1 00:00:00,240 --> 00:00:10,810 [Music] 2 00:00:19,010 --> 00:00:13,610 all right so I'm just signal if it's not 3 00:00:22,070 --> 00:00:19,020 or this stops working so I am SIA and 4 00:00:24,920 --> 00:00:22,080 I'm a graduate student at Cornell at the 5 00:00:27,590 --> 00:00:24,930 Carl Sagan Institute I work with Lisa 6 00:00:29,600 --> 00:00:27,600 Colton Egger I also work with Jack the 7 00:00:31,460 --> 00:00:29,610 color got from his few talks ago and he 8 00:00:33,650 --> 00:00:31,470 actually made me this image for my 9 00:00:34,970 --> 00:00:33,660 research so if you become friends with 10 00:00:37,189 --> 00:00:34,980 him sometimes he makes artists 11 00:00:38,840 --> 00:00:37,199 conception of your research so today I'm 12 00:00:40,099 --> 00:00:38,850 gonna talk to you about my most recent 13 00:00:42,380 --> 00:00:40,109 oh my god 14 00:00:44,060 --> 00:00:42,390 project which is a post main-sequence 15 00:00:45,349 --> 00:00:44,070 habitability and I'm gonna tell you what 16 00:00:48,349 --> 00:00:45,359 the post main sequence is because I'm 17 00:00:51,520 --> 00:00:48,359 aware that you're not all astronomers so 18 00:00:54,410 --> 00:00:51,530 my thesis is basically about how 19 00:00:56,090 --> 00:00:54,420 habitability and planetary atmospheres 20 00:00:58,219 --> 00:00:56,100 would change throughout stellar 21 00:00:59,630 --> 00:00:58,229 evolution so if we want to put earth 22 00:01:02,029 --> 00:00:59,640 around another star 23 00:01:03,619 --> 00:01:02,039 it wouldn't be earth anymore because 24 00:01:05,060 --> 00:01:03,629 that star is different it has a 25 00:01:07,190 --> 00:01:05,070 different brightness and it's giving off 26 00:01:08,840 --> 00:01:07,200 different types of light and the light 27 00:01:10,690 --> 00:01:08,850 the star is giving off it affects 28 00:01:13,070 --> 00:01:10,700 everything in the planet if tribes the 29 00:01:16,550 --> 00:01:13,080 chemistry of the atmosphere surface 30 00:01:18,680 --> 00:01:16,560 temperature everything so you really 31 00:01:21,320 --> 00:01:18,690 have to think about what star your 32 00:01:23,090 --> 00:01:21,330 planet is around and I don't just do 33 00:01:27,370 --> 00:01:23,100 that I also think about where is that 34 00:01:35,360 --> 00:01:32,060 where is the star in evolution so amber 35 00:01:38,390 --> 00:01:35,370 briefly talked about how stars evolved 36 00:01:40,490 --> 00:01:38,400 so here's the life cycle of our Sun so 37 00:01:43,310 --> 00:01:40,500 right now it's on what we call the main 38 00:01:46,280 --> 00:01:43,320 sequence so the core is fusing hydrogen 39 00:01:49,820 --> 00:01:46,290 into helium and the main sequence takes 40 00:01:50,930 --> 00:01:49,830 up most of the life of most stars but 41 00:01:53,480 --> 00:01:50,940 there's all this other stuff that 42 00:01:55,160 --> 00:01:53,490 happens too so you might have all heard 43 00:01:57,530 --> 00:01:55,170 that one day the Sun is going to become 44 00:01:59,630 --> 00:01:57,540 huge and come out and destroy earth so 45 00:02:02,840 --> 00:01:59,640 that is true and that's what I'm going 46 00:02:06,950 --> 00:02:02,850 to be talking about today so it's gonna 47 00:02:09,319 --> 00:02:06,960 get really big and you could see here I 48 00:02:12,440 --> 00:02:09,329 actually have plotted out this is what's 49 00:02:13,280 --> 00:02:12,450 going to happen to our own Sun so here 50 00:02:16,429 --> 00:02:13,290 we have 51 00:02:19,100 --> 00:02:16,439 with time this orange line is the radius 52 00:02:20,690 --> 00:02:19,110 of the Sun this green region here is the 53 00:02:22,729 --> 00:02:20,700 habitable zone where