1 00:00:10,160 --> 00:00:06,940 [Music] 2 00:00:11,360 --> 00:00:10,170 thank you very much it's a great 3 00:00:14,169 --> 00:00:11,370 pleasure to be here and it's a great 4 00:00:16,640 --> 00:00:14,179 pleasure to be able to give you such a 5 00:00:19,010 --> 00:00:16,650 sort of peak given the freedom to give 6 00:00:21,920 --> 00:00:19,020 in quite a long talk so I can go into 7 00:00:25,570 --> 00:00:21,930 the details which I kind of enjoy from 8 00:00:28,880 --> 00:00:25,580 time to time so I was given the topic of 9 00:00:34,490 --> 00:00:28,890 atmospheric escape no other qualifiers 10 00:00:37,189 --> 00:00:34,500 after that but I've through simplified 11 00:00:39,530 --> 00:00:37,199 it slightly to a master escape of highly 12 00:00:41,000 --> 00:00:39,540 irradiated exoplanets and there's a good 13 00:00:41,510 --> 00:00:41,010 reason for that which I'll show you in a 14 00:00:43,520 --> 00:00:41,520 second 15 00:00:46,069 --> 00:00:43,530 and I've also simplified it further that 16 00:00:48,440 --> 00:00:46,079 I'm just going to focus on atmospheric 17 00:00:50,000 --> 00:00:48,450 escape that's thermally driven so driven 18 00:00:54,680 --> 00:00:50,010 by heating rather than any other 19 00:00:56,119 --> 00:00:54,690 processes so the reason why I think we 20 00:00:59,000 --> 00:00:56,129 should be thinking about atmospheric 21 00:01:01,160 --> 00:00:59,010 escape for highly irradiated planets is 22 00:01:03,709 --> 00:01:01,170 when we look at the kind of exoplanets 23 00:01:05,359 --> 00:01:03,719 that we're going to be able to probe 24 00:01:11,000 --> 00:01:05,369 over the coming decade 25 00:01:15,850 --> 00:01:11,010 they are dominated by two a sort of 26 00:01:18,289 --> 00:01:15,860 facts so these are sort of test yields 27 00:01:21,890 --> 00:01:18,299 they're small planets all less than four 28 00:01:23,660 --> 00:01:21,900 Earth radii you can go to this this 29 00:01:26,570 --> 00:01:23,670 catalogue this also includes some sort 30 00:01:28,760 --> 00:01:26,580 of estimation of what the tests extended 31 00:01:30,620 --> 00:01:28,770 mission will do so now we're in the era 32 00:01:32,780 --> 00:01:30,630 that Tess's sort of finished its first 33 00:01:34,850 --> 00:01:32,790 year operations it's into its second 34 00:01:36,440 --> 00:01:34,860 year of operations and now it's going 35 00:01:38,149 --> 00:01:36,450 into the extend emission you find two 36 00:01:40,310 --> 00:01:38,159 things when you go through these yields 37 00:01:42,590 --> 00:01:40,320 firstly that the majority of the planets 38 00:01:45,560 --> 00:01:42,600 that we're gonna find are billions of 39 00:01:48,859 --> 00:01:45,570 years old but they're also incredibly 40 00:01:51,800 --> 00:01:48,869 highly irradiated right so this is earth 41 00:01:54,020 --> 00:01:51,810 down here this is mercury and our solar 42 00:01:56,149 --> 00:01:54,030 system and this is where the majority of 43 00:01:58,580 --> 00:01:56,159 the exoplanets we're gonna discover and 44 00:02:00,920 --> 00:01:58,590 be able to characterize in the next 45 00:02:03,139 --> 00:02:00,930 decade sit so they're sort of at a 46 00:02:05,990 --> 00:02:03,149 radiation level that's a hundred or 47 00:02:07,580 --> 00:02:06,000 hundred times or thirty times bigger 48 00:02:11,289 --> 00:02:07,590 than the earth and our order at least an 49 00:02:14,150 --> 00:02:11,299 order of magnitude larger than mercury 50 00:02:15,740 --> 00:02:14,160 this is even more pronounced when you 51 00:02:18,050 --> 00:02:15,750 look at the small planet so the small 52 00:02:19,190 --> 00:02:18,060 planets are gonna again be dominated by 53 00:02:22,460 --> 00:02:19,200 being these highly 54 00:02:26,449 --> 00:02:22,470 radiated plants now this is important 55 00:02:29,780 --> 00:02:26,459 because irradiation drives escape and 56 00:02:35,300 --> 00:02:29,790 the fact they're also old also has 57 00:02:39,259 --> 00:02:35,310 another consequence given that escape 58 00:02:42,290 --> 00:02:39,269 tends to be driven by the x-rays and the 59 00:02:45,680 --> 00:02:42,300 Eevee that the star outputs which is 60 00:02:50,119 --> 00:02:45,690 much much larger in the stars youth than 61 00:02:52,130 --> 00:02:50,129 when we see these today this means that 62 00:02:54,170 --> 00:02:52,140 for all the small exoplanets that we're 63 00:02:56,509 --> 00:02:54,180 probably gonna get spectral for the next 64 00:03:00,410 --> 00:02:56,519 10 years atmospheric escape will have 65 00:03:01,850 --> 00:03:00,420 already sculpted their atmosphere so 66 00:03:04,069 --> 00:03:01,860 this is a process that we're gonna need 67 00:03:06,860 --> 00:03:04,079 to understand in order to meet 68 00:03:08,539 --> 00:03:06,870 understand the compositions and those 69 00:03:10,580 --> 00:03:08,549 properties of the atmospheres that we're 70 00:03:12,800 --> 00:03:10,590 going to be detecting over the next 10 71 00:03:14,420 --> 00:03:12,810 years and there's lots of work to do 72 00:03:17,270 --> 00:03:14,430 especially as we move towards the 73 00:03:23,240 --> 00:03:17,280 terrestrial planets this problem is sort 74 00:03:25,640 --> 00:03:23,250 of somewhat unsolved so in this talk I'm 75 00:03:27,979 --> 00:03:25,650 gonna go through a few things I'm gonna 76 00:03:29,990 --> 00:03:27,989 talk about the the very basic physics of 77 00:03:32,120 --> 00:03:30,000 thermal escape what do I mean what are 78 00:03:33,890 --> 00:03:32,130 the the different regimes that you might 79 00:03:35,780 --> 00:03:33,900 think about I'm gonna then talk about 80 00:03:38,840 --> 00:03:35,790 sort of hydrogen helium dominated 81 00:03:40,640 --> 00:03:38,850 atmospheres and this is where in the 82 00:03:42,710 --> 00:03:40,650 exit pipe community we sort of focused 83 00:03:43,910 --> 00:03:42,720 our theoretical work over the last ten 84 00:03:47,240 --> 00:03:43,920 years and we've had quite a bit of a 85 00:03:48,949 --> 00:03:47,250 success then I'm going to talk about 86 00:03:52,160 --> 00:03:48,959 water loss from habitable zone planets 87 00:03:53,569 --> 00:03:52,170 around M dwarfs this is a very important 88 00:03:57,319 --> 00:03:53,579 problem if we want to start thinking 89 00:03:59,270 --> 00:03:57,329 about habitability of M dwarfs is that 90 00:04:01,120 --> 00:03:59,280 they have due to their stellar evolution 91 00:04:04,000 --> 00:04:01,130 they have quite a different track to 92 00:04:07,550 --> 00:04:04,010 temperate planets around sun-like stars 93 00:04:09,410 --> 00:04:07,560 if I if I get time I'm going to allude 94 00:04:11,360 --> 00:04:09,420 to perhaps a pathway to how we can 95 00:04:14,120 --> 00:04:11,370 understand as farik escape from more 96 00:04:17,529 --> 00:04:14,130 complicated heavy element or secondary 97 00:04:19,759 --> 00:04:17,539 atmospheres and that's we're sort of my 98 00:04:21,740 --> 00:04:19,769 favorite topic at the moment which is 99 00:04:23,600 --> 00:04:21,750 sort of silicate vapor atmospheres 100 00:04:24,980 --> 00:04:23,610 around ultra short period planets these 101 00:04:27,140 --> 00:04:24,990 are planets that are so close to the 102 00:04:29,690 --> 00:04:27,150 star the star is actually able to melt 103 00:04:31,399 --> 00:04:29,700 their rocky surface and former that's to 104 00:04:32,600 --> 00:04:31,409 look at vapor atmosphere and throughout 105 00:04:36,320 --> 00:04:32,610 this talk angular sort of 106 00:04:38,300 --> 00:04:36,330 also point to the problems that we need 107 00:04:43,010 --> 00:04:38,310 to theoretical problems that we need to 108 00:04:45,830 --> 00:04:43,020 address over the next 10 years or so so 109 00:04:47,450 --> 00:04:45,840 the physics of family-driven escape so I 110 00:04:49,490 --> 00:04:47,460 said in this talking I'm going to only 111 00:04:52,240 --> 00:04:49,500 focus on thermally driven escape escape 112 00:04:55,159 --> 00:04:52,250 driven by heating there is a poster 113 00:04:58,760 --> 00:04:55,169 which is on impact driven escape which I 114 00:05:00,950 --> 00:04:58,770 encourage you to go look at as well so 115 00:05:03,679 --> 00:05:00,960 family is driven escape and it's the 116 00:05:08,119 --> 00:05:03,689 most simple keynote cartoon version is 117 00:05:10,159 --> 00:05:08,129 that the star is heating out putting 118 00:05:12,110 --> 00:05:10,169 some photons and it heats the planet's 119 00:05:13,850 --> 00:05:12,120 atmosphere heats the surface layers of 120 00:05:16,070 --> 00:05:13,860 the planet's atmosphere and that 121 00:05:20,719 --> 00:05:16,080 atmosphere becomes hot enough that it 122 00:05:24,709 --> 00:05:20,729 can escape from the planet in more 123 00:05:27,950 --> 00:05:24,719 detail there are a couple of limits of 124 00:05:30,200 --> 00:05:27,960 this process so if you consider the 125 00:05:31,999 --> 00:05:30,210 planet's atmosphere which i've shown 126 00:05:34,399 --> 00:05:32,009 here these are atoms in the planet's 127 00:05:36,290 --> 00:05:34,409 atmosphere the base of the planets down 128 00:05:38,869 --> 00:05:36,300 here and the top of the atmosphere is up 129 00:05:41,570 --> 00:05:38,879 here so under the stratification of 130 00:05:44,119 --> 00:05:41,580 gravity the density is much much lower 131 00:05:45,950 --> 00:05:44,129 close to the surface of the planet and 132 00:05:48,350 --> 00:05:45,960 it sorry it's much the density of the 133 00:05:49,610 --> 00:05:48,360 gas is much much higher lower close to 134 00:05:52,369 --> 00:05:49,620 the surface of the planet but it's much 135 00:05:54,079 --> 00:05:52,379 much lower at higher altitudes and our 136 00:05:57,980 --> 00:05:54,089 photons from our star come in and they 137 00:06:00,469 --> 00:05:57,990 heat and in order to understand what 138 00:06:03,589 --> 00:06:00,479 regimes you are in the thermal escape 139 00:06:07,519 --> 00:06:03,599 there's two sort of critical radii in 140 00:06:10,369 --> 00:06:07,529 this atmosphere so there's the where the 141 00:06:13,309 --> 00:06:10,379 particle mean free path equals the 142 00:06:15,350 --> 00:06:13,319 atmospheric scale height so this is the 143 00:06:17,269 --> 00:06:15,360 distance the particles travel before 144 00:06:20,719 --> 00:06:17,279 they collide with another gas particle 145 00:06:22,790 --> 00:06:20,729 if your reach the point where the mean 146 00:06:25,760 --> 00:06:22,800 free path of the particles is larger 147 00:06:27,499 --> 00:06:25,770 than the planets scale height then the 148 00:06:29,149 --> 00:06:27,509 atoms in the atmosphere essentially sort 149 00:06:33,079 --> 00:06:29,159 of going up and down 150 00:06:34,790 --> 00:06:33,089 never colliding with another atom so 151 00:06:37,879 --> 00:06:34,800 they're behaving in a sort of 152 00:06:40,010 --> 00:06:37,889 collisionless way below this limit where 153 00:06:42,139 --> 00:06:40,020 the density is high enough the mean free 154 00:06:44,839 --> 00:06:42,149 path is shorter than the scale height 155 00:06:45,980 --> 00:06:44,849 the gas behaves more like a fluid the 156 00:06:52,909 --> 00:06:45,990 collisionless process 157 00:06:55,189 --> 00:06:52,919 there's another critical density or 158 00:06:56,809 --> 00:06:55,199 critical radius in the atmosphere it's 159 00:06:59,839 --> 00:06:56,819 where the particles thermal energy 160 00:07:01,520 --> 00:06:59,849 exceeds the bind their binding energy 161 00:07:04,820 --> 00:07:01,530 their gravitational binding energy so if 162 00:07:07,129 --> 00:07:04,830 you're above this radius you have enough 163 00:07:10,879 --> 00:07:07,139 