1 00:00:07,670 --> 00:00:12,440 Welcome to the third annual upon your first lecture in Planetary Geology. 2 00:00:13,070 --> 00:00:16,760 The name of the lecture series is in recognition of the generous support the 3 00:00:16,760 --> 00:00:21,220 Department has received from one of its alumni on the Keith OLBERMANN costume. 4 00:00:21,800 --> 00:00:31,520 So as the lap on offer a staff ski associate professor of planetary geology, it falls on me to introduce our speaker, Professor Raymond here. 5 00:00:31,730 --> 00:00:39,510 Burke was recently arrived here in Oxford last July to become the Hailey Professor of Physics. 6 00:00:39,510 --> 00:00:42,650 So he is of course, familiar to many of you in the room now. 7 00:00:43,760 --> 00:00:50,000 His research involves developing conceptual and analytical models, addressing big picture questions in climate, 8 00:00:50,330 --> 00:00:54,800 incorporating physical as well as chemical and biological processes. 9 00:00:55,400 --> 00:01:05,360 And he's grown from the presence climate to such earlier or exotic environments as the snowball earth, the early Earth and early Mars. 10 00:01:06,140 --> 00:01:15,980 So he has been involved also in assessing the socio political aspects of climate change, and he was one of the lead authors in the third IPCC report. 11 00:01:16,880 --> 00:01:20,960 So his background includes an undergraduate degree in physics from Harvard, 12 00:01:21,170 --> 00:01:29,310 a fellowship at applied maths and theoretical physics at Cambridge, a Ph.D. in aeronautics and Astronautics from MIT. 13 00:01:29,960 --> 00:01:36,080 Faculty positions in meteorology at MIT, in Geosciences at Princeton, in the University of Chicago, 14 00:01:36,350 --> 00:01:44,090 and most recently, a sabbatical as the Carl the King Carl the 16th Gustaf professor at Stockholm University. 15 00:01:44,720 --> 00:01:54,860 He is a fellow of the AGU, is a fellow of the American Academy of Arts and Sciences, and he is a chevalier of the academic. 16 00:01:55,490 --> 00:02:01,550 My apologies to French speaker and an avid accordionist. 17 00:02:02,900 --> 00:02:09,950 His interest presently take him beyond the present earth system to the early Earth, to other planets, and to exoplanets. 18 00:02:09,950 --> 00:02:18,500 And while he professes to have so far limited himself to spiritual objects, he plans on exploring other shaped bodies in the near future. 19 00:02:19,250 --> 00:02:21,200 And we look forward to hearing what that means. 20 00:02:22,640 --> 00:02:29,330 So for the moment, he is going to tell us about the origin and evolution of exoplanet atmospheres and oceans. 21 00:02:29,360 --> 00:02:43,140 Okay. Thank you. Thank you very much. It's very nice to be here. The reference to non spherical objects is basically asteroids. 22 00:02:43,160 --> 00:02:47,450 I didn't think that there could be anything so interesting about objects without an atmosphere, 23 00:02:47,450 --> 00:02:51,410 but there's as since I've come here, the asteroids have started to look more and more interesting. 24 00:02:51,560 --> 00:02:55,430 But in this talk, it will be all or all spherical objects. 25 00:02:55,430 --> 00:03:01,160 I provided my talk with a kind of subtitle or re title, The Geology of Planetary Atmospheres. 26 00:03:01,460 --> 00:03:07,280 This this is a lecture series on planetary geology. 27 00:03:07,550 --> 00:03:15,980 And as I've gotten more and more involved in exoplanets, I realised that that the the boundaries between geology, 28 00:03:15,980 --> 00:03:24,710 between processes that we think of as involving rocks and processes that we think of as involving ices or clouds or atmospheric substances, 29 00:03:25,010 --> 00:03:27,650 those those boundaries have gotten more and more blurred. 30 00:03:27,950 --> 00:03:35,450 And various questions that we're beginning to treat in atmospheric sciences and planetary atmospheres start to look more and more 31 00:03:35,870 --> 00:03:44,570 geological and need to draw more and more on bodies of knowledge that are traditionally held in in geology and earth science departments. 32 00:03:44,960 --> 00:03:55,400 I want to I want to acknowledge my collaborators funding whose might me get that cursor out of the way? 33 00:03:56,810 --> 00:04:00,890 My collaborator funding, who is one of, is my graduate student, 34 00:04:01,730 --> 00:04:08,570 funded by the NASA's Astrobiology Institute and my recent post-doc, Robin Wordsworth, who's now on the faculty of Harvard. 35 00:04:08,570 --> 00:04:10,490 But who both of them collaborate, 36 00:04:10,760 --> 00:04:18,739 contributed a great deal to many of the papers and results that I'm going to be talking about today and the funding for a lot of this work earlier. 37 00:04:18,740 --> 00:04:25,430 Part of this work came from the Virtual Planetary Laboratory, one of NASA's Astrobiology Institutes. 38 00:04:26,240 --> 00:04:29,600 So this is the canonical scatterplot. 39 00:04:29,600 --> 00:04:38,990 Just to give you an idea of the greatly expanding territory we have for planetary geology, we used to have just the solar system to think about, 40 00:04:39,620 --> 00:04:43,819 but now we have a vast number of new objects about which we're learning more and more, 41 00:04:43,820 --> 00:04:47,090 which knowing the existence of these objects is quite interesting. 42 00:04:47,420 --> 00:04:53,270 Even this graph is a little bit outdated. Is this goes back to 2011, there quite a lot more dots in here. 43 00:04:53,450 --> 00:05:03,950 But just to situate you generally in terms of the range of different temperatures and compositions, we may be dealing with this this axis. 44 00:05:04,550 --> 00:05:14,570 This axis is the is the amount of energy received from the planets star normalised to how much energy the earth receives from the sun at one. 45 00:05:14,840 --> 00:05:20,930 So anything along this line one would have an earth like temperature if it had an earth like atmosphere. 46 00:05:21,140 --> 00:05:29,570 And this is on a long plus that we're going out two factors of 10,000 here and 1/1000 and 1/1000 over here then. 47 00:05:30,740 --> 00:05:41,030 So this is think of this is roughly temperature. This is this axis here is the radius of the planet in units of Earth Radio, either five Earth radii. 48 00:05:41,270 --> 00:05:49,639 And that provides that provides a window into that provides a window into the composition because things that are big things 49 00:05:49,640 --> 00:05:56,780 that are sufficiently big are or are certain to be hydrogen dominated because hydrogen is the only thing abundant hydrogen, 50 00:05:56,780 --> 00:05:59,750 helium things that are abundant enough to make something that big. 51 00:05:59,900 --> 00:06:05,540 As you get into these smaller things, you have the possibility for a for more rocky compositions. 52 00:06:05,840 --> 00:06:14,270 And so now we found that some of these smallish things actually have low densities density similar to what water would be if you squeezed it. 53 00:06:14,270 --> 00:06:18,560 So there are a lot of surprises all along, all along the way. 54 00:06:18,860 --> 00:06:27,139 But I want to focus a lot of the possibilities for planetary geology come from the fact that we now know a lot of planets, atmospheric geology, 55 00:06:27,140 --> 00:06:30,620 that we now know a lot of planets in the range where we need to think about the 56 00:06:30,620 --> 00:06:35,780 composition of atmospheres that are that are not necessarily hydrogen dominated. 57 00:06:35,990 --> 00:06:43,190 But the other other cases where we have to think about planetary geology or atmospheric geology is how do these very hot things, 58 00:06:43,190 --> 00:06:47,630 even gas giants, these planets are hydrogen dominated, 59 00:06:47,780 --> 00:06:53,899 but they're so hot that the cloud forming materials are things like institute that we that we 60 00:06:53,900 --> 00:06:59,840 would think of or even iron vapour that we would normally think of as as minerals on on earth. 61 00:07:00,830 --> 00:07:09,980 And each of these dots is one, one planet candidate from the from the Kepler planetary detection detection mission. 62 00:07:10,310 --> 00:07:15,080 And so you can see we're actually edging into seeing more and more of these earth sized things. 63 00:07:15,350 --> 00:07:21,499 And so and in some cases we can even characterise some things about the atmosphere we can characterise 64 00:07:21,500 --> 00:07:26,300 in many cases the density of these objects which gives us another window on the composition. 