it looks as though it's rained here it seems to have rained methane and more recently we found that there are in fact large lakes especially clustered around the North Pole I'm going to skip a little bit about the chemistry here but the bottom line is we think that methane is being released from the interior of Titan from these interesting complexes where you have tennis balls that know where you have the this represents a matrix of ice with methane molecules trapped inside the ice what we call a clathrate this actually exists on earth in some places at the bottom of the ocean floor where it's very cold and it's a way to store methane and we think that's how methane is stored and slowly being released from the interior of Titan although there are some other ideas about this and we think that it's released over time through cryovolcanism or ice volcanoes so there seem to be ice volcanoes on Titan and this is from radar imaging from the Cassini mission there seem to be these ice volcanoes which are probably releasing methane which is pooling into these lakes on the surface and also leading to this interesting chemistry and interesting climate and probably is being lost ultimately at the same rate as it's being produced and it is clearly being replenished by something we think it's cryovolcanism from the interior so the climate of Titan actually seems to be a very dynamic process that depends also on what's going on with the surface geology now oh very recently Cassini has taken these this is sort of bizarrely colorized but these these images that show a lake which is roughly the size of the Great Lakes on earth which you know may not sound that big but remember how small the planet Titan is well tripping over myself here in my excitement so so for Titan that represents a much larger fraction of the surface area than the Great Lakes another cool radar image showing what appears to be bodies of liquid on Titan and a lot of erosional well here we go and pushing the wrong button a lot of erosional features and sort of hints of these kind of branching dendritic channels that imply rainfall leading to this pooling of methane so as I mentioned earth is near this triple point of water it's part of what makes Earth such an interesting place is that the surface temperature is in this range near the triple point of water so you can have water exists as a solid a liquid and a gas on earth creating all these great phenomena and Titan seems to have the same kind of phenomena but it's a result of being near the triple point of methane now Titan doesn't have earth like oceans as I mentioned only scattered vagues so interestingly although it's often been mentioned that Titan is sort of a vision of the ancient earth with this prebiotic organic chemistry that may give us clues to the origin of life that's true but interestingly our colleague Jonathan Looney no planetary scientist at the University of Arizona has recently pointed out that Titan in a sense may be more like a vision of Earth's future because eventually the sun's going to keep warming up as it has been in the past and eventually the long-term future of Earth without some bizarre intervention by intelligent species you know if an intelligent species ever appears on earth ultimately the long-term fate of the earth is global warming left to its own devices because the Sun will heat up and in a sense it may go through a phase of looking like Titan where the oceans are gone and you've got these scattered lakes so chemically Titan gives us a window into our organic origins our past but climatically it pre Sage's our future so I just want to present a few conclusions to you now and then I'll pause and I'd love to take your questions so a few conclusions planetary climate is really complex and difficult to predict radical climate change does happen on planets we see the evidence don't let this happen to your planet Earth has been remarkably stable but that of course is no guarantee of future performance even fatal climate change is nothing new there have been extinction events on earth due to climate change in the past even fatal climate change caused by life is probably nothing new I told you about those evil oxygen generators destroying the methane greenhouse and pushing the earth into a catastrophic snowball what is new perhaps is premeditated climate change we can see it coming so that gives us a certain responsibility and we need all the help we can get including data from other planets earth of course is unique but these planetary observations and modeling they do give us a reality check on our assumptions about climate and they provide an indispensable perspective on the uniqueness passed and fate of the earth so one more kind of weird thought I'll leave you with it's obvious that we are rapidly changing the atmosphere so in the short run we have to get a handle on this we have to understand the role we're playing and avoid this kind of inadvertent chant the climate change we're changing the planet there's no doubt about it and so that gives us a responsibility to figure out how it works and consciously decide what role we want to play rather than stumbling into a role we may not want to play but over the long run interestingly that's not enough to stop accidentally changing the planet in the long run we're gonna have to go much farther than that the first step is to stop accidentally changing the planet but that's just the first step if we're gonna survive for thousands millions heck who knows billions of years I'd like to think that you know we've at least got a shot at it then we're going to need to go further and to avoid disaster we're going to have to purposefully change the climate ultimately the development and survival of a healthy and functioning global society on any planet maybe even this one will depend upon the skills of the local inhabitants at climate control the survival of all life on