1 00:00:00,720 --> 00:00:11,410 [Music] 2 00:00:16,790 --> 00:00:14,120 hi well as you've seen from the talk so 3 00:00:20,060 --> 00:00:16,800 far we clearly completely understand 4 00:00:23,570 --> 00:00:20,070 life on Earth so our next question is 5 00:00:25,540 --> 00:00:23,580 where might we find life beyond our 6 00:00:28,940 --> 00:00:25,550 planets 7 00:00:31,600 --> 00:00:28,950 say this our Sun is one of a hundred 8 00:00:34,490 --> 00:00:31,610 billion stars in the Milky Way galaxy 9 00:00:38,360 --> 00:00:34,500 and when we talk about extrasolar 10 00:00:43,130 --> 00:00:38,370 planets we're saying extra as in outside 11 00:00:46,640 --> 00:00:43,140 and solar means the Sun so an extrasolar 12 00:00:51,290 --> 00:00:46,650 planets or exoplanets is a planet that 13 00:00:54,350 --> 00:00:51,300 orbits a star that is not our Sun I in 14 00:00:56,510 --> 00:00:54,360 the last 20 or 25 years we have 15 00:01:00,980 --> 00:00:56,520 discovered over three and a half 16 00:01:03,770 --> 00:01:00,990 thousand exoplanets roughly one-third of 17 00:01:07,880 --> 00:01:03,780 those have a radius that is less than 18 00:01:12,349 --> 00:01:07,890 twice the size of the earth so we have 19 00:01:14,989 --> 00:01:12,359 all these earth sized worlds but could 20 00:01:15,529 --> 00:01:14,999 any of them be inhabited and how would 21 00:01:22,370 --> 00:01:15,539 we know 22 00:01:24,230 --> 00:01:22,380 Oh 1998 96 96 percent of exoplanets have 23 00:01:27,499 --> 00:01:24,240 been discovered through one of two 24 00:01:29,599 --> 00:01:27,509 techniques the first of these is known 25 00:01:32,629 --> 00:01:29,609 as the radial velocity technique or 26 00:01:35,629 --> 00:01:32,639 Doppler bubble and here the planet's 27 00:01:38,870 --> 00:01:35,639 gravity causes the star to make a very 28 00:01:41,149 --> 00:01:38,880 small movement a tiny wobble that pushes 29 00:01:44,149 --> 00:01:41,159 it towards and away from the earth and 30 00:01:47,149 --> 00:01:44,159 as it moves towards and away from us 31 00:01:49,849 --> 00:01:47,159 it's light gets stretched and compressed 32 00:01:52,340 --> 00:01:49,859 and stretching and compressing these 33 00:01:55,340 --> 00:01:52,350 wavelengths turn it from slightly redder 34 00:01:58,039 --> 00:01:55,350 to slightly bluer and if we can measure 35 00:02:01,429 --> 00:01:58,049 that we get a sense of the mass of the 36 00:02:03,590 --> 00:02:01,439 planet that might be orbiting it the 37 00:02:06,349 --> 00:02:03,600 second technique is called the transit 38 00:02:08,960 --> 00:02:06,359 method and here the planet passes 39 00:02:11,930 --> 00:02:08,970 between the star and where we're viewing 40 00:02:14,900 --> 00:02:11,940 on earth and as it passes across the 41 00:02:17,420 --> 00:02:14,910 star surface a tiny bit of the light is 42 00:02:21,500 --> 00:02:17,430 obscured to indicate a planet might be 43 00:02:23,149 --> 00:02:21,510 there not typically this tells us 44 00:02:26,270 --> 00:02:23,159 two pieces of information about the 45 00:02:29,390 --> 00:02:26,280 planet the first is something about its 46 00:02:31,729 --> 00:02:29,400 physical size if the planet has been 47 00:02:34,640 --> 00:02:31,739 found through the transit technique the 48 00:02:38,210 --> 00:02:34,650 amount of light obscures tells us about 49 00:02:39,979 --> 00:02:38,220 the planets radius alternatively if the 50 00:02:42,649 --> 00:02:39,989 planet is found through the Doppler 51 00:02:45,229 --> 00:02:42,659 wobble technique the size of the wobble 52 00:02:47,930 --> 00:02:45,239 that is