65 00:07:26,930 --> 00:07:35,930 And so, so the, the, the things get especially interesting for, think for planets that are, are more that are smaller and potentially rocky. 66 00:07:36,200 --> 00:07:37,130 So these are some of. 67 00:07:37,580 --> 00:07:45,080 And there's a particular interest in planets that are in the so-called habitable zone, which should be called the potentially habitable zone. 68 00:07:45,500 --> 00:07:54,320 These are planets that are that are that are at a distance from their star, where given the right kind of atmosphere, 69 00:07:54,950 --> 00:07:58,820 they could have temperatures that would support liquid water at the surface of the planet. 70 00:07:59,540 --> 00:08:05,030 And the habitable planets, the possibly habitable planets, 71 00:08:05,270 --> 00:08:12,590 really are generally thought of as being the smaller ones which could happen, which have the potential to have a rocky surface. 72 00:08:12,860 --> 00:08:16,910 Jupiter, a Jupiter, a gas giant could have habitable temperatures. 73 00:08:17,150 --> 00:08:23,690 But that but biologists tend to think that you need some kind of substrate for life to evolve on at least initially. 74 00:08:24,020 --> 00:08:30,650 And so one doesn't think of gas giants, even with the right temperature as having as having a habitable layer. 75 00:08:30,800 --> 00:08:38,480 So these are all the small planets in what is generally called the habitable zone that have been found just by the Kepler mission alone. 76 00:08:38,780 --> 00:08:44,700 They're quite a lot of them there. These are the ones around stars. 77 00:08:44,740 --> 00:08:50,620 These are those are main sequence stars that have a surface temperature like the sun, a mass similar to the sun. 78 00:08:50,630 --> 00:08:54,770 There's only one of those. And then K stars are slightly smaller, cooler stars. 79 00:08:55,010 --> 00:08:59,690 And then M stars are the most common form of star in the universe. 80 00:08:59,690 --> 00:09:06,440 And they provide terrific, terrific real estate for potentially habitable, habitable planets. 81 00:09:06,920 --> 00:09:14,809 There are relatively few m star and star planetary detections in Kepler receptor wasn't really configured to to look at M stars. 82 00:09:14,810 --> 00:09:19,520 It was worth configured to look at G stars, which are more which are like our sun. 83 00:09:19,800 --> 00:09:26,540 But these are very interesting planets. But so but although we call these, does that potentially have the potentially habitable zone? 84 00:09:26,990 --> 00:09:33,710 None of these planets would have a climate anything like Earth if they didn't have have the right kind of atmosphere. 85 00:09:33,750 --> 00:09:36,830 That doesn't have to be in it has the same kind of atmosphere as Earth. 86 00:09:37,100 --> 00:09:44,810 But there are some kinds of atmospheres that could give you conventional liquid water, habitable conditions and others which which which don't. 87 00:09:45,110 --> 00:09:51,920 And right now, we have very little information about whether any of these planets, except for Earth, has an atmosphere. 88 00:09:52,520 --> 00:09:56,570 And and that's the big breakthrough that's going to come in the near future. 89 00:09:56,780 --> 00:10:01,219 But even though we have very little data yet about how much about what kind of atmosphere, 90 00:10:01,220 --> 00:10:05,990 if any, these these habitable zone, these small habitable zone planets have, 91 00:10:06,470 --> 00:10:12,080 we can start thinking about we can start thinking about what kind of atmosphere they might have 92 00:10:12,380 --> 00:10:18,010 based on what we know about how atmospheres actually are made and in some ways in atmosphere. 93 00:10:18,080 --> 00:10:23,350 So why I call this one of the reasons I call this subject atmosphere. 94 00:10:23,390 --> 00:10:30,410 The geology of planetary atmospheres is that atmospheres are not something that a planet is endowed with at the beginning. 95 00:10:30,650 --> 00:10:38,479 It doesn't just come in and sit there. And monsters are actually an outgrowth of of what's happening in the interior of a planet. 96 00:10:38,480 --> 00:10:49,100 Atmospheres are very dynamic entities that that involve which sit between to search to sources and sinks. 97 00:10:49,790 --> 00:11:01,790 And so at the and so at the at the ground or and the interior, we have we have things that are outcast from the interior of the planet. 98 00:11:02,210 --> 00:11:10,760 So everything is so the amount of what's out guest is connected with subjects like volcanism, mantle dynamics and so forth. 99 00:11:10,760 --> 00:11:16,370 The chemistry of, of the, of the mantle and also the early planetary formation system, 100 00:11:16,370 --> 00:11:23,689 which determines which elements are segregated into a core and which ones are in a dynamic layer like a convecting mantle, 101 00:11:23,690 --> 00:11:26,929 which can in principle exchange or out gas into the interior. 102 00:11:26,930 --> 00:11:36,830 And you get things like water vapour, nitrogen, hydrogen, methane, carbon dioxide, outgassing from from the interior of a planet. 103 00:11:37,640 --> 00:11:47,150 You some of those things and the right conditions will condense into an ocean or dissolve in an ocean on the earth and perhaps other planets. 104 00:11:47,150 --> 00:11:51,440 You have thin continental crust, which can be subducted. And so the chemical reactions, 105 00:11:51,440 --> 00:11:56,809 notably the formation of carbonates that happens through silicate rock reactions and the continental 106 00:11:56,810 --> 00:12:02,570 crust can be subducted where the where some of those some of those volatiles are recycled. 107 00:12:02,570 --> 00:12:08,360 So you have all these interchanges with the surface, many of which are are affected strongly by life. 108 00:12:08,360 --> 00:12:14,120 If the planet has life. Then you've got atmospheric dynamics which determines things like how much 109 00:12:14,330 --> 00:12:18,740 water or other contemptible substances makes it up into the upper atmosphere. 110 00:12:19,280 --> 00:12:25,189 The vertical structure of temperature in the atmosphere, providing cold trap determines. 111 00:12:25,190 --> 00:12:32,719 And we'll see more of this later in the talk. Determines to a large extent whether any water vapour in our case makes it into the upper 112 00:12:32,720 --> 00:12:37,400 parts of the atmosphere where ultraviolet from the star can break it up into hydrogen. 113 00:12:37,420 --> 00:12:42,239 And an oxygen where after the hydrogen escapes to space, obviously can get oxygen, 114 00:12:42,240 --> 00:12:48,750 gets left behind and reacts with iron and sulphur and the crust can get bound up or then later eventually 115 00:12:49,230 --> 00:12:53,940 accumulate in the atmosphere and then later help by photosynthesis build up an oxygen atmosphere. 116 00:12:54,390 --> 00:13:01,140 So you've got all sorts of exchanges at this end where the atmosphere and the ocean interact 117 00:13:01,140 --> 00:13:05,700 with the crust in the interior and then you've got loss of substances to space on. 118 00:13:06,210 --> 00:13:11,970 For earth like conditions, it's really only hydrogen that can be lost very rapidly and with a good flux. 119 00:13:11,970 --> 00:13:13,260 Other things do trickle out. 120 00:13:13,440 --> 00:13:20,909 But on hotter planets or planets that are bombarded with more ultraviolet or more stellar winds, even carbon can be lost from that. 121 00:13:20,910 --> 00:13:26,910 From the top. The planet's evolving by losing volatiles from the top, it's exchanging with the crust. 122 00:13:27,180 --> 00:13:30,660 What you sequester in the crust determines a lot about what is shielded, 123 00:13:30,780 --> 00:13:34,770 what can be shielded from loss up here, what can be generated if you lose atmosphere. 124 00:13:35,070 --> 00:13:41,070 But you also have volatiles coming in from space, comets, whatever, bring in volatiles. 125 00:13:41,820 --> 00:13:49,890 So it's a to a change up there as well. And and and so in between where we live is, is, is this atmosphere. 126 00:13:50,550 --> 00:13:53,840 But to some extent, if you know something about what goes out, what can go out here, 127 00:13:53,870 --> 00:14:01,199 if you know enough about what the planet is made out of, you should be able to reconstruct what kinds of things are in the atmosphere. 128 00:14:01,200 --> 00:14:03,720 And so in the game with exoplanets right now, 129 00:14:03,940 --> 00:14:11,579 we're largely we're largely at the stage not having enough data to directly observe exoplanet atmospheres for small planets. 