WEBVTT 0 00:00:00.000 --> 00:00:02.240 Andrew Dunkley: Hi there. Thanks for joining us. This is a Q 1 00:00:02.240 --> 00:00:04.920 and A edition of Space Nuts. My name is 2 00:00:04.920 --> 00:00:07.340 Andrew Dunkley. Thanks for your company. Uh, 3 00:00:07.340 --> 00:00:09.040 coming up, we're going to answer audience 4 00:00:09.040 --> 00:00:12.040 questions. Um, one from Ken. Uh, 5 00:00:12.160 --> 00:00:14.840 I'm going to paraphrase his 500,000 word 6 00:00:14.840 --> 00:00:16.920 question by saying, why don't the numbers add 7 00:00:16.920 --> 00:00:18.960 up when turning hydrogen into helium? 8 00:00:19.760 --> 00:00:22.240 Also, a question from Mark about caves on 9 00:00:22.480 --> 00:00:25.440 Mars and Casey wants 10 00:00:25.440 --> 00:00:28.040 to talk about changes in stars. 11 00:00:28.040 --> 00:00:30.440 That's all coming up on this Q and A edition 12 00:00:30.440 --> 00:00:33.420 of space nuts. 15 seconds. Guidance is 13 00:00:33.420 --> 00:00:36.102 internal. 10, 9, 14 00:00:36.284 --> 00:00:38.946 ignition sequence start. Space nuts. 15 00:00:39.018 --> 00:00:40.397 Jonti Horner: 5, 4, 3, 2. 16 00:00:40.469 --> 00:00:43.298 Andrew Dunkley: 1. 2, 3, 4, 5, 5, 4, 3, 17 00:00:43.370 --> 00:00:44.060 2, 1. 18 00:00:44.140 --> 00:00:45.260 Jonti Horner: Space nuts. 19 00:00:45.340 --> 00:00:47.180 Andrew Dunkley: Astronauts report it feels good. 20 00:00:48.460 --> 00:00:50.540 I just got a text to say my car's been 21 00:00:50.540 --> 00:00:52.260 serviced, so I'll be back in about 20 minutes 22 00:00:52.260 --> 00:00:53.820 if you just want to. Hang on. I'm kidding. 23 00:00:54.100 --> 00:00:56.100 Uh, joining us to answer all those questions 24 00:00:56.100 --> 00:00:58.020 is Professor Jonty Horner, professor of 25 00:00:58.020 --> 00:01:00.180 Astrophysics at the University of Southern 26 00:01:00.180 --> 00:01:01.660 Queensland. Hi, Jonty. Good day. 27 00:01:01.660 --> 00:01:02.360 Jonti Horner: How are you going to. 28 00:01:03.070 --> 00:01:05.230 Andrew Dunkley: I am m. All right. Good to see you again. 29 00:01:05.390 --> 00:01:06.750 Jonti Horner: It's good to be back. I was going to say the 30 00:01:06.750 --> 00:01:08.390 amount I've been talking too much. You've 31 00:01:08.390 --> 00:01:11.110 probably got time to go and get the car and I 32 00:01:11.110 --> 00:01:11.590 could probably 33 00:01:11.590 --> 00:01:14.430 Andrew Dunkley: ask you a question, bolt down and get the car 34 00:01:14.430 --> 00:01:17.430 and come back just in time to hear the end 35 00:01:17.430 --> 00:01:18.190 of the first sentence. 36 00:01:18.190 --> 00:01:20.590 Jonti Horner: Yes, and I do apologise to listeners if I've 37 00:01:20.590 --> 00:01:23.110 rambled on too much, but it's when you get to 38 00:01:23.110 --> 00:01:24.790 talk about your hobby and people have to 39 00:01:24.790 --> 00:01:26.630 listen, it's, you know, hard not to get 40 00:01:26.630 --> 00:01:28.430 excited and it is, isn't it? 41 00:01:28.610 --> 00:01:28.930 Andrew Dunkley: It is. 42 00:01:29.330 --> 00:01:31.210 Let's get, uh, straight into our first 43 00:01:31.210 --> 00:01:34.210 question. Hi, Andrew and Jonty. I'm going to 44 00:01:34.210 --> 00:01:35.930 say it's not what he wrote, but anyway, it 45 00:01:35.930 --> 00:01:38.050 doesn't matter. Ken, uh, from Maroochydore, 46 00:01:38.210 --> 00:01:40.570 longtime listener and fan and love the way 47 00:01:40.570 --> 00:01:43.490 you make complex issues sound simple. I am 48 00:01:43.490 --> 00:01:45.650 trying to understand the basic fusion 49 00:01:45.650 --> 00:01:47.930 reaction that both me and my accountant are 50 00:01:47.930 --> 00:01:50.330 struggling with. Uh, the basic fusion 51 00:01:50.330 --> 00:01:52.850 reaction in our sun converts hydrogen to 52 00:01:52.850 --> 00:01:55.370 helium. To summarise the reaction, four 53 00:01:55.370 --> 00:01:58.340 hydrogen nuclei, I.e. four protons, 54 00:01:58.420 --> 00:02:01.060 go through two steps to create one 55 00:02:01.060 --> 00:02:04.020 helium nucleus containing two neutrons 56 00:02:04.020 --> 00:02:06.700 and two protons. Additionally, gamma rays, 57 00:02:06.700 --> 00:02:09.140 neutrinos and positrons are released. 58 00:02:09.460 --> 00:02:12.420 My anatomy textbook tells me that about 59 00:02:12.420 --> 00:02:14.740 600 million tonnes of hydrogen convert to 60 00:02:14.740 --> 00:02:17.660 596 million tonnes of helium every 61 00:02:17.660 --> 00:02:20.380 second. The 4 million tonnes is 62 00:02:20.380 --> 00:02:23.300 conveyed to energy as per E equals 63 00:02:23.300 --> 00:02:26.300 MC squared. If neutrons had a lower 64 00:02:26.300 --> 00:02:28.890 mass than protons it would all make perfect, 65 00:02:28.960 --> 00:02:31.840 perfect sense, but they don't. They have a 66 00:02:31.840 --> 00:02:34.720 higher mass. So the mass of the helium 67 00:02:34.720 --> 00:02:37.160 nucleus is higher than the mass of the four 68 00:02:37.160 --> 00:02:39.960 protons. All the explanations I've read 69 00:02:39.960 --> 00:02:42.360 sound pretty dodgy, and my accountant says he 70 00:02:42.360 --> 00:02:44.240 could never get away with such, such 71 00:02:44.240 --> 00:02:46.160 explanations with the tax department. 72 00:02:47.520 --> 00:02:49.880 Could you please explain the devil in the 73 00:02:49.880 --> 00:02:52.480 detail that I'm missing? I, uh, love it. 74 00:02:52.480 --> 00:02:54.360 That's a great question. And thanks for the 75 00:02:54.360 --> 00:02:56.260 research, Ken. Hope all is well in 76 00:02:56.260 --> 00:02:58.740 Maroochydore. Not far from you, just a bit 77 00:02:58.740 --> 00:02:59.540 further up the coast. 78 00:02:59.540 --> 00:03:02.180 Jonti Horner: Yes, out to the coast and up a bit north of 79 00:03:02.180 --> 00:03:04.380 Brisbane, up on the sunshine course, which is 80 00:03:04.620 --> 00:03:05.580 kind of lovely area. 81 00:03:05.580 --> 00:03:08.260 Andrew Dunkley: It's kind of, it's only kind of lovely. 82 00:03:08.260 --> 00:03:09.820 Jonti Horner: Yeah, only kind of lovely. It's getting, 83 00:03:09.900 --> 00:03:11.780 getting very aggressively more and more 84 00:03:11.780 --> 00:03:13.540 touristed. Tracks a slightly different 85 00:03:13.540 --> 00:03:15.460 tourist demographic to the Gold coast, which 86 00:03:15.460 --> 00:03:18.060 is south of Brisbane, um, but is still 87 00:03:18.540 --> 00:03:20.300 a little bit more touristy than you'd like 88 00:03:20.300 --> 00:03:22.340 it. It's a little bit like hippie central, 89 00:03:22.340 --> 00:03:25.310 but not to the level of Byron nuts. 90 00:03:25.310 --> 00:03:27.710 Andrew Dunkley: Yeah, I get you. Yeah, yeah, yeah. 91 00:03:27.870 --> 00:03:30.390 Byron is the hippie, uh, capital of the, of 92 00:03:30.390 --> 00:03:33.270 the country, I think. Or to, to 93 00:03:33.270 --> 00:03:36.150 be more like Nimbin a bit further down. 94 00:03:36.150 --> 00:03:38.910 That's, that's very, very hippie. 95 00:03:39.150 --> 00:03:41.950 Anyway, um, so, 96 00:03:41.950 --> 00:03:43.950 yeah, he doesn't understand the balance. It 97 00:03:43.950 --> 00:03:46.950 doesn't. It doesn't. To paraphrase, why don't 98 00:03:46.950 --> 00:03:48.990 the numbers add up when turning hydrogen into 99 00:03:48.990 --> 00:03:50.790 helium? That's the short version of the 100 00:03:50.790 --> 00:03:51.070 question. 101 00:03:51.150 --> 00:03:52.950 Jonti Horner: And I totally get that. Because if you look 102 00:03:52.950 --> 00:03:55.580 at the masses of protons and 103 00:03:55.580 --> 00:03:58.460 neutrons in isolation and add them together, 104 00:03:58.700 --> 00:04:01.660 helium is two protons, two neutrons. Add them 105 00:04:01.660 --> 00:04:04.140 together, taking the mass of a proton and the 106 00:04:04.140 --> 00:04:06.220 mass of a neutron, and you get a given value 107 00:04:06.220 --> 00:04:09.220 for the mass of a helium nucleus. And 108 00:04:09.220 --> 00:04:10.940 then you look at the mass of a helium nucleus 109 00:04:10.940 --> 00:04:13.380 and it isn't that mass. And that doesn't make 110 00:04:13.380 --> 00:04:15.900 sense because if you've got four nucleons 111 00:04:16.540 --> 00:04:19.260 together, surely the mass of the nucleus is 112 00:04:19.260 --> 00:04:21.980 the four nucleons added together. And that's 113 00:04:21.980 --> 00:04:23.820 effectively the fundamental of what's being 114 00:04:23.820 --> 00:04:26.380 said here. Added to which a, uh, 115 00:04:26.420 --> 00:04:29.300 hydrogen nucleus is a proton, a deuterium 116 00:04:29.300 --> 00:04:30.820 nucleus is a proton and a neutron, but 117 00:04:30.820 --> 00:04:33.620 hydrogen nucleus is a proton. Four hydrogen 118 00:04:33.620 --> 00:04:36.260 nuclei go together to make a helium nucleus, 119 00:04:36.260 --> 00:04:38.700 which is 2 protons, 2 neutrons and M. In the 120 00:04:38.700 --> 00:04:40.620 process, you kick a few things out and do a 121 00:04:40.620 --> 00:04:43.540 few weird things, surely. Therefore, 122 00:04:43.540 --> 00:04:46.420 four hydrogen nuclei have the mass of 123 00:04:46.420 --> 00:04:49.220 four protons. One helium nucleus has a mass 124 00:04:49.220 --> 00:04:51.620 of two Protons plus two neutrons. And when 125 00:04:51.620 --> 00:04:53.920 you get the