 Gris. Roi. Ryddo i hefyd. Ryddi'n ei gweld ar bod, rydw i'n ddim yn gallu ti'n gweithio i gyd, o'r anfer ystod ar y sefynd â CSI. Roedd am Nicolaus Braithwaith. Roedd am sailor y Ministerio Ffaculataeth, tecomod, eich bydd o'r enghreifanc a'r math. Roedd am ffraith a ffraith o'r anfer o bobl ond hynny'n i hefyd o'n ymhlwgiau yn cael eu leisiau. Os rydw i'r anfer o gweithio i'n siŵr teach and knowledge exchange portfolios. I'm also delighted that we can deliver this one here on campus in a COVID-conplaint way, of course, and it's been so long, since we've been in this room doing this sort of thing. Very exciting. Now, each year the vice-chancellor invites some of the recently appointed professors to give an inaugural lecture. Over the course of a year our series provides an opportunity to celebrate academic excellence, gyda'r cydweithio, yn ymdyn nhw'n gwybod yn ymdyn nhw'n gymryd. Ond oedd cyfnodd yn ei wneud yn ymdyn nhw, rwy'n ei wneud, gan ymdyn nhw'n gweithio yma, mae'r cyfnodd yn ymdyn nhw wedi'u gwneud ar gyfer y siwr. A hynny'n gallu ei chyfodd i'w dechrau, ac mae'n cwyleu'r yma, i'n cefnodd i'r ymdyn nhw ac mae'n ddych chi'n gweithio'i gweithio'r llyfodd i'r llennig a gofodd i gyd yn dŷch yn ysglet. O'r prysgwladdau yma, mae'n dyn nhw'n ffrwng, mae'n rŵn o'n ddweud o'r rymwy. Mae'n ddweud yn hynny'n gwybod, dyma'n ddweud. Ac efallai'n gweithio'r pwysig, eich cyfwyrdau, yn ymgyrch yn safon. Yn ymgyrch, mae'n gweithio. Ar y ddweud hynny, mae'n ddweud hynny. Ac mae'n ddweud hynny'n gweithio'n gweithio'n diogelio'r honi. Ac mae'n ddweud y mwyaf. Fy rhai fawr yn ei fawr, fel gyda'r fawr yn ymgyrch yn gallu amser y fawr ar y cyfle o fynd. Felly mae'r cwestiynau, ddweud eich bod yn eich gwasanaeth. Felly eich bod yn i fwyf yn sicr, wille'r gwasanaeth, boedd yna ti'n gweithio'n gweithio i fynd â ymgyrch yn ei fawr yn eich gweithio'n gweithio. Yn ymryd i'r fawr, rwy'n gweithio'n gweithio'n gweithio'n gweithio'n gweithio, ond nid o fwy fawr. Ond oedd ydych chi'n gweithio'n gweithio, ein colli Cymru, Stephen Lewis, profesiad yng ngwylwyr ar gyfer ei phyllwch yn ysgolodd. Rwy'n ei ei fod o'r syniadau yn gyfrifiadol, a rwy'n ymgyrch yn fwy o'r dynamu ar y cyfnoddau. Ac oedd eich gwaith arall o'r ddiddordeb yn y ddechrau gallwn ffordd y gallwn i'w gweithio'r llwyr o'r flannu. A ydych chi'n rwy'n amdano'r gyda'r hyn yn ffodol, a'i'n gwybod y gallwn i'n gweithio'r llwyr o'r llwyr i'w gweithio'r llwyr i'w gweithio'r flannu. A rwy'n gweld i'r ffyrdd yna, ond rwy'n gweithio'r llwyr i'r flannu. Dwi'n gweithio'r gweithio'r colleg Shyla Ross o'r llwyr ni, os yw'r gwnaeth, yn ystafell o'r llwyr. Stephen joined us and it was shortly after he joined us that I lured him into that because I found out he was a meteorologist at heart. He joined us in 2005 as a research fellow and by 2009 he had advanced to senior research fellow, 2010 transferred over to being a senior lecturer and by 2017 professor, professor of atmospheric physics. Now, his understanding includes the dynamics of climate systems, that's why it's part of the title. And forecasting the weather for spacecraft missions and interpreting the atmospheric observations that they return is really important. In fact it is important to space exploration as the early forecasts were on earth for exploration of all types by land, by sea and particularly by air. He's won awards for his work on spacecraft teams including NASA Mars Reconnaissance, orbit emissions and the curiosity and perseverance rover things. Sorry things, rovers run out of words. Back on earth it's important to note that he is a fellow of the Royal Meteorological Society and in that course that we produced together he was very effective in linking us up with that organisation. He's been the academic consultant as you would expect on the number of BBC series, Wild Weather, that would be one of his and a perfect planet. And that's a perfect point for me to pause and introduce tonight's speaker, Professor Stephen Lewis. Thank you Nick and good evening everyone. So I was asked to give an inaugural and I'd already given a talk recently about the planets and so I thought what could I do that was a little bit different. And I'd really like to theme this around, what can other planets tell us about the earth? This is of course a view of the earth's atmosphere but it's a view from space. It's actually been taken by an astronaut on the International Space Station and it's a view of sunset and you can see the various layers of the atmosphere. The weather that we are accustomed to is all in the lowest part below the bright line where you can see the clouds and then the middle and upper atmosphere above the stratosphere and mesosphere. So that's the earth. What about other planets in the solar system anyway? Well almost all planets have an atmosphere, it's arguable with what Mercury does, but all the other planets have a significant atmosphere and these are our two neighbours, Venus, Earth and Mars from left to right. I don't know why that's gone forward without me touching it. And you can see that each of them are dominated by atmospheres to different degrees. Venus completely covered with clouds, earth, a mixture of clouds and some land and Mars only very thin, cirrus clouds. And these planets have suffered different fates but really the differences in the surface conditions on each planet are much more due to the atmosphere than to anything else. Venus well known for a runaway greenhouse effect and temperature source enough to melt lead, Mars essentially a frozen desert. There's certainly not the only atmospheres, in fact not most of the atmosphere, this is an image of Neptune. It's an image I'm rather fond of actually because it was actually the last planetary picture just about taken by the Voyager 2 spacecraft as it flew out of the solar system back in the late 80s, I think 1989. It was the late 80s and I was actually in California at the time this image was taken. It's the first time I was involved in a NASA event in which a spacecraft flew past the planet. So the last of Voyager from the grand tour of the 1970s and the first space mission I was involved in, beautiful blue planet with some streaks of white cloud just visible above and the great dark spot which is no longer there in the centre of the image. Moving on to another planet, this is Jupiter when it comes down to it. It's the biggest atmosphere of them all. It is basically all atmosphere down to a level at which the physics becomes rather strange when we enter metallic hydrogen dominated region. This is a view of Jupiter we didn't have in my day anyway when I was first a research student. This is an image from the NASA Juno spacecraft which is operating now and it's actually a view down over Jupiter's north pole. So until recently we'd never seen the poles of Jupiter because of course from a telescope we tend to see the equator rather well and the poles are very foreshortened and the same from the Voyager spacecraft simply flew by in the plane of the ecliptic, the plane where all the planets orbit the sun. But you can see that Jupiter's atmosphere is just a fantastic fluid dynamics playground. If you're into fluid dynamics this is the place to go. It's full of whirls and vortices, very active systems all the time thrashing around. In fact the particular vortex I started my PhD on is this one. This is a more recent image but it's a nice image of Jupiter's famous great red spot. This is a vast vortex. You could fit at least two earths within it so that gives you an idea of the scale we're talking about. The vortex rotates every few days, the gas whirls all around the outside. The other kind of interesting thing about it is that it's been there for a very long time. It's changed in size and colour a little bit but it's a little controversial who first saw it but there's certainly a record of Robert Hook seeing it in 1660. He wrote it up in the first field transfer of the Royal Society. So we know that he saw it. It's likely, although it's not clear that Cassini, the Italian astronomer who was operating in Paris at the time, also saw it. It's a little unclear who saw it first but that doesn't really matter. The point is they both saw it. The reason why it was first seen at that time was not because it formed then probably but because telescopes were just being invented that were good enough to see it with. This is a fantastic feature. It's often described as a hurricane or you will see it said it's to be like a hurricane. It's nothing whatsoever like a hurricane actually. It's completely the opposite. It's actually a high pressure system, an anti cyclone. It's in the southern hemisphere which is why it's rotating the way it is. I did my research on the dynamics of this feature and it does have an analogue in earth. The earth analogue is actually a blocking high. A very stable high pressure weather system. Obviously the winter of 1963 was a particularly bad winter, a good year otherwise I might point out, but it was a bad winter. The reason why was because a blocking high like this was sitting over the country just holding that cold weather