130 00:14:11,580 --> 00:14:15,780 In most cases, with the exception of one that I will show you, 131 00:14:16,230 --> 00:14:20,910 we are playing the game of of knowing something about what the composition of the system is 132 00:14:20,910 --> 00:14:26,309 by looking at the spectrum of the star and trying to figure out what range of atmospheres 133 00:14:26,310 --> 00:14:30,840 a planet could build given its temperature because we know its orbit and from that we can 134 00:14:30,840 --> 00:14:36,600 infer its temperature and try to find a self-consistent atmosphere and temperature model. 135 00:14:36,990 --> 00:14:41,790 So this is the universe, as it appeared to astrophysicists, 136 00:14:41,790 --> 00:14:49,950 as is generally thought of by astrophysicists, the primarily the universe is hydrogen and helium. 137 00:14:50,310 --> 00:14:54,240 The Big Bang did make a little bit of lithium and beryllium, which gets tense. 138 00:14:54,270 --> 00:15:01,980 It tends to be rather quickly consumed in stars. But you can, not far wrong in just taking the universe is originally just hydrogen and helium. 139 00:15:02,310 --> 00:15:06,629 And then there are all these other things. Everything else is called metals. 140 00:15:06,630 --> 00:15:13,290 And so that's that's astrophysical geology as it was generally conceived in the term 141 00:15:13,290 --> 00:15:18,840 metallicity in a system which characterises various planetary systems or stars, 142 00:15:19,440 --> 00:15:26,670 refers to the ratio of these not of these things heavier than helium two to hydrogen, to hydrogen and helium. 143 00:15:27,030 --> 00:15:30,510 It's not very geological, but it's the beginning of a kind of kind of geology. 144 00:15:30,810 --> 00:15:37,380 But now that we have exoplanets in the astrophysical literature, you start to see this other substance, which is called rock. 145 00:15:38,400 --> 00:15:43,140 And, and so then we get a little bit closer to, to to geology. 146 00:15:44,010 --> 00:15:52,919 And so so there's there's increasing interest in what this substance is and in various 147 00:15:52,920 --> 00:15:58,260 planetary systems and how it interacts with what kinds of atmospheres you might have. 148 00:15:58,260 --> 00:16:03,780 Now in terms of of where this where these metals come from, the the metals, 149 00:16:03,780 --> 00:16:07,950 as geologists think of them and and rock as geologists would think of them, 150 00:16:08,550 --> 00:16:14,160 that that's all a matter of nucleosynthesis, which I'll get to in the next slide. 151 00:16:14,160 --> 00:16:17,970 But, but just as an example of the sort of things that, you know, 152 00:16:18,000 --> 00:16:23,610 elements that you use that you see or elements of substances that you assemble a planet with, 153 00:16:23,610 --> 00:16:27,030 you've got things that we conventionally think of as metals, 154 00:16:27,030 --> 00:16:34,620 like the like sodium and iron and nickel, etc., which tend to segregate into into a very dense core. 155 00:16:34,800 --> 00:16:40,410 There are some other things that actually make that are metals like magnesium or calcium or iron that 156 00:16:40,410 --> 00:16:50,580 make that make compounds with silicate and make up the bulk of what we normally consider rock silicate. 157 00:16:50,720 --> 00:16:58,200 The earth is mostly a silicate silicate envelope around a metallic iron nickel core with various contaminants. 158 00:16:58,890 --> 00:17:09,030 And these kinds of things here, like calcium carbonate and and silica and various silicates, make up what we can eventually consider to be rock. 159 00:17:09,030 --> 00:17:19,260 But actually there are these other things that we that on earth we think of as atmospheric constituents into CO2, carbon monoxide, water, methane. 160 00:17:19,890 --> 00:17:33,510 But if you're on if you're on Triton, which is a satellite of Pluto, that that has a temperature of maybe 80 Kelvin at the surface, nitrogen isn't. 161 00:17:34,410 --> 00:17:42,730 Well, if you are Triton. What? There is no more volatile on Triton than than quartz is on earth. 162 00:17:43,090 --> 00:17:48,280 So water is a rock on Triton and water is basically a rock on, on on Titan. 163 00:17:48,550 --> 00:17:54,070 The satellite of Saturn is as as well. And so. 164 00:17:54,340 --> 00:17:57,459 And on the other hand, if you get to some of these really hot exoplanets, 165 00:17:57,460 --> 00:18:02,590 the hot Jupiters and the hot rocky planets, I'm going to show you many of these things. 166 00:18:02,830 --> 00:18:10,000 For vapours that can form quite substantial rock vapour atmospheres and condense and form clouds which are actually observable, 167 00:18:10,540 --> 00:18:15,969 observable even from from the earth by various spectroscopic techniques. 168 00:18:15,970 --> 00:18:24,520 And so, so really as we expand our range of temperatures, we have to generalise your thinking about what we actually mean by a rock or mineral, 169 00:18:24,520 --> 00:18:32,919 because in essence, the things that we call rock or rocks or minerals on earth there are nothing different from a form of ice. 170 00:18:32,920 --> 00:18:39,069 And ice is a rock at a at happens to be at a certain temperature range that we tend to think make sense, 171 00:18:39,070 --> 00:18:45,219 make us call it ice and and so so so the boundary between these things which 172 00:18:45,220 --> 00:18:49,570 may be in the atmosphere or may be condensed in other cases and form oceans, 173 00:18:49,570 --> 00:18:58,030 there's a lot of interest in carbon dioxide oceans. The boundary between these these and these things is not the basis of physical properties. 174 00:18:58,030 --> 00:19:04,450 It's just a matter of what what temperature range you're thinking about now in terms of where these things come from. 175 00:19:05,590 --> 00:19:09,729 It's all a matter of nucleosynthesis in stars. 176 00:19:09,730 --> 00:19:19,000 In the beginning, you basically have hydrogen mainly and and the first generation stars don't have any of this stuff that makes planets interesting. 177 00:19:19,000 --> 00:19:24,130 And it can can possibly get can make earth like planets or make us make any form of life. 178 00:19:24,430 --> 00:19:34,930 You just have you basically have hydrogen being fused into helium and first generation stars sufficiently massive stars make everything, 179 00:19:35,080 --> 00:19:40,659 loosely speaking, make everything up until iron all these fun things that we know and love. 180 00:19:40,660 --> 00:19:45,490 Carbon, oxygen, nitrogen, silicon up to, up to, up to iron. 181 00:19:46,030 --> 00:19:48,730 You don't actually need supernovas to make those things. 182 00:19:48,970 --> 00:19:55,900 Some of those so heavy elements of those metals, as they're called in rock forming substances, 183 00:19:56,110 --> 00:20:05,020 can just can just be blown off by gas, by a by a gas, just the wind, stellar winds, basically outgassing from stars, as it were. 184 00:20:05,740 --> 00:20:07,629 So some gets out into the rest of the universe. 185 00:20:07,630 --> 00:20:17,740 But a lot of it a lot of a lot of the this these heavier materials only easily get dispersed through through the rest of the galaxy, 186 00:20:18,190 --> 00:20:23,500 through supernovas. A supernova is not only help to disperse all the other stuff that is made, 187 00:20:24,100 --> 00:20:30,610 but they also create heavier elements like uranium and thorium, which exist in the earth in very small quantities, 188 00:20:30,910 --> 00:20:39,550 but are part of the engine that makes plate tectonics go, that makes mantle convection go, drive volcanism and so forth, and then all those things. 189 00:20:39,760 --> 00:20:46,570 So all those things get into some nebula that condenses into planets. 190 00:20:46,840 --> 00:20:59,559 But but the galaxy is not well-mixed. And so the particular recipe, the particular combination of elements we have on Earth is not is not universal. 191 00:20:59,560 --> 00:21:08,110 And so, so, so we have to actually learn how to think about how rocky planets might behave if you had different elements in the mix. 192 00:21:08,770 --> 00:21:15,700 But this is just an example. This is an estimate. It's hard to actually the estimate what what solar composition really is. 193 00:21:15,700 --> 00:21:24,610 But if you assume that what's in the outer part of the sun is typical of what's what the it originally in the in the in the solar 194 00:21:25,540 --> 00:21:37,750 and the nebula this this is this is abundance relative abundance with silicon scale to ten to the sixth on a low on a long scale. 195 00:21:38,350 --> 00:21:43,720 And so this is this is what's called solar composition or at least an estimate of solar composition. 