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Cosmic Queries: The Big Crunch, Gravitational Waves, and Planetary Cores
In this engaging Q&A episode of Space Nuts, hosts Andrew Dunkley and Professor Jonti Horner explore a variety of thought-provoking questions from listeners. Delving into the mysteries of the universe, they tackle topics such as the Big Crunch, the nature of gravitational waves, the implications of shifting magnetic poles, and the intriguing composition of gas and ice giants.
Episode Highlights:
- The Big Crunch and Light: Andrew and Jonti discuss the concept of the Big Crunch, examining how light and energy would behave as the universe contracts. They explore the potential for a reverse Big Bang scenario and the scientific implications of such a cataclysmic event.
- Gravitational Waves Interference: Listener Bob poses a fascinating question about what happens when gravitational waves intersect. The hosts explain the interference patterns that could arise and the complexities involved in understanding these phenomena, especially in the context of current gravitational wave detection technology.
- Shifting Magnetic Poles: Paddy's query about the behavior of Earth's magnetic field during a pole flip leads to a discussion on the historical occurrences of geomagnetic reversals and their effects on the planet. Andrew and Jonti clarify misconceptions and provide insights into the potential impacts on technology and life on Earth.
- Richie Cores of Gas and Ice Giants: Martin's inquiry into the composition of gas and ice giants prompts a deep dive into planetary formation theories. The hosts discuss how scientists determine whether these planets have rocky cores and what alternative structures might exist within them, shedding light on the complexity of our solar system.
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Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
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00:00:02 --> 00:00:03 Andrew Dunkley: Hi there. Thanks again for joining us. This
00:00:03 --> 00:00:06 is Space Nuts, a Q and A edition. My name is
00:00:06 --> 00:00:08 Andrew Dunkley, your host. Uh, terrific to
00:00:08 --> 00:00:11 have your company. Questions that we will be
00:00:11 --> 00:00:14 answering on today's program include the Big
00:00:14 --> 00:00:16 Crunch, gravitational waves,
00:00:16 --> 00:00:19 shifting magnetic poles, uh,
00:00:19 --> 00:00:22 the use of the term dust. Somebody's got
00:00:22 --> 00:00:25 maybe an issue with that. And questions
00:00:25 --> 00:00:28 about gas and ice giants and why do we
00:00:28 --> 00:00:30 think they've got rocky cores. That's all
00:00:30 --> 00:00:32 coming up on this episode of space nuts.
00:00:33 --> 00:00:35 Voice Over Guy: 15 seconds. Guidance is internal.
00:00:35 --> 00:00:38 10, 9. Ignition
00:00:38 --> 00:00:41 sequence time. Space nuts. 5, 4, 3,
00:00:41 --> 00:00:44 2. 1, 2, 3, 4, 5, 5, 4,
00:00:44 --> 00:00:47 3, 2, 1. Space nuts. Astronauts It
00:00:47 --> 00:00:47 feels good.
00:00:48 --> 00:00:51 Andrew Dunkley: And joining us for what will be the last time
00:00:51 --> 00:00:54 in a little while, because Fred's coming back
00:00:54 --> 00:00:56 next week, Jonti Horner, professor of
00:00:56 --> 00:00:57 astrophysics at the University of Southern
00:00:57 --> 00:00:59 Queensland. Hi, Jonti.
00:00:59 --> 00:01:00 Jonti Horner: Good afternoon. How are you going?
00:01:00 --> 00:01:02 Andrew Dunkley: Ah, uh, pretty good. And you?
00:01:03 --> 00:01:05 Jonti Horner: Uh, not too bad, you know, dealing with the
00:01:05 --> 00:01:07 usual kind of too much work, not enough fun.
00:01:07 --> 00:01:10 Looking forward to a trip to a conference
00:01:10 --> 00:01:11 next week. I'm down to the Australian Space
00:01:11 --> 00:01:13 Research Conference, which is always my
00:01:13 --> 00:01:16 favorite meeting of the year. So it's perfect
00:01:16 --> 00:01:17 timing for Fred to return because I wouldn't
00:01:17 --> 00:01:19 have been easily available next week anyway.
00:01:19 --> 00:01:21 And, um, time to hand over. And everybody
00:01:21 --> 00:01:23 listening can breathe a huge sigh of relief
00:01:23 --> 00:01:25 because normality has been restored.
00:01:26 --> 00:01:27 Andrew Dunkley: Ah, no, it's not like that.
00:01:27 --> 00:01:30 Uh, in fact, um, in fact, that's where we can
00:01:30 --> 00:01:32 start because we, uh, do have some
00:01:32 --> 00:01:35 comments from the audience. Uh, this came
00:01:35 --> 00:01:38 from Sam in British Columbia. He says, I just
00:01:38 --> 00:01:40 wanted to say how helpful I
00:01:41 --> 00:01:43 found the answer to the Lagrange points in
00:01:43 --> 00:01:44 Mass question
00:01:46 --> 00:01:48 and how much I enjoy Johnny Horner's
00:01:48 --> 00:01:51 explanations, musings and answers. I know
00:01:51 --> 00:01:53 sometimes they seem a little more detailed
00:01:53 --> 00:01:56 than chatty, but I really enjoy that
00:01:56 --> 00:01:58 extra detail and context. I found the spatial
00:01:58 --> 00:02:01 contours explanation extremely useful. Thank
00:02:01 --> 00:02:03 you. So, um, you got a bit of a fan there.
00:02:04 --> 00:02:06 And another comment that I came across
00:02:06 --> 00:02:09 on our, um, podcast
00:02:09 --> 00:02:12 group Facebook page. I appreciated all the
00:02:12 --> 00:02:14 attention Andrew and Jonti devoted to the
00:02:14 --> 00:02:16 government shutdown. My family suffered
00:02:16 --> 00:02:19 personally. That came from Martin. Although,
00:02:19 --> 00:02:20 uh, there was someone else who didn't
00:02:20 --> 00:02:23 appreciate us going down the political line.
00:02:23 --> 00:02:26 But because of the impact that had on NASA
00:02:26 --> 00:02:29 particularly, uh, it was probably something,
00:02:29 --> 00:02:31 uh, that was worth discussing.
00:02:31 --> 00:02:33 Jonti Horner: Yeah, I think it is important. I understand
00:02:33 --> 00:02:36 that people don't like it when you get into
00:02:36 --> 00:02:38 politics too much and to your political
00:02:38 --> 00:02:40 views. But I think in this case it's
00:02:40 --> 00:02:42 something where colleagues of mine were being
00:02:42 --> 00:02:44 directly affected. I know people
00:02:45 --> 00:02:47 who had more than four weeks without pay. And
00:02:47 --> 00:02:50 we're here to talk about what's happening
00:02:50 --> 00:02:52 with space and um, exploration and
00:02:52 --> 00:02:54 research. And when there's something that's
00:02:54 --> 00:02:56 impeding that, it's important to discuss it.
00:02:56 --> 00:02:59 And it's doubly important I think when people
00:02:59 --> 00:03:01 are trying to use it for political capital to
00:03:02 --> 00:03:04 perpetuate lies about alien
00:03:04 --> 00:03:07 spacecraft, you know, um, you need to
00:03:07 --> 00:03:09 set the record straight to correct other
00:03:09 --> 00:03:10 people training into politics when they
00:03:10 --> 00:03:12 shouldn't do so. You know, I appreciate the
00:03:12 --> 00:03:14 comments. I love the positive feedback. I ah,
00:03:14 --> 00:03:16 try and not get too political in terms of my
00:03:16 --> 00:03:18 own views on stuff, but there are some topics
00:03:18 --> 00:03:20 which we do need to cross. And you know, my
00:03:20 --> 00:03:22 heart does go out to those who were directly
00:03:22 --> 00:03:24 impacted by the shutdown for whatever the
00:03:24 --> 00:03:26 reasons the shutdown was happening. It's not
00:03:26 --> 00:03:27 good when you have to go m more than a month
00:03:27 --> 00:03:29 without food, particularly for those families
00:03:29 --> 00:03:31 who have two people who are both government
00:03:31 --> 00:03:33 employees and have children with mouths to
00:03:33 --> 00:03:33 feed.
00:03:34 --> 00:03:35 Andrew Dunkley: Yeah, and we were talking, we're talking
00:03:35 --> 00:03:37 thousands upon thousands of people. So it
00:03:37 --> 00:03:38 wasn't just a handful.
00:03:39 --> 00:03:41 Uh, let's move on to our first set of
00:03:41 --> 00:03:44 questions. Beau in Melbourne has sent us two
00:03:44 --> 00:03:47 questions, uh, via our audio stream.
00:03:47 --> 00:03:49 Uh, let's see what he wants to find out.
00:03:50 --> 00:03:52 Beau: Hello, Andrew and Professor, uh, Jonti
00:03:52 --> 00:03:55 Horner. Is Beau here? Yes. Your second
00:03:55 --> 00:03:57 favorite B.O. from Melbourne, Australia.
00:03:58 --> 00:04:01 I have a question for you, but first I would
00:04:01 --> 00:04:04 like to do a fact check please. Um,
00:04:04 --> 00:04:07 a couple of episodes ago, um, Professor
00:04:07 --> 00:04:10 Watson, uh, talked about the Gnab Gib or
00:04:10 --> 00:04:13 the Big Crunch. And basically he said,
00:04:13 --> 00:04:16 ah, at the end of the Gnab Gib, um, matter
00:04:16 --> 00:04:18 will come closer to one another, uh, as the
00:04:18 --> 00:04:21 effect of gravity takes over and we uh, will
00:04:21 --> 00:04:24 end up in one giant singularity and
00:04:24 --> 00:04:27 collapse. Uh, what he didn't say
00:04:27 --> 00:04:29 was the uh, effect of that on
00:04:29 --> 00:04:32 light. Now my understanding is that
00:04:32 --> 00:04:35 um, obviously as stars and galaxies come
00:04:35 --> 00:04:37 closer together, the sky will get brighter
00:04:37 --> 00:04:40 and brighter and uh, as matter starts to
00:04:40 --> 00:04:43 fuse, uh, will give out more heat and more
00:04:43 --> 00:04:45 uh, light as well. So essentially
00:04:47 --> 00:04:50 will end up in a reverse Big Bang, uh, and
00:04:50 --> 00:04:52 then we will all come to a big blinding,
00:04:52 --> 00:04:55 uh, end, um, both matter and uh,
00:04:55 --> 00:04:58 light coming together in a reverse Big Bang.
00:04:58 --> 00:05:01 So I just wanted to see if that is correct,
00:05:01 --> 00:05:04 uh, regarding light. I'd love to hear
00:05:04 --> 00:05:05 Jonty's view on that.