thermal energy to escape from the 164 00:07:14,200 --> 00:07:10,889 planets gravity and the thermal escape 165 00:07:17,659 --> 00:07:14,210 regime you end up sitting in depends on 166 00:07:21,140 --> 00:07:17,669 which of these radii you encounter first 167 00:07:22,670 --> 00:07:21,150 as you go up in the atmosphere so if we 168 00:07:25,490 --> 00:07:22,680 think about a weakly irradiated 169 00:07:31,490 --> 00:07:25,500 atmosphere first it's not very hot it's 170 00:07:33,469 --> 00:07:31,500 not very hot then you need to go high up 171 00:07:36,080 --> 00:07:33,479 into the atmosphere before you have 172 00:07:38,749 --> 00:07:36,090 sufficient thermal energy to be unbound 173 00:07:40,999 --> 00:07:38,759 from the planets gravity so the point at 174 00:07:42,860 --> 00:07:41,009 which the article thermal energy exceeds 175 00:07:46,580 --> 00:07:42,870 the gravitational potential energy is 176 00:07:48,920 --> 00:07:46,590 very very high up in the atmosphere and 177 00:07:51,080 --> 00:07:48,930 it's higher compared to where the 178 00:07:52,760 --> 00:07:51,090 particle mean free path is approximately 179 00:07:57,460 --> 00:07:52,770 equal to the scale and this also has 180 00:07:59,629 --> 00:07:57,470 another name the exobase now this has a 181 00:08:04,550 --> 00:07:59,639 consequence for how you might escape 182 00:08:07,249 --> 00:08:04,560 because as I said earlier still getting 183 00:08:09,649 --> 00:08:07,259 used to this pointer any of the 184 00:08:11,779 --> 00:08:09,659 particles that are above this EXO 185 00:08:13,300 --> 00:08:11,789 baseline here where the particle premi 186 00:08:15,320 --> 00:08:13,310 path is bigger than the scale height 187 00:08:18,499 --> 00:08:15,330 basically don't collide with another 188 00:08:21,649 --> 00:08:18,509 atom they behave almost in a collision 189 00:08:23,899 --> 00:08:21,659 'less manner so if you envisage that you 190 00:08:26,240 --> 00:08:23,909 have some sort of velocity or energy 191 00:08:29,120 --> 00:08:26,250 distribution for those particles any 192 00:08:32,329 --> 00:08:29,130 particle that gained sufficient kinetic 193 00:08:34,730 --> 00:08:32,339 energy that is no longer bound to the 194 00:08:39,440 --> 00:08:34,740 planets gravity can just freely escape 195 00:08:43,069 --> 00:08:39,450 into space so you sort of lose this tail 196 00:08:44,240 --> 00:08:43,079 of this distribution here is it so if 197 00:08:46,940 --> 00:08:44,250 this was a Maxwell Boltzmann 198 00:08:48,769 --> 00:08:46,950 distribution then this would be sort of 199 00:08:53,210 --> 00:08:48,779 you'd be out in the exponential tail 200 00:08:55,280 --> 00:08:53,220 Maxwell Boltzmann distribution so this 201 00:08:57,500 --> 00:08:55,290 tells you because you're out in this 202 00:08:59,390 --> 00:08:57,510 Maxwell Boltzmann distribution in its 203 00:08:59,840 --> 00:08:59,400 exponential function this is not a very 204 00:09:06,290 --> 00:08:59,850 very 205 00:09:07,910 --> 00:09:06,300 process of losing your atmosphere so 206 00:09:11,480 --> 00:09:07,920 this is the kind of atmospheric escape 207 00:09:13,999 --> 00:09:11,490 that's driving some losses from the 208 00:09:18,079 --> 00:09:14,009 earth today and the mass loss rate from 209 00:09:20,780 --> 00:09:18,089 the Earth's atmosphere is very very long 210 00:09:23,569 --> 00:09:20,790 it is longer than sort of one atmosphere 211 00:09:26,990 --> 00:09:23,579 per sort of under a billion years which 212 00:09:28,220 --> 00:09:27,000 is pretty good for habitability we're 213 00:09:30,710 --> 00:09:28,230 not gonna lose our atmosphere in the 214 00:09:32,180 --> 00:09:30,720 next few years which is good we might 215 00:09:36,379 --> 00:09:32,190 ruin it in the next few years but we're 216 00:09:38,689 --> 00:09:36,389 not gonna lose it but there's an 217 00:09:41,540 --> 00:09:38,699 opposite limit which is when you become 218 00:09:44,090 --> 00:09:41,550 strongly irradiated and you swish where 219 00:09:49,519 --> 00:09:44,100 those two heights appear in your 220 00:09:51,050 --> 00:09:49,529 atmosphere so now you have your where 221 00:09:52,819 --> 00:09:51,060 your particle thermal energy exceeds 222 00:09:55,639 --> 00:09:52,829 your gravitational potential deep in 223 00:09:57,590 --> 00:09:55,649 your atmosphere compared to where your 224 00:09:59,990 --> 00:09:57,600 EXO bases which is much much higher and 225 00:10:01,370 --> 00:10:00,000 now you have sufficient thermal energy 226 00:10:03,829 --> 00:10:01,380 to escape the planet's gravitational 227 00:10:07,790 --> 00:10:03,839 well and what you do is you drive a 228 00:10:10,040 --> 00:10:07,800 hydrodynamic wind so you drive a 229 00:10:12,019 --> 00:10:10,050 pressure driven wind that escapes from 230 00:10:13,850 --> 00:10:12,029 the planets gravity and instead of 231 00:10:15,199 --> 00:10:13,860 losing just this sort of exponential 232 00:10:17,480 --> 00:10:15,209 tail of your Maxwell Boltzmann 233 00:10:20,179 --> 00:10:17,490 distribution of your gas particles you 234 00:10:23,780 --> 00:10:20,189 lose the bulk now this is a much more 235 00:10:26,269 --> 00:10:23,790 efficient process so once you're in the 236 00:10:28,660 --> 00:10:26,279 hydrodynamic regime or once you're in 237 00:10:30,829 --> 00:10:28,670 this strongly irradiated regime 238 00:10:32,720 --> 00:10:30,839 atmospheric escape and hydrodynamic 239 00:10:34,999 --> 00:10:32,730 escape is a very very efficient process 240 00:10:36,949 --> 00:10:35,009 and it can dramatically alter your 241 00:10:42,530 --> 00:10:36,959 atmosphere over the billions of years 242 00:10:44,809 --> 00:10:42,540 but a planet has to evolve so in a 243 00:10:46,670 --> 00:10:44,819 little more detail this is a now is that 244 00:10:49,759 --> 00:10:46,680 a slice through one of those large 245 00:10:51,710 --> 00:10:49,769 simulations just showing the temperature 246 00:10:53,360 --> 00:10:51,720 structure as a function of altitude in 247 00:10:55,939 --> 00:10:53,370 the velocity structures a function of 248 00:10:57,949 --> 00:10:55,949 altitude so this is for a typical highly 249 00:11:00,439 --> 00:10:57,959 irradiated hydrogen helium dominated 250 00:11:04,100 --> 00:11:00,449 atmosphere that's the route sort of 0.1 251 00:11:06,650 --> 00:11:04,110 au from its star the UV and the x-rays 252 00:11:09,110 --> 00:11:06,660 heat the upper atmospheres to about 10 253 00:11:11,240 --> 00:11:09,120 to the 4 Kelvin and this is sufficient 254 00:11:12,360 --> 00:11:11,250 to drive this very powerful hydrodynamic 255 00:11:14,939 --> 00:11:12,370 outflow 256 00:11:19,259 --> 00:11:14,949 and one of the critical things that also 257 00:11:21,840 --> 00:11:19,269 happens in this process is the gas 258 00:11:24,480 --> 00:11:21,850 starts off subsonic and then it becomes 259 00:11:25,679 --> 00:11:24,490 supersonic at large radius once the gas 260 00:11:28,920 --> 00:11:25,689 is supersonic 261 00:11:32,069 --> 00:11:28,930 there's no way but anything that happens 262 00:11:33,509 --> 00:11:32,079 out here to tell the planet's atmosphere 263 00:11:35,670 --> 00:11:33,519 about what's going on 264 00:11:37,290 --> 00:11:35,680 you can only propagate information at 265 00:11:39,809 --> 00:11:37,300 the sound speed so if you're traveling 266 00:11:41,400 --> 00:11:39,819 faster than the sound speed any 267 00:11:42,869 --> 00:11:41,410 information you try and send backwards 268 00:11:47,629 --> 00:11:42,879 is just going to be infected out with 269 00:11:58,079 --> 00:11:47,639 you so anything that happens outside the 270 00:12:00,569 --> 00:11:58,089 sonic point here which also turns out to 271 00:12:01,949 --> 00:12:00,579 be exactly roughly where the thermal 272 00:12:04,139 --> 00:12:01,959 energy exceeds the gravitational 273 00:12:05,759 --> 00:12:04,149 potential energy is not going to affect 274 00:12:08,100 --> 00:12:05,769 your output so you can do basically 275 00:12:10,049 --> 00:12:08,110 whatever you want outside here and it's 276 00:12:13,110 --> 00:12:10,059 not gonna affect why what happened so 277 00:12:15,239 --> 00:12:13,120 you can put your exobase up here you can 278 00:12:17,639 --> 00:12:15,249 become collisionless or equations of 279 00:12:19,559 --> 00:12:17,649 hydrodynamics no longer apply the flow 280 00:12:22,860 --> 00:12:19,569 doesn't care you still get this 281 00:12:24,929 --> 00:12:22,870 hydrodynamic escape however if you push 282 00:12:27,569 --> 00:12:24,939 your exobase down we're back in the 283 00:12:30,179 --> 00:12:27,579 jeans escapement even though I've solved 284 00:12:32,280 --> 00:12:30,189 the problem assuming the equations of 285 00:12:34,590 --> 00:12:32,290 hydrodynamics apply this is not 286 00:12:38,129 --> 00:12:34,600 applicable so I have to go to the jeans 287 00:12:40,319 --> 00:12:38,139 escape so you can think of the 288 00:12:43,619 --> 00:12:40,329 transition from roughly the transition 289 00:12:46,619 --> 00:12:43,629 from hydrodynamic escape to jeans escape 290 00:12:49,679 --> 00:12:46,629 being roughly when the exo basis of the 291 00:12:51,299 --> 00:12:49,689 sonic point of these output and that's a 292 00:12:56,090 --> 00:12:51,309 good way to think about and that's how 293 00:12:59,309 --> 00:12:56,100 we actually calculate this transition in 294 00:13:01,230 --> 00:12:59,319 numerical simulations so in reality one 295 00:13:03,600 --> 00:13:01,240 would want to solve the collisional 296 00:13:05,249 --> 00:13:03,610 Boltzmann equation that go straight from 297 00:13:07,110 --> 00:13:05,259 the hydrodynamic limit all the way to 298 00:13:09,749 --> 00:13:07,120 the non hydrodynamic collisionless limit 299 00:13:12,299 --> 00:13:09,759 that is computationally impossible so 300 00:13:14,549 --> 00:13:12,309 what we typically do is we solve the 301 00:13:16,530 --> 00:13:14,559 equations of hydrodynamics we check that 302 00:13:18,809 --> 00:13:16,540 you're in the hydrodynamic limit through 303 00:13:23,360 --> 00:13:18,819 this criterion and if you're not then 304 00:13:33,320 --> 00:13:27,680 so a little more going into the details 305 00:13:36,050 --> 00:13:33,330 so this is our planet's atmosphere here 306 00:13:38,840 --> 00:13:36,060 this is a atmosphere surrounding surface 307 00:13:42,470 --> 00:13:38,850 of a planet and we have two heating 308 00:13:45,530 --> 00:13:42,480 sources in these cases the first heating 309 00:13:47,360 --> 00:13:45,540 sources is photons from the star and a 310 00:13:50,560 --> 00:13:47,370 second heating source especially if you 311 00:13:54,500 --> 00:13:50,570 have a big atmosphere or a young ages is 312 00:13:56,570 --> 00:13:54,510 thermal heating from the interior and 313 00:13:58,880 --> 00:13:56,580 this gives you sort of a layered 314 00:14:01,010 --> 00:13:58,890 structure as to the the heating profile 315 00:14:03,950 --> 00:14:01,020 so in hydrogen helium dominated 316 00:14:07,490 --> 00:14:03,960 atmospheres first you absorb the the EUV 317 00:14:11,840 --> 00:14:07,500 photons then you absorb the x-rays and 318 00:14:14,450 --> 00:14:11,850 the f UV driven photons and then you 319 00:14:16,730 --> 00:14:14,460 have a region with is heated both 320 00:14:21,860 --> 00:14:16,740 bolometric ly by the star and from the 321 00:14:23,600 --> 00:14:21,870 star's interior and all the kind of 322 00:14:25,820 --> 00:14:23,610 atmospheric escape i'm going to talk 323 00:14:27,740 --> 00:14:25,830 about in this talk is driven basically 324 00:14:29,870 --> 00:14:27,750 from these