Earth not just us but all the other species we share this planet with will eventually depend upon our learning how to intervene and manipulate planetary climate what a horrible responsibility but I think that's that's the truth of the matter and with that I will stop talking and entertain questions thank you very much thank you dr. Grinspoon for an entertaining and illuminating talk little scary but entertaining illuminating thank you those of you who have to leave but for everyone else we are going to have a period of questions now and the way it works here in the Silicon Valley astronomy lectures is that we've set up two microphones in the rough center of the auditorium we already have eager questioners lined up to give you a good example if you have a question or a very brief comment we encourage you to come to the microphone line up I'm going to ask dr. Grinspoon to be fair and to take questions from one microphone and then the other alternately and we please do want you to keep your questions short so everyone has a chance to participate speak loudly into the microphone and then dr. Grinspoon will answer each question and we invite you to be part of the program now thanks okay don't worry I'm not gonna sing I'm just cutting myself most from the podium so uh let's see so just so you won't think I'm a closeted leftist oh I'll start with the right-side enormous volcanoes in the time line okay the question was about Mars and the enormous volcanoes in the time line well the first thing I would say is uh as the gentleman mentioned Mars does have these huge volcanoes Mars has many volcanic features but but it has a small number of really really giant volcanoes all sort of clustered in one area of the planet called the the Tharsis province and that seems to be a pretty ancient feature that is there's some evidence locally in some places for more recent volcanic flows on Mars and there there's a little bit of debate about how recent that is because of course we don't have actual samples from Mars to take into our lab and look at the isotopes and say it's exactly you know three point seven four three billion years old what we do is we count the creators of different areas and we add them up and we have models for how often creators are hitting Mars and we have rough ideas about the ages and it seems as though most of the volcanism is very very ancient probably most of it was all over all over with well over three billion years ago there may be some places on Mars where they're volcanic flows that are just a few million years old and maybe even some ongoing activity there's some hints of things like methane in the atmosphere and some hints of activity but the basic story of Mars is that most of the geological activity ended a long long time ago billions of years ago when Mars was really a young planet and that's why the surface of Mars is so full of craters in so many areas and so beautifully preserved we can see features that are billions of years old you don't see anything like that on earth because it's so more recently active probably a longer answer than you wanted but the basic punchline is that they're really really old question from the other side comets you said right but on comets or just on a planet in general okay okay so the question is are there planets where there are traces of creatures in life well yes there's definitely one that we know of this one right here that's the only definite answer I can give you now if you ask me what I think based on science and probability and and sort of my most informed guess or my most informed answer I can give you I would say yes almost certainly there are other planets where there are creatures and things that probably are very much like on earth that is we looked very hard at the history of life on Earth and we try to understand is there anything so special about Earth that would make it the only place where there could be life and we don't see anything that's that special there are a lot of unusual things about earth but each one of those things like the liquid water the volcanoes we think they're probably these these features do exist on other planets so we believe I think most of us the answer to your question is yes there are other planets but have we found them yet I mean that is other planets with life but have we found them yet no but we're looking sir good talk I have a question about say your experience with Venus when you're doing a runaway greenhouse you've mentioned that if you have a water vapor in the atmosphere that increases the it traps the infrared radiation and so it tends to make the problem worse basically but the role of clouds can be reflectivity albedo it sort of counters that in the case of Venus does that give you you personally some idea of what Matt hat might happen with earth the role of clouds as you warm up the planet great question and you sort of caught me because I mentioned I realized you know I mentioned that cloud feedback which is a a negative feedback you heat up the planet it gets cloudy or it cools things that kind of stabilizes and then I mentioned well on Venus we think that there was this runaway greenhouse because you heated up the planet and water vapor evaporated and it led to this positive feedback because water is a greenhouse gas and I actually thought to myself tonight well I wonder if anybody will notice that these two things I've mentioned are sort of paradoxical and you did notice because it both happen water both heats things up because it's a greenhouse gas and cools things down because it makes clouds since there's a positive and a negative feedback and it really depends on the details of what kinds of clouds are being made what altitude they're at what the particle sizes are which one of those factors wins out on a planet it can actually go either way and on earth the cloud feedback helps keep things stable but if you have a planet if you have