induces in the star tells us 53 00:02:50,210 --> 00:02:47,940 about the planets minimum mass the 54 00:02:53,030 --> 00:02:50,220 second thing we typically know is how 55 00:02:56,509 --> 00:02:53,040 much starlight so how much radiation is 56 00:02:59,030 --> 00:02:56,519 reaching the planet from its star now 57 00:03:01,210 --> 00:02:59,040 this is not the same as knowing the 58 00:03:04,729 --> 00:03:01,220 temperature on the planet's surface 59 00:03:06,770 --> 00:03:04,739 indeed in our own solar system Venus 60 00:03:09,530 --> 00:03:06,780 receives roughly twice the amount of 61 00:03:11,330 --> 00:03:09,540 sunlight compared to the earth and if 62 00:03:14,420 --> 00:03:11,340 you were to guess at Venus's surface 63 00:03:16,280 --> 00:03:14,430 temperature based on this number you 64 00:03:20,539 --> 00:03:16,290 might think venus had a surface 65 00:03:22,069 --> 00:03:20,549 temperature of 27 30 degrees sounds 66 00:03:25,190 --> 00:03:22,079 quite nice maybe go there for a holiday 67 00:03:29,839 --> 00:03:25,200 in fact the surface temperature of Venus 68 00:03:31,970 --> 00:03:29,849 is 460 Celsius it melts lead and the 69 00:03:34,729 --> 00:03:31,980 longest a spacecraft has ever survived 70 00:03:37,819 --> 00:03:34,739 on the Venetian surface is less than two 71 00:03:40,039 --> 00:03:37,829 hours so these two properties don't tell 72 00:03:42,559 --> 00:03:40,049 us anything about the surface conditions 73 00:03:44,629 --> 00:03:42,569 and it's the surface conditions we're 74 00:03:47,900 --> 00:03:44,639 really interested in when we want to 75 00:03:52,220 --> 00:03:47,910 think about life so what does it take to 76 00:03:54,650 --> 00:03:52,230 be an earth well size is certainly part 77 00:03:57,050 --> 00:03:54,660 of it if the planet is vastly bigger 78 00:03:59,720 --> 00:03:57,060 than the earth the chances are it would 79 00:04:02,420 --> 00:03:59,730 be like Jupiter with a colossal 80 00:04:05,330 --> 00:04:02,430 atmosphere and no real surface that 81 00:04:07,759 --> 00:04:05,340 anything could live upon however as 82 00:04:10,250 --> 00:04:07,769 we've heard from marine there's also our 83 00:04:12,710 --> 00:04:10,260 planet's magnetic fields that protects 84 00:04:15,470 --> 00:04:12,720 us from the worst of the sun's flares 85 00:04:17,689 --> 00:04:15,480 and radiation we see this as a Northern 86 00:04:20,270 --> 00:04:17,699 Lights occasionally a strong flare may 87 00:04:23,029 --> 00:04:20,280 damage our GPS systems but it doesn't 88 00:04:26,659 --> 00:04:23,039 sterilize our surface because we have 89 00:04:28,939 --> 00:04:26,669 this protective magnetic field we also 90 00:04:31,010 --> 00:04:28,949 have volcanoes which don't initially 91 00:04:33,230 --> 00:04:31,020 seem like a good thing but in fact 92 00:04:35,379 --> 00:04:33,240 helped generate our atmosphere that we 93 00:04:38,350 --> 00:04:35,389 breathe 94 00:04:41,860 --> 00:04:38,360 rock-type helps also regulate the amount 95 00:04:44,529 --> 00:04:41,870 of greenhouse gases in our air and the 96 00:04:47,619 --> 00:04:44,539 presence of water as we've heard our 97 00:04:50,170 --> 00:04:47,629 planet was probably born dry and later 98 00:04:52,839 --> 00:04:50,180 had a delivery of icy meteorites that 99 00:04:54,610 --> 00:04:52,849 gave us our oceans so you could have a 100 00:04:56,980 --> 00:04:54,620 planet that was very similar to the 101 00:04:59,320 --> 00:04:56,990 earth but without the presence of a 102 00:05:02,080 --> 00:04:59,330 giant planet like Jupiter to start 103 00:05:04,179 --> 00:05:02,090 