liquid water could 54 00:02:25,610 --> 00:02:22,739 exist and then we have the orbits of 55 00:02:27,740 --> 00:02:25,620 Earth Jupiter and Saturn and this red 56 00:02:29,809 --> 00:02:27,750 shaded in region is the red giant branch 57 00:02:31,610 --> 00:02:29,819 so that's when the star is getting 58 00:02:34,430 --> 00:02:31,620 really big and expanding what you could 59 00:02:36,940 --> 00:02:34,440 see with the radius and also here the 60 00:02:40,550 --> 00:02:36,950 Sun will come out and touch earth so 61 00:02:42,199 --> 00:02:40,560 that's not good for us but what I'm 62 00:02:44,869 --> 00:02:42,209 gonna focus on is look at right here 63 00:02:48,349 --> 00:02:44,879 Jupiter and Saturn are going to be in 64 00:02:50,089 --> 00:02:48,359 the habitable zone of our Sun so what's 65 00:02:52,759 --> 00:02:50,099 exciting about that is that means that 66 00:02:55,160 --> 00:02:52,769 object like Europa are going to thaw out 67 00:02:58,610 --> 00:02:55,170 and those oceans are going to be exposed 68 00:03:00,440 --> 00:02:58,620 for everyone to see the atmosphere so we 69 00:03:03,080 --> 00:03:00,450 could maybe detect life there so right 70 00:03:05,599 --> 00:03:03,090 now we can't but if it were well we 71 00:03:07,280 --> 00:03:05,609 would be dead but in the future we might 72 00:03:10,490 --> 00:03:07,290 be able to remotely detect life on 73 00:03:12,559 --> 00:03:10,500 objects like Europa so for this talk the 74 00:03:15,229 --> 00:03:12,569 questions I want to answer are how long 75 00:03:17,420 --> 00:03:15,239 could a planet or a moon remain in the 76 00:03:19,520 --> 00:03:17,430 habitable zone of a post main sequence 77 00:03:21,710 --> 00:03:19,530 star and then what were the atmospheres 78 00:03:23,930 --> 00:03:21,720 and the UV environments of those stars 79 00:03:28,009 --> 00:03:23,940 look like because very important for 80 00:03:29,539 --> 00:03:28,019 habitability so to briefly go over the 81 00:03:32,390 --> 00:03:29,549 post main sequence here we have the 82 00:03:34,819 --> 00:03:32,400 luminosity evolution of stars of 83 00:03:37,729 --> 00:03:34,829 different masses so first there's the 84 00:03:40,640 --> 00:03:37,739 red giant branch so the core has run out 85 00:03:43,220 --> 00:03:40,650 of hydrogen diffuse so it starts fusing 86 00:03:45,050 --> 00:03:43,230 hydrogen in a shell around the core and 87 00:03:47,390 --> 00:03:45,060 when this happens the star becomes very 88 00:03:49,220 --> 00:03:47,400 big so it expands it cools and becomes 89 00:03:50,629 --> 00:03:49,230 very luminous so with all these 90 00:03:53,599 --> 00:03:50,639 different luminosity tracks the red 91 00:03:56,210 --> 00:03:53,609 giant branch is this first peak so 92 00:03:57,229 --> 00:03:56,220 finally the core will reach the high 93 00:03:59,000 --> 00:03:57,239 enough temperature and pressure 94 00:04:01,460 --> 00:03:59,010 conditions and it will finally be able 95 00:04:03,229 --> 00:04:01,470 to start to fuse helium in the core so 96 00:04:05,509 --> 00:04:03,239 this is the horizontal branch so this is 97 00:04:06,920 --> 00:04:05,519 the area between the peaks and you'll 98 00:04:08,119 --> 00:04:06,930 see it's different for stars of 99 00:04:10,729 --> 00:04:08,129 different masses which I'll get into 100 00:04:12,949 --> 00:04:10,739 more so a horizontal branch and then 101 00:04:15,379 --> 00:04:12,959 just like before with hydrogen the star 102 00:04:16,550 --> 00:04:15,389 is gonna run out of core helium and it's 103 00:04:18,710 --> 00:04:16,560 gonna freak out again and it's gonna 104 00:04:20,750 --> 00:04:18,720 start fusing helium the shell on