196 00:21:44,110 --> 00:21:47,680 You can see it, of course, you have hydrogen and helium are way up there. 197 00:21:47,980 --> 00:21:57,430 But but carbon, nitrogen, oxygen, magnesium, silica, sulphur, they're all very abundant. 198 00:21:57,550 --> 00:22:01,959 They're all abundant. And so so all these things that we used to make. 199 00:22:01,960 --> 00:22:11,920 So there's a lot of oxygen around. We make silicates out of combinations of things of of calcium, magnesium, silicon and oxygen. 200 00:22:11,920 --> 00:22:13,000 There's plenty of that around. 201 00:22:13,630 --> 00:22:23,450 But then then we have these things that form many of the key atmospheric gases for Earth, like temperatures, carbon, nitrogen and oxygen. 202 00:22:23,450 --> 00:22:28,120 And there's a competition when you're building a planet between where the oxygen goes, 203 00:22:28,120 --> 00:22:36,370 most of our oxygen winds up and various silicates and you're that's points up in the cell bulk silicate bulk silicate earth. 204 00:22:37,510 --> 00:22:44,319 But then there's then these things go through the hydrogen mostly winds up in the star and then the giant 205 00:22:44,320 --> 00:22:49,150 planets and then whatever's left behind is what you make your what you can make a rocky planets out of, 206 00:22:49,480 --> 00:22:54,910 plus some little contamination, some debris has of giant hydrogen dominated. 207 00:22:55,120 --> 00:22:58,059 We could have a lot of silicates in there in their atmosphere, 208 00:22:58,060 --> 00:23:07,320 but we have to learn how to think about how what different ways planets could be assembled if if we had systems which had more wear carbon. 209 00:23:07,330 --> 00:23:11,080 So I'm going to add more carbon, for example, relative to oxygen. 210 00:23:11,380 --> 00:23:18,010 Okay. Now I'll come back later to the difference to the difference between solar composition and 211 00:23:18,220 --> 00:23:24,220 what we think made up the planetesimals that the rocky planets were put together out of. 212 00:23:24,580 --> 00:23:33,790 So I'm going to tell three stories. I'm going to tell three, three different stories that in some sense can be considered atmospheric geology. 213 00:23:34,930 --> 00:23:40,000 The first is a story where the atmosphere is geological, 214 00:23:40,540 --> 00:23:48,520 where the atmosphere itself is is dominantly made of various kinds of rock vapours or things that we conventionally consider rocks on earth. 215 00:23:49,090 --> 00:23:54,070 And largely based on one fascinating object 55 can create. 216 00:23:55,600 --> 00:24:01,630 And then I'm going to talk spent quite a bit of time talking about nitrogen, 217 00:24:02,260 --> 00:24:09,399 which in the Earth's atmosphere is represented dominantly by, by and too, but which is a but, 218 00:24:09,400 --> 00:24:17,320 which undergoes a lot of which which has a lot of other chemical forms largely created by both forms of life on earth, 219 00:24:17,620 --> 00:24:27,430 but which play a big role in, in the nitrogen cycling on the Earth and also in the in in the way life works all together. 220 00:24:27,670 --> 00:24:30,010 And nitrogen is a very mysterious substance, 221 00:24:30,010 --> 00:24:40,690 but it turns out to be way more important to habitability and making a planet that is conceivably earth like than than is often, often considered. 222 00:24:41,260 --> 00:24:46,210 It's a very difficult substance to think about. And then I'm going to tell a very rich story of carbon. 223 00:24:46,240 --> 00:24:50,550 Carbon is the most familiar story in the last couple of months. 224 00:24:50,560 --> 00:24:57,220 So many interesting things came out about these two stories that I decided to truncate, 225 00:24:57,550 --> 00:25:05,440 what I was going to say about carbon and just tell you basically one important thing where the one of the many ways that the carbon cycle, 226 00:25:05,950 --> 00:25:13,810 that the deep carbon cycle comes into fundamentally into notions of planetary habitability. 227 00:25:15,010 --> 00:25:17,889 So there's going to be a very a very abridged story. 228 00:25:17,890 --> 00:25:26,020 But this is already a very, you know, a lot of carbon cycle stuff is will already be fairly familiar to many of you here. 229 00:25:26,020 --> 00:25:30,999 And I just and so I will talk about the less familiar the less familiar story. 230 00:25:31,000 --> 00:25:38,770 And of course, the carbon cycle story is one that's still being written by us as we massively perturb the carbon cycle on Earth. 231 00:25:38,780 --> 00:25:45,280 We're really a force of more than geological proportions in terms of the way that the normal carbon cycle, 232 00:25:46,120 --> 00:25:52,150 deep carbon cycle would work on a on a cell, a rocky planet with silicate carbonate. 233 00:25:52,730 --> 00:25:58,740 Okay. So now it's going to. Magma oceans and rock vapour atmospheres. 234 00:26:01,510 --> 00:26:10,510 So the planet that simulates that, that's kind of the poster child for for this subject of geology of atmospheres, 235 00:26:10,510 --> 00:26:14,720 rock paper atmospheres is is 55 cancri. 236 00:26:14,740 --> 00:26:24,610 Most of the new planets we work on don't have names, and there isn't even a real convention for naming, for actually giving these planets real name. 237 00:26:24,620 --> 00:26:28,779 So they're named according to they're named according to what star they're around. 238 00:26:28,780 --> 00:26:32,950 So 55 Cancri is a star in the constellation of cancer. 239 00:26:33,820 --> 00:26:39,160 It's not quite visible to the naked eye, I don't think. And but it's right here. 240 00:26:39,160 --> 00:26:47,870 You can find if you find Gemini and you find constellation of cancer, the crab right up here by this point is is the star. 241 00:26:47,870 --> 00:26:52,779 And there are there are five planets known in this system, 242 00:26:52,780 --> 00:27:02,049 which the one I'm going to talk about is is E and this is not anybody's idea of a habitable world, 243 00:27:02,050 --> 00:27:07,330 but it's nonetheless a very something that illuminates our picture of planets quite well. 244 00:27:08,080 --> 00:27:16,149 It's actually and to let you know a little bit more about this, the system 55 Cancri is actually a double star system. 245 00:27:16,150 --> 00:27:19,600 It turns out that planets are very common around double stars. 246 00:27:20,830 --> 00:27:29,020 And so 55 Cancri actually is a is a slightly cooler g type main sequence star, 247 00:27:29,200 --> 00:27:39,339 a little bit cooler than the sun has a photosphere temperature of 50 about 5400 kelvin and it has a companion quite a long way away, 248 00:27:39,340 --> 00:27:47,290 which is an m dwarf, an end sequence low mass star 55 B This is not actually close enough to significantly 249 00:27:47,290 --> 00:27:52,960 perturb the orbits or or provide any illumination for for for these planets in here. 250 00:27:53,680 --> 00:27:58,600 But so here's a star that is basically basic as a luminosity almost as much as the sun. 251 00:27:58,600 --> 00:28:09,070 So it's a bright star and 55 Cancri e is orbiting so close that its orbital period is three quarters of an Earth Day. 252 00:28:09,100 --> 00:28:13,640 So mercury is a hot place. It has an orbit of 80, 88 Earth Day. 253 00:28:13,660 --> 00:28:22,030 So here's the thing that is is so is is sitting whizzing around once every three quarters or three quarters of an Earth Day. 254 00:28:22,780 --> 00:28:25,540 And then so it's in a very it's in a very close orbit. 255 00:28:25,540 --> 00:28:34,630 And in fact, the the the at the distance that's implied by its orbital period, we get the distance from Newton's law and the orbital period. 256 00:28:35,500 --> 00:28:46,809 The, the, the, it's so close that it's the illumination, the amount, this flux of stellar energy going into going towards the planet is, 257 00:28:46,810 --> 00:28:57,310 is more than 4000 times the more than 4000 times the watts per square metre that the earth gets from 258 00:28:57,310 --> 00:29:04,299 the sun and and using the Steffen Boltzmann law sigma cheat of the fourth to solve for temperature. 259 00:29:04,300 --> 00:29:08,110 Even if you had no interesting atmosphere, a greenhouse effect or anything like this. 260 00:29:08,500 --> 00:29:15,879 The temperature in equilibrium with the sub stellar point it would be about 3000 kelvin so it's it's similar. 261 00:29:15,880 --> 00:29:19,570 It's above the liquid. It's above the melting point of most kinds of rocks. 