layers here but in Helga's 325 00:14:32,150 --> 00:14:29,880 talk later in the session she's going to 326 00:14:35,710 --> 00:14:32,160 talk about a type of mass law for the 327 00:14:38,270 --> 00:14:35,720 driven by heating from the interior and 328 00:14:44,120 --> 00:14:38,280 you may be aware there's a little bit of 329 00:14:46,160 --> 00:14:44,130 debate as to what is driving mass loss 330 00:14:47,540 --> 00:14:46,170 from sub Neptune's and super Earths and 331 00:14:50,210 --> 00:14:47,550 the reason there's a little bit of 332 00:14:52,220 --> 00:14:50,220 debate is that this entire fluid 333 00:14:55,100 --> 00:14:52,230 structure of heating is not improperly 334 00:14:58,790 --> 00:14:55,110 solved in simulations so what people 335 00:15:02,380 --> 00:14:58,800 like me tend to do is just sort of 336 00:15:04,850 --> 00:15:02,390 ignore this bit and just do this but and 337 00:15:06,650 --> 00:15:04,860 what he'll cos model is doing at the 338 00:15:09,110 --> 00:15:06,660 moment is just doing this part and 339 00:15:10,910 --> 00:15:09,120 ignoring this part so there's a little 340 00:15:13,490 --> 00:15:10,920 bit of debate because these models have 341 00:15:16,790 --> 00:15:13,500 not been combined and this is work in 342 00:15:18,170 --> 00:15:16,800 progress that needs to be done I also 343 00:15:20,990 --> 00:15:18,180 want to point out that this layered 344 00:15:23,090 --> 00:15:21,000 structure is only necessarily true for 345 00:15:25,220 --> 00:15:23,100 hydra dan le marquis and i can imagine 346 00:15:27,110 --> 00:15:25,230 an envisaged because x-rays are 347 00:15:30,410 --> 00:15:27,120 preferentially absorbed by heavy 348 00:15:31,850 --> 00:15:30,420 elements and and metals is that if you 349 00:15:33,740 --> 00:15:31,860 go to secondary atmospheres you could 350 00:15:35,180 --> 00:15:33,750 reverse this kind of legend and this 351 00:15:38,950 --> 00:15:35,190 could have interesting effects for the 352 00:15:44,570 --> 00:15:42,740 so there is a very simple way to 353 00:15:47,019 --> 00:15:44,580 describe this process it's called energy 354 00:15:49,670 --> 00:15:47,029 limited escape you may have heard of it 355 00:15:52,130 --> 00:15:49,680 it's a it's a sort of back of the 356 00:15:54,920 --> 00:15:52,140 envelope calculation and what you do is 357 00:16:02,060 --> 00:15:54,930 you say I have summer radiation from the 358 00:16:04,400 --> 00:16:02,070 star and in some unit time my planets 359 00:16:08,810 --> 00:16:04,410 area the area the planet subtends the 360 00:16:12,079 --> 00:16:08,820 star absorbs that energy and then it 361 00:16:14,990 --> 00:16:12,089 takes that energy and it uses it to 362 00:16:18,530 --> 00:16:15,000 unbind a fraction Delta M of the 363 00:16:21,200 --> 00:16:18,540 atmosphere then you go aha 364 00:16:24,460 --> 00:16:21,210 this looks magnificent I have Delta M 365 00:16:31,630 --> 00:16:24,470 here and Delta T here I can rearrange 366 00:16:33,860 --> 00:16:31,640 and I can get a mass loss rate so I have 367 00:16:35,930 --> 00:16:33,870 basically by equating the flux I'm 368 00:16:38,090 --> 00:16:35,940 absorbing from the star with the 369 00:16:40,370 --> 00:16:38,100 potential I'm escaping for all I can get 370 00:16:42,920 --> 00:16:40,380 an approximate expression and I can make 371 00:16:47,120 --> 00:16:42,930 it an exactly it's exact expression by 372 00:16:49,970 --> 00:16:47,130 sticking in a fudge factor and then I 373 00:16:52,490 --> 00:16:49,980 can call this the efficiency and this 374 00:16:54,680 --> 00:16:52,500 efficiency basically accounts for all of 375 00:16:56,840 --> 00:16:54,690 our ignorance it accounts for stuff we 376 00:16:59,450 --> 00:16:56,850 don't under or can't more or need to 377 00:17:02,240 --> 00:16:59,460 model with simulations so some radiative 378 00:17:04,100 --> 00:17:02,250 losses hydrodynamic losses and losses 379 00:17:07,010 --> 00:17:04,110 due to ionization right if you have a a 380 00:17:09,650 --> 00:17:07,020 high energy photon like an e UV photon 381 00:17:12,260 --> 00:17:09,660 come in the way it heats is by ionizing 382 00:17:14,600 --> 00:17:12,270 a hydrogen matter so an enormous amount 383 00:17:16,579 --> 00:17:14,610 of its energy goes into unbinding the 384 00:17:19,550 --> 00:17:16,589 electron from the hydrogen so you don't 385 00:17:22,309 --> 00:17:19,560 can't actually use EUV photons at 100% 386 00:17:24,590 --> 00:17:22,319 efficiency in fact you only use a small 387 00:17:32,460 --> 00:17:24,600 fraction of any UV photon to actually do 388 00:17:38,880 --> 00:17:36,350 the other key point is unsurprisingly 389 00:17:40,800 --> 00:17:38,890 when you do simulations the mass loss 390 00:17:44,280 --> 00:17:40,810 efficiency is not constant this should 391 00:17:46,190 --> 00:17:44,290 not be a shocking result to you and you 392 00:17:50,220 --> 00:17:46,200 can see that it varies this is just one 393 00:17:51,630 --> 00:17:50,230 numerical calculation for one flux a one 394 00:17:54,630 --> 00:17:51,640 stellar age you can see that the 395 00:17:56,460 --> 00:17:54,640 efficiency varies by about an order 396 00:17:58,950 --> 00:17:56,470 matter of magnitude but if you were to 397 00:18:00,990 --> 00:17:58,960 sort of put a gun to my head and force 398 00:18:02,580 --> 00:18:01,000 me I'd say the efficiency is about ten 399 00:18:04,320 --> 00:18:02,590 percent for the sub Neptune's and 400 00:18:09,480 --> 00:18:04,330 super-earth and about one percent for 401 00:18:11,400 --> 00:18:09,490 the hot Jupiter you can also see that it 402 00:18:13,320 --> 00:18:11,410 doesn't even have to scale linearly with 403 00:18:14,850 --> 00:18:13,330 flux so this is a nice plot from 404 00:18:17,250 --> 00:18:14,860 ruth-marie clay showing the mass loss 405 00:18:20,070 --> 00:18:17,260 rate as a function of input UV flux so 406 00:18:22,110 --> 00:18:20,080 low UV fluxes you get an almost linear 407 00:18:24,630 --> 00:18:22,120 scaling this is what you would expect 408 00:18:27,890 --> 00:18:24,640 from this energy limited process but as 409 00:18:30,540 --> 00:18:27,900 you go to higher and higher fluxes the 410 00:18:32,460 --> 00:18:30,550 scaling with mass loss rate this box 411 00:18:34,320 --> 00:18:32,470 gets weaker and weaker and weaker and 412 00:18:36,900 --> 00:18:34,330 this is well understood in terms of a 413 00:18:39,510 --> 00:18:36,910 physical process this is where radiative 414 00:18:44,880 --> 00:18:39,520 recombinations kick in and you get much 415 00:18:48,150 --> 00:18:44,890 lower efficiency mass loss the other 416 00:18:50,910 --> 00:18:48,160 thing you note is that sort of in the 417 00:18:54,420 --> 00:18:50,920 strictest definition of the word mass 418 00:18:56,700 --> 00:18:54,430 loss is not always energy limited so 419 00:18:59,190 --> 00:18:56,710 what this energy limit really means is 420 00:19:01,500 --> 00:18:59,200 you take your heating and you convert it 421 00:19:03,420 --> 00:19:01,510 into PDV work as you're expanding from 422 00:19:06,210 --> 00:19:03,430 the planets potential and you get mass 423 00:19:08,250 --> 00:19:06,220 loss this means that the sort of 424 00:19:11,130 --> 00:19:08,260 dominant loss mechanism that you would 425 00:19:15,330 --> 00:19:11,140 expect to be playing a role in this 426 00:19:20,220 --> 00:19:15,340 process is energy losses in PDV work and 427 00:19:22,620 --> 00:19:20,230 this isn't actually true for the entire 428 00:19:24,570 --> 00:19:22,630 region of parameter space but again 429 00:19:28,140 --> 00:19:24,580 these are just two examples of two 430 00:19:31,140 --> 00:19:28,150 calculations but two fluxes are higher 431 00:19:34,290 --> 00:19:31,150 flux and a lower flux so this blue 432 00:19:36,600 --> 00:19:34,300 region here for UV heating is what you 433 00:19:41,240 --> 00:19:36,610 would expect roughly energy limited so 434 00:19:44,100 --> 00:19:41,250 the flux in is mostly lost as PDV work 435 00:19:46,290 --> 00:19:44,110 but there are other regions where this 436 00:19:48,930 --> 00:19:46,300 really the recombination process 437 00:19:50,900 --> 00:19:48,940 dominates we're hydrogen atoms recombine 438 00:19:53,040 --> 00:19:50,910 that gives you very efficient cooling 439 00:19:56,370 --> 00:19:53,050 also the other thing you should note 440 00:19:58,110 --> 00:19:56,380 about the energy limited formula is the 441 00:20:00,990 --> 00:19:58,120 mass loss rate goes to infinity as the 442 00:20:05,160 --> 00:20:01,000 mass goes to zero which also sounds a 443 00:20:07,290 --> 00:20:05,170 bit weird and it is weird and it's wrong 444 00:20:10,260 --> 00:20:07,300 and eventually you just you run out of 445 00:20:12,330 --> 00:20:10,270 photons basically if you only have 446 00:20:13,950 --> 00:20:12,340 certain number of photon so you can only 447 00:20:15,360 --> 00:20:13,960 ionize a certain number of hydrogen 448 00:20:19,980 --> 00:20:15,370 atoms and you can only get a certain 449 00:20:22,830 --> 00:20:19,990 amount of mass so a sort of very low 450 00:20:24,510 --> 00:20:22,840 gravities you need to also take into 451 00:20:26,820 --> 00:20:24,520 account the number of photons they're 452 00:20:30,440 --> 00:20:26,830 going into the output not just the 453 00:20:34,320 --> 00:20:30,450 energy of those photons so it seems like 454 00:20:37,500 --> 00:20:34,330 perhaps energy limited mass loss it's 455 00:20:39,480 --> 00:20:37,510 not a bad approximation for the super 456 00:20:41,070 --> 00:20:39,490 Earths and said not Toomes well one of 457 00:20:43,050 --> 00:20:41,080 the other things to realize is if they 458 00:20:45,690 --> 00:20:43,060 truly are hydrogen helium dominated 459 00:20:48,080 --> 00:20:45,700 atmospheres when they formed a very very 460 00:20:50,640 --> 00:20:48,090 young ages they were much much larger 461 00:20:55,650 --> 00:20:50,650 they would have sort of sat on this side 462 00:20:57,360 --> 00:20:55,660 of the lot so while the energy limited 463 00:20:59,250 --> 00:20:57,370 formalism is a great formalism for 464 00:21:03,210 --> 00:20:59,260 understanding the details of what's 465 00:21:05,910 --> 00:21:03,220 going on and it's a great formalism for 466 00:21:07,350 --> 00:21:05,920 sort of getting an idea of how important 467 00:21:09,690 --> 00:21:07,360 you think atmospheric escape and how 468 00:21:10,560 --> 00:21:09,700 important you think mass loss is if you 469 00:21:13,350 --> 00:21:10,570 really want to do sophisticated 470 00:21:15,960 --> 00:21:13,360 calculations then unfortunately like 471 00:21:18,420 --> 00:21:15,970 many things in modern physics you need 472 00:21:23,220 --> 00:21:18,430 to go to more detailed numerical 473 00:21:25,830 --> 00:21:23,230 calculation so the first part of this 474 00:21:28,530 --> 00:21:25,840 sort of review is I'm going to focus on 475 00:21:30,000 --> 00:21:28,540 kind of key results from escape from 476 00:21:34,860 --> 00:21:30,010 hydrogen helium rich highly irradiated 477 00:21:38,400 --> 00:21:34,870 excellent so we have these two main 478 00:21:41,820 --> 00:21:38,410 sources of heating from stars we have 479 00:21:43,590 --> 00:21:41,830 x-ray photons and EUV photons for 480 00:21:49,230 --> 00:21:43,600 hydrogen helium dominated atmospheres 481 00:21:51,660 --> 00:21:49,240 the e UV is absorbed first so the UV is 482 00:21:53,250 --> 00:21:51,670 absorbed first and then the x-rays go a 483 00:21:59,190 --> 00:21:53,260 bit deeper in the atmosphere and you 484 00:22:01,139 --> 00:21:59,200 drive some output