numbers off Wikipedia, that would 126 00:04:53.920 --> 00:04:55.680 suggest that the helium nucleus should be 127 00:04:55.680 --> 00:04:57.480 more massive than hydrogen and you should 128 00:04:57.800 --> 00:05:00.080 lose energy rather than create it, because 129 00:05:00.080 --> 00:05:02.880 you've had to create mass. Fundamentally in 130 00:05:02.880 --> 00:05:04.840 actuality though, the mass of the helium 131 00:05:04.840 --> 00:05:07.720 nucleus is lower than the mass of two 132 00:05:07.720 --> 00:05:10.680 protons plus two neutrons. And that's 133 00:05:10.680 --> 00:05:12.640 where the misunderstandings coming in, or not 134 00:05:12.640 --> 00:05:14.000 really misunderstanding, that's where the 135 00:05:14.000 --> 00:05:16.440 complexity and the confusion comes in 136 00:05:17.320 --> 00:05:19.080 and takes everybody a little bit to get your 137 00:05:19.080 --> 00:05:20.440 head around this when you first come across 138 00:05:20.440 --> 00:05:23.280 it. Helium nucleus, quite rightly is 139 00:05:23.280 --> 00:05:25.820 made of two protons and two neutrons. But 140 00:05:25.820 --> 00:05:28.180 those two protons and neutrons are held 141 00:05:28.180 --> 00:05:30.220 together. They're bound together by the 142 00:05:30.220 --> 00:05:32.620 nuclear force, held in strongly enough that 143 00:05:32.620 --> 00:05:34.860 the repulsion from the two positively charged 144 00:05:34.860 --> 00:05:37.140 things don't blow it apart. So there is 145 00:05:37.140 --> 00:05:38.980 something going on called the binding energy. 146 00:05:39.380 --> 00:05:41.259 And the binding energy is the amount of 147 00:05:41.259 --> 00:05:43.620 energy you would have to throw at a helium 148 00:05:43.620 --> 00:05:46.460 nucleus to separate the two protons and 149 00:05:46.460 --> 00:05:48.820 the two neutrons and make them fly through 150 00:05:48.820 --> 00:05:51.500 space separately. Again with the energy and 151 00:05:51.500 --> 00:05:54.350 mass equivalence. If you were to do that, 152 00:05:54.750 --> 00:05:57.390 you would then have 4, 4 nucleons 153 00:05:57.390 --> 00:05:58.950 independently of each other, which would have 154 00:05:58.950 --> 00:06:01.670 the mass we've just calculated. But you've 155 00:06:01.670 --> 00:06:03.910 had to add energy and energy is equivalent to 156 00:06:03.910 --> 00:06:06.630 mass. So what it's saying is that the mass of 157 00:06:06.630 --> 00:06:09.510 a helium nucleus is lower than the 158 00:06:09.510 --> 00:06:11.590 mass you would expect from the four nucleons 159 00:06:11.590 --> 00:06:13.510 because of the effect of this binding energy 160 00:06:13.510 --> 00:06:15.910 that's in there. And that binding energy is 161 00:06:15.910 --> 00:06:18.430 something we can calculate. It's helium is 162 00:06:18.430 --> 00:06:20.230 remarkably high compared to the things on 163 00:06:20.230 --> 00:06:22.800 either side of it. Helium 3 hydrogen, 3 164 00:06:22.800 --> 00:06:25.480 lithium, and that is incredibly tightly 165 00:06:25.480 --> 00:06:27.720 bound. That binding energy 166 00:06:28.280 --> 00:06:30.120 is what leads to the little bit of mass 167 00:06:30.120 --> 00:06:32.560 deficit with the helium atom being lighter 168 00:06:32.560 --> 00:06:34.600 than the four nucleons that went to make it. 169 00:06:35.080 --> 00:06:37.999 And it's that energy that's released. Now 170 00:06:37.999 --> 00:06:40.200 this is why nuclear fusion can work, because 171 00:06:40.680 --> 00:06:43.480 if you put four nucleons 172 00:06:43.480 --> 00:06:45.860 together from hydrogen atoms and make ah, 173 00:06:45.860 --> 00:06:48.360 from hydrogen nuclei to make a helium nuclei 174 00:06:48.840 --> 00:06:50.640 with the binding energy, it means you get 175 00:06:50.640 --> 00:06:53.610 more energy out than you get in. You produce 176 00:06:53.610 --> 00:06:56.490 energy. And that's true if you fuse 177 00:06:56.490 --> 00:06:58.450 helium. Helium is difficult. You can't fuse 178 00:06:58.450 --> 00:07:01.250 it to anything until carbon because 179 00:07:01.250 --> 00:07:04.250 lithium, beryllium, boron have a 180 00:07:04.250 --> 00:07:06.890 lower binding energy per nucleon than helium 181 00:07:06.890 --> 00:07:09.330 does. So you actually have to put energy in 182 00:07:09.330 --> 00:07:11.450 to fuse helium to those things rather than 183 00:07:11.450 --> 00:07:13.090 getting energy out. So that doesn't happen. 184 00:07:13.650 --> 00:07:16.530 Helium can fuse to carbon, but you need 185 00:07:16.530 --> 00:07:18.770 three helium nuclei to collide at once. 186 00:07:19.250 --> 00:07:22.170 Which is hard. From then on, from carbon 187 00:07:22.170 --> 00:07:23.810 upwards, you can get a little bit of energy 188 00:07:24.350 --> 00:07:25.830 from fusing heavier and heavier things 189 00:07:25.830 --> 00:07:28.790 together until you get to iron. Iron 56 190 00:07:28.790 --> 00:07:31.470 has the highest amount of binding energy per 191 00:07:31.470 --> 00:07:34.070 nucleon. So if you try and fuse 192 00:07:34.070 --> 00:07:36.990 hydrogen, fuse iron atoms to make a heavier 193 00:07:36.990 --> 00:07:39.710 atom than iron, you have to put more energy 194 00:07:39.710 --> 00:07:42.270 in than you get out. And that's what causes 195 00:07:42.270 --> 00:07:44.430 stars fundamentally to go supernova, is that 196 00:07:44.430 --> 00:07:46.190 they fuse heavier and heavier things to iron 197 00:07:46.190 --> 00:07:48.110 and then the fuel sources cut off suddenly, 198 00:07:49.550 --> 00:07:51.470 they then collapse. You get a boom because of 199 00:07:51.470 --> 00:07:54.060 the shockwave going bouncy, bouncy. Some of 200 00:07:54.060 --> 00:07:56.190 the energy from that supernova, 201 00:07:56.190 --> 00:07:59.140 uh, gets taken up in the fusion of iron to 202 00:07:59.140 --> 00:08:01.020 make heavier elements and gets sunk into 203 00:08:01.020 --> 00:08:03.020 that, which is where we get all the elements 204 00:08:03.020 --> 00:08:05.300 heavier than iron, everything up to uranium 205 00:08:05.460 --> 00:08:08.420 and beyond those things heavier than 206 00:08:08.420 --> 00:08:11.260 iron, the binding energy per nucleon gets 207 00:08:11.260 --> 00:08:13.620 lower and lower the further up you go. Which 208 00:08:13.620 --> 00:08:16.420 is why for things heavier than iron, 209 00:08:16.980 --> 00:08:19.460 nuclear fusion costs energy, but nuclear 210 00:08:19.460 --> 00:08:22.180 fission liberates energy because you're going 211 00:08:22.180 --> 00:08:24.500 back up the slope again. So uranium 212 00:08:24.500 --> 00:08:26.400 fissioning to be become lighter elements 213 00:08:26.480 --> 00:08:28.280 gives off energy because of that binding 214 00:08:28.280 --> 00:08:30.400 energy difference. It's all part of the same 215 00:08:30.400 --> 00:08:32.520 thing. Now I, I understand that 216 00:08:32.520 --> 00:08:35.400 intuitively this really isn't a 217 00:08:35.400 --> 00:08:37.520 satisfying answer because this binding energy 218 00:08:37.520 --> 00:08:39.680 sounds a bit like your accountant thinking 219 00:08:39.680 --> 00:08:41.160 you've got a tax dodge. It's a bit like 220 00:08:41.160 --> 00:08:43.870 capital gains tax or fringe benefits or, or 221 00:08:43.870 --> 00:08:46.520 uh, what is it? Negative gearing? Binding 222 00:08:46.520 --> 00:08:48.400 energy may well be the negative gearing of 223 00:08:48.400 --> 00:08:50.240 the cosmos because it's when you put four 224 00:08:50.240 --> 00:08:51.960 nucleons together, they're wear less than 225 00:08:51.960 --> 00:08:53.040 they would do on their own. 226 00:08:53.610 --> 00:08:56.040 Um, it's ultimate waste loss plan. But it is 227 00:08:56.040 --> 00:08:58.980 this bind that leads to the mass you 228 00:08:58.980 --> 00:09:01.420 would measure for a helium nucleus being less 229 00:09:01.420 --> 00:09:03.420 than the mass you would measure for hydrogen 230 00:09:03.420 --> 00:09:06.180 nuclei. And it's a mass as you measure, not 231 00:09:06.180 --> 00:09:08.180 the masses of the individual components. If 232 00:09:08.180 --> 00:09:10.060 you took them out and put them on their own, 233 00:09:10.540 --> 00:09:13.539 that is the important thing. This is usually 234 00:09:13.539 --> 00:09:15.180 skipped in the explanations. And this is 235 00:09:15.180 --> 00:09:17.900 where the challenges come in. Because in the 236 00:09:17.900 --> 00:09:20.380 explanations you just say a helium atom is 237 00:09:20.380 --> 00:09:22.620 less massive than four hydrogen atoms. 