an earth-like planet and you move it closer to the Sun and people have done this experiment you know in computers not as far as we know not in a real solar system near you but what happens is that that that other feedback the water vapor greenhouse effect overwhelms the clouds and you end up with a situation like Venus where Venus is about as cloudy as a planet can be Venus is completely cloudy it's cloudy everywhere all the time it has a huge reflectivity of about over over on the albedo of Venus is over 0.7 that is over 70% of the sunlight reflects which is in fact why on a night like this if you look into the West you'll see Venus is such a bright object in the western sky the reason we see Venus as this beautiful evening star and sometimes morning star is because of those clouds we you know it wouldn't be nearly as noticeable if if it wasn't completely cloudy so so Venus looks like a planet that tried to resist the runaway greenhouse by becoming completely cloudy and reflecting as much sunlight as it could but it still it wasn't enough so the answer to your question is yes people have modeled this very carefully and yes that does help us understand what happened on Venus and it turns out though that your question is is a really good one because understanding the role of clouds in the runaway greenhouse is the biggest problem we have right now and understanding the history of Venus there's still a huge uncertainty in our models of how long Venus kept its water and how rapidly it heated up and how rapidly the water was lost and the biggest problem is that it's very hard to model clouds in a realistic three-dimensional way on a planet and in fact and that's also the biggest problem or one of the biggest problems probably the biggest problem and understanding climate change on earth is that nobody really knows how to model clouds very well now I mean we're getting better at it but it's very hard to model clouds on a very different planet from one that we see now we can model clouds on the current earth because we can check we have a reality check with satellite data and so forth but the behavior of and how they respond to climate and how they change climate is is one of the things that climate modelers still have a lot of trouble doing and that affects our ability to understand the future of Earth to some degree and it definitely understood it definitely limits our ability to understand the past on Venus so that actually my research group in Colorado that's one of the main things we're working on right now is actually trying to answer your question we've got a big computer model and we're we're you know trying to do the details of clouds what happens when two particles hit each other and you know do they coagulate and make a bigger particle and then how fast does that particle fall out of the sky and how fast do things evaporating you have to really look at the details and then try to extrapolate that to what's happening on a whole planet and how its responding the radiation it's a it's ugly actually but but you have to do it if you really want to understand how these things happened sir on Mars I understand from what you said that the extinction of volcanic activity on Mars quashed the green housing of Mars now what about Earth in the future when a volcanic activity and tectonic activity is extinguished would that have somewhat of an effect like that before or after the counteracting effect of the increasing brightness of the Sun well if the volcanoes of Earth shut down that would happen but almost surely that won't happen before radical changes on the Sun that is the Sun has a finite lifetime within which until which it acts re the Sun has a finite lifetime after which it will turn into a very different kind of star it will burn up most of its hydrogen and the interior structure and temperature will fundamentally change they'll turn into something called a red giant and you know torch the earth basically that will probably that happen in you know something like 5 billion years thermal models of the earth suggest that it probably the interior he'd probably has longer than that so I think the the external effects ultimately will overwhelm the kind of effects you're talking about but if that's not true if the earth does go through some kind of interior transition and cool off faster than we think it's going to and the volcanoes shut down yes that will affect climate radically yes I assume the definition of life includes plants and animals if it is so then basically we consume oxygen and give carbon dioxide and plants are different is any any impact in the climate control because even though life is defined as in one entity but there are two variables I heard that the preface of your question but I'm not sure I understand the punchline so so life yes has these two components certain kinds of life the plants make oxygen consume carbon dioxide and then we of course consume outright and make carbon what was your question how do we have then the plants and animals have different impact on climate control even we'll even though we define life as one entity one item yeah yes certainly and certainly they have different different impact on the climate and yeah so if we just got rid of the animals and but the plants consume co2 and make oxygen then yeah I I think you know if you added up the cumulative effect that probably would would take things in in the right direction of course but then we wouldn't we wouldn't get to enjoy the fruits of that but yeah absolutely it's a complex balance there's a carbon cycle and an oxygen cycle that that comes comes through the biosphere and through the solid earth as well and the and the climate ultimately as a result of all of these what we call sources and sinks that by sinks we just things that are removing carbon and and a lot of those are biological and understand the whole climate balance yeah you have to include