00:05:06 --> 00:05:09 Um, now my question is related to
00:05:09 --> 00:05:12 gravitational waves. Uh, we
00:05:12 --> 00:05:14 know that gravitational waves, ah,
00:05:14 --> 00:05:17 distort the fabric of space time.
00:05:18 --> 00:05:21 Um, In a wave pattern. We also know
00:05:21 --> 00:05:23 that multiple gravitational wave exist,
00:05:24 --> 00:05:26 um, because there are, you know, black hole
00:05:26 --> 00:05:28 collisions and black hole neutron star
00:05:28 --> 00:05:30 collisions happening, um, throughout the
00:05:30 --> 00:05:33 universe. Now what happens when
00:05:33 --> 00:05:36 those two gravitational waves meet
00:05:36 --> 00:05:38 each other? Um, particularly what would
00:05:38 --> 00:05:41 happen to, um, I guess the interference
00:05:41 --> 00:05:44 patterns as the waves, uh, starts overlapping
00:05:44 --> 00:05:46 each other at the peaks and the troughs
00:05:46 --> 00:05:48 during, do we see any
00:05:49 --> 00:05:51 changes to space time itself?
00:05:52 --> 00:05:55 Do we see, for example, time speed up,
00:05:55 --> 00:05:57 slow down or stop? Do we see gravity,
00:05:58 --> 00:06:00 um, cease or increase
00:06:00 --> 00:06:03 or decrease? Um, um,
00:06:04 --> 00:06:05 just wanted to know what would happen to
00:06:05 --> 00:06:07 space time and that interference patterns,
00:06:07 --> 00:06:09 the peaks to troughs. Um, love to hear
00:06:09 --> 00:06:12 Professor John de Horner's view on that. Um,
00:06:12 --> 00:06:13 thank you very much and please.
00:06:13 --> 00:06:14 Jonti Horner: Keep up your good work.
00:06:15 --> 00:06:17 Andrew Dunkley: Thank you, Beau. Uh, great questions.
00:06:17 --> 00:06:20 Uh, we'll probably start with the big crunch
00:06:20 --> 00:06:22 and the effect on light. Now,
00:06:22 --> 00:06:25 um, I suppose we have to consider
00:06:26 --> 00:06:28 the timing of events because the universe
00:06:28 --> 00:06:31 is still expanding, Although now they're
00:06:31 --> 00:06:33 starting to think that acceleration is no
00:06:33 --> 00:06:36 longer speeding up, it's slowing down
00:06:36 --> 00:06:38 or that the expansion, um, but
00:06:38 --> 00:06:41 it's still expanding. Far as we're aware at
00:06:41 --> 00:06:44 this point in time. Uh, Fred has told us in
00:06:44 --> 00:06:46 the past that it will expand to the point
00:06:46 --> 00:06:48 where everything will move so far apart that
00:06:48 --> 00:06:51 we will just be by ourselves in the universe,
00:06:51 --> 00:06:53 in blackness. Um, so
00:06:54 --> 00:06:55 the question is, is that still going to
00:06:55 --> 00:06:58 happen? And even if it
00:06:58 --> 00:07:01 does, and there is a big crunch,
00:07:01 --> 00:07:03 what's going to happen to all the light
00:07:03 --> 00:07:05 anyway? So it's a really
00:07:05 --> 00:07:07 fascinating area.
00:07:07 --> 00:07:10 Jonti Horner: It is, and it's really complicated. It's
00:07:10 --> 00:07:12 dealing with things that are incredibly far
00:07:12 --> 00:07:13 in the distant future.
00:07:13 --> 00:07:16 Andrew Dunkley: Um, it is week or the week after, I think.
00:07:16 --> 00:07:18 Jonti Horner: Absolutely. Um, well, with the way that time
00:07:18 --> 00:07:20 seems to pass quicker and quicker as I get
00:07:20 --> 00:07:22 older, it does probably mean that it will be
00:07:22 --> 00:07:25 next week, but it's a difficult one.
00:07:25 --> 00:07:27 So there is still some debate over whether
00:07:27 --> 00:07:30 the universe will continue to expand forever
00:07:30 --> 00:07:32 or whether it will turn around and begin to
00:07:32 --> 00:07:34 collapse. And reminds me of the Arthur C.
00:07:34 --> 00:07:36 Clarke quote about life elsewhere, which I'm
00:07:36 --> 00:07:38 going to butcher and paraphrase in this case,
00:07:39 --> 00:07:41 which is that two possibilities exist and
00:07:41 --> 00:07:44 both are equally terrifying. You know,
00:07:44 --> 00:07:46 either, you know, we expand forever or we
00:07:46 --> 00:07:48 don't. And they're equally scary in many
00:07:48 --> 00:07:50 ways. But assuming that we did collapse back
00:07:50 --> 00:07:53 down to a point. Now that will likely happen
00:07:53 --> 00:07:56 at the point when all the stars have died,
00:07:56 --> 00:07:59 um, when everything has come to an end. And
00:07:59 --> 00:08:01 so you'll probably have a universe full of
00:08:01 --> 00:08:03 non luminous stuff and black holes. And
00:08:03 --> 00:08:05 that's about it maybe so far away in the
00:08:05 --> 00:08:07 future that even the biggest black holes have
00:08:07 --> 00:08:09 evaporated from Hawking radiation. But
00:08:09 --> 00:08:12 whatever will happen, whatever is left will
00:08:12 --> 00:08:14 be squashed into an ever smaller place that
00:08:14 --> 00:08:16 will include all of the radiation that's
00:08:16 --> 00:08:19 going through the universe. Now we see the
00:08:19 --> 00:08:21 cosmic microwave background, and we see it
00:08:21 --> 00:08:23 at, uh, um, very long wavelengths, at
00:08:23 --> 00:08:26 microwave wavelengths, with an approximate
00:08:26 --> 00:08:28 temperature of like 2.9 Kelvin or something
00:08:28 --> 00:08:30 like that. I can't remember the exact number.
00:08:30 --> 00:08:32 That's because that light is redshifted,
00:08:32 --> 00:08:34 because the universe has expanded and
00:08:34 --> 00:08:36 stretched that energy out. If the universe
00:08:36 --> 00:08:39 collapsed back in, you'd be going the
00:08:39 --> 00:08:40 opposite. You'd be blue, shifting all the
00:08:40 --> 00:08:42 radiation. So as you squash the universe into
00:08:42 --> 00:08:45 an ever smaller space because of the quirk of
00:08:45 --> 00:08:47 the fact that there is nothing outside the
00:08:47 --> 00:08:49 universe, the universe is both infinite and
00:08:49 --> 00:08:52 finite at the same time. So you can't be
00:08:52 --> 00:08:53 outside the universe, because that's
00:08:53 --> 00:08:56 meaningless. All of the light and all of the
00:08:56 --> 00:08:57 energy in the universe will remain in the
00:08:57 --> 00:08:59 universe as the universe gets smaller. So my
00:08:59 --> 00:09:02 understanding is that as you get towards a
00:09:02 --> 00:09:04 high, hypothetical Big Crunch, the
00:09:04 --> 00:09:05 temperature, the pressure and the density
00:09:05 --> 00:09:07 will just increase and increase and increase.
00:09:07 --> 00:09:09 And, um, the universe will end in a very,
00:09:09 --> 00:09:11 very hot mess, effectively. So it will be
00:09:11 --> 00:09:13 like running the Big Bang backwards. There'll
00:09:13 --> 00:09:15 be differences. We don't fully understand
00:09:15 --> 00:09:18 what will happen and how it will all go. We
00:09:18 --> 00:09:20 don't know whether that would trigger another
00:09:20 --> 00:09:22 Big Bang, because, to be honest, we don't
00:09:22 --> 00:09:24 know enough about that time of the universe.
00:09:24 --> 00:09:26 And certainly I'm nowhere near, uh, the
00:09:26 --> 00:09:28 forefront of researching that to give a more
00:09:28 --> 00:09:30 educated opinion. But I know that the closer
00:09:30 --> 00:09:32 you get to the Big Bang looking back, the
00:09:32 --> 00:09:34 harder it is to be exactly sure what
00:09:34 --> 00:09:35 happened. Because the less information we
00:09:35 --> 00:09:38 have and the harder you're having to push our
00:09:38 --> 00:09:40 understanding of physics to the point it
00:09:40 --> 00:09:42 breaks down. And the same will be true going
00:09:42 --> 00:09:43 the other way. You're just reaching
00:09:43 --> 00:09:46 temperatures and pressures that make no
00:09:46 --> 00:09:48 sense. You have periods when different
00:09:48 --> 00:09:51 forces were combined into a single force. I
00:09:51 --> 00:09:53 do not know with my level of knowledge
00:09:53 --> 00:09:55 whether the expectation is that those
00:09:55 --> 00:09:57 transitions would happen at the same point
00:09:57 --> 00:09:59 going back as they did coming forward.
00:10:00 --> 00:10:03 So I think that the exact details of
00:10:03 --> 00:10:06 how the Big Crunch would go, uh, are still
00:10:06 --> 00:10:08 very much up for debate if it were to happen.
00:10:08 --> 00:10:10 But I think it's very fair to say that it
00:10:10 --> 00:10:12 will be very bright, very hot, very
00:10:12 --> 00:10:14 unpleasant, and we wouldn't be around to
00:10:14 --> 00:10:15 enjoy it.
00:10:15 --> 00:10:18 Andrew Dunkley: No, definitely. Well, yeah. It's like the
00:10:18 --> 00:10:19 restaurant at the end of the universe in
00:10:19 --> 00:10:22 hitchhikers. You know, if we're not going
00:10:22 --> 00:10:25 to sit there and enjoy a wonderful dinner
00:10:25 --> 00:10:26 while it all happens around us, it's um,
00:10:27 --> 00:10:30 yeah, I'd say humanity be long gone by then
00:10:30 --> 00:10:32 or transition into something else, I don't
00:10:32 --> 00:10:34 know. But I certainly don't think it would be
00:10:34 --> 00:10:36 like rewinding a film and watching it all
00:10:36 --> 00:10:39 just happen in reverse. There'll be some
00:10:39 --> 00:10:41 cataclysmic effect for sure.
00:10:42 --> 00:10:44 Uh, the main question Beau wanted answered
00:10:44 --> 00:10:46 was about gravitational waves. And they're
00:10:46 --> 00:10:48 out there, they're happening, we're detecting
00:10:48 --> 00:10:50 them all the time. Um,
00:10:51 --> 00:10:53 but what happens when they cross each other?
00:10:53 --> 00:10:55 What's the effect? I would equate it to
00:10:55 --> 00:10:58 throwing two pebbles in a pond and the waves
00:10:58 --> 00:11:00 just cross over and that'd be it.
