Exploding Black Holes, Lunar Mysteries, and Cosmic Questions In this enlightening Q&A edition of Space Nuts , hosts Andrew Dunkley and Professor Jonti Horner tackle an array of fascinating questions from listeners. From the enigmatic nature of supercharged neutrinos linked to black holes to the mysteries of the Moon's surface, this episode is a deep dive into the cosmos.
Episode Highlights:
- Supercharged Neutrinos and Black Holes: Nick's intriguing question about the detection of a supercharged neutrino prompts a discussion on the theoretical concept of exploding black holes and Hawking radiation. Jonti explains the complexities of black hole evaporation and the potential implications for our understanding of the universe.
- The Dark Side of the Moon: Andrew returns with her questions about the far side of the Moon, exploring why it appears less damaged than the near side. Jonti provides insights into the Moon’s geological history and the differences in surface features that contribute to this phenomenon.
- Shallow Craters on the Moon: Continuing with Andrew's inquiries, the hosts discuss the nature of lunar craters and why many appear shallower than expected. Jonti elaborates on the processes that lead to complex craters and their unique characteristics compared to simpler ones.
- Planet Formation and Solar System Dynamics: Eli's two-part question leads to a discussion about the composition of planets in our solar system and how their formation relates to the elements present in the Sun. The hosts delve into the nuances of planetary formation and the role of distance from the Sun in determining a planet's composition.
- Speed of the Solar System: Eli's second question prompts an exploration of how fast our solar system could travel without causing noticeable effects on Earth. Jonti explains the implications of high speeds in a dense stellar environment and how it might alter our cosmic perspective.
For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. (https://www.spacenutspodcast.com/) Follow us on social media at SpaceNutsPod on Facebook, Instagram, and more. We love engaging with our community, so be sure to drop us a message or comment on your favorite platform.
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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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Episode link: https://play.headliner.app/episode/33322213?utm_source=youtube
00:00:00 --> 00:00:03 Hi there. Thanks for joining us on a Q&A
00:00:03 --> 00:00:05 edition of Space Nuts. Andrew Dunley
00:00:05 --> 00:00:07 here, your host. Great to have your
00:00:07 --> 00:00:09 company. Coming up, we've got a few
00:00:09 --> 00:00:11 questions. Nick is going to ask about
00:00:11 --> 00:00:14 supercharged neutrinos. Andrea is making
00:00:14 --> 00:00:16 a return appearance. She's got a couple
00:00:16 --> 00:00:18 of questions about the dark side of the
00:00:18 --> 00:00:21 moon and shallow craters. And Eli is
00:00:21 --> 00:00:24 asking about elements and the speed of
00:00:24 --> 00:00:25 objects. And if we've got time, we'll
00:00:26 --> 00:00:27 chuck another question into the mix as
00:00:27 --> 00:00:30 well. All coming up on this edition of
00:00:30 --> 00:00:31 Space Nuts.
00:00:31 --> 00:00:36 >> 15 seconds. Guidance is internal. 10 9g
00:00:36 --> 00:00:38 Ignition sequence start.
00:00:38 --> 00:00:39 >> Space nuts.
00:00:39 --> 00:00:41 >> 5 4 3 2
00:00:41 --> 00:00:43 >> 1 2 3 4 5 5 4 3 2 1
00:00:44 --> 00:00:45 >> Space Nuts.
00:00:45 --> 00:00:48 >> Astronauts report. It feels good.
00:00:48 --> 00:00:51 >> And with Freda away Jonty can play. It's
00:00:51 --> 00:00:54 uh Professor Jonty her professor of
00:00:54 --> 00:00:56 astrophysics at the University of
00:00:56 --> 00:00:58 Southern Queensland. Jonty, hello again.
00:00:58 --> 00:00:59 >> Good afternoon. How are you going?
00:00:59 --> 00:01:02 >> I'm well. Great to see you. I think we
00:01:02 --> 00:01:05 should just go straight into it and uh
00:01:05 --> 00:01:07 hit you with our first question. It's a
00:01:07 --> 00:01:10 it's a topic I'm not overly familiar
00:01:10 --> 00:01:12 with, but uh this one comes from Nick.
00:01:12 --> 00:01:14 Uh I just read that a supercharged
00:01:14 --> 00:01:18 neutrino was detected by the Kilometer
00:01:18 --> 00:01:21 Cube Nutrino telescope and a theory was
00:01:21 --> 00:01:23 put forward that it came from an
00:01:23 --> 00:01:25 exploding black hole. Please explain how
00:01:25 --> 00:01:28 a black hole can explode. Love the show,
00:01:28 --> 00:01:31 Nick. Thank you, Nick. We love that you
00:01:31 --> 00:01:33 love the show. Thank Thank you for
00:01:33 --> 00:01:35 sending in a question. Um, exploding
00:01:35 --> 00:01:39 black holes. Um, I I seem to remember
00:01:39 --> 00:01:40 Fred might have written a book about
00:01:40 --> 00:01:43 something like that once. Um, but
00:01:43 --> 00:01:45 anyway, um, do they explode or do they
00:01:45 --> 00:01:47 merge or do they collapse? They they
00:01:47 --> 00:01:49 eventually disappear. I know that
00:01:49 --> 00:01:51 >> things now, you know, straight up. I'm
00:01:51 --> 00:01:53 not a cosmologist or a cosmetologist
00:01:53 --> 00:01:55 which I always used to joke about
00:01:55 --> 00:01:57 cosmologists being cosmetologist and
00:01:57 --> 00:01:58 then it turns out a cosmetologist is a
00:01:58 --> 00:02:02 real thing. So never mind. Um that's
00:02:02 --> 00:02:04 further from my area of expertise. So
00:02:04 --> 00:02:06 any answer I give take with a larger
00:02:06 --> 00:02:09 grain of salt. You know as is always the
00:02:09 --> 00:02:10 way you know you the further you go from
00:02:10 --> 00:02:12 your expertise the more out of date your
00:02:12 --> 00:02:15 knowledge is. My knowledge on exploding
00:02:15 --> 00:02:19 or rather evaporating black holes goes
00:02:19 --> 00:02:20 back to basically when I was in
00:02:20 --> 00:02:22 undergrad and I was doing lots of
00:02:22 --> 00:02:24 courses in lots of different things and
00:02:24 --> 00:02:27 this goes back to some of the work that
00:02:27 --> 00:02:29 made Steven Hawking so worldrenowned.