shoveling in these icy meteorites we 104 00:05:09,159 --> 00:05:04,189 might not have ever had a water delivery 105 00:05:11,980 --> 00:05:09,169 service and plate tectonics the fact our 106 00:05:14,409 --> 00:05:11,990 crust is broken up into bite-sized 107 00:05:17,290 --> 00:05:14,419 chunks helps with cooling and helps 108 00:05:21,219 --> 00:05:17,300 generate our magnetic field so it takes 109 00:05:25,029 --> 00:05:21,229 a lot to be an earth and we don't know 110 00:05:27,730 --> 00:05:25,039 very much about exoplanets yet our 111 00:05:30,730 --> 00:05:27,740 newest missions are aimed at finding us 112 00:05:33,070 --> 00:05:30,740 a little bit more the aim is to start 113 00:05:36,219 --> 00:05:33,080 looking at light that has passed through 114 00:05:38,159 --> 00:05:36,229 the planet's atmosphere and as the light 115 00:05:41,170 --> 00:05:38,169 passes through a planet's atmosphere 116 00:05:44,019 --> 00:05:41,180 certain wavelengths are absorbed by the 117 00:05:45,869 --> 00:05:44,029 molecules in the atmosphere so if those 118 00:05:49,629 --> 00:05:45,879 are missing when we see the Starlight 119 00:05:52,329 --> 00:05:49,639 that gives a hint of what the gases are 120 00:05:54,100 --> 00:05:52,339 in the planets air and therefore what 121 00:05:58,180 --> 00:05:54,110 might be going on on the planet's 122 00:06:01,119 --> 00:05:58,190 surface so we have a fingerprint to 123 00:06:03,459 --> 00:06:01,129 identify gases in terms of missing 124 00:06:07,149 --> 00:06:03,469 wavelengths that have been absorbed by 125 00:06:09,420 --> 00:06:07,159 the planet's atmosphere so we end up 126 00:06:11,619 --> 00:06:09,430 with something like this where the dips 127 00:06:16,959 --> 00:06:11,629 correspond to certain elements in the 128 00:06:18,999 --> 00:06:16,969 air so can list identify life well one 129 00:06:22,540 --> 00:06:19,009 way to test will be to look at a planet 130 00:06:25,269 --> 00:06:22,550 we know has life and see if these gases 131 00:06:26,829 --> 00:06:25,279 can confirm that whereas only one planet 132 00:06:29,860 --> 00:06:26,839 we know that has life that's this one 133 00:06:33,429 --> 00:06:29,870 and fortunately we got the chance to 134 00:06:36,820 --> 00:06:33,439 observe it in 1989 NASA's Galileo 135 00:06:39,040 --> 00:06:36,830 spacecraft was on its way to Jupiter but 136 00:06:40,929 --> 00:06:39,050 on route it's swung by the earth and 137 00:06:44,230 --> 00:06:40,939 took a look at our planet with his 138 00:06:47,709 --> 00:06:44,240 instruments so Galileo viewed the earth 139 00:06:48,629 --> 00:06:47,719 from just a thousand kilometers away so 140 00:06:51,959 --> 00:06:48,639 if it couldn't 141 00:06:54,209 --> 00:06:51,969 find detectable life we're in trouble so 142 00:06:57,269 --> 00:06:54,219 what did Galileo see well in particular 143 00:07:00,330 --> 00:06:57,279 Galileo saw three things it saw the 144 00:07:03,119 --> 00:07:00,340 presence of water it saw the presence of 145 00:07:06,029 --> 00:07:03,129 oxygen and it saw the presence of 146 00:07:07,980 --> 00:07:06,039 methane so are these enough to 147 00:07:11,399 --> 00:07:07,990 definitely say life because they're all 148 00:07:13,080 --> 00:07:11,409 related to life on the earth well the 149 00:07:15,629 --> 00:07:13,090 paper that published this result in 150 00:07:18,659 --> 00:07:15,639 nature was led by Carl Sagan a famous 151 00:07:22,140 --> 00:07:18,669 science communicator and he concluded it 152 00:07:24,409 --> 00:07:22,150 was strongly suggestive of life but he 153 00:07:28,559 --> 00:07:24,419 wasn't prepared to say it was definite 154 00:07:32,279 --> 00:07:28,569 so why not well what we're hunting for 155 00:07:35,459 --> 00:07:32,289 is a bio signature a signature of 156 00:07:39,529 --> 00:07:35,469 biological activity let's take a look at 157 00:07:43,200 --> 00:07:39,539 each of the things Galileo saw water on 158 00:07:46,350 --> 00:07:43,210 earth life is found wherever there is 159 00:07:50,519 --> 00:07:46,360 water and this includes some deeply 160 00:07:53,219 --> 00:07:50,529 unlikely places for example in deep sea 161 00:07:56,519 --> 00:07:53,229 hydrothermal vents that exist on the 162 00:07:59,129 --> 00:07:56,529 ocean floor there is no light that 163 00:08:01,860 --> 00:07:59,139 reaches this place sunlight cannot 164 00:08:04,589 --> 00:08:01,870 penetrate that deep the temperature 165 00:08:07,499 --> 00:08:04,599 around these vents can be 400 Celsius 166 00:08:11,189 --> 00:08:07,509 and there is crushing pressures from the 167 00:08:13,219 --> 00:08:11,199 ocean and yet we can find a thriving 168 00:08:16,320 --> 00:08:13,229 ecosystem here 169 00:08:19,409 --> 00:08:16,330 the same is true at the opposite end of 170 00:08:22,769 --> 00:08:19,419 the extreme with glaciers of frozen 171 00:08:25,139 --> 00:08:22,779 water and even places like the acidic 172 00:08:28,010 --> 00:08:25,149 lakes found in Yellowstone National Park 173 00:08:31,139 --> 00:08:28,020 all of these are found to contain life 174 00:08:33,659 --> 00:08:31,149 so regardless of the other conditions it 175 00:08:38,130 --> 00:08:33,669 seems that water gives you life on Earth 176 00:08:41,699 --> 00:08:38,140 and the reason for this is that water is 177 00:08:44,880 --> 00:08:41,709 a great solvent so if we look at the 178 00:08:48,090 --> 00:08:44,890 cells for life we can see that water can 179 00:08:51,540 --> 00:08:48,100 deliver nutrients and it can flush away 180 00:08:54,720 --> 00:08:51,550 toxic wastes that might kill a cell it's 181 00:08:57,540 --> 00:08:54,730 also great at chemistry for biological 182 00:09:01,980 --> 00:08:57,550 systems allowing us to build large 183 00:09:04,199 --> 00:09:01,990 complex molecules that life needs but 184 00:09:06,960 --> 00:09:04,209 what you're alone does not prove life 185 00:09:09,780 --> 00:09:06,970 it's great for life but it's not proof 186 00:09:12,870 --> 00:09:09,790 life is there for example in our own 187 00:09:15,180 --> 00:09:12,880 solar system the Jovian moon of Ganymede 188 00:09:18,180 --> 00:09:15,190 is thought to have deep oceans 189 00:09:21,570 --> 00:09:18,190 underneath its icy crust but it's not 190 00:09:24,840 --> 00:09:21,580 thought to be habitable okay so how 191 00:09:27,180 --> 00:09:24,850 about oxygen well on earth oxygen is 192 00:09:30,210 --> 00:09:27,190 primarily produced by photosynthesis 193 00:09:32,490 --> 00:09:30,220 that is plants are using sunlight for 194 00:09:36,120 --> 00:09:32,500 energy and they're producing oxygen as a 195 00:09:39,240 --> 00:09:36,130 by-product now star light is going to be 196 00:09:41,730 --> 00:09:39,250 a major energy source for most planets 197 00:09:45,660 --> 00:09:41,740 that we know of so it's not unreasonable 198 00:09:48,480 --> 00:09:45,670 to assume that life on other planets may 199 00:09:53,670 --> 00:09:48,490 also use photosynthesis and generate 200 00:09:56,639 --> 00:09:53,680 oxygen as the same byproducts but it's 201 00:09:59,670 --> 00:09:56,649 not the only way oxygen can be produced 202 00:10:02,630 --> 00:09:59,680 in particular ultraviolet light