and lasted for about a month, which is a long time for earth weather. This feature has clearly been here for 400 years or getting on for that plus we don't know when it formed. So an amazingly long lift feature. Over to a much smaller planet now, but to show another atmosphere in action. This is Mars. This is North Pole of Mars. I'm sticking to polar pictures for now. So this is a beautiful view of the North Pole of Mars. The ice cap you can see on the right hand side of the image is essentially a water ice cap. People will often think of Mars as this dry dusty desert, which is true to a large extent, but look at the active water cycle going on here. There's a huge ice on the surface in the polar cap. More towards the centre of the image. This huge bank of cloud here is Stratocumulus cloud. If you've done understanding the weather you might recognise that. It's quite unusual to see so much Stratocumulus cloud on Mars, but this is Stratocumulus cloud. And then further down over to the left we're going towards the equator and there's fogs actually and thin cirrus cloud. So these are all water ice clouds. So there's an active water cycle going on even on repeatedly the driest of dry planets. So plenty of atmospheric excitement going on there as well. And I'll produce some examples from Mars later in the talk. So as Nick mentioned, one of the... I think actually one of the most interesting, almost different parts of my job at the OU has always been to work as an academic consultant on various co-productions with the BBC. A natural one that happened recently in 2019 was the planets with Brian Cox. And I was involved in a lot of the science of this, you may have the poster. So it was natural that I was involved in that. But more recently, actually over a long period of time, but the programme was finally shown this year, a perfect planet with David Attenborough which you may notice doesn't involve a lot of other planets. It involves a lot of animals and the earth. And yet I worked on this series and I can remember vividly, I was sitting at home working through some scripts or looking at some images on my computer. And with the respect and deference that my children have always given me, one of my daughters came in and said, well what do you know about that? So that's the motive for this talk really. Why do they put a planetary scientist on a programme about the earth? Well, here's the earth's atmosphere. This is some spaces nearer than you think I always like to say. You would get a view not unlike this if you travelled about the same distance as you would travel to London from here upwards. It's not very far away at all. This is obviously a view from the international space station, so the actual photograph has been taken from higher up, but you can see a Soyuz capsule approaching in the lower part of the image. But all the weather you can see going on down here is all within a few kilometres of the surface. The tops of these clouds are all well below 10 kilometres. So a rather sobering thought perhaps is that all the life that we know about in the entire universe exists within a layer of a few kilometres of the surface of this planet at the moment. We're really living in the thinnest of shells around the earth. If the earth was an apple, it would be thinner than the skin of an apple. That's the only place where we know life exists. So it's a very precarious position to be in perhaps in some ways. That brings me on to how do we study the earth's atmosphere? Well, what a scientist would normally like to do, if you want to study a fluid system, you go into the laboratory and you spin it faster or you heat it up a bit more or you do something to it and change the parameters and see what happens. Probably a bad idea if you've only got one atmosphere to live in. So I'd like to talk a little bit about how we study the earth and why other planets might help with that study. Well, two ways we could do experiments in atmospheric science is we have to look at different systems that we can do experiments with without affecting the real thing, hopefully. So just two examples I've worked on here in Sketchform anyway. On the left, a rotating tank experiment. You probably don't get an idea of the scale. This is actually an EU facility in Grenoble that I've done some experiments on. And this is a 14-metre rotating turntable. Several metres deep. If I can just point to... You might see there's some computer screens up here. You can walk along this plank here and several people can sit on this plank when it's operating. It operates in the dark because the only way we can find out what the fluid is doing is by shooting sheets of lasers at different heights in the tank. This is an example of one in the lower left. And then we use essentially clever video-tracking technology to track the motions. And the reason why it's still valuable to do experiments with actual real fluids is that we can access a range of scales that you just can't access in a computer simulation at the moment, even. We have a tank that's 14 metres across, but the fluids move on scales of millimetres. And so we can access that whole range of scales and range of motions. The other side of the slide is actually what I'm going to talk about much more tonight because it's more commonly done for the plants I'm going to talk about is a giant numerical model. Now, the way we model an atmosphere is that we effectively split it up into lots of little boxes. This is conceptually what happens. It may not actually happen according to the precise technique used, but effectively we divide the atmosphere up into a whole bunch of boxes, both in the horizontal and in the vertical, stacks of boxes in the vertical. And then we solve the various equations we want to solve for each box. And so the more boxes you can have, if you like, the more resolution you've got. It's a bit like having an HDTV rather than an old-fashioned conventional TV. We can go to a higher resolution with a bigger computer and we can make something that hopefully looks more like an atmosphere. The trouble is that atmospheres are rather complicated and I've got to put a lot of different equations into each box. And here's just a few of them, really. There will be a test on the equations on the top right at the end before you get your glass of wine. Effectively, though, it's not that... I'm joking slightly, but I don't really expect you to follow all the bits, but the point is that there's lots of different science. In fact, these might be rather better called kitchen sink models than global. They're called global circulation models, but we effectively have to throw in everything that we think is important, and it turns out that a lot of things are important. So the first three items are kind of the equations of fluid dynamics. This is just Newton's second law written in a slightly unfamiliar form because you're in a rotating frame of reference on the planet. That's why there's some extra terms there. And there's gravity to worry about whether there's other things going on. But it's Newton's second law. Its acceleration equals force divided by mass. We then have some other... So the good old classical physics, really. Continuity in equation of state. We need to under... So continuity basically says mass is conserved. The equation of state describes... We're describing a gas. We could equally well put in a different equation of state if we were describing a liquid of an ocean. Then we've got the law of thermodynamics. Effectively, conservation of energy. There's a little term here that looks rather innocent, which is the Q on the right-hand side of this. Whenever a physicist write a scripty letter, that often means that something quite dark and deep buried there. In this case, it's basically everything else I'm going to talk about. It's about 90% of the computer time involved in solving these equations for the boxes. What goes on in the Q to calculate what Q is. So, for example, we need to know about radiative transfer at different wavelengths. We need to understand about sunlight coming in. Infrared radiation going out. The scattering of both. The absorption of both. There's cloud of nice physics. You've seen some clouds of nice. We need to know about how things condense, supply and precipitate. We need to worry about the surface. So we need to talk to some geologists and geomorphologists because we need to know the shape of the surface and we need to know the properties of the surface from the surface to the atmosphere. If we were on the earth, we'd need to know about the ocean as well. Then aerosol physics, hugely important particles from volcanoes or from dust storms. And then atmospheric photochemistry. So, chemistry turns out to be a huge time hog on these models because we have to track instead of just tracking a gas, we track every species that we think is important and then we make more react in the boxes. So, we have to talk to chemists. And then sometimes if you're working on the earth, you talk to biologists. And sometimes even some people will even put economics models in all