262 00:29:19,930 --> 00:29:25,390 What's more, planets that are this close to their star have such strong tidal stresses that 263 00:29:25,750 --> 00:29:30,370 unless we are completely wrong about all sorts of notions of tidal stress, 264 00:29:30,370 --> 00:29:37,600 that they're almost certainly tied locked to the to the to the star, just like the moon is tied like to the earth. 265 00:29:37,990 --> 00:29:46,960 So and it has a fairly circular orbit. So so there's one point on this planet, one geographical point where where it's noon all the time, 266 00:29:47,890 --> 00:29:51,010 and there's a nightside which never gets any stellar energy. 267 00:29:51,760 --> 00:29:58,480 And so that actually makes the sub stellar point especially hot because you're not losing if it were if you were in our atmosphere. 268 00:29:58,990 --> 00:30:06,110 We'll talk about that issue soon. If there were no atmosphere, you don't lose any energy by bye bye. 269 00:30:06,130 --> 00:30:10,570 Heat flowing away to the night side of the planet or cooler parts of the planet. 270 00:30:11,230 --> 00:30:18,370 And and so so the picture of this planet is that you would have you would have a permanent magma ocean. 271 00:30:19,030 --> 00:30:23,259 You have a permanent magma ocean on the on the day side. 272 00:30:23,260 --> 00:30:29,049 And who knows what's on the nightside. But we now have some idea of what the temperature of the nightside is from very recent observations. 273 00:30:29,050 --> 00:30:36,370 Just it just came out in the last two months. This in terms of the size and the likely composition, it's two earth radii. 274 00:30:36,400 --> 00:30:44,170 So it's in a range of of radio sizes that are generally called super-Earths and it's masses eight Earth masses. 275 00:30:44,170 --> 00:30:52,879 Actually, it's been upgraded somewhat. The density with with this mass and radius is a little bit light for a rocky planet. 276 00:30:52,880 --> 00:31:00,050 It couldn't really be compatible with much of an iron core some of the initial thoughts on this planet or that it was actually. 277 00:31:00,130 --> 00:31:09,730 The two, the density was too low to even be pure silicate and that it either had either was mostly silicate with some kind of a massive 278 00:31:09,730 --> 00:31:17,980 get a gaseous envelope or that it was to bring down the mean density or it might have been pure carbon or carbon dominated, 279 00:31:17,980 --> 00:31:23,080 which was cute because if you make a planet mean the end of carbon, the interior is one big diamond. 280 00:31:23,830 --> 00:31:27,330 And so reporters like all of that recently, the masses, 281 00:31:27,660 --> 00:31:35,350 the density has been upgraded a bit to where maybe this thing is not carbon dominated, but could be a silicate dominated thing. 282 00:31:35,350 --> 00:31:40,630 But it's still a it's a fairly low density, a fairly low density density object. 283 00:31:42,310 --> 00:31:48,280 And so so the question is, okay, if this has a magma ocean, permanent magma ocean on the dayside, 284 00:31:48,280 --> 00:31:53,290 is the magma ocean just some isolated thing sitting there radiating to space? 285 00:31:54,040 --> 00:31:57,310 Or is or will it generate an atmosphere of its own? 286 00:31:57,640 --> 00:32:03,860 And this is where you have to go to someone who knows experimental petrology knows how 287 00:32:03,990 --> 00:32:11,590 how to how to deal with equilibrium of vapours with with melts of geological substances. 288 00:32:11,590 --> 00:32:21,940 Because in temperatures that we in moderate temperatures that we're used to in terms of oceans, like if you heat up water, 289 00:32:21,940 --> 00:32:30,219 if you have water at water at 300 kelvin or so, the vapour that's an equilibrium with water at 300 Kelvin is is water vapour. 290 00:32:30,220 --> 00:32:40,120 You get water vapour out if you have CO2 at at temperatures of around 300 Kelvin, the the we're actually a little bit less than 300 Kelvin. 291 00:32:40,120 --> 00:32:43,120 Let's say the what you have out here is the CO2 atmosphere. 292 00:32:43,300 --> 00:32:47,230 Of course, if you get if you put CO2 in a 2000 Kelvin atmosphere, 293 00:32:47,230 --> 00:32:54,190 it starts to thermally dissociate and you'll get mostly carbon monoxide and oxygen and even water can thermally dissociate. 294 00:32:54,490 --> 00:33:00,190 But this is even more so this business of of dissociation of the components, 295 00:33:00,190 --> 00:33:09,190 the molecular components of the melt is even more significant when you're talking about these fairly complex silicate melts. 296 00:33:09,580 --> 00:33:14,409 And so if and so if you were to take something that was representative of the 297 00:33:14,410 --> 00:33:18,430 bulk silicate earth and you have various compounds like this in the melt, 298 00:33:18,430 --> 00:33:23,080 you put it at 3000 Kelvin even though you have say silica in here, 299 00:33:23,800 --> 00:33:34,750 what actually out gases is not CO2, but most of the vapour that you get out is a silicon oxide and you make some oxygen, 300 00:33:34,750 --> 00:33:41,440 O2 and things like that and that even if you have two or three, you would get quite a lot of iron vapour out and things like that. 301 00:33:41,590 --> 00:33:53,709 And the, the, this is the standard stuff of, of a lot of, of Cosmo chemistry and, and experimental petrology and so forth. 302 00:33:53,710 --> 00:34:03,730 And, and there aren't that many experiments on the directly looking at the composition of rock vapours in equilibrium with melts. 303 00:34:03,730 --> 00:34:03,969 In fact, 304 00:34:03,970 --> 00:34:10,629 I was just talking to the experimental Petrology group today about the possibility that you might be able to directly look at some of these things. 305 00:34:10,630 --> 00:34:15,490 But the inference of what composition you get in the rock vapour atmosphere over a 306 00:34:15,490 --> 00:34:22,299 magma ocean have been mostly done in terms of have been mostly done by indirectly 307 00:34:22,300 --> 00:34:26,650 by measuring gives free energies in various ways and then and then minimising 308 00:34:26,650 --> 00:34:33,070 Gibbs Gibbs energy to figure out what vapours you have in equilibrium with a melt. 309 00:34:33,070 --> 00:34:39,760 And so this is the so this is the generalisation, as it were, of the causes factor in relationship. 310 00:34:39,760 --> 00:34:44,050 We used to figure out how much humidity you have in the in the Earth's atmosphere. 311 00:34:44,800 --> 00:34:53,680 And so this is temperature here. And if I just pick out a couple lines here so that this this red line is is is cellulose. 312 00:34:54,130 --> 00:35:07,120 So this is a this is more or less bulk silicate earth composition at temperatures of of to of around 2500 Kelvin the SIO which is 313 00:35:07,120 --> 00:35:15,760 this red line way dominates over silica CO2 is a logarithmic scale which is about an order of magnitude lower and vapour pressure. 314 00:35:16,120 --> 00:35:24,939 So you actually get mostly soil. That's quite important from the standpoint of observations and also the climate because CO2 is like CO2, 315 00:35:24,940 --> 00:35:30,010 it's a tri atomic molecule, it's a good greenhouse gas, it's a hot greenhouse gas, it's a good greenhouse gas. 316 00:35:30,400 --> 00:35:39,010 SIO being diatomic has very well separated spectral lines and so like something like H.f. or SEO, it has very distinct spectral characteristics, 317 00:35:39,010 --> 00:35:46,570 character, but doesn't, doesn't actually doesn't actually block much trapped much infrared because the lines are too well separated. 318 00:35:46,810 --> 00:35:52,990 But down here actually sodium with something like a box on earth, the dominant atmosphere is sodium. 319 00:35:52,990 --> 00:36:00,010 At 2500 Kelvin, you generate you generate something like a 200 millibars sodium vapour atmosphere. 320 00:36:00,360 --> 00:36:06,599 When you get up to 3500 Kelvin, it's the SIO is the silicon oxide that that dominates the atmosphere. 321 00:36:06,600 --> 00:36:13,740 And at 3500 Kelvin you sow on 55 cancri you'd expect something like a one bar, 322 00:36:14,310 --> 00:36:19,590 something like a one bar Soho atmosphere with a little bit of sodium mixed in. 323 00:36:19,590 --> 00:36:25,470 And the picture is schematic picture of 55 cancri with something like this, 324 00:36:26,310 --> 00:36:29,970 all the volatiles, carbon and so forth at these temperatures should have escaped. 325 00:36:30,960 --> 00:36:37,860 And and then you you are cooking out SIO and sodium and then smaller amounts of these other things which then 326 00:36:37,860 --> 00:36:43,830 stream away because there's high pressure here at the saturation vapour pressures on that previous graph. 