the plants and the animals as well as the volcanoes and the the weathering reactions that I told you about catastrophic climate changes I was wondering especially on the planet Earth but also in our surrounding planets um the phenomenon of the polar shift I'm wondering is this real how often does it happen and it happens slowly or quickly what are you what are your thoughts on that at all the phenomenon of the polar shift well there there are a few things that that might fit the description of what you're talking about there are magnetic field reversals that do happen if you look at the history of the Earth's magnetic field the North Pole actually switches from where it is now to where the South Pole is now and it's done this many many times and we don't really understand what will happen during one of those transitions in fact some people think that one is approaching because there's some not really strong evidence but some evidence that the field may be shifting and getting a little weaker right now we don't really know and it's a good question people I've heard people pose this question before but I've never really seen anybody modeling it if there is a brief transition time when the pole is switching when when there's not much of a field what effects does that potentially have an atmosphere and climate because right now the Earth's magnetic field sort of holds off the solar wind and keeps the solar wind from stripping atmosphere away as I described that it does on Mars because Mars doesn't have anything like Earth's magnetic field so we don't completely know but we do know that this has happened many many times and certainly nothing catastrophic has happened and there isn't a strong climate record that indicates that that much happens when that but the other thing you might be talking about is is polar wander and there are two things that have happened one is that the the magnetic field is not completely fixed in space it moves around some because it's ultimately the result of fluid motions in the Earth's core but also the solid part of the earth the crust moves or around a lot if you look you know it's sort of the animated picture of the surface of the earth over many hundreds of millions of years that the continents all you know continental drift and plate tectonics they all move around so places you can look at the magnetic signature in places that are at the equator now where once at the poles and that actually has a big effect on climate it turns out and we're still trying to completely understand this but there have been times in the past when more of the continents are are gathered sort of around the equator and other times when they're gathered more of the poles just by kind of random motion and it turns out that that may actually have a big effect on when you get things like a snowball earth because it's easier for instance to freeze over a continent than it is to freeze over an ocean because the the heat capacity that it takes a lot you have to remove a lot more heat if there's a deep ocean somewhere than just to sort of make a frosting over the land and so it turns out that where the continents are at any given time in geological history due to that wandering of the continents has a big effect on the on the effect on let's see has a big effect on how easy it is to change the Earth's climate at different times and so all these different processes that I've been talking about I didn't mention this so I'm glad you brought it up they have a much larger or smaller effect depending on those sort of random semi random motions of where the continents are so I hope I answered your question the best I understood it thank you okay the four people who are standing now may speak but not all at once and then and then we're gonna have to stop so sir so this actually is related I think to what you were talking about least with the magnetic field when you're talking about the the loss of atmosphere on Mars and you're talking I heard you mentioned the the impact theory that you know blows off the atmosphere what I didn't hear you mentioned which is the one I've actually heard more about I don't know if it's overly popularized does have to do more with the magnetic field of Mars and the fact that because Mars goes cool and the core stops rotating that there's no magnetic field without a magnetic field there's more exposure to or wind which strips away the atmosphere and I was you didn't mention that at all as part of what might have caused margins loss of atmosphere so I was wondering if you would comment on that yeah absolutely a very good point I mean what I did mention was that that one of the boss processes is that the solar wind strips away atoms from the top of the atmosphere and their various details of how that can happen but basically you know there are these charged particles coming from the Sun that have a lot of energy and if they just hit the top of an atmosphere they these collisions are very energetic and then you know they can just smash into molecules and break them up and smash into atoms and they just go flying off the planet and the smaller planet like Mars is much more vulnerable to that because escape velocity is lower but the part that I didn't mention that I'm glad you brought up is that this may have been different in the ancient past of Mars because if Mars was well when Mars was more geologically active and those big volcanoes were being made and so forth it may well have had a strong magnetic field because the reason why Earth has a strong magnetic field now has to do ultimately with the Dynamo the heat engine in the deep interior of the Earth and Mars doesn't seem to have that going on now but it probably did at one point and honestly we don't understand enough about how magnetic fields are generated to have a very good theory about when Mars had a magnetic field if it did have a strong one and when that would have shut