00:11:00 --> 00:11:02 Jonti Horner: Yeah, I've done a bit of reading around on
00:11:02 --> 00:11:04 this one because honestly, I haven't got the
00:11:04 --> 00:11:07 foggies coming into this. So my
00:11:07 --> 00:11:10 default assumption is that, ah, the waves
00:11:10 --> 00:11:11 would interfere in the same way that
00:11:11 --> 00:11:13 electromagnetic waves interfere in that
00:11:13 --> 00:11:15 they'd add, um, together. So you'd get a peak
00:11:15 --> 00:11:17 and a trough would cancel out a peak and a
00:11:17 --> 00:11:20 peak would lead to constructive interference.
00:11:20 --> 00:11:22 So you'd get bigger and smaller
00:11:23 --> 00:11:25 instantaneous amplitudes.
00:11:26 --> 00:11:28 You'd get an interference pattern reading
00:11:28 --> 00:11:31 around online. Um, it seems that that is
00:11:31 --> 00:11:34 broadly the consensus, so long as you
00:11:34 --> 00:11:36 are a long way away from a strong
00:11:36 --> 00:11:38 gravitational field, so you're a long way
00:11:38 --> 00:11:40 away from the source of these things, or
00:11:40 --> 00:11:42 you're a long way away from something like a
00:11:42 --> 00:11:45 black hole. And apparently the physics of
00:11:45 --> 00:11:48 the general relativistic treatment of
00:11:48 --> 00:11:51 this gets incredibly gnarly. When you get
00:11:51 --> 00:11:53 to those kind of situations and nobody's
00:11:53 --> 00:11:55 really sure what happened, the maths gets
00:11:55 --> 00:11:57 difficult. And the point is you're pushing
00:11:57 --> 00:11:58 the boundaries of what we know and what we
00:11:58 --> 00:12:01 can observe into the unknown. So what you
00:12:01 --> 00:12:03 have to do is you have to develop possible
00:12:04 --> 00:12:07 answers and um, test them, build
00:12:07 --> 00:12:09 theories, make predictions, see what happens.
00:12:09 --> 00:12:12 But I think in general, if, for example,
00:12:12 --> 00:12:14 one of our big gravitational wave detectors,
00:12:14 --> 00:12:17 two waves came in at once, you would
00:12:17 --> 00:12:20 probably, at that instantaneous location, you
00:12:20 --> 00:12:21 get an extra large peak or an extra large
00:12:21 --> 00:12:24 trough, or they'd cancel out. But because you
00:12:24 --> 00:12:26 might have more than one detector around the
00:12:26 --> 00:12:28 earth, thanks to the directions of motion,
00:12:28 --> 00:12:30 you'd only have that specific type of
00:12:30 --> 00:12:33 interference at that specific detector. So it
00:12:33 --> 00:12:35 will probably give us a signal that, if
00:12:35 --> 00:12:36 you've got multiple gravitational wave
00:12:36 --> 00:12:39 detectors around the globe, would be distinct
00:12:39 --> 00:12:41 and identifiable and would allow you to test
00:12:41 --> 00:12:44 that interference, if that makes sense.
00:12:44 --> 00:12:46 Now my understanding of the typical
00:12:46 --> 00:12:48 gravitational wave events that we see is that
00:12:48 --> 00:12:50 you've, ah, got these waves that are building
00:12:50 --> 00:12:53 up from inspiraling neutron stars or black
00:12:53 --> 00:12:54 holes, or a neutron star and a black hole
00:12:54 --> 00:12:56 about to collide, where you get
00:12:57 --> 00:13:00 very low frequency, very low amplitude waves
00:13:00 --> 00:13:02 that build to a sharp crescendo, which is why
00:13:02 --> 00:13:05 you get these attempts to sonify the data,
00:13:05 --> 00:13:07 where you get this rising whistle, rising in
00:13:07 --> 00:13:10 pitch and rising in volume. So the idea is
00:13:10 --> 00:13:12 that you get a lot of small waves first and
00:13:12 --> 00:13:13 then you get a really big build to a
00:13:13 --> 00:13:16 crescendo and then fall off. So typically you
00:13:16 --> 00:13:17 probably wouldn't observe this happening with
00:13:17 --> 00:13:20 our current technology unless you have the
00:13:20 --> 00:13:22 incredible good fortune to have two events
00:13:23 --> 00:13:25 where you get the peak arriving at the same
00:13:25 --> 00:13:27 time. And that'll be the interesting test.
00:13:28 --> 00:13:30 So, yeah, to summarize, I don't think anybody
00:13:30 --> 00:13:32 fully knows, but because you're pushing the
00:13:32 --> 00:13:34 bounds of what is known. But it seems to be
00:13:34 --> 00:13:36 that the consensus is that in open space,
00:13:36 --> 00:13:39 away from really significant masses or away
00:13:39 --> 00:13:42 from the sources of the waves, they would
00:13:42 --> 00:13:43 just have normal kind of constructive and
00:13:43 --> 00:13:46 destructive interference as the peaks and
00:13:46 --> 00:13:47 troughs go across each other.
00:13:48 --> 00:13:51 Andrew Dunkley: Okie dokie. There you are. Uh, thank you, Bo.
00:13:51 --> 00:13:52 Great question.
00:13:54 --> 00:13:57 Jonti Horner: 0G and I feel fine. Space nuts.
00:13:58 --> 00:14:00 Andrew Dunkley: Uh, our next question comes from Paddy,
00:14:01 --> 00:14:04 uh, reflecting on the discussion around the
00:14:04 --> 00:14:06 shifting of the magnetic poles. If they were
00:14:06 --> 00:14:09 to flip, how would the field
00:14:09 --> 00:14:12 behave as it transitioned? Uh,
00:14:12 --> 00:14:15 the equator, uh, would it
00:14:15 --> 00:14:17 spin with the Earth's, uh, rotation? Would it
00:14:17 --> 00:14:20 let in more debris, solar radiation and
00:14:20 --> 00:14:23 or, uh, uh, cosmic particles?
00:14:23 --> 00:14:26 And to go full Hollywood disaster
00:14:26 --> 00:14:29 movie, given the, uh, visual representation
00:14:29 --> 00:14:31 of the mega magnetic field suggests an apple
00:14:31 --> 00:14:34 shape. Uh, could the funnel of the
00:14:34 --> 00:14:37 magnetic field become like a magnifying glass
00:14:37 --> 00:14:39 scorching the earth as it crosses the
00:14:39 --> 00:14:39 equator?
00:14:40 --> 00:14:40 Jonti Horner: Love, uh, the show.
00:14:40 --> 00:14:42 Andrew Dunkley: Keep up the great work. That's from Paddy.
00:14:42 --> 00:14:44 He's put a bit of thought into this and I
00:14:44 --> 00:14:47 love the sci fi component. But, um,
00:14:47 --> 00:14:50 yeah, is this in your
00:14:50 --> 00:14:51 ballpark, this kind of thing?
00:14:52 --> 00:14:55 Jonti Horner: Uh, as an astrophysicist, it's
00:14:55 --> 00:14:57 closer to my ballpark than the gnabs and the
00:14:57 --> 00:15:00 dark energy stuff. I mean, I'm still not, I
00:15:00 --> 00:15:02 would argue, an expert, but I'm close to it
00:15:02 --> 00:15:03 and I have done a bit of reading. Now what I
00:15:03 --> 00:15:06 would say here is actually, um, the
00:15:06 --> 00:15:09 Wikipedia page for geomagnetic reversal
00:15:09 --> 00:15:11 is a really interesting read. It's very in
00:15:11 --> 00:15:13 depth and contains a lot of good historical
00:15:13 --> 00:15:16 information. So while I acknowledge Wikipedia
00:15:16 --> 00:15:17 is very much secondary rather than primary
00:15:17 --> 00:15:20 Resource, I think for topics like this and
00:15:20 --> 00:15:22 topics in astronomy, the articles tend to
00:15:22 --> 00:15:24 stay fairly on task and fairly accurate
00:15:24 --> 00:15:26 because people will fix them if they break
00:15:26 --> 00:15:28 very quickly. Um, and that
00:15:29 --> 00:15:30 reading that should, to some degree,
00:15:30 --> 00:15:32 immediately put Paddy's mind at rest in terms
00:15:32 --> 00:15:34 of the Earth getting baked or scorched or
00:15:34 --> 00:15:36 Hollywood disaster movie type things
00:15:36 --> 00:15:38 happening at the time of a field reversal.
00:15:38 --> 00:15:40 Because we've had at least
00:15:40 --> 00:15:43 183reversals in the last 83 million
00:15:43 --> 00:15:45 years, which means that these things have
00:15:45 --> 00:15:48 happened regularly through the period of
00:15:48 --> 00:15:51 the Earth being inhabited and have not caused
00:15:51 --> 00:15:53 any mass extinctions. There have been some
00:15:53 --> 00:15:56 suggestions that periods where
00:15:56 --> 00:15:58 you get magnetic field locked in one
00:15:58 --> 00:16:01 direction for very long periods of time,
00:16:01 --> 00:16:03 which last happened during the Cretaceous
00:16:03 --> 00:16:06 period, where you had something like a 50
00:16:06 --> 00:16:08 million year period where the magnetic field
00:16:08 --> 00:16:10 didn't flip. There have been some suggestions
00:16:10 --> 00:16:13 that when those very long periods of time
00:16:13 --> 00:16:16 come to an end, that it could trigger a
00:16:16 --> 00:16:18 certain amount of added volcanic
00:16:18 --> 00:16:21 activity and stuff like this. And that may
00:16:21 --> 00:16:23 lead to some traumas for life, but never
00:16:23 --> 00:16:26 quite at the level of a mass extinction. And
00:16:26 --> 00:16:29 there's a couple of beautiful, um, figures
00:16:29 --> 00:16:30 plotting out the
00:16:31 --> 00:16:34 flips that have happened going back about
00:16:34 --> 00:16:36 180 million years,
00:16:37 --> 00:16:39 talking about these periods where the
00:16:39 --> 00:16:41 magnetic field gets locked into a single
00:16:41 --> 00:16:43 orientation. Nothing much happens for a long
00:16:43 --> 00:16:46 time, which is known as a superchron. And
00:16:46 --> 00:16:48 then you get other times when you get more
00:16:48 --> 00:16:51 flips in a short period than typical. There's
00:16:51 --> 00:16:53 one here, 51 reversals occurred during a 12
00:16:53 --> 00:16:56 million period centered on, I think it's 15
00:16:56 --> 00:16:59 million years ago. So you get periods where
00:16:59 --> 00:17:01 there's a lot more of them happening. You
00:17:01 --> 00:17:03 also get periods where it tries to flip and
00:17:03 --> 00:17:05 then goes back to how it was. Uh, so the idea
00:17:05 --> 00:17:07 that you had from school that the Earth's
00:17:07 --> 00:17:09 magnetic field is essentially, we have a
00:17:09 --> 00:17:10 giant bar magnet in the middle of the Earth,
00:17:10 --> 00:17:12 and it's very controlled and static. As we
00:17:12 --> 00:17:14 said on the podcast a few weeks ago, that has
00:17:14 --> 00:17:17 fallen by the wayside. Now, the magnetic
00:17:17 --> 00:17:20 field being generated by wibbly wobbliness
00:17:20 --> 00:17:22 and convection currents and all sorts in the
00:17:22 --> 00:17:24 Earth's outer core through a dynamo effect is
00:17:24 --> 00:17:27 fairly well understood. And, um, these field
00:17:27 --> 00:17:30 reversals are something that falls out
00:17:30 --> 00:17:32 naturally in modeling. So people have not had
00:17:32 --> 00:17:34 to hugely increase the capacity of their
00:17:34 --> 00:17:36 modeling ability when modeling the behavior
00:17:36 --> 00:17:39 of the outer core to make them happen. They
00:17:39 --> 00:17:41 happen naturally from the way the models are
00:17:41 --> 00:17:43 set up, which is really interesting. What
00:17:43 --> 00:17:46 seems to happen is that, uh, unlike the sun,
00:17:46 --> 00:17:48 where you get the magnetic field reversals at
00:17:48 --> 00:17:50 about the time when the Sun's magnetic field
00:17:50 --> 00:17:52 gets the strongest. And that's all down to
00:17:52 --> 00:17:55 the tangling up of the magnetic field lines
00:17:55 --> 00:17:57 as the sun rotates as a fluid body, not a
00:17:57 --> 00:18:00 solid body. On the Earth, the magnetic
00:18:00 --> 00:18:02 field reversals tend to occur at times of low
00:18:02 --> 00:18:05 magnetic field. So what tends to happen is
00:18:05 --> 00:18:06 that the dynamo becomes less effective.
