1 00:00:10,810 --> 00:00:07,080 [Music] 2 00:00:13,209 --> 00:00:10,820 thank you so obviously we don't have a 3 00:00:15,730 --> 00:00:13,219 photo of an actual magma ocean so I 4 00:00:18,700 --> 00:00:15,740 found this this really pretty picture of 5 00:00:20,820 --> 00:00:18,710 a lava like near in Congo I'm gonna have 6 00:00:24,070 --> 00:00:20,830 like a couple of different versions of 7 00:00:28,240 --> 00:00:24,080 photos of this lava lake but you can see 8 00:00:30,310 --> 00:00:28,250 this is looking at a pool of lava that 9 00:00:33,490 --> 00:00:30,320 is on the surface of a planet and it's 10 00:00:34,930 --> 00:00:33,500 got volatile is coming out of it so this 11 00:00:38,619 --> 00:00:34,940 is sort of the effect we're gonna talk 12 00:00:42,729 --> 00:00:38,629 about a lot is the interaction of lavas 13 00:00:45,250 --> 00:00:42,739 and volatile elements in the composition 14 00:00:47,829 --> 00:00:45,260 and the evolution of atmospheres on 15 00:00:50,439 --> 00:00:47,839 planets with magma oceans and I want to 16 00:00:53,290 --> 00:00:50,449 take a minute just to recognize my 17 00:00:56,289 --> 00:00:53,300 collaborators many of whom are here 18 00:00:59,169 --> 00:00:56,299 Kavi polygons are our chair Robyn 19 00:01:01,329 --> 00:00:59,179 Wordsworth Edwin kite secret Rondon and 20 00:01:03,279 --> 00:01:01,339 then of course my my former advisors 21 00:01:05,680 --> 00:01:03,289 Linda Elkins Hinton and Bruce Phegley 22 00:01:08,800 --> 00:01:05,690 and to the choice a celeb as well like 23 00:01:11,230 --> 00:01:08,810 to put on this way anyway so let's start 24 00:01:14,350 --> 00:01:11,240 with a little disco description of what 25 00:01:15,969 --> 00:01:14,360 exactly a magma ocean is and for the 26 00:01:19,240 --> 00:01:15,979 purposes of my track I'm just going to 27 00:01:22,630 --> 00:01:19,250 call it magma ocean anything that is a a 28 00:01:25,410 --> 00:01:22,640 very large body of silicate melts which 29 00:01:29,109 --> 00:01:25,420 may have some sort of crystals within it 30 00:01:32,889 --> 00:01:29,119 that is occupying a large portion of the 31 00:01:35,469 --> 00:01:32,899 surface of a terrestrial planet the 32 00:01:38,349 --> 00:01:35,479 figure on the Left sorry on the right 33 00:01:41,499 --> 00:01:38,359 here is showing how we usually think 34 00:01:43,179 --> 00:01:41,509 that magma oceans are evolving based on 35 00:01:48,370 --> 00:01:43,189 the temperature structure within the 36 00:01:50,380 --> 00:01:48,380 planet so this the red portions here are 37 00:01:51,999 --> 00:01:50,390 where we have silicate liquid blues 38 00:01:53,980 --> 00:01:52,009 portions are we have where we have 39 00:01:55,779 --> 00:01:53,990 solidified magma ocean and the screen 40 00:01:57,849 --> 00:01:55,789 down here at the bottom is assuming that 41 00:02:00,969 --> 00:01:57,859 we didn't fully melt our mantle so we 42 00:02:03,160 --> 00:02:00,979 have some unmelted residual down at the 43 00:02:05,440 --> 00:02:03,170 bottom of the planet I'm the black 44 00:02:07,929 --> 00:02:05,450 curves here are the melting temperatures 45 00:02:10,540 --> 00:02:07,939 of the silicate that's making up this 46 00:02:12,700 --> 00:02:10,550 planet for those of you who don't think 47 00:02:13,990 --> 00:02:12,710 about silicate melts um it's important 48 00:02:15,880 --> 00:02:14,000 to remember that they are multi 49 00:02:17,760 --> 00:02:15,890 component species and so they don't have 50 00:02:20,940 --> 00:02:17,770 a single melting point 51 00:02:23,760 --> 00:02:20,950 they have to the solidus is the point at 52 00:02:26,100 --> 00:02:23,770 which the first little bit of mount 53 00:02:27,990 --> 00:02:26,110 forms in the system and then we also 54 00:02:28,680 --> 00:02:28,000 have the liquidus which is this curve 55 00:02:37,290 --> 00:02:28,690 here 56 00:02:40,170 --> 00:02:37,300 of silicate is finally melting so in 57 00:02:44,430 --> 00:02:40,180 this region in between we have partial 58 00:02:46,560 --> 00:02:44,440 melt and so we have sort of this this 59 00:02:48,390 --> 00:02:46,570 dash line is sort of the dividing line 60 00:02:52,740 --> 00:02:48,400 between why we would think of this as 61 00:02:56,520 --> 00:02:52,750 more liquid present within a solid 62 00:02:58,320 --> 00:02:56,530 matrix of crystals versus a solid sort 63 00:03:01,590 --> 00:02:58,330 of floating around in what is dominantly 64 00:03:03,930 --> 00:03:01,600 a liquid in this upper region okay so 65 00:03:06,210 --> 00:03:03,940 the verdict more or less vertical lines 66 00:03:08,940 --> 00:03:06,220 here with the temperatures at the top 67 00:03:11,610 --> 00:03:08,950 are 80 of bats so we think was in the 68 00:03:14,010 --> 00:03:11,620 silicate mount portion within the melt 69 00:03:15,360 --> 00:03:14,020 the viscosity is pretty low and studies 70 00:03:17,700 --> 00:03:15,370 are convecting on pretty rapid 71 00:03:19,860 --> 00:03:17,710 timescales and so the temperature 72 00:03:22,590 --> 00:03:19,870 profile of the magma ocean is following 73 00:03:24,510 --> 00:03:22,600 an 80 of that and for the purposes of 74 00:03:26,640 --> 00:03:24,520 the the model is then we are going to 75 00:03:28,770 --> 00:03:26,650 talk about here what we typically assume 76 00:03:30,990 --> 00:03:28,780 is that the 80 of that first intersects 77 00:03:33,900 --> 00:03:31,000 these melting points at the bottom of 78 00:03:35,480 --> 00:03:33,910 the mantle and so what's happening is we 79 00:03:38,010 --> 00:03:35,490 get the first a little bit of 80 00:03:40,830 --> 00:03:38,020 solidification is happening down at the 81 00:03:44,040 --> 00:03:40,840 bottom of your mantle and the remainder 82 00:03:45,690 --> 00:03:44,050 the top remains liquid and so if you 83 00:03:50,250 --> 00:03:45,700 have an atmosphere you'll be interacting 84 00:03:52,890 --> 00:03:50,260 with the liquid for the duration of the 85 00:03:54,900 --> 00:03:52,900 mag motion time period there is a little 86 00:03:57,420 --> 00:03:54,910 bit of a complication here and that we 87 00:03:58,230 --> 00:03:57,430 don't really know the melting profile of 88 00:03:59,640 --> 00:03:58,240 supers 89 00:04:02,699 --> 00:03:59,650 we don't really know melting profiles 90 00:04:05,699 --> 00:04:02,709 much beyond the pressure regime of the 91 00:04:09,300 --> 00:04:05,709 Earth's mantle and even that is somewhat 92 00:04:12,000 --> 00:04:09,310 disputed some experiments suggest that 93 00:04:13,560 --> 00:04:12,010 there is a bit of a curvature to the 94 00:04:15,060 --> 00:04:13,570 solidus and the liquidus that would 95 00:04:18,330 --> 00:04:15,070 indicate that you should start getting 96 00:04:22,290 --> 00:04:18,340 your first sort of crystals forming sort 97 00:04:25,640 --> 00:04:22,300 of in mid mantle regions where you might 98 00:04:28,110 --> 00:04:25,650 end up with a basal Mazal magma ocean 99 00:04:30,800 --> 00:04:28,120 with the planet sort of solidifying from 100 00:04:33,140 --> 00:04:30,810 both in both directions at the same time 101 00:04:34,490 --> 00:04:33,150 but for the models I'm mostly gonna be 102 00:04:37,990 --> 00:04:34,500 talking about today we're gonna assume 103 00:04:41,450 --> 00:04:38,000 that the solidus is nice and decreasing 104 00:04:42,950 --> 00:04:41,460 means so that we're only going to start 105 00:04:46,670 --> 00:04:42,960 solidifying at the bottom of the mantle 106 00:04:49,220 --> 00:04:46,680 um so I'm gonna talk to split this talk 107 00:04:51,890 --> 00:04:49,230 up a little bit into first where do we 108 00:04:55,220 --> 00:04:51,900 find magma oceans and then talk a little 109 00:04:58,010 --> 00:04:55,230 bit more after that about the the 110 00:05:00,620 --> 00:04:58,020 dominant processes that different kinds 111 00:05:02,780 --> 00:05:00,630 of magma oceans would experience so 112 00:05:05,450 --> 00:05:02,790 let's start first with where do we find 113 00:05:07,790 --> 00:05:05,460 magma oceans this is just another 114 00:05:10,280 --> 00:05:07,800 schematic of a magma ocean here where we 115 00:05:12,260 --> 00:05:10,290 have the convecting liquid and crystals 116 00:05:15,580 --> 00:05:12,270 falling out towards the bottom of mantle 117 00:05:19,370 --> 00:05:15,590 and we have an atmosphere on top so 118 00:05:21,740 --> 00:05:19,380 there's sort of three major places where 119 00:05:24,460 --> 00:05:21,750 where I think we're finding magma oceans 120 00:05:28,010 --> 00:05:24,470 and these are sort of separated by the 121 00:05:30,050 --> 00:05:28,020 dominant heat source that's producing 122 00:05:32,180 --> 00:05:30,060 these magma oceans and I left one off 123 00:05:33,469 --> 00:05:32,190 here which is tidal heating I'm not 124 00:05:33,950 --> 00:05:33,479 going to talk about tidal heating here 125 00:05:36,170 --> 00:05:33,960 at all 126 00:05:37,700 --> 00:05:36,180 um so the first I'm going to talk about 127 00:05:39,820 --> 00:05:37,710 is young cleanness and this is what we 128 00:05:43,490 --> 00:05:39,830 usually think of for the solar system 129 00:05:46,880 --> 00:05:43,500 and a lot of the magma ocean models are 130 00:05:49,070 --> 00:05:46,890 really based on on models developed in 131 00:05:51,409 --> 00:05:49,080 the solar system especially those models 132 00:05:52,219 --> 00:05:51,419 developed by Matsui and obby in the 133 00:05:56,750 --> 00:05:52,229 mid-80s 134 00:05:59,719 --> 00:05:56,760 and for the formation of Earth and Venus 135 00:06:03,469 --> 00:05:59,729 and Mars so the figure on the left is 136 00:06:04,550 --> 00:06:03,479 showing the evolution of the mass and 137 00:06:07,159 --> 00:06:04,560 radius of the planet 138 00:06:09,710 --> 00:06:07,169 as it is growing from an accretion ulm 139 00:06:13,190 --> 00:06:09,720 aatul so the radius of the planet is 140 00:06:16,310 --> 00:06:13,200 increasing to the right on this x-axis 141 00:06:18,320 --> 00:06:16,320 here and the y-axis is showing the mass 142 00:06:21,310 --> 00:06:18,330 of the atmosphere and so what's 143 00:06:24,620 --> 00:06:21,320 happening thing is as volatile material 144 00:06:26,870 --> 00:06:24,630 material is coming in with the solid 145 00:06:28,730 --> 00:06:26,880 material and it's being delivered into 146 00:06:31,610 --> 00:06:28,740 the atmosphere so you have pretty rapid 147 00:06:34,610 --> 00:06:31,620 atmospheric growth um this figure on the 148 00:06:37,340 --> 00:06:34,620 right is from a related model from a Bay 149 00:06:39,320 --> 00:06:37,350 and is showing the evolution of the 150 00:06:41,690 --> 00:06:39,330 pressure and temperature at the surface 151 00:06:44,760 --> 00:06:41,700 of the planet as a result of many of 152 00:06:47,249 --> 00:06:44,770 these rapid impact 153 00:06:49,230 --> 00:06:47,259 so we have a rapid increase in the 154 00:06:51,689 --> 00:06:49,240 pressure as the mass of the atmosphere 155 00:06:53,550 --> 00:06:51,699 is growing and because these collisions 156 00:06:56,070 --> 00:06:53,560 are occurring quickly and the heat is 157 00:06:58,290 --> 00:06:56,080 not being dissipated the surface 158 00:06:59,850 --> 00:06:58,300 temperature of the planet is growing and 159 00:07:01,620 --> 00:06:59,860 it's growing here in a stochastic way 160 00:07:04,460 --> 00:07:01,630 because these are impacts of variable 161 00:07:08,270 --> 00:07:04,470 size and variable duration and so forth 162 00:07:11,249 --> 00:07:08,280 so this is sort of the standard picture 163 00:07:14,100 --> 00:07:11,259 that came out in the 80s and early 90s 164 00:07:17,159 --> 00:07:14,110 for how planets grew in the solar system 165 00:07:20,219 --> 00:07:17,169 and how the early atmosphere grew and 166 00:07:22,110 --> 00:07:20,229 this implies that you have these you 167 00:07:24,810 --> 00:07:22,120 know you have these massive surface 168 00:07:26,700 --> 00:07:24,820 temperatures that would require the the 169 00:07:29,879 --> 00:07:26,710 planets to become fully molten all the 170 00:07:32,210 --> 00:07:29,889 way through the other method in in 171 00:07:34,740 --> 00:07:32,220 addition to just this sort of singular 172 00:07:37,920 --> 00:07:34,750 and many small impacts could produce 173 00:07:39,719 --> 00:07:37,930 this this magma ocean now the more 174 00:07:43,080 --> 00:07:39,729 favourable method for doing this is a 175 00:07:47,400 --> 00:07:43,090 singular giant impact such as the one 176 00:07:49,890 --> 00:07:47,410 that we think created the first moon in 177 00:07:51,510 --> 00:07:49,900 fact the moon is actually the only 