238 00:09:23.270 --> 00:09:25.950 Ergo some mass has been lost. Therefore 239 00:09:25.950 --> 00:09:28.150 energy is produced by equals MC squared. And 240 00:09:28.150 --> 00:09:30.150 it skips all this discussion of the particle 241 00:09:30.150 --> 00:09:32.990 physics underpinning it on um, this binding 242 00:09:32.990 --> 00:09:35.510 energy. As always, there is a fairly 243 00:09:35.750 --> 00:09:37.950 detailed discussion of this in the wikipedia 244 00:09:37.950 --> 00:09:39.990 page for Helium 4. Talking about the 245 00:09:39.990 --> 00:09:41.550 stability and that's got the binding energy 246 00:09:41.550 --> 00:09:43.870 curve in. There is also discussions of 247 00:09:43.870 --> 00:09:45.430 binding energy and that out there. And 248 00:09:45.430 --> 00:09:48.350 particle Physics out there. It is basically 249 00:09:48.350 --> 00:09:50.230 though, that the binding energy causes this 250 00:09:50.230 --> 00:09:52.590 mass deficit. And it's that mass deficit that 251 00:09:52.590 --> 00:09:55.440 has been converted to energy that it's 252 00:09:55.440 --> 00:09:58.080 in liberated in fusion. So I 253 00:09:58.080 --> 00:10:00.720 appreciate it is not the most satisfying 254 00:10:00.720 --> 00:10:03.200 answer, but that's our 255 00:10:03.200 --> 00:10:06.080 understanding of the why behind all of this. 256 00:10:06.400 --> 00:10:08.360 And the proof is in the pudding. Fusion 257 00:10:08.360 --> 00:10:11.280 happens. It produces energy at the 258 00:10:11.280 --> 00:10:13.080 right level that we calculate that all, all 259 00:10:13.080 --> 00:10:15.840 of our models suggest it should do. So it 260 00:10:15.840 --> 00:10:17.680 seems that this is a very accurate 261 00:10:18.560 --> 00:10:21.080 representation of how the world works, even 262 00:10:21.080 --> 00:10:23.160 if it doesn't immediately feel 263 00:10:23.880 --> 00:10:26.800 satisfying and commonsensical. And uh, 264 00:10:26.840 --> 00:10:28.560 part of that is that common sense we've 265 00:10:28.560 --> 00:10:31.160 developed based on the experience of the 266 00:10:31.160 --> 00:10:33.280 world around us at our scales, at macroscopic 267 00:10:33.280 --> 00:10:34.720 scales. And the further you go from the 268 00:10:34.720 --> 00:10:37.120 conditions in this room, the less accurate 269 00:10:37.120 --> 00:10:39.720 modern sense, common sense is at predicting 270 00:10:39.960 --> 00:10:42.680 the outcomes of things. And that's why 271 00:10:42.680 --> 00:10:44.280 it's hard to work these things out. 272 00:10:45.480 --> 00:10:48.400 Andrew Dunkley: Yeah, it's like, I mean, listening 273 00:10:48.400 --> 00:10:50.520 to your explanation would be the same as me 274 00:10:50.520 --> 00:10:53.400 trying to explain to a kangaroo how to use 275 00:10:53.400 --> 00:10:55.980 a pedestrian crossing. So, you know, 276 00:10:55.980 --> 00:10:58.940 it's. I can understand Ken's 277 00:10:58.940 --> 00:11:01.540 frustration. Um, but 278 00:11:02.100 --> 00:11:05.090 if I understand your explanation thoroughly, 279 00:11:05.090 --> 00:11:08.060 um, Ken, what, what Jonty was saying 280 00:11:08.060 --> 00:11:09.620 was that shift happens. 281 00:11:11.620 --> 00:11:14.620 That's basically it, I think. But thanks for 282 00:11:14.620 --> 00:11:17.020 the question. Great to hear from you. This is 283 00:11:17.020 --> 00:11:18.940 a Q and A edition of Space Nuts with Andrew 284 00:11:18.940 --> 00:11:20.900 Dunkley and Professor Johnty Horner. 285 00:11:25.430 --> 00:11:26.310 Jonti Horner: Space Nuts. 286 00:11:26.390 --> 00:11:29.350 Andrew Dunkley: Okay, Jonty, our next question says, 287 00:11:29.530 --> 00:11:31.750 uh, Fred Watson was talking about caves on 288 00:11:31.750 --> 00:11:34.430 Mars and that got me thinking. The caves on 289 00:11:34.430 --> 00:11:36.750 Earth are, uh, primarily made of limestone, 290 00:11:36.750 --> 00:11:39.430 which has high concentrations of CO2 291 00:11:39.830 --> 00:11:42.030 that was locked in by millions of years of 292 00:11:42.030 --> 00:11:44.030 sea creatures popping into the sea, creating 293 00:11:44.030 --> 00:11:46.310 a layer on the seabed that could be, 294 00:11:47.350 --> 00:11:50.200 uh, um, seabed. Could it be the same effect 295 00:11:50.200 --> 00:11:53.080 on Mars? No. Punctuation caught me out 296 00:11:53.080 --> 00:11:55.930 there. If so, I need to ask, ah, 297 00:11:56.040 --> 00:11:58.000 the question. Um, you get, 298 00:11:58.730 --> 00:12:01.360 uh. If 299 00:12:01.360 --> 00:12:04.160 so, I don't need to ask the next question. 300 00:12:04.670 --> 00:12:06.640 Um, you get what I mean. But the next 301 00:12:06.640 --> 00:12:09.520 question is, if caves are deep enough, 302 00:12:09.520 --> 00:12:12.080 could it be possible that the atmosphere at 303 00:12:12.080 --> 00:12:15.040 the base of these caves could be dense enough 304 00:12:15.040 --> 00:12:17.000 to create a stable atmosphere with higher 305 00:12:17.000 --> 00:12:19.640 concentrations of oxygen for life? And could 306 00:12:19.640 --> 00:12:22.180 that life be looking at Earth with 307 00:12:22.180 --> 00:12:23.260 envious eyes? 308 00:12:23.340 --> 00:12:24.380 Jonti Horner: Yeah, very funny. 309 00:12:24.540 --> 00:12:27.340 Andrew Dunkley: Hope not. Uh, Mark? Uh, thank you, Mark. 310 00:12:27.500 --> 00:12:30.380 So, um, caves on Earth, we. Yeah, not all of 311 00:12:30.380 --> 00:12:31.940 them, but uh, quite a lot of them are 312 00:12:31.940 --> 00:12:34.780 limestone. Um, could it be the 313 00:12:34.780 --> 00:12:37.740 same way as caves were created 314 00:12:37.740 --> 00:12:40.140 on Mars? I think that's the initial question. 315 00:12:40.700 --> 00:12:43.140 Jonti Horner: So I'd stress here, I'm Not a geophysicist, 316 00:12:43.140 --> 00:12:45.780 but the limestone we get on Earth is stuff 317 00:12:45.780 --> 00:12:47.420 that is now above sea level that was once 318 00:12:47.420 --> 00:12:49.900 below sea level. You had all these calcium 319 00:12:49.900 --> 00:12:52.600 shelled creatures die and fall to the bottom 320 00:12:52.600 --> 00:12:54.760 of the, uh, ocean and then get compacted over 321 00:12:54.760 --> 00:12:57.360 millions of years to form this rock. And then 322 00:12:57.360 --> 00:12:59.120 plate tectonics lifted the rock above the 323 00:12:59.120 --> 00:13:01.480 surface of the ocean. I guess on Mars you'd 324 00:13:01.480 --> 00:13:03.080 probably argue the oceans went away. There's 325 00:13:03.080 --> 00:13:05.280 not plate tectonics to lift things up, but 326 00:13:05.280 --> 00:13:07.960 the places that were ocean now no longer 327 00:13:08.040 --> 00:13:10.440 are. Ah, this is 328 00:13:11.000 --> 00:13:13.240 predisposed on the idea that you develop 329 00:13:13.560 --> 00:13:16.520 things with enough calcium 330 00:13:16.840 --> 00:13:18.920 to be able to make shells and stuff like 331 00:13:18.920 --> 00:13:21.840 that. Um, I believe, and I stand to 332 00:13:21.840 --> 00:13:23.120 be corrected on this, that the things that 333 00:13:23.120 --> 00:13:25.060 make calcium are typically 334 00:13:25.620 --> 00:13:28.020 oxygen breathers, not carbon dioxide 335 00:13:28.020 --> 00:13:30.180 breathers. But I may be wrong on that. Um, 336 00:13:30.180 --> 00:13:32.340 they die, they precipitate stuff out. Now, 337 00:13:32.740 --> 00:13:34.700 the first point is whether they could be 338 00:13:34.700 --> 00:13:36.540 limestone caves on Mars. Ah, now that would 339 00:13:36.540 --> 00:13:39.460 be predisposed on the appropriate 340 00:13:39.620 --> 00:13:42.060 evolution of life to get to the point where 341 00:13:42.060 --> 00:13:43.900 you have things that could leave fossils, 342 00:13:43.900 --> 00:13:45.820 that could leave shells and stuff. And we 343 00:13:45.820 --> 00:13:48.580 haven't yet found any fossils of such life on 344 00:13:48.580 --> 00:13:51.060 Mars. And without such life, you couldn't get 345 00:13:51.060 --> 00:13:53.010 limestone. I think think will be an open 346 00:13:53.010 --> 00:13:54.760 question. I suspect if we got Earth, uh, 347 00:13:54.810 --> 00:13:56.970 scientists and stuff like that in on the 348 00:13:56.970 --> 00:13:59.450 show, they'd have good reasons why limestone 349 00:13:59.450 --> 00:14:01.410 will be unlikely to be common on Mars. 350 00:14:01.410 --> 00:14:04.210 Because, yes, you did have oceans and lakes, 351 00:14:04.770 --> 00:14:07.410 but was there, ah, enough time for 352 00:14:07.410 --> 00:14:09.650 enough deposits to be made of shelled 353 00:14:09.650 --> 00:14:12.290 creatures which we don't even know evolved? 