00:18:07 --> 00:18:09 Things become confused in the inner core. You
00:18:09 --> 00:18:11 can even get periods where you get multiple
00:18:11 --> 00:18:14 north and south poles while the magnetic
00:18:14 --> 00:18:16 field in the dynamo breaks down and reasserts
00:18:16 --> 00:18:18 itself, and then it flips over. There is some
00:18:18 --> 00:18:20 discussion over how quick this can happen
00:18:20 --> 00:18:23 with most studies seem to suggest it can take
00:18:23 --> 00:18:25 anything from 2 to 12 years.
00:18:26 --> 00:18:28 But sometimes it could be quicker, sometimes
00:18:28 --> 00:18:30 it could be slower. It's all complex, and
00:18:30 --> 00:18:33 it's because it's all tied to this turbulent
00:18:33 --> 00:18:35 roiling of the liquid metal in the outer
00:18:35 --> 00:18:38 core. What this means is that,
00:18:38 --> 00:18:40 uh, firstly, if you shift where the north and
00:18:40 --> 00:18:42 south magnetic poles of the Earth are, they
00:18:42 --> 00:18:44 will rotate with the Earth. Uh, that's in
00:18:44 --> 00:18:47 fact what we see with pulsars. Why we get the
00:18:47 --> 00:18:49 pulsars is that the magnetic fields and the
00:18:49 --> 00:18:52 rotation axis are not lined up. So you get a
00:18:52 --> 00:18:54 magnetic hotspot on the surface of the
00:18:54 --> 00:18:56 pulsar, uh, where you get the magnetic polis,
00:18:56 --> 00:18:58 where any material around will be funneled
00:18:58 --> 00:19:00 down the magnetic field to hit there. You get
00:19:00 --> 00:19:02 this hot spot. You get lots of radiation
00:19:02 --> 00:19:05 emitted from the poles. And as, uh,
00:19:05 --> 00:19:08 the pulsar rotates, those poles sweep
00:19:08 --> 00:19:10 like lighthouse beams, and we get pulses of
00:19:10 --> 00:19:13 radio waves when that beam sweeps across us.
00:19:13 --> 00:19:15 So it's fairly well understood that the
00:19:15 --> 00:19:17 magnetic field rotates with the Earth. And
00:19:17 --> 00:19:20 therefore, if the
00:19:20 --> 00:19:23 magnetic pole was in Kenya or somewhere like
00:19:23 --> 00:19:25 that, it was somewhere near the equator, it
00:19:25 --> 00:19:27 will be rotating with the Earth. That's kind
00:19:27 --> 00:19:28 of how it would work. And, um, that will
00:19:28 --> 00:19:31 probably happen if the flip was the north
00:19:31 --> 00:19:34 pole wandering to the Earth's south pole. In
00:19:34 --> 00:19:35 reality, though, it seems that these
00:19:35 --> 00:19:38 reversals are more almost like the Earth's
00:19:38 --> 00:19:40 magnetic fields weaken. They become
00:19:40 --> 00:19:43 disestablished, you get all this confusion,
00:19:43 --> 00:19:45 and then a new field establishes itself,
00:19:45 --> 00:19:48 which I think is probably part of the
00:19:48 --> 00:19:51 reason that the flips are even less periodic
00:19:51 --> 00:19:53 than you think. They're talked about as being
00:19:53 --> 00:19:55 totally random. But I suspect that's added to
00:19:55 --> 00:19:57 by the fact that, that if you wipe out the
00:19:57 --> 00:19:59 Earth's magnetic field and turn it on again,
00:19:59 --> 00:20:02 if you imagine you had a 50, 50 chance of it
00:20:02 --> 00:20:04 being north south, and a 50, 50 transmit
00:20:04 --> 00:20:06 being south north, then only half of the Time
00:20:06 --> 00:20:08 it weakened, would you get it flipped to the
00:20:08 --> 00:20:10 other polarity. And so that might be part of
00:20:10 --> 00:20:13 what's going on there. So it's all really,
00:20:13 --> 00:20:16 really complex. What would happen is that we
00:20:16 --> 00:20:18 would get to some degree a greater flux of
00:20:18 --> 00:20:20 radiation hitting the top of the Earth's
00:20:20 --> 00:20:22 atmosphere. The charged particles that get
00:20:22 --> 00:20:24 diverted around us by the magnetic field, it
00:20:24 --> 00:20:27 will get less effective. But it's worth
00:20:27 --> 00:20:29 noting that our atmosphere is incredibly
00:20:29 --> 00:20:32 effective protection for us anyway. I saw one
00:20:32 --> 00:20:34 article saying our atmosphere is as effective
00:20:34 --> 00:20:36 at protecting against the solar wind and
00:20:36 --> 00:20:38 charged particles as a 3 meter layer of
00:20:38 --> 00:20:40 concrete would be. So the atmosphere does a
00:20:40 --> 00:20:43 very, very good job. Uh, which is why it
00:20:43 --> 00:20:46 seems that these magnetic field weakenings
00:20:46 --> 00:20:48 don't lead to m mass extinctions and things.
00:20:48 --> 00:20:50 They will have a bit of an effect on the
00:20:50 --> 00:20:53 upper atmosphere stuff will happen. There
00:20:53 --> 00:20:55 are suggestions that maybe you could get a
00:20:55 --> 00:20:56 little bit of additional atmospheric
00:20:56 --> 00:20:58 stripping happening during these times from
00:20:58 --> 00:21:01 solar radiation, but effectively the impact
00:21:01 --> 00:21:03 would not be that great on the surface of the
00:21:03 --> 00:21:06 Earth. It would probably play merry havoc
00:21:06 --> 00:21:08 with scouts who are doing orienteering and
00:21:08 --> 00:21:10 people doing the Duke of Edinburgh Reward and
00:21:10 --> 00:21:12 things like this where you follow a map and
00:21:12 --> 00:21:13 you've got to use a map and a compass.
00:21:13 --> 00:21:15 Because if the North Pole is in a different
00:21:15 --> 00:21:17 place every year and weaker, uh, that's going
00:21:17 --> 00:21:20 to be a pain for navigation. There would
00:21:20 --> 00:21:21 doubtless be significant effects on
00:21:21 --> 00:21:24 technology, obviously, and we
00:21:24 --> 00:21:26 saw last week with a really good solar storm
00:21:26 --> 00:21:28 and Aurora again, that we are to some degree
00:21:28 --> 00:21:31 at the mercy of big solar storms. We
00:21:31 --> 00:21:32 discussed in the past the likelihood of
00:21:32 --> 00:21:34 events like the Carrington event being a
00:21:34 --> 00:21:36 problem for satellites and for unshielded
00:21:36 --> 00:21:38 electronics on the surface of the Earth. And
00:21:38 --> 00:21:40 if the Earth's magnetic field were weaker or
00:21:40 --> 00:21:43 were in the process of reversing, then an
00:21:43 --> 00:21:44 equal strength solar storm would do more
00:21:44 --> 00:21:47 damage because less of it would be deflected.
00:21:48 --> 00:21:49 Um, but you wouldn't end up with the kind of
00:21:49 --> 00:21:52 giant lens baking strip along the Earth.
00:21:52 --> 00:21:54 Um, fortunately or unfortunately, depending
00:21:54 --> 00:21:55 on your point of view and your love of
00:21:55 --> 00:21:58 Hollywood dramatics, that should be fine.
00:21:59 --> 00:22:00 It would be an interesting event.
00:22:00 --> 00:22:03 There are people who keep suggesting that
00:22:03 --> 00:22:05 this kind of thing is imminent. The problem
00:22:05 --> 00:22:08 there is imminent in geological timescales
00:22:08 --> 00:22:10 doesn't mean imminent on a human timescale.
00:22:10 --> 00:22:12 So the last reversal, I believe, was about
00:22:12 --> 00:22:15 780 years ago. The
00:22:15 --> 00:22:17 average timing of them seems to be out every
00:22:17 --> 00:22:19 half a million years. So people say we're
00:22:19 --> 00:22:22 overdue. That skips the fact
00:22:22 --> 00:22:23 that actually the timings are very random.
00:22:23 --> 00:22:25 It's A bit like waiting for a bus. I use this
00:22:25 --> 00:22:26 analogy all the time. You know, if you've got
00:22:26 --> 00:22:28 a bus due every five minutes, you may wait
00:22:28 --> 00:22:31 half an hour and five come along at once. You
00:22:31 --> 00:22:33 did? No. And, um, with these kind of
00:22:33 --> 00:22:35 reversals, that's exacerbated by the fact
00:22:35 --> 00:22:37 that we tend to get long blocks and short
00:22:37 --> 00:22:39 blocks. So I'm looking just at the last 5
00:22:39 --> 00:22:41 million years. And if you go from 5 million
00:22:41 --> 00:22:44 years ago, um, black on this
00:22:44 --> 00:22:46 plot is the polarity we have now on white is
00:22:46 --> 00:22:49 the other one. 5.01 million years ago, it
00:22:49 --> 00:22:51 flipped so that south was at the top. Then
00:22:51 --> 00:22:54 4.89 million years ago, we had, what
00:22:54 --> 00:22:57 is it, 80 years of our current polarity.