from the 203 00:10:06,690 --> 00:10:02,640 star can break apart water molecules 204 00:10:09,389 --> 00:10:06,700 into oxygen and hydrogen now a planet 205 00:10:12,060 --> 00:10:09,399 with the mass of roughly the earth can't 206 00:10:14,880 --> 00:10:12,070 hold on to a gas that is as light as 207 00:10:18,090 --> 00:10:14,890 hydrogen so in this case the hydrogen 208 00:10:22,440 --> 00:10:18,100 escapes and you get left with an oxygen 209 00:10:24,470 --> 00:10:22,450 atmosphere without life and again we 210 00:10:27,930 --> 00:10:24,480 have an example in our own solar system 211 00:10:30,780 --> 00:10:27,940 the Jovian moons have tenuous oxygen 212 00:10:33,420 --> 00:10:30,790 atmospheres and that's because the UV is 213 00:10:36,000 --> 00:10:33,430 breaking apart the ice with water water 214 00:10:38,400 --> 00:10:36,010 molecules on the surface the hydrogen is 215 00:10:42,780 --> 00:10:38,410 escaping and you're left with the oxygen 216 00:10:45,840 --> 00:10:42,790 but definitely no trees so what about 217 00:10:48,569 --> 00:10:45,850 methane well on earth methane is 218 00:10:51,030 --> 00:10:48,579 typically found due to microbes in the 219 00:10:55,590 --> 00:10:51,040 guts of animals and it's also produced 220 00:10:57,930 --> 00:10:55,600 by decomposing plants but again in our 221 00:11:01,230 --> 00:10:57,940 solar system we have a counter example 222 00:11:04,170 --> 00:11:01,240 so Saturn's moon Titan has a methane 223 00:11:07,079 --> 00:11:04,180 atmosphere it's roughly 5% methane and 224 00:11:09,420 --> 00:11:07,089 that's produced because underneath Titan 225 00:11:12,630 --> 00:11:09,430 surface there's thought to be a methane 226 00:11:13,890 --> 00:11:12,640 sea which it gets ejected to the surface 227 00:11:17,269 --> 00:11:13,900 through volcanoes 228 00:11:23,430 --> 00:11:17,279 so we have a methane atmosphere but uh 229 00:11:27,360 --> 00:11:23,440 no cows becomes so our best bet may be a 230 00:11:31,710 --> 00:11:27,370 combination of these markers for example 231 00:11:35,700 --> 00:11:31,720 if we had oxygen and methane maybe that 232 00:11:39,360 --> 00:11:35,710 would be indication of life so if left 233 00:11:42,720 --> 00:11:39,370 alone and not replenished oxygen plus 234 00:11:45,750 --> 00:11:42,730 methane forms carbon dioxide so 235 00:11:48,900 --> 00:11:45,760 therefore if we see methane and oxygen 236 00:11:51,810 --> 00:11:48,910 and it hasn't formed it has an oil and 237 00:11:56,850 --> 00:11:51,820 carbon dioxide that suggests something 238 00:11:59,040 --> 00:11:56,860 is continuously producing it but you 239 00:12:01,230 --> 00:11:59,050 could imagine a system where you might 240 00:12:04,140 --> 00:12:01,240 have say a planet with this tenuous 241 00:12:07,050 --> 00:12:04,150 oxygen atmosphere produced by light and 242 00:12:10,500 --> 00:12:07,060 maybe a moon with a methane atmosphere 243 00:12:13,079 --> 00:12:10,510 and the signatures might overlap so we 244 00:12:15,390 --> 00:12:13,089 would think we were seeing one body with 245 00:12:17,250 --> 00:12:15,400 both oxygen and methane but actually 246 00:12:20,610 --> 00:12:17,260 there were two that were very close 247 00:12:22,890 --> 00:12:20,620 together so the bottom line is when we 248 00:12:25,980 --> 00:12:22,900 start looking for alien life we're going 249 00:12:28,920 --> 00:12:25,990 to have to be very cautious and as Carl 250 00:12:32,250 --> 00:12:28,930 Sagan said extraordinary claims require 251 00:12:35,430 --> 00:12:32,260 extraordinary evidence so I think our 252 00:12:37,740 --> 00:12:35,440 next generation of telescopes will find 253 00:12:39,540 --> 00:12:37,750 evidence that could be life but we 254 00:12:43,290 --> 00:12:39,550 should expect to spend many decades 255 00:12:45,540 --> 00:12:43,300 arguing over whether actually is but 256 00:12:48,540 --> 00:12:45,550 assuming we find this bio signature 257 00:12:52,320 --> 00:12:48,550 where might we find life that wasn't 258 00:12:56,040 --> 00:12:52,330 earth well according to earth the life 259 00:12:59,910 --> 00:12:56,050 recipe requires three things it requires 260 00:13:01,769 --> 00:12:59,920 water for our bio car biological 261 00:13:05,850 --> 00:13:01,779 reactions to build up our complex 262 00:13:09,000 --> 00:13:05,860 molecules it requires biogenic elements 263 00:13:13,230 --> 00:13:09,010 so the elements of life carbon hydrogen 264 00:13:16,019 --> 00:13:13,240 oxygen for living systems and it 265 00:13:20,519 --> 00:13:16,029 requires an energy source something to 266 00:13:22,350 --> 00:13:20,529 power life's metabolisms so where might 267 00:13:23,190 --> 00:13:22,360 we find environments that are different 268 00:13:25,230 --> 00:13:23,200 from ours 269 00:13:27,570 --> 00:13:25,240 but might still have these key 270 00:13:32,329 --> 00:13:30,150 one exciting possibility is actually 271 00:13:35,790 --> 00:13:32,339 Europa one of the moons of Jupiter and 272 00:13:39,690 --> 00:13:35,800 this does have we suspect we know a 273 00:13:43,590 --> 00:13:39,700 strong sir a large subsurface ocean now 274 00:13:46,670 --> 00:13:43,600 by definition big ocean water check no 275 00:13:47,880 --> 00:13:46,680 problem what about our biological 276 00:13:50,850 --> 00:13:47,890 elements 277 00:13:54,329 --> 00:13:50,860 well we think Europa probably could have 278 00:13:57,090 --> 00:13:54,339 them meteorites which come from comets 279 00:13:59,970 --> 00:13:57,100 and asteroids can definitely form the 280 00:14:02,009 --> 00:13:59,980 beginnings of organic molecules and we 281 00:14:04,710 --> 00:14:02,019 think these arrived on earth we know 282 00:14:07,620 --> 00:14:04,720 Europa is pockmarked from collisions 283 00:14:10,350 --> 00:14:07,630 with these bodies so if they could go 284 00:14:13,079 --> 00:14:10,360 through the ice we would expect the 285 00:14:16,370 --> 00:14:13,089 ocean to be infused with these organic 286 00:14:20,639 --> 00:14:16,380 ingredients so okay let's give it a tick 287 00:14:22,410 --> 00:14:20,649 how about energy well Jupiter's an 288 00:14:24,690 --> 00:14:22,420 awfully a long way away from the Sun 289 00:14:28,530 --> 00:14:24,700 it's not going to be receiving much 290 00:14:30,740 --> 00:14:28,540 sunlight however it turns out to have an 291 00:14:33,530 --> 00:14:30,750 alternative energy source 292 00:14:36,569 --> 00:14:33,540 Europa's orbit is slightly elliptical 293 00:14:40,019 --> 00:14:36,579 due to the pull from neighbouring moons 294 00:14:42,269 --> 00:14:40,029 IO and Ganymede and this means that it 295 00:14:44,850 --> 00:14:42,279 comes closer to Jupiter and then it 296 00:14:47,130 --> 00:14:44,860 moves a bit further away and as it does 297 00:14:50,639 --> 00:14:47,140 Jupiter's gravity strengthens and 298 00:14:53,160 --> 00:14:50,649 weakens and this means the moon is 299 00:14:56,910 --> 00:14:53,170 actually flexed like squeezing a flake 300 00:15:00,240 --> 00:14:56,920 stress ball and as this flexing occurs 301 00:15:05,430 --> 00:15:00,250 the moon is heated and we call this 302 00:15:09,480 --> 00:15:05,440 tidal heating so tick Europa may indeed 303 