354 00:14:12.770 --> 00:14:14.690 So there's a lot of complexity there. It's 355 00:14:14.690 --> 00:14:16.570 obviously something, I don't know for 356 00:14:16.570 --> 00:14:19.490 definite whether you could have limestone 357 00:14:19.490 --> 00:14:22.170 on Mars. Um, I haven't heard of it being 358 00:14:22.170 --> 00:14:25.080 detected on Mars, but absence of evidence 359 00:14:25.080 --> 00:14:26.680 is not evidence of absence. But I don't 360 00:14:26.680 --> 00:14:28.240 believe it is common, otherwise we'd be 361 00:14:28.240 --> 00:14:30.320 fairly well aware of it. But there are other 362 00:14:30.320 --> 00:14:32.120 ways you can get caves on Earth. And I mean, 363 00:14:32.120 --> 00:14:35.080 we've got lava tubes and lava caves up 364 00:14:35.080 --> 00:14:37.600 in North Queensland in Uladulla. We've got 365 00:14:37.760 --> 00:14:39.200 similar things have been found on the Moon 366 00:14:39.200 --> 00:14:42.080 and Mars. There are skylights and lava tubes 367 00:14:42.480 --> 00:14:44.920 on Mars that people have even suggested could 368 00:14:44.920 --> 00:14:47.840 be suitable places for humans to 369 00:14:47.840 --> 00:14:49.560 go and live. Because if you're underground, 370 00:14:49.560 --> 00:14:51.800 you're shielded from radiation. And of 371 00:14:51.800 --> 00:14:53.440 course, if you're in a cave, you can seal the 372 00:14:53.440 --> 00:14:56.020 entrance and fill it with air, which would be 373 00:14:56.020 --> 00:14:58.380 good. Now that kind of links to the second 374 00:14:58.380 --> 00:15:01.180 part of the question here from Mark, which is 375 00:15:01.180 --> 00:15:02.940 if you have caves deep enough, could you have 376 00:15:02.940 --> 00:15:04.860 enough atmosphere in those caves to have 377 00:15:05.340 --> 00:15:08.020 atmospheric pressure? I think that's 378 00:15:08.020 --> 00:15:10.979 unlikely here because those cave 379 00:15:10.979 --> 00:15:13.020 systems would probably be connected to the 380 00:15:13.180 --> 00:15:16.020 surface and air would diffuse out of 381 00:15:16.020 --> 00:15:18.860 them. So you equilibriate and you don't 382 00:15:18.940 --> 00:15:21.740 go into the cave in the lava tube on Earth, 383 00:15:21.740 --> 00:15:24.020 and suddenly it's 3 atmospheres. Because if 384 00:15:24.020 --> 00:15:25.860 it was 3 atmospheres, the air would be pushed 385 00:15:25.860 --> 00:15:28.720 out the entrance. So I don't 386 00:15:28.720 --> 00:15:30.720 think you get to atmospheric pressure in 387 00:15:30.720 --> 00:15:33.080 these caves unless they were very, very deep 388 00:15:33.400 --> 00:15:35.600 and were sealed and the air was sealed in 389 00:15:35.600 --> 00:15:37.880 from when the atmospheric pressure was higher 390 00:15:37.880 --> 00:15:39.680 and it hadn't escaped. But with the porosity 391 00:15:39.680 --> 00:15:40.920 of the rocks, I think that would be very 392 00:15:40.920 --> 00:15:43.880 unlikely. The next thing is about there being 393 00:15:43.880 --> 00:15:46.240 oxygen in those caves. And I think of all of 394 00:15:46.240 --> 00:15:48.440 these things, that is the least likely 395 00:15:48.760 --> 00:15:50.760 because Mars 396 00:15:51.320 --> 00:15:54.270 doesn't have much, if any free oxygen 397 00:15:54.270 --> 00:15:56.310 in the atmosphere, because oxygen reacts with 398 00:15:56.390 --> 00:15:59.350 everything. And on Mars, there are bits of 399 00:15:59.350 --> 00:16:00.990 methane being produced. We're not quite sure 400 00:16:00.990 --> 00:16:03.270 what's going on there, but the oxygen, free 401 00:16:03.270 --> 00:16:06.030 oxygen from Mars has been very 402 00:16:06.030 --> 00:16:08.950 effectively absorbed into the surface through 403 00:16:08.950 --> 00:16:11.510 chemistry. Um, big part of why Mars looks 404 00:16:11.510 --> 00:16:12.950 red, of course, is that you can effectively 405 00:16:12.950 --> 00:16:15.310 say the surface is rusted iron 406 00:16:15.310 --> 00:16:18.270 oxide. The oxygen in the air has reacted with 407 00:16:18.270 --> 00:16:19.990 the iron in the surface and 408 00:16:19.990 --> 00:16:22.750 Andrew Dunkley: been locked up like a lot of Australia. 409 00:16:22.910 --> 00:16:25.910 Jonti Horner: Yes. Um, now you can produce some oxygen in 410 00:16:25.910 --> 00:16:28.670 Mars's atmosphere. If you get water into the 411 00:16:28.670 --> 00:16:30.590 atmosphere, and there is a very small amount, 412 00:16:30.590 --> 00:16:32.950 traces of ox of water in Mars's atmosphere, 413 00:16:32.950 --> 00:16:35.430 we do get water clouds there. Without an 414 00:16:35.430 --> 00:16:37.710 ozone layer, some of that water, particularly 415 00:16:37.710 --> 00:16:38.950 the water that gets highest in the 416 00:16:38.950 --> 00:16:41.830 atmosphere, will get dissociated. It will get 417 00:16:41.830 --> 00:16:43.750 broken into hydrogen and oxygen by 418 00:16:43.750 --> 00:16:46.310 ultraviolet radiation and the hydrogen will 419 00:16:46.310 --> 00:16:48.550 then escape because hydrogen atoms travel so 420 00:16:48.550 --> 00:16:50.670 quickly that Mars gravity can't hold them, 421 00:16:50.990 --> 00:16:52.750 which means the hydrogen goes away and the 422 00:16:52.890 --> 00:16:55.090 oxygen is left behind. So you will be 423 00:16:55.090 --> 00:16:57.090 producing small trace amounts of oxygen in 424 00:16:57.090 --> 00:16:59.530 Mars's atmosphere all the time. But then the 425 00:16:59.690 --> 00:17:02.050 oxygen would then be used up in chemistry and 426 00:17:02.050 --> 00:17:04.890 removed. So in order to have large amounts of 427 00:17:04.890 --> 00:17:06.730 oxygen in one of these caves, you'd need a 428 00:17:06.730 --> 00:17:09.330 source of oxygen, and you'd need that source 429 00:17:09.330 --> 00:17:11.570 to provide enough oxygen that the oxygen can 430 00:17:11.570 --> 00:17:13.370 overcome everything that's trying to remove 431 00:17:13.370 --> 00:17:16.210 it. Now, on Earth, it took a 432 00:17:16.210 --> 00:17:18.090 huge fraction of Earth's life before you got 433 00:17:18.090 --> 00:17:20.290 the great oxidation event for life to 434 00:17:20.290 --> 00:17:21.570 actually get to the point where it could 435 00:17:21.570 --> 00:17:23.640 produce more oxygen than the Earth, uh, 436 00:17:23.690 --> 00:17:26.590 system could absorb. So to have abundant 437 00:17:26.590 --> 00:17:28.550 oxygen on Mars, uh, strikes me as Very 438 00:17:28.550 --> 00:17:31.230 unlikely. Maybe possible that in the future 439 00:17:31.230 --> 00:17:32.790 that will change though, because if we went 440 00:17:32.790 --> 00:17:35.550 to Mars, then one of the ways people are 441 00:17:35.550 --> 00:17:37.230 thinking the first human habitats will be 442 00:17:37.230 --> 00:17:39.230 built will be to go to the caves in the lava 443 00:17:39.230 --> 00:17:42.230 tunnels and live there. And then you can make 444 00:17:42.230 --> 00:17:44.230 a sealed environment that you can then pump 445 00:17:44.230 --> 00:17:46.910 with an artificial atmosphere. So it could be 446 00:17:46.910 --> 00:17:49.310 that if you ask that question in 20 years 447 00:17:49.310 --> 00:17:52.030 time, Mark, the answer would be yes. There 448 00:17:52.030 --> 00:17:53.950 are caves with high enough atmospheric 449 00:17:53.950 --> 00:17:56.460 concentrations for life. We've put them 450 00:17:56.460 --> 00:17:58.420 there. Would they be looking back at Earth 451 00:17:58.420 --> 00:18:00.860 with anxious eyes, with envious eyes? I guess 452 00:18:00.860 --> 00:18:02.660 it depends on the person who's emigrated 453 00:18:02.660 --> 00:18:05.220 there. There's these fabulous ideas of what 454 00:18:05.220 --> 00:18:07.060 humanity will look like when we're a multi 455 00:18:07.060 --> 00:18:09.900 planet species. But the thing that stuck with 456 00:18:09.900 --> 00:18:11.579 me more than anything else was this amazing 457 00:18:11.579 --> 00:18:14.189 Talk from a doctor in 2012, 2013, 458 00:18:14.304 --> 00:18:16.620 2014 at one of our space research conferences 459 00:18:17.100 --> 00:18:19.300 who basically talked about the difficulty 460 00:18:19.300 --> 00:18:22.180 humans have reproducing when you go even 461 00:18:22.180 --> 00:18:24.300 very slightly away from standard temperature 462 00:18:24.300 --> 00:18:26.340 pressure at sea level. Talked about the 463 00:18:26.340 --> 00:18:29.000 challenges at invaders had into South 464 00:18:29.000 --> 00:18:30.600 America when they reached the high Andes. 465 00:18:30.600 --> 00:18:32.320 They couldn't colonise there because they 466 00:18:32.320 --> 00:18:35.000 weren't able to reproduce. Talking about very 467 00:18:35.000 --> 00:18:37.240 slight changes in conditions being enough to 468 00:18:37.240 --> 00:18:39.880 render our ability to have children 469 00:18:40.120 --> 00:18:42.760 null and void. On Mars you've got one third 470 00:18:42.760 --> 00:18:45.720 gravity. Unless you get dystopian science 471 00:18:45.720 --> 00:18:48.400 fiction future where women enter 472 00:18:48.400 --> 00:18:50.560 centrifuges for nine months in order to carry 473 00:18:50.560 --> 00:18:52.360 a child to term, in order to simulate one 474 00:18:52.360 --> 00:18:55.350 ghost. The perspective is at least in the 475 00:18:55.350 --> 00:18:58.310 relatively near future, humanity on the 476 00:18:58.310 --> 00:19:00.270 moon, humanity on Mars will be 477 00:19:01.070 --> 00:19:03.430 not self sustaining. We won't be able to have 478 00:19:03.430 --> 00:19:05.950 children there. And so it may well be that 479 00:19:05.950 --> 00:19:08.950 Mars becomes a interplanetary retirement 480 00:19:08.950 --> 00:19:11.270 home. People sow their wild oats, live their 481 00:19:11.270 --> 00:19:13.110 lives and then go to Mars later in life for 482 00:19:13.110 --> 00:19:15.750 the adventure. And then would they look back 483 00:19:15.750 --> 00:19:17.190 with envy? Well, they'd probably look back 484 00:19:17.190 --> 00:19:18.830 with a little bit of longing, but also they'd 485 00:19:18.830 --> 00:19:20.510 have the excitement of where they are are. 486 00:19:20.830 --> 00:19:22.990 So it could be that in 20 years time, 30 487 00:19:22.990 --> 00:19:25.950 years time, there will be life in the caves 488 00:19:26.350 --> 00:19:28.990 with artificially enhanced oxygen levels. 