00:22:57 --> 00:22:59 Then it flipped back and we had 17 years.
00:22:59 --> 00:23:02 Then it flipped back for 17 years, back
00:23:02 --> 00:23:05 for 18 years, back for 8
00:23:05 --> 00:23:07 years, and then there was a 60
00:23:08 --> 00:23:09 600 year gap.
00:23:11 --> 00:23:13 And so it's very, very spotty. The last flip
00:23:13 --> 00:23:16 was 780 years ago. Before
00:23:16 --> 00:23:18 that it was only a 12 year gap.
00:23:19 --> 00:23:21 Um, and then there was a very long period
00:23:21 --> 00:23:23 between 1.0, uh, 6 and 1.78 million years
00:23:23 --> 00:23:26 ago, when it was the opposite polarity,
00:23:26 --> 00:23:29 except for a single measurement at 1.19
00:23:29 --> 00:23:30 million years ago, when it was the other way
00:23:30 --> 00:23:33 around. So that was a very short flip. So, in
00:23:33 --> 00:23:35 all honesty, saying that we're overdue for it
00:23:35 --> 00:23:37 is a bit like bumping into somebody grumpy at
00:23:37 --> 00:23:39 the bus stop because the bus is 30 seconds
00:23:39 --> 00:23:41 late. In all honesty, you've got no clue when
00:23:41 --> 00:23:43 that bus is going to arrive. And looking at
00:23:43 --> 00:23:46 the time periods in the Cretaceous, there's
00:23:46 --> 00:23:49 two or three of these megalong breaks, these
00:23:49 --> 00:23:51 superchrons that have been identified. Two
00:23:51 --> 00:23:52 are very confident ones, a bit more
00:23:52 --> 00:23:54 controversial, but the most recent one in the
00:23:54 --> 00:23:57 Cretaceous was more than 50 million years
00:23:57 --> 00:23:59 with a single polarity. And that's the
00:23:59 --> 00:24:01 equivalent of being at the bus stop. But the
00:24:01 --> 00:24:02 buses are on strike.
00:24:02 --> 00:24:05 Andrew Dunkley: Yes, yes. Wouldn't be a problem in
00:24:05 --> 00:24:07 Japan. They are very strict about their
00:24:07 --> 00:24:09 timing. In fact, I remember a story a couple
00:24:09 --> 00:24:11 of years ago about a train driver who lost
00:24:11 --> 00:24:13 his job for being two minutes late.
00:24:13 --> 00:24:15 Jonti Horner: Yeah. So I remember that in Switzerland. One
00:24:15 --> 00:24:17 of the bizarre experiences when I first moved
00:24:17 --> 00:24:19 to Switzerland for my first postdoc, kind of,
00:24:20 --> 00:24:22 um, 20 years ago, 22 years ago, was being on
00:24:22 --> 00:24:24 the train platform and the train was slightly
00:24:24 --> 00:24:26 late and, um, people were checking their
00:24:26 --> 00:24:28 watches and correcting their watches because
00:24:28 --> 00:24:30 they thought that their watch was wrong
00:24:30 --> 00:24:31 rather than the train being late.
00:24:31 --> 00:24:32 Andrew Dunkley: Wow.
00:24:32 --> 00:24:34 Jonti Horner: And it's like, I'm used to British trends,
00:24:34 --> 00:24:36 where if they come on the correct week,
00:24:36 --> 00:24:38 you're lucky, you know? Yes.
00:24:39 --> 00:24:40 Andrew Dunkley: The. Australia's a bit like that. Although
00:24:40 --> 00:24:42 they're pretty good most of the time. You
00:24:42 --> 00:24:44 only ever hear about them when the press has
00:24:44 --> 00:24:45 decided to stick the knife in.
00:24:45 --> 00:24:47 Jonti Horner: Absolutely. Yeah.
00:24:47 --> 00:24:49 Andrew Dunkley: Ah, nine times out of ten that'll be okay.
00:24:49 --> 00:24:50 Jonti Horner: At least most places have trains. I don't
00:24:50 --> 00:24:52 know if I've told this story before, but my
00:24:52 --> 00:24:53 understanding of the reason that we don't
00:24:53 --> 00:24:55 have a fast train from Toowoomba to Brisbane
00:24:56 --> 00:24:57 is that there used to be a train service. And
00:24:57 --> 00:25:00 in the 1950s, the family that ran the coach
00:25:00 --> 00:25:03 service on the roads from Toowoomba to
00:25:03 --> 00:25:04 Brisbane got elected to the Toowoomba Council
00:25:05 --> 00:25:06 and shut down the railway, because it was.
00:25:08 --> 00:25:10 And so 70 years later, we still have no fast
00:25:10 --> 00:25:12 rail to Brisbane. And it comes up every few
00:25:12 --> 00:25:13 years that we should have it. And it just
00:25:13 --> 00:25:14 never got going again.
00:25:16 --> 00:25:18 Andrew Dunkley: Yeah, I'm sure there's a lot of that going
00:25:18 --> 00:25:21 on. Um, but. Great question, Patty. And
00:25:21 --> 00:25:23 it sort of throws a curveball, um,
00:25:24 --> 00:25:26 into, um, you know, if it happens, if
00:25:26 --> 00:25:29 there is a magnetic pole flip,
00:25:30 --> 00:25:32 um, does that mean we are no longer down
00:25:32 --> 00:25:33 under, but up over?
00:25:34 --> 00:25:34 Jonti Horner: Absolutely.
00:25:36 --> 00:25:39 Andrew Dunkley: Yes, that could be the case.
00:25:39 --> 00:25:41 Oh, uh, gosh, no. We don't want to cause any
00:25:41 --> 00:25:43 trouble. Let's just leave things as they, uh,
00:25:43 --> 00:25:45 are. Thanks, Paddy. This is Space Nuts with
00:25:45 --> 00:25:47 Andrew Dunkley and John Dee Horner.
00:25:50 --> 00:25:52 Okay, we checked all four systems, and.
00:25:52 --> 00:25:55 Jonti Horner: Being with a go, Space Nuts, our.
00:25:55 --> 00:25:57 Andrew Dunkley: Next question comes from Howard Bennett.
00:25:57 --> 00:26:00 Howard is in Penang in Malaysia.
00:26:00 --> 00:26:03 Uh, I have a question about the term
00:26:03 --> 00:26:03 dust.
00:26:04 --> 00:26:04 Jonti Horner: Dust.
00:26:05 --> 00:26:07 Andrew Dunkley: Dust. The word is used indiscriminately
00:26:08 --> 00:26:10 throughout astrophysics with no real
00:26:10 --> 00:26:13 definition. I don't know. Um,
00:26:14 --> 00:26:17 uh, I know it's not the same as the dust
00:26:17 --> 00:26:20 bunnies under my bed, but what exactly is the
00:26:20 --> 00:26:22 space dust that obscures our heart
00:26:23 --> 00:26:26 of, uh, galaxies and inhabits the empty space
00:26:26 --> 00:26:28 between galaxies, not to mention moon dust
00:26:28 --> 00:26:31 and deadly dust storms on Mars? Most
00:26:31 --> 00:26:34 confusing. Uh, maybe we need a new word.
00:26:35 --> 00:26:37 So when we refer to dust in space,
00:26:38 --> 00:26:40 what are we talking about? And is it all the
00:26:40 --> 00:26:41 same stuff?
00:26:41 --> 00:26:44 Jonti Horner: It's all sorts of stuff, basically, but the
00:26:44 --> 00:26:47 commonality is that it's small pieces of
00:26:47 --> 00:26:49 solid material. So that's effectively what
00:26:49 --> 00:26:52 you're talking about. It becomes
00:26:53 --> 00:26:54 confusing occasionally in the solar system,
00:26:54 --> 00:26:56 for example, when we draw the line between
00:26:56 --> 00:26:59 meteoroids, which are, uh, particles of,
00:26:59 --> 00:27:00 effectively, dust going around the sun, and
00:27:00 --> 00:27:02 asteroids, which are bigger things going
00:27:02 --> 00:27:04 around the sun. And typically, people place A
00:27:04 --> 00:27:07 division there at about a meter diameter. So
00:27:07 --> 00:27:09 the same object that's 1.1 meters across,
00:27:09 --> 00:27:12 you'd call a small asteroid at uh, 0.9 meters
00:27:12 --> 00:27:14 would be a meteoroid. And that's just because
00:27:14 --> 00:27:17 we have to have a boundary somewhere. Um,
00:27:17 --> 00:27:19 and materials that are considered dust in
00:27:19 --> 00:27:22 space will include things that at home you'd
00:27:22 --> 00:27:25 consider ice. If it's solid, it's
00:27:25 --> 00:27:28 dust. And um, the hodred is the lessings can
00:27:28 --> 00:27:30 be solid. When it comes to the stuff on the
00:27:30 --> 00:27:32 moon then you're talking about the dust being
00:27:33 --> 00:27:35 surface rocks that have been pulverized by
00:27:35 --> 00:27:38 impacts. So you have these tiny
00:27:38 --> 00:27:41 particles of martian, of lunar regoliths,
00:27:41 --> 00:27:43 sorry, which are uh, small pieces of dust
00:27:43 --> 00:27:45 because they're small pieces of solid
00:27:45 --> 00:27:48 material. Lunar dust is pretty brutal
00:27:48 --> 00:27:49 because there's no moisture and no weathering
00:27:49 --> 00:27:52 there. So it's incredibly sharp edged and
00:27:52 --> 00:27:54 abrasive. And that's why it's such a problem
00:27:54 --> 00:27:57 for future astronauts. It's why it's a
00:27:57 --> 00:27:58 problem technologically. It's why when they
00:27:58 --> 00:28:01 came back they had to clean the astronauts
00:28:01 --> 00:28:02 vacuum them.
00:28:02 --> 00:28:05 Andrew Dunkley: I think they did. Ah, I remember Buzz Aldrin
00:28:05 --> 00:28:07 described walking on the moon as walking on
00:28:07 --> 00:28:08 talcum powder.