00:02:29 --> 00:02:31 Now obviously for a lot of people
00:02:31 --> 00:02:33 Stephven Hawking became a global name
00:02:33 --> 00:02:34 with the publication of a brief history
00:02:34 --> 00:02:36 of time which did a very good job of
00:02:36 --> 00:02:38 explaining very complicated things in a
00:02:38 --> 00:02:40 way that people could at least feel like
00:02:40 --> 00:02:42 they had a grasp of. Um, I remember
00:02:42 --> 00:02:44 reading it as a kid and it made my head
00:02:44 --> 00:02:46 hurt, but it in a good way. I could
00:02:46 --> 00:02:47 actually follow it. It was well
00:02:47 --> 00:02:49 explained. One of the things that
00:02:49 --> 00:02:51 Stephven Hawking did fairly early in his
00:02:51 --> 00:02:53 career, I think in like 1974 or
00:02:53 --> 00:02:55 something, was do some very theoretical
00:02:55 --> 00:02:58 work on black holes where he postulated
00:02:58 --> 00:03:00 that black holes could lose weight
00:03:00 --> 00:03:02 through a process called Hawking
00:03:02 --> 00:03:05 radiation. And the idea is that black
00:03:05 --> 00:03:08 holes can effectively be considered to
00:03:08 --> 00:03:11 have a temperature and to radiate energy
00:03:11 --> 00:03:14 and therefore mass away into space. And
00:03:14 --> 00:03:15 the smaller the black hole, the hotter
00:03:15 --> 00:03:17 it is, so the quicker it would radiate.
00:03:17 --> 00:03:19 And this is all backed up by
00:03:19 --> 00:03:20 ridiculously complex physics and
00:03:20 --> 00:03:22 mathematics that is way beyond my level
00:03:22 --> 00:03:25 of full understanding. But part of the
00:03:25 --> 00:03:27 idea behind it is that what we think of
00:03:27 --> 00:03:28 as the empty vacuum of space is actually
00:03:28 --> 00:03:31 not a true vacuum, but is instead
00:03:31 --> 00:03:34 constantly populated by pairs of matter
00:03:34 --> 00:03:35 and antimatter particles that
00:03:35 --> 00:03:37 spontaneously create and then collide
00:03:37 --> 00:03:39 with each other and disappear again. And
00:03:39 --> 00:03:41 if these if such an event happens near
00:03:42 --> 00:03:43 the event horizon of a black hole, one
00:03:43 --> 00:03:44 of the particles falls into the black
00:03:44 --> 00:03:46 hole, the other escapes and it seemed to
00:03:46 --> 00:03:48 lose mass, lose energy and radiation
00:03:48 --> 00:03:51 going along with that. Now the bigger
00:03:51 --> 00:03:53 the black hole, the colder it would be.
00:03:54 --> 00:03:56 So the slower it radiates anyway, but
00:03:56 --> 00:03:58 also the bigger it is, the more
00:03:58 --> 00:04:00 effectively it can feed from its
00:04:00 --> 00:04:02 environment. Even if that's little bits
00:04:02 --> 00:04:04 of dust falling in, or if it's near a
00:04:04 --> 00:04:05 star, it can feed off that star, get an
00:04:05 --> 00:04:08 accretion disc. So the black holes that
00:04:08 --> 00:04:11 form in the modern universe are formed
00:04:11 --> 00:04:13 by stars reaching the end of their lives
00:04:13 --> 00:04:15 and are massive. They're more massive
00:04:15 --> 00:04:16 than the sun by a long way. They're
00:04:16 --> 00:04:18 formed from stars much more massive than
00:04:18 --> 00:04:21 the sun. You get massive black holes,
00:04:21 --> 00:04:23 you get intermediate mass black holes,
00:04:23 --> 00:04:24 and you get super massive black holes.
00:04:24 --> 00:04:26 And they're all the big whopping ones.
00:04:26 --> 00:04:27 And the time scale, as I understand it,
00:04:28 --> 00:04:29 for those black holes to decay through
00:04:29 --> 00:04:33 Hawking radiation is ridiculously,
00:04:33 --> 00:04:35 ridiculously, ridiculously longer than
00:04:35 --> 00:04:36 the age of the universe.
00:04:36 --> 00:04:36 >> Yes.
00:04:36 --> 00:04:38 >> And they're probably not emitting
00:04:38 --> 00:04:40 Hawking radiation at a level that we
00:04:40 --> 00:04:42 could detect because they are very cold
00:04:42 --> 00:04:45 in his quantification of it. However, at
00:04:45 --> 00:04:47 the birth of the universe when the
00:04:47 --> 00:04:48 temperature and pressure was immense
00:04:48 --> 00:04:51 after the big bang, there were
00:04:51 --> 00:04:53 theoretically a class of black holes
00:04:53 --> 00:04:56 created called primordial black holes.