489 00:19:29.070 --> 00:19:31.230 Looking back at Earth, watching the news and 490 00:19:31.230 --> 00:19:33.230 all the rest of it, but I don't think at the 491 00:19:33.230 --> 00:19:34.270 minute that that's the case. 492 00:19:35.070 --> 00:19:38.030 Andrew Dunkley: Okay, fair enough. Uh, and uh, just one 493 00:19:38.030 --> 00:19:40.110 more point, Mark. I just did a quick search 494 00:19:40.110 --> 00:19:42.550 about could there be limestone on Mars? And 495 00:19:42.550 --> 00:19:44.390 according to an article in Science 496 00:19:44.390 --> 00:19:46.590 AstroDailyPod which dates back nearly 20 497 00:19:46.590 --> 00:19:49.350 years now, uh, yes, limestone, specifically 498 00:19:49.350 --> 00:19:51.950 carbonate minerals likely exist on Mars, but 499 00:19:53.220 --> 00:19:55.780 probably not in massive thick sedimentary 500 00:19:55.780 --> 00:19:58.300 beds found On Earth, while early Mars was 501 00:19:58.300 --> 00:20:00.380 warmer and wetter, supporting the potential 502 00:20:00.380 --> 00:20:03.140 for carbonate formation, the planet lacked 503 00:20:03.140 --> 00:20:05.100 the extensive oceans and tectonic plate 504 00:20:05.100 --> 00:20:07.860 activity required to build large limestone 505 00:20:07.860 --> 00:20:10.660 deposits. So there you are. They 506 00:20:10.660 --> 00:20:13.420 think there possibly is limestone 507 00:20:13.420 --> 00:20:16.020 on Mars, but not uh, enough to do 508 00:20:16.100 --> 00:20:18.900 what we've seen on Earth. Uh, 509 00:20:18.900 --> 00:20:21.620 but great question and uh, certainly food for 510 00:20:21.620 --> 00:20:24.400 thought, uh, and appreciate it. Mark, thanks 511 00:20:24.400 --> 00:20:25.120 for sending it in. 512 00:20:25.200 --> 00:20:27.440 This is Space Nuts. Andrew Dunkley here with 513 00:20:27.440 --> 00:20:28.800 Professor Jonty Horner. 514 00:20:33.100 --> 00:20:34.480 Jonti Horner: M. Space Nuts. 515 00:20:34.640 --> 00:20:37.360 Andrew Dunkley: And you're listening to a Q and A edition. 516 00:20:37.360 --> 00:20:39.920 We've got one more question to tackle. Hello, 517 00:20:39.920 --> 00:20:42.560 this is Casey from Colorado, she's one of our 518 00:20:42.560 --> 00:20:45.000 regular contributors. I have some questions 519 00:20:45.000 --> 00:20:47.840 about stars. Why do the activity levels of 520 00:20:47.840 --> 00:20:50.640 stars change? What causes solar cycles? 521 00:20:50.640 --> 00:20:53.420 Does every type of star go through solar 522 00:20:53.420 --> 00:20:56.100 cycling? Love the show, Hope you're both 523 00:20:56.100 --> 00:20:58.780 well. Uh, thanks Casey from Colorado. 524 00:20:59.080 --> 00:21:01.500 Um, it's a good question because we don't 525 00:21:01.500 --> 00:21:03.340 really talk about this sort of thing much, 526 00:21:03.420 --> 00:21:06.060 but uh, we're just about to go out of 527 00:21:06.340 --> 00:21:09.140 uh, the peak of solar activity 528 00:21:09.140 --> 00:21:12.100 in our own Solar System, the 11 year cycle 529 00:21:12.100 --> 00:21:15.060 that they talk about. Uh, so that's probably 530 00:21:15.060 --> 00:21:17.940 where we should start. We know the sun goes 531 00:21:17.940 --> 00:21:20.920 through an 11 year cycle and um, 532 00:21:22.080 --> 00:21:24.520 and we witness different things during those 533 00:21:24.520 --> 00:21:27.200 11 years because it's constantly changing. 534 00:21:27.360 --> 00:21:29.900 Jonti Horner: Yeah, it's worth stressing Shreya, that 535 00:21:29.900 --> 00:21:32.600 uh, effectively all stars are uh, 536 00:21:32.600 --> 00:21:35.560 inherently variable to some degree. And 537 00:21:35.560 --> 00:21:37.680 our sun is actually incredibly low 538 00:21:37.680 --> 00:21:39.920 variability compared to many stars. 539 00:21:40.400 --> 00:21:43.080 The solar cycle we observe is 540 00:21:43.080 --> 00:21:45.960 arguably a 22ish year cycle with 541 00:21:45.960 --> 00:21:48.600 two peaks and two minima. And the subtlety 542 00:21:48.600 --> 00:21:50.680 there is we get solar maximum when there are 543 00:21:50.680 --> 00:21:52.740 lots of sunspots, lots of activity, more 544 00:21:52.740 --> 00:21:55.300 aurora and solar minimum when we've got fewer 545 00:21:55.300 --> 00:21:57.660 sunspots, less activity, fewer aurora. 546 00:21:58.060 --> 00:22:00.700 And we get those on and about an 11 year 547 00:22:00.700 --> 00:22:02.860 cycle from one peak to the next, sometimes a 548 00:22:02.860 --> 00:22:05.300 bit shorter, sometimes a bit longer. But the 549 00:22:05.300 --> 00:22:08.260 origin of the solar cycles with the 550 00:22:08.260 --> 00:22:10.860 sun is the Sun's magnetic field. The sun 551 00:22:11.420 --> 00:22:13.340 has a magnetic field that runs from the North 552 00:22:13.340 --> 00:22:15.900 Pole to the South Pole. And it 553 00:22:15.900 --> 00:22:18.860 rotates in such a way that the rotation 554 00:22:18.860 --> 00:22:20.620 period at the equator and the rotation period 555 00:22:20.620 --> 00:22:22.900 at the poles are different rotates as a fluid 556 00:22:22.900 --> 00:22:25.200 body. So the time it takes the Sun's equator 557 00:22:25.200 --> 00:22:27.440 to rotate is a couple of days quicker than 558 00:22:27.440 --> 00:22:30.240 the poles. The magnetic field lines running 559 00:22:30.240 --> 00:22:32.480 from the North Pole to the South Pole get 560 00:22:32.480 --> 00:22:34.040 hooked up in the material and gradually get 561 00:22:34.040 --> 00:22:36.720 wound up a bit like an elastic band. And so 562 00:22:36.720 --> 00:22:38.600 the Sun's magnetic field gets more and more 563 00:22:38.600 --> 00:22:41.160 complicated through the 11 years, starts to 564 00:22:41.160 --> 00:22:42.800 get kinks and the kinks break through the 565 00:22:42.800 --> 00:22:44.760 surface. So you get locations where the 566 00:22:44.760 --> 00:22:46.400 magnetic field comes out of the surface, 567 00:22:46.400 --> 00:22:48.640 loops up and goes back down. And in the 568 00:22:48.640 --> 00:22:50.640 places where it's nearly vertical, it cools 569 00:22:50.640 --> 00:22:52.360 the surface of the sun because it suppresses 570 00:22:52.360 --> 00:22:53.690 convection of new energy from, from 571 00:22:53.690 --> 00:22:55.890 underneath, leading to cooler spots which 572 00:22:55.890 --> 00:22:58.410 look darker and therefore are sunspots. And 573 00:22:58.410 --> 00:22:59.930 gradually the sun gets more and more wound 574 00:22:59.930 --> 00:23:02.810 up. Sunspot activity begins at high latitudes 575 00:23:02.810 --> 00:23:04.530 and works its way down towards the equator 576 00:23:04.850 --> 00:23:07.010 and eventually around solar maximum, you get 577 00:23:07.010 --> 00:23:09.650 the field line starting to snap and break and 578 00:23:09.650 --> 00:23:12.290 you get a polar reversal happen. The north 579 00:23:12.290 --> 00:23:14.250 pole becomes a south pole and the south pole 580 00:23:14.250 --> 00:23:16.490 becomes a north pole and then it all begins 581 00:23:16.490 --> 00:23:18.690 again. So the reason we talk about a 22 year 582 00:23:18.690 --> 00:23:21.540 cycle is you get solar maximum 583 00:23:21.540 --> 00:23:23.380 with north pole to the north, well, north 584 00:23:23.380 --> 00:23:25.940 pole to the top, and then a minimum, then 585 00:23:25.940 --> 00:23:27.900 solar maximum with the south pole to the top, 586 00:23:27.900 --> 00:23:29.780 then a minimum, then you're back to where you 587 00:23:29.780 --> 00:23:32.780 started from. Roughly. Those 588 00:23:32.780 --> 00:23:35.380 cycles are driven by the magnetic activity of 589 00:23:35.380 --> 00:23:37.660 the sun and they vary the brightness of our 590 00:23:37.660 --> 00:23:39.660 star, um, by a vanishingly small amount. It's 591 00:23:39.660 --> 00:23:42.620 an incredibly stable star. I think you're 592 00:23:42.620 --> 00:23:44.460 talking about variability on the level, about 593 00:23:44.460 --> 00:23:47.310 one part in 2, 10,000, something 594 00:23:47.310 --> 00:23:49.390 like that. Now that is such a low level of 595 00:23:49.390 --> 00:23:51.670 variability that if we were observing an 596 00:23:51.990 --> 00:23:54.350 other star, we probably wouldn't be able to 597 00:23:54.350 --> 00:23:56.070 pick up the variability in the total 598 00:23:56.070 --> 00:23:58.310 brightness, but we would be able to pick up 599 00:23:58.310 --> 00:24:00.990 the magnetic activity. And this is magnetic 600 00:24:00.990 --> 00:24:03.870 activity. And star spots are uh, one of the 601 00:24:03.870 --> 00:24:05.790 challenges for people trying to find 602 00:24:05.790 --> 00:24:08.030 exoplanets because a star spot can mimic as 603 00:24:08.030 --> 00:24:10.150 an exoplanet and stellar activity like the 604 00:24:10.150 --> 00:24:13.150 Sun's magnetic cycle and the star. So SAR 605 00:24:13.150 --> 00:24:16.070 spots that go with it can actually be mimic 606 00:24:16.070 --> 00:24:17.910 a radial velocity planet. So there's a lot of 607 00:24:17.910 --> 00:24:20.350 work done in when we think we've got a signal 608 00:24:20.590 --> 00:24:22.350 confirming that it is actually a planet and 609 00:24:22.350 --> 00:24:24.550 not a star spot. So you've got that kind of 610 00:24:24.550 --> 00:24:25.310 stellar activity. 