178 00:07:54,570 --> 00:07:51,520 object in the solar system for which we 179 00:07:57,330 --> 00:07:54,580 have solid evidence that there in fact 180 00:08:00,060 --> 00:07:57,340 was a magma ocean every other planet 181 00:08:01,710 --> 00:08:00,070 including the earth and Venus and in 182 00:08:03,060 --> 00:08:01,720 many of the small planetesimals that 183 00:08:07,260 --> 00:08:03,070 people think had many motions 184 00:08:10,430 --> 00:08:07,270 it's all very circumstantial but for the 185 00:08:13,610 --> 00:08:10,440 moon people had originally thought that 186 00:08:18,210 --> 00:08:13,620 when the first apollo samples came back 187 00:08:20,550 --> 00:08:18,220 the composition of the crust of the moon 188 00:08:23,249 --> 00:08:20,560 is shown in this this sort of diagram 189 00:08:25,640 --> 00:08:23,259 over here this is sort of a less 190 00:08:29,640 --> 00:08:25,650 colorful version of that diagram from 191 00:08:32,790 --> 00:08:29,650 1970 the crust of the moon is made of 192 00:08:34,680 --> 00:08:32,800 this component called anorthosite it's a 193 00:08:38,420 --> 00:08:34,690 it's Donnelly made out of the mineral 194 00:08:42,810 --> 00:08:38,430 inner site which is a very light 195 00:08:45,990 --> 00:08:42,820 low-density mineral and the way people 196 00:08:48,540 --> 00:08:46,000 thought that this was created this crust 197 00:08:52,019 --> 00:08:48,550 of in our society is that you have a 198 00:08:54,630 --> 00:08:52,029 magma ocean created as the Moon is 199 00:08:56,180 --> 00:08:54,640 forming by this giant impact you melt 200 00:08:58,130 --> 00:08:56,190 most of the planet and the 201 00:09:00,890 --> 00:08:58,140 begin fractionally crystallizing it and 202 00:09:03,230 --> 00:09:00,900 so what that means is that um your 203 00:09:05,390 --> 00:09:03,240 crystallizing different minerals out of 204 00:09:08,000 --> 00:09:05,400 the silicate melt within the magma ocean 205 00:09:10,490 --> 00:09:08,010 and it's separating out so those 206 00:09:12,320 --> 00:09:10,500 minerals are falling down to the bottom 207 00:09:14,990 --> 00:09:12,330 of the magma ocean and separating from 208 00:09:17,240 --> 00:09:15,000 the melt and so the milk composition is 209 00:09:19,550 --> 00:09:17,250 evolving and so then the minerals that 210 00:09:21,980 --> 00:09:19,560 are coming out next have a slightly 211 00:09:24,590 --> 00:09:21,990 different composition once you get to a 212 00:09:26,720 --> 00:09:24,600 certain fraction of Mount crystallized 213 00:09:29,600 --> 00:09:26,730 you can begin to crystallize this 214 00:09:32,330 --> 00:09:29,610 mineral and our site which turns out to 215 00:09:34,910 --> 00:09:32,340 be lower density than the silicate 216 00:09:37,880 --> 00:09:34,920 liquid it's crystallizing out of and so 217 00:09:41,660 --> 00:09:37,890 what happens is it floats it floats to 218 00:09:45,410 --> 00:09:41,670 the top and it makes this rich crust of 219 00:09:47,720 --> 00:09:45,420 the early moon and this process had been 220 00:09:49,910 --> 00:09:47,730 seen before on the earth in magma 221 00:09:53,180 --> 00:09:49,920 chambers we had seen an earth ID 222 00:09:55,550 --> 00:09:53,190 floatation crust with within magma 223 00:09:57,470 --> 00:09:55,560 chambers and there there are other 224 00:09:59,900 --> 00:09:57,480 pieces of evidence for the lunar magma 225 00:10:05,000 --> 00:09:59,910 ocean including there's a component 226 00:10:06,890 --> 00:10:05,010 called creep kr EEP for potassium rare 227 00:10:08,750 --> 00:10:06,900 earth elements and phosphorus 228 00:10:11,270 --> 00:10:08,760 this is appears to be that's sort of the 229 00:10:14,030 --> 00:10:11,280 residual of the magma ocean it's the 230 00:10:16,160 --> 00:10:14,040 last little bit that crystallized and it 231 00:10:18,290 --> 00:10:16,170 has all the incompatible elements that 232 00:10:21,200 --> 00:10:18,300 didn't want to freeze out in the earlier 233 00:10:23,810 --> 00:10:21,210 stages of crystallization and then the 234 00:10:26,210 --> 00:10:23,820 other sort of evidence for lunar magma 235 00:10:28,670 --> 00:10:26,220 ocean comes from the ages of these 236 00:10:31,310 --> 00:10:28,680 crustal materials that were brought back 237 00:10:33,890 --> 00:10:31,320 by Apollo and from lunar meteorites this 238 00:10:35,960 --> 00:10:33,900 is a timeline of lunar formation and 239 00:10:39,020 --> 00:10:35,970 differentiation from lineal Constanta 240 00:10:41,240 --> 00:10:39,030 and work on the lunar magma ocean where 241 00:10:44,000 --> 00:10:41,250 you can see lunar formation from giant 242 00:10:46,579 --> 00:10:44,010 impact is out here about 4.5 four 243 00:10:49,640 --> 00:10:46,589 billion years and you have the magma 244 00:10:52,610 --> 00:10:49,650 ocean sorry the formation of the moon 245 00:10:56,720 --> 00:10:52,620 from the disk of material that's ejected 246 00:10:59,720 --> 00:10:56,730 from the earth these bars over here are 247 00:11:01,790 --> 00:10:59,730 ages for lunar crustal materials and 248 00:11:03,500 --> 00:11:01,800 these are quite a bit older than most of 249 00:11:07,070 --> 00:11:03,510 the other materials that we have access 250 00:11:09,320 --> 00:11:07,080 to from planetary sized bodies and much 251 00:11:12,860 --> 00:11:09,330 older in fact than anything that we have 252 00:11:14,900 --> 00:11:12,870 me from the earth and then these blue 253 00:11:18,880 --> 00:11:14,910 bars are highlighting the predicted 254 00:11:22,370 --> 00:11:18,890 magma ocean lifetimes from models 255 00:11:23,810 --> 00:11:22,380 initial models put the lifetime at only 256 00:11:26,090 --> 00:11:23,820 ten million years which wasn't really 257 00:11:29,030 --> 00:11:26,100 enough to account for the ages of these 258 00:11:31,310 --> 00:11:29,040 many different minerals from the from 259 00:11:34,220 --> 00:11:31,320 the lunar surface but the addition of 260 00:11:39,170 --> 00:11:34,230 tidal heating allowed the extension of 261 00:11:42,230 --> 00:11:39,180 this crystallization timescale so this 262 00:11:44,420 --> 00:11:42,240 is again and this is amongst the best 263 00:11:46,880 --> 00:11:44,430 evidence that we have that magma oceans 264 00:11:49,910 --> 00:11:46,890 are a real phenomenon within the solar 265 00:11:52,579 --> 00:11:49,920 system now the giant impact would have 266 00:11:54,560 --> 00:11:52,589 almost inevitably also melted the earth 267 00:11:56,360 --> 00:11:54,570 but again we don't have much in the way 268 00:11:57,800 --> 00:11:56,370 of geologic evidence from this time 269 00:12:02,240 --> 00:11:57,810 period on the earth because the earth is 270 00:12:03,980 --> 00:12:02,250 a very geologically active body but we 271 00:12:08,000 --> 00:12:03,990 think it ended up with a massive 272 00:12:10,100 --> 00:12:08,010 atmosphere and it cooled well relatively 273 00:12:13,639 --> 00:12:10,110 quickly compared to many other planets 274 00:12:15,860 --> 00:12:13,649 um and we think that these giant impacts 275 00:12:18,860 --> 00:12:15,870 are pretty common and in planet 276 00:12:21,440 --> 00:12:18,870 formation this is from the work of Eliza 277 00:12:23,780 --> 00:12:21,450 Quintana looking at giant impact 278 00:12:25,880 --> 00:12:23,790 frequency in n-body simulations of 279 00:12:28,010 --> 00:12:25,890 planet formation and what she found was 280 00:12:31,069 --> 00:12:28,020 that for any given object if you track 281 00:12:33,699 --> 00:12:31,079 its impact history many of them 282 00:12:37,720 --> 00:12:33,709 experienced on the order of two to three 283 00:12:41,150 --> 00:12:37,730 giant impacts before they before the 284 00:12:43,760 --> 00:12:41,160 accretionary period is over so the earth 285 00:12:47,120 --> 00:12:43,770 likely the giant impact that formed the 286 00:12:49,550 --> 00:12:47,130 moon wasn't necessarily the first my 287 00:12:55,430 --> 00:12:49,560 giant impact generated mag motion that 288 00:12:57,920 --> 00:12:55,440 the earth experienced okay so moving on 289 00:13:00,530 --> 00:12:57,930 from a young planet so that's how you 290 00:13:03,250 --> 00:13:00,540 would potentially generate magnet oceans 291 00:13:05,990 --> 00:13:03,260 on large planets as they are forming 292 00:13:08,300 --> 00:13:06,000 amongst the exoplanet population we now 293 00:13:11,180 --> 00:13:08,310 have evidence for four planets that are 294 00:13:13,850 --> 00:13:11,190 extremely hot and they are likely bare 295 00:13:16,370 --> 00:13:13,860 rocky planets but nonetheless may have a 296 00:13:19,730 --> 00:13:16,380 magma ocean on their day side at least 297 00:13:22,519 --> 00:13:19,740 this is just a mass radius diagram where 298 00:13:24,980 --> 00:13:22,529 the planets are color-coded by the flux 299 00:13:27,439 --> 00:13:24,990 that they receive and converted here 300 00:13:29,360 --> 00:13:27,449 into an equilibrium temperature so I 301 00:13:31,759 --> 00:13:29,370 don't need and this is a sort of an 302 00:13:33,710 --> 00:13:31,769 artist's impression of Cobra 7b which 303 00:13:36,590 --> 00:13:33,720 was one of the first super Earths 304 00:13:39,170 --> 00:13:36,600 discovered by the co-wrote mission was 305 00:13:42,970 --> 00:13:39,180 shortly followed by Kepler 10b which has 306 00:13:45,769 --> 00:13:42,980 a very similar orbital period and 307 00:13:47,749 --> 00:13:45,779 equilibrium temperature so these first 308 00:13:49,790 --> 00:13:47,759 planets that we discovered in the super 309 00:13:52,400 --> 00:13:49,800 earth regime you know they have super 310 00:13:53,960 --> 00:13:52,410 Earths earth-like densities but they 311 00:13:56,799 --> 00:13:53,970 have temperatures equilibrium 312 00:14:01,519 --> 00:13:56,809 temperatures of around 2000 Kelvin and 313 00:14:05,210 --> 00:14:01,529 most basaltic melts form at temperatures 314 00:14:08,239 --> 00:14:05,220 of a thousand to 1200 Kelvin some up to 315 00:14:10,519 --> 00:14:08,249 1500 Kelvin so this is more than hot 316 00:14:13,939 --> 00:14:10,529 enough just from the stellar insulation 317 00:14:17,840 --> 00:14:13,949 to melt the surface the de sides of 318 00:14:20,179 --> 00:14:17,850 these planets um and then this the last 319 00:14:21,559 --> 00:14:20,189 kind of magma ocean planet that I want 320 00:14:23,780 --> 00:14:21,569 to talk about is these sort of hot 321 00:14:26,600 --> 00:14:23,790 runaway greenhouse when it set they 322 00:14:29,179 --> 00:14:26,610 again the the heat source here is still 323 00:14:30,949 --> 00:14:29,189 stellar insulation but the stellar 324 00:14:33,559 --> 00:14:30,959 insulation isn't sufficient without an 325 00:14:35,749 --> 00:14:33,569 atmosphere to melt the surface and in 326 00:14:37,910 --> 00:14:35,759 some cases some ways these are also 327 00:14:39,559 --> 00:14:37,920 related to the young planets because we 328 00:14:42,759 --> 00:14:39,569 think mag motions on the young planets 329 00:14:46,850 --> 00:14:42,769 are related to this greenhouse effect 330 00:14:49,309 --> 00:14:46,860 but the the main component of 331 00:14:52,610 --> 00:14:49,319 atmospheres that that people with solar 332 00:14:55,579 --> 00:14:52,620 system and modelling history like to use 333 00:14:57,860 --> 00:14:55,589 is water because water is one of the 334 00:14:59,720 --> 00:14:57,870 most abundant volatiles we don't see 335 00:15:02,299 --> 00:14:59,730 hydrogen helium atmospheres on rocky 336 00:15:05,540 --> 00:15:02,309 planets in the solar system and so this 337 00:15:08,059 --> 00:15:05,550 is the dominant volatile component and 338 00:15:09,799 --> 00:15:08,069 it's a very good greenhouse gas and so 339 00:15:11,269 --> 00:15:09,809 this is just a simple calculation that I 340 00:15:13,759 --> 00:15:11,279 did with sort of a great atmosphere 341 00:15:16,819 --> 00:15:13,769 model to see how much water you would 342 00:15:19,129 --> 00:15:16,829 need in the atmosphere of some of the 343 00:15:20,840 --> 00:15:19,139 known super-earth planets in order to 344 00:15:24,559 --> 00:15:20,850 bring the surface temperature up to two 345 00:15:26,480 --> 00:15:24,569 thousand Kelvin so the these the x-axis 346 00:15:28,970 --> 00:15:26,490 here is stellar insulation relative to 347 00:15:31,449 --> 00:15:28,980 the earth with the earth on the far left 348 00:15:34,699 --> 00:15:31,459 hand side and this y-axis is the 349 00:15:35,990 --> 00:15:34,709 pressure of water vapour in the 350 00:15:38,869 --> 00:15:36,000 atmosphere needed to 351 00:15:41,329 --> 00:15:38,879 melt the surface and for reference this 352 