00:04:56 --> 00:04:58 So these were black holes that were not
00:04:58 --> 00:05:01 born from the fiery death of a star, but
00:05:01 --> 00:05:04 were instead born out of the big bang
00:05:04 --> 00:05:05 and the pressures and the temperatures.
00:05:05 --> 00:05:07 And these could be black holes down to
00:05:07 --> 00:05:09 the mass of a thumbnail or down really
00:05:09 --> 00:05:11 really tiny ones, planet mass black
00:05:11 --> 00:05:12 holes. Y
00:05:12 --> 00:05:14 >> the smaller you are as a black hole, the
00:05:14 --> 00:05:16 more quickly you radiate things away. So
00:05:16 --> 00:05:19 the shorter your lifetime and so you
00:05:19 --> 00:05:20 have this idea that these primordial
00:05:20 --> 00:05:24 black holes evaporate it over time and
00:05:24 --> 00:05:25 effectively none of them will survive to
00:05:25 --> 00:05:28 the current day. Those evaporating black
00:05:28 --> 00:05:31 holes would evaporate over time and give
00:05:31 --> 00:05:33 off radiation that we have never yet
00:05:33 --> 00:05:35 detected. But a black hole coming to the
00:05:35 --> 00:05:37 end of its life will evaporate faster
00:05:37 --> 00:05:39 and faster. There's a quote on an
00:05:39 --> 00:05:41 article I found recently which may be
00:05:41 --> 00:05:43 tied to this. Um, an article entitled,
00:05:43 --> 00:05:45 "An exploding black hole could reveal
00:05:45 --> 00:05:47 the foundations of the universe,
00:05:47 --> 00:05:49 published from September last year,
00:05:49 --> 00:05:51 talking about the predictions that as
00:05:51 --> 00:05:54 our technology gets better in the coming
00:05:54 --> 00:05:55 years, we may be able to detect this
00:05:55 --> 00:05:58 Hawking radiation in an event where the
00:05:58 --> 00:05:59 black hole reaches its critical phase
00:06:00 --> 00:06:02 and evaporates entirely within the next
00:06:02 --> 00:06:04 few years." So, not quite the neutrino
00:06:04 --> 00:06:05 discovery that we were talking about in
00:06:05 --> 00:06:07 the question, but a related thing. And
00:06:07 --> 00:06:10 there's a quote here from Andrea Tham
00:06:10 --> 00:06:13 who associate professor Andrea Tham. I I
00:06:13 --> 00:06:14 do hate it when articles don't give
00:06:14 --> 00:06:17 people's well- earned titles until later
00:06:17 --> 00:06:18 in the sentence or don't give them at
00:06:18 --> 00:06:19 all.
00:06:19 --> 00:06:21 >> Um which is another rant I could go on
00:06:21 --> 00:06:22 that's separate but it's particularly
00:06:22 --> 00:06:26 affects my um early career colleagues
00:06:26 --> 00:06:28 and affects colleagues from
00:06:28 --> 00:06:30 nontraditional backgrounds and stuff and
00:06:30 --> 00:06:33 it's a very dim demonizing
00:06:33 --> 00:06:35 thing diminishing thing. It lowers their
00:06:35 --> 00:06:37 expertise. Anyway, this is a quote from
00:06:37 --> 00:06:39 associate professor Andrea Tham from
00:06:39 --> 00:06:42 University of Massachusetts Amhurst
00:06:42 --> 00:06:43 says, "As primordial black holes
00:06:43 --> 00:06:46 evaporate, they become ever lighter, so
00:06:46 --> 00:06:48 hotter, they therefore emit even more
00:06:48 --> 00:06:50 radiation. It's a runaway process until
00:06:50 --> 00:06:52 they explode."
00:06:52 --> 00:06:54 >> It's that Hawking radiation that our
00:06:54 --> 00:06:56 telescopes can detect.
00:06:56 --> 00:06:56 >> Yeah.
00:06:56 --> 00:06:57 >> So, what's happening is you've got these
00:06:57 --> 00:06:59 primordial black holes that are really
00:06:59 --> 00:07:02 itty bitty diddy ones that are therefore
00:07:02 --> 00:07:04 evaporating quicker than they can gain
00:07:04 --> 00:07:05 mass. they'll be on this critical
00:07:05 --> 00:07:07 threshold. And so you get this runaway
00:07:07 --> 00:07:09 death where the more massive ones live
00:07:09 --> 00:07:12 longer before they get small enough to
00:07:12 --> 00:07:15 finally evaporate and then explode. And
00:07:15 --> 00:07:18 so I would guess that the observation of
00:07:18 --> 00:07:21 this super neutrino that has been linked
00:07:22 --> 00:07:23 potentially to an exploding black hole
00:07:23 --> 00:07:26 is not two black holes colliding. not a
00:07:26 --> 00:07:28 modern black hole formed from the death
00:07:28 --> 00:07:30 of stars but rather is a death of a
00:07:30 --> 00:07:33 primordial black hole as would be
00:07:33 --> 00:07:35 predicted by this research by Steven
00:07:35 --> 00:07:37 Hawking more than 50 years ago in the
00:07:37 --> 00:07:40 form of Hawking radiation. So that's my
00:07:40 --> 00:07:42 thinking on what's happening here. Now
00:07:42 --> 00:07:45 obviously I am not an expert. Um I've
00:07:45 --> 00:07:48 said previously on many places that in a
00:07:48 --> 00:07:49 lot of disciplines and when we're
00:07:49 --> 00:07:51 teaching our undergrads we often say
00:07:51 --> 00:07:53 avoid Wikipedia. Wikipedia is not a
00:07:53 --> 00:07:54 static resource. It's a fluid resource
00:07:54 --> 00:07:56 and it's often wrong and I know for
00:07:56 --> 00:07:58 journalists it's probably often
00:07:58 --> 00:07:59 something you cautioned don't get your
00:07:59 --> 00:08:01 facts from Wikipedia
00:08:01 --> 00:08:03 >> for astrophysics and particularly the
00:08:03 --> 00:08:05 more technical and hardcore ends of
00:08:05 --> 00:08:08 astrophysics. Wikipedia is actually very
00:08:08 --> 00:08:10 reliable because very few people will be
00:08:10 --> 00:08:12 interested in maliciously editing a web
00:08:12 --> 00:08:15 page because frankly they'll go after
00:08:15 --> 00:08:17 other topics that are more triggering.