sorts of things. So, the point is that it's not just although my specialty if you like are the top three lines that I need to talk to lots of other people. It's a huge collaborative effort. Virtually the whole of STEM science and some people from outside STEM in formulating parts of these models. So, it's an interesting an interesting exercise. So, next I thought to talk a little bit about weather and climate because there's always there's always some confusion between the two. And there's a rather infamous quote, climate is what we expect, weather is what we get. Which to some extent tells you something about what's going on. Often attributed to Mark Twain although that's apparently is not correct. And then it's since been attributed to Robert Heinlen in the 1950s but I don't think that's right either because there's records of it being coming from America. It came from some book of American student answers to exams or something from the early 20th century. So, we don't know really where it comes from. But it's some perhaps sums up the point. So, individual weather events are how the atmosphere changes from day to day. Why is today different from yesterday or why is tomorrow different again? That's weather if you like. And actually we can predict these with large numerical models of the type I've described. And surprisingly our skill is actually getting better, you may not believe it but our weather forecasts are about a day better every decade that's a sort of rule of thumb. So, what that means is that a weather forecast now for five days ahead is as accurate or skillful as a weather forecast was three days ahead 20 years ago. The main reason for that is actually part well there's a combination of reasons. Partly the models and partly the fact that we've got better observations we've got more satellites and so we know more about what the atmosphere is like now. Climate on the other hand is a sort of average you can think of it as an average perhaps on a decadal timescale formally on a 30 year timescale although often the 10 year climates are published and it's also about the pattern of variations so if we're thinking 10 or 30 years ahead how the question I'm sometimes asked is well you can only predict the weather a week ahead how do you know anything about climate 10 or 20 years ahead and the answer it actually sort of stems from something that one of the members of my family was fond of saying when I was younger which is you never meet a poor bookie and that's essentially the answer here. So you can think of it, this is a rather simple minded analogy but you can think of it this way I believe that there are games on which people wage your money which involves throwing two dice and it's something to do with the score you get. So if I threw two dice and you ask me what will the score be next time you throw them that's an incredibly difficult problem actually. On the other hand if you ask me what would you expect the score to be I can solve that rather easily in my head. So to give you an example let's say I is this going to go ahead. So we can think of predicting what's going to happen next time as a weather forecast. It would actually be very hard but there's nothing fundamental that would stop you from doing this you could have you just need to know exactly where the dice were at the start of the throw exactly what orientation they were in exactly what velocity they were moving with and you'd need to know all about the material properties of the dice the material properties of the surface they were going to hit the air and you could throw a massive supercomputer calculation at this and in principle you could try to work out what those dice were going to land on. I have to say I think it would be very very difficult it would drive vast resources and it would also be very subject to tiny uncertainties in the initial conditions of the dice because they're going to bounce and collide and a lot of things will happen. So you can think of that a bit like an analogy for a weather forecast probably even harder this is really quite a hard problem you'd have to throw a lot of physics at it. On the other hand if you ask me what you would expect the score to be well assuming the dice aren't biased of course I know there's 36 possible answers and six of them are going to be seven so a sixth of the time I expect to get seven as the total that's the climate and equally there's a distribution progressively less likely to get numbers that are different from seven until I get to two or twelve which are both going to happen one time in 36. So I can actually very easily describe the climate and you might even think that you could push this analogy a bit further I don't want to push it too far that if we started to bias the dice a little bit that might be climate change. So why do we get weather anyway? What's going on? This is a sort of simplified picture of the earth but it could be any planet actually. A beam of sunlight hitting somewhere near the equator falls on less surface area than it would do if it hits a higher latitude. And effectively what happens is that the tropics on average day and night over the year absorb 300 watts per square metre from the sunlight but they actually only emit 250 watts per square metre and in contrast the poles absorb 50 watts per square metre but emit 150 watts per square metre. So what's going on? Well clearly the energy isn't being created or destroyed. What's happening is that the atmosphere and the oceans to some extent on earth is transporting the heat from the equator to the poles. And in classical thermodynamics a lot of which came about in the 19th century for reasons not unconnected probably with the industrial revolution this is called a heat engine. You can think of it engines move because often certain types of engines move because you heat parts of them to hotter temperatures than other parts and they move in response. And effectively that's what the atmosphere is doing as well. And you might wonder how powerful an engine is it. Typically the earth's atmosphere which is not particularly big atmosphere is about a 5 petawatt heat engine. Now that's quite a hard number to visualise. So I've tried to break it down for you. 5 petawats is 5 with 15 zeros after it. And I tried to think of the biggest sort of mechanical engine that I could think of. And imagine the space shuttle just after it's lifted off the space shuttle with all its boosters firing at maximum as it tries to accelerate away from the launch pad. You would need half a million of those to bring to get to 5 petawats. Or maximum thrust. Well another way of thinking about it is what's the peak electricity consumption of Great Britain. Well actually the most ever recorded which was recorded in winter two years ago on a cold day was about 100,000 times less than this. So it's a vast amount of power. More loosely somebody's tried to estimate the total power consumption in all forms of the human world. Everything we do. Oil, coal, wood electricity all added up. And it's still 25 times less than this steam engine that's cranking on above our heads right now. So weather is pretty powerful. So how does the atmosphere actually move? Well this is a classic figure from understanding the weather book actually from the OU. It's a chap called Hadley explained the tropical circulation as large cells and this these are the blue cells near the equator here so rising motion at the equator and then falling motion away from the equator and the reason why he was interested in these was this was the 18th century and he was interested in the trade winds. He's trying to explain the trade winds. And effectively that's a it's not exactly what happens but it's a good it's a good picture having your mind. But then about 100 years later a bit more in the 19th century an American meteorologist called William Ferrell suggested well there must be some other cells rotating the other way to carry the heat onto the poles because we know the poles are emitting about three times as much heat as they're receiving. The poles would be a lot colder if we didn't have an atmosphere. We've drawn these in purple. You will often still see them to this day in books and all over the internet as ferrell cells. There's a small problem with ferrell cells which is that they're not actually there if you go and look. There's nothing like that happening. Well there's something like that happening but it's only like that in the average sense. What actually happens is that the motion breaks down. It's not this simple sort of two-dimensional overturning circulation like a cell. It actually breaks down into wave-like motions. And we're familiar with these actually because when the peaks and crests of the waves pass over us we say we're a low-pressure system and this is exactly the weather that's passing over us right now actually. We're in a low. Not a very strong low but a low nonetheless. So the motion up here is not this ferrell cell at all so if you ever see that picture feel it with a pinch of salt or colour it purple as we did and try to remember that