00:28:08 --> 00:28:10 Jonti Horner: Yeah, very, very slippery, lots of very fine
00:28:10 --> 00:28:12 dust particles. With the exception that
00:28:12 --> 00:28:15 talcum powder is a lot less abrasive. Um,
00:28:15 --> 00:28:17 I think a better analogy, although it's not
00:28:17 --> 00:28:20 perfect, to the kind of things you get that
00:28:20 --> 00:28:21 cause miner's lung and things like that,
00:28:21 --> 00:28:23 where you've got particles of dust being
00:28:23 --> 00:28:26 created by explosions or digging underground
00:28:26 --> 00:28:28 that haven't had time to be rounded off by
00:28:29 --> 00:28:31 moisture and weathering yet. And they cause
00:28:31 --> 00:28:34 huge problems for people who inhale them. I
00:28:34 --> 00:28:35 believe that was a part of the problem with
00:28:35 --> 00:28:37 asbestos when you inhale it actually it's to
00:28:37 --> 00:28:38 do with the sharpness of the particles and
00:28:38 --> 00:28:41 the damage that they do. So that's the kind
00:28:41 --> 00:28:43 of mundus stuff. Similarly when we talk about
00:28:43 --> 00:28:46 dust zones on Mars, the dust there are those
00:28:46 --> 00:28:49 particles of solid material that are small
00:28:49 --> 00:28:50 enough that they can be lofted into the
00:28:50 --> 00:28:52 atmosphere through a variety of processes.
00:28:52 --> 00:28:55 Not just the wind, but there are solar, ah,
00:28:55 --> 00:28:58 radiation processes that can levitate dust
00:28:58 --> 00:29:01 off the surface of Mars, um, including
00:29:02 --> 00:29:04 um, one that is really fascinating that I did
00:29:04 --> 00:29:06 some research on with colleagues again 20
00:29:06 --> 00:29:09 years ago now, which is this weird
00:29:09 --> 00:29:12 photo, um, with light
00:29:12 --> 00:29:14 based effect. We're familiar with kind of
00:29:15 --> 00:29:17 radiation pressure and the Ponting Robertson
00:29:17 --> 00:29:19 effect. These are things we talk about a lot.
00:29:19 --> 00:29:20 But there's also something called
00:29:20 --> 00:29:23 photophoresis which is
00:29:23 --> 00:29:25 to do with the Absorption and re emission
00:29:26 --> 00:29:28 of light from very small dust grains
00:29:29 --> 00:29:32 that when you're at a, ah, very specific size
00:29:32 --> 00:29:34 range, can exert a really intense force.
00:29:35 --> 00:29:37 So what happens is, uh, when your dust
00:29:37 --> 00:29:40 grain absorbs some light, it
00:29:40 --> 00:29:42 temporarily has a temperature gradient on it.
00:29:43 --> 00:29:45 That temperature gradient depends on how big
00:29:45 --> 00:29:47 the dust grain is. Whether the near side or
00:29:47 --> 00:29:48 the far side of the dust grain gets hot.
00:29:48 --> 00:29:50 Because if the light penetrates most of the
00:29:50 --> 00:29:52 way through, the far side is a bit that
00:29:52 --> 00:29:54 absorbs it and gets hot. So you get a dust
00:29:54 --> 00:29:55 grain that's hotter on one side than another.
00:29:56 --> 00:29:58 If that dust is in an atmosphere that is not
00:29:58 --> 00:30:00 too dense and not too low density,
00:30:01 --> 00:30:04 the gas particles from the point of
00:30:04 --> 00:30:06 view of the dust grain will be perceived as
00:30:06 --> 00:30:09 single impactors, single billiard
00:30:09 --> 00:30:11 balls. And when they hit the dust
00:30:11 --> 00:30:13 grain, they stick briefly and then leave
00:30:13 --> 00:30:15 again. And if they hit the hot side, they'll
00:30:15 --> 00:30:17 leave with more energy than when they leave
00:30:17 --> 00:30:20 the cool side. So you get a
00:30:20 --> 00:30:22 force. Now, this is a really
00:30:22 --> 00:30:24 quirky force I'd never come across until I
00:30:24 --> 00:30:26 saw talk from a couple of physicists who were
00:30:26 --> 00:30:29 talking about dust grains on Mars. Um, we
00:30:29 --> 00:30:31 looked into it in the form of what this would
00:30:31 --> 00:30:33 have as an effect for planet formation disks
00:30:33 --> 00:30:36 and stuff like this. But what's really quirky
00:30:36 --> 00:30:38 is that this is only effective over a
00:30:38 --> 00:30:40 relatively small range of gas pressures.
00:30:40 --> 00:30:43 If the gas is too thin, doesn't happen. M if
00:30:43 --> 00:30:46 the gas is too dense or that individual
00:30:46 --> 00:30:48 probabilistic single gas molecules adhering
00:30:48 --> 00:30:51 and leaving doesn't happen. But in those
00:30:51 --> 00:30:54 range of pressures, it can be up to 10 or 100
00:30:54 --> 00:30:55 times stronger than all the other forces.
00:30:56 --> 00:30:58 And, um, can Mars atmosphere, particularly in
00:30:58 --> 00:31:00 the highlands, is the right pressure that
00:31:00 --> 00:31:02 this can actually levitate dust grains off
00:31:02 --> 00:31:04 the surface of Mars and is viewed as
00:31:04 --> 00:31:05 potentially been helping to trigger those
00:31:05 --> 00:31:07 dust zones to start the dust getting kicked
00:31:07 --> 00:31:10 up into the atmosphere. So all sorts of
00:31:10 --> 00:31:12 really cool stuff there. The other thing that
00:31:12 --> 00:31:14 I found out from those physicists that we
00:31:14 --> 00:31:17 worked with, um, way back then is that
00:31:17 --> 00:31:19 when you buy the little light windmills that
00:31:19 --> 00:31:21 you can get in an evacuated shell that are
00:31:21 --> 00:31:23 meant to show radiation pressure, they're
00:31:23 --> 00:31:25 actually not there using photophoresis
00:31:25 --> 00:31:27 because there is some atmosphere in that
00:31:27 --> 00:31:29 bubble still. And, um, the Havel's one is
00:31:29 --> 00:31:31 colored white, one is colored black, the
00:31:31 --> 00:31:33 black side gets hotter and you get this
00:31:33 --> 00:31:36 photophoresis force happening rather than
00:31:36 --> 00:31:39 radiation pressure, which is interesting and
00:31:39 --> 00:31:42 quirky. Coming back to the question, all the
00:31:42 --> 00:31:44 way to the question is whenever astronomers
00:31:44 --> 00:31:47 use the term dust, then what they're meaning
00:31:47 --> 00:31:49 is particles of solid material
00:31:49 --> 00:31:52 that are too small to be considered asteroids
00:31:52 --> 00:31:55 or planets or things like this. That gets
00:31:55 --> 00:31:57 a catch all of dust. And it behaves very much
00:31:57 --> 00:32:00 like dust in the Earth's atmosphere. Red
00:32:00 --> 00:32:01 light penetrates it more easily than yellow
00:32:01 --> 00:32:03 light, which penetrates more easily than blue
00:32:03 --> 00:32:05 light. Because the longer the wavelength, the
00:32:05 --> 00:32:07 better you can pass through. Which is why if
00:32:07 --> 00:32:10 you look at photographs of some of the
00:32:10 --> 00:32:12 wonderful dark nebulae in the night sky, like
00:32:12 --> 00:32:14 the Coalsack Nebula, which is ahead of the
00:32:14 --> 00:32:16 EMU in the sky to the traditional owners of
00:32:16 --> 00:32:18 the M land here in Australia. Like many of
00:32:18 --> 00:32:20 the Barnard Nebulas, Barnard did a big study
00:32:20 --> 00:32:23 of finding dark nebulae all across the sky.
00:32:23 --> 00:32:25 If you look at photographs of those that have
00:32:25 --> 00:32:27 been taken in full color and you zoom in
00:32:27 --> 00:32:29 around the peripheries of those clouds,
00:32:29 --> 00:32:31 you'll see that the stars right at the edge
00:32:31 --> 00:32:33 look red. And that's because he's seeing them
00:32:33 --> 00:32:35 through the outer edge of the dust cloud. And
00:32:35 --> 00:32:37 the blue and the yellow light is scattered
00:32:37 --> 00:32:39 away. The red light penetrates through. And
00:32:39 --> 00:32:41 you can see this very well. If you look at
00:32:41 --> 00:32:42 some of the famous photos of the Coalsack
00:32:42 --> 00:32:45 Nebula, it's really, really distinct and
00:32:45 --> 00:32:47 noticeable. And it's because dust is dust is
00:32:47 --> 00:32:50 dust. I appreciate it gets confusing because
00:32:50 --> 00:32:53 we use the term in so very many contexts
00:32:53 --> 00:32:55 as a throwaway thing and
00:32:55 --> 00:32:58 to our experience on Earth because it's warm
00:32:58 --> 00:33:01 here. You don't consider flakes of ice and
00:33:01 --> 00:33:03 snowflakes as dust, but if you were.
00:33:03 --> 00:33:05 Andrew Dunkley: Or smoke, you don't think about smoke as
00:33:05 --> 00:33:08 dust, but that's exactly what it is. Can you
00:33:08 --> 00:33:10 see that photo I took during the bushfires a
00:33:10 --> 00:33:11 few years ago?
00:33:11 --> 00:33:14 Jonti Horner: Yeah. What's spooky about that is that I've
00:33:14 --> 00:33:17 seen the sky diminished and denuded
00:33:17 --> 00:33:19 by bushfire smoke. And I've
00:33:19 --> 00:33:22 also seen it from, um,
00:33:23 --> 00:33:25 dust storms. Dust that's been kicked up and
00:33:25 --> 00:33:26 alligated off the surface of the Earth. And I
00:33:26 --> 00:33:29 would have never expected this. But when it's
00:33:29 --> 00:33:32 really, really bad, they both lead to a very
00:33:32 --> 00:33:34 red sky. But when it's not that
00:33:34 --> 00:33:35 intense, you can actually tell the
00:33:35 --> 00:33:37 difference. Because the sky looks different
00:33:37 --> 00:33:40 between lofted dust and smoke, you actually
00:33:40 --> 00:33:43 get a very different kind of reddening that
00:33:43 --> 00:33:45 makes the particles of different sizes. But
00:33:45 --> 00:33:47 if I took a bucket of smoke or a bucket of
00:33:47 --> 00:33:50 snowflakes into space and scattered them into
00:33:50 --> 00:33:52 the solar system, they'd just be considered
00:33:52 --> 00:33:54 dust. Yeah. Small pieces of solid
00:33:54 --> 00:33:55 material.
00:33:55 --> 00:33:58 Andrew Dunkley: There you go. Um, Howard, if you can think
00:33:58 --> 00:34:01 of a set of names to cover
00:34:01 --> 00:34:04 the Various categories let, uh, us know.
00:34:04 --> 00:34:07 But, um, I think just using the term dust
00:34:07 --> 00:34:10 is probably the easiest way to deal with
00:34:10 --> 00:34:12 it, by the sound of things. Thanks for your
00:34:12 --> 00:34:14 question. Hope all is well in Malaysia.