00:15:11,370 --> 00:15:09,490 have all three key ingredients so how do 304 00:15:14,460 --> 00:15:11,380 we find out well 305 00:15:17,220 --> 00:15:14,470 Europa's in our solar system so let's go 306 00:15:19,740 --> 00:15:17,230 and there's two future missions that are 307 00:15:22,620 --> 00:15:19,750 going to be exploring this the first is 308 00:15:25,410 --> 00:15:22,630 deuce Jupiter icy moon Explorer mission 309 00:15:27,930 --> 00:15:25,420 this is a mission led by the European 310 00:15:30,329 --> 00:15:27,940 Space Agency but has a strong 311 00:15:33,750 --> 00:15:30,339 association with Japan's JAXA as well 312 00:15:36,540 --> 00:15:33,760 and juice will launch in 2022 and arrive 313 00:15:38,670 --> 00:15:36,550 in 2030 and is going to be exploring a 314 00:15:39,639 --> 00:15:38,680 number of the moons principally Ganymede 315 00:15:42,129 --> 00:15:39,649 but also 316 00:15:44,470 --> 00:15:42,139 Europa following that is going to be 317 00:15:46,660 --> 00:15:44,480 NASA's you rope a clipper which is 318 00:15:48,609 --> 00:15:46,670 hoping to launch sometime in the 2020s 319 00:15:51,189 --> 00:15:48,619 if the mission is finally approved and 320 00:15:54,160 --> 00:15:51,199 this would be a mission focused on 321 00:15:58,449 --> 00:15:54,170 Europa with plans to see if there's any 322 00:16:00,759 --> 00:15:58,459 detectable signs of life however this is 323 00:16:02,859 --> 00:16:00,769 all very well when we can go to the 324 00:16:06,309 --> 00:16:02,869 place but if we're going to start 325 00:16:09,790 --> 00:16:06,319 looking at exoplanets subsurface life is 326 00:16:11,829 --> 00:16:09,800 going to be really hard to spot we need 327 00:16:15,579 --> 00:16:11,839 life that can interact with the planet's 328 00:16:17,040 --> 00:16:15,589 atmosphere so what about detectable life 329 00:16:21,249 --> 00:16:17,050 on exoplanets 330 00:16:24,340 --> 00:16:21,259 well Gliese a 1214 B is interesting 331 00:16:26,980 --> 00:16:24,350 because its density is weird it has a 332 00:16:29,619 --> 00:16:26,990 density that's too low to be a rocky 333 00:16:34,119 --> 00:16:29,629 planet like the earth but too high for 334 00:16:37,329 --> 00:16:34,129 gas so what is it well we think it may 335 00:16:40,449 --> 00:16:37,339 be a water world with a global ocean 336 00:16:44,230 --> 00:16:40,459 covering the whole planet could that be 337 00:16:47,530 --> 00:16:44,240 habitable it got water but for a surface 338 00:16:50,650 --> 00:16:47,540 ocean we have some problems namely our 339 00:16:54,309 --> 00:16:50,660 atmosphere so on earth carbon dioxide 340 00:16:56,110 --> 00:16:54,319 keeps our earth warm and the quantity is 341 00:16:59,470 --> 00:16:56,120 controlled by something called the 342 00:17:02,650 --> 00:16:59,480 carbon cycle so here the carbon dioxide 343 00:17:05,289 --> 00:17:02,660 in the air comes down as rain it reacts 344 00:17:08,049 --> 00:17:05,299 with the rocks and forms a solid the 345 00:17:09,460 --> 00:17:08,059 solid get washed into the ocean and then 346 00:17:12,730 --> 00:17:09,470 eventually it's returned to the 347 00:17:15,909 --> 00:17:12,740 atmosphere through volcanoes now during 348 00:17:18,610 --> 00:17:15,919 the early stages of our Earth's life the 349 00:17:21,669 --> 00:17:18,620 Sun was cooler and dimmer and this 350 00:17:24,159 --> 00:17:21,679 actually would have reduced the reaction 351 00:17:26,799 --> 00:17:24,169 with the rock and so we would have ended 352 00:17:29,769 --> 00:17:26,809 up pumping more carbon dioxide into the 353 00:17:31,930 --> 