00:15:43,129 --> 00:15:41,339 dash line here is the amount of water on 353 00:15:46,160 --> 00:15:43,139 the surface of the earth today that's 354 00:15:49,910 --> 00:15:46,170 about 300 bars and so most of these need 355 00:15:53,059 --> 00:15:49,920 around one bar ten bars now whether 356 00:15:54,530 --> 00:15:53,069 that's a stable atmosphere or not it's a 357 00:15:56,689 --> 00:15:54,540 different matter but they don't need 358 00:16:00,619 --> 00:15:56,699 very much atmosphere at all to cause 359 00:16:04,340 --> 00:16:00,629 their surfaces to melt this is a very 360 00:16:05,540 --> 00:16:04,350 well-known subject that people have 361 00:16:09,290 --> 00:16:05,550 studied a lot this runaway greenhouse 362 00:16:11,150 --> 00:16:09,300 phenomenon for water-rich Worlds this is 363 00:16:14,480 --> 00:16:11,160 a calculation of the runaway greenhouse 364 00:16:17,139 --> 00:16:14,490 limit for a steam atmosphere from Cape 365 00:16:20,780 --> 00:16:17,149 Romano in this review paper by a coma 366 00:16:24,350 --> 00:16:20,790 this is the outgoing long-wave radiation 367 00:16:26,269 --> 00:16:24,360 from the planet as a function of the 368 00:16:28,460 --> 00:16:26,279 water vapor pressure in the atmosphere 369 00:16:30,980 --> 00:16:28,470 so you can see that as soon as you get 370 00:16:33,650 --> 00:16:30,990 above this runaway greenhouse threshold 371 00:16:36,710 --> 00:16:33,660 as you add water to your atmosphere you 372 00:16:39,559 --> 00:16:36,720 have to get out to really really hot 373 00:16:42,110 --> 00:16:39,569 temperatures in order to hit radio of 374 00:16:44,360 --> 00:16:42,120 equilibrium so if you say have a hundred 375 00:16:48,490 --> 00:16:44,370 bars of water vapor in your atmosphere 376 00:16:51,199 --> 00:16:48,500 and you're receiving a thousand watts of 377 00:16:52,699 --> 00:16:51,209 stellar radiation then your surface 378 00:16:56,509 --> 00:16:52,709 temperature is around two thousand 379 00:17:00,619 --> 00:16:56,519 Kelvin okay so I wanted to highlight 380 00:17:03,799 --> 00:17:00,629 here a poster by Denisha cut job on this 381 00:17:06,380 --> 00:17:03,809 kind of steam and co2 mixed atmosphere 382 00:17:09,140 --> 00:17:06,390 so you should go check out her poster 383 00:17:12,289 --> 00:17:09,150 i'm keiko maja mono has looked at at 384 00:17:14,929 --> 00:17:12,299 sort of the magma ocean occurrence as a 385 00:17:17,990 --> 00:17:14,939 function of cellar age and orbital 386 00:17:20,210 --> 00:17:18,000 distance for G dwarf stars the color 387 00:17:23,059 --> 00:17:20,220 coding here is the amount of water a 388 00:17:27,169 --> 00:17:23,069 planet needs to have to maintain a magma 389 00:17:30,020 --> 00:17:27,179 ocean for this stellar age these are 390 00:17:32,060 --> 00:17:30,030 planets orbiting G dwarfs she's 391 00:17:34,669 --> 00:17:32,070 highlighting here the giant impact stage 392 00:17:36,770 --> 00:17:34,679 so planets out here at Earth orbit 393 00:17:40,010 --> 00:17:36,780 cannot really maintain a magma ocean 394 00:17:42,710 --> 00:17:40,020 beyond the giant impact stage the magma 395 00:17:44,779 --> 00:17:42,720 oceans cool off much too quickly there's 396 00:17:47,360 --> 00:17:44,789 this sort of critical orbital distance 397 00:17:48,430 --> 00:17:47,370 at which point at some point the planet 398 00:17:50,320 --> 00:17:48,440 cools off to 399 00:17:52,779 --> 00:17:50,330 a point where you can get liquid water 400 00:17:56,980 --> 00:17:52,789 to form and once that does the runaway 401 00:18:00,279 --> 00:17:56,990 greenhouse atmosphere collapses and you 402 00:18:03,879 --> 00:18:00,289 get a significant drop in your surface 403 00:18:05,799 --> 00:18:03,889 temperature so for this sort of Venus 404 00:18:08,799 --> 00:18:05,809 like orbital period you get this sort of 405 00:18:12,249 --> 00:18:08,809 peak if you have like one earth ocean of 406 00:18:14,409 --> 00:18:12,259 water in the length of time that you can 407 00:18:16,330 --> 00:18:14,419 have your magma ocean surviving and of 408 00:18:21,180 --> 00:18:16,340 course the more water you have the 409 00:18:24,610 --> 00:18:21,190 longer your mag motion can survive um 410 00:18:27,850 --> 00:18:24,620 okay so I'm gonna jump now to talking 411 00:18:29,830 --> 00:18:27,860 about some of more of the dynamics and 412 00:18:31,990 --> 00:18:29,840 the chemistry of the processes going on 413 00:18:33,759 --> 00:18:32,000 on these different kinds of planets I'm 414 00:18:35,710 --> 00:18:33,769 gonna come back to those planets that 415 00:18:38,740 --> 00:18:35,720 are very volatile rich and I'm gonna 416 00:18:42,639 --> 00:18:38,750 start first of all with the lava worlds 417 00:18:46,810 --> 00:18:42,649 discovered in the exoplanet sample I 418 00:18:48,970 --> 00:18:46,820 mean I'm gonna start with my with some 419 00:18:51,430 --> 00:18:48,980 of the initial models for that were 420 00:18:54,159 --> 00:18:51,440 based on Co row 7 being Kepler 10b this 421 00:18:56,440 --> 00:18:54,169 is sort of an artist's impression from 422 00:19:00,039 --> 00:18:56,450 this big paper by Elaine Legare and and 423 00:19:02,710 --> 00:19:00,049 many many co-authors so this is an 424 00:19:04,210 --> 00:19:02,720 artist rendition of what this planet 425 00:19:06,730 --> 00:19:04,220 would look like the assumption being 426 00:19:09,129 --> 00:19:06,740 that this planet is tidally locked and 427 00:19:11,110 --> 00:19:09,139 synchronously rotating and so it has a 428 00:19:13,389 --> 00:19:11,120 permanent dayside in a permanent night 429 00:19:18,340 --> 00:19:13,399 side and that permanent day side is 430 00:19:20,680 --> 00:19:18,350 covered with a lava pool with of course 431 00:19:22,210 --> 00:19:20,690 the peak temperature occurring at the 432 00:19:25,810 --> 00:19:22,220 sub stellar point and dropping off 433 00:19:28,600 --> 00:19:25,820 rapidly towards the Terminator and so 434 00:19:30,820 --> 00:19:28,610 the the edges of this magma ocean pool 435 00:19:32,350 --> 00:19:30,830 are going to occur before you hit the 436 00:19:35,830 --> 00:19:32,360 Terminator because the Terminator is 437 00:19:38,769 --> 00:19:35,840 quite cold and the atmospheric pressure 438 00:19:41,799 --> 00:19:38,779 is determined here under the assumption 439 00:19:46,269 --> 00:19:41,809 that these planets are volatile free by 440 00:19:49,240 --> 00:19:46,279 a silicate vaporization model so this 441 00:19:51,749 --> 00:19:49,250 was based on some of our previous models 442 00:19:54,820 --> 00:19:51,759 that we had actually developed for 443 00:19:58,269 --> 00:19:54,830 modeling the composition of volcanic 444 00:20:00,910 --> 00:19:58,279 gasses on Jupiter's moon Io this is the 445 00:20:05,110 --> 00:20:00,920 the predicted gas composition as a 446 00:20:05,740 --> 00:20:05,120 action of temperature for for a silicate 447 00:20:09,040 --> 00:20:05,750 melts 448 00:20:11,530 --> 00:20:09,050 where the dominant gas here is sodium 449 00:20:13,270 --> 00:20:11,540 because sodium is a very volatile 450 00:20:16,690 --> 00:20:13,280 relatively volatile element in a 451 00:20:21,240 --> 00:20:16,700 silicate system and the the next most 452 00:20:24,520 --> 00:20:21,250 abundant gases are oxygen and co2 453 00:20:26,170 --> 00:20:24,530 because oxygen is in fact the most 454 00:20:27,580 --> 00:20:26,180 abundant element in silicate melt 455 00:20:30,300 --> 00:20:27,590 systems and then you have things like 456 00:20:34,540 --> 00:20:30,310 silicon monoxide and magnesium and iron 457 00:20:38,080 --> 00:20:34,550 atomic species I mean this model also 458 00:20:42,820 --> 00:20:38,090 looked at fractional evaporation of this 459 00:20:45,490 --> 00:20:42,830 system so if you have a massive pressure 460 00:20:47,920 --> 00:20:45,500 gradient you should expect to get winds 461 00:20:49,690 --> 00:20:47,930 driving away from this sub stellar point 462 00:20:52,390 --> 00:20:49,700 where most of your material is 463 00:20:55,240 --> 00:20:52,400 evaporating and might cause some 464 00:20:57,970 --> 00:20:55,250 compositional evolution of this pool and 465 00:21:00,280 --> 00:20:57,980 this model handles the fractional 466 00:21:02,200 --> 00:21:00,290 vaporization the x-axis here is the 467 00:21:05,500 --> 00:21:02,210 fraction of the silicate that has 468 00:21:08,680 --> 00:21:05,510 evaporated and this is showing the 469 00:21:12,060 --> 00:21:08,690 composition of the gas phase so what you 470 00:21:14,950 --> 00:21:12,070 see is that the sodium and potassium are 471 00:21:16,390 --> 00:21:14,960 depleted the first from this melt pool 472 00:21:19,210 --> 00:21:16,400 because they're the most volatile 473 00:21:22,800 --> 00:21:19,220 elements present followed by iron iron 474 00:21:25,500 --> 00:21:22,810 is in fact very volatile and followed 475 00:21:27,940 --> 00:21:25,510 and after the words you have a 476 00:21:29,920 --> 00:21:27,950 composition mostly dominated by silicon 477 00:21:31,870 --> 00:21:29,930 magnesium and if you keep going far 478 00:21:37,770 --> 00:21:31,880 enough you'll get out to a composition 479 00:21:44,950 --> 00:21:43,240 Ito at all in 2015 did another round of 480 00:21:47,140 --> 00:21:44,960 calculations of this kind of silicate 481 00:21:49,360 --> 00:21:47,150 vapor atmosphere and they calculated 482 00:21:52,720 --> 00:21:49,370 temperature and pressure profiles for 483 00:21:54,850 --> 00:21:52,730 different sort of substellar equilibrium 484 00:21:56,680 --> 00:21:54,860 temperatures and what they found was 485 00:21:59,860 --> 00:21:56,690 that once you get above the knee Coulomb 486 00:22:02,530 --> 00:21:59,870 temperature of about 2000 Kelvin you end 487 00:22:06,270 --> 00:22:02,540 up getting a temperature inversion in 488 00:22:10,060 --> 00:22:06,280 the atmosphere and then I calculated the 489 00:22:12,659 --> 00:22:10,070 secondary Eclipse steps for a variety of 490 00:22:16,830 --> 00:22:12,669 these lava world planet 491 00:22:18,600 --> 00:22:16,840 um from the infrared out to the the Fox 492 00:22:20,970 --> 00:22:18,610 and sorry the the optical out to the 493 00:22:22,529 --> 00:22:20,980 far-infrared and you get some features 494 00:22:24,480 --> 00:22:22,539 coming from the atmosphere you have 495 00:22:26,820 --> 00:22:24,490 sodium and potassium lines and the 496 00:22:28,320 --> 00:22:26,830 optical and these features here I 497 00:22:32,240 --> 00:22:28,330 believe are due to the silicon monoxide 498 00:22:35,659 --> 00:22:32,250 gas so those are potentially observable 499 00:22:39,149 --> 00:22:35,669 with James Webb and the other 500 00:22:42,690 --> 00:22:39,159 observational tests you can make for 501 00:22:45,629 --> 00:22:42,700 these planets is to test whether in fact 502 00:22:47,310 --> 00:22:45,639 you have heat redistribution from the 503 00:22:50,639 --> 00:22:47,320 day side to the night side in which case 504 00:22:52,350 --> 00:22:50,649 you would expect a more a lower 505 00:22:54,450 --> 00:22:52,360 temperature contrast from day to night 506 00:22:56,549 --> 00:22:54,460 and that would potentially indicate that 507 00:22:58,110 --> 00:22:56,559 rather than having lost over volatile as 508 00:23:02,639 --> 00:22:58,120 they might in fact still have a 509 00:23:07,889 --> 00:23:02,649 significant volatile envelope um work 510 00:23:10,680 --> 00:23:07,899 with so Edwin kite led a study taking 511 00:23:13,289 --> 00:23:10,690 this model for the silicate evaporation 512 00:23:15,659 --> 00:23:13,299 of this this melt pool and included some 513 00:23:17,639 --> 00:23:15,669 more dynamics to it so what he found was 514 00:23:20,159 --> 00:23:17,649 that you get evaporation at the subsolar 515 00:23:22,350 --> 00:23:20,169 point but in fact you get condensation 516 00:23:24,419 --> 00:23:22,360 of that material back onto the pool 517 00:23:26,610 --> 00:23:24,429 before you reach the Terminator or the 518 00:23:28,950 --> 00:23:26,620 edges of the pool and you'll get a 519 00:23:31,799 --> 00:23:28,960 dungeon a disc additional evaporation 520 00:23:33,330 --> 00:23:31,809 from out here and so in fact the regions 521 00:23:34,980 --> 00:23:33,340 where you're losing more of your mass is 522 00:23:38,460 --> 00:23:34,990 coming from the edges of the pool 523 00:23:41,759 --> 00:23:38,470 because an it can leave the boundaries 524 00:23:44,190 --> 00:23:41,769 of the pool before rican dancing and so 525 00:23:46,529 --> 00:23:44,200 you do still have this this flow of 526 00:23:49,620 --> 00:23:46,539 material