00:34:17 --> 00:34:19 Jonti Horner: Three, two, one.
00:34:20 --> 00:34:20 Space. No.
00:34:21 --> 00:34:23 Andrew Dunkley: Uh, our final question today comes from
00:34:23 --> 00:34:24 Martin.
00:34:25 --> 00:34:27 Berman Gorvine: Hello, space nuts.
00:34:28 --> 00:34:30 Martin Berman Gorvine here,
00:34:30 --> 00:34:33 writer extraordinaire, uh, in many
00:34:33 --> 00:34:35 genres, with yet another question.
00:34:36 --> 00:34:39 How do we determine whether the gas
00:34:39 --> 00:34:42 giants and. Or the ice
00:34:42 --> 00:34:44 giants have rocky
00:34:44 --> 00:34:47 cores? And if they do not
00:34:47 --> 00:34:50 have rocky cores, what might they
00:34:50 --> 00:34:51 have inside?
00:34:52 --> 00:34:55 Possibly of tangential relevance.
00:34:56 --> 00:34:59 I saw an article that
00:34:59 --> 00:35:01 appeared earlier this year in
00:35:01 --> 00:35:04 scitech Daily saying
00:35:04 --> 00:35:04 that
00:35:07 --> 00:35:09 analysis of Hubble data shows that
00:35:09 --> 00:35:12 methane has been depleted at
00:35:12 --> 00:35:15 Uranus poles in recent
00:35:15 --> 00:35:18 decades, which begs the question,
00:35:19 --> 00:35:22 is Uranus outgassing methane?
00:35:22 --> 00:35:25 Oh, sorry, sorry. I shouldn't have said that.
00:35:25 --> 00:35:27 I don't know what came over me. Uh,
00:35:27 --> 00:35:30 I will, uh, do penance immediately.
00:35:31 --> 00:35:33 Berman Gorvine, over and
00:35:34 --> 00:35:34 out.
00:35:35 --> 00:35:38 Andrew Dunkley: Thanks, Martin. I did wonder where
00:35:38 --> 00:35:40 he was going with that. I shouldn't have been
00:35:40 --> 00:35:42 surprised. Um, so to
00:35:42 --> 00:35:45 gas and ice giants, um,
00:35:46 --> 00:35:48 if they don't have rocky cores, what do they
00:35:48 --> 00:35:51 have? I mean, there's been some suggestions
00:35:51 --> 00:35:53 that some of them just have a liquid center,
00:35:53 --> 00:35:56 like a nice, you know, chocolate you get at
00:35:56 --> 00:35:59 Christmas. Um, could they all
00:35:59 --> 00:36:01 be different? I mean, did they all have to
00:36:01 --> 00:36:03 have the same kind of thing? It's not, you
00:36:03 --> 00:36:05 know, we're not talking about dust here.
00:36:05 --> 00:36:06 Jonti Horner: Well, there's a couple of different things
00:36:06 --> 00:36:09 that lead into this and should make the
00:36:09 --> 00:36:11 distinction between the planets we have in
00:36:11 --> 00:36:13 the solar system and objects elsewhere. Um,
00:36:14 --> 00:36:15 because the only planets that we can get up
00:36:15 --> 00:36:17 close and personal to are the ones here at,
00:36:17 --> 00:36:17 um, Home.
00:36:17 --> 00:36:18 Andrew Dunkley: Yeah.
00:36:18 --> 00:36:20 Jonti Horner: The background here is that traditional views
00:36:20 --> 00:36:23 of planet formation involve a process called
00:36:23 --> 00:36:26 core accretion. So this is where you take the
00:36:26 --> 00:36:27 solid material, the dust from the
00:36:27 --> 00:36:30 protoplanetary disk. And if you're out beyond
00:36:30 --> 00:36:32 the ice line, that dust includes a lot of icy
00:36:32 --> 00:36:34 material, solid material, agglomerates,
00:36:34 --> 00:36:36 forming bigger and bigger objects until
00:36:36 --> 00:36:38 eventually get something massive enough to
00:36:38 --> 00:36:40 start gathering the gases and hold onto them.
00:36:40 --> 00:36:41 Because whether you keep hold of an
00:36:41 --> 00:36:43 atmosphere or not depends on your mass and
00:36:43 --> 00:36:45 the strength of your gravity. The more
00:36:45 --> 00:36:47 massive you are, the more gas you can hold
00:36:47 --> 00:36:49 onto, but also the more capable you'll be of
00:36:49 --> 00:36:51 capturing hydrogen and helium, which are the
00:36:51 --> 00:36:53 main gases in the universe.
00:36:55 --> 00:36:58 So the idea is that Jupiter and Saturn got
00:36:58 --> 00:37:00 to 10 or 12 earth masses, which is kind of
00:37:00 --> 00:37:02 viewed as being the threshold for gathering
00:37:02 --> 00:37:04 up the hydrogen and helium gas
00:37:05 --> 00:37:07 fairly quickly. Hoovered up a lot of hydrogen
00:37:07 --> 00:37:09 and helium. And they became the gas giants.
00:37:09 --> 00:37:11 And that's why the name gas giants has been
00:37:11 --> 00:37:14 used for Uranus and Neptune. They
00:37:14 --> 00:37:15 never really got big enough to gather
00:37:15 --> 00:37:17 hydrogen and helium before the hydrogen and
00:37:17 --> 00:37:19 helium had been blown away. But they gathered
00:37:19 --> 00:37:22 huge mantles of methane,
00:37:22 --> 00:37:25 ethane, ammonia, things that are
00:37:25 --> 00:37:27 typically ice at that kind of distance
00:37:28 --> 00:37:30 under gas phase, depending exactly how far
00:37:30 --> 00:37:32 away you are. And so you've got these objects
00:37:32 --> 00:37:35 that are uh, significantly composed of
00:37:35 --> 00:37:38 material that could be considered ices or
00:37:39 --> 00:37:41 gases that are more massive, so therefore
00:37:41 --> 00:37:44 have a lower, a higher escape velocity
00:37:44 --> 00:37:47 and therefore are easier to hold onto with a
00:37:47 --> 00:37:49 lower mass. So the distinction between the
00:37:49 --> 00:37:51 ice giants and the gas giants is a
00:37:51 --> 00:37:53 compositional one. And it's to do with how
00:37:53 --> 00:37:56 they formed. They always used to just all be
00:37:56 --> 00:37:59 called gas giants. The ice giants idea came
00:37:59 --> 00:38:01 in with different models of planet formation.
00:38:01 --> 00:38:04 Because what we tend to do with planet name
00:38:04 --> 00:38:07 classification with things like
00:38:07 --> 00:38:09 whether Ceres is an asteroid or a dwarf
00:38:09 --> 00:38:11 planet, or both, whether Pluto's a planet or
00:38:11 --> 00:38:13 a dwarf planet. What we tend to do is we tend
00:38:13 --> 00:38:16 to place boundaries as humans to allow us to
00:38:16 --> 00:38:19 group like with like and separate things that
00:38:19 --> 00:38:21 are functionally different in origin or have
00:38:21 --> 00:38:23 a different history. And we do this in our
00:38:23 --> 00:38:25 day to day lives. We have children and
00:38:25 --> 00:38:28 pensioners, we have adults, we have
00:38:28 --> 00:38:30 people who suddenly wake up one morning and
00:38:30 --> 00:38:32 they can drive a car the day before. They
00:38:32 --> 00:38:33 were legally not allowed to do so because
00:38:33 --> 00:38:35 they've crossed this magic threshold. It's a
00:38:35 --> 00:38:38 very human thing. The nature of them
00:38:38 --> 00:38:40 in terms of having cores is therefore
00:38:41 --> 00:38:43 initially an outcome of our best
00:38:43 --> 00:38:44 understanding of how these things could form.
00:38:45 --> 00:38:47 The idea is that you need to form a kernel of
00:38:47 --> 00:38:49 solid material to get enough mass
00:38:49 --> 00:38:52 in order to accrete the gas. Now there's an
00:38:52 --> 00:38:55 alternate model which probably ties into the
00:38:55 --> 00:38:57 formation of objects in binary star systems,
00:38:57 --> 00:38:59 where when you've got a much more massive
00:38:59 --> 00:39:02 disk of material around a star, you can get
00:39:02 --> 00:39:04 an instantaneous gravitational instability
00:39:05 --> 00:39:07 where you get a, ah, very gas heavy object
00:39:08 --> 00:39:10 formed very, very quickly that
00:39:10 --> 00:39:12 wouldn't need a core as a nucleus around
00:39:12 --> 00:39:15 which it forms. It would have solid material
00:39:15 --> 00:39:17 in it. But that solid material would just be
00:39:17 --> 00:39:20 at the level that the background material
00:39:20 --> 00:39:22 would have. So the composition of an object
00:39:22 --> 00:39:24 formed in this way from this gravitational
00:39:24 --> 00:39:27 instability would be the same as a bulk
00:39:27 --> 00:39:29 composition of the disk. The composition of
00:39:29 --> 00:39:31 an object that forms from core accretion
00:39:31 --> 00:39:33 would be richer in the solid material because
00:39:33 --> 00:39:35 they form a big amount of solids before they
00:39:35 --> 00:39:37 gather any gas. Once they're at the point of
00:39:37 --> 00:39:40 gathering the gas, they gather everything in
00:39:40 --> 00:39:42 the same amounts as they're in the disk. So
00:39:42 --> 00:39:44 you end up with something that has a large
00:39:44 --> 00:39:47 amount of disk like composition, plus
00:39:47 --> 00:39:50 a chunk of solids added in. But the thing is,
00:39:50 --> 00:39:51 the bulk of those solids are down at the
00:39:51 --> 00:39:53 bottom, so you can't really measure that
00:39:53 --> 00:39:55 remotely. So how do you tell them apart?