off and that's one of the things that we can answer with future Mars exploration because you you know you can actually measure the the remnant magnetic field in rocks and we've been able to do that a little bit on Mars actually from orbit we've seen something that igniters that imply probably that there was a strong magnetic field at some point in Mars is passed and so you're right so so when there was that would have helped protect an early atmosphere of course it couldn't have protected from those that impact stripping I talked about impacts don't care if there's a magnetic field or not but some of these other things that are stripping the atmosphere away Mars would have been more protected when it did have presumably a strong magnetic field last thing I wanted to ask is I'm an astronomy teacher at high school level so when I explained right how Mars atmosphere might have been lost should I be telling them more about the impact theory or should I just say you know what we really don't know well I think I think you should tell them about the impact theory because it's for one thing what base you teach yeah well I mean for one thing I mean it's people people just love hearing about impacts people people of all ages things things that explode are exciting and but but I mean more seriously we see the craters on the surface so it's not conjectured that these impacts happened the part that isn't completely solid is the model of what exactly happens to an atmosphere because you know we can't we actually do experiments in small scale there's a gun over here at Ames the Ames vertical gun where they you know they do these hyper velocity experiments and try to simulate it and try to scale that up to what happens on a planet but you know so there's some looseness in the theory there but at the same time we know the impacts happen we know how energetic they are and it's certain that a fair amount of atmosphere got stripped that way so I think it's a really good thing to tell them about because you can connect it to actual evidence but but I would also tell them about the changing magnetic field and that you know and and it's always good to tell kids what we don't know to and the fact that Mars probably had a field generated similarly to the way Earth's is generated but that we you know there's a lot we don't know about that and a lot we need to keep exploring to find out is a good message to tell them as well sir think about the early history on amitabh checked both warmer and larger than Titan in terms of climate and atmosphere okay yeah I got a little worried when you started asking me about Ganymede because dr. Jeff Moore who's sort of the world expert on on Ganymede or one of them is sitting here in the second row so I thought oh I'm gonna have to talk about Ganymede and Geoff's sitting here watching me but the okay but the question well okay why why does Ganymede not have an atmosphere and Titan has an atmosphere right I mean they're almost the same size you know there are these two huge moons and a Ganymede is is a large icy moon of Jupiter and titans of large icy moon of Saturn Ganymede has you know virtue no atmosphere and Titan has this huge one so it's a good question I actually wrote a paper with some colleagues from Ames several years ago with an answer to that question I don't know if it's right but what we said was we looked at the early impact history of Ganymede versus Titan and thing is when you have an icy body and you have comets hitting it which that you surely had a lot of when when these when these bodies were young a low velocity comet can actually add to the atmosphere of a young moon a high velocity comic strips atmosphere away like like on Mars but but of course comets are ice balls so if you have a low enough velocity impact what happens that ice melts and actually you know you get water and methane you you're adding to the atmosphere so the interesting thing is if you look at the likely velocity distribution of comets hitting Ganymede it's much higher than the velocity distribution of comets hitting Titan for two reasons one well basically as you get closer to the Sun velocities increase you know things are basically falling towards the Sun but also Ganymede formed within Jupiter's massive gravitational field which is you know even Saturn is big but it's not nearly as big as Jupiter not nearly as massive and so the velocities of things coming close to Jupiter are much higher so if you actually do some calculations and do the physics it kind of works that you the Comets end up stripping away any ancient atmosphere from Ganymede and actually producing an early atmosphere on Titan but it's more complicated than that because probably they were originally made of different stuff and Titan forming farther out in the solar system probably got more methane and was Ganymede was probably less methane rich and I've told you tonight about the strong role that methane has played in maintaining the atmosphere which otherwise probably wouldn't exist on Titan so it also probably has to do with original composition and the different composition of Isis at Jupiter's orbit versus Saturn's orbit thank you sure and they oh you've got two more questioners right so I was the the penalty question now how long does it take to get from an earth-like planet to a vyas like planet and what's the possibility of that happening to earth oh great question okay how long did it take Venus to go from an earth-like state to a Venus like state and could that happen in the future on earth the first question the first thing comes to my mind is boy I would love to know the answer to that that's fundamentally the the central research problem that I'm working on now and have been working on for years and when I when I write proposals to NASA asking for money you know they're they're ten pages long and they have lots of figures and references but if I had to summarize