611 00:24:25.310 --> 00:24:28.230 Now most stars are significantly, uh, more 612 00:24:28.230 --> 00:24:29.830 variable than the sun. And there's a lot of 613 00:24:29.830 --> 00:24:31.950 other ways stars can vary. We think that 614 00:24:32.590 --> 00:24:35.070 most sun like stars will have sunspot cycles 615 00:24:35.070 --> 00:24:36.710 like the sun, and it's due to the structure 616 00:24:36.710 --> 00:24:39.590 of the convective and the radiative zones and 617 00:24:39.590 --> 00:24:41.310 all the rest of it. The internal structure of 618 00:24:41.310 --> 00:24:42.870 the sun, a bit like the Earth, has a crust, a 619 00:24:42.870 --> 00:24:45.550 mantle and a car. The magnetic field in the 620 00:24:45.550 --> 00:24:47.670 top layer of the sun can get tangled up. 621 00:24:49.030 --> 00:24:50.750 Stars of different masses have a bit of a 622 00:24:50.750 --> 00:24:52.630 different structure, but there's A lot of 623 00:24:52.790 --> 00:24:55.030 other ways that stars can be variable. And so 624 00:24:55.030 --> 00:24:57.270 we have a very wide variety of different 625 00:24:57.270 --> 00:24:59.670 types of variable stars. There are flare 626 00:24:59.670 --> 00:25:01.750 stars like Proxima Centauri, which have 627 00:25:02.070 --> 00:25:04.670 stellar activity that can occasionally be a 628 00:25:04.670 --> 00:25:06.310 super flare that can cause the star's 629 00:25:06.310 --> 00:25:07.870 brightness to change by almost a factor of 630 00:25:07.870 --> 00:25:10.110 100. And I normally talk about Proxima 631 00:25:10.110 --> 00:25:12.310 Centauri being 100 times too fancy with the 632 00:25:12.310 --> 00:25:14.950 naked eye, but in one mega flare it had a few 633 00:25:14.950 --> 00:25:16.430 years ago, it almost reached the edge of 634 00:25:16.430 --> 00:25:18.830 naked eye visibility. That flare was that 635 00:25:18.830 --> 00:25:21.550 intense. You've then got a, ah, large number 636 00:25:21.550 --> 00:25:23.590 of stars that vary in brightness. Bixa 637 00:25:23.590 --> 00:25:26.430 pulsate Bixa size changes fundamentally 638 00:25:26.910 --> 00:25:29.430 and usually these are stars coming towards 639 00:25:29.430 --> 00:25:30.630 the end of the life entering a bit of 640 00:25:30.630 --> 00:25:33.390 instability for various reasons. Some of them 641 00:25:33.390 --> 00:25:35.350 are only just moving off the main sequence or 642 00:25:35.350 --> 00:25:38.190 are very young. Others are super giant stars 643 00:25:38.190 --> 00:25:41.050 with different kinds of variability. But 644 00:25:41.050 --> 00:25:43.250 that variability causes their 645 00:25:43.890 --> 00:25:46.490 diameter to change, causes them to pulsate. 646 00:25:46.490 --> 00:25:47.690 And that's because they're just slightly out 647 00:25:47.690 --> 00:25:49.650 of equilibrium. When they're at their 648 00:25:49.650 --> 00:25:52.370 smallest they get hotter, they're putting out 649 00:25:52.370 --> 00:25:54.690 more energy because they're a bit hotter. 650 00:25:55.180 --> 00:25:57.850 Um, the surface layers therefore are pushed 651 00:25:57.850 --> 00:26:00.570 outwards with more force than gravity can 652 00:26:00.570 --> 00:26:02.970 push them in and they start to expand, they 653 00:26:02.970 --> 00:26:04.530 go through the equilibrium point but because 654 00:26:04.530 --> 00:26:06.770 they're still expanding they keep going. As 655 00:26:06.770 --> 00:26:08.890 the stars outer layers get bigger and bigger, 656 00:26:09.210 --> 00:26:12.050 the star cools. Because when you 657 00:26:12.050 --> 00:26:14.570 take a gas and you increase its volume, 658 00:26:14.810 --> 00:26:16.370 you lower the pressure and you lower the 659 00:26:16.370 --> 00:26:18.970 temperature so that material cools 660 00:26:19.210 --> 00:26:21.530 and eventually is giving out less energy 661 00:26:22.330 --> 00:26:25.090 than gravity pulling in would cause and it 662 00:26:25.090 --> 00:26:27.090 starts to collapse again. So instead of like 663 00:26:27.090 --> 00:26:29.130 the sun staying at that very fixed radius 664 00:26:29.130 --> 00:26:31.010 because gravity and radiation are balanced 665 00:26:31.010 --> 00:26:33.360 perfectly, you can get this oscillating 666 00:26:33.360 --> 00:26:34.960 behaviour where you overshoot in both 667 00:26:34.960 --> 00:26:37.240 directions. And um, sometimes that's fairly 668 00:26:37.240 --> 00:26:39.200 small, sometimes that's fairly large. And it 669 00:26:39.200 --> 00:26:41.240 happens at different phases of stars lives in 670 00:26:41.240 --> 00:26:43.960 different ways. One of the most famous types 671 00:26:43.960 --> 00:26:45.840 of variable stars are known as the Cepheid 672 00:26:45.840 --> 00:26:48.440 variable stars. And um, these are somewhat 673 00:26:48.440 --> 00:26:50.360 evolved stars coming towards the end of their 674 00:26:50.360 --> 00:26:52.880 life where the pulsation period 675 00:26:53.520 --> 00:26:56.480 is directly linked to how luminous a star is. 676 00:26:58.010 --> 00:27:00.450 So two similar stars, but one's brighter than 677 00:27:00.450 --> 00:27:03.050 the other intrinsically, put them at the same 678 00:27:03.050 --> 00:27:04.810 distance, one's more luminous, looks 679 00:27:04.810 --> 00:27:06.690 brighter, they will pulsate with different 680 00:27:06.690 --> 00:27:08.410 periods. And if you can measure the period, 681 00:27:08.970 --> 00:27:11.210 you can measure how luminous that star is. 682 00:27:11.370 --> 00:27:13.490 And that makes Cepheid variables an excellent 683 00:27:13.490 --> 00:27:16.050 step on our distance ladder. Because you see 684 00:27:16.050 --> 00:27:17.690 a star that's a certain Brightness, you don't 685 00:27:17.690 --> 00:27:19.810 really know how far away it is. But if you 686 00:27:19.810 --> 00:27:21.810 can measure the period of the Cepheid 687 00:27:21.810 --> 00:27:23.900 variable pulsating, that tells you 688 00:27:23.900 --> 00:27:26.020 intrinsically how luminous that star is, 689 00:27:26.660 --> 00:27:28.660 which means we can work out its distance. So 690 00:27:28.660 --> 00:27:29.620 they're really useful. 691 00:27:30.020 --> 00:27:32.740 Some stars are astonishingly variable. 692 00:27:33.040 --> 00:27:35.900 Um, among the stars with the biggest 693 00:27:35.900 --> 00:27:37.700 variation in brightness from brightest to 694 00:27:37.700 --> 00:27:40.260 faintest, um, are known as the Myra stars. 695 00:27:40.720 --> 00:27:43.100 Ah, Myra, the archetypal one is known as 696 00:27:43.100 --> 00:27:45.460 Myra, the wonderful Myra at its brightest 697 00:27:45.860 --> 00:27:48.700 is easily visible with a naked eye at 698 00:27:48.700 --> 00:27:50.900 its fantasy, you need a telescope to see it. 699 00:27:50.980 --> 00:27:52.500 And a few of these stars have 700 00:27:53.360 --> 00:27:54.960 amplitudes, the difference in brightness 701 00:27:54.960 --> 00:27:57.240 between the brightest and faintest that are 702 00:27:57.240 --> 00:27:58.760 such that they vary in brightness by more 703 00:27:58.760 --> 00:28:01.520 than a factor of 10,000. Um, a couple of 704 00:28:01.520 --> 00:28:04.040 examples here, Chi Cygni, which at its 705 00:28:04.040 --> 00:28:06.560 brightness is a magnitude 3.3 star, so 706 00:28:06.560 --> 00:28:08.120 comfortable with the naked eye, but not that 707 00:28:08.120 --> 00:28:10.360 bright at, ah, its Faintest is magnitude 708 00:28:10.360 --> 00:28:13.120 14.2. Um, that is 709 00:28:13.120 --> 00:28:16.040 a factor of about 25,000 in brightness 710 00:28:16.040 --> 00:28:18.400 between brightest and faintests. That is 711 00:28:19.110 --> 00:28:21.990 so long a period that that was discovered, 712 00:28:21.990 --> 00:28:24.550 that variability back in 1686. 713 00:28:25.110 --> 00:28:27.430 You've got a wide variety of mirror type 714 00:28:27.430 --> 00:28:29.390 stars dominating the stars with the biggest 715 00:28:29.390 --> 00:28:31.750 variability. But there are other type ones in 716 00:28:31.750 --> 00:28:34.629 there. Arcarona Borealis is a famous one in 717 00:28:34.629 --> 00:28:36.990 the bowl of the northern crown, normally only 718 00:28:36.990 --> 00:28:39.630 barely visible with the naked eye. So carbon 719 00:28:39.630 --> 00:28:42.150 star, where the mirror stars 720 00:28:42.550 --> 00:28:44.710 have a periodic variation, they're pulsating 721 00:28:44.710 --> 00:28:47.150 in a broadly periodic way with periods of a 722 00:28:47.150 --> 00:28:49.650 year or more. Acherona 723 00:28:49.650 --> 00:28:51.370 Borealis is different. It shines along, 724 00:28:51.370 --> 00:28:52.890 shines along, shines along and then suddenly 725 00:28:52.890 --> 00:28:54.250 it's like somebody drops a curtain in front 726 00:28:54.250 --> 00:28:57.050 of it and its brightness plunges and then it 727 00:28:57.050 --> 00:28:59.250 gradually brightens up again. And that is not 728 00:28:59.250 --> 00:29:01.930 exactly periodic. It's known as a carbon 729 00:29:01.930 --> 00:29:03.960 star. And what's happening is that, ah, 730 00:29:03.960 --> 00:29:05.770 occasionally it's got a huge amount of carbon 731 00:29:05.770 --> 00:29:08.170 in its atmosphere. Occasionally the carbon 732 00:29:08.170 --> 00:29:10.330 condenses into soot, blocking the light from 733 00:29:10.330 --> 00:29:12.610 underneath. That cools the outer layers, 734 00:29:12.610 --> 00:29:14.490 which gets this runaway condensation of 735 00:29:14.490 --> 00:29:16.810 carbon carbon into soot. That traps the 736 00:29:16.810 --> 00:29:19.210 radiation from inside, so the heat builds up 737 00:29:19.210 --> 00:29:20.850 inside until eventually the carbon gets 738 00:29:20.850 --> 00:29:22.970 turned back into a gas again. The clouds 739 00:29:22.970 --> 00:29:24.330 clear and the star brightens again. 