so as I said 485 00:22:03,389 --> 00:22:01,149 earlier the key for understanding what's 486 00:22:05,340 --> 00:22:03,399 going on and what's doing the driving is 487 00:22:07,169 --> 00:22:05,350 where the sonic point sits in the sound 488 00:22:08,940 --> 00:22:07,179 flow because if anything goes on after 489 00:22:11,519 --> 00:22:08,950 the sonic point you can't tell the 490 00:22:13,680 --> 00:22:11,529 planet's atmosphere event so you can 491 00:22:16,110 --> 00:22:13,690 have two different types of outflows you 492 00:22:17,610 --> 00:22:16,120 can have sort of X ray driven outflow 493 00:22:19,830 --> 00:22:17,620 where you get the sonic point in the X 494 00:22:21,990 --> 00:22:19,840 ray driven regime and all the UV photons 495 00:22:23,759 --> 00:22:22,000 are absorbed outside the sign points so 496 00:22:25,799 --> 00:22:23,769 we call this X ray driven flow and the e 497 00:22:29,549 --> 00:22:25,809 UV cannot affect the mass what's right 498 00:22:31,680 --> 00:22:29,559 so when you take that flux in the energy 499 00:22:34,500 --> 00:22:31,690 limited formula and you call it x UV 500 00:22:36,360 --> 00:22:34,510 flux the X ray and UV you have to sort 501 00:22:37,860 --> 00:22:36,370 of decide how much of the X rays and how 502 00:22:41,460 --> 00:22:37,870 much of the e UV do I put into that 503 00:22:43,230 --> 00:22:41,470 block and you need to understand the 504 00:22:46,110 --> 00:22:43,240 structure of the outflow to decide how 505 00:22:48,419 --> 00:22:46,120 you do obviously you can go to the other 506 00:22:51,750 --> 00:22:48,429 limit now where the sonic point now sits 507 00:22:53,159 --> 00:22:51,760 in the UV driven flow and the experts 508 00:22:54,299 --> 00:22:53,169 are playing a minor role all they're 509 00:22:58,259 --> 00:22:54,309 really doing is puffing off the 510 00:23:00,389 --> 00:22:58,269 atmosphere slightly more so it turns out 511 00:23:02,549 --> 00:23:00,399 that this dominates at high fluxes and 512 00:23:04,710 --> 00:23:02,559 hi Stella x-ray luminosities you can 513 00:23:06,389 --> 00:23:04,720 sort of envisage that it's because the 514 00:23:07,950 --> 00:23:06,399 more and more heating you kind of dump 515 00:23:10,710 --> 00:23:07,960 into this outflow structure the more 516 00:23:12,480 --> 00:23:10,720 powerful the outflow more the faster the 517 00:23:14,250 --> 00:23:12,490 velocity increases so the likelihood 518 00:23:16,620 --> 00:23:14,260 that you cross the sonic point in the X 519 00:23:18,840 --> 00:23:16,630 ray heated regime rather than the e UV 520 00:23:21,810 --> 00:23:18,850 heated regime is gonna be at high 521 00:23:23,789 --> 00:23:21,820 stellar Foxit than high luminosity so 522 00:23:26,310 --> 00:23:23,799 this really matter it means that this 523 00:23:30,180 --> 00:23:26,320 kind of mass loss may be important early 524 00:23:32,779 --> 00:23:30,190 in the planets life so this is perhaps 525 00:23:35,879 --> 00:23:32,789 what's driving the evolution that we see 526 00:23:45,889 --> 00:23:35,889 but when we compare two direct 527 00:23:50,370 --> 00:23:48,600 it's gonna be the e UV that's important 528 00:23:52,379 --> 00:23:50,380 so this is something we also have to 529 00:23:53,759 --> 00:23:52,389 bear in mind that are the simulations 530 00:23:55,950 --> 00:23:53,769 and the models of atmospheric escape 531 00:23:59,190 --> 00:23:55,960 we're comparing to observe exoplanets 532 00:24:01,289 --> 00:23:59,200 today really applicable to what might 533 00:24:02,180 --> 00:24:01,299 have been going on early in the planets 534 00:24:05,700 --> 00:24:02,190 lifetime 535 00:24:09,450 --> 00:24:05,710 that's the complication and also I just 536 00:24:11,639 --> 00:24:09,460 want to sort of emphasize that the UV 537 00:24:13,180 --> 00:24:11,649 and the x-ray flux also is is not 538 00:24:15,220 --> 00:24:13,190 constant with time there's a 539 00:24:17,290 --> 00:24:15,230 actually a very nice correlation between 540 00:24:19,330 --> 00:24:17,300 the UV flux and the x-ray flux as a 541 00:24:23,050 --> 00:24:19,340 function of the x-ray Fox will start but 542 00:24:25,330 --> 00:24:23,060 so I Estella x-ray flux is the star puts 543 00:24:27,850 --> 00:24:25,340 more of its energy in the x-rays newbee 544 00:24:30,250 --> 00:24:27,860 so this kind of enhances this idea that 545 00:24:32,260 --> 00:24:30,260 x-ray driven rather than EUV driven flow 546 00:24:36,940 --> 00:24:32,270 is going to be more important at early 547 00:24:39,340 --> 00:24:36,950 times so the all important things are 548 00:24:42,130 --> 00:24:39,350 what are the mass loss rates and what do 549 00:24:44,170 --> 00:24:42,140 they do to the pockets so this is sort 550 00:24:45,940 --> 00:24:44,180 of one example of one calculation for 551 00:24:47,890 --> 00:24:45,950 one age of one flux and you can take 552 00:24:50,140 --> 00:24:47,900 these calculations and you can put them 553 00:24:52,870 --> 00:24:50,150 together and you can sort of model the 554 00:24:55,360 --> 00:24:52,880 evolution of planetary atmospheres over 555 00:24:57,810 --> 00:24:55,370 that lifetimes so this is a calculation 556 00:25:00,250 --> 00:24:57,820 for our highly irradiated hot Jupiter 557 00:25:02,230 --> 00:25:00,260 and it doesn't lose very much mass there 558 00:25:04,990 --> 00:25:02,240 are two reasons for this right I said 559 00:25:08,220 --> 00:25:05,000 earlier that the efficiencies for hot 560 00:25:10,810 --> 00:25:08,230 Jupiters are quite low about one percent 561 00:25:13,060 --> 00:25:10,820 but also hot Jupiters have a lot of mass 562 00:25:17,080 --> 00:25:13,070 to start with so it's quite hard to 563 00:25:19,080 --> 00:25:17,090 completely remove or completely strip a 564 00:25:23,290 --> 00:25:19,090 giant planet so hot Jupiters are safe 565 00:25:26,020 --> 00:25:23,300 however for these sub Neptune's they are 566 00:25:28,600 --> 00:25:26,030 strongly affected by this process this 567 00:25:30,820 --> 00:25:28,610 is again for the two reasons the mass 568 00:25:34,150 --> 00:25:30,830 loss rates are much more efficient for 569 00:25:35,830 --> 00:25:34,160 these sub Neptune's and they have a lot 570 00:25:41,760 --> 00:25:35,840 less I'd and helium to start with so you 571 00:25:44,290 --> 00:25:41,770 can significantly scope excuse me so 572 00:25:46,630 --> 00:25:44,300 while giant planets are not Jupiter's 573 00:25:48,160 --> 00:25:46,640 are going to be losing mass grandmas 574 00:25:50,980 --> 00:25:48,170 farik escape and it'd be nice to 575 00:25:52,570 --> 00:25:50,990 characterize this observational e the 576 00:25:54,490 --> 00:25:52,580 things that are gonna be really affected 577 00:25:57,400 --> 00:25:54,500 are these sub natoons in the case of 578 00:25:59,320 --> 00:25:57,410 hydrogen helium dominated ones the other 579 00:26:01,600 --> 00:25:59,330 thing I want to sort of emphasize is 580 00:26:03,490 --> 00:26:01,610 that when we are thinking about 581 00:26:06,190 --> 00:26:03,500 comparing our atmospheric model 582 00:26:08,380 --> 00:26:06,200 atmospheric escape models to direct 583 00:26:11,830 --> 00:26:08,390 observational traces of this the 584 00:26:14,170 --> 00:26:11,840 outflows are 3d and this is a really 585 00:26:16,990 --> 00:26:14,180 really hard numerical problem so I think 586 00:26:19,480 --> 00:26:17,000 still currently there are more observed 587 00:26:21,250 --> 00:26:19,490 exoplanets for which we know they are 588 00:26:25,210 --> 00:26:21,260 undergoing atmospheric escape then there 589 00:26:26,950 --> 00:26:25,220 are 3d simulation and most of the 3d 590 00:26:30,160 --> 00:26:26,960 simulations again for numerical 591 00:26:32,050 --> 00:26:30,170 are not the real planets we kind of sort 592 00:26:36,880 --> 00:26:32,060 of make them extra puffy to help our 593 00:26:38,590 --> 00:26:36,890 numerical simulations or so the kind of 594 00:26:40,510 --> 00:26:38,600 structure you get in pure hydrogen I 595 00:26:42,400 --> 00:26:40,520 make our clothes sort of somewhat 596 00:26:44,170 --> 00:26:42,410 reasonably well-established from these 597 00:26:46,150 --> 00:26:44,180 simulations now so the star is sort of 598 00:26:48,880 --> 00:26:46,160 sitting over here somewhere 599 00:26:50,680 --> 00:26:48,890 it's radiating the planet it drives this 600 00:26:52,810 --> 00:26:50,690 outflow off the dayside of the planet 601 00:26:55,050 --> 00:26:52,820 which then sort of wraps around behind 602 00:26:58,210 --> 00:26:55,060 the Nightside and you get sort of nice 603 00:27:01,870 --> 00:26:58,220 kelvin-helmholtz like instabilities if 604 00:27:03,700 --> 00:27:01,880 you then look on the larger scales then 605 00:27:05,140 --> 00:27:03,710 these simulations sort of start 606 00:27:09,040 --> 00:27:05,150 interacting with the circumstellar 607 00:27:11,050 --> 00:27:09,050 environment with some nice recent work 608 00:27:13,630 --> 00:27:11,060 by John McCann and he's here and he has 609 00:27:16,960 --> 00:27:13,640 a poster on some even newer simulations 610 00:27:18,910 --> 00:27:16,970 that he promises are for realistic 611 00:27:22,990 --> 00:27:18,920 planets not super puffy planet so I 612 00:27:24,460 --> 00:27:23,000 encourage you to check that out so when 613 00:27:27,520 --> 00:27:24,470 we're thinking about comparing our 614 00:27:29,740 --> 00:27:27,530 simulations to sort of direct 615 00:27:31,240 --> 00:27:29,750 observational traces of atmospheric 616 00:27:33,550 --> 00:27:31,250 escape they're gonna need to sort of 617 00:27:35,350 --> 00:27:33,560 think about this 3d structure and we're 618 00:27:37,450 --> 00:27:35,360 gonna need to try and put some effort 619 00:27:39,220 --> 00:27:37,460 into pushing our numerical models 620 00:27:40,210 --> 00:27:39,230 further and trying to actually finally 621 00:27:44,440 --> 00:27:40,220 get to the point where there are more 622 00:27:46,390 --> 00:27:44,450 models than observations so I'm gonna 623 00:27:47,590 --> 00:27:46,400 sort of briefly cover this because some 624 00:27:50,890 --> 00:27:47,600 of the other speakers are going to talk 625 00:27:52,660 --> 00:27:50,900 more about interpreting observations - 626 00:27:54,100 --> 00:27:52,670 that was very escape at the moment there 627 00:27:57,700 --> 00:27:54,110 are sort of two good traces of 628 00:27:59,110 --> 00:27:57,710 atmospheric escape there's a lyman-alpha 629 00:28:01,210 --> 00:27:59,120 transit so this is where you do a 630 00:28:03,550 --> 00:28:01,220 transit style observation but instead of 631 00:28:06,070 --> 00:28:03,560 doing it in a broad band you do it in a 632 00:28:08,680 --> 00:28:06,080 narrow narrow line that has a strong 633 00:28:10,930 --> 00:28:08,690 sensitivity to material you might find 634 00:28:15,220 --> 00:28:10,940 in the Alpha so the lyman-alpha has a 635 00:28:17,200 --> 00:28:15,230 strong up acity to neutral hydrogen so 636 00:28:19,990 --> 00:28:17,210 what you can see this is the lyman-alpha 637 00:28:21,720 --> 00:28:20,000 profile unfortunately the center of the 638 00:28:23,920 --> 00:28:21,730 line is completely obscured by 639 00:28:25,660 --> 00:28:23,930 interstellar absorption so we don't know 640 00:28:27,520 --> 00:28:25,670 what's going on here we can only look 641 00:28:29,950 --> 00:28:27,530 what's going on in the wings so the 642 00:28:32,710 --> 00:28:29,960 black line is what the lyman-alpha from 643 00:28:34,870 --> 00:28:32,720 the star looks like when the planet is 644 00:28:37,950 --> 00:28:34,880 behind the star and you can see