actually what's going on here is waves. So let's look at a real picture of the earth from a satellite that's actually just for convenience sitting right over the equator and right over the prime meridian. So right over the Greenwich Meridian and right over the equator. You can see the Hadley cells you can see it really here or their impact anyway. There's a band of white cloud near the equator. It wanders around a bit with the seasons and this is February so it wanders around a little bit. But you can certainly see the impact of the Hadley cells the equator is quite green isn't it under those bands of clouds. There's rainforest in South America and across through Africa near the equator. This is where there's rising motion the air rains out and the moisture leaves the air as it rises. Now you can also see the effect of the Hadley cells where they come down again at the end of the Hadley cells because that's when the air which is now dried out is descending and it's pretty clear that there's some deserts. The Sahara is impossible to miss in this image but there's also drier sort of more deserty land in the southern hemisphere at a similar latitude away from the equator. So this is the impact the Hadley cells but if you start to look here at higher latitudes in both the northern hemisphere in Europe maybe and across the North Atlantic and in the southern hemisphere as well you can see that the motion looks different it's rather swirly it's the clouds are in a spiral pattern and this here is a low pressure system and there's another low pressure system here these are cyclonic systems, weather systems so this is what I was talking about this is where the ferrule cell is really the average activity of a lot of waves and instabilities going on and that's what gives us our weather. So that's a nice picture of the Earth's atmosphere Can we study other planets? I've talked about the Earth and the importance of the Earth is clear because we live in it we need to understand our atmosphere but why study other planets? I think the first motivation is fairly obvious that they're just fascinating places in their own right I hope you like the picture of Jupiter I certainly enjoyed that I find that fascinating understanding the flows and similarly Mars and why it's different from the Earth but we also want to understand things like how the solar system has evolved in life perhaps the Earth wasn't always the best place for life four billion years ago it might well not have been so understanding the atmosphere is important for understanding the solar system and then as Nick mentioned spacecraft exploration operational safety we need to understand the atmosphere it's actually becoming more important as we get more advanced with our spacecraft because we try to push closer to the engineering envelope we don't build in such huge margins and so when we're pushing close to that envelope we need to understand the density of the atmosphere we're flying through very often and what its variability is but actually what I'd like to talk about tonight is none of those things it's the idea of comparative planetology which is often cited by surface scientists really, really fully explored we certainly understand other planets by understanding a bit about the Earth but I'd like to ask really is can we look at other planets and actually transfer something can we learn something that we can bring back to Earth and I'm going to argue that there have been a few examples from Mars research that we have done things that we've learnt are more important than some of the planets so we studied them a bit more and then actually oh they turn out to happen on the Earth as well to the greater extent in the modern Earth and also this comes back to the idea of experiments again maybe we're looking at things that are way outside we're going to test our models really stress test our models on objects that are way outside our current experience of climate on Earth so a few examples and I'm going to bring all these examples are from Mars so how do we understand Mars, well these are all models that have run at the Open University now so we have as I was describing a global climate model of Mars global circulation model and we can run it in what I like to think of as a climate mode which is on the left it's a global model but it's a fairly coarse resolution picture if you like because we're going to run the model for a long time we can run it in a sort of weather mode which is the same model but simply turned up to higher resolution so we can't run it for so long but we're going to look at more individual events in more detail and then for one to get really detailed we have to go down to the limited area models or in this case what we call a mesoscale model a medium scale model and those who know a little bit about Mars might recognise why this particular model was run because this is Gale crater in the centre the purple is Gale crater the little bit of yellow in the middle is Mount Sharp and if you've got very good eyesight there's a little black circle in the purple and that is actually where the curiosity rover landed so all of these models are run at the OU which we've developed over a period of time and in collaboration with many workers at other universities as well of course I should say but you also need data it's no good having a great model but if you don't know how to start your model off what your initial conditions are if you like then what good does it do you and another mission I've been involved with is Mars Reconnaissance Orbiter this is the Mars climate sounder instrument and this gives you an idea of what this is real Mars data you're looking at the image of Mars is just there for reference the picture of Mars with the dust and the surface but that is an image of Mars taken contemporaneously with this data so the dust storms that you can see are reflected in the data but the data are these coloured curtains we called data curtains that are surrounding the planet and this particular instrument flies around Mars it orbits Mars roughly every two hours so it orbits the planet about between 12 and 13 times a day from pole to pole and every time it passes over it makes thermal sanding so the colours represent temperature in the atmosphere with a much expanded vertical scale exaggerated vertical scale so that you can see them and you can see there's all sorts of issues with this in some places the bottoms of profiles are cut off sometimes that's because you're going through a dusty region and they can't retrieve the temperature when the atmosphere is too dusty sometimes it's just because of various things that have happened on the spacecraft it's had to roll or maneuver or something so you had to turn the instrument off for a while but this is a good day we've got about 13 orbits and you can see that each of these curtains is drawn down it crosses the equator but another issue with this data all these data is that it's not a synchronous picture it's asynchronous data so in other words we fly and take one data curtain and it doesn't come back to take the next data curtain until two hours later and the problem with atmospheres unlike planetary surfaces is that they move and in that two hours in which the data in which you've been flying around the other side of the planet everything's moved a bit so it's a bit like the old wagon wheels on the movie problem where everything's aliased and you don't see things change while you're looking at them so how do we cope with that well a technique which I've been involved in developing for the last 30 years really called data assimilation which is used on the earth for getting the initial state for a weather forecast we use it for a slightly different purpose on Mars so in other words we've got our observations which have the problems of the limited coverage uncertainties but nonetheless they're real data so they're massively valuable that's actually what the atmosphere is doing now which is what we want to find out and we've got the model which is great because it's got global coverage it's got a nice uniform sampling but we don't know what state it should be in what the initial state should be and data assimilation is all about bringing those two things together combining them in a statistical way and eventually coming up with a if you like a model state that most plausibly best fits the data that we've got and that's another way of thinking about that is that we're using our knowledge of physics to interpolate between the observations and we see something else two hours later but we know that it's moving we can think we can work out what the winds are and so we can make some prediction some forecast as to how it's changed during that time and we can combine our knowledge of physics with our simple knowledge of the observations to make something that's a bit more than some of the parts all we hope so the first example of the value of this is landing one of these rovers the Curiosity rover sitting in Gayle Crater I showed you before how the Gayle Crater model was embedded within the global