00:39:55 --> 00:39:58 Well, to be honest, for things around other
00:39:58 --> 00:40:01 stars, we can't yet. So what we need to do
00:40:01 --> 00:40:03 instead is look at their orbits and the
00:40:03 --> 00:40:06 structures of the system and um, see how they
00:40:06 --> 00:40:09 fit with these different formation
00:40:09 --> 00:40:12 models. Um, and this is, I think going to,
00:40:12 --> 00:40:13 in the next few years lead to a shift in how
00:40:13 --> 00:40:16 we define what a brown dwarf is. Where
00:40:16 --> 00:40:18 historically a brown dwarf was something
00:40:18 --> 00:40:20 between 13 Jupiter masses and about 80
00:40:20 --> 00:40:23 Jupiter masses, was something that was a
00:40:23 --> 00:40:25 failed star rather than a giant planet. But
00:40:25 --> 00:40:27 we're finding objects that blur that boundary
00:40:27 --> 00:40:29 more and more. And I think we'll probably
00:40:29 --> 00:40:31 shift to a different definition which looks
00:40:31 --> 00:40:33 at, uh, the formation mechanism and the
00:40:33 --> 00:40:35 presence of a core. So if you've got
00:40:35 --> 00:40:36 something twice the mass of Jupiter bit
00:40:36 --> 00:40:38 formed through this gravitational instability
00:40:38 --> 00:40:41 method, that will be a very low mass brown
00:40:41 --> 00:40:43 dwarf. Whereas if you've got something 20
00:40:43 --> 00:40:45 Jupiter masses, that has a solid core, that
00:40:45 --> 00:40:48 will be a very massive planet because it
00:40:48 --> 00:40:49 formed through core accretion. I think that's
00:40:49 --> 00:40:52 probably where we're going. That means
00:40:52 --> 00:40:54 then that you can draw inferences on this
00:40:54 --> 00:40:56 based on the structure of the planetary
00:40:56 --> 00:40:58 system you've got, based on the orbits of the
00:40:58 --> 00:41:00 objects, because these different formation
00:41:00 --> 00:41:02 mechanisms would form very different systems.
00:41:02 --> 00:41:05 But here in the solar system, we actually
00:41:05 --> 00:41:08 can eventually figure out whether
00:41:08 --> 00:41:10 giant planets have got a solid core or not.
00:41:10 --> 00:41:13 In order to do that, we need spacecraft to be
00:41:13 --> 00:41:15 orbiting those planets for a lengthy period
00:41:15 --> 00:41:17 of time, preferably on highly elongated
00:41:17 --> 00:41:19 orbits like Juno. This was one of the key
00:41:19 --> 00:41:22 points of the Juno mission, where you've got
00:41:22 --> 00:41:24 a spacecraft going round on highly
00:41:24 --> 00:41:26 elongated orbit which is
00:41:27 --> 00:41:29 experiencing the gravitational pull from the
00:41:29 --> 00:41:31 planet. And when you're very close to the
00:41:31 --> 00:41:34 planet, your orbit is not just sensitive
00:41:34 --> 00:41:36 to the mass of the planet, as if all of the
00:41:36 --> 00:41:37 mass was at a single point in the middle of
00:41:37 --> 00:41:40 the planet, you actually become sensitive to
00:41:40 --> 00:41:42 the distribution of mass within the planet.
00:41:43 --> 00:41:45 Fundamentally, a planet that has a lot of gas
00:41:45 --> 00:41:47 on top and a small dense core that has a
00:41:47 --> 00:41:50 varying density throughout will affect the
00:41:50 --> 00:41:53 spacecraft differently to how a planet that
00:41:53 --> 00:41:55 was uniform in density throughout would do.
00:41:55 --> 00:41:57 Now, to some degree, we do this on Earth,
00:41:57 --> 00:42:00 where people map the density variations at a
00:42:00 --> 00:42:03 very local scale for, um, GPS
00:42:03 --> 00:42:04 satellites and things like that. And you've
00:42:04 --> 00:42:06 seen beautiful gravitational maps of the
00:42:06 --> 00:42:09 Earth where it looks like a deformed potato
00:42:09 --> 00:42:11 effect. Yes. So same kind of idea with
00:42:11 --> 00:42:14 Jupiter and Saturn. By using the data from
00:42:14 --> 00:42:17 Juno, by using Cassini data from around
00:42:17 --> 00:42:19 Saturn, we have a fairly good idea that those
00:42:19 --> 00:42:21 planets do actually have
00:42:22 --> 00:42:25 cores of solid and liquid material deep
00:42:25 --> 00:42:27 within them that would have formed through
00:42:27 --> 00:42:29 this core accretion process. So that's why we
00:42:29 --> 00:42:31 can be fairly confident that they have rocky
00:42:31 --> 00:42:34 cores here, where rocky is basically meaning
00:42:34 --> 00:42:36 anything solid. There'll be iron and nickel,
00:42:36 --> 00:42:38 there'll be water ice, and there'll also be
00:42:38 --> 00:42:40 liquid metallic hydrogen and things like
00:42:40 --> 00:42:42 this. But there will be a solid kernel at the
00:42:42 --> 00:42:45 core from which those planets form. There is
00:42:46 --> 00:42:48 some interest that comes from this because I
00:42:48 --> 00:42:50 think Jupiter's core, I think it was
00:42:50 --> 00:42:53 Jupiter's rather than Saturn's, the data has
00:42:53 --> 00:42:55 revealed is there, uh, it's a bit more
00:42:55 --> 00:42:57 massive than expected, but also more spread
00:42:57 --> 00:43:00 out and slushy. And that is thought to be
00:43:00 --> 00:43:02 potentially evidence of a late giant impact
00:43:02 --> 00:43:04 on Jupiter, where there was a late addition
00:43:04 --> 00:43:07 of a big chunk of solid material in much same
00:43:07 --> 00:43:10 way that there was a giant impact that formed
00:43:10 --> 00:43:12 the Earth and the moon, A giant impact that
00:43:12 --> 00:43:14 stripped the surface of Mercury away, leaving
00:43:14 --> 00:43:16 Mercury denuded. Giant impacts were a huge
00:43:16 --> 00:43:19 part of planet formation. But in order to be
00:43:19 --> 00:43:22 absolutely definitively sure that you have a
00:43:22 --> 00:43:24 solid core, you need those close up
00:43:24 --> 00:43:26 spacecraft measurements to be able to
00:43:26 --> 00:43:27 distinguish the
00:43:28 --> 00:43:30 subtleties in the gravitational field that
00:43:30 --> 00:43:32 result from something that is not uniformly
00:43:32 --> 00:43:35 dense but has a varying density and has a,
00:43:35 --> 00:43:38 I guess, significant internal structure. We
00:43:38 --> 00:43:40 can do that in the solar system. We haven't
00:43:40 --> 00:43:42 yet done that for Uranus and Neptune because
00:43:42 --> 00:43:44 we've never had orbiters go to those planets.
00:43:44 --> 00:43:46 And I look forward to the day that we manage
00:43:46 --> 00:43:48 that. But even if those missions start being
00:43:48 --> 00:43:49 planned now, they probably won't launch till
00:43:49 --> 00:43:52 the 2000-40s. I will be retired by the time
00:43:52 --> 00:43:53 they get there, but I'll still be watching on
00:43:53 --> 00:43:56 eagerly for the planets round of the stars.
00:43:56 --> 00:43:59 We have to draw on the nature of the
00:43:59 --> 00:44:01 planetary system. They're moving the orbits
00:44:01 --> 00:44:02 and draw inferences then on which of the
00:44:02 --> 00:44:05 formation mechanisms that they had. And
00:44:05 --> 00:44:07 that's where the complexity about brown dwarf
00:44:07 --> 00:44:10 versus giant planet comes from as well.
00:44:10 --> 00:44:12 So it's a wonderfully deep and complex
00:44:12 --> 00:44:14 question. In terms of the methane on
00:44:14 --> 00:44:17 Uranus, I think that is not that Uranus
00:44:17 --> 00:44:19 is outgassing the methane, it's keeping the
00:44:19 --> 00:44:21 methane to itself. A bit like when I put the
00:44:21 --> 00:44:23 dogs in a locked room um, they keep their
00:44:23 --> 00:44:25 methane to themselves, and it's sometimes not
00:44:25 --> 00:44:27 that pleasant when I go back in there. Um,
00:44:27 --> 00:44:29 but rather the methane levels varying because
00:44:29 --> 00:44:32 of the time of year and the seasonality of
00:44:32 --> 00:44:34 weather on Uranus. I think that's probably
00:44:34 --> 00:44:35 what's happening there.
00:44:36 --> 00:44:38 Andrew Dunkley: Okay. Uh, it's a great question. Uh, Martin
00:44:38 --> 00:44:41 always comes up with a ripper or two from
00:44:41 --> 00:44:42 time to time. And some good questions as
00:44:42 --> 00:44:44 well. And, uh, yeah, that was.
00:44:45 --> 00:44:47 That was a good one. Thank you, Martin. And
00:44:48 --> 00:44:50 thanks. Thanks for the joke. Loved it.
00:44:51 --> 00:44:53 Um, and that's where we are going to
00:44:54 --> 00:44:56 finish up. And, Jonti, thank you for filling
00:44:56 --> 00:44:59 in for the last seven weeks or so while
00:44:59 --> 00:45:02 Fred took a vacay. Uh, we really
00:45:02 --> 00:45:04 do appreciate it, and, uh, we'll certainly
00:45:04 --> 00:45:06 have you back down the track. Thank you.
00:45:06 --> 00:45:07 Jonti Horner: It's always a pleasure. And in the meantime,
00:45:07 --> 00:45:09 I'll keep my eye on the Facebook group and
00:45:09 --> 00:45:12 cheer on people sharing Nightwish videos. Uh,
00:45:12 --> 00:45:13 I saw that. That made me happy.
00:45:13 --> 00:45:13 Berman Gorvine: Yeah.
00:45:13 --> 00:45:15 Andrew Dunkley: Yeah, I knew someone would.
00:45:15 --> 00:45:15 Jonti Horner: Yeah.
00:45:15 --> 00:45:18 Andrew Dunkley: Uh, fantastic than Jonti. Thank you very
00:45:18 --> 00:45:18 much.
00:45:18 --> 00:45:20 Jonti Horner: That's a pleasure. I'll catch you next time.
00:45:20 --> 00:45:22 Andrew Dunkley: Okay, Bye. Bye. Uh, Jonti Horner, professor
00:45:22 --> 00:45:24 of astrophysics at the university University
00:45:25 --> 00:45:27 of Southern Queensland, uh, filling in for
00:45:27 --> 00:45:30 Fred for the last several weeks. And we will,
00:45:30 --> 00:45:32 uh, get him back on in the not too distant
00:45:32 --> 00:45:35 future. And thanks to Huw in the studio. Huw
00:45:35 --> 00:45:38 couldn't be with us today because, um, he's
00:45:38 --> 00:45:40 been having trouble sitting. Uh, and he went
00:45:40 --> 00:45:42 to the doctor, and the doctor said, you've
00:45:42 --> 00:45:44 got a ring around your anus. Oh, I couldn't
00:45:44 --> 00:45:45 help it. Thanks, Martin.
00:45:45 --> 00:45:48 Jonti Horner: You inspired me. I'm done being
00:45:48 --> 00:45:49 locked in a room with my dog.
00:45:51 --> 00:45:53 Yes. Yes, indeed.
00:45:53 --> 00:45:55 Andrew Dunkley: All right, we're done. Thanks for your
00:45:55 --> 00:45:56 company. We'll catch you on the next episode
00:45:56 --> 00:45:58 of Space Nuts. Bye. Bye.
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