as the 645 00:28:41,129 --> 00:28:37,960 planet comes into transit you get huge 646 00:28:43,139 --> 00:28:41,139 props in black this is a 50% drop in 647 00:28:46,230 --> 00:28:43,149 pluck so if you remember what a transit 648 00:28:49,590 --> 00:28:46,240 observation means you're obscuring some 649 00:28:51,060 --> 00:28:49,600 fraction of the stellar surface right so 650 00:28:54,119 --> 00:28:51,070 in this case the lyman-alpha is 651 00:28:57,119 --> 00:28:54,129 obscuring 50% of the stars right 652 00:28:59,789 --> 00:28:57,129 remember in broadband optical a planet 653 00:29:03,930 --> 00:28:59,799 typically blocks only sort of less than 654 00:29:06,210 --> 00:29:03,940 1% this is a huge block and you actually 655 00:29:09,239 --> 00:29:06,220 know this is atmospheric escape because 656 00:29:11,759 --> 00:29:09,249 a 50% transit radius would imply this 657 00:29:15,210 --> 00:29:11,769 material that is temporarily associated 658 00:29:16,710 --> 00:29:15,220 so it's going around with the planet but 659 00:29:19,470 --> 00:29:16,720 it's not balanced the bun it's outside 660 00:29:20,869 --> 00:29:19,480 the palace roof so the interpretation is 661 00:29:23,940 --> 00:29:20,879 something like this that you have some 662 00:29:28,980 --> 00:29:23,950 escaping cloud that is obscuring some 663 00:29:31,560 --> 00:29:28,990 enormous fraction of the star and it's 664 00:29:34,129 --> 00:29:31,570 highly asymmetric in the transit profile 665 00:29:37,859 --> 00:29:34,139 due to the 3d natures of these floats 666 00:29:40,529 --> 00:29:37,869 the really exciting one is these recent 667 00:29:44,159 --> 00:29:40,539 helium detections helium metastable line 668 00:29:46,049 --> 00:29:44,169 I'm not going to talk about this because 669 00:29:49,019 --> 00:29:46,059 Antonia has an entire talk on this topic 670 00:29:50,460 --> 00:29:49,029 later in this session but this is super 671 00:29:52,169 --> 00:29:50,470 exciting because it can be done at high 672 00:29:54,419 --> 00:29:52,179 spectral resolution and as we learned 673 00:29:58,470 --> 00:29:54,429 from Jane earlier in the week high 674 00:30:02,369 --> 00:29:58,480 spectral resolution is really useful for 675 00:30:04,320 --> 00:30:02,379 getting kinematic information so I've 676 00:30:06,389 --> 00:30:04,330 talked a little bit now about the basics 677 00:30:09,779 --> 00:30:06,399 of thermal escape the basic physics of 678 00:30:11,070 --> 00:30:09,789 hydrogen helium dominated thermal escape 679 00:30:15,450 --> 00:30:11,080 are now going to talk about how it 680 00:30:16,889 --> 00:30:15,460 affects the population of exoplanets and 681 00:30:18,899 --> 00:30:16,899 there is a poster on this topic by a 682 00:30:24,629 --> 00:30:18,909 pink kite so I encourage you to give as 683 00:30:27,720 --> 00:30:24,639 well so here's my cartoony picture of 684 00:30:30,299 --> 00:30:27,730 what's going on you have a star which 685 00:30:31,680 --> 00:30:30,309 has some planets which all have I didn't 686 00:30:33,539 --> 00:30:31,690 helium atmospheres when they born so 687 00:30:35,759 --> 00:30:33,549 it's a solid core surrounded by a 688 00:30:38,249 --> 00:30:35,769 hydrogen helium atom and I'm gonna let 689 00:30:40,619 --> 00:30:38,259 this system of all under the influence 690 00:30:43,139 --> 00:30:40,629 that mascara escape so you can see that 691 00:30:45,060 --> 00:30:43,149 all the planets at young times basically 692 00:30:50,249 --> 00:30:45,070 most of them sit up here and quite large 693 00:30:51,630 --> 00:30:50,259 radio look 5 to 10 Earth radii these are 694 00:30:53,640 --> 00:30:51,640 not giant planets these 695 00:30:57,270 --> 00:30:53,650 sort of typical sub Neptune's that have 696 00:30:59,040 --> 00:30:57,280 five to ten earth masses with 10% arjun 697 00:31:00,720 --> 00:30:59,050 helium say so they have very large 698 00:31:02,310 --> 00:31:00,730 radiuses at early time so for the 699 00:31:04,650 --> 00:31:02,320 handful of planets that we can get 700 00:31:06,780 --> 00:31:04,660 constraints on their properties at early 701 00:31:09,000 --> 00:31:06,790 times it's really crucial to testing 702 00:31:11,070 --> 00:31:09,010 these kinds of models as well do our 703 00:31:13,350 --> 00:31:11,080 planets really five to ten a low-mass 704 00:31:16,290 --> 00:31:13,360 fire twenty five to ten Earth radii at a 705 00:31:20,430 --> 00:31:16,300 young ages now I'm going to let this 706 00:31:23,160 --> 00:31:20,440 system evolve so the planets start 707 00:31:25,650 --> 00:31:23,170 losing their hydrogen helium some 708 00:31:27,990 --> 00:31:25,660 planets in fact completely lose their 709 00:31:31,770 --> 00:31:28,000 hydrogen helium atmospheres whereas some 710 00:31:33,420 --> 00:31:31,780 planets retaining and at the end of the 711 00:31:35,580 --> 00:31:33,430 simulation you tend to end up with two 712 00:31:37,110 --> 00:31:35,590 types of paths and it's a completely 713 00:31:39,600 --> 00:31:37,120 lose their hydrogen helium atmosphere so 714 00:31:43,770 --> 00:31:39,610 they become what we've called stripped 715 00:31:45,540 --> 00:31:43,780 cause or they retain I didn't kill him 716 00:31:48,030 --> 00:31:45,550 so you typically have two types of 717 00:31:50,190 --> 00:31:48,040 planets these stripped cores or planets 718 00:31:51,930 --> 00:31:50,200 that have roughly about one percent 719 00:31:55,910 --> 00:31:51,940 I didn't helium in their atmospheres at 720 00:31:59,220 --> 00:31:55,920 the end of this evolution and this is 721 00:32:02,240 --> 00:31:59,230 radio speaker diagram now have this gap 722 00:32:07,410 --> 00:32:02,250 in it in theory terms this is called the 723 00:32:09,030 --> 00:32:07,420 evaporation Balaton so I want to sort of 724 00:32:10,500 --> 00:32:09,040 briefly understand why you get this 725 00:32:14,730 --> 00:32:10,510 valley it's actually quite simple to 726 00:32:17,040 --> 00:32:14,740 understand if you think of the mass loss 727 00:32:19,530 --> 00:32:17,050 timescale so this is the instantaneous 728 00:32:20,760 --> 00:32:19,540 time it would take you to lose the 729 00:32:21,600 --> 00:32:20,770 amount of mass you have in your 730 00:32:23,490 --> 00:32:21,610 atmosphere it's basically your 731 00:32:26,340 --> 00:32:23,500 atmosphere divided by your instantaneous 732 00:32:29,880 --> 00:32:26,350 mass loss rate as a function of your 733 00:32:31,470 --> 00:32:29,890 embolus fraction then in that simple 734 00:32:32,910 --> 00:32:31,480 energy limited argument so this is a 735 00:32:35,220 --> 00:32:32,920 perfect place where you can use that 736 00:32:37,500 --> 00:32:35,230 simple energy limited argument what sets 737 00:32:40,350 --> 00:32:37,510 your mass loss rate is how much of the 738 00:32:42,660 --> 00:32:40,360 Stars flux you can absorb so very very 739 00:32:44,880 --> 00:32:42,670 low enveloped mass fractions oil 740 00:32:49,710 --> 00:32:44,890 atmosphere masses the radius of the 741 00:32:52,200 --> 00:32:49,720 planet is completely set by the radius 742 00:32:53,670 --> 00:32:52,210 of this solid core right so as I add 743 00:32:55,590 --> 00:32:53,680 more and more atmosphere it doesn't 744 00:32:57,720 --> 00:32:55,600 change the radius of the planet a great 745 00:32:59,610 --> 00:32:57,730 deal so it doesn't change the flux I 746 00:33:01,500 --> 00:32:59,620 absorb from the star a great deal the 747 00:33:03,900 --> 00:33:01,510 atmosphere has negligible mass to the 748 00:33:04,529 --> 00:33:03,910 planet's mass so I haven't changed the 749 00:33:10,109 --> 00:33:04,539 mass loss rate 750 00:33:12,389 --> 00:33:10,119 increase my envelope mass fraction for 751 00:33:14,430 --> 00:33:12,399 small envelope mass right then I'm going 752 00:33:17,189 --> 00:33:14,440 to get to the point where the atmosphere 753 00:33:19,499 --> 00:33:17,199 is so big now it dominates the radius of 754 00:33:22,439 --> 00:33:19,509 the planet and what sets how this mass 755 00:33:25,019 --> 00:33:22,449 loss rate time scale evolved is how big 756 00:33:26,699 --> 00:33:25,029 the atmosphere expands as I add mats and 757 00:33:28,109 --> 00:33:26,709 it turns out the micro physics of 758 00:33:31,310 --> 00:33:28,119 hydrogen helium atmospheres means that 759 00:33:34,019 --> 00:33:31,320 the atmospheres expands so rapidly that 760 00:33:35,399 --> 00:33:34,029 the they absorb so much more plucks at 761 00:33:37,889 --> 00:33:35,409 the mass loss rate goes through the roof 762 00:33:42,269 --> 00:33:37,899 and the mass loss rate time scale comes 763 00:33:46,759 --> 00:33:42,279 back down so they have something that 764 00:33:52,799 --> 00:33:48,839 approximately where the atmosphere or 765 00:33:56,230 --> 00:33:52,809 the envelope doubles the cause radius so 766 00:33:59,950 --> 00:33:56,240 if I have some time 767 00:34:03,520 --> 00:33:59,960 now to lose my atmosphere this is the 768 00:34:05,320 --> 00:34:03,530 sort of time my star is bright then I 769 00:34:08,410 --> 00:34:05,330 can get two types of evolutionary 770 00:34:11,710 --> 00:34:08,420 pathways if I start off here where I 771 00:34:14,290 --> 00:34:11,720 have lots of atmosphere Matt and I start 772 00:34:16,090 --> 00:34:14,300 losing mass right I have my mask lost 773 00:34:18,550 --> 00:34:16,100 timescales less than the time I have to 774 00:34:20,760 --> 00:34:18,560 lose math I'm going to start pushing up 775 00:34:23,860 --> 00:34:20,770 this curve I'm gonna start losing mass 776 00:34:25,390 --> 00:34:23,870 but I'm gonna get to the point where the 777 00:34:27,640 --> 00:34:25,400 mass loss timescale for my current 778 00:34:30,010 --> 00:34:27,650 planet structure now exceeds the amount 779 00:34:31,720 --> 00:34:30,020 of time I have to lose mass and my 780 00:34:34,090 --> 00:34:31,730 planet becomes stable so you can see 781 00:34:36,730 --> 00:34:34,100 that in these trucks yeah you start 782 00:34:39,340 --> 00:34:36,740 losing mass and then atmosphere becomes 783 00:34:43,390 --> 00:34:39,350 stable and you stay there but if I start 784 00:34:45,250 --> 00:34:43,400 on the other side yeah I start losing 785 00:34:47,050 --> 00:34:45,260 mass my mass was time scale gets shorter 786 00:34:50,950 --> 00:34:47,060 and shorter and shorter and I just enter 787 00:34:53,890 --> 00:34:50,960 a runaway so you see that you actually 788 00:34:55,810 --> 00:34:53,900 and it's set by basically the stability 789 00:34:58,150 --> 00:34:55,820 point is where you have an atmosphere 790 00:35:05,410 --> 00:34:58,160 that doubles the cores radius that this 791 00:35:09,070 --> 00:35:05,420 is where the transition takes part so we 792 00:35:11,320 --> 00:35:09,080 have a model and this is one of the few 793 00:35:13,330 --> 00:35:11,330 times where the fluff area has been 794 00:35:16,030 --> 00:35:13,340 slightly ahead of the observations we 795 00:35:18,340 --> 00:35:16,040 had a model and we now have observations 796 00:35:22,660 --> 00:35:18,350 that by I look in pretty good agreement 797 00:35:24,580 --> 00:35:22,670 with the observations so if you look at 798 00:35:26,350 --> 00:35:24,590 it in a bit more detail you find that 799 00:35:28,810 --> 00:35:26,360 the peaks are separated by this factor 800 00:35:31,210 --> 00:35:28,820 of two in radius so we have a very very 801 00:35:33,490 --> 00:35:31,220 good simple physical understanding of 802 00:35:36,400 --> 00:35:33,500 why they should be separated by a factor 803 00:35:39,100 --> 00:35:36,410 of two in radius these are the stripped 804 00:35:40,690 --> 