model so we run the global model we we wanted to land Curiosity the problem with landing these things it's a big beast, you often see these images on the news and it's unclear how big they are so Curiosity won't park in a standard American parking space we've tried it it takes about one and a half parking spaces it's like a big four wheel drive vehicle it weighs about a metric ton which is heavy for a spacecraft and you have to land safely on the surface when it arrived at Mars it was travelling at 21,000 miles an hour kilometers an hour I think and it has to stop in about six minutes but it doesn't want to stop too soon or you left dangling up in the air or stop too late in which case you hit the surface rather hard and so that involves knowing a detailed density profile of the atmosphere but the problem is on Earth you would solve this problem by probably going and looking at some past record you would get a weather station nearby where you were landing and go and look at the record unfortunately no one set up a weather station network on Mars so we had to predict or try to predict from first principles and I'll show you some forecasts these are real genuine forecasts as I made for both Curiosity and Perseverance there a little on the left is Curiosity which landed in 2012 and on the right Perseverance which landed this year and in each case the continuous line is the forecast so in the case of Curiosity it's actually a forecast for it's not the day of landing because there wasn't any observation the instruments weren't all turned on at that point but we just compared after the event the forecast of the surface pressure at the Curiosity site for a week several from about nine days after landing on the right is a forecast of surface pressure at the Perseverance site it's a little different because I've just folded it in by time of days so the black line is now an average and the grey line is some distribution about that average of what I think the surface pressure will be over several days and on the left the black little bars are the actual measurements made by the Curiosity lander on the right the coloured dots are the actual measurements made by the Perseverance lander and you can see we're not totally without skill firstly the hard almost the biggest worry was would we even get the surface pressure right because the surface pressure varies very strongly with the time of year and we do seem to have got that nailed down which was one of the biggest concerns but the second thing is how does the surface pressure change with time of day and in the case of Curiosity it changes rather simply the surface pressure is high early in the morning and low late in the afternoon falls very rapidly during the day and the cycle repeats it's a bit like Los Angeles every day is the same at least it is at this time of year Perseverance is a bit more interesting so we actually predicted this that we would get a high pressure at 8 o'clock in the morning but we'd get another high pressure at 8 o'clock in the evening if you think about this you might understand are you familiar with something that's high twice a day well it's a tide it's actually a thermal tide though it's not a gravitational tide it's a thermal tide from the sun going around but the fact that we were able to relatively well it's not perfect certainly I wouldn't claim perfection but we got the right phase and amplitude I would say of the main components of the tides right for each site it's quite satisfying the other aspect of these forecasts are two to four years before the landings happened so they're quite long range forecasts they're really climatology forecasts they're climate forecasts not weather forecasts but there wasn't a lot of weather certainly not at the curiosity site on the other hand then you could argue where we predicted there wouldn't be a lot of weather so there's a bit more weather going on at Perseverance that's one of the reasons why the fit isn't perfect but there's not a lot they're both quite near the equator okay the next topic let's talk about is Mars weather we talked a bit about weather systems this again is a visualisation from our global circulation model at the OU and the colour scale which the label hasn't come out unfortunately the colour scale is water ice clouds and the little vectors give you an idea of winds and actually what you're looking at here is this is winter time in the northern hemisphere on Mars and you're seeing a jet stream around the pole very familiar to us from Earth and in fact the jet stream splits in this example you can see where a puff of cloud towards the centre of the image has come off more towards the equator and that's a splitting jet stream is a classic phenomenon in terrestrial meteorology as well so just like the Earth there's a winter jet stream and there are waves that go around this jet stream I'll show you some of the waves now this is now a real image of Mars it's in the spring it's not the winter north pole so it's just the north pole has just lit up in the spring and the white towards the top is the polar ice cap but I think you can see hopefully pretty clearly actually there's a spiral system here there's another puff of dust here this is all dust you can see there's not much cloud there's a little cloud over on this side all this stuff that looks like cloud is actually dust that's being thrown up that's what's showing you the weather but there's certainly a cyclonic low pressure system here and in fact if you look very closely you might see over here an arc of a weather front again shown up by dust which stretches over the edge of the polar cap now we can run our model for the same time as this and here's um it won't look immediately like it global model but it's from the same time as this image and what you can hopefully see here is that the it's not simply warmer at the equator and colder at the pole there's something going on and that's something I would suggest is that warm air is coming up it's being drawn up this way and cold air is being pushed down this way from the pole and in fact this triangular pattern is very familiar to a terrestrial meteorologist it's called a warm sector and this is exactly what's happening a low pressure system is up here and these are weather fronts here's a cold front being forming our model can't quite resolve a cold front because it's got a limited resolution but quite a good resolution in this it's run at weather resolution so there's a cold front happening down here and a warm front here and in fact where I've put the laser pointer now it's pretty much exactly where we're sitting or would be sitting right now we're in a warm sector tonight in fact the warm front passed over us very early this morning there's a cold front sitting up in Northern England right now near the Scottish border and it's going to push down over us tonight tomorrow morning sorry it will reach Milton Keynes tomorrow morning in the early sometime before lunchtime so sometime before lunchtime tomorrow we're going to get a band of rain come down which is associated with this air being pushed together at the front the cold air being pushed down so this is a very terrestrial like situation in fact back to understanding the weather here's the picture from the classic the classic earth if you do earth meteorology this is a classic low pressure system over the North Atlantic that everybody will learn about from the Norwegian School of Meteorology through to the modern day and this is the warm sector a cold air, a cold front here there's the warm sector in that triangle and warm air being pushed and drawn that way and that front there is what you could see delineated by dust in the image of Mars onto something a little bit more complicated if I've got time I think this is something from a paper I published with colleagues in 2016 and it's actually it's quite a complicated figure so I won't have time to explain this at all but I'll try to explain the main features so what you're looking at here is if you like a map of storminess where it's red there's a lot of weather going on there's a lot of highs and lows passing over the location where it's green it's quite calm the weather's the same every day if you like it's a bit like curiosity and this is the north pole this is the south pole there's not much weather at the equator and this is time along this axis for several years we've reconstructed the Mars weather for several years the Mars years are all numbered now for convenience it's not an international system yet but this is Mars years 24 to 26 a Mars year is about two earth years long so it's quite a lot of data and so if we just focus on the northern hemisphere where we are up to about 50 degrees let's put on a few boxes to draw your attention here to mid latitudes so just look at these mid latitudes this is autumn this is where we are right now that would have been September 21 in earth units and so we're sitting about here now and this is where all the storms happen so the storms come south from the polar cap as the polar jet stream comes southwards but then