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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