00:35:39,110 course and these are the planets with 805 00:35:42,730 --> 00:35:40,700 atmospheres that double the cause radius 806 00:35:49,150 --> 00:35:42,740 that a maximally stable those that have 807 00:35:51,970 --> 00:35:49,160 the longest mass if you look at just 808 00:35:54,730 --> 00:35:51,980 planets that have their properties 809 00:35:56,890 --> 00:35:54,740 measured from asteroseismology so this 810 00:35:58,540 --> 00:35:56,900 is where you use basically the 811 00:36:01,690 --> 00:35:58,550 oscillations of the star to get 812 00:36:03,340 --> 00:36:01,700 incredibly precise stellar parameters so 813 00:36:05,080 --> 00:36:03,350 you in turn you can get incredibly 814 00:36:07,210 --> 00:36:05,090 precise planetary parameters so you can 815 00:36:09,160 --> 00:36:07,220 measure the stars the planets radius 816 00:36:10,019 --> 00:36:09,170 down to something like one or two 817 00:36:14,909 --> 00:36:10,029 percent 818 00:36:16,439 --> 00:36:14,919 then you can see that you really this 819 00:36:19,049 --> 00:36:16,449 gap sort of sticks out like a sore thumb 820 00:36:23,459 --> 00:36:19,059 now and you can actually measure the 821 00:36:28,049 --> 00:36:23,469 slope here and what the slope is saying 822 00:36:30,479 --> 00:36:28,059 is that at long periods I have low 823 00:36:33,719 --> 00:36:30,489 fluxes so the only planets I can strip 824 00:36:35,519 --> 00:36:33,729 are those with low masses where as I go 825 00:36:37,049 --> 00:36:35,529 to higher and higher fluxes I can strip 826 00:36:39,359 --> 00:36:37,059 higher and higher mass cores 827 00:36:41,279 --> 00:36:39,369 so the valley should increase in radius 828 00:36:43,019 --> 00:36:41,289 and this is a great test just seeing 829 00:36:46,049 --> 00:36:43,029 that slope is a great test that what's 830 00:36:48,119 --> 00:36:46,059 going on is driven by its evaporation 831 00:36:50,849 --> 00:36:48,129 process but you can also compare it to 832 00:36:53,699 --> 00:36:50,859 detail so this is the slope you would 833 00:36:57,359 --> 00:36:53,709 expect if you had constant efficiency 834 00:36:59,279 --> 00:36:57,369 energy limited this is the observed 835 00:37:02,129 --> 00:36:59,289 slope so you can see there clearly 836 00:37:03,779 --> 00:37:02,139 inconsistent however if you use the 837 00:37:05,549 --> 00:37:03,789 slightly more sophisticated numerical 838 00:37:08,219 --> 00:37:05,559 models you should count for this 839 00:37:09,599 --> 00:37:08,229 variable efficiency then they're in 840 00:37:11,959 --> 00:37:09,609 agreement with observation so what's 841 00:37:14,729 --> 00:37:11,969 essentially going on here is that lower 842 00:37:17,039 --> 00:37:14,739 core radii lower core masses you have a 843 00:37:18,719 --> 00:37:17,049 weap less deep potential so the 844 00:37:20,699 --> 00:37:18,729 atmosphere can escape quite quickly 845 00:37:23,369 --> 00:37:20,709 doesn't have time to lose a lot of 846 00:37:25,559 --> 00:37:23,379 energy to radiation whereas for the deep 847 00:37:27,899 --> 00:37:25,569 potentials a high mass course the large 848 00:37:29,279 --> 00:37:27,909 cause up here it takes a while for the 849 00:37:31,139 --> 00:37:29,289 gas to actually escape the planets 850 00:37:33,419 --> 00:37:31,149 potential so it has a lot of time to 851 00:37:35,429 --> 00:37:33,429 lose energy due to radius its efficiency 852 00:37:36,689 --> 00:37:35,439 so these flows are quite efficient down 853 00:37:41,129 --> 00:37:36,699 here in these flows are fairly 854 00:37:43,229 --> 00:37:41,139 inefficient so constant efficiency mass 855 00:37:46,409 --> 00:37:43,239 loss is already ruled out but by 856 00:37:47,999 --> 00:37:46,419 observations but when we attempt to do 857 00:37:51,329 --> 00:37:48,009 something numerically it's in Rafah 858 00:37:52,949 --> 00:37:51,339 Greek but one of the key inclusions and 859 00:37:54,479 --> 00:37:52,959 this is sort of a segue to the next part 860 00:37:56,879 --> 00:37:54,489 of the talk about the habitability of 861 00:37:59,099 --> 00:37:56,889 Endor is that the majority of the 862 00:38:01,499 --> 00:37:59,109 terrestrial planets we observe in the 863 00:38:03,419 --> 00:38:01,509 exoplanet form with a large hydrogen 864 00:38:05,699 --> 00:38:03,429 helium atmosphere and I know I have some 865 00:38:07,589 --> 00:38:05,709 science community here so I'm going to 866 00:38:10,109 --> 00:38:07,599 be explicit by what I mean by large 867 00:38:12,449 --> 00:38:10,119 large means several percent 868 00:38:15,149 --> 00:38:12,459 I don't helium atmospheres by mass or in 869 00:38:16,109 --> 00:38:15,159 bars several million bars of hydrogen 870 00:38:18,719 --> 00:38:16,119 helium when they were born 871 00:38:20,309 --> 00:38:18,729 so not sort of large when people say 872 00:38:22,049 --> 00:38:20,319 earth had a large hydrogen helium 873 00:38:23,870 --> 00:38:22,059 atmosphere there was ten or a hundred 874 00:38:26,360 --> 00:38:23,880 baths this is sort of 875 00:38:28,220 --> 00:38:26,370 several thousand times larger so this 876 00:38:31,580 --> 00:38:28,230 has really important consequences for 877 00:38:33,440 --> 00:38:31,590 habitability perhaps if we were having 878 00:38:35,600 --> 00:38:33,450 this conference on a moon surrounding a 879 00:38:38,300 --> 00:38:35,610 giant planet I would be even outrageous 880 00:38:40,490 --> 00:38:38,310 enough to suggest the planets don't form 881 00:38:42,350 --> 00:38:40,500 a natural life fashion they all have to 882 00:38:44,090 --> 00:38:42,360 have hydrogen helium atmospheres the own 883 00:38:45,890 --> 00:38:44,100 interests or pilots we see at ones that 884 00:38:48,500 --> 00:38:45,900 use them but we know from the solar 885 00:38:51,560 --> 00:38:48,510 system that's Moxley so that's a planet 886 00:38:53,110 --> 00:38:51,570 formation puzzle but we also have this 887 00:38:58,130 --> 00:38:53,120 habitability issue 888 00:39:00,310 --> 00:38:58,140 so if planets form predominantly with 889 00:39:02,660 --> 00:39:00,320 large hydrogen helium atmospheres 890 00:39:05,090 --> 00:39:02,670 they're not going to be habitable even 891 00:39:08,560 --> 00:39:05,100 if they said in the habitable zone so 892 00:39:13,180 --> 00:39:08,570 how can we have habitable planets around 893 00:39:15,650 --> 00:39:13,190 stars well fortunately M dwarfs are 894 00:39:17,840 --> 00:39:15,660 incredibly active so perhaps we can blow 895 00:39:20,360 --> 00:39:17,850 off this hydrogen helium atmosphere and 896 00:39:23,330 --> 00:39:20,370 become happy so we have this sort of 897 00:39:25,400 --> 00:39:23,340 three phase suggestion about can 898 00:39:28,100 --> 00:39:25,410 habitable zone planets around them 899 00:39:30,220 --> 00:39:28,110 dwarfs become terrestrial planets so can 900 00:39:33,020 --> 00:39:30,230 they lose their initial hydrogen helium 901 00:39:35,300 --> 00:39:33,030 atmosphere inventory then can they 902 00:39:36,590 --> 00:39:35,310 retain their secondary atmosphere and if 903 00:39:40,250 --> 00:39:36,600 they can retain their atmosphere can 904 00:39:42,230 --> 00:39:40,260 they retain water you know so I'm going 905 00:39:44,360 --> 00:39:42,240 to focus on the two things that people 906 00:39:46,040 --> 00:39:44,370 have actually done work on this is 907 00:39:50,960 --> 00:39:46,050 that's the most important part and there 908 00:39:52,490 --> 00:39:50,970 is almost nothing on this so and the 909 00:39:54,350 --> 00:39:52,500 question you should be asking yourself 910 00:39:57,230 --> 00:39:54,360 when I'm gonna talk through some of the 911 00:39:59,660 --> 00:39:57,240 latest results is is habitability about 912 00:40:00,950 --> 00:39:59,670 around M dwarfs fine-tuned or not I'm 913 00:40:02,390 --> 00:40:00,960 not going to tell you whether it's 914 00:40:06,050 --> 00:40:02,400 fine-tuned or not I'm going to leave it 915 00:40:09,200 --> 00:40:06,060 up to you so and one of the key 916 00:40:10,850 --> 00:40:09,210 differences is that the evolution of M 917 00:40:12,770 --> 00:40:10,860 dwarfs in terms of their star's 918 00:40:15,830 --> 00:40:12,780 evolution is significantly different for 919 00:40:19,630 --> 00:40:15,840 some like stuff so this is the evolution 920 00:40:23,180 --> 00:40:19,640 of a planet's black body temperature 921 00:40:25,490 --> 00:40:23,190 it's basically in a earth-like orbit at 922 00:40:27,740 --> 00:40:25,500 the earth-like age so this is the 923 00:40:29,300 --> 00:40:27,750 stellar track for the Sun so you can see 924 00:40:31,370 --> 00:40:29,310 that stellar luminosity increasing this 925 00:40:33,290 --> 00:40:31,380 is the faint young Sun problem the 926 00:40:35,060 --> 00:40:33,300 pollen was talking about yesterday if 927 00:40:36,590 --> 00:40:35,070 you go to a low mass star then it has a 928 00:40:38,980 --> 00:40:36,600 completely different rap 929 00:40:41,810 --> 00:40:38,990 Northy understand problem it's a sort of 930 00:40:44,750 --> 00:40:41,820 inferno young sons problem that the star 931 00:40:46,610 --> 00:40:44,760 is much much brighter and if you turn 932 00:40:49,010 --> 00:40:46,620 this into what it's doing to the high 933 00:40:51,130 --> 00:40:49,020 energy output the high energy output of 934 00:40:54,050 --> 00:40:51,140 these two stars is extremely different 935 00:40:56,300 --> 00:40:54,060 so for the M star here two point four 936 00:40:58,040 --> 00:40:56,310 solar mass star you can have a flux that 937 00:41:01,970 --> 00:40:58,050 sort of a thousand times the current 938 00:41:04,790 --> 00:41:01,980 earth irradiation even at Agee so this 939 00:41:07,160 --> 00:41:04,800 is extreme differences in radiation so 940 00:41:10,160 --> 00:41:07,170 only a factor of a sort of roughly more 941 00:41:12,320 --> 00:41:10,170 than two in solar mass can make almost 942 00:41:14,510 --> 00:41:12,330 sort of one or two orders of magnitude 943 00:41:16,670 --> 00:41:14,520 difference in the total amount of high 944 00:41:22,100 --> 00:41:16,680 energy flux you will see over the pumps 945 00:41:24,800 --> 00:41:22,110 right so can you use this extra UV flux 946 00:41:26,750 --> 00:41:24,810 to lose your - team atmosphere well of 947 00:41:29,330 --> 00:41:26,760 course you that it depends on how 948 00:41:31,760 --> 00:41:29,340 massive you are so if you're a a 949 00:41:34,220 --> 00:41:31,770 low-mass planets round a point for solar 950 00:41:35,690 --> 00:41:34,230 mass star and you can completely use 951 00:41:38,060 --> 00:41:35,700 your hydrogen helium and become a 952 00:41:41,600 --> 00:41:38,070 terrestrial potentially habitable world 953 00:41:43,550 --> 00:41:41,610 quite quickly if you're a sort of 0.9 F 954 00:41:46,340 --> 00:41:43,560 a star then it sort of depends its 955 00:41:50,290 --> 00:41:46,350 initial condition dependent and if you 956 00:41:55,580 --> 00:41:53,750 the other key issue right is well 957 00:41:59,870 --> 00:41:55,590 perhaps I can lose my hydrogen helium 958 00:42:03,730 --> 00:41:59,880 but can I retain my water and because of 959 00:42:06,950 --> 00:42:03,740 its pre main sequence evolution of the 960 00:42:08,600 --> 00:42:06,960 low mass star even if I'm in the 961 00:42:11,960 --> 00:42:08,610 habitable zone at say four and a half 962 00:42:14,960 --> 00:42:11,970 billion years I'm always gonna go 963 00:42:16,670 --> 00:42:14,970 through a runaway greenhouse phase where 964 00:42:18,380 --> 00:42:16,680 I am going to potentially lose water so 965 00:42:20,480 --> 00:42:18,390 this is ice plot from the ground bars 