what I say in those proposals in one sentence it would be the question you just asked me but the the best models that have been done to date suggest that you can get from an earth to a Venus it's something like 600 million years but the problem with those models is that they haven't incorporated clouds correctly and clouds could slow down that process due to the feedback effect that I mentioned you start evaporating the oceans the planet gets cloudy or that can cool things down and maybe slow that process down and so we really don't know but it's obviously less than several billion years and probably at least a few hundred million and you know hopefully someday soon we'll have a better answer than that the other part of your question could this happen to earth as I mentioned ultimately it must happen to earth if the Sun keeps warming up unless you know something or somebody intervenes now I think what you're really asking is could we induce this on earth and the answer is probably not the fact is that the amount of global warming that it would take to get us in serious trouble and in fact to get the biosphere of Earth even in serious trouble and it's much harder to harm the biosphere than it is to harm us is a tiny fraction of the amount of global warming it would take to actually you know boil off the oceans and turn earth into Venus so I don't think the real mess I mean you hear people saying well look at Venus look at Earth the comparison you know the message is that this is what could happen to earth if we're not careful and you know it makes a nice kind of cautionary tale but I really don't think that that's the real message of Venus the real message of Venus is that our climate models work because to first order we really can we put in these same equations on a radically different planet with lots of co2 and we get the right answer we get the right surface temperature in the right atmospheric structure for Venus so it it's a lesson it teaches us how to do better climate modeling but it's not really the worry isn't that we're going to turn earth anytime soon into Venus it's too you know we just have to do a tiny fraction of that to really be in trouble thank you sure sir my question has to do with volcanism is dependent on plate tectonics right it's plate tectonics and volcanism time dependent and what causes it to shut down okay great question so volcanism depends on plate tectonics and is that time dependent and what causes to shut down yes it is time dependent for instance if you look at Mars there was lots of all kind of volcanism in the past now there either isn't any or it's very rare and very occasional so what changed what changed was the the thermal evolution of the planet losing heat planets form hot they all form hot because planetary formation is a violent process of accretion collisions of smaller objects which at high velocities which releases a lot of heat and they also form with a lot of radioactive materials in their interior heavy elements that are that are decaying and releasing heat and that's still going on in Mars and Earth and all the planets but it's that heat of formation hanging onto that heat of formation it's hard for a smaller planet just due to basic physics if you take a bunch of potatoes out of the oven you'll notice that the big ones stay hot longer and the small ones cool off faster it's exactly the same phenomenon with planets and for the same reason the it's what we call the surface to volume ratio that the there's more surface area for the same amount of stuff on a small object and so small planets cool off faster and you lose enough of that internal heat and that kind of convection engine I mean plate tectonics is ultimately a heat engine it's the way the earth loses its internal heat if you lose enough heat on a planet that will stop that convection will slow down or stop and plate tectonics will stop and that geological activity that sustains the volcanoes will stop so so that transition can happen and does happen on planets it's just a it is a question of time scale and a very large planet will hold on to its heat for a long time I mean the earth has probably not lost its lost you know I don't know what the number numbers are and if any of you planetary genius is sitting near the front no feel free to shout it out but the earth certainly hasn't lost half of its original heat it's some smaller fraction than that and it's billions of years the time scale and so on a planet the size of Earth are larger that time scale may well be longer than the time scale for the evolution of the Sun which is why but interestingly Venus seems to have gone through a transition in its interior dynamics and we don't know yet if that's because it actually cooled off below some critical threshold or what I think is more likely is that the glass of water on Venus actually affected the global tectonic system because you dry out a planet like Earth and without those hydrated minerals in the interior it really changes the the way plate tectonic it changes the way rocks deform they get much stiffer and it's harder to do plate tectonics on a planet that's not sort of lubricated by water so there are many things that can that can affect this but um anyway so that's that's a long-winded answer but yes that that transition can happen but it's it happens much more rapidly on small planet like Mars so anyways I think we've probably used up our time so thank you all very much for coming it's been really fun thanks a lot thank you all we'll see you may 23rd drive safely

Channel: SVAstronomyLectures

Views: 16,417

Rating: 4.5263157 out of 5

Keywords: Astronomy, science, planets, planetary science, Mars, Earth, Venus, solar system, climate change, greenhouse effect, planetary evolution, David Grinspoon, Grinspoon, global warming, Space, climate, other worlds

Id: mQgnYw9tPj0

Length: 97min 58sec (5878 seconds)

Published: Wed Apr 24 2013