00:08:17 --> 00:08:19 But also people who are interested in
00:08:19 --> 00:08:20 this stuff and have the knowledge tend
00:08:20 --> 00:08:22 to be very obsessive and if they spot
00:08:22 --> 00:08:23 something wrong they fix it very
00:08:23 --> 00:08:25 quickly. The result of that is if you
00:08:25 --> 00:08:28 Google Hawking radiation the Wikipedia
00:08:28 --> 00:08:31 page is very lengthy goes into a lot of
00:08:31 --> 00:08:33 detail includes some of the maths that
00:08:33 --> 00:08:35 makes my head hurt and makes me want to
00:08:35 --> 00:08:37 cry a little bit um talking about black
00:08:37 --> 00:08:40 hole evaporation and things like this.
00:08:40 --> 00:08:41 Now
00:08:41 --> 00:08:43 the equation for black hole evaporation
00:08:44 --> 00:08:45 that's on here which is based on the
00:08:45 --> 00:08:49 Hawking work gives a evaporation time
00:08:49 --> 00:08:55 for a black hole of 2.14 * 10 67 years.
00:08:55 --> 00:08:59 So that's 2.14 multiplied by 10 with 67
00:08:59 --> 00:09:01 zeros
00:09:01 --> 00:09:03 multiplied by the mass of the black hole
00:09:03 --> 00:09:05 divided the by the mass of the sun to
00:09:05 --> 00:09:08 the power three. So if you've got a
00:09:08 --> 00:09:11 black hole that is one solar mass, it
00:09:11 --> 00:09:14 will take 2.14 * 10 67 years to
00:09:14 --> 00:09:15 evaporate. And the more massive it is,
00:09:15 --> 00:09:17 the larger that number gets.
00:09:17 --> 00:09:17 >> Yeah.
00:09:17 --> 00:09:20 >> To the power 3. So the multiplier here
00:09:20 --> 00:09:22 is get the mass of the black hole as
00:09:22 --> 00:09:23 measured in units of the mass of the
00:09:23 --> 00:09:27 sun. Cube that number and then multiply
00:09:27 --> 00:09:31 it by 2.14 * 10 67 and you get a
00:09:31 --> 00:09:34 headache. But you get a number. Now the
00:09:34 --> 00:09:38 mass of the sun is what? 2 * 10 30
00:09:38 --> 00:09:39 kilos,
00:09:39 --> 00:09:45 >> right? Mass of the earth is 5.97 * 10 24
00:09:45 --> 00:09:48 kilos. So that is effectively
00:09:48 --> 00:09:51 um 2 * 10 - 6 solar mass. It's about a
00:09:51 --> 00:09:52 millionth of a solar mass. So we'll just
00:09:52 --> 00:09:55 say it's 1 millionth of a solar mass. 1
00:09:55 --> 00:09:57 millionth
00:09:57 --> 00:10:02 cubed is 1 * 10 - 18. That means a black
00:10:02 --> 00:10:04 hole the mass of the earth would decay
00:10:04 --> 00:10:06 much more quickly. it would decay in
00:10:06 --> 00:10:09 only 10^ the 49 years which is still
00:10:10 --> 00:10:12 much much much much longer than the age
00:10:12 --> 00:10:13 of the universe but you can play this
00:10:13 --> 00:10:16 game with everything. I am too fat. You
00:10:16 --> 00:10:17 know, we talk about health and
00:10:17 --> 00:10:20 everything on the show before. I am a
00:10:20 --> 00:10:22 fair bit more than 100 kilos, but let's
00:10:22 --> 00:10:25 assume I was 100 kilos. Um, just because
00:10:25 --> 00:10:26 that's an aspirational goal and it would
00:10:26 --> 00:10:28 be nice if it were true one day. In
00:10:28 --> 00:10:30 fact, I'm 100 kilos and you make me a
00:10:30 --> 00:10:32 black hole. Um, I would be sad but
00:10:32 --> 00:10:34 probably wouldn't have long to think
00:10:34 --> 00:10:38 about it. At 100 kilos, I would be 10
00:10:38 --> 00:10:42 the 28 times less massive than the sun
00:10:42 --> 00:10:45 roughly. The sun is 10 to the 30. I'm 10
00:10:45 --> 00:10:49 2 10 the 28 is a difference 10 28 cubed
00:10:49 --> 00:10:54 is 28 56 84 so that's 10 84
00:10:54 --> 00:10:57 so that means I would disintegrate in 2
00:10:57 --> 00:11:02 * 10 67 * 10 - 84 which is about 10 -17
00:11:02 --> 00:11:05 years so suddenly a jumpy mass black
00:11:05 --> 00:11:08 hole would disintegrate and evaporate in
00:11:08 --> 00:11:11 a tiny fraction of a millisecond
00:11:11 --> 00:11:13 so these primordial mass black holes
00:11:13 --> 00:11:15 that evaporate
00:11:15 --> 00:11:19 are doing so because they're very small.