966 00:42:22,400 --> 00:42:20,490 that showing stellar mass as a function 967 00:42:24,230 --> 00:42:22,410 of orbital period here the sort of 968 00:42:28,610 --> 00:42:24,240 habitable burn zone boundaries you 969 00:42:32,030 --> 00:42:28,620 optimistic not optimistic and this is 970 00:42:34,760 --> 00:42:32,040 the time you spend in the runaway 971 00:42:36,590 --> 00:42:34,770 greenhouse space so sort of sun-like 972 00:42:40,430 --> 00:42:36,600 stars it's basically a switch either 973 00:42:42,650 --> 00:42:40,440 nothing or all your time but for lower 974 00:42:44,540 --> 00:42:42,660 mass stars because of this pre main 975 00:42:46,610 --> 00:42:44,550 sequence evolution they spend a decent 976 00:42:49,070 --> 00:42:46,620 fraction five hundred a few hundred 977 00:42:50,010 --> 00:42:49,080 million years of their life in upon away 978 00:42:53,280 --> 00:42:50,020 Green hasn't 979 00:42:55,760 --> 00:42:53,290 so in order to be habitable you need to 980 00:42:58,560 --> 00:42:55,770 be able to retain your water 981 00:43:01,710 --> 00:42:58,570 so these are some against that these are 982 00:43:04,890 --> 00:43:01,720 energy limited calculations constant 983 00:43:06,900 --> 00:43:04,900 efficiency calculations for water loss 984 00:43:09,120 --> 00:43:06,910 as a function of position in the 985 00:43:12,210 --> 00:43:09,130 habitable zone for different masses so 986 00:43:15,030 --> 00:43:12,220 you can see for the sort of unlike low 987 00:43:16,770 --> 00:43:15,040 hi I'm a stars basically you retain all 988 00:43:19,590 --> 00:43:16,780 your water but for the lower mass stars 989 00:43:22,800 --> 00:43:19,600 you get a quick switch to basically you 990 00:43:25,380 --> 00:43:22,810 lose it all so the solution to this is 991 00:43:27,570 --> 00:43:25,390 well if I'm going to lose lots of water 992 00:43:31,290 --> 00:43:27,580 but I still want water I'll just pile a 993 00:43:35,010 --> 00:43:31,300 lot more water on so stop it so you can 994 00:43:36,840 --> 00:43:35,020 do that and you can do a bit better but 995 00:43:38,280 --> 00:43:36,850 this sort of the outcome of this 996 00:43:39,960 --> 00:43:38,290 calculation and you can keep doing this 997 00:43:41,940 --> 00:43:39,970 and keep doing this but the outcome of 998 00:43:43,530 --> 00:43:41,950 this kind of suggestion is that you're 999 00:43:45,810 --> 00:43:43,540 either gonna be in two different 1000 00:43:47,940 --> 00:43:45,820 completely different limits either 1001 00:43:50,760 --> 00:43:47,950 you're just gonna be a desert world you 1002 00:43:52,710 --> 00:43:50,770 have nothing or you had so much water to 1003 00:43:56,880 --> 00:43:52,720 start with that you end up like a 1004 00:44:01,230 --> 00:43:58,920 and there's a poster on this topic by 1005 00:44:04,410 --> 00:44:01,240 Kevin Moore cajoling courage you to take 1006 00:44:06,360 --> 00:44:04,420 a look at so I'm gonna talk a little bit 1007 00:44:10,550 --> 00:44:06,370 more about the physics of water loss and 1008 00:44:13,140 --> 00:44:10,560 perhaps a possible solution out of this 1009 00:44:15,840 --> 00:44:13,150 there's still work in process so this is 1010 00:44:20,250 --> 00:44:15,850 my this is my atmosphere again I have my 1011 00:44:22,170 --> 00:44:20,260 photons coming in but now I add in now I 1012 00:44:24,870 --> 00:44:22,180 add in some water molecules and these 1013 00:44:27,660 --> 00:44:24,880 are going to be associated by UV photons 1014 00:44:33,830 --> 00:44:27,670 now I have some layer in my atmosphere I 1015 00:44:41,340 --> 00:44:38,370 and my atomic oxygen is gonna start to 1016 00:44:45,810 --> 00:44:41,350 diffuse up through the atmosphere maybe 1017 00:44:48,630 --> 00:44:45,820 because the oxygen has a an atomic mass 1018 00:44:52,230 --> 00:44:48,640 of 16 whereas atomic hydrogen has a 1019 00:44:54,030 --> 00:44:52,240 atomic mass of 1 the oxygen is gonna 1020 00:44:56,070 --> 00:44:54,040 have a slightly smaller scale height so 1021 00:45:10,930 --> 00:44:56,080 once I get high up in the atmosphere 1022 00:45:19,430 --> 00:45:14,890 so I'll continue talking 1023 00:45:24,200 --> 00:45:19,440 so do so obviously the sort of the 1024 00:45:26,599 --> 00:45:24,210 critical process now is I have sort of a 1025 00:45:29,299 --> 00:45:26,609 mixture of hydrogen and oxygen at the 1026 00:45:32,839 --> 00:45:29,309 top of the atmosphere but the oxygen is 1027 00:45:36,680 --> 00:45:32,849 much more massive than the hydrogen 1028 00:45:39,740 --> 00:45:36,690 atoms so the question is is the outflow 1029 00:45:44,120 --> 00:45:39,750 powerful enough to drag the oxygen atoms 1030 00:45:50,599 --> 00:45:44,130 away or do the oxygen atoms are they 1031 00:45:52,309 --> 00:45:50,609 held there under gravity and you can 1032 00:45:55,130 --> 00:45:52,319 work this out it's quite simple it's a 1033 00:45:57,680 --> 00:45:55,140 simple little calculation and you can 1034 00:46:00,620 --> 00:45:57,690 calculate the mass of the atom that you 1035 00:46:02,690 --> 00:46:00,630 can drag along it some outflow and 1036 00:46:04,609 --> 00:46:02,700 basically 210 depends on the power of 1037 00:46:10,519 --> 00:46:04,619 the outflow and the collision cross 1038 00:46:14,329 --> 00:46:10,529 section between iDEN and oxygen there 1039 00:46:15,859 --> 00:46:14,339 are also some other limits so you can 1040 00:46:18,529 --> 00:46:15,869 also limit your mass loss rate by 1041 00:46:22,670 --> 00:46:18,539 obviously how fast you dissociate the 1042 00:46:26,960 --> 00:46:22,680 water and also how fast you diffuse the 1043 00:46:28,730 --> 00:46:26,970 oxygen through the atmosphere so both 1044 00:46:36,140 --> 00:46:28,740 these processes can slow down the water 1045 00:46:37,789 --> 00:46:36,150 law which is a possible way out the 1046 00:46:39,980 --> 00:46:37,799 critical thing I want to point out is 1047 00:46:41,390 --> 00:46:39,990 that this depends on the property of the 1048 00:46:45,650 --> 00:46:41,400 outflow depends on the temperature of 1049 00:46:47,690 --> 00:46:45,660 the outlet so we did some very simple 1050 00:46:50,799 --> 00:46:47,700 calculations for traffice 1 and 1051 00:46:52,970 --> 00:46:50,809 basically assumed the hydrogen helium 1052 00:46:54,730 --> 00:46:52,980 properties assume the temperatures we 1053 00:46:57,410 --> 00:46:54,740 get from hydrogen helium outflows and 1054 00:46:59,509 --> 00:46:57,420 calculated how this might affect the 1055 00:47:03,440 --> 00:46:59,519 water loss so this is the standard 1056 00:47:06,109 --> 00:47:03,450 energy limited loss but as soon as you 1057 00:47:08,329 --> 00:47:06,119 start dragging the oxygen atoms with you 1058 00:47:10,099 --> 00:47:08,339 which is what happening in these grey 1059 00:47:11,809 --> 00:47:10,109 lines they weigh much more so you need 1060 00:47:14,080 --> 00:47:11,819 to use more of your energy to get those 1061 00:47:17,500 --> 00:47:14,090 oxygen atoms on your potential you 1062 00:47:20,110 --> 00:47:17,510 lower the total watt loss rate so it 1063 00:47:24,340 --> 00:47:20,120 looks like in these calculations Travis 1064 00:47:28,060 --> 00:47:24,350 one is kind of in these limits the 1065 00:47:29,680 --> 00:47:28,070 Travis one one but we did something I 1066 00:47:31,600 --> 00:47:29,690 did this calculation so I can say this 1067 00:47:33,280 --> 00:47:31,610 we did something fairly stupid which was 1068 00:47:35,680 --> 00:47:33,290 that we use the temperature that came 1069 00:47:37,600 --> 00:47:35,690 from the hydrogen helium dominated 1070 00:47:40,030 --> 00:47:37,610 outlets and there's astronomer I know 1071 00:47:44,050 --> 00:47:40,040 that oxygen is a ridiculously powerful 1072 00:47:46,330 --> 00:47:44,060 cool so these are sort of beautiful 1073 00:47:47,830 --> 00:47:46,340 images of star forming clusters this is 1074 00:47:49,210 --> 00:47:47,840 the kind of thing I did on my PhD there 1075 00:47:50,740 --> 00:47:49,220 about three to ten thousand Kelvin 1076 00:47:52,510 --> 00:47:50,750 roughly what these atmospheres 1077 00:47:54,040 --> 00:47:52,520 temperatures ah and when you look at 1078 00:47:56,740 --> 00:47:54,050 these false color images these are not 1079 00:47:58,600 --> 00:47:56,750 real images right some of the colors in 1080 00:47:59,260 --> 00:47:58,610 here and I think it's blue is an oxygen 1081 00:48:01,510 --> 00:47:59,270 cooling 1082 00:48:05,230 --> 00:48:01,520 oxygen is a very powerful coolant with 1083 00:48:06,700 --> 00:48:05,240 high temperatures even in solar 1084 00:48:09,040 --> 00:48:06,710 metallicity gas so if you're thinking 1085 00:48:10,480 --> 00:48:09,050 about increasing the oxygen abundance by 1086 00:48:12,040 --> 00:48:10,490 several thousand then it's gonna be 1087 00:48:13,870 --> 00:48:12,050 really important so the question that I 1088 00:48:16,570 --> 00:48:13,880 am suggesting that we're working on now 1089 00:48:19,030 --> 00:48:16,580 is this oxygen act as a break to water 1090 00:48:20,830 --> 00:48:19,040 so as you increase the flux you're going 1091 00:48:23,040 --> 00:48:20,840 to increase the temperature so that's 1092 00:48:25,360 --> 00:48:23,050 gonna mean you're gonna increase the 1093 00:48:27,340 --> 00:48:25,370 mass that you can drag and you can start 1094 00:48:28,630 --> 00:48:27,350 to drag oxygen with you if you start 1095 00:48:30,850 --> 00:48:28,640 dragging oxygen with you it's gonna 1096 00:48:32,470 --> 00:48:30,860 start to cool the flow that's gonna do 1097 00:48:34,030 --> 00:48:32,480 reduce this crossover mass and you're 1098 00:48:36,880 --> 00:48:34,040 gonna start not being able to track this 1099 00:48:38,590 --> 00:48:36,890 gently so and then you're going to 1100 00:48:42,850 --> 00:48:38,600 increase the temperature again so do you 1101 00:48:44,950 --> 00:48:42,860 get some sort of stable so if this sort 1102 00:48:48,220 --> 00:48:44,960 of bifurcation between desert world's 1103 00:48:51,040 --> 00:48:48,230 and kevin costner worlds what we're 1104 00:48:53,350 --> 00:48:51,050 really suggesting for these m planets or 1105 00:48:56,770 --> 00:48:53,360 can we end up with something more in 1106 00:49:03,720 --> 00:48:56,780 between so this is work in progress to 1107 00:49:05,710 --> 00:49:03,730 be done so atmospheric loss from 1108 00:49:08,080 --> 00:49:05,720 terrestrial planets and secondary 1109 00:49:09,490 --> 00:49:08,090 element dominated planets and this is 1110 00:49:12,520 --> 00:49:09,500 the key question we should be asking 1111 00:49:14,950 --> 00:49:12,530 ourselves as a field especially for M 1112 00:49:17,320 --> 00:49:14,960 dwarf habitable zone five key targets 1113 00:49:18,970 --> 00:49:17,330 for upcoming missions it can highly 1114 00:49:20,710 --> 00:49:18,980 irradiated terrestrial planets rotate an 1115 00:49:23,790 --> 00:49:20,720 atmosphere or are we just wasting our 1116 00:49:29,410 --> 00:49:27,670 so I'm going to end on a suggestion 1117 00:49:31,210 --> 00:49:29,420 and this is something we're working on 1118 00:49:32,770 --> 00:49:31,220 this but perhaps we have these two 1119 00:49:36,040 --> 00:49:32,780 separate pathways to forming a 1120 00:49:38,380 --> 00:49:36,050 terrestrial planet we have what I'm 1121 00:49:40,060 --> 00:49:38,390 calling born terrestrial planets so 1122 00:49:42,010 --> 00:49:40,070 planets are formed somewhat like solar 1123 00:49:43,750 --> 00:49:42,020 system planets they didn't form fully 1124 00:49:45,370 --> 00:49:43,760 before the gas this dispersed they 1125 00:49:48,790 --> 