the 105 00:04:22,490 --> 00:04:20,760 asymptotic giant branch which is sort of 106 00:04:24,709 --> 00:04:22,500 similar to the red giant branch and 107 00:04:26,379 --> 00:04:24,719 that's the second peak here so what I 108 00:04:29,170 --> 00:04:26,389 want you to take away from this is 109 00:04:31,629 --> 00:04:29,180 even though these three phases happen to 110 00:04:33,459 --> 00:04:31,639 all these stars it's very different the 111 00:04:36,219 --> 00:04:33,469 time skills are very different and the 112 00:04:38,350 --> 00:04:36,229 luminosity change is very dependent on 113 00:04:39,760 --> 00:04:38,360 the mass of the star so obviously the 114 00:04:41,679 --> 00:04:39,770 habitable zone during the post main 115 00:04:45,189 --> 00:04:41,689 sequence is really going to depend on 116 00:04:47,649 --> 00:04:45,199 the mass of the star so when I was 117 00:04:49,839 --> 00:04:47,659 looking what I did is I looked at all 118 00:04:51,459 --> 00:04:49,849 these different star masses and I found 119 00:04:53,409 --> 00:04:51,469 if I want something to stay in the 120 00:04:55,959 --> 00:04:53,419 habitable zone for like the longest 121 00:04:59,860 --> 00:04:55,969 continuous time the horizontal branch is 122 00:05:02,439 --> 00:04:59,870 the best bet so it's pretty stable if 123 00:05:06,159 --> 00:05:02,449 you look here here is the evolution of a 124 00:05:08,140 --> 00:05:06,169 1.5 solar mass star so again we have the 125 00:05:10,269 --> 00:05:08,150 radius of the star we have the habitable 126 00:05:12,369 --> 00:05:10,279 zone the red shaded region is the red 127 00:05:13,990 --> 00:05:12,379 giant branch blue is asymptotic giant 128 00:05:15,999 --> 00:05:14,000 branch and in between is the horizontal 129 00:05:18,040 --> 00:05:16,009 branch so look it's pretty stable there 130 00:05:19,689 --> 00:05:18,050 that's pretty nice and on the red timer 131 00:05:22,600 --> 00:05:19,699 and it's moving it's changing really 132 00:05:24,939 --> 00:05:22,610 quickly so a planet would not enjoy that 133 00:05:26,860 --> 00:05:24,949 and this blue line is the orbit I 134 00:05:28,480 --> 00:05:26,870 calculated so if a planet was there 135 00:05:30,369 --> 00:05:28,490 that's the maximum amount of time could 136 00:05:31,990 --> 00:05:30,379 stay in the habitable zone so 137 00:05:34,059 --> 00:05:32,000 unsurprisingly when I look at these 138 00:05:35,860 --> 00:05:34,069 different stars the habitable zone time 139 00:05:37,869 --> 00:05:35,870 scales the longest possible one is 140 00:05:40,119 --> 00:05:37,879 basically the length of the horizontal 141 00:05:42,579 --> 00:05:40,129 branch but what's interesting here is 142 00:05:45,159 --> 00:05:42,589 the length of the horizontal branch does 143 00:05:47,350 --> 00:05:45,169 not linearly scale with the lifetime of 144 00:05:48,939 --> 00:05:47,360 the star so a star like the Sun the 145 00:05:52,360 --> 00:05:48,949 horizontal branch is actually only about 146 00:05:53,230 --> 00:05:52,370 1% of the Suns total lifetime but for 147 00:05:55,200 --> 00:05:53,240 more massive stars 148 00:05:58,059 --> 00:05:55,210 it's almost 30 percent of its lifetime 149 00:05:59,980 --> 00:05:58,069 so if you look here here we have the 150 00:06:02,409 --> 00:05:59,990 absolute values of the horizontal the 151 00:06:04,209 --> 00:06:02,419 time on the horizontal branch so for 152 00:06:06,519 --> 00:06:04,219 higher math stars is actually much 153 00:06:08,709 --> 00:06:06,529 longer and this is a bit 154 00:06:10,450 --> 00:06:08,719 counterintuitive because the more 155 00:06:11,079 --> 00:06:10,460 massive a star is the shorter its 156 