coming from the dayside i'm 527 00:23:51,419 --> 00:23:49,630 sorry from the substellar point moving 528 00:23:52,710 --> 00:23:51,429 around to the night side but mantle 529 00:23:56,039 --> 00:23:52,720 convection should be sort of 530 00:24:00,149 --> 00:23:56,049 replenishing this pool from the the 531 00:24:03,240 --> 00:24:00,159 bottom of the pool the convection within 532 00:24:07,230 --> 00:24:03,250 the pool is sort of determined by the 533 00:24:09,240 --> 00:24:07,240 composition and the density evolution of 534 00:24:11,940 --> 00:24:09,250 the chemical boundary layer at the 535 00:24:14,850 --> 00:24:11,950 surface so the solid line in this figure 536 00:24:17,360 --> 00:24:14,860 is taking the evolution of that surface 537 00:24:20,580 --> 00:24:17,370 layer in calculating the density of it 538 00:24:22,860 --> 00:24:20,590 so this is the sort of residual material 539 00:24:24,629 --> 00:24:22,870 density and so you can see that this is 540 00:24:26,700 --> 00:24:24,639 for a book silicate Earth sort of 541 00:24:30,240 --> 00:24:26,710 composition which is relatively 542 00:24:32,190 --> 00:24:30,250 low in iron oxide and you get a marginal 543 00:24:34,500 --> 00:24:32,200 decrease in the density of this surface 544 00:24:37,860 --> 00:24:34,510 layer until you get out to here where 545 00:24:40,350 --> 00:24:37,870 it's initially returns back to the same 546 00:24:44,760 --> 00:24:40,360 and the highest density you get is out 547 00:24:48,080 --> 00:24:44,770 here at about 70 percent evaporated but 548 00:24:53,850 --> 00:24:48,090 what happens if you have more iron oxide 549 00:24:59,850 --> 00:24:53,860 in your in your sorry in your bulk 550 00:25:02,820 --> 00:24:59,860 composition is that the the evaporation 551 00:25:05,490 --> 00:25:02,830 of that surface layer produces material 552 00:25:07,769 --> 00:25:05,500 that is lower density and so it's 553 00:25:10,049 --> 00:25:07,779 buoyant and so this this upper layer 554 00:25:12,779 --> 00:25:10,059 remains buoyant and you never get full 555 00:25:15,870 --> 00:25:12,789 overturn of that layer and so this layer 556 00:25:17,820 --> 00:25:15,880 can evolve into becoming more calcium 557 00:25:19,769 --> 00:25:17,830 and aluminum dominated and you would 558 00:25:23,519 --> 00:25:19,779 expect these kinds of planets to have 559 00:25:25,950 --> 00:25:23,529 sort of compositionally uniform but 560 00:25:29,669 --> 00:25:25,960 evolved surfaces of this sort of 561 00:25:33,000 --> 00:25:29,679 composition for materials that have less 562 00:25:35,130 --> 00:25:33,010 iron and their bulk composition this 563 00:25:38,250 --> 00:25:35,140 fractional vaporization leads to this 564 00:25:40,909 --> 00:25:38,260 this boundary layer becoming denser over 565 00:25:43,620 --> 00:25:40,919 time and so it will eventually overturn 566 00:25:47,279 --> 00:25:43,630 and so you can get variable and patchy 567 00:25:51,779 --> 00:25:47,289 surfaces or sort of uniform surfaces 568 00:25:54,570 --> 00:25:51,789 depending on the the relative timescales 569 00:25:58,440 --> 00:25:54,580 of the chemical and the thermal over 570 00:26:00,510 --> 00:25:58,450 turn times of these planets so I think 571 00:26:01,980 --> 00:26:00,520 these planets are extremely interesting 572 00:26:04,260 --> 00:26:01,990 and I think there's a lot of interesting 573 00:26:06,019 --> 00:26:04,270 work still to be done on them in order 574 00:26:08,220 --> 00:26:06,029 to understand them better and hopefully 575 00:26:10,830 --> 00:26:08,230 observations with James Webb would be 576 00:26:12,240 --> 00:26:10,840 able to improve our understanding here 577 00:26:14,399 --> 00:26:12,250 but I think some outstanding questions 578 00:26:16,169 --> 00:26:14,409 on these planets are are these a lot of 579 00:26:16,889 --> 00:26:16,179 planets in fact completely devoid of 580 00:26:18,960 --> 00:26:16,899 volatiles 581 00:26:22,110 --> 00:26:18,970 this was sort of a starting assumption 582 00:26:24,360 --> 00:26:22,120 that we made and it hasn't really been 583 00:26:25,980 --> 00:26:24,370 tested if they have a thin volatile 584 00:26:27,810 --> 00:26:25,990 envelope that might not be 585 00:26:31,289 --> 00:26:27,820 distinguishable from the mass and radius 586 00:26:35,810 --> 00:26:31,299 of the planets but potentially it could 587 00:26:39,269 --> 00:26:35,820 be determine from secondary eclipses and 588 00:26:40,350 --> 00:26:39,279 the reason obviously that this problem 589 00:26:42,270 --> 00:26:40,360 hasn't been done be 590 00:26:44,340 --> 00:26:42,280 is because as as James Owen was telling 591 00:26:45,810 --> 00:26:44,350 us earlier these escape problems are 592 00:26:47,910 --> 00:26:45,820 pretty hard especially when you're 593 00:26:51,120 --> 00:26:47,920 talking about heavier elements and not 594 00:26:53,610 --> 00:26:51,130 just hydrogen and helium so then the 595 00:26:56,490 --> 00:26:53,620 question is how much of the if if these 596 00:26:59,039 --> 00:26:56,500 are just silicate planets how much of 597 00:27:03,270 --> 00:26:59,049 the heavy elements can evaporate from 598 00:27:05,940 --> 00:27:03,280 them can you start to lose sodium from 599 00:27:08,490 --> 00:27:05,950 your planet altogether for instance um 600 00:27:10,860 --> 00:27:08,500 and then the model here of this 601 00:27:13,080 --> 00:27:10,870 lava-like sort of assumes a synchronous 602 00:27:16,159 --> 00:27:13,090 rotation and the question is whether 603 00:27:19,620 --> 00:27:16,169 this is valid for all of these planets 604 00:27:22,860 --> 00:27:19,630 have they all fully most of them are 605 00:27:25,320 --> 00:27:22,870 likely fully tidally locked but what 606 00:27:26,669 --> 00:27:25,330 about true polar wander jeremy LeConte 607 00:27:29,070 --> 00:27:26,679 has showed that this is possible for 608 00:27:32,419 --> 00:27:29,080 planets in the habitable zone is this 609 00:27:35,190 --> 00:27:32,429 possible for these clothes and planets 610 00:27:36,659 --> 00:27:35,200 possibly not all of them but maybe a 611 00:27:38,400 --> 00:27:36,669 subset of them would not be fully 612 00:27:42,600 --> 00:27:38,410 synchronously rotating and then what are 613 00:27:46,950 --> 00:27:42,610 the implications for the surface 614 00:27:49,560 --> 00:27:46,960 environment of this planet um so now I'm 615 00:27:51,299 --> 00:27:49,570 gonna switch gears again from this and 616 00:27:53,549 --> 00:27:51,309 leave you with those open questions for 617 00:27:55,860 --> 00:27:53,559 lab of planets and go back to more 618 00:27:59,130 --> 00:27:55,870 volatile rich planets and talk about 619 00:28:02,280 --> 00:27:59,140 volatile and magma ocean of interactions 620 00:28:04,560 --> 00:28:02,290 and I like this figure for of this lava 621 00:28:06,060 --> 00:28:04,570 lake again because you have these gases 622 00:28:08,280 --> 00:28:06,070 coming out of it that's really 623 00:28:10,080 --> 00:28:08,290 emphasizing that the vocals are actually 624 00:28:12,539 --> 00:28:10,090 coming out of this lava there they're 625 00:28:15,330 --> 00:28:12,549 dissolved in the lava here and so 626 00:28:17,159 --> 00:28:15,340 there's a real interaction between lavas 627 00:28:22,470 --> 00:28:17,169 and the atmosphere in these kinds of 628 00:28:24,930 --> 00:28:22,480 systems so the water will partition as 629 00:28:27,200 --> 00:28:24,940 the magma ocean crystallizes and cools 630 00:28:29,430 --> 00:28:27,210 off between the melt and the solid 631 00:28:33,240 --> 00:28:29,440 within the Earth's mantle there's 632 00:28:34,890 --> 00:28:33,250 there's probably at least the same 633 00:28:39,120 --> 00:28:34,900 amount of water as there is on the 634 00:28:41,730 --> 00:28:39,130 surface possibly more um although that 635 00:28:44,190 --> 00:28:41,740 is still pretty highly debated this 636 00:28:45,780 --> 00:28:44,200 figure on the left is showing the 637 00:28:48,090 --> 00:28:45,790 solubility of water in different 638 00:28:50,040 --> 00:28:48,100 minerals within the Earth's mantle today 639 00:28:50,659 --> 00:28:50,050 you can see there's a region here called 640 00:28:53,119 --> 00:28:50,669 the transit 641 00:28:55,369 --> 00:28:53,129 where there's potential for a lot of 642 00:28:57,139 --> 00:28:55,379 water storage capability but it's not 643 00:29:00,440 --> 00:28:57,149 really known yet whether there is 644 00:29:03,499 --> 00:29:00,450 actually water this much water in that 645 00:29:05,629 --> 00:29:03,509 region so the water once the magma ocean 646 00:29:08,330 --> 00:29:05,639 starts to crystallize will be stored in 647 00:29:12,499 --> 00:29:08,340 these nominally anhydrous minerals like 648 00:29:14,960 --> 00:29:12,509 olivine so olivine is mg 2 SiO 4 it does 649 00:29:18,289 --> 00:29:14,970 not have water in its chemical formula 650 00:29:22,489 --> 00:29:18,299 so the water is stored in small spaces 651 00:29:25,460 --> 00:29:22,499 in the crystal lattice mostly as as Oh H 652 00:29:27,049 --> 00:29:25,470 groups um but the abundance of water 653 00:29:28,789 --> 00:29:27,059 that you can store in the olivine is 654 00:29:31,310 --> 00:29:28,799 dependent on the pressure and the depth 655 00:29:34,460 --> 00:29:31,320 within the planet in within magma ocean 656 00:29:36,049 --> 00:29:34,470 models we parameterize the way that 657 00:29:39,710 --> 00:29:36,059 water will partition between the melt 658 00:29:42,039 --> 00:29:39,720 and the solid phase by a partition 659 00:29:44,690 --> 00:29:42,049 coefficient so these are based on 660 00:29:48,080 --> 00:29:44,700 experimental measurements of how water 661 00:29:49,489 --> 00:29:48,090 will distribute itself in a system and 662 00:29:51,560 --> 00:29:49,499 so this is just the concentration of 663 00:29:53,539 --> 00:29:51,570 water in the crystal phase divided by 664 00:29:56,599 --> 00:29:53,549 the concentration in a coexisting melt 665 00:29:59,930 --> 00:29:56,609 phase and for many of the minerals found 666 00:30:02,599 --> 00:29:59,940 commonly within the earth that value is 667 00:30:04,999 --> 00:30:02,609 below one which indicates that the water 668 00:30:07,580 --> 00:30:05,009 actually wants to stay as long as it can 669 00:30:09,950 --> 00:30:07,590 in the melt phase and so what happens is 670 00:30:11,930 --> 00:30:09,960 that as the magma ocean starts to 671 00:30:15,139 --> 00:30:11,940 crystallize water will become more 672 00:30:17,989 --> 00:30:15,149 abundant in the melt phase but you will 673 00:30:22,999 --> 00:30:17,999 still always retain some amount of water 674 00:30:26,289 --> 00:30:23,009 in your solid silicate minerals this is 675 00:30:28,759 --> 00:30:26,299 showing the solubility of water and co2 676 00:30:34,430 --> 00:30:28,769 within different kinds of silicate melts 677 00:30:37,249 --> 00:30:34,440 so this is as a function of pressure for 678 00:30:39,649 --> 00:30:37,259 both of these this is water in co2 the 679 00:30:41,479 --> 00:30:39,659 solubility is somewhat dependent on the 680 00:30:44,930 --> 00:30:41,489 actual composition of the silicate 681 00:30:46,509 --> 00:30:44,940 material and so you know we take models 682 00:30:49,070 --> 00:30:46,519 for the earth and apply them to 683 00:30:51,560 --> 00:30:49,080 exoplanets but understanding the 684 00:30:53,570 --> 00:30:51,570 composition space of the solubility for 685 00:30:56,840 --> 00:30:53,580 many of these volatiles is going to be 686 00:31:00,729 --> 00:30:56,850 very important in the future 687 00:31:04,070 --> 00:31:00,739 so water is has a has a high solubility 688 00:31:06,380 --> 00:31:04,080 sio2 is is somewhat soluble but it 689 00:31:08,870 --> 00:31:06,390 actually partition more preferentially 690 00:31:11,210 --> 00:31:08,880 into the atmosphere and stay in the in 691 00:31:13,370 --> 00:31:11,220 the melt um the other thing is that 692 00:31:15,649 --> 00:31:13,380 these volatile is actually interact with 693 00:31:18,320 --> 00:31:15,659 each other within the melt phase and so 694 00:31:21,110 --> 00:31:18,330 um if you have both water and co2 695 00:31:25,009 --> 00:31:21,120 dissolved within the melt they live each 696 00:31:29,659 --> 00:31:25,019 other solubility so along an isobar here 697 00:31:32,659 --> 00:31:29,669 this is 1 kilo bar if you have 400 parts 698 00:31:36,500 --> 00:31:32,669 per million of co2 you're limited to two 699 00:31:40,310 --> 00:31:36,510 weight percent of water for instance so 700 00:31:42,049 --> 00:31:40,320 the this is because the the the ball 701 00:31:45,879 --> 00:31:42,059 tools are reacting to the the mutual 702 00:31:48,440 --> 00:31:45,889 pressure of the of the fluid the 703 00:31:51,139 --> 00:31:48,450 volatile solubility within the mount 704 00:31:53,840 --> 00:31:51,149 also depends on a factor called the 705 00:31:58,070 --> 00:31:53,850 oxidation state or the oxygen fugacity 706 00:32:00,799 --> 00:31:58,080 of the system this is a compilation of 707 00:32:03,350 --> 00:32:00,809 different volatile dissolved within 708 00:32:05,690 --> 00:32:03,360 silicate melt as a function of oxygen 709 00:32:08,600 --> 00:32:05,700 fugacity and I have a quick side here 710 00:32:11,690 --> 00:32:08,610 just to explain very quickly what oxygen 711 00:32:13,460 --> 00:32:11,700 fugacity is um within a gas phase you 712 00:32:16,009 --> 00:32:13,470 can consider oxygen fugacity just the 713 00:32:19,549 --> 00:32:16,019 partial pressure of the oxygen but 714 00:32:23,299 --> 00:32:19,559 within a solid or a liquid phase um the 715 00:32:27,350 --> 00:32:23,309 oxygen fugacity is more of a potential 716 00:32:29,840 --> 00:32:27,360 measure of the relative abundances of 717 00:32:34,370 --> 00:32:29,850 elements that have different valence 718 00:32:36,350 --> 00:32:34,380 States so that is within a silicate the 719 00:32:39,860 --> 00:32:36,360 the dominant element that is current 720 00:32:42,860 --> 00:32:39,870 controlling this is is iron so iron has 721 00:32:45,680 --> 00:32:42,870 three major valence states within a 722 00:32:47,840 --> 00:32:45,690 silicate planet that is metal which is 723 00:32:51,019 --> 00:32:47,850 found in the core predominantly there's 724 00:32:53,269 --> 00:32:51,029 iron 2 plus an iron 3 plus and so this 725 00:32:57,379 --> 00:32:53,279 valence state is determining how much 726 00:32:59,990 --> 00:32:57,389 oxygen the iron can react with so if one 727 00:33:01,850 --> 00:33:00,000 of the dominant controlling reactions 728 00:33:04,100 --> 00:33:01,860 especially during core formation is this 729 00:33:06,970 --> 00:33:04,110 iron website buffer so the presence of 730 00:33:10,639 --> 00:33:06,980 metal will limit the amount of oxygen 731 00:33:12,500 --> 00:33:10,649 Piazzi of a system but the oxygen is 732 00:33:16,549 --> 00:33:12,510 reacting with the metal and making this 733 00:33:20,000 --> 00:33:16,559 iron two-plus and the oxygen fugacity is 734 00:33:22,279 --> 00:33:20,010 within an outgassing system will also 735 00:33:25,850 --> 00:33:22,289 control the composition of the gas phase 736 00:33:28,880 --> 00:33:25,860 so the oxygen Piazzi is proportional to 737 00:33:31,970 --> 00:33:28,890 the relative abundances of say water 738 00:33:35,779 --> 00:33:31,980 vapor to hydrogen or co2 to carbon 739 00:33:39,140 --> 00:33:35,789 monoxide so to go back to this figure of 740 00:33:43,220 --> 00:33:39,150 the volatile solubilities at low oxygen 741 00:33:45,740 --> 00:33:43,230 fugacities we favor reduced forms of the 742 00:33:48,110 --> 00:33:45,750 volatiles like methane is the dominant 743 00:33:49,880 --> 00:33:48,120 form of carbon as you go to higher 744 00:33:52,279 --> 00:33:49,890 oxygen fugacity as you favor more 745 00:33:56,060 --> 00:33:52,289 oxygen-rich volatiles like carbonates 746 00:33:58,340 --> 00:33:56,070 for instance molecular hydrogen which is 747 00:34:01,310 --> 00:33:58,350 shown in this figure here is much more 748 00:34:04,430 --> 00:34:01,320 soluble in melts that have a low oxygen 749 00:34:06,830 --> 00:34:04,440 fee acity and at higher oxygen fugacity 750 00:34:10,580 --> 00:34:06,840 as you favor water as the hydrogen 751 00:34:15,139 --> 00:34:10,590 bearing species so I encourage you also 752 00:34:17,119 --> 00:34:15,149 to go look at the poster of Sakuraba who 753 00:34:22,220 --> 00:34:17,129 is looking at volatile partitioning 754 00:34:25,220 --> 00:34:22,230 during impacts on the early Earth ok and 755 00:34:27,950 --> 00:34:25,230 water also influences the melting point 756 00:34:30,260 --> 00:34:27,960 of silicates this is I showed you 757 00:34:33,649 --> 00:34:30,270 earlier a model of the solidus and 758 00:34:36,889 --> 00:34:33,659 liquidus of the magma ocean many times 759 00:34:39,829 --> 00:34:36,899 we assume a dry solidus this is where 760 00:34:41,450 --> 00:34:39,839 we're looking at the measured melting 761 00:34:43,730 --> 00:34:41,460 point of a system that didn't contain 762 00:34:46,159 --> 00:34:43,740 water but we know in fact that if you 763 00:34:47,750 --> 00:34:46,169 add water into that system you lower the 764 00:34:50,180 --> 00:34:47,760 the melting point sometimes 765 00:34:53,780 --> 00:34:50,190 substantially so these are three very 766 00:34:55,820 --> 00:34:53,790 different parameters ations for the wet 767 00:34:57,620 --> 00:34:55,830 solidus for the Earth's mantle so you 768 00:34:59,650 --> 00:34:57,630 can see that some of these would predict 769 00:35:03,050 --> 00:34:59,660 that the Earth's mantle should melt at 770 00:35:05,690 --> 00:35:03,060 two or three hundred Kelvin 771 00:35:10,130 --> 00:35:05,700 lower than you would predict if the 772 00:35:12,109 --> 00:35:10,140 mantle were dry um this can also 773 00:35:14,930 --> 00:35:12,119 influence magma ocean solidification 774 00:35:17,750 --> 00:35:14,940 times this is just a comparison of 775 00:35:20,359 --> 00:35:17,760 solidification times if we assume a dry 776 00:35:22,640 --> 00:35:20,369 solidus and this blue curve versus with 777 00:35:24,620 --> 00:35:22,650 the wet solidus in this red curve so if 778 00:35:28,490 --> 00:35:24,630 you have a large amount of water in your 779 00:35:29,720 --> 00:35:28,500 system you can potentially increase 780 00:35:31,309 --> 00:35:29,730 the amount of time it takes your 781 00:35:36,950 --> 00:35:31,319 magnetization to solidify pretty 782 00:35:38,660 --> 00:35:36,960 significantly one one thing that people 783 00:35:42,800 --> 00:35:38,670 have brought up a couple of times now is 784 00:35:44,510 --> 00:35:42,810 this idea of a fuzzy core for for giant 785 00:35:46,940 --> 00:35:44,520 planets potentially for sudden Neptune's 786 00:35:50,780 --> 00:35:46,950 and I think also for these steam 787 00:35:53,630 --> 00:35:50,790 atmosphere planets at some point water 788 00:35:56,690 --> 00:35:53,640 and rock become fully miscible within 789 00:35:58,670 --> 00:35:56,700 one another so water we know is in small 790 00:36:01,870 --> 00:35:58,680 quantities soluble in Iraq or in the 791 00:36:07,609 --> 00:36:01,880 melt at high pressures and temperatures 792 00:36:11,599 --> 00:36:07,619 the water rock mixture is is a single 793 00:36:13,940 --> 00:36:11,609 fluid so this is the phase diagram for 794 00:36:16,670 --> 00:36:13,950 the basalt water system basalts a very 795 00:36:18,859 --> 00:36:16,680 common melt on the earth this is showing 796 00:36:23,200 --> 00:36:18,869 at at pressures below this critical 797 00:36:26,510 --> 00:36:23,210 point um you have that for most of this 798 00:36:29,990 --> 00:36:26,520 phase space you have a basaltic solid 799 00:36:32,089 --> 00:36:30,000 and you have the basalt a fluid then you 800 00:36:33,800 --> 00:36:32,099 get above the melting point of the solid 801 00:36:36,349 --> 00:36:33,810 and now you have solid and melts and 802 00:36:39,290 --> 00:36:36,359 then you have a milk and you have over 803 00:36:41,120 --> 00:36:39,300 here a separate water base fluid once 804 00:36:43,790 --> 00:36:41,130 you get to higher pressures above this 805 00:36:47,030 --> 00:36:43,800 critical point now you only have one 806 00:36:49,040 --> 00:36:47,040 fluid okay and this the conditions here 807 00:36:50,359 --> 00:36:49,050 are not very extreme this is about five 808 00:36:56,800 --> 00:36:50,369 giga pascals 809 00:37:01,730 --> 00:36:56,810 and about sorry about 14 1200 1300 810 00:37:03,920 --> 00:37:01,740 degrees C so at some point within these 811 00:37:07,849 --> 00:37:03,930 exoplanet systems we may reach the point 812 00:37:10,010 --> 00:37:07,859 where we have fully miscible water in 813 00:37:13,700 --> 00:37:10,020 Rock system at high pressures within the 814 00:37:15,620 --> 00:37:13,710 interior of a part of our planet this is 815 00:37:19,309 --> 00:37:15,630 a concept we first discussed at a 816 00:37:22,940 --> 00:37:19,319 workshop back in last February February 817 00:37:28,339 --> 00:37:22,950 2018 that 10 Lichtenberg had organized 818 00:37:30,940 --> 00:37:28,349 at University of Zurich and yeah so the 819 00:37:34,520 --> 00:37:30,950 question is what is at what sort of 820 00:37:36,109 --> 00:37:34,530 envelope mass and planet mass do we have 821 00:37:37,700 --> 00:37:36,119 stopped having this sharp boundary 822 00:37:39,620 --> 00:37:37,710 between the silicate mantle and the 823 00:37:42,360 --> 00:37:39,630 envelope I think that's very interesting 824 00:37:45,030 --> 00:37:42,370 impression for future research 825 00:37:48,060 --> 00:37:45,040 um one other thing I wanted to point out 826 00:37:50,400 --> 00:37:48,070 about the silicate Mount and the effect 827 00:37:54,960 --> 00:37:50,410 that water has on it is the density of 828 00:37:55,800 --> 00:37:54,970 the melt this is a figure on the top 829 00:37:57,660 --> 00:37:55,810 left here 830 00:38:01,890 --> 00:37:57,670 I'm sorry top right here showing the 831 00:38:04,080 --> 00:38:01,900 density of a a prototype Mountain 832 00:38:06,300 --> 00:38:04,090 prototype sort of the analog for the 833 00:38:07,950 --> 00:38:06,310 Earth's mantle as a function of the 834 00:38:09,960 --> 00:38:07,960 water content so you can see is going 835 00:38:15,060 --> 00:38:09,970 from about 3.7 grams per centimeter 836 00:38:17,850 --> 00:38:15,070 cubed down to about 3.2 if you add 20 837 00:38:20,250 --> 00:38:17,860 weight percent of water into this into 838 00:38:22,350 --> 00:38:20,260 this melt this is at about 15 GPA um 839 00:38:25,080 --> 00:38:22,360 over here on the Left I've calculated 840 00:38:26,520 --> 00:38:25,090 the equation of states the densities as 841 00:38:29,430 --> 00:38:26,530 a function of pressure and comparing it 842 00:38:32,760 --> 00:38:29,440 just with the standard solid silicate 843 00:38:35,460 --> 00:38:32,770 model for that most people use for mass 844 00:38:39,390 --> 00:38:35,470 radius diagrams this which is this blue 845 00:38:43,440 --> 00:38:39,400 curve the red curve is the dry silicate 846 00:38:45,330 --> 00:38:43,450 melt and then this yellow curve is the 847 00:38:47,790 --> 00:38:45,340 hydrated silicate melt with about 5 848 00:38:51,300 --> 00:38:47,800 weight percent water and you can see 849 00:38:54,090 --> 00:38:51,310 this is affecting mostly the upper upper 850 00:38:55,440 --> 00:38:54,100 layers of the planet but that's where 851 00:38:59,190 --> 00:38:55,450 you're going to get the largest radius 852 00:39:01,320 --> 00:38:59,200 increase so potentially we are sort of 853 00:39:04,620 --> 00:39:01,330 under estimating radius for planets that 854 00:39:08,160 --> 00:39:04,630 have a magma ocean and I also recommend 855 00:39:11,940 --> 00:39:08,170 you go talk to Edwin kite about how 856 00:39:16,680 --> 00:39:11,950 hydrogen and silicate melts might affect 857 00:39:19,380 --> 00:39:16,690 the radii of sub Neptune's in terms of 858 00:39:22,020 --> 00:39:19,390 other processes going on in the magma 859 00:39:25,950 --> 00:39:22,030 ocean the degassing process is one that 860 00:39:28,650 --> 00:39:25,960 really requires a lot more study because 861 00:39:31,650 --> 00:39:28,660 it's not clear whether we have what 862 00:39:33,870 --> 00:39:31,660 model of degassing can actually be 863 00:39:36,000 --> 00:39:33,880 achieved within a magma ocean most 864 00:39:39,000 --> 00:39:36,010 models including my own assume 865 00:39:41,190 --> 00:39:39,010 continuous degassing so that's sort of 866 00:39:43,440 --> 00:39:41,200 highlighted by this upper row of figures 867 00:39:45,690 --> 00:39:43,450 here and what we assume is that the 868 00:39:48,780 --> 00:39:45,700 silicate melt at some point reaches its 869 00:39:52,050 --> 00:39:48,790 saturation point at the surface and then 870 00:39:54,380 --> 00:39:52,060 it out gasses some amount of volatile 871 00:39:56,350 --> 00:39:54,390 zin to the atmosphere to remain at that 872 00:39:59,950 --> 00:39:56,360 saturation point 873 00:40:02,770 --> 00:39:59,960 um and this is controlled sorted by the 874 00:40:06,630 --> 00:40:02,780 diffusivity of the volatile out of the 875 00:40:13,630 --> 00:40:10,720 observations