740 00:29:24.650 --> 00:29:26.610 Andrew Dunkley: So that's, I was, I was just going to 741 00:29:26.610 --> 00:29:28.570 stupidly suggest that it was soot. 742 00:29:28.650 --> 00:29:31.610 Jonti Horner: Yeah, it is, it's a carbon star. And a Corona 743 00:29:31.610 --> 00:29:34.290 Borealis is the archetypal, most 744 00:29:34.290 --> 00:29:36.490 famous one. It's described as a low mass 745 00:29:36.490 --> 00:29:38.290 yellow supergiant. So again, it's a star 746 00:29:38.290 --> 00:29:39.850 coming towards the end of its life, 747 00:29:40.640 --> 00:29:43.580 um, every so often can be after just 748 00:29:43.580 --> 00:29:45.980 a few months, or it can be a few years. It 749 00:29:45.980 --> 00:29:48.260 can dim by as much as a factor of 10,000 750 00:29:48.500 --> 00:29:51.220 because it kind of suits up, clouds up. 751 00:29:51.460 --> 00:29:53.300 And if you look at the light curve of that. 752 00:29:53.300 --> 00:29:54.940 If you're bored, have a look at the light 753 00:29:54.940 --> 00:29:57.780 curve on Wikipedia, because it's really 754 00:29:57.780 --> 00:29:59.980 head scratching. It shows you how random this 755 00:29:59.980 --> 00:30:01.980 is and how hard it must have been for people 756 00:30:01.980 --> 00:30:04.780 to understand. Um, there was an incredible 757 00:30:04.780 --> 00:30:06.860 deep minimum that happened in the, the 758 00:30:06.860 --> 00:30:09.660 mid-2010s, I think it was, where it 759 00:30:09.660 --> 00:30:11.700 dimmed and then it stayed dim for ages. 760 00:30:12.020 --> 00:30:13.780 Normally it's bright and then it dims for a 761 00:30:13.780 --> 00:30:15.460 bit and then it brightens up fairly quickly. 762 00:30:16.260 --> 00:30:19.020 But fundamentally, there's a huge variety of 763 00:30:19.020 --> 00:30:21.940 ways in which stars can vary intrinsically 764 00:30:21.940 --> 00:30:24.860 themselves. Their brightness can vary. It 765 00:30:24.860 --> 00:30:27.300 is known from discussions with the 766 00:30:27.300 --> 00:30:28.540 traditional owners of the land here in 767 00:30:28.540 --> 00:30:30.300 Australia that the variability of 768 00:30:30.300 --> 00:30:32.180 Beetlejuice, Nal, Deborah, and two bright red 769 00:30:32.180 --> 00:30:34.760 giant, giant red supergiant stars in our 770 00:30:34.760 --> 00:30:37.520 summer sky, Northern Hemisphere winter sky, 771 00:30:37.760 --> 00:30:39.480 are variable. We saw that with the great 772 00:30:39.480 --> 00:30:41.640 dimming of Beetlejuice about a decade ago. 773 00:30:41.640 --> 00:30:44.080 Now, that kind of variability has been known 774 00:30:44.080 --> 00:30:46.000 for hundreds, if not thousands of years among 775 00:30:46.080 --> 00:30:48.280 traditional owners around the world who look 776 00:30:48.280 --> 00:30:50.960 at the night sky so that stars 777 00:30:50.960 --> 00:30:53.320 varying intrinsically in brightness, the star 778 00:30:53.320 --> 00:30:56.120 itself varying. And, um, it's a wonderful 779 00:30:56.120 --> 00:30:57.920 rabbit hole for people to wander down. It's 780 00:30:57.920 --> 00:30:59.760 another area of astronomy where amateur 781 00:30:59.760 --> 00:31:02.470 astronomy contribute a lot because there's 782 00:31:02.470 --> 00:31:04.510 very active variable star observers who will 783 00:31:04.510 --> 00:31:05.910 go out there and measure the brightness of 784 00:31:05.910 --> 00:31:08.110 stars repeatedly to track when they vary. 785 00:31:08.670 --> 00:31:10.910 We get a lot of that knowledge. You've then 786 00:31:10.910 --> 00:31:12.870 got a second type of stellar variability 787 00:31:12.870 --> 00:31:15.870 which is not intrinsic, but is extrinsic. 788 00:31:15.870 --> 00:31:18.110 What I mean by that is an intrinsically 789 00:31:18.110 --> 00:31:20.990 variable star is a star itself changing. An 790 00:31:20.990 --> 00:31:23.590 extrinsic variation is something else causing 791 00:31:23.590 --> 00:31:25.750 the brightness of the star to change. You 792 00:31:25.750 --> 00:31:27.310 know, put your hand in front of the star. The 793 00:31:27.310 --> 00:31:28.430 stars dissipate because your hand's 794 00:31:28.430 --> 00:31:31.110 absorbing. All the lights disappeared. We 795 00:31:31.110 --> 00:31:33.390 have multiple star systems where we have 796 00:31:33.390 --> 00:31:36.270 eclipsing binaries. Algol is possibly the 797 00:31:36.270 --> 00:31:38.310 most famous of these. The winking demon star, 798 00:31:38.630 --> 00:31:40.790 whose brightness drops by about a factor of 799 00:31:40.790 --> 00:31:43.630 three every couple of days. And that 800 00:31:43.630 --> 00:31:46.070 star is bright enough to be easily visible 801 00:31:46.070 --> 00:31:48.310 with the naked eye. And, um, the 802 00:31:48.470 --> 00:31:50.750 variability in its brightness is sufficiently 803 00:31:50.750 --> 00:31:52.830 large that it's easily noticeable with the 804 00:31:52.830 --> 00:31:55.830 naked eye. So its brightness varies. I 805 00:31:55.830 --> 00:31:57.840 think it's every 70 hours or so. I just want 806 00:31:57.840 --> 00:31:59.520 to cheque it out. Um, 807 00:32:01.000 --> 00:32:03.720 no, it's less often Than that. Algol's 808 00:32:03.720 --> 00:32:06.680 brightness varies every 2.86 days. 809 00:32:07.640 --> 00:32:10.640 So every 2.86 days, the brightness of 810 00:32:10.640 --> 00:32:13.240 the star drops from magnitude 2.1 to 3.4. 811 00:32:13.240 --> 00:32:15.240 That's a brightness change of about a factor 812 00:32:15.240 --> 00:32:18.160 of three times, roughly. And, uh, it dims for 813 00:32:18.160 --> 00:32:20.280 about 10 hours and then brightens up again. 814 00:32:20.840 --> 00:32:23.200 Became known as a winking demon star that has 815 00:32:23.200 --> 00:32:26.040 been known to be variable since prehistory. 816 00:32:26.040 --> 00:32:29.000 In reality, there's allegations 817 00:32:29.000 --> 00:32:31.080 that perhaps an Egyptian calendar that talked 818 00:32:31.080 --> 00:32:32.840 about unlucky days may have been linked to 819 00:32:32.840 --> 00:32:35.680 that. That's questionable. Where it is 820 00:32:35.680 --> 00:32:37.120 really interesting, though, is the 821 00:32:37.520 --> 00:32:40.400 variability of Algol was first explained 822 00:32:40.720 --> 00:32:43.480 by John Goodrich, who is one of 823 00:32:43.480 --> 00:32:45.480 those heroes of astronomy you don't hear 824 00:32:45.480 --> 00:32:47.680 about very often, mainly because he lived a 825 00:32:47.680 --> 00:32:50.160 very short life. He presented findings in May 826 00:32:50.750 --> 00:32:53.670 1783 to suggest that the 827 00:32:53.670 --> 00:32:55.790 variability, the periodic variability of 828 00:32:55.790 --> 00:32:58.470 Algol was caused by a dark body or a dimmer 829 00:32:58.470 --> 00:33:01.390 body passing in front of it every 2.86 days. 830 00:33:01.790 --> 00:33:04.430 He was awarded a medal for this, I believe. 831 00:33:04.430 --> 00:33:06.509 He never got to receive the medal because he 832 00:33:06.509 --> 00:33:09.350 died, as I say, very, very young. Died at the 833 00:33:09.350 --> 00:33:12.030 age of 21. Got the Copley Medal in 834 00:33:12.030 --> 00:33:14.870 1783, I think he was. Uh, passed away 835 00:33:14.870 --> 00:33:17.150 three years after that. So in just 21 years 836 00:33:17.150 --> 00:33:20.110 old, he contributed hugely to our modern 837 00:33:20.110 --> 00:33:22.670 knowledge of variable stars. And, um, you 838 00:33:22.670 --> 00:33:24.070 know, it's very unfortunate that he passed 839 00:33:24.070 --> 00:33:26.990 away at such a young age, but he was able to 840 00:33:26.990 --> 00:33:28.950 explain this variability that had been 841 00:33:28.950 --> 00:33:30.710 clearly known for a very long time. It's 842 00:33:30.710 --> 00:33:32.590 obvious to the naked eye that this star gets 843 00:33:32.590 --> 00:33:35.470 dimmer. It's not a subtle effect, but he 844 00:33:35.470 --> 00:33:37.350 was the one who was able to explain it. 845 00:33:38.630 --> 00:33:41.110 Despite his challenges. He was someone with 846 00:33:41.350 --> 00:33:44.310 certain physical disabilities. He was someone 847 00:33:44.310 --> 00:33:46.680 who had a very difficult life. But he had 848 00:33:46.680 --> 00:33:48.560 such a visionary intellect at the time to 849 00:33:48.560 --> 00:33:50.720 come up with the explanation that this 850 00:33:50.720 --> 00:33:52.920 periodic variability and the style of it and 851 00:33:52.920 --> 00:33:55.000 the frequency and the depth of it being so 852 00:33:55.000 --> 00:33:57.760 repeatable was because this was actually 853 00:33:57.840 --> 00:34:00.560 two objects going around each other. Ties in 854 00:34:00.560 --> 00:34:02.160 with the exoplanet chat we had earlier, 855 00:34:02.320 --> 00:34:04.480 because in a way, this is the indirect 856 00:34:04.640 --> 00:34:07.120 discovery of the binarity of Algol. 