00:06:13,659 --> 00:06:11,089 lifetime 157 00:06:16,119 --> 00:06:13,669 but the more massive a star is the 158 00:06:19,119 --> 00:06:16,129 easier it is for the core to become hot 159 00:06:21,839 --> 00:06:19,129 enough to fuse helium in the core so 160 00:06:24,969 --> 00:06:21,849 it's really around higher mass stars 161 00:06:26,800 --> 00:06:24,979 particular like 22.3 solar masses but 162 00:06:29,409 --> 00:06:26,810 they have the longest habitable zone 163 00:06:31,329 --> 00:06:29,419 lifetimes four-post main sequence which 164 00:06:33,999 --> 00:06:31,339 usually these stars are left out of 165 00:06:36,879 --> 00:06:34,009 habitability searches so this is their 166 00:06:39,030 --> 00:06:36,889 chance post main sequence so I 167 00:06:41,910 --> 00:06:39,040 calculated the habitable zones 168 00:06:44,280 --> 00:06:41,920 for hosts between 1.3 and 3.5 solar 169 00:06:46,530 --> 00:06:44,290 masses and the reason for this isn't 170 00:06:49,430 --> 00:06:46,540 just because the horizontal branch is 171 00:06:52,890 --> 00:06:49,440 longer but also because these stars 172 00:06:55,620 --> 00:06:52,900 exist so for a star like our Sun it 173 00:06:57,930 --> 00:06:55,630 takes about 11 billion years to reach 174 00:06:59,280 --> 00:06:57,940 the post main sequence and if you know 175 00:07:03,240 --> 00:06:59,290 anything about the galaxy the oldest 176 00:07:05,820 --> 00:07:03,250 stars are 11 billion years old so I only 177 00:07:08,730 --> 00:07:05,830 I made the decision to only study stars 178 00:07:11,000 --> 00:07:08,740 that exists so can't say I'm not 179 00:07:14,580 --> 00:07:11,010 realistic 180 00:07:16,680 --> 00:07:14,590 so what I did after I calculated these 181 00:07:18,810 --> 00:07:16,690 orbits of maximum probability is I also 182 00:07:21,810 --> 00:07:18,820 look at the atmospheres of these planets 183 00:07:23,670 --> 00:07:21,820 and I did this using XO prime which is a 184 00:07:26,040 --> 00:07:23,680 1d couple of climate photochemistry 185 00:07:28,260 --> 00:07:26,050 model it's sort of like a cousin of 186 00:07:31,590 --> 00:07:28,270 Atmos which I know a lot of people use 187 00:07:33,270 --> 00:07:31,600 and what it does is it as a climate code 188 00:07:36,300 --> 00:07:33,280 in a photochemistry code and they sort 189 00:07:38,820 --> 00:07:36,310 of talk to each other so what I do is I 190 00:07:41,070 --> 00:07:38,830 put in put a star spectrum I specify 191 00:07:42,510 --> 00:07:41,080 things like the distance the initial 192 00:07:44,580 --> 00:07:42,520 conditions of the atmosphere which I 193 00:07:46,170 --> 00:07:44,590 look at earth-like planets because earth 194 00:07:49,110 --> 00:07:46,180 is the only planet we know about light 195 00:07:50,760 --> 00:07:49,120 so start there and the climate code will 196 00:07:52,350 --> 00:07:50,770 use the chemistry in the atmosphere to 197 00:07:53,880 --> 00:07:52,360 calculate a temperature throughout the 198 00:07:55,170 --> 00:07:53,890 atmosphere then it goes over to the 199 00:07:57,210 --> 00:07:55,180 photochemistry code and it will 200 00:07:59,580 --> 00:07:57,220 calculate the chemistry based on the 201 00:08:01,410 --> 00:07:59,590 incoming stellar radiation but also the 202 00:08:04,230 --> 00:08:01,420 temperature and the two of them go back 203 00:08:06,660 --> 00:08:04,240 and forth until it agrees with a planet 204 00:08:08,250 --> 00:08:06,670 at this distance from this star is what 205 00:08:10,800 --> 00:08:08,260 the temperature and the chemistry would 206 00:08:12,750 --> 00:08:10,810 look like for it to be in equilibrium so 207 00:08:15,150 --> 00:08:12,760 