something rather unexpected happens we would expect certainly and higher in the atmosphere this does happen the storms just get stronger and stronger and they're strongest in the middle of winter which is when the temperature gradient is the largest that's what you'd expect and then they die away again in the spring and then near the surface this is only two kilometres above the ground this is what the weather you'd be experiencing if you were on the surface of Mars in fact something rather bizarre happens all the big storms happen during the autumn they build up and up and then they sort of calm down right in the middle of winter so this would be Christmas time on earth the winter solstice so the middle of this box is if you like late December on earth and we have a feature that's very strongly apparent in this data set which models didn't produce until I have done this reanalysis, this combination of data with models and it's become known now as the solstice report it's known on Mars that dust storms are slightly less common at this time because the weather is less active and rather intriguingly the idea has come back to earth and there are just hints it's not so strong as this example there are just hints that actually this happens on earth too that you get most the strongest storms happen in the autumn and in the spring early spring but don't happen right in the middle of winter you tend to get quite calm whether on Christmas day if you like think of it that way and the same thing happens to a much weaker extent in the southern hemisphere I haven't got time to discuss why now but the same sort of phenomenon seems to happen so there's a phenomenon that we discovered on Mars because it's much stronger but actually people have come back north pacific weather on earth next dust Mars is all about dust storms this is actually a pretty small dust storm you can see it's moving from right to left across one of the northern plains on Mars and dust is a major driver in the Mars climate this is some work done by a recent PhD student Paul Streeter in myself looking really people have been interested in Mars in Mars dust since the late 60s it's a constant mystery why you sometimes get the storms and you don't always get them and what impact they have and dust is obviously a massive factor for the climate it's well known I think that if you have plenty of dust in the atmosphere less sunlight will get through to the surface and the surface will be cooler during the day that seems fairly self-evident this is the old nuclear winter idea but actually at night something different happens and it's a bit like having a cloudy night on earth if you have a cloudy night you tend to not get a frost in the morning because the infrared radiation sent up from the surface as the surface cools is instead scattered in all directions by the dust and some of it is scattered back down to the ground and it actually keeps the ground a bit warmer than it would be if the dust wasn't there it's a sort of greenhouse effect and actually the net effect of the two in this state comparing a duster year that Paul ran shows you this complex pattern but certainly some places on Mars are much warmer when there's dust near the surface than they would be without the dust and some places are cooler so Mars has a complicated greenhouse effect and on earth dust storms are important now but they tended to be less modelled because the earth's climate is dominated by clouds water ice clouds whereas on Mars water ice clouds are less relevant I'll just show you the Mars a storm developing in our Mars model so a little orientation guide first this little map of Mars for those who are not familiar with the planet this is a standard sort of equal angle map so the northern hemisphere of Mars don't worry about the names but the northern hemisphere of Mars is essentially flat and it's a big plain the various Planitia planes the southern hemisphere on the other hand is a warm colour that means it's high and rocky it's rough and some of the most dominant features of course are the giant volcanoes Olympus Mons three times the height of Mount Everest and the footprint of that volcano is the size of France which is quite big for a volcano especially on a small planet Tharsis Ridge three volcanoes along here Montes so that just gives you a little orientation guide to what you're going to be seeing so we're now going to because the movie was shot from a different angle we're going to turn the map upside down and rotate it a bit of an angle and so we're looking down from the north now so you look out for Olympus Mons on the right and the Tharsis Ridge here and then Elysium this way so hopefully the movie will work and this is showing the beginning of a dust storm a global dust storm which started in 2018 in our model and don't let me down now please it worked in practice that is just typical isn't it why did it work just before the talk no here we go okay I've managed to do it with the key so you can see the dust so the surface is just this is actually the dust in our model being blown around and with exaggerated vertical heights to gael here is Olympus Mons the giant volcano it's an exaggerated vertical heights to gael but it would actually be rather flat because it's got such a large footprint but you can see the dust blowing around and one thing you might well be able to see is that the way it seems to slosh around and that sloshing is the thermal tide that's following the sun moving from left to right but now you'll see a dust storm really kicking off in the Tharsis region lifted up every day when the combination of the thermal tide and this is if you like a three-dimensional four-dimensional reconstruction of a real dust storm on Mars that we can run in our model okay well I said there's dust important on earth too and I'll just give you an example this is actually an image I just it's not hard to find a dust storm on earth actually this you may be familiar with finding dust on your car or your windows sometimes and it's always said to be from the Sahara this is a fantastic example this is actually an image of the earth from June this year from the 16th of June and I will show you the dust storm it's in this region we'll blow it up a little bit there's the Sahara you can see the sort of rather sickly yellow colour orange colour it's the dust being blown off it and it's being blown all the way to Central America it's actually raining out in the Caribbean and in Central America so planetary scale dust storms happening right now well a few months ago anyway and so understanding dust storms is important for the present day of that atmosphere it's clearly even in this image dominated by clouds but it nonetheless plays a role and we've improved our understanding of dust on earth through looking at Mars dust has probably also been more important in the past than the earth as well okay I'll move on to the next topic now which is about climate history these are dry riverbeds on Mars but they're not recently dry they were probably dried up about 4 billion years ago it's an incredibly ancient surface so we know Mars was a lot warmer and wetter than it was now because you don't get riverbeds like this without rain nowadays Mars is dry but you still see ice this is actually an image taken by an instrument called cassis on the Bysigas Orbiter sometimes it's going to automatic anyway so this is an image taken by an instrument that has actually co-managed at the open university so some of the people some of the people who choose the images it takes are sitting in the audience now I think and this is Corolev Crater in Northern Hemisphere of Mars and the winds here have brought a frost down from the northern polar cap so this white water ice doesn't sit there all year it's just been brought down by the winds now very thin layer of frost bit more bit larger region of a crisp alteration this is an example from a PhD project that I'm running at the moment with no use student Laurie and Foley and this is Leo Crater it's a huge crater in the northern hemisphere of Mars but there's lots of signs an image on the left so there's lots of signs if you're a geomorphologist that there's been a very aqueous alteration in the past in this crater so we've actually zoomed in our limited area model we're measuring where the ice is accumulating and now the great thing is with our model we can do play games that we can't play in real life we can look back in history so we can go back to previous times on Mars when the climate was different we can change the orbital parameters of Mars and see if things change then can we understand how these features are formed over the history of Mars so it's another thing we can do with the model there's no surfaces as ancient as these riverbeds on Earth I should say that Mars preserves features that are much more ancient because of the activity on the Earth and then finally looking again at the global scale so this is going back to the dust storm we saw this is some images prepared in collaboration with James Holmes and on the left is the sort of