of silicate melts in lavas 876 00:40:16,300 --> 00:40:13,640 on the earth and and looking at love at 877 00:40:18,100 --> 00:40:16,310 degassing suggest that some amount of 878 00:40:21,760 --> 00:40:18,110 degassing is controlled by bubble 879 00:40:23,530 --> 00:40:21,770 formation and bubble nucleation so this 880 00:40:26,070 --> 00:40:23,540 is work from Jenny sue Colley and she 881 00:40:28,750 --> 00:40:26,080 suggests that there might be in some 882 00:40:31,810 --> 00:40:28,760 situations instead of this continuous 883 00:40:34,390 --> 00:40:31,820 degassing catastrophic degassing and so 884 00:40:35,980 --> 00:40:34,400 catastrophic degassing would in order to 885 00:40:38,650 --> 00:40:35,990 nucleate your bubbles you actually 886 00:40:41,590 --> 00:40:38,660 require an oversaturation of the 887 00:40:43,180 --> 00:40:41,600 volatile within your silicate milk and 888 00:40:45,310 --> 00:40:43,190 you also require the presence of 889 00:40:47,410 --> 00:40:45,320 nucleation agents so you have to have 890 00:40:48,820 --> 00:40:47,420 some kind of crystals and sort of the 891 00:40:50,560 --> 00:40:48,830 right kind of crystals floating around 892 00:40:53,290 --> 00:40:50,570 in your silicate in order to allow 893 00:40:55,060 --> 00:40:53,300 bubbles to nucleate and then allow them 894 00:41:00,810 --> 00:40:55,070 to percolate up to the surface where 895 00:41:03,730 --> 00:41:00,820 they can be gas so the idea here is that 896 00:41:05,650 --> 00:41:03,740 there might be some hindrances to this 897 00:41:08,290 --> 00:41:05,660 happening this bubble nucleation process 898 00:41:10,930 --> 00:41:08,300 you don't get to the super saturation 899 00:41:13,750 --> 00:41:10,940 point for instance and then the 900 00:41:16,060 --> 00:41:13,760 degassing would occur very catastrophic 901 00:41:18,630 --> 00:41:16,070 ly sorted at the very end stage of the 902 00:41:23,050 --> 00:41:18,640 magma ocean when you do enrich your melt 903 00:41:26,320 --> 00:41:23,060 much more in the volatile and this would 904 00:41:27,730 --> 00:41:26,330 be by compaction of the accumulate so 905 00:41:29,230 --> 00:41:27,740 you have crystals floating in your 906 00:41:32,590 --> 00:41:29,240 liquid and the bubbles are sort of 907 00:41:35,230 --> 00:41:32,600 trapped within that that mush of 908 00:41:36,940 --> 00:41:35,240 crystals and liquid and so it's once 909 00:41:38,950 --> 00:41:36,950 those start to compact under their own 910 00:41:40,570 --> 00:41:38,960 self gravity that the bull the Bulls 911 00:41:41,380 --> 00:41:40,580 would be free to escape and so this 912 00:41:43,930 --> 00:41:41,390 might happen 913 00:41:47,140 --> 00:41:43,940 in sort of localized occurrences and 914 00:41:49,150 --> 00:41:47,150 sort of catastrophic ly at the end stage 915 00:41:50,710 --> 00:41:49,160 of magma ocean and then there's 916 00:41:52,990 --> 00:41:50,720 possibility that some planets may have 917 00:41:55,390 --> 00:41:53,000 minimal to no degassing and this is if 918 00:41:57,280 --> 00:41:55,400 they never have enough of all tools to 919 00:41:59,020 --> 00:41:57,290 reach this saturation condition for 920 00:42:01,180 --> 00:41:59,030 either that continuous or they 921 00:42:02,830 --> 00:42:01,190 catastrophic degassing so at some point 922 00:42:04,630 --> 00:42:02,840 you might have a planet with a low 923 00:42:06,640 --> 00:42:04,640 enough volatile abundance that most the 924 00:42:07,960 --> 00:42:06,650 volatiles are going to remain trapped 925 00:42:12,250 --> 00:42:07,970 within the 926 00:42:16,420 --> 00:42:12,260 interior of the planet I'm gonna skip 927 00:42:19,120 --> 00:42:16,430 the next slide for time and go and 928 00:42:21,670 --> 00:42:19,130 switch on to to looking at some of the 929 00:42:24,339 --> 00:42:21,680 actual models for these planets this is 930 00:42:26,650 --> 00:42:24,349 going back to work by keiko hamana and 931 00:42:28,660 --> 00:42:26,660 she was again looking at the two types 932 00:42:30,609 --> 00:42:28,670 of planets that you might have depending 933 00:42:31,990 --> 00:42:30,619 on the orbital period of the planet and 934 00:42:36,040 --> 00:42:32,000 so these are sort of Earth and Venus 935 00:42:38,020 --> 00:42:36,050 analogs where you have type 1 planets 936 00:42:40,359 --> 00:42:38,030 are far enough away from their star that 937 00:42:42,450 --> 00:42:40,369 the water this is again with the 938 00:42:46,900 --> 00:42:42,460 assumption of a water vapor atmosphere 939 00:42:49,810 --> 00:42:46,910 that they can cool off without losing a 940 00:42:52,630 --> 00:42:49,820 much atmosphere and eventually form an 941 00:42:54,490 --> 00:42:52,640 ocean so the cooling time scale here is 942 00:42:58,060 --> 00:42:54,500 a few million years for this earth-like 943 00:43:00,550 --> 00:42:58,070 planet and you get water collapsing out 944 00:43:02,849 --> 00:43:00,560 of the atmosphere into an ocean in 945 00:43:06,220 --> 00:43:02,859 contrast for type 2 planets like 946 00:43:07,990 --> 00:43:06,230 potentially like Venus what happens is 947 00:43:10,420 --> 00:43:08,000 that they remain in the magma ocean 948 00:43:14,380 --> 00:43:10,430 phase for a much more extended period of 949 00:43:15,880 --> 00:43:14,390 time and they have this water layer and 950 00:43:18,520 --> 00:43:15,890 their atmosphere and some of it starts 951 00:43:20,890 --> 00:43:18,530 to escape and so in Caicos models 952 00:43:23,710 --> 00:43:20,900 actually the magma ocean only eventually 953 00:43:25,780 --> 00:43:23,720 cools off because you lose enough water 954 00:43:28,390 --> 00:43:25,790 for the surface to finally start to cool 955 00:43:32,470 --> 00:43:28,400 off but there is never any condensation 956 00:43:35,140 --> 00:43:32,480 of water in these models um so James 957 00:43:37,120 --> 00:43:35,150 Owen brought this paper up in his talk 958 00:43:39,630 --> 00:43:37,130 but I'll come back to lure and Parnes 959 00:43:43,120 --> 00:43:39,640 who showed this for exoplanets for 960 00:43:45,810 --> 00:43:43,130 m-dwarf habitable zone planets they are 961 00:43:48,839 --> 00:43:45,820 looking at how the stellar radiation 962 00:43:51,070 --> 00:43:48,849 changes with with time and stellar mass 963 00:43:52,660 --> 00:43:51,080 so this is a calculation from their 964 00:43:54,880 --> 00:43:52,670 paper of the fraction of runaway 965 00:43:56,079 --> 00:43:54,890 greenhouse flux that a planet on the 966 00:43:57,820 --> 00:43:56,089 inner edge of the habitable zone 967 00:44:00,849 --> 00:43:57,830 receives over the course of its lifetime 968 00:44:03,250 --> 00:44:00,859 four stars that are sudden-like down to 969 00:44:04,900 --> 00:44:03,260 a tenth of the solar mass and so again 970 00:44:06,849 --> 00:44:04,910 this kind of planet would remain in the 971 00:44:09,160 --> 00:44:06,859 magma ocean phase if it has a runaway 972 00:44:11,620 --> 00:44:09,170 greenhouse atmosphere for most of its 973 00:44:15,760 --> 00:44:11,630 lifetime and this then leads to the 974 00:44:18,550 --> 00:44:15,770 problem of escape of the atmosphere and 975 00:44:20,109 --> 00:44:18,560 James showed this as well this is water 976 00:44:22,190 --> 00:44:20,119 loss from these planets through this 977 00:44:24,420 --> 00:44:22,200 energy 978 00:44:26,670 --> 00:44:24,430 approximation for the atmospheric escape 979 00:44:28,109 --> 00:44:26,680 where the assumption is that the water 980 00:44:30,569 --> 00:44:28,119 is photo lysing in the upper atmosphere 981 00:44:33,539 --> 00:44:30,579 and you're losing most of the hydrogen 982 00:44:36,120 --> 00:44:33,549 and some amount of the oxygen so here 983 00:44:39,960 --> 00:44:36,130 red is complete loss of one ocean mass 984 00:44:41,670 --> 00:44:39,970 of water and then the oxygen builds up 985 00:44:44,549 --> 00:44:41,680 in the atmosphere especially for these 986 00:44:48,930 --> 00:44:44,559 intermediate-mass stars you get up to 987 00:44:51,479 --> 00:44:48,940 300 bars of oxygen in the atmosphere so 988 00:44:53,819 --> 00:44:51,489 what we wanted to look at was to try a 989 00:44:56,819 --> 00:44:53,829 similar kind of model and see how 990 00:45:00,539 --> 00:44:56,829 actually the oxygen would react with the 991 00:45:01,680 --> 00:45:00,549 magma ocean itself so we originally did 992 00:45:03,569 --> 00:45:01,690 this myself 993 00:45:06,210 --> 00:45:03,579 rubbing Wordsworth's and some other 994 00:45:09,150 --> 00:45:06,220 clubbers at Harvard did this for GJ 995 00:45:11,489 --> 00:45:09,160 11:30 to be many you're probably 996 00:45:13,440 --> 00:45:11,499 familiar with this planet it's around an 997 00:45:14,640 --> 00:45:13,450 M dwarf star about point two solar 998 00:45:17,460 --> 00:45:14,650 masses 999 00:45:19,650 --> 00:45:17,470 it's very earth-like in density it's not 1000 00:45:22,559 --> 00:45:19,660 in the Hat alone it's about 400 Kelvin 1001 00:45:23,880 --> 00:45:22,569 equilibrium temperature but we wanted to 1002 00:45:25,650 --> 00:45:23,890 look at this planet and see if it were 1003 00:45:28,890 --> 00:45:25,660 possible for it to continue outgassing 1004 00:45:31,140 --> 00:45:28,900 over the course of its lifetime and 1005 00:45:32,660 --> 00:45:31,150 whether it would have some kind of 1006 00:45:35,729 --> 00:45:32,670 residual atmosphere that we could 1007 00:45:38,160 --> 00:45:35,739 observe so this is the the magma ocean 1008 00:45:40,019 --> 00:45:38,170 model just again we have water dissolved 1009 00:45:42,359 --> 00:45:40,029 in the magma in the melt 1010 00:45:44,279 --> 00:45:42,369 we're solidifying from the bottom up and 1011 00:45:45,930 --> 00:45:44,289 we have this atmosphere that's the 1012 00:45:48,210 --> 00:45:45,940 pressure of this atmosphere is set by 1013 00:45:50,370 --> 00:45:48,220 this continuous degassing limit where 1014 00:45:52,920 --> 00:45:50,380 we're we're at solubility I sorry 1015 00:45:54,710 --> 00:45:52,930 saturation at the surface um and we have 1016 00:45:57,239 --> 00:45:54,720 X UV radiation hitting the atmosphere 1017 00:46:01,349 --> 00:45:57,249 and we're assuming the sort of energy 1018 00:46:02,999 --> 00:46:01,359 limited escape formula and so we 1019 00:46:06,059 --> 00:46:03,009 compared results for two different 1020 00:46:09,450 --> 00:46:06,069 models for the XUV flex evolution of the 1021 00:46:12,599 --> 00:46:09,460 m dwarf in and for James we used an 1022 00:46:15,150 --> 00:46:12,609 efficiency factor of 0.3 so maybe a 1023 00:46:17,099 --> 00:46:15,160 little high and then we looked at a 1024 00:46:19,710 --> 00:46:17,109 range at the results for a range of 1025 00:46:21,960 --> 00:46:19,720 initial water abundances for the planet 1026 00:46:24,599 --> 00:46:21,970 and iron oxide abundances for the mantle 1027 00:46:27,150 --> 00:46:24,609 and this is where the oxygen is reacting 1028 00:46:30,779 --> 00:46:27,160 out of the atmosphere and into the 1029 00:46:32,370 --> 00:46:30,789 planetary mantle and also highlight 1030 00:46:34,120 --> 00:46:32,380 Robyn Wordsworth is going to talk about 1031 00:46:37,809 --> 00:46:34,130 a further development of this mod 1032 00:46:39,970 --> 00:46:37,819 four habitable zone planets tomorrow so 1033 00:46:44,019 --> 00:46:39,980 this is just a quick example of a magma 1034 00:46:47,200 --> 00:46:44,029 ocean evolution calculation where we're 1035 00:46:50,160 --> 00:46:47,210 modeling the thermal structure of the 1036 00:46:53,380 --> 00:46:50,170 planet how it cools over its lifetime 1037 00:46:55,450 --> 00:46:53,390 the magma ocean is effectively over when 1038 00:46:58,690 --> 00:46:55,460 the so this is the surface temperature 1039 00:47:01,480 --> 00:46:58,700 in the mantle temperature diverge and 1040 00:47:03,339 --> 00:47:01,490 here we get a solid surface and so we no 1041 00:47:05,859 --> 00:47:03,349 longer have atmosphere and mantle 1042 00:47:08,490 --> 00:47:05,869 exchange going on this bottom figure is 1043 00:47:11,799 --> 00:47:08,500 showing the evolution of the water 1044 00:47:13,960 --> 00:47:11,809 inventory between the magma ocean which 1045 00:47:16,960 --> 00:47:13,970 is here the atmosphere in this dash line 1046 00:47:18,579 --> 00:47:16,970 and the dotted line is within the solid 1047 00:47:20,170 --> 00:47:18,589 mantle so you can see we always have 1048 00:47:24,779 --> 00:47:20,180 some amount of water remaining within 1049 00:47:27,999 --> 00:47:24,789 the mantle interior so the magma ocean 1050 00:47:29,680 --> 00:47:28,009 lifetime depends very strongly