I did this and I modeled atmospheres of 208 00:08:17,550 --> 00:08:15,160 planets at the 180 equivalent and also 209 00:08:19,920 --> 00:08:17,560 several points along these orbits of 210 00:08:21,960 --> 00:08:19,930 maximum habitability and when I say why 211 00:08:23,700 --> 00:08:21,970 don't you equivalent here all I mean is 212 00:08:26,250 --> 00:08:23,710 just a distance where the planet would 213 00:08:29,220 --> 00:08:26,260 receive the same total amount of flux 214 00:08:32,850 --> 00:08:29,230 that Earth does so basically I'm just 215 00:08:35,760 --> 00:08:32,860 like earth for the purposes of this talk 216 00:08:37,260 --> 00:08:35,770 so this code outputs a lot of stuff but 217 00:08:39,409 --> 00:08:37,270 for the purposes of this talk I'm just 218 00:08:42,960 --> 00:08:39,419 gonna focus on you be to the ground so 219 00:08:45,660 --> 00:08:42,970 UV is really important because it's what 220 00:08:49,200 --> 00:08:45,670 we need to live but too much UV would 221 00:08:51,420 --> 00:08:49,210 kill everything so it's important we 222 00:08:54,930 --> 00:08:51,430 usually it divided up into three 223 00:08:57,240 --> 00:08:54,940 regime's UVA UVB and UVC so we have here 224 00:08:59,790 --> 00:08:57,250 demonstrating how much of these three 225 00:09:02,820 --> 00:08:59,800 regimes reach the ground on earth so UVA 226 00:09:07,019 --> 00:09:02,830 is actually good for us it's what causes 227 00:09:09,150 --> 00:09:07,029 vitamin D to be produced in our skin and 228 00:09:10,980 --> 00:09:09,160 if not variational do by ozone but 229 00:09:14,460 --> 00:09:10,990 that's okay it's good for us life 230 00:09:16,170 --> 00:09:14,470 probably need to UVA UVB if you've ever 231 00:09:20,699 --> 00:09:16,180 had sunburn 232 00:09:24,960 --> 00:09:20,709 thanks CTV be also tanning so UVB in 233 00:09:26,910 --> 00:09:24,970 small doses is okay but too much will 234 00:09:29,910 --> 00:09:26,920 probably cause things like skin cancer 235 00:09:33,030 --> 00:09:29,920 so most of UVB is shielded by our ozone 236 00:09:35,190 --> 00:09:33,040 layer and then there's UVC which ruins 237 00:09:37,740 --> 00:09:35,200 everything so it can literally break up 238 00:09:40,920 --> 00:09:37,750 heart DNA so luckily with our 239 00:09:43,650 --> 00:09:40,930 atmospheric shielding of ozone almost no 240 00:09:45,780 --> 00:09:43,660 UVC you reaches the ground here but if 241 00:09:47,550 --> 00:09:45,790 we were on a different planet from a 242 00:09:48,990 --> 00:09:47,560 different star the chemistry would be 243 00:09:50,269 --> 00:09:49,000 different so we don't know if you guys 244 00:09:52,769 --> 00:09:50,279 aren't shielding would be enough and 245 00:09:55,860 --> 00:09:52,779 what's interesting here is that ozone 246 00:09:58,890 --> 00:09:55,870 which shield us from UVC is created by 247 00:10:00,269 --> 00:09:58,900 UVC so we'll have oxygen molecules 248 00:10:02,190 --> 00:10:00,279 flying around they'll get hit by a 249 00:10:05,160 --> 00:10:02,200 photon it needs to be a photon less than 250 00:10:06,840 --> 00:10:05,170 240 nanometers to break it apart so UVC 251 00:10:08,880 --> 00:10:06,850 and it'll recombine with a background 252 00:10:13,440 --> 00:10:08,890 molecule which is usually something like 253 00:10:15,269 --> 00:10:13,450 nitrogen so UVC creates what shields us 254 00:10:18,840 --> 00:10:15,279 from UVC and this causes some 255 00:10:21,480 --> 00:10:18,850 interesting relationships later on so if 256 00:10:23,760 --> 00:10:21,490 we look at the you the environments a 257 00:10:25,590 --> 00:10:23,770 planet at the 1a you have equivalent 258 00:10:28,230 --> 00:10:25,600 this is what you get 259 00:10:31,199 --> 00:10:28,240 so if you're into spectral types here 260 00:10:32,880 --> 00:10:31,209 they are these are nearby post- and 261 00:10:34,199 --> 00:10:32,890 stars but if you don't like spectral 262 00:10:35,519 --> 00:10:34,209 types or don't know they are all you 263 00:10:37,470 --> 00:10:35,529 need to know is these are the hottest 264 00:10:40,610 --> 00:10:37,480 and it progressively gets to cooler and 265 00:10:45,360 --> 00:10:40,620 the sun's there because we live there so 266 00:10:48,389 --> 00:10:45,370 so what's interesting here is that it is 267 00:10:50,850 --> 00:10:48,399 the cooler targets that have the most 268 00:10:52,440 --> 00:10:50,860 UVC to the ground so that might seem 269 00:10:54,630 --> 00:10:52,450 counterintuitive because stars are 270 00:10:56,819 --> 00:10:54,640 basically like black bodies so hotter 271 00:10:59,370 --> 00:10:56,829 stars are giving off more higher energy 272 00:11:02,100 --> 00:10:59,380 photons which means they're giving off 273 00:11:04,580 --> 00:11:02,110 more UV but it's these really hot stars 274 00:11:06,440 --> 00:11:04,590 they give off so much UV 275 00:11:10,580 --> 00:11:06,450 that means they're creating a lot of 276 00:11:12,560 --> 00:11:10,590 ozone and it's these low UV targets that 277 00:11:13,910 --> 00:11:12,570 even though there's not that much UV 278 00:11:16,450 --> 00:11:13,920 reaching the planet 279 00:11:20,360 --> 00:11:16,460 it just can't produce enough ozone to 280 00:11:22,160 --> 00:11:20,370 shield the planet so this has 281 00:11:23,960 --> 00:11:22,170 interesting implications not just for 282 00:11:26,390 --> 00:11:23,970 post main-sequence stars but anyone who 283 00:11:29,120 --> 00:11:26,400 cares about looking for planets around 284 00:11:31,760 --> 00:11:29,130 lower mass stars which is something that 285 00:11:33,560 --> 00:11:31,770 people like to do so even though just 286 00:11:35,900 --> 00:11:33,570 remember even though the star doesn't 287 00:11:37,280 --> 00:11:35,910 have as much UV it might actually have 288 00:11:41,420 --> 00:11:37,290 more UV on the surface because it just 289 00:11:44,720 --> 00:11:41,430 can't create this ozone and also along 290 00:11:46,310 --> 00:11:44,730 with doing the 1iu equivalent I modeled 291 00:11:48,980 --> 00:11:46,320 what a planet would be like if it was on 292 00:11:50,540 --> 00:11:48,990 this orbit of maximum habitability what 293 00:11:52,430 --> 00:11:50,550 it would look like during its lifetime 294 00:11:55,640 --> 00:11:52,440 on the post main sequence habitable zone 295 00:11:57,050 --> 00:11:55,650 so for this star I chose a 2.3 solar 296 00:12:00,140 --> 00:11:57,060 mass star because it is the longest 297 00:12:01,730 --> 00:12:00,150 habitable zone timescale and I modeled 298 00:12:03,140 --> 00:12:01,740 it at the beginning of the horizontal 299 00:12:07,460 --> 00:12:03,150 branch and at the beginning of the 300 00:12:10,970 --> 00:12:07,470 asymptotic giant branch so even though I 301 00:12:12,860 --> 00:12:10,980 just said that these cooler targets and 302 00:12:15,530 --> 00:12:12,870 this would be a cooler target it'd be 303 00:12:19,220 --> 00:12:15,540 around 4000 Kelvin it doesn't create as 304 00:12:21,530 --> 00:12:19,230 much ozone because with these habitable 305 00:12:23,930 --> 00:12:21,540 zones it has to be sort of near the edge 306 00:12:25,250 --> 00:12:23,940 of the outer edge of the habitable zone 307 00:12:28,100 --> 00:12:25,260 to stay habitable for as long as 308 00:12:29,660 --> 00:12:28,110 possible it actually cuts down the UV 309 00:12:32,090 --> 00:12:29,670 coming in by enough that even though 310 00:12:34,460 --> 00:12:32,100 much ozone isn't being created there's 311 00:12:37,010 --> 00:12:34,470 just not that much hitting it at all so 312 00:12:39,829 --> 00:12:37,020 this is actually safe which I know might 313 00:12:41,570 --> 00:12:39,839 be confusing so basically you always 314 00:12:43,010 --> 00:12:41,580 have to model the photochemistry in the 315 00:12:43,760 --> 00:12:43,020 ozone production because it is not 316 00:12:49,010 --> 00:12:43,770 intuitive 317 00:12:50,660 --> 00:12:49,020 but it will be like so if you aren't 318 00:12:53,960 --> 00:12:50,670 listening to anything I said just now 319 00:12:56,329 --> 00:12:53,970 which is fine I were all tired even the 320 00:12:58,940 --> 00:12:56,339 projectors tired apparently this is what 321 00:13:01,430 --> 00:12:58,950 I want you to remember so during the 322 00:13:03,740 --> 00:13:01,440 post main sequence the stars get really 323 00:13:05,510 --> 00:13:03,750 big the habitable zone moves out it's 324 00:13:08,000 --> 00:13:05,520 not going to be good for planets that 325 00:13:10,070 --> 00:13:08,010 were originally habitable like Earth but 326 00:13:12,740 --> 00:13:10,080 these planets that would have been past 327 00:13:14,780 --> 00:13:12,750 the frost line initially are going to be 328 00:13:17,210 --> 00:13:14,790 habitable so it could thaw a lot of 329 00:13:18,329 --> 00:13:17,220 things and it can reveal subsurface life 330 00:13:20,340 --> 00:13:18,339 if you 331 00:13:21,900 --> 00:13:20,350 look for something habitable it's good 332 00:13:23,369 --> 00:13:21,910 to look for a star on the horizontal 333 00:13:26,759 --> 00:13:23,379 branch which there are a bunch of them 334 00:13:28,590 --> 00:13:26,769 nearby actually so that's convenient 335 00:13:31,619 --> 00:13:28,600 you want to look there because it's a 336 00:13:33,660 --> 00:13:31,629 relatively stable time period the 337 00:13:35,879 --> 00:13:33,670 longest habitability timescales are 338 00:13:37,439 --> 00:13:35,889 actually for more massive stars so 339 00:13:39,480 --> 00:13:37,449 unlike when we look at me and sequence 340 00:13:41,670 --> 00:13:39,490 lifetimes we actually want to look at 341 00:13:43,110 --> 00:13:41,680 higher mass stars which is convenient 342 00:13:44,549 --> 00:13:43,120 because it's these higher mass stars 343 00:13:47,189 --> 00:13:44,559 that are already on the post main 344 00:13:51,150 --> 00:13:47,199 sequence so it's nice when reality is 345 00:13:53,160 --> 00:13:51,160 convenient and yeah so when these stars 346 00:13:55,610 --> 00:13:53,170 get big they expand the temperature goes 347 00:13:58,110 --> 00:13:55,620 down so there's less UV but that could 348 00:13:58,920 --> 00:13:58,120 result in more UV in the planet's 349 00:14:02,790 --> 00:13:58,930 surface 350 00:14:04,799 --> 00:14:02,800 so and if you want to learn more and our 351 00:14:07,410 --> 00:14:04,809 sad that this talk is short this is 352 00:14:12,259 --> 00:14:07,420 published this work in the Astrophysical 353 00:14:29,999 --> 00:14:26,819 any questions thank you well I talked 354 00:14:31,889 --> 00:14:30,009 about the presence of UV radiation and 355 00:14:34,079 --> 00:14:31,899 and its effects on life so you are 356 00:14:36,569 --> 00:14:34,089 looking for something to block UV 357 00:14:39,840 --> 00:14:36,579 radiation as effectively as possible but 358 00:14:45,239 --> 00:14:39,850 on earth we definitely know that even 359 00:14:46,110 --> 00:14:45,249 when UVC was basically unaltered life 360 00:14:47,610 --> 00:14:46,120 did evolve 361 00:14:49,860 --> 