857 00:34:07.520 --> 00:34:09.160 You don't know that there are two stars there 858 00:34:09.160 --> 00:34:10.960 because you t two stars separately. They're 859 00:34:10.960 --> 00:34:13.239 circles close together. You can't separate 860 00:34:13.239 --> 00:34:16.079 them with telescopes, modular, hugely massive 861 00:34:16.079 --> 00:34:18.399 interferometers we have today. But you can 862 00:34:18.399 --> 00:34:20.919 infer the two stars there by the 863 00:34:20.919 --> 00:34:23.439 extrinsic variability, the variability of the 864 00:34:23.439 --> 00:34:25.439 light we receive because one blocks light 865 00:34:25.439 --> 00:34:28.199 from the other, fundamentally. So that also 866 00:34:28.919 --> 00:34:31.599 causes cyclical variations in 867 00:34:31.599 --> 00:34:33.199 brightness. But it's not the star in this 868 00:34:33.199 --> 00:34:36.199 case varying. It's a result of the 869 00:34:36.199 --> 00:34:38.039 environment around the star blocking some of 870 00:34:38.039 --> 00:34:38.289 the light. 871 00:34:39.640 --> 00:34:42.120 Andrew Dunkley: Yeah. Okay, so the answer to 872 00:34:42.120 --> 00:34:44.320 Casey's questions are, uh, fundamentally, 873 00:34:44.320 --> 00:34:46.129 yes, um, 874 00:34:46.840 --> 00:34:49.680 stars. Most stars probably have some sort of 875 00:34:49.680 --> 00:34:52.480 variability, some more than others. Uh, the 876 00:34:52.480 --> 00:34:55.240 solar cycles are caused by the buildup 877 00:34:55.240 --> 00:34:57.800 of, um, activity 878 00:34:59.000 --> 00:35:01.920 and um. Yeah. Does every type of 879 00:35:01.920 --> 00:35:03.400 star go through solar cycling? 880 00:35:03.400 --> 00:35:05.220 Jonti Horner: Probably. Does it? It's one of. Like I said, 881 00:35:05.220 --> 00:35:06.540 it's one of the big challenges for us with 882 00:35:06.540 --> 00:35:08.420 our radial velocity work. Looking for planet 883 00:35:08.420 --> 00:35:11.260 trans is filtering out the stellar 884 00:35:11.260 --> 00:35:12.820 cycles and that's particularly a problem for 885 00:35:12.820 --> 00:35:14.740 finding planets like Jupiter on a Jupiter 886 00:35:14.740 --> 00:35:17.020 like orbit. Jupiter goes around the sun every 887 00:35:17.020 --> 00:35:19.820 11.86 years. The solar cycle is about 888 00:35:19.820 --> 00:35:22.780 11 years. It's m hard to disentangle the two. 889 00:35:23.180 --> 00:35:25.860 There's also a fascinating branch of science 890 00:35:25.860 --> 00:35:27.660 and one of my colleagues at Uni SQ is one of 891 00:35:27.660 --> 00:35:29.660 the world's experts in this. Um, Professor 892 00:35:29.660 --> 00:35:32.400 Simon Murphy. This is a discipline called 893 00:35:32.400 --> 00:35:35.160 asteroseismology. We know about the 894 00:35:35.160 --> 00:35:37.560 Earth's interior because of earthquakes. We 895 00:35:37.560 --> 00:35:39.120 can figure out the crust, the core, the 896 00:35:39.120 --> 00:35:41.200 mantle by how different types of seismic 897 00:35:41.200 --> 00:35:43.240 waves pass through the Earth's interior. So 898 00:35:43.240 --> 00:35:44.920 we'll listen to the Earth ringing like a bell 899 00:35:44.920 --> 00:35:46.439 after an earthquake and we can use that 900 00:35:46.439 --> 00:35:48.840 information to sense what the interior 901 00:35:48.840 --> 00:35:51.440 structure is and how it varies. The science 902 00:35:51.440 --> 00:35:53.680 of astroseismology is doing the same kind of 903 00:35:53.680 --> 00:35:55.480 thing with stars, looking at how they wibble 904 00:35:55.480 --> 00:35:58.150 and wobble to map out their interior and 905 00:35:58.150 --> 00:35:59.910 understand it. And that's fundamentally tied 906 00:35:59.910 --> 00:36:02.350 to the variability. Now Simon's got a couple 907 00:36:02.350 --> 00:36:04.430 of PhD students working with him and doing 908 00:36:04.430 --> 00:36:06.830 some fabulous work, um, including 909 00:36:07.790 --> 00:36:09.350 Guy, um, called Tom Love, who's down in New 910 00:36:09.350 --> 00:36:10.950 Zealand, who's an amateur astronomer there, 911 00:36:10.950 --> 00:36:13.390 doing a PhD, just finishing up with us. Where 912 00:36:13.390 --> 00:36:15.590 they're looking with Simon at these 913 00:36:15.590 --> 00:36:18.270 asteroseismology, wibbly wobbliness and also 914 00:36:18.270 --> 00:36:20.950 at the variability of stars. Looking 915 00:36:20.950 --> 00:36:23.670 at a group of stars called the Delta Scuti 916 00:36:23.670 --> 00:36:25.740 stars, which are a particular type of 917 00:36:25.740 --> 00:36:28.380 oscillating, varying vibrating 918 00:36:28.460 --> 00:36:31.340 star, looking at how their interiors behave, 919 00:36:31.340 --> 00:36:33.500 looking at how old they are. So we can better 920 00:36:33.500 --> 00:36:36.060 understanding of the physics going on and a 921 00:36:36.060 --> 00:36:38.380 better understanding of where these stars sit 922 00:36:38.380 --> 00:36:41.060 in the storey of stellar lives. So this kind 923 00:36:41.060 --> 00:36:44.020 of question is one that leads 924 00:36:44.020 --> 00:36:46.380 to whole, uh, rafts of amazing science that's 925 00:36:46.380 --> 00:36:47.700 been done. And I think like everything we 926 00:36:47.700 --> 00:36:50.140 discuss on the show, these questions are all, 927 00:36:50.290 --> 00:36:52.290 all entryways to rabbit holes that can go as 928 00:36:52.290 --> 00:36:53.170 deep as you want to. 929 00:36:54.290 --> 00:36:57.290 Andrew Dunkley: Yes, absolutely. There you are, 930 00:36:57.290 --> 00:36:59.070 Casey. Thanks for the question, really, uh, 931 00:36:59.370 --> 00:37:01.690 really interesting. And um, yeah, it's 932 00:37:01.690 --> 00:37:02.170 fascinating. 933 00:37:02.170 --> 00:37:04.730 Stars. I, I've been spending a lot of time 934 00:37:04.730 --> 00:37:07.570 outside of my telescope recently, uh, and 935 00:37:07.970 --> 00:37:09.970 photographing where I can 936 00:37:11.170 --> 00:37:13.410 some of the, the big stars that are visible. 937 00:37:13.550 --> 00:37:16.410 Um, um, I think I did I get serious 938 00:37:16.410 --> 00:37:18.610 recently. I can't remember. I've got a couple 939 00:37:18.610 --> 00:37:20.330 of good ones. I got Alpha Centauri the other 940 00:37:20.330 --> 00:37:23.270 night, which turned out really well. Uh, but 941 00:37:23.270 --> 00:37:24.950 yeah, thanks for the question, Casey. If you 942 00:37:24.950 --> 00:37:27.030 have questions for us, please send them in 943 00:37:27.030 --> 00:37:29.950 via our website spacenutspodcast.com 944 00:37:30.350 --> 00:37:32.590 and click on the Ask me anything button at 945 00:37:32.590 --> 00:37:35.070 the top. It's labelled ama. You can leave 946 00:37:35.150 --> 00:37:37.310 text or audio messages. If you've got a 947 00:37:37.310 --> 00:37:39.030 device with a microphone, you're all set. 948 00:37:39.030 --> 00:37:41.550 Such as a, I don't know, cell phone, mobile 949 00:37:41.550 --> 00:37:44.550 phone, um, tablet, anything like that. 950 00:37:44.550 --> 00:37:47.360 Or your computer. The got built in mics 951 00:37:47.360 --> 00:37:49.560 these days and just tell us who you are and 952 00:37:49.560 --> 00:37:51.040 where you're from and we'd be happy to try 953 00:37:51.040 --> 00:37:53.920 and solve your riddles. Uh, and have a 954 00:37:53.920 --> 00:37:55.160 look around while you're there. Cheque out 955 00:37:55.160 --> 00:37:56.960 the shop. Cheque out. Uh, Astronomy 956 00:37:56.960 --> 00:37:58.600 AstroDailyPod. Maybe sign up for your daily 957 00:37:58.600 --> 00:38:01.240 feed of astronomical news and 958 00:38:01.320 --> 00:38:03.360 click the supporter tab if you'd like to help 959 00:38:03.360 --> 00:38:06.360 us out. That is totally optional. Uh, and 960 00:38:06.360 --> 00:38:08.200 thank you Jonty for all your help today. 961 00:38:08.360 --> 00:38:09.800 Jonti Horner: Absolute pleasure. It's always good to have a 962 00:38:09.800 --> 00:38:10.120 chat. 963 00:38:10.680 --> 00:38:12.910 Andrew Dunkley: We'll see you soon when we talk, uh, 964 00:38:12.910 --> 00:38:15.280 Astrobiology Part two. 965 00:38:15.770 --> 00:38:17.960 Uh, that is Professor Johnty Horner from the 966 00:38:17.960 --> 00:38:20.950 University of Southern Queensland. And uh, 967 00:38:20.950 --> 00:38:23.160 thanks to Huw in the studio, couldn't uh, be 968 00:38:23.160 --> 00:38:26.160 with us today? Huw? Um, he's an ex radio 969 00:38:26.160 --> 00:38:28.160 guy so he thinks he's a star, 970 00:38:28.970 --> 00:38:31.440 uh, which means his equator rotates more than 971 00:38:31.440 --> 00:38:33.200 his north and south and he's back in hospital 972 00:38:33.200 --> 00:38:36.120 with a twisted bow. And from me, Andrew 973 00:38:36.120 --> 00:38:38.960 Dunkley. Terrible. Thanks for your company. 974 00:38:38.960 --> 00:38:40.680 We'll catch you on the next episode of Space 975 00:38:40.680 --> 00:38:41.840 Network Nuts. Bye bye. 976 00:38:43.120 --> 00:38:45.400 Jonti Horner: You've been listening to the Space Nuts 977 00:38:45.400 --> 00:38:48.360 podcast available at 978 00:38:48.360 --> 00:38:50.320 Apple Podcasts, Spotify, 979 00:38:50.560 --> 00:38:53.280 iHeartRadio or your favourite podcast 980 00:38:53.280 --> 00:38:55.000 player. You can also stream on 981 00:38:55.000 --> 00:38:56.640 demand@bytes.com. 982 00:38:57.040 --> 00:38:59.080 Andrew Dunkley: this has been another quality podcast 983 00:38:59.080 --> 00:39:01.200 production from bytes.com.