327 00:36:44,670 --> 00:36:50,880 They go up, they cool off by adiabatic cooling, you make clouds, but the clouds are made of SIO and sodium and so forth. 328 00:36:51,810 --> 00:37:02,370 And they're basically expanding into a vacuum. And if the pressure gradient is big enough, you get a supersonic flow from from the magma ocean. 329 00:37:02,520 --> 00:37:08,879 And most of this stuff then condenses out before it gets very far to the Nightside in the Nightside is is really cold, 330 00:37:08,880 --> 00:37:13,680 maybe as low as 100 kelvin or something like that, depending on the internal, internal heat flux. 331 00:37:13,680 --> 00:37:20,880 And so so there are mathematical models of this kind of rock vapour atmosphere which actually are quite analogous to a much colder, 332 00:37:21,480 --> 00:37:34,980 much colder situation in the solar system, SO2, sulphur dioxide at the temperatures of of EOE, the satellite IO actually generates local atmosphere. 333 00:37:35,010 --> 00:37:41,220 Is that snow out on to the surface and have supersonic flow from the source to their sinking condensation, 334 00:37:41,430 --> 00:37:47,160 which are mathematically very analogous to these things, except there more more components involved. 335 00:37:47,760 --> 00:37:53,940 There's a lot of interesting stuff to think about in terms of in terms of what this magma ocean actually does, 336 00:37:53,940 --> 00:37:57,840 how hard is it melt down in how to connect up to the interior flow and so forth? 337 00:37:58,050 --> 00:38:04,500 But you would have a lot of interesting patterns deposited on to the surface as you segregate, 338 00:38:04,500 --> 00:38:08,550 you fracture these various minerals and snow them out in different places, 339 00:38:08,760 --> 00:38:14,040 and then the oxygen make make a lot of oxygen when you do this, which actually doesn't condense out anywhere. 340 00:38:14,040 --> 00:38:20,879 And we tend to build up into an oxygen atmosphere if it doesn't escape to space, which is one of the calculations I'm gearing up to do. 341 00:38:20,880 --> 00:38:25,320 But now the reality on this planet is this is interesting enough. 342 00:38:25,350 --> 00:38:31,470 This is a very interesting sort of climate system, but the reality is even weirder. 343 00:38:31,740 --> 00:38:39,600 This this this was a result that just came out this year by the group at University College London. 344 00:38:39,930 --> 00:38:44,970 Now, this is a typical way that one tries to determine what's in the atmosphere of planets. 345 00:38:45,900 --> 00:38:53,370 The U. Of 55 cancri crosses in front of its star, and so it blocks some of the starlight. 346 00:38:53,640 --> 00:38:59,580 But you can also you can observe that transit. You can observe how much starlight is blocked at different frequencies. 347 00:38:59,580 --> 00:39:05,819 And so the planet looks bigger at some frequencies than others. And that's a measure of where the atmosphere absorbs or scatters. 348 00:39:05,820 --> 00:39:12,330 Well, and so this is this is a measure this is from from Hubble, I think. 349 00:39:12,330 --> 00:39:20,460 And the and they and the data are they are the vertical grey grey lines. 350 00:39:21,270 --> 00:39:29,790 And so this is the this is the the how much light is blocked in parts per million relative to the total starlight. 351 00:39:30,480 --> 00:39:39,120 And it ramps up, it ramps up this, this, this red line is what you would expect for a pure hydrogen atmosphere. 352 00:39:39,840 --> 00:39:45,900 This green line is what you expect with it for a pure hydrogen atmosphere that that that carries 353 00:39:46,110 --> 00:39:51,600 some additional solar composition contaminants up out altitudes where you can absorb it, 354 00:39:52,470 --> 00:39:55,830 where you can observe it by this kind of by this kind of technique. 355 00:39:56,130 --> 00:39:59,400 And it's very the data is not great. 356 00:39:59,400 --> 00:40:00,510 The error bars are pretty big, 357 00:40:00,510 --> 00:40:08,800 but it's still more compatible with having a low molecular weight atmosphere like hydrogen than any other thing anyone's been able to to think about. 358 00:40:08,820 --> 00:40:17,580 That's really very, very hard to swallow because at these temperatures and this close to a star, hydrogen should have escaped long ago. 359 00:40:18,000 --> 00:40:21,540 So so there are physical problems with the hydrogen atmosphere. 360 00:40:21,930 --> 00:40:28,980 And that was bad enough as that was perplexing enough. How can you actually keep a hydrogen atmosphere on something like this? 361 00:40:29,820 --> 00:40:32,730 And then then they've got even more puzzling. 362 00:40:33,150 --> 00:40:43,590 Paper by Bryce Demaree came out just about a month ago in which by looking at the emission, the thermal emission from the planet as it's going around, 363 00:40:44,070 --> 00:40:51,510 as it's going around in its orbit, you see different you see the planet from different angles at different at different times in its orbit. 364 00:40:51,510 --> 00:40:54,810 So you get to see the different proportions of dayside versus nightside. 365 00:40:55,230 --> 00:40:59,970 There's this dot here is the sub stellar point, which should be. 366 00:41:00,090 --> 00:41:08,520 Hottest point on the planet. This and then these are the temperatures, the north south, average temperatures on the planet. 367 00:41:09,190 --> 00:41:15,299 The people who make these kinds of phase curve measurements like to plot them on a map. 368 00:41:15,300 --> 00:41:17,459 There's no actual resolution in this direction. 369 00:41:17,460 --> 00:41:23,190 It's just a way of trying to make you think more about what you know, what you're looking at on the planet here. 370 00:41:23,820 --> 00:41:34,200 And and so the the hot spot is phase shifted from relative to this sub stellar point, which means that there has to be heat transport, 371 00:41:34,200 --> 00:41:41,010 there has to be systematic heat transport over in this direction, which is also also demands a fairly massive atmosphere to move that heat around. 372 00:41:41,190 --> 00:41:46,230 And it has to that atmosphere has to be for transporting heat quite effectively because 373 00:41:46,440 --> 00:41:52,319 at temperatures of around 3000 Kelvin segment to the fourth is radiating so fast. 374 00:41:52,320 --> 00:41:56,700 You've got to move heat fast to make up for just how quickly the atmosphere is cooling off. 375 00:41:56,910 --> 00:42:04,469 What's more, the nightside is 1300 Kelvin and the Nightside gets no stellar radiation at all, has no energy source. 376 00:42:04,470 --> 00:42:08,190 The energy source by diffusion of heat from the interior is trivial. 377 00:42:08,820 --> 00:42:16,920 And so somehow you have to move energy to the nightside also to keep the temperature to to 13 to 1300 Kelvin. 378 00:42:17,490 --> 00:42:22,530 And so so that doesn't this doesn't demand a hydrogen atmosphere. 379 00:42:23,220 --> 00:42:30,810 We can start to ask questions now. We can start to do modelling and say, can we, can we get this kind of pattern with the hydrogen atmosphere? 380 00:42:32,460 --> 00:42:37,380 And that's that's a job for three dimensional climate modelling, which is one of the things I do. 381 00:42:38,370 --> 00:42:49,889 And so and so my student finally was able to adapt our, our planet, our exoplanet model to do pure hydrogen and pure CO2 atmospheres. 382 00:42:49,890 --> 00:42:57,870 There are a lot of a lot of these all going on in these simulations which, which I don't have time to talk about and a lot of subtleties. 383 00:42:57,870 --> 00:43:05,579 But the upshot is that is that, hey, this is there's this sub stellar point right here in both of these cases, 384 00:43:05,580 --> 00:43:10,080 right at the centre, hydrogen has very high heat capacity. 385 00:43:10,650 --> 00:43:21,900 If you if you were to I just arbitrarily show ten bars of hydrogen here the if we put in a pure hydrogen atmosphere 386 00:43:22,110 --> 00:43:31,080 with no extra stellar absorbers no extra solar absorbers then so that you have a deep convective troposphere, 387 00:43:32,070 --> 00:43:37,440 then actually the hydrogen is is so good at transporting heat that you get a 388 00:43:37,440 --> 00:43:43,430 pretty isothermal planet around 2000 Kelvin and we're doing the sweep know 389 00:43:43,860 --> 00:43:48,329 we may be able to get something that looks like the data with a lower with a 390 00:43:48,330 --> 00:43:52,020 lower hydrogen content in the atmosphere like a one bar hydrogen atmosphere. 