00:14:47,620 well before the great oxygenation event 362 00:14:52,049 --> 00:14:49,870 so yeah can you speculate a bit that's 363 00:14:54,329 --> 00:14:52,059 do you know how critical it even is to 364 00:14:56,340 --> 00:14:54,339 have this huy protected environments and 365 00:14:58,169 --> 00:14:56,350 and whether you know maybe it doesn't 366 00:15:00,749 --> 00:14:58,179 matter much of maybe to beneficial for 367 00:15:03,179 --> 00:15:00,759 the appearance of life to have Sun yeah 368 00:15:05,009 --> 00:15:03,189 so that's a really good question so in 369 00:15:06,660 --> 00:15:05,019 the time of early Earth there wasn't 370 00:15:09,509 --> 00:15:06,670 much oxygen there definitely was no 371 00:15:12,689 --> 00:15:09,519 ozone and we know that life did exist 372 00:15:15,299 --> 00:15:12,699 here on earth so it is debated then 373 00:15:17,999 --> 00:15:15,309 because it looks like life evolves when 374 00:15:22,319 --> 00:15:18,009 UVC was hitting the ground in really 375 00:15:24,210 --> 00:15:22,329 high quantities so it is a bit strange 376 00:15:25,889 --> 00:15:24,220 so some people believe that life started 377 00:15:28,650 --> 00:15:25,899 under the oceans so even though there 378 00:15:31,890 --> 00:15:28,660 wasn't a zone shilling water is really 379 00:15:33,930 --> 00:15:31,900 efficient at stopping UVC so some people 380 00:15:36,750 --> 00:15:33,940 think that it still wasn't an issue even 381 00:15:38,760 --> 00:15:36,760 though there was no ozone and some 382 00:15:40,620 --> 00:15:38,770 people actually think so there's a lot 383 00:15:43,230 --> 00:15:40,630 of different opinions here and since we 384 00:15:45,630 --> 00:15:43,240 can't travel back in time we don't 385 00:15:50,130 --> 00:15:45,640 really know the best part of 386 00:15:53,100 --> 00:15:50,140 astrobiology so so some people think 387 00:15:56,100 --> 00:15:53,110 that maybe like needed UVC to just sort 388 00:15:59,280 --> 00:15:56,110 of get sparked and start up so maybe you 389 00:16:01,710 --> 00:15:59,290 need UVC initially and then you need to 390 00:16:04,170 --> 00:16:01,720 be shielded from UVC because obviously 391 00:16:07,620 --> 00:16:04,180 if suddenly the ozone layer left we 392 00:16:09,600 --> 00:16:07,630 would all die pretty quickly so that's a 393 00:16:14,640 --> 00:16:09,610 yeah that's a good question I wish I 394 00:16:17,550 --> 00:16:14,650 knew the answer that question so yeah so 395 00:16:19,560 --> 00:16:17,560 for your models that you're eating on 396 00:16:21,240 --> 00:16:19,570 your climate you set an initial some 397 00:16:22,320 --> 00:16:21,250 sort of chemical abundance where did you 398 00:16:23,550 --> 00:16:22,330 get that was that from like stellar 399 00:16:26,580 --> 00:16:23,560 spectra or is that from like dis 400 00:16:28,590 --> 00:16:26,590 observations or would you use Duchy as 401 00:16:30,660 --> 00:16:28,600 your initial for the planetary 402 00:16:34,400 --> 00:16:30,670 atmosphere yeah yeah so we basically 403 00:16:36,930 --> 00:16:34,410 just use initial earth conditions so 404 00:16:38,550 --> 00:16:36,940 we've experimented with some other ones 405 00:16:39,660 --> 00:16:38,560 there are some people who was trying to 406 00:16:42,390 --> 00:16:39,670 do this stuff throughout Earth's 407 00:16:44,130 --> 00:16:42,400 geological history but for this work we 408 00:16:45,720 --> 00:16:44,140 just use basically earth like 409 00:16:47,880 --> 00:16:45,730 composition and then we let the model 410 00:16:49,830 --> 00:16:47,890 evolve to get to the point where it 411 00:16:59,480 --> 00:16:49,840 would be under those conditions okay