00:11:19 --> 00:11:20 You could, if you wanted to, and I'll
00:11:20 --> 00:11:21 leave this as an exercise to the reader
00:11:21 --> 00:11:23 because me doing mental arithmetic is
00:11:23 --> 00:11:25 not the most exciting thing, you could
00:11:25 --> 00:11:27 work out what mass a black hole would
00:11:27 --> 00:11:31 have to be to evaporate after 13.8
00:11:31 --> 00:11:34 billion years, which is about how old
00:11:34 --> 00:11:36 the universe is. The reason that's an
00:11:36 --> 00:11:37 interesting one is if there were any
00:11:37 --> 00:11:40 primordial mass black holes of that mass
00:11:40 --> 00:11:43 >> and they were to evaporate, they would
00:11:43 --> 00:11:44 be evaporating in the very near
00:11:44 --> 00:11:46 universe.
00:11:46 --> 00:11:47 And that would make them much easier to
00:11:48 --> 00:11:49 detect because the intensity of
00:11:49 --> 00:11:52 radiation we detect is proportional to
00:11:52 --> 00:11:54 one over the square of the distance. So
00:11:54 --> 00:11:55 if something's twice as far away, it's
00:11:55 --> 00:11:57 four times fainter. If it's three times
00:11:57 --> 00:12:00 as far away, it's nine times fainter. So
00:12:00 --> 00:12:02 I don't know. I'm not a black hole
00:12:02 --> 00:12:04 expert by any means. I I say that all
00:12:04 --> 00:12:06 the time.
00:12:06 --> 00:12:08 But if there were a black hole of that
00:12:08 --> 00:12:12 mass formed at the big bang, then maybe
00:12:12 --> 00:12:13 they would be evaporating in the
00:12:13 --> 00:12:15 relatively local universe and they're
00:12:15 --> 00:12:16 the ones that have been most likely to
00:12:16 --> 00:12:20 detect. I do not, however, know what the
00:12:20 --> 00:12:23 distribution of masses for primordial
00:12:24 --> 00:12:25 black holes would be. It's possibly on
00:12:25 --> 00:12:28 this Wikipedia page, but have a look and
00:12:28 --> 00:12:30 find out if it's your kind of thing. But
00:12:30 --> 00:12:33 hopefully that explains why there's a
00:12:33 --> 00:12:34 turnover point where things will decay
00:12:34 --> 00:12:36 in less than the age of the universe or
00:12:36 --> 00:12:38 more than the edge of the universe. And
00:12:38 --> 00:12:39 that mass is somewhere between the mass
00:12:39 --> 00:12:42 of a Jonty and the mass of the Earth.
00:12:42 --> 00:12:44 Okay. Fascinating. Yeah. All right.
00:12:44 --> 00:12:46 Thank you, Nick. Uh and Nick uh you
00:12:46 --> 00:12:49 might have heard us talking a week or
00:12:49 --> 00:12:52 two or three or four back uh about uh
00:12:52 --> 00:12:55 what they think might be the discovery
00:12:55 --> 00:12:57 of a primordial black hole. So that's a
00:12:57 --> 00:12:59 story worth looking up as well. Thanks
00:12:59 --> 00:13:01 for your question. This is Space Nuts
00:13:01 --> 00:13:04 Q&A edition with Andrew Dunley and Jonty
00:13:04 --> 00:13:08 Horner.
00:13:08 --> 00:13:09 >> G and I feel fine.
00:13:09 --> 00:13:10 >> Space Nuts.
00:13:10 --> 00:13:12 >> Uh, now Jonty, we've got an audio
00:13:12 --> 00:13:14 question that comes from a repeat
00:13:14 --> 00:13:17 offender. Uh, her name's Andrea.
00:13:17 --> 00:13:19 >> Hi guys. Um, got a couple of questions
00:13:19 --> 00:13:22 I'm hoping you can help me with. Um, the
00:13:22 --> 00:13:26 first question I have is, um, why does
00:13:26 --> 00:13:29 the dark side of the moon not have
00:13:29 --> 00:13:31 anywhere near as much damage as the face
00:13:31 --> 00:13:35 of the moon? Um,
00:13:35 --> 00:13:39 my second question is, um,
00:13:39 --> 00:13:42 why are the craters so shallow on the
00:13:42 --> 00:13:43 moon? Considering
00:13:44 --> 00:13:47 the size of some of the impacts zones
00:13:47 --> 00:13:49 and craters, um they all seem to be the
00:13:49 --> 00:13:51 same depth and which is quite shallow.
00:13:51 --> 00:13:54 Um especially if you look at Teao, which
00:13:54 --> 00:13:58 is 3 mi wide, um with an incredibly
00:13:58 --> 00:14:02 shallow crater. Um if you could explain
00:14:02 --> 00:14:05 for me why that occurs, that would be
00:14:05 --> 00:14:07 absolutely amazing. Thank you very much.