state just before that dust storm we saw so there's the dust over the planet Mars we're in the south now so the southern hemisphere is towards us and on the right we've put some other features of the model so the blue is the water vapor in the atmosphere and the pink is the water ice clouds there are a few clouds just as you saw on the image of Mars way back near the start of the talk and lower clouds near the poles but this is a sort of typical state when Mars is a bit dusty but not very dusty and only a week later this happens so there's the dust storm blows up maybe I can talk backwards and forwards and you'll see the impact of the dust storm on the water so the dust storm is just kicked up here in the Tharsis region and the water has been blown much higher in the atmosphere the atmosphere is warmed up there's fewer clouds water is transported much higher why is that significant well if water is transported high in the atmosphere it gets broken down by photochemical reactions to its constituent atoms and they escape to space and so maybe understanding the escape rate from these sort of processes the role of dust storms in escape is what is a key to understanding the history of Mars how did Mars dry out so much we still don't fully know but certainly a large amount of water is probably escaped to space and we're trying to work out now how fast it's escaping and what's governing it and it seems that dust storms are maybe a key to the escape rate so I'm just going to finish now with this image I was rather struck by this image it's actually been taken by actually a camera that is mounted on a small spacecraft that was taken from Mars and the camera is for looking at the surface in high resolution but it was turned back on Earth at some point and this camera which has roughly the power of a really top of the range amateur telescope so if you the sort of telescope that if you're a really keen amateur astronomer you might have in your back garden so if you were a Mars astronomer this is the view of the Earth so that we can actually see you can certainly see we've got clouds it's straight out for HG Wales if somebody was sitting on Mars now they could see us they could see we were different from the moon certainly you can see the moon in the top right and I hope that gives a little perspective on one reason why you do planetary science because you're going a different perspective on the Earth than you have sitting looking from below only so with that I would like to thank you for your attention Thank you very much Stephen we're going to go over there in just a moment or you can set off now and I'll join you just to say we've got to hear questions from people in the lecture theatre if you like we're not going to use the microphone so if you just speak clearly and loudly I will relate through my microphone to people online if you'd like to send them in by email to the address which is there on screen it'll then be relayed by voice back to me and I'll try and repeat it so that's what we're going to do it would be good if you could identify yourself by name makes you feel a bit more friendly say who you are and have you got a question for us right at the beginning Helen from online yeah I have from online it's from somebody called Alex Wood he's got two questions you mentioned the large physical model in a spinning tank is still useful at the current rate at the current rate program how many of our computer models can achieve the same smaller resolution over the same large figure okay first of all can I just repeat it essentially comparing the analogue computer of the big tank experiment and the numerical models that Stephen does before breakfast yeah well and after breakfast I have to say it's a very difficult question because when do you really and I think actually we'll always want the real fluid experiment because we always want to validate and test our models it's a very dangerous situation to get into where you believe one model and you believe that's reality I'm certainly a modeler and I love my models but I would still like to test them against reality occasionally so that's one factor we're still well away from getting the full range of scales so to give you an example on the whole planet if you like we can resolve down to with a single model we can probably resolve down to scales of several kilometres on a global with a global model of the earth with the very large computer clusters but remember that air doesn't really viscosity doesn't real viscosity doesn't happen in air until you're on a scale of about one millimetre so we still have this whole grey area between the tiny motions and one millimetre and the motions out at several kilometres and that grey area is a large part of the complications that are in these models how do you describe the effect of the small scale that we know about we know how viscosity works in fluids on tiny scales to the large scale so good examples of that are extreme weather events which are often in the past haven't been forecast very well so I'm thinking of something like the Camelford floods in Cornwall for example where they didn't capture the full extent of the intensity of the rain because the model simply couldn't go down to a small enough scale so I think there's always going to be a place for looking at reality as well as looking at models but we're still well away from just thinking that computer models can do everything it's not just rotating tanks it's rotating the earth as well and you're on the planet to your experiment and other planets exactly so we're a million miles away from being able to simulate Jupiter which is a vast range of scales on the earth so several earths could fit inside the great red spot Jupiter moves and thrashes around on small scales just like the earth but then it's ten times bigger so he has a second question you mentioned that a weather forecast accuracy is extending by one day per decade how long do you think that rate of progress will continue and are those theoretical limits so this is the forecast the one day per decade improvement how long can we go on Steven well that's not I'm not sure I can say I can say precisely I think we're probably starting to level off now it's not that we can't carry on improving but improvement gets harder and harder and harder so the tiniest famously the whole idea of chaotic systems the tiniest change in the initial conditions grows exponentially with time so that if you like buying a day into the future is progressively more and more expensive I don't think computing power at the moment is computing power is not increasing at the rate it was actually computers aren't getting that much more powerful but more importantly we've actually improved our observing system so much so in the past the big flaw was that we perhaps had lots of observations in let's say north western Europe where there's a lot of people a lot of money as well and weather stations very few observations in Africa that that sort of ballpark has been leveled a lot by the coverage from satellites so as we have more and more satellites the difference between the northern southern hemisphere of the planet has been evened up and the southern hemisphere forecast was pretty bad a few years ago and it's now a few decades ago certainly but it's now caught up rapidly with the northern hemisphere forecast but of course that will tend to even out to use satellites more and rely on individual people and weather reports less okay thank you very much question in the room I see one from John Zaneki Thank you very much Stephen fascinating talk Exoplanets we know what 5000 or so planets beyond their own solar system do you expect in your lifetime that you will be studying weather on some of those exoplanets or is that fancy weather I don't know climate yes because we do that already we've done that already we've modelled hot Jupiters large Jupiter size planets near stars with different rotation rates so we can do that in the broadest but can you measure at the moment you can't measure very well no you can measure only the simplest, broadest large scale parameters so yes you can't validate the models in the way I'm comfortable with with an Earth model we should always be humble in the face of how complex these systems are I talked about Venus difference between Venus and Titan actually an Earth of Mars Earth of Mars are rapidly rotating planets and they have similar weather dynamics Venus and Titan are slow rotators and their atmospheres super rotate massively if we didn't know they super rotated massively until a few years ago we wouldn't have been able to predict that with models models don't reproduce super rotation that well and we've made a little advances on that but I would argue that we would never have we never seen Venus we would have a very bad idea of what its circulation is actually or at least we wouldn't know we were wrong for a long time another question down here from online has the study of atmospheres on other planets made you more anxious about climate change on Earth because of the fragility of our atmosphere can I