than on 1051 00:47:35,170 --> 00:47:29,690 the initial water abundance for the 1052 00:47:38,279 --> 00:47:35,180 planet this is going from yeah a few few 1053 00:47:41,950 --> 00:47:38,289 million years out to a few billion years 1054 00:47:44,470 --> 00:47:41,960 depending on the also the XUV flux so 1055 00:47:49,289 --> 00:47:44,480 again this planet often can only cool 1056 00:47:52,839 --> 00:47:49,299 off if it loses all of its water this 1057 00:47:54,640 --> 00:47:52,849 this is highlighting sort of the range 1058 00:47:56,470 --> 00:47:54,650 of lifetimes that we expect for the 1059 00:48:01,150 --> 00:47:56,480 Earth's magma ocean and the Earth's 1060 00:48:03,370 --> 00:48:01,160 water abundance and this is the amount 1061 00:48:05,230 --> 00:48:03,380 of water that the planet is left with at 1062 00:48:07,420 --> 00:48:05,240 the end of these simulations so these 1063 00:48:12,039 --> 00:48:07,430 are five billion years long again this 1064 00:48:14,140 --> 00:48:12,049 is the initial bulk water abundance and 1065 00:48:16,329 --> 00:48:14,150 this is the fraction of water that is 1066 00:48:19,720 --> 00:48:16,339 lost from the planet depending on these 1067 00:48:22,029 --> 00:48:19,730 XUV models so the pink indicates that 1068 00:48:24,190 --> 00:48:22,039 for this low xev model we actually have 1069 00:48:25,900 --> 00:48:24,200 a fair amount of water left within the 1070 00:48:29,380 --> 00:48:25,910 planet but it's all trapped within the 1071 00:48:32,109 --> 00:48:29,390 mantle as I'll show you here okay so 1072 00:48:34,120 --> 00:48:32,119 that's again the Earth's water i'mso 1073 00:48:35,980 --> 00:48:34,130 then to go to the oxygen the oxygen is 1074 00:48:37,809 --> 00:48:35,990 taken up in the magma ocean again by 1075 00:48:40,329 --> 00:48:37,819 reaction with iron because it's the 1076 00:48:42,099 --> 00:48:40,339 dominant element that has this multiple 1077 00:48:44,410 --> 00:48:42,109 valence states within the silicate melt 1078 00:48:46,779 --> 00:48:44,420 often we think in magma ocean models 1079 00:48:47,850 --> 00:48:46,789 that we're starting only with the iron 1080 00:48:50,820 --> 00:48:47,860 two plus four 1081 00:48:53,580 --> 00:48:50,830 and so here we we set the initial iron 1082 00:48:56,010 --> 00:48:53,590 three-plus to zero and allow reaction as 1083 00:48:57,780 --> 00:48:56,020 the oxygen diffuses back down through 1084 00:49:03,510 --> 00:48:57,790 the atmosphere with the melt to make 1085 00:49:06,810 --> 00:49:03,520 this this iron three-plus form um and 1086 00:49:08,400 --> 00:49:06,820 here are the results for the atmospheric 1087 00:49:11,490 --> 00:49:08,410 oxygen um buttons at the end of this 1088 00:49:14,190 --> 00:49:11,500 five billion year evolution timeline so 1089 00:49:17,490 --> 00:49:14,200 this is showing the high xev and low XUV 1090 00:49:20,250 --> 00:49:17,500 models this is for iron oxide in the 1091 00:49:24,240 --> 00:49:20,260 planets mantle and the initial water 1092 00:49:25,980 --> 00:49:24,250 abundance so for this high exiting model 1093 00:49:27,720 --> 00:49:25,990 we essentially end up with with really 1094 00:49:29,820 --> 00:49:27,730 no atmosphere left on this planet we 1095 00:49:32,280 --> 00:49:29,830 would if we go out and observe it we 1096 00:49:34,950 --> 00:49:32,290 might expect to find a Barrett Rock if 1097 00:49:37,830 --> 00:49:34,960 the atmospheric evolution has slightly 1098 00:49:40,260 --> 00:49:37,840 lower XUV and then we might expect sort 1099 00:49:42,360 --> 00:49:40,270 of a tenuous oxygen atmosphere and there 1100 00:49:43,950 --> 00:49:42,370 is still water on this planet but it's 1101 00:49:47,670 --> 00:49:43,960 trapped in the interior so there might 1102 00:49:51,630 --> 00:49:47,680 be some slow leaky outgassing coming 1103 00:49:52,950 --> 00:49:51,640 from the planets interior I'm at higher 1104 00:49:56,330 --> 00:49:52,960 water abundance as we get sort of 1105 00:49:59,730 --> 00:49:56,340 moderate oxygen levels of a few bars 1106 00:50:01,710 --> 00:49:59,740 again no real high no real water left 1107 00:50:03,900 --> 00:50:01,720 but if you go up to these sort of 1108 00:50:06,570 --> 00:50:03,910 extreme water initial water abundances 1109 00:50:08,400 --> 00:50:06,580 of ten to twenty weight percent which 1110 00:50:10,050 --> 00:50:08,410 might be above the limit where the model 1111 00:50:12,180 --> 00:50:10,060 starts breaking down you see you retain 1112 00:50:15,450 --> 00:50:12,190 this thick water atmosphere you have 1113 00:50:17,160 --> 00:50:15,460 several killer bars of oxygen and the 1114 00:50:19,170 --> 00:50:17,170 atmosphere and these planets are still 1115 00:50:21,870 --> 00:50:19,180 in this magma ocean stage because they 1116 00:50:25,880 --> 00:50:21,880 haven't cooled off and they can't cool 1117 00:50:29,280 --> 00:50:25,890 off because they have too much water um 1118 00:50:31,380 --> 00:50:29,290 if we look at the at what happens to the 1119 00:50:34,020 --> 00:50:31,390 action for these planets actually most 1120 00:50:37,110 --> 00:50:34,030 of the oxygen escapes so this is showing 1121 00:50:39,570 --> 00:50:37,120 the fraction of oxygen that remains that 1122 00:50:42,390 --> 00:50:39,580 actually reacts with the mantle of the 1123 00:50:46,110 --> 00:50:42,400 planets again this is the water and iron 1124 00:50:49,770 --> 00:50:46,120 in the mantle the color here is the 1125 00:50:51,450 --> 00:50:49,780 fraction in percent of the total oxygen 1126 00:50:53,550 --> 00:50:51,460 remaining so this is about eight to ten 1127 00:50:55,680 --> 00:50:53,560 percent of the oxygen remains within the 1128 00:50:57,960 --> 00:50:55,690 mantle and this is for the low xeb model 1129 00:51:01,200 --> 00:50:57,970 for the high XUV model in fact almost 1130 00:51:04,589 --> 00:51:01,210 all of the oxygen escape escapes 1131 00:51:07,410 --> 00:51:04,599 but as as james owen mentioned the 1132 00:51:10,859 --> 00:51:07,420 oxygen might in fact be a coolant in 1133 00:51:13,380 --> 00:51:10,869 this outflow and so so it's not clear 1134 00:51:15,390 --> 00:51:13,390 exactly how well this energy limited 1135 00:51:18,960 --> 00:51:15,400 formula for the oxygen escape is working 1136 00:51:21,829 --> 00:51:18,970 so everything limit the oxygen loss so 1137 00:51:24,990 --> 00:51:21,839 we turn it off and run the model again 1138 00:51:26,970 --> 00:51:25,000 then what we get is that in fact most of 1139 00:51:29,430 --> 00:51:26,980 the oxygen reacts with the planet's 1140 00:51:32,400 --> 00:51:29,440 mantle this is up to ninety percent is 1141 00:51:34,589 --> 00:51:32,410 reacting and this dividing line here is 1142 00:51:36,720 --> 00:51:34,599 essentially because well we have too 1143 00:51:39,000 --> 00:51:36,730 much oxygen being produced from this 1144 00:51:40,770 --> 00:51:39,010 water and the mantle can't hold on to it 1145 00:51:45,859 --> 00:51:40,780 it doesn't have enough iron oxide down 1146 00:51:49,770 --> 00:51:45,869 at this lower sorry upper left-hand side 1147 00:51:51,900 --> 00:51:49,780 so we have more mantle oxidation when 1148 00:51:57,059 --> 00:51:51,910 there is no oxygen loss up to ninety 1149 00:51:59,700 --> 00:51:57,069 percent okay and then that leaves me 1150 00:52:02,069 --> 00:51:59,710 very quickly to talk a little bit about 1151 00:52:06,780 --> 00:52:02,079 the evolution of the Earth's mantle 1152 00:52:09,809 --> 00:52:06,790 oxidation state so the we can measure 1153 00:52:11,819 --> 00:52:09,819 the Earth's oxidation state both at the 1154 00:52:14,010 --> 00:52:11,829 present day through looking at basalts 1155 00:52:18,150 --> 00:52:14,020 and other material coming out of the 1156 00:52:20,039 --> 00:52:18,160 mantle and we get values around around 1157 00:52:22,380 --> 00:52:20,049 this quartz feel like magnetite buffer 1158 00:52:23,819 --> 00:52:22,390 which is quite a bit above the iron 1159 00:52:26,099 --> 00:52:23,829 phosphate buffer that I talked about a 1160 00:52:28,349 --> 00:52:26,109 little bit before um and we have 1161 00:52:30,839 --> 00:52:28,359 measurements of proxies going back to 1162 00:52:33,150 --> 00:52:30,849 about 3.8 billion years which is sort of 1163 00:52:35,430 --> 00:52:33,160 the limit of our rock record and it 1164 00:52:37,829 --> 00:52:35,440 seems to have a pretty constant value 1165 00:52:39,990 --> 00:52:37,839 and so people have have long assumed 1166 00:52:41,849 --> 00:52:40,000 that the composition of volcanic gases 1167 00:52:44,280 --> 00:52:41,859 coming out of the Earth's interior has 1168 00:52:46,170 --> 00:52:44,290 been essentially the same over geologic 1169 00:52:49,440 --> 00:52:46,180 history because of this constant 1170 00:52:50,970 --> 00:52:49,450 oxidation state during during planet 1171 00:52:52,650 --> 00:52:50,980 formation however when there is metal 1172 00:52:56,039 --> 00:52:52,660 present and reacting with the magma 1173 00:52:58,829 --> 00:52:56,049 ocean and reacting with the silicate 1174 00:53:02,640 --> 00:52:58,839 mantle the predicted oxidation state of 1175 00:53:04,410 --> 00:53:02,650 the earth is down here it's 8 log units 1176 00:53:09,250 --> 00:53:04,420 below the present-day 1177 00:53:12,310 --> 00:53:09,260 or down to eight log units and so I'm 1178 00:53:14,530 --> 00:53:12,320 there have been a lot of people a lot of 1179 00:53:17,320 --> 00:53:14,540 models to try to explain this over time 1180 00:53:20,770 --> 00:53:17,330 through various mechanisms by accretion 1181 00:53:23,490 --> 00:53:20,780 of oxidized material by a slow oxidation 1182 00:53:26,200 --> 00:53:23,500 of hydrogen loss maybe have very slow 1183 00:53:28,090 --> 00:53:26,210 change in oxidation state over this 1184 00:53:31,620 --> 00:53:28,100 first half a million half a billion 1185 00:53:35,190 --> 00:53:31,630 years but I'm gonna talk you through 1186 00:53:38,140 --> 00:53:35,200 very quickly a possible oxidation 1187 00:53:41,260 --> 00:53:38,150 mechanism that's related solely to the 1188 00:53:42,430 --> 00:53:41,270 chemistry of the silicate melt and then 1189 00:53:45,250 --> 00:53:42,440 I'm not going to talk about this 1190 00:53:47,440 --> 00:53:45,260 actually because I won't have time so 1191 00:53:50,260 --> 00:53:47,450 this is a processes that happens during 1192 00:53:52,930 --> 00:53:50,270 core formation and it should be pretty 1193 00:53:54,790 --> 00:53:52,940 intrinsic to the process for many 1194 00:53:57,550 --> 00:53:54,800 terrestrial planets and what happens is 1195 00:53:59,470 --> 00:53:57,560 so we have both silicate and metal being 1196 00:54:03,340 --> 00:53:59,480 delivered to the planet at is as it's 1197 00:54:04,960 --> 00:54:03,350 growing and we have some equilibration 1198 00:54:06,460 --> 00:54:04,970 going on between the silicate in the 1199 00:54:08,920 --> 00:54:06,470 metal in fact we think that there is 1200 00:54:11,560 --> 00:54:08,930 some amount of silicon and oxygen 1201 00:54:13,150 --> 00:54:11,570 present within the Earth's core today 1202 00:54:15,190 --> 00:54:13,160 and that's because the density of 1203 00:54:18,970 --> 00:54:15,200 Earth's core is slightly below that of 1204 00:54:20,710 --> 00:54:18,980 pure iron and which is why I'm including 1205 00:54:23,080 --> 00:54:20,720 these reactions here so we have iron 1206 00:54:25,960 --> 00:54:23,090 metal reacting with silicates in the in 1207 00:54:28,030 --> 00:54:25,970 the liquid and you get some amount of 1208 00:54:30,310 --> 00:54:28,040 silicon and some amount of oxygen going 1209 00:54:31,960 --> 00:54:30,320 into your metal phase that is then 1210 00:54:35,140 --> 00:54:31,970 sinking to the bottom of your planet and 1211 00:54:37,630 --> 00:54:35,150 forming your metallic core and that's 1212 00:54:40,410 --> 00:54:37,640 governed by these equilibrium constants 1213 00:54:43,000 --> 00:54:40,420 over here here's a very complicated 1214 00:54:46,000 --> 00:54:43,010 formula for this from that has been 1215 00:54:48,090 --> 00:54:46,010 calibrated from experiments and then the 1216 00:54:50,550 --> 00:54:48,100 other reaction we can add into this now 1217 00:54:53,410 --> 00:54:50,560 because we now have some new 1218 00:54:55,540 --> 00:54:53,420 experimental data on silicate melts at 1219 00:54:58,540 --> 00:54:55,550 higher pressures is this reaction down 1220 00:55:02,770 --> 00:54:58,550 here at the bottom so what this reaction 1221 00:55:06,190 --> 00:55:02,780 is showing is that we have the mantle is 1222 00:55:08,590 --> 00:55:06,200 dominated by this iron two-plus in the 1223 00:55:10,810 --> 00:55:08,600 in the silicate melt but at high 1224 00:55:13,690 --> 00:55:10,820 pressure what happens is the volume 1225 00:55:16,270 --> 00:55:13,700 change of this reaction shifts in favor 1226 00:55:19,500 --> 00:55:16,280 of iron three-plus so at high pressures 1227 00:55:21,840 --> 00:55:19,510 iron three-plus becomes stabilized 1228 00:55:24,090 --> 00:55:21,850 and in order to charge balance this 1229 00:55:26,820 --> 00:55:24,100 reaction you have to also produce some 1230 00:55:28,950 --> 00:55:26,830 metal so this is kind of complicated but 1231 00:55:31,410 --> 00:55:28,960 what happens is if you can separate this 1232 00:55:33,359 --> 00:55:31,420 metal at the time that this reaction is 1233 00:55:35,849 --> 00:55:33,369 happening remove it from your mantle 1234 00:55:38,220 --> 00:55:35,859 system now you've effectively increased 1235 00:55:40,260 --> 00:55:38,230 your iron to oxygen ratio in the mantle 1236 00:55:42,270 --> 00:55:40,270 and this is connected of course to 1237 00:55:44,820 --> 00:55:42,280 outgassing through the oxygen fugacity 1238 00:55:47,760 --> 00:55:44,830 of the system so the higher the iron 1239 00:55:50,849 --> 00:55:47,770 three-plus abundance the higher your 1240 00:55:53,510 --> 00:55:50,859 oxygen fugacity is going to be so we've 1241 00:55:56,960 --> 00:55:53,520 done some calculations using some newer 1242 00:55:58,980 --> 00:55:56,970 experimental data on this prior 1243 00:56:01,710 --> 00:55:58,990 calculations would put the iron 1244 00:56:04,260 --> 00:56:01,720 three-plus abundance within the silicate 1245 00:56:06,570 --> 00:56:04,270 melt at as a function of pressure along 1246 00:56:08,250 --> 00:56:06,580 this green curve here and so core 1247 00:56:10,830 --> 00:56:08,260 information we think happens at pretty 1248 00:56:13,170 --> 00:56:10,840 high pressures up to 50 to 60 Giga 1249 00:56:14,670 --> 00:56:13,180 Pascal's within the planet and that 1250 00:56:18,090 --> 00:56:14,680 pressure should probably grow as a 1251 00:56:20,820 --> 00:56:18,100 function of planet size but so this 1252 00:56:23,010 --> 00:56:20,830 original low pressure data would suggest 1253 00:56:25,460 --> 00:56:23,020 that you don't really produce any of 1254 00:56:28,950 --> 00:56:25,470 this iron three-plus in the mantle um 1255 00:56:31,200 --> 00:56:28,960 but this new experimental data gives us 1256 00:56:33,390 --> 00:56:31,210 this curve up here which at the 1257 00:56:35,130 --> 00:56:33,400 conditions that we think for the average 1258 00:56:37,590 --> 00:56:35,140 core formation conditions of the Earth's 1259 00:56:39,599 --> 00:56:37,600 gives us about one-and-a-half percent of 1260 00:56:44,460 --> 00:56:39,609 iron three-plus and that matches the 1261 00:56:46,320 --> 00:56:44,470 present-day so with this new data we can 1262 00:56:48,349 --> 00:56:46,330 now match the oxidation state of the 1263 00:56:51,780 --> 00:56:48,359 Earth's mantle 1264 00:56:53,910 --> 00:56:51,790 during core information so I'm gonna 1265 00:56:58,730 --> 00:56:53,920 skip through a lot of this because it's 1266 00:57:02,130 --> 00:56:58,740 complicated but what happens is is that 1267 00:57:04,380 --> 00:57:02,140 you have during this time of core 1268 00:57:06,240 --> 00:57:04,390 formation you have a really low oxygen 1269 00:57:09,750 --> 00:57:06,250 fugacity and so you expect really 1270 00:57:11,640 --> 00:57:09,760 reduced gases like hydrogen h2 and 1271 00:57:14,370 --> 00:57:11,650 carbon monoxide to be your outgassing 1272 00:57:16,349 --> 00:57:14,380 species as you increase the oxidation 1273 00:57:18,300 --> 00:57:16,359 state of the mantle you should expect a 1274 00:57:21,870 --> 00:57:18,310 shift from that kind of composition to 1275 00:57:25,920 --> 00:57:21,880 more water and co2 rich atmospheres and 1276 00:57:29,580 --> 00:57:25,930 so because this reaction is a function 1277 00:57:31,590 --> 00:57:29,590 of pressure of this of this reaction it 1278 00:57:32,089 --> 00:57:31,600 might be a function of planet size as 1279 00:57:34,699 --> 00:57:32,099 well 1280 00:57:36,859 --> 00:57:34,709 and so you might expect a shift in the 1281 00:57:39,140 --> 00:57:36,869 oxidation state from smaller planets 1282 00:57:46,039 --> 00:57:39,150 being more reduced to the larger planets 1283 00:57:52,519 --> 00:57:46,049 being more oxidized okay okay so I'll 1284 00:57:55,189 --> 00:57:52,529 just skip really quickly from that so so 1285 00:57:57,079 --> 00:57:55,199 by the time our planet is fully formed 1286 00:57:59,299 --> 00:57:57,089 we should be at an oxidation state for 1287 00:58:04,459 --> 00:57:59,309 the earth at least where we favor water 1288 00:58:05,959 --> 00:58:04,469 and co2 compositions but this is a 1289 00:58:07,519 --> 00:58:05,969 calculation that we did for the book 1290 00:58:09,229 --> 00:58:07,529 silicate earth where you can see that 1291 00:58:11,599 --> 00:58:09,239 it's not just water and co2 in this 1292 00:58:14,420 --> 00:58:11,609 atmosphere there's a lot more minor 1293 00:58:17,359 --> 00:58:14,430 species like sulphur dioxide you have a 1294 00:58:19,130 --> 00:58:17,369 lot of lots of file elements and these 1295 00:58:20,689 --> 00:58:19,140 are all contributing to the spectra 1296 00:58:22,430 --> 00:58:20,699 they're contributing to the rate at 1297 00:58:25,160 --> 00:58:22,440 which the planet is cooling from the 1298 00:58:27,229 --> 00:58:25,170 upper atmosphere this is a calculation 1299 00:58:29,900 --> 00:58:27,239 of the emission spectra of the top of 1300 00:58:33,589 --> 00:58:29,910 the atmosphere that Roxanna looper did 1301 00:58:36,349 --> 00:58:33,599 with these gas compositions compared to 1302 00:58:40,400 --> 00:58:36,359 models of pure waters sorry this is a 1303 00:58:42,469 --> 00:58:40,410 model of 90% water and 10% co2 so that 1304 00:58:46,870 --> 00:58:42,479 composition on the previous page is in 1305 00:58:49,279 --> 00:58:46,880 the red the blue is another complicated 1306 00:58:51,229 --> 00:58:49,289 continental crust composition and you 1307 00:58:53,839 --> 00:58:51,239 can see a significant difference in the 1308 00:58:56,239 --> 00:58:53,849 spectra of this planet this could be 1309 00:58:58,599 --> 00:58:56,249 observable in for instance giant impacts 1310 00:59:01,339 --> 00:58:58,609 this could be observable in these hot 1311 00:59:03,400 --> 00:59:01,349 exoplanets that have surface magma 1312 00:59:06,049 --> 00:59:03,410 oceans caused by the steam atmosphere 1313 00:59:09,349 --> 00:59:06,059 but it also affects the cooling time 1314 00:59:11,539 --> 00:59:09,359 scale for for Earth in particular 1315 00:59:13,999 --> 00:59:11,549 so I'll just bump through this really 1316 00:59:16,519 --> 00:59:14,009 quickly this is the cooling timescale if 1317 00:59:18,769 --> 00:59:16,529 you take that continental crust derived 1318 00:59:20,359 --> 00:59:18,779 atmosphere you get a cooling timescale 1319 00:59:23,660 --> 00:59:20,369 for the Earth's magma ocean of about 1320 00:59:25,549 --> 00:59:23,670 200,000 years for that bulk silicate 1321 00:59:28,099 --> 00:59:25,559 Earth composition you get two million 1322 00:59:32,299 --> 00:59:28,109 years so that's a factor of 10 in 1323 00:59:36,589 --> 00:59:32,309 cooling timescale okay so with that I am 1324 00:59:39,079 --> 00:59:36,599 going to jump to my conclusion slide and 1325 00:59:40,339 --> 00:59:39,089 I'll tell you I think one of the big 1326 00:59:42,769 --> 00:59:40,349 things to take away from this is that 1327 00:59:44,449 --> 00:59:42,779 the planetary oxidation state is 1328 00:59:45,650 --> 00:59:44,459 determined during the magma ocean stage 1329 00:59:48,320 --> 00:59:45,660 for many plain 1330 00:59:51,320 --> 00:59:48,330 it might be a function of the planet 1331 00:59:53,180 --> 00:59:51,330 sighs I think we really need some 1332 00:59:55,250 --> 00:59:53,190 improved models to understand the 1333 00:59:57,560 --> 00:59:55,260 evolution of oxidation state for both 1334 00:59:59,090 --> 00:59:57,570 Earth's and other planets and then I 1335 01:00:01,400 --> 00:59:59,100 think there's a lot of interesting 1336 01:00:03,380 --> 01:00:01,410 outstanding issues to work on for the 1337 01:00:05,300 --> 01:00:03,390 lava worlds whether they have volatile 1338 01:00:07,730 --> 01:00:05,310 x' or not whether they're synchronously 1339 01:00:10,010 --> 01:00:07,740 rotating the runaway greenhouse planets 1340 01:00:13,000 --> 01:00:10,020 and what their atmospheric compositions 1341 01:00:15,530 --> 01:00:13,010 are what their spectra are and whether 1342 01:00:17,960 --> 01:00:15,540 atmospheric escape is sculpting their 1343 01:00:20,360 --> 01:00:17,970 compositions and then we need a lot of 1344 01:00:22,070 --> 01:00:20,370 experimental data so if you're inspired 1345 01:00:23,570 --> 01:00:22,080 by Maggie's talk earlier and want to get 1346 01:00:25,940 --> 01:00:23,580 into experiments there's plenty of 1347 01:00:35,990 --> 01:00:25,950 things to measure okay so with that 1348 01:00:38,150 --> 01:00:36,000 thank you okay we covered a lot of 1349 01:00:50,440 --> 01:00:38,160 ground but we have a question for time 1350 01:00:56,360 --> 01:00:54,560 thanks for a great talk this might be 1351 01:01:00,590 --> 01:00:56,370 very naive question but at the very 1352 01:01:04,490 --> 01:01:00,600 lower planet size regime is there any 1353 01:01:08,870 --> 01:01:04,500 evidence the mercury love oceans and or 1354 01:01:12,050 --> 01:01:08,880 outgassing and could any constraints on 1355 01:01:14,300 --> 01:01:12,060 that be used to to help inform the 1356 01:01:18,380 --> 01:01:14,310 interior cooling rate models for that 1357 01:01:19,970 --> 01:01:18,390 very low size right right so there there 1358 01:01:22,670 --> 01:01:19,980 has been obviously suggestions that 1359 01:01:24,440 --> 01:01:22,680 mercury lost a lot of its mantle due to 1360 01:01:26,480 --> 01:01:24,450 a giant impact and then you would assume 1361 01:01:28,730 --> 01:01:26,490 that some portion of the the remaining 1362 01:01:30,530 --> 01:01:28,740 planet might have melted as well um we 1363 01:01:33,410 --> 01:01:30,540 don't have really good evidence from the 1364 01:01:37,700 --> 01:01:33,420 the present set of observations for a 1365 01:01:46,520 --> 01:01:37,710 magma ocean but you know Steve - he has 1366 01:01:55,550 --> 01:01:46,530 a model does anyone have a burning 1367 01:01:59,550 --> 01:01:57,180 great talk 1368 01:02:01,830 --> 01:01:59,560 Ted c'mon sake Chicago so a couple 1369 01:02:04,980 --> 01:02:01,840 people in this room a couple years ago 1370 01:02:07,590 --> 01:02:04,990 tried to explain 55 canker ease thermal 1371 01:02:10,830 --> 01:02:07,600 phase curve using a hydrogen nitrogen 1372 01:02:12,750 --> 01:02:10,840 atmosphere is that like is that okay if 1373 01:02:16,650 --> 01:02:12,760 there's a magma ocean a lava lava ocean 1374 01:02:18,450 --> 01:02:16,660 or is that not okay chemically um I mean 1375 01:02:19,920 --> 01:02:18,460 I think you'd you could definitely still 1376 01:02:22,830 --> 01:02:19,930 have a magma ocean with a hydrogen 1377 01:02:26,340 --> 01:02:22,840 nitrogen atmosphere I think the question 1378 01:02:29,370 --> 01:02:26,350 for me is whether a hydrogen atmosphere 1379 01:02:31,680 --> 01:02:29,380 is stable against the escape certainly I 1380 01:02:33,780 --> 01:02:31,690 think that planet has to have some kind 1381 01:02:40,650 --> 01:02:33,790 of atmosphere to explain it's it's lower 1382 01:02:42,210 --> 01:02:40,660 density yeah yeah I'll just comment as 1383 01:02:44,550 --> 01:02:42,220 we said as Mark and I said in the paper 1384 01:02:46,770 --> 01:02:44,560 we don't think that a hydrogen 1385 01:02:50,550 --> 01:02:46,780 atmosphere is actually plausible because 1386 01:02:53,940 --> 01:02:50,560 of the escape problem but if you really 1387 01:02:56,400 --> 01:02:53,950 believe the phase shift of the hotspot 1388 01:02:57,960 --> 01:02:56,410 that forces you in the direction of a 1389 01:03:00,510 --> 01:02:57,970 hydrogen a hydrogen rich atmosphere 1390 01:03:03,300 --> 01:03:00,520 which is really problematic right right 1391 01:03:04,350 --> 01:03:03,310 and in order to account for the HCN 1392 01:03:06,240 --> 01:03:04,360 observation if you believe that 1393 01:03:08,970 --> 01:03:06,250 observation is hard to do that without 1394 01:03:12,990 --> 01:03:08,980 some significant hydrogen bearing