00:14:07 --> 00:14:10 Oh, and this is Andrea from Wanoo. and
00:14:10 --> 00:14:14 Andrew uh wannoo is actually a nunga or
00:14:14 --> 00:14:18 wjak nunga uh people word um that
00:14:18 --> 00:14:22 actually means the area of the digging
00:14:22 --> 00:14:25 stick. Unfortunately not pet kangaroo
00:14:25 --> 00:14:27 although I have had one of those as
00:14:27 --> 00:14:29 well. Thanks guys. Take care.
00:14:29 --> 00:14:31 >> Thanks Andrea. Lovely to hear from you.
00:14:31 --> 00:14:33 I'm glad she explained that. Um, you
00:14:33 --> 00:14:33 probably don't know what she's talking
00:14:34 --> 00:14:36 about, Jonty, but um, when Andrea last
00:14:36 --> 00:14:38 sent us an audio question and she said
00:14:38 --> 00:14:40 she was from Woo, I translated that to
00:14:40 --> 00:14:43 an indigenous word meaning I want a pet
00:14:43 --> 00:14:44 kangaroo.
00:14:44 --> 00:14:47 So, yeah, I know I was being silly, but
00:14:47 --> 00:14:49 um, no, it's um, place of the digging
00:14:49 --> 00:14:52 stick. Didn't know that. So um of course
00:14:52 --> 00:14:53 a digging stick was one of the uh
00:14:53 --> 00:14:57 implements that the ancient indigenous
00:14:57 --> 00:14:59 peoples of Australia used to use to uh
00:14:59 --> 00:15:03 to dig up food um grubs and other other
00:15:03 --> 00:15:05 bush tucker as we call it these days.
00:15:05 --> 00:15:07 So, it's probably worth mentioning for
00:15:07 --> 00:15:09 the listeners who are not in Australia
00:15:09 --> 00:15:11 that many of the Australian places have
00:15:11 --> 00:15:14 names that derive from the languages of
00:15:14 --> 00:15:15 the traditional owners of the land of
00:15:16 --> 00:15:17 the indigenous people of Australia who
00:15:18 --> 00:15:19 had many different countries with many
00:15:19 --> 00:15:22 different language groups. And the
00:15:22 --> 00:15:24 origin of the names is not always that
00:15:24 --> 00:15:27 wellknown or understood because during
00:15:27 --> 00:15:29 the invasion of Australia and during the
00:15:29 --> 00:15:30 events that happened all the way through
00:15:30 --> 00:15:32 to the 1970s there was a fairly
00:15:32 --> 00:15:34 aggressive attempt to even if you
00:15:34 --> 00:15:36 weren't wiping out the people to get rid
00:15:36 --> 00:15:37 of the culture and to get rid of the
00:15:37 --> 00:15:39 knowledge. Now I've just looked up to
00:15:39 --> 00:15:43 Womba where I am to o wa
00:15:43 --> 00:15:46 I live about 20ks west of there. Toua is
00:15:46 --> 00:15:47 an indigenous name. It's a really
00:15:47 --> 00:15:49 interesting town because it's like the
00:15:49 --> 00:15:51 Florida of Queensland. All the old
00:15:51 --> 00:15:53 people come here to retire.
00:15:53 --> 00:15:55 >> It's a beautiful place because
00:15:55 --> 00:15:59 Queensland has a particular climate, but
00:15:59 --> 00:16:01 Touumba is a moderated version of that
00:16:01 --> 00:16:03 climate because it sits on the Great
00:16:03 --> 00:16:05 Dividing Range at about 700 meters above
00:16:05 --> 00:16:07 sea level. So, it's not as humid as the
00:16:07 --> 00:16:08 coast. It doesn't get as hot as the
00:16:08 --> 00:16:10 coast. It has very lovely dry winters.
00:16:10 --> 00:16:14 Anyway, the name of Toumba is probably
00:16:14 --> 00:16:18 based on a word from likely the Gable or
00:16:18 --> 00:16:21 Jawar peoples. Not entirely sure, but if
00:16:21 --> 00:16:23 you look around for the origin of
00:16:23 --> 00:16:26 Towumba as a word, there's lots of
00:16:26 --> 00:16:27 suggestions. There is a suggestion that
00:16:27 --> 00:16:29 it was a word for swamp because Toumba
00:16:29 --> 00:16:31 sits in this swampy area on top of the
00:16:31 --> 00:16:33 hills. According to the Touumba regional
00:16:33 --> 00:16:35 council, it may have been named after a
00:16:35 --> 00:16:38 property in the area in the 1850s.
00:16:38 --> 00:16:40 Or it may have come from an Aboriginal
00:16:40 --> 00:16:42 word meaning either place where water
00:16:42 --> 00:16:44 sits, which would be the swamp thing, or
00:16:44 --> 00:16:46 place of melon, or place where reeds
00:16:46 --> 00:16:49 grow, or berries place, or white man.
00:16:49 --> 00:16:50 There are other things saying meeting of
00:16:50 --> 00:16:53 the waters or saying the name of Touumba
00:16:53 --> 00:16:55 maybe an anglicized version of the word
00:16:55 --> 00:16:58 bua which meant thunder in the dialect
00:16:58 --> 00:17:00 of the upper bett and gander tribes. So
00:17:00 --> 00:17:03 we just don't know and does make me a
00:17:03 --> 00:17:04 little bit sad. We talk about indigenous
00:17:04 --> 00:17:06 astronomy a bit and the wonderful work
00:17:06 --> 00:17:08 that um professor Dwayne Hammer and his
00:17:08 --> 00:17:09 students have done over the years
00:17:10 --> 00:17:11 working with the indigenous people of
00:17:11 --> 00:17:13 Australia but it does make me sad how
00:17:13 --> 00:17:14 much of this knowledge is lost where you
00:17:14 --> 00:17:16 don't even know the origin of the name.