391 00:43:52,020 --> 00:43:58,190 But actually we have, we tried things with a with a what with lower surface pressure of hydrogen. 392 00:43:58,200 --> 00:43:59,729 We and it's really a very, 393 00:43:59,730 --> 00:44:08,550 very narrow range of pressures for which you get the right kind of phase shift of the hot spot relative to the relative to the sub stellar point. 394 00:44:08,730 --> 00:44:16,110 This is with a pure CO2 atmosphere, which is much more plausible in terms of being able to hold on to a high molecular weight atmosphere, 395 00:44:16,860 --> 00:44:20,940 although real in reality of these temperatures, it would be part CO2 and part C0. 396 00:44:21,690 --> 00:44:28,440 There's the sub stellar point. You get these characteristic wave patterns on the nightside and cold spot there. 397 00:44:28,440 --> 00:44:33,780 The temperatures are a little bit too cold, but around around a thousand Kelvin and the dayside a little bit, 398 00:44:33,780 --> 00:44:36,419 not quite hot enough up to about 2600 Kelvin. 399 00:44:36,420 --> 00:44:45,600 But but with with carbon dioxide which gives you different wave speeds in the atmosphere and different and and different heat capacity, 400 00:44:45,600 --> 00:44:51,120 we actually get the phase shift about right. But so this is just to give you the flavour that we're at the stage now with the data 401 00:44:51,120 --> 00:44:55,860 that we can get and we can start to test hypotheses about what's in the atmosphere. 402 00:44:56,310 --> 00:44:59,370 So, so there's a lot more to do, to do with this. 403 00:44:59,370 --> 00:45:04,529 But one place we now have to think more of now that now that there's evidence that 404 00:45:04,530 --> 00:45:08,820 there is some kind of atmosphere other than a local thin rock vapour atmosphere, 405 00:45:09,120 --> 00:45:13,139 we have to start thinking about what what you out? 406 00:45:13,140 --> 00:45:21,870 Gas from a magma ocean. If you've got some carrier gas above, what if you have an H2, CO2 or water vapour atmosphere above the magma ocean? 407 00:45:22,710 --> 00:45:27,990 What how does that affect the chemistry of what's in the of what's in the atmosphere? 408 00:45:28,800 --> 00:45:32,700 And in particular the simulations I showed you did not have the rock vapour 409 00:45:32,700 --> 00:45:36,810 clouds in and they did not have the latent heat released from from rock vapour. 410 00:45:37,500 --> 00:45:41,850 And that we're we're quite a long way off from being able to handle that kind of dynamics. 411 00:45:41,850 --> 00:45:48,180 And so and so the next stage in trying to do this is to understand how the condenses will rock vapour mixed into a 412 00:45:48,390 --> 00:45:55,709 conventional background gas effects the the radiating temperature of the planet by affecting the temperature directly. 413 00:45:55,710 --> 00:45:59,940 But also by. By affecting the outgoing radiation by. 414 00:46:00,000 --> 00:46:04,500 Clouds. Okay. So now let's go on to nitrogen for somewhat briefly. 415 00:46:06,510 --> 00:46:09,840 In some ways, nitrogen is a rather boring gas. It's like the air. 416 00:46:10,290 --> 00:46:13,319 It's it's there. But you don't think about it very much. 417 00:46:13,320 --> 00:46:18,299 In fact, in Earth, it is the air. It's about 80% of the air. N2 is not very reactive. 418 00:46:18,300 --> 00:46:21,630 It's practically a noble gas doesn't form minerals easily. 419 00:46:22,140 --> 00:46:28,770 And therefore, unlike, say, carbon, there's not much cycling between the atmosphere and the mantle. 420 00:46:30,240 --> 00:46:33,959 And it's also not a greenhouse gas. It's a little bit of a greenhouse gas. 421 00:46:33,960 --> 00:46:41,490 But but but it's a very weak, very weak greenhouse effect, at least at Earth like temperatures. 422 00:46:41,850 --> 00:46:45,929 And it only condenses at very low temperatures. So it just sort of sits there not doing very much. 423 00:46:45,930 --> 00:46:52,650 But it turns out to be one of the key gases in the evolution of planetary atmosphere in the termination of climate. 424 00:46:52,920 --> 00:46:57,750 There are multiple reasons for this, many of which I've been working on over the last few years. 425 00:46:58,110 --> 00:47:04,379 One is that it affects this cold trap that I mentioned that protects water vapour from getting up into the upper 426 00:47:04,380 --> 00:47:11,850 parts of the atmosphere where it can break up under ultraviolet ultraviolet illumination and then escape to space. 427 00:47:12,060 --> 00:47:14,100 If you have a lot of nitrogen in your atmosphere, 428 00:47:14,310 --> 00:47:22,350 the temperature goes down very rapidly with height because the heat release by condensing water is shared over a bigger mass. 429 00:47:22,440 --> 00:47:28,830 So you you get something close to a dry 80 about for nitrogen, you get very cold minimum temperature. 430 00:47:29,010 --> 00:47:33,360 And so by clause, yes, Klapper and all the water vapour is trapped is trapped down low. 431 00:47:33,570 --> 00:47:35,490 If you take away a lot of the nitrogen, 432 00:47:35,760 --> 00:47:41,220 then then the temperature contrast in the vertical and you can just show this from straightforward thermodynamics is very weak, 433 00:47:41,520 --> 00:47:44,010 which means that you have very moist upper atmosphere. 434 00:47:44,520 --> 00:47:51,030 This water vapour is then exposed to energetic ultraviolet which breaks it up and the hydrogen escapes 435 00:47:51,270 --> 00:47:58,500 oxygen is left behind which which on a rocky planet reacts with with various minerals in the crust. 436 00:47:59,070 --> 00:48:06,390 And you essentially have permanent water loss. This is this is believed to be what happened to Venus and how Venus got to be the way it is now. 437 00:48:06,660 --> 00:48:09,239 There's another way that nitrogen affects the atmosphere, 438 00:48:09,240 --> 00:48:14,640 although nitrogen isn't much of a great greenhouse gas itself or another way the nitrogen affects the climate, 439 00:48:15,180 --> 00:48:24,120 the nitrogen isn't much of greenhouse gas itself. Spectral lines that do absorb infrared would be very, very thin if it weren't for collisions. 440 00:48:24,690 --> 00:48:29,370 And so the collisions of nitrogen with being has gases like CO2 or water vapour 441 00:48:30,150 --> 00:48:34,290 have a very strong effect on the on the strength of the greenhouse effect. 442 00:48:34,290 --> 00:48:45,630 So, so so if you have this is the infrared cooling to space, the generalisation of signatory to the forth as a function of the surface temperature, 443 00:48:45,900 --> 00:48:50,520 four atmospheres containing 1% CO2 and water vapour, 444 00:48:50,520 --> 00:48:57,660 50% saturated and a vertical structure on the 80 of that, the standard sort of climate calculation. 445 00:48:58,410 --> 00:49:02,280 So this is with an earth like atmosphere with roughly one bar of carbon dioxide, 446 00:49:02,280 --> 00:49:06,960 you you balance the outgoing infrared, the cooling, the space against the amount of sunlight received. 447 00:49:07,170 --> 00:49:13,650 You get the surface temperature. And let's say that we have a surface temperature of 280 with a conventional one bar nitrogen atmosphere. 448 00:49:13,890 --> 00:49:17,760 If you give the you are two bars of nitrogen at the surface. 449 00:49:17,850 --> 00:49:23,790 Just the increase in the greenhouse gas from collision or broadening gets your surface temperature up to 292. 450 00:49:23,940 --> 00:49:29,100 You lose some of that because in reality with two bars you reflect a little more sunlight by really scattering. 451 00:49:29,340 --> 00:49:31,140 But but the greenhouse effect wins. 452 00:49:31,350 --> 00:49:37,680 But if you go down to a quarter bar of nitrogen, your temperature goes down to 270 Kelvin and the Earth freezes over. 453 00:49:38,220 --> 00:49:45,090 And so a quarter of our nitrogen doesn't look very good for the early earth, especially when when the sun was fainter than it is now. 454 00:49:45,090 --> 00:49:52,560 But well, the world will see a surprise in the next couple of slides with regard to that. 455 00:49:52,860 --> 00:50:01,800 So there's another way that the nitrogen affects the climate, which could partly offset that pressure effect that I showed in the previous slide. 456 00:50:02,550 --> 00:50:07,230 If this these are from some simulations that are coming out in proper succession. 457 00:50:08,280 --> 00:50:13,290 This is the altitude and this is the latitude equator, North Pole Circle. 