00:49:45,380 didn't end up with large hydrants named 1126 00:49:50,980 --> 00:49:48,800 atmospheres we have terrestrial planets 1127 00:49:55,750 --> 00:49:50,990 have formed by a stripping of large 1128 00:49:57,670 --> 00:49:55,760 hydrants so obviously the atmospheres 1129 00:50:04,270 --> 00:49:57,680 we're gonna get is gonna be some sort of 1130 00:50:06,190 --> 00:50:04,280 balance between resupply and loss so if 1131 00:50:07,660 --> 00:50:06,200 the answer we're gonna get gonna be 1132 00:50:09,250 --> 00:50:07,670 dependent on these two different 1133 00:50:12,160 --> 00:50:09,260 evolutionary pathways are there going to 1134 00:50:14,260 --> 00:50:12,170 be two distinct separate types of 1135 00:50:15,880 --> 00:50:14,270 terrestrial planet atmosphere that point 1136 00:50:18,880 --> 00:50:15,890 to their formation mechanisms or is it 1137 00:50:21,160 --> 00:50:18,890 more of a continuum and this is a key 1138 00:50:22,960 --> 00:50:21,170 theoretical problem and observational 1139 00:50:26,590 --> 00:50:22,970 problem right that we need to focus to 1140 00:50:30,520 --> 00:50:26,600 the observations give us and this is 1141 00:50:33,370 --> 00:50:30,530 something we're working on now and I'm 1142 00:50:36,070 --> 00:50:33,380 out of time so I'm gonna skip what I 1143 00:50:38,800 --> 00:50:36,080 think perhaps a sort of way to get at 1144 00:50:40,780 --> 00:50:38,810 these which is loss from highly 1145 00:50:43,480 --> 00:50:40,790 irradiated rocky planet they're so hot 1146 00:50:45,070 --> 00:50:43,490 to melt their surface in the escape we 1147 00:50:47,020 --> 00:50:45,080 can observe them so that this is a good 1148 00:50:49,870 --> 00:50:47,030 way to test our secondary - severe loss 1149 00:50:52,330 --> 00:50:49,880 may quite have time to go through all 1150 00:51:02,940 --> 00:50:52,340 these slides so I finished there and 1151 00:51:11,670 --> 00:51:07,270 thank you very thank you very much we 1152 00:51:18,010 --> 00:51:13,620 [Music] 1153 00:51:22,680 --> 00:51:18,020 this desert please state your name and 1154 00:51:27,730 --> 00:51:22,690 affiliation jeremy'll account generous 1155 00:51:31,300 --> 00:51:27,740 so I was intrigued by the fact that so 1156 00:51:34,030 --> 00:51:31,310 you when we look at this straight course 1157 00:51:36,460 --> 00:51:34,040 from from Capra so of course it means 1158 00:51:41,200 --> 00:51:36,470 that even the strip course start with a 1159 00:51:43,960 --> 00:51:41,210 big hydrogen atmosphere but then this is 1160 00:51:47,530 --> 00:51:43,970 for for Capra targets so it means for f 1161 00:51:50,950 --> 00:51:47,540 JK stars basically so you can have 1162 00:51:52,480 --> 00:51:50,960 implied that for M dwarfs the the 1163 00:51:55,870 --> 00:51:52,490 mechanism of the formation mechanism 1164 00:51:58,240 --> 00:51:55,880 would be the same but at least I feel 1165 00:52:00,579 --> 00:51:58,250 that around M dwarfs the disc should be 1166 00:52:03,220 --> 00:52:00,589 less massive or or at least comparable 1167 00:52:07,240 --> 00:52:03,230 the the types of further away from the 1168 00:52:10,630 --> 00:52:07,250 star comparable to sides of the the mass 1169 00:52:13,750 --> 00:52:10,640 of the star so do you have evidence to 1170 00:52:19,440 --> 00:52:13,760 support that they should be born with a 1171 00:52:21,820 --> 00:52:19,450 lot of hydrogen so so there is evidence 1172 00:52:23,829 --> 00:52:21,830 so you're right the Kepler data is 1173 00:52:27,099 --> 00:52:23,839 dominated by ftk stars there are some 1174 00:52:29,170 --> 00:52:27,109 few M stars and this whole feature so 1175 00:52:30,839 --> 00:52:29,180 yanti nu has a nice paper from 2018 1176 00:52:34,660 --> 00:52:30,849 where she shows this whole feature 1177 00:52:37,320 --> 00:52:34,670 extends down into the M Dwarfs I'll also 1178 00:52:40,240 --> 00:52:37,330 make a comment about your feeling your 1179 00:52:42,099 --> 00:52:40,250 feeling that the gas disks and dust 1180 00:52:45,370 --> 00:52:42,109 disks are less massive around emboss 1181 00:52:48,400 --> 00:52:45,380 which is the empirical fact right but if 1182 00:52:50,920 --> 00:52:48,410 you look at the mass contained in the 1183 00:52:53,339 --> 00:52:50,930 exoplanet population it's actually more 1184 00:52:58,050 --> 00:52:53,349 massive around the lower master and 1185 00:53:01,270 --> 00:52:58,060 there's more so that's an intriguing 1186 00:53:03,250 --> 00:53:01,280 question so at the moment given the 1187 00:53:05,140 --> 00:53:03,260 observed data we have there is no 1188 00:53:07,210 --> 00:53:05,150 evidence apart from the terrestrial 1189 00:53:09,940 --> 00:53:07,220 planets in our solar system that planets 1190 00:53:15,160 --> 00:53:09,950 form without large hydrogen which i 1191 00:53:25,640 --> 00:53:23,450 right yes so how well-defined is the the 1192 00:53:26,180 --> 00:53:25,650 core envelope boundary for these sub 1193 00:53:27,830 --> 00:53:26,190 napkins 1194 00:53:29,630 --> 00:53:27,840 given what we're learning about fuzzy 1195 00:53:31,280 --> 00:53:29,640 cores for for Jupiter so that is a 1196 00:53:34,430 --> 00:53:31,290 excellent question 1197 00:53:41,270 --> 00:53:34,440 as a question to which I can answer with 1198 00:53:43,100 --> 00:53:41,280 a feeling so so one of the the things 1199 00:53:46,600 --> 00:53:43,110 that we know about this hydrogen helium 1200 00:53:48,680 --> 00:53:46,610 loss is that the radiative cooling is 1201 00:53:51,440 --> 00:53:48,690 sort of slightly super so low 1202 00:53:54,620 --> 00:53:51,450 metallicity is dominated by the metals 1203 00:53:56,270 --> 00:53:54,630 so if you do have a fuzzy core boundary 1204 00:53:59,510 --> 00:53:56,280 where you start getting into a hydrant 1205 00:54:00,950 --> 00:53:59,520 helium atmosphere that is increasing in 1206 00:54:06,410 --> 00:54:00,960 metals the mass loss rate is going to 1207 00:54:07,700 --> 00:54:06,420 drop like a stone right so it when I say 1208 00:54:09,080 --> 00:54:07,710 they're stripped cause right there 1209 00:54:11,330 --> 00:54:09,090 they're stripped in the sense that we 1210 00:54:13,940 --> 00:54:11,340 have no radius evidence for a large 1211 00:54:15,710 --> 00:54:13,950 hiding claim atmosphere so it may turn 1212 00:54:17,120 --> 00:54:15,720 out when we start looking at these super 1213 00:54:18,920 --> 00:54:17,130 Earths and as part of that suggestion 1214 00:54:21,890 --> 00:54:18,930 these terrestrial planet pathways but 1215 00:54:24,170 --> 00:54:21,900 they do retain a thin veneer of hydrogen 1216 00:54:28,280 --> 00:54:24,180 and that could be coming from this fuzzy 1217 00:54:30,920 --> 00:54:28,290 cool aspect but it's not it can't be a 1218 00:54:32,810 --> 00:54:30,930 very extended fuzzy core other you 1219 00:54:34,850 --> 00:54:32,820 otherwise you wouldn't be able to get 1220 00:54:49,010 --> 00:54:34,860 this process if if it was and which is 1221 00:54:51,500 --> 00:54:49,020 wrong anymore with a magnetic field help 1222 00:54:53,960 --> 00:54:51,510 display to do your calculation take that 1223 00:54:58,720 --> 00:54:53,970 yeah yeah so someone always asked me 1224 00:55:06,890 --> 00:55:03,470 so yes so magnetic fields suppress mass 1225 00:55:09,170 --> 00:55:06,900 loss for hydrodynamic driven and they do 1226 00:55:11,900 --> 00:55:09,180 it because you have a these outflows or 1227 00:55:14,000 --> 00:55:11,910 strongly ionized for they're coupled to 1228 00:55:16,820 --> 00:55:14,010 the magnetic fields ideal MHD is a very 1229 00:55:18,740 --> 00:55:16,830 good approximation so you get close 1230 00:55:20,540 --> 00:55:18,750 field lines close to the equator this is 1231 00:55:22,310 --> 00:55:20,550 where most of the energy is the 1232 00:55:24,680 --> 00:55:22,320 positives you only get in efficient flow 1233 00:55:26,690 --> 00:55:24,690 along the poles so this significant 1234 00:55:29,390 --> 00:55:26,700 we reduces the mass loss rate by about 1235 00:55:32,900 --> 00:55:29,400 an order of magnitude so you can play 1236 00:55:37,609 --> 00:55:32,910 this whole game again with this process 1237 00:55:39,800 --> 00:55:37,619 and compared to the radius gap data so 1238 00:55:41,630 --> 00:55:39,810 if you do that as you increase the field 1239 00:55:44,480 --> 00:55:41,640 strength you can still you still get the 1240 00:55:47,480 --> 00:55:44,490 same process you just need to calm p'n 1241 00:55:49,250 --> 00:55:47,490 sait for the reduced last loss rates by 1242 00:55:53,480 --> 00:55:49,260 reducing the mass of the planets you're 1243 00:55:57,050 --> 00:55:53,490 losing so instead of favoring rocky 1244 00:55:59,930 --> 00:55:57,060 cores with basically zero fields we 1245 00:56:02,180 --> 00:55:59,940 favor icy course with strong fields the 1246 00:56:03,920 --> 00:56:02,190 fact that the ten also planets down here 1247 00:56:06,530 --> 00:56:03,930 that have measured masses are all 1248 00:56:10,339 --> 00:56:06,540 consistent with like rock perhaps points 1249 00:56:14,030 --> 00:56:10,349 to me to suggest that these things don't 1250 00:56:17,210 --> 00:56:14,040 have Pankau spills or one gas fields and 1251 00:56:18,859 --> 00:56:17,220 I mean here the field strength at the 1252 00:56:20,690 --> 00:56:18,869 top of the hydrogen helium a pursuer you 1253 00:56:23,510 --> 00:56:20,700 double the core strength so if you have 1254 00:56:25,550 --> 00:56:23,520 a one cows earth-like field it's gonna 1255 00:56:28,130 --> 00:56:25,560 be point one gal by the time you get to 1256 00:56:30,140 --> 00:56:28,140 the pub bar so it doesn't matter so to 1257 00:56:31,849 --> 00:56:30,150 make this work you need dynamo generated 1258 00:56:33,440 --> 00:56:31,859 fields in subnet tune something we don't 1259 00:56:35,839 --> 00:56:33,450 have in the total system so we have no 1260 00:56:37,970 --> 00:56:35,849 idea what it does but at least it's 1261 00:56:47,630 --> 00:56:37,980 saying to me they don't generate a few 1262 00:56:51,980 --> 00:56:47,640 gas fields the mass loss rate by 1263 00:56:53,690 --> 00:56:51,990 diffusion limited process is not not 1264 00:56:55,309 --> 00:56:53,700 relevant here because you have 1265 00:56:59,480 --> 00:56:55,319 considered only the energy limited the 1266 00:57:00,920 --> 00:56:59,490 escape yeah so I I did point out that 1267 00:57:03,319 --> 00:57:00,930 you can slow these processes down 1268 00:57:05,630 --> 00:57:03,329 especially for the water loss by either 1269 00:57:08,480 --> 00:57:05,640 limits due to just associating the water 1270 00:57:10,250 --> 00:57:08,490 or diffusing the hydrogen through a very 1271 00:57:13,010 --> 00:57:10,260 oxygen-rich atmosphere and that does 1272 00:57:14,839 --> 00:57:13,020 slow down the mass loss rates in those 1273 00:57:18,380 --> 00:57:14,849 Lugar and barns calculations I 1274 00:57:20,780 --> 00:57:18,390 considered they also consider the 1275 00:57:22,309 --> 00:57:20,790 diffusion limit and they argued for 1276 00:57:24,380 --> 00:57:22,319 their calculations based on their 1277 00:57:26,390 --> 00:57:24,390 temperatures drop right which is based 1278 00:57:28,130 --> 00:57:26,400 on not including oxygen cooling they 1279 00:57:31,910 --> 00:57:28,140 argued that energy limit was more 1280 00:57:33,470 --> 00:57:31,920 applicable but when the calculation is 1281 00:57:35,480 --> 00:57:33,480 done properly that may not be true and 1282 00:57:38,120 --> 00:57:35,490 the diffusion limit may be another way 1283 00:57:50,670 --> 00:57:38,130 to save our water on