00:17:16 --> 00:17:18 So it's wonderful that in this case we
00:17:18 --> 00:17:20 actually know where the name comes from
00:17:20 --> 00:17:21 and we can tag that. So when you're
00:17:22 --> 00:17:23 looking at the map of Australia and
00:17:23 --> 00:17:25 think a lot of the places are unusual
00:17:25 --> 00:17:27 from the perspective of someone from an
00:17:27 --> 00:17:29 Anglo background or from a European
00:17:29 --> 00:17:31 background because even though it's a
00:17:31 --> 00:17:33 primarily English-speaking country
00:17:33 --> 00:17:37 nowadays with a with that you know Anglo
00:17:37 --> 00:17:38 heritage a lot of the names are actually
00:17:38 --> 00:17:41 from the traditional owners even if the
00:17:41 --> 00:17:43 heritage of that name itself is lost.
00:17:43 --> 00:17:47 >> Yes. Uh where I live, do is supposedly a
00:17:47 --> 00:17:49 wordy word for red earth because the
00:17:49 --> 00:17:53 soil here is red. Uh which might sound
00:17:53 --> 00:17:55 horrifying to people. Uh it is when you
00:17:55 --> 00:17:57 get a dust storm and everything turns
00:17:57 --> 00:17:59 red.
00:17:59 --> 00:18:01 >> And when it gets wet and your bring it
00:18:01 --> 00:18:04 in because the red soil marks everything
00:18:04 --> 00:18:05 up, you know,
00:18:05 --> 00:18:07 >> dog goes out and gets their paws muddy
00:18:07 --> 00:18:09 and brings in red footprints.
00:18:09 --> 00:18:11 >> Red footprints on a light colored
00:18:11 --> 00:18:14 carpet. No. Terrible stuff. And of
00:18:14 --> 00:18:17 course, one that relates to astronomy is
00:18:17 --> 00:18:20 warmer, which is an indigenous word for
00:18:20 --> 00:18:23 uh the the implement they used to launch
00:18:23 --> 00:18:25 a spear. Rather than just throw the
00:18:25 --> 00:18:28 spear, they used to have a speciallymade
00:18:28 --> 00:18:29 um
00:18:29 --> 00:18:31 I suppose you'd call it a like a
00:18:31 --> 00:18:35 handheld catapult and it um and it
00:18:35 --> 00:18:37 >> and and it Yeah. And it flung the spear
00:18:37 --> 00:18:39 at greater speed and distance. And
00:18:39 --> 00:18:41 that's uh yeah it was called a WMAR and
00:18:41 --> 00:18:43 of course WRA rocket range is where
00:18:43 --> 00:18:47 Australia's uh early space efforts were
00:18:47 --> 00:18:48 uh were launched from in South
00:18:48 --> 00:18:50 Australia. So yeah it's um yeah it's
00:18:50 --> 00:18:52 fascinating history really is and
00:18:52 --> 00:18:54 >> of course the atal that I mentioned
00:18:54 --> 00:18:55 there I just double checked because it's
00:18:55 --> 00:18:58 like I remember an atal being a thing
00:18:58 --> 00:18:59 that used for throwing space turns out
00:18:59 --> 00:19:01 that that was an Aztec implement that
00:19:01 --> 00:19:02 served the same kind of process. So the
00:19:02 --> 00:19:05 word atal apparently comes from Aztec.
00:19:05 --> 00:19:08 >> Oh wow. I didn't know that. Back to you,
00:19:08 --> 00:19:09 Andrea. Yes.
00:19:09 --> 00:19:11 >> Uh, now the dark Okay, two questions.
00:19:11 --> 00:19:14 Dark side of the moon, uh, smoother.
00:19:14 --> 00:19:16 Now, I I've always been aware that the
00:19:16 --> 00:19:19 the side we can see is so rugged and and
00:19:19 --> 00:19:21 pockmarked and mountainous.
00:19:21 --> 00:19:21 >> Yes.
00:19:21 --> 00:19:24 >> But the side that we cannot see that
00:19:24 --> 00:19:26 Artemus 2 recently had a look at and
00:19:26 --> 00:19:28 where the Chinese have been running
00:19:28 --> 00:19:31 around on their little scooters, um,
00:19:31 --> 00:19:33 it's smoother. Why?
00:19:33 --> 00:19:38 >> Well, this is a weird one. So it looks
00:19:38 --> 00:19:39 more uniform when you look at it. And
00:19:40 --> 00:19:41 I'm I'm saying that very carefully
00:19:41 --> 00:19:43 rather than smoother because smoother
00:19:43 --> 00:19:46 invokes polished or smooth. Like your
00:19:46 --> 00:19:47 skin when you're a kid is a lot smoother
00:19:47 --> 00:19:48 than your skin when you get to my age
00:19:48 --> 00:19:50 and you've got all the wrinkles, right?
00:19:50 --> 00:19:50 >> Yeah.
00:19:50 --> 00:19:51 >> Um
00:19:51 --> 00:19:52 >> all the scars. See this one?
00:19:52 --> 00:19:53 >> Yeah.