458 00:50:13,680 --> 00:50:21,660 And so and in an atmosphere that has a small amount of water vapour mixed in with a large amount of non danceable nitrogen, 459 00:50:22,260 --> 00:50:30,659 the relative humidity, the percentage of saturation can be quite low because there are various ways of creating some saturated air dynamically. 460 00:50:30,660 --> 00:50:34,980 That's one of the things that we talk about in this paper. So this is with earth like nitrogen. 461 00:50:35,160 --> 00:50:42,960 But as you reduce the amount of nitrogen for a given temperature, then the atmosphere becomes more and more saturated. 462 00:50:44,040 --> 00:50:49,440 And and so the greenhouse effect of water vapour gets stronger and stronger. 463 00:50:49,710 --> 00:50:55,260 And it turns out that if it weren't for this, if it weren't for this sub saturation effect, 464 00:50:55,260 --> 00:50:59,590 the earth would already be in a or in a range where it would turn. 465 00:50:59,720 --> 00:51:05,510 To Venus, where we would go into a runaway greenhouse, where all the oceans would evaporate into the atmosphere. 466 00:51:06,170 --> 00:51:11,420 And so this sub saturation effect, which is made possible by a non pronounceable background gas, 467 00:51:11,690 --> 00:51:16,160 especially one that doesn't heat up the surface too much, actually is very important. 468 00:51:16,670 --> 00:51:21,320 And of course, nitrogen is the stuff of life. Nitrogen, nitrogen. 469 00:51:21,650 --> 00:51:28,490 The end to bond is really hard to break. But this wonderful biologic you can break it with with lightning. 470 00:51:29,330 --> 00:51:39,800 But other than that, biology mostly does it the this wonderful enzyme nitrogenous, which is in bacteria and root nodules of legumes. 471 00:51:40,040 --> 00:51:50,810 It's in and it's in various kinds of even if it's in blue green algae, it's in green sulphur bacteria, very early metabolism, it can make ammonium. 472 00:51:51,530 --> 00:51:56,060 And then once you have oxygen, the the ammonium can oxidise to nitrate. 473 00:51:56,180 --> 00:51:58,730 And both of these things are biologically available. 474 00:51:58,760 --> 00:52:06,820 Ultimately, they work their way into amino acids or bases of all proteins and also the base pairs that are in rDNA. 475 00:52:06,830 --> 00:52:16,390 So nitrogen biologists have no idea how you could get or get biology, at least anything like what we know working without nitrogen. 476 00:52:16,400 --> 00:52:21,020 So it's quite important. But nitrogen is almost not there on earth at all. 477 00:52:21,020 --> 00:52:30,020 There's very little of it. And so remember in the and in solar and in solar abundance, nitrogen out to carbon, we're all about the same. 478 00:52:30,560 --> 00:52:40,760 This is the abundance in and see when comrades which are often taken as in as as is similar to what the earth, what rocky planets are made of. 479 00:52:41,090 --> 00:52:46,310 And so carbon is quite depleted relative to the oxygen and nitrogen is extremely depleted. 480 00:52:47,240 --> 00:52:52,910 But notice that this is .001 here. The Earth is even more depleted in nitrogen than conjugate. 481 00:52:52,910 --> 00:52:57,770 So contracts are depleted in nitrogen relative to solar abundance. 482 00:52:57,980 --> 00:53:04,580 And then the earth is depleted in nitrogen, insofar as we know at all relative to current to contract, 483 00:53:04,580 --> 00:53:08,500 because you have something like a part 4000 of nitrogen and contracts, 484 00:53:08,720 --> 00:53:14,720 but three parts per million of nitrogen based on rather crude estimates of how much nitrogen might be in the mantle. 485 00:53:15,470 --> 00:53:20,870 And so, so, so the difference between how much we have in having nothing is really quite important. 486 00:53:22,040 --> 00:53:26,540 And but this raises a lot of a lot of questions. 487 00:53:27,310 --> 00:53:35,990 If if you if you were to lose an ocean or lose a lot of CO2 by either a young stage of a star when there 488 00:53:35,990 --> 00:53:42,200 is a lot of ultraviolet or when or or if you had the moon forming collision or something like that, 489 00:53:42,350 --> 00:53:47,839 you could be generated by outgassing. But nitrogen has no place to hide. 490 00:53:47,840 --> 00:53:52,310 If you lose it, it's gone for good. You may be able to hide some of it in the mantle. 491 00:53:52,520 --> 00:53:59,870 If you make a lot of ammonium nitrate that can substitute can can be incorporated into various mineral crystals to some extent, 492 00:53:59,870 --> 00:54:05,239 but you mostly need life to do that to any great extent. But so there's a question, you know, what is the evidence? 493 00:54:05,240 --> 00:54:08,720 Can nitrogen really exchange with the rocky planets interior? 494 00:54:08,900 --> 00:54:15,379 And so this is the other big surprise that came out this year, is that by looking at the size of I, 495 00:54:15,380 --> 00:54:20,510 looking at the size of vesicles in ancient lava, 3 to 3 and a half billion year old lavas, 496 00:54:21,140 --> 00:54:29,840 and and using some fairly clever techniques since the pressure of these law is which there's geological argument that these formed 497 00:54:29,840 --> 00:54:40,010 at sea level the pressure at the near the surface of the lavas when they solidify determines the pressure the size of the bubbles, 498 00:54:40,010 --> 00:54:46,670 the vesicles and these and these lavas. And they have a good argument that these vesicles were their size was preserved. 499 00:54:47,330 --> 00:54:50,480 And so this is the paper that just came out in nature geosciences. 500 00:54:50,730 --> 00:54:58,820 They they they find an indication that the total surface pressure on the earth in the archaean may have been as low as a quarter of a bar, 501 00:54:59,000 --> 00:55:06,320 and which would imply that there was a whole lot of nitrogen cycling. And what does that tell us about nitrogen cycling on other planets? 502 00:55:06,890 --> 00:55:12,200 And do you need to know what was the role of life in allowing that amount of nitrogen cycling? 503 00:55:12,200 --> 00:55:16,190 And is it real? Of course, you know, when it comes to single study syndrome. 504 00:55:16,490 --> 00:55:20,300 Okay. So there's no time. I mean, you just have to skip the story of carbon altogether. 505 00:55:20,990 --> 00:55:26,270 And then the because we're I knew I knew this would probably happen. 506 00:55:26,510 --> 00:55:33,709 But let me just point out that that we are really poised to be able to characterise it to test some of 507 00:55:33,710 --> 00:55:39,530 these hypotheses much better and characterise what is in the atmospheres of these small rocky planets, 508 00:55:39,530 --> 00:55:48,950 because they have all these missions that will be able to cover more spectral space both from the ground and from space and and for 509 00:55:48,950 --> 00:55:55,220 the first time characterise what's in the atmosphere of small rocky planets and give us more data to test some of our theories. 510 00:55:55,490 --> 00:55:59,300 But to make sense of all of it, we really need to. 511 00:55:59,810 --> 00:56:05,060 Think more broadly about how things that are traditionally thought of as geology interact 512 00:56:05,060 --> 00:56:11,570 with things that are traditionally thought of as astrophysics or or or atmospheric science. 513 00:56:11,570 --> 00:56:17,210 And so it it's very much like the story of the old style of thinking about planets was 514 00:56:17,780 --> 00:56:20,880 very much like the story of the blind in the story of the blind man and the elephant. 515 00:56:20,930 --> 00:56:26,749 You know, this one this this one thinks that, you know, it's like a snake, it's like a spear and so forth. 516 00:56:26,750 --> 00:56:32,870 And I've been through this once where we had to learn how to see the whole elephant when I was a graduate student at MIT. 517 00:56:33,500 --> 00:56:40,100 You know, there were these various disciplines in atmospheric and oceanic science, like geophysical fluid dynamics, radiative transfer and so forth. 518 00:56:40,120 --> 00:56:46,279 And and the we sort of talk to each other, but these were sort of considered separate things with separate specialities. 519 00:56:46,280 --> 00:56:50,269 But we had to learn how to see the whole that whole elephant with regard to 520 00:56:50,270 --> 00:56:55,399 atmospheres and oceans and where we are right now with this new generation, 521 00:56:55,400 --> 00:56:59,000 this new, vastly expanded territory of planetary and atmosphere, 522 00:56:59,010 --> 00:57:08,390 geology is learning how to see the whole elephant with regard to the integrated picture of atmospheres and rock. 523 00:57:08,630 --> 00:57:09,080 Thank you.