just have a very good question this is of course COP26 that we're in the middle of and worrying about the fragility of our atmosphere based on insights that you get from space Steven yes I think the simple answer is yes I've been well aware of climate issues since the 80s when I started working in this field it's obvious that we I'm a planetary scientist I talked to earth scientists a great deal of the time and it is a concern I wouldn't say I wouldn't go into the total doom and gloom scenario thinking well we're going to end up like Venus in a runaway greenhouse where the oceans are boiled if they were in the oceans and the planet is hot enough to melt lead on the surface actually maybe we will end up like Venus but probably not for a billion years that's not going to be that's not human climate change that's way outside that scope but it does show you the vast the vast range of parameters if you like that atmosphere can settle over it there's no reason why a planet should be as accommodating and as as nice as the earth it's just well whether you are regarded as luck or how you want to regard that we've evolved to enjoy the climate we've got there's been a lot of crises that no other had the earth had a slightly different climate we have a natural greenhouse effect of about 33 degrees if we didn't have that natural greenhouse effect we would be frozen we wouldn't be life on earth if we have a greenhouse effect a bit more we could push over the edge and various drastic effects could happen so yes I'm certainly well aware I don't think we should I don't think we should panic but equally I don't think we should now it's always going to be okay I'm certainly well aware of how just really how thin how thin the skin we live in it's always quite interesting to remember that if you went five kilometres that way you probably couldn't survive and if you went a kilometer or two that way you couldn't survive it's not very far in the scale of the universe I should never eat an apple and feel the same again any other question from the room I'll give you online one more chance if we've got another oh yes please you mentioned about Mars drying out how closely to understand why it's drying out or how it dried out I've just repeated this is the loss of water from Mars way of course we do understand well it's certainly a topic that many people are working on very hard we know what do we know we know it was wetter than it is now but we're talking a long time ago 4.5 billion years the sun formed about 4.6 billion years ago the planet formed about 4.5 billion years ago we're talking within the first half billion years so this is incredibly far back in time there's nothing that old that we can find on the surface of the earth for example it's all been turned around a lot more since then so it's not an easy problem we know that Mars so we know Mars was wet I think we can be pretty confident that it had precipitation of some kind whether that was snow or rain I can't swear to but I suspect it was both we know that Mars went through a phase of being much more icy but there were still mega floods there's signatures of mega floods all over the surface where the ice is broken and washed away features we then and that was about up to about 3.5 billion years ago and then we know that the last 3 billion years Mars has been well it's varied the climate has changed but it's not changed to that extent it's varied between different states so we know we know that there's been this big change why is a question that many people would like to answer but it's a big challenge I think the story I will give you is something along the lines of we know that Mars had a magnetic field in the past and that magnetic field is really only fossilised now there's no active the active magnetic field is almost gone now is it the case that the magnetic field stopped for some reason and was disrupted and when the magnetic field stopped the atmosphere was less protected and all this water that was being transported into the upper atmosphere that's certainly part of the story but there's a chicken and egg here was it the case that the water the magnetic field stopped because the water stopped Mars doesn't have active plate tectonics in the same way as the earth does it doesn't have moving plates anyway so it's a very different planet and I think the answer is we're gradually piecing it together and it's missions like the upper atmosphere satellite maven that's oppressing now and our sort of studies of the lower and middle atmosphere trying to tie together trying to work out what the lost rate is if we can pin down what the water lost rate is now in the recent past and the recent past might be 3 billion years then maybe we can have a better estimate there's probably a lot of water under the surface of Mars as well we know there's a lot of ice under the surface so water's sunk down 500 metre deep sea in the northern hemisphere of Mars in the past just on the basis of thinking well it's probably about like the earth it's not that different in terms of composition so that's the long answer the short answer is we don't I wouldn't say no but there's lots of ideas and it's probably connected with a series of catastrophic events which were to do with the atmosphere cooling probably the atmosphere lost a lot of mass the atmosphere is probably a much thicker atmosphere in the past because it would have to have liquid water exposed to the surface if you expose water on the surface of Mars now it would rapidly freeze and then sublimate it won't you won't have liquid water so the answer is something pretty bad happened but we it's hard to say what at the moment still but it's an interesting question I think we should have one more so there's some comments about being a fantastic talk but there is one more question online from Dr. Liz Carbon from the School of Physical Sciences here so you've talked about morning and evening, spring and summer and so on but each planet has a different year length and day length and in some cases the axis of the planet has a different orientation how does this affect the prediction of weather on different planets so that's the relationship between the planetary cycles of day and night and years and so on and weather so one of the reasons I talked quite a bit about Mars is probably because in those respects Mars is the most like Earth it's year is twice as almost twice as long as the Earth's but actually Mars is tilted with respect to its orbit around the sun by almost the same angle as the Earth is currently and that means you get the same sort of pattern of spring, summer autumn, winter and also Mars rotates only a bit slower than the Earth a day on Mars, a solar day on Mars is about 24 hours and 40 minutes in our time this is a great problem if you work on a Mars mission actually because I know a lot of colleagues in JPL in California who drive these rovers are driven mad because they have a basically have an app and work on Mars time and of course if you're slipping 40 minutes a day it does horrors to your body clock but none the less Mars is very similar to the Earth it rotates to the same sort of period a day is about the same length it has the same pattern of seasons other planets are different so Jupiter for example rotates very fast it rotates to the 9 hour period but also it's sitting almost upright so it doesn't really have seasons it's kind of if you like spring all the time same on Venus actually Venus is sitting almost upright but it rotates very slowly Venus has a very strange situation depending on which way you look at it you can either say it rotates backwards or it's upside down it doesn't matter which view you take but it rotates the opposite way to all the other planets but it also rotates very slowly so a day on Venus a solar day is very different from a rotation period on Earth we talk about a day quite casually there are different sorts of days there's a rotation period of the planets and there's also a solar day which is when the sun is in the same position of the sky and they're about 4 minutes different on Earth 24 hours is actually a solar day the Earth rotates a bit faster than that but on Venus they're hugely different so it's a very strange place if you were walking on the surface of Venus I'd recommend it you could keep up with the same local time of day pretty much as you walked around the planet it moves around the planet at that sort of speed so yeah in each case and that's part of testing the models so if I go back to my tank in the laboratory what do I want to do well I want to spin it twice as fast or I want to spin it half as fast and that's exactly what the planets give you systems that rotate at slightly different rates okay thank you very much I think we're going to let Stephen off at that point and I'm going to walk over here and save time say Stephen that was an absolutely fabulous lecture I have never understood that the weather even when we were writing a course of that title itself quite so well as I do for having spoken to you this evening so I thank you very much for that Stephen