00:17:29,779 air than we were taking out and this 354 00:17:34,510 --> 00:17:31,940 would allow our planet to stay warm 355 00:17:37,149 --> 00:17:34,520 during these early cooler years when 356 00:17:40,480 --> 00:17:37,159 life was beginning to start if we don't 357 00:17:44,350 --> 00:17:40,490 have a carbon cycle because carbon 358 00:17:46,930 --> 00:17:44,360 cycles need land you have to get exactly 359 00:17:49,240 --> 00:17:46,940 the right amount of radiation hitting 360 00:17:51,639 --> 00:17:49,250 the planets which becomes a lot less 361 00:17:52,890 --> 00:17:51,649 likely and means the planet is not 362 00:17:54,630 --> 00:17:52,900 resilient 363 00:17:57,930 --> 00:17:54,640 to slight changes in the amount of 364 00:17:59,940 --> 00:17:57,940 radiation is receiving so we're unsure 365 00:18:03,150 --> 00:17:59,950 whether a Waterworld could indeed be 366 00:18:05,790 --> 00:18:03,160 habitable another planets that's hit the 367 00:18:08,250 --> 00:18:05,800 news a lot are the Trappist system these 368 00:18:11,970 --> 00:18:08,260 came to light in February this year and 369 00:18:14,700 --> 00:18:11,980 everyone got very excited so Trappist 1e 370 00:18:18,600 --> 00:18:14,710 is a planet that orbits its star in just 371 00:18:21,690 --> 00:18:18,610 six days but its star is very very dim 372 00:18:24,390 --> 00:18:21,700 so Trappist 1e actually receives a very 373 00:18:28,680 --> 00:18:24,400 similar amount of radiation as the earth 374 00:18:31,620 --> 00:18:28,690 does from the Sun however it is so close 375 00:18:33,870 --> 00:18:31,630 to the star that we expect one side of 376 00:18:37,500 --> 00:18:33,880 the planet to be facing the star at all 377 00:18:39,960 --> 00:18:37,510 times in the same way the moon always is 378 00:18:43,020 --> 00:18:39,970 pointing to the earth and the reason for 379 00:18:46,080 --> 00:18:43,030 this is that at such close proximity a 380 00:18:49,500 --> 00:18:46,090 bulge is raised due to the gravity of 381 00:18:52,710 --> 00:18:49,510 the star on the planet and as the planet 382 00:18:56,400 --> 00:18:52,720 tries to rotate the star's gravity drags 383 00:18:59,460 --> 00:18:56,410 on this bulge and causes the planet to 384 00:19:03,800 --> 00:18:59,470 turn so that one side is always facing 385 00:19:06,510 --> 00:19:03,810 the star and we call this tidal locking 386 00:19:09,990 --> 00:19:06,520 and what this means is the planet is a 387 00:19:13,740 --> 00:19:10,000 split world one side of Perpetual day 388 00:19:15,960 --> 00:19:13,750 that can get very hot on one side of icy 389 00:19:18,840 --> 00:19:15,970 night that is always facing away from 390 00:19:21,750 --> 00:19:18,850 the star now if the planet's atmosphere 391 00:19:25,080 --> 00:19:21,760 is thick enough you could have winds 392 00:19:27,390 --> 00:19:25,090 that redistributed that heat and in 393 00:19:30,780 --> 00:19:27,400 which case it might be possible to have 394 00:19:33,450 --> 00:19:30,790 this twilight zone between the cold side 395 00:19:36,240 --> 00:19:33,460 and the hot side when liquid for water 396 00:19:39,750 --> 00:19:36,250 could form and the star was always on 397 00:19:41,610 --> 00:19:39,760 the horizon so the bottom line is yet we 398 00:19:44,010 --> 00:19:41,620 don't quite know what it takes to be a 399 00:19:46,890 --> 00:19:44,020 habitable planet because we only have 400 00:19:49,560 --> 00:19:46,900 one example but with future missions and 401 00:19:55,120 --> 00:19:49,570 our new telescopes we're on the brink of 402 00:20:28,630 --> 00:19:57,130 [Applause]