00:19:53 --> 00:19:55 >> That's from a golf that's from a golf
00:19:55 --> 00:19:56 club. My neighbor hit me in the face
00:19:56 --> 00:19:57 with a seven iron.
00:19:58 --> 00:19:58 >> Yeah.
00:19:58 --> 00:19:59 >> It wasn't malicious. It was the back
00:19:59 --> 00:20:01 swing. I was standing too close. I was
00:20:01 --> 00:20:02 going to say about the adventures of
00:20:02 --> 00:20:04 having double, you know, they do
00:20:04 --> 00:20:06 something to pass the time. The reason
00:20:06 --> 00:20:07 that I'm being careful in my wording
00:20:07 --> 00:20:09 here and saying it looks more uniform
00:20:09 --> 00:20:11 rather than it's smoother is actually I
00:20:11 --> 00:20:13 don't think it is smoother, but I think
00:20:13 --> 00:20:15 it definitely does look more uniform. On
00:20:15 --> 00:20:17 the near side of the moon, it should be
00:20:17 --> 00:20:19 said that we're talking near side and
00:20:19 --> 00:20:20 far side. The dark side of the moon is
00:20:20 --> 00:20:22 simply the side of the moon pointed away
00:20:22 --> 00:20:24 from the sun and that rotates around as
00:20:24 --> 00:20:26 the moon goes around the earth, which is
00:20:26 --> 00:20:27 why we get the phases. Right? If you're
00:20:27 --> 00:20:29 stood on the moon, you'll get at a given
00:20:29 --> 00:20:31 location two weeks of daytime and two
00:20:31 --> 00:20:32 weeks of nighttime. And when it's
00:20:32 --> 00:20:34 nighttime for you, you'd be on the dark
00:20:34 --> 00:20:36 side of the moon. But when the moon's
00:20:36 --> 00:20:37 new, the dark side points towards us.
00:20:37 --> 00:20:39 The far side of the moon always points
00:20:39 --> 00:20:41 away from the Earth. Now, on the near
00:20:41 --> 00:20:43 side of the moon, which is a side we're
00:20:43 --> 00:20:47 familiar with, the view we get is very
00:20:47 --> 00:20:49 non-uniform because we've got the Mare
00:20:49 --> 00:20:51 and the non-mar regions. So the Mari are
00:20:51 --> 00:20:53 the seas which make up the man in the
00:20:53 --> 00:20:55 moon or whatever picture you have which
00:20:55 --> 00:20:57 are these flood bassalt areas. And then
00:20:57 --> 00:21:00 you've got the non-mari areas which are
00:21:00 --> 00:21:03 more traditionally rocky object looking.
00:21:03 --> 00:21:06 >> He's he's the drunk man in the moon uh
00:21:06 --> 00:21:08 here because he's upside down.
00:21:08 --> 00:21:11 >> Absolutely. Yeah. It's those areas that
00:21:11 --> 00:21:14 make the drunk man are flood bassalt
00:21:14 --> 00:21:16 outpourings on the near side of the moon
00:21:16 --> 00:21:18 that were formed early in the moon's
00:21:18 --> 00:21:20 formation. If you ascribe to the idea
00:21:20 --> 00:21:22 that there was a late heavy bombardment
00:21:22 --> 00:21:25 when the impact rate spiked, then they
00:21:25 --> 00:21:26 are thought to have formed there. But in
00:21:26 --> 00:21:28 actuality, evidence for the late heavy
00:21:28 --> 00:21:30 bombardment has pretty much dissipated.
00:21:30 --> 00:21:32 So the closer you are to impact studies
00:21:32 --> 00:21:34 and studies of the moon, the less
00:21:34 --> 00:21:35 strongly you hold to the idea of the
00:21:35 --> 00:21:37 late heavy bombardment was a thing. But
00:21:37 --> 00:21:39 as with all science, the further you get
00:21:39 --> 00:21:41 from certain expertise, the more out of
00:21:41 --> 00:21:43 date your knowledge is. So the late
00:21:43 --> 00:21:44 heavy bombardment is quite often still
00:21:44 --> 00:21:46 viewed as cannon in a lot of areas
00:21:46 --> 00:21:47 whereas those who were closest to the
00:21:48 --> 00:21:49 topic have a lot more doubt that it ever
00:21:50 --> 00:21:51 happened. But anyway on the near side of
00:21:51 --> 00:21:54 the moon you've got
00:21:54 --> 00:21:58 areas of the moon that didn't have a mar
00:21:58 --> 00:22:01 didn't have a flood bassalt outpouring
00:22:01 --> 00:22:03 and you've got areas that did. And then
00:22:03 --> 00:22:05 overlaid on that you've got some more
00:22:05 --> 00:22:06 recent impacts which are the rare
00:22:06 --> 00:22:09 craters where you've got weathered
00:22:09 --> 00:22:10 material on the surface that looks
00:22:10 --> 00:22:12 darker and an impact comes along digs
00:22:12 --> 00:22:13 through the darker material to the
00:22:13 --> 00:22:15 unweathered material below and splashes
00:22:15 --> 00:22:17 it across the surface. So the near side
00:22:17 --> 00:22:18 of the moon looks very non-uniform
00:22:18 --> 00:22:20 because you've got that disparity
00:22:20 --> 00:22:22 between the flood bassels and the non-
00:22:22 --> 00:22:25 flood basel. And the non- flood basel is
00:22:25 --> 00:22:27 an older surface because the flood basel
00:22:27 --> 00:22:28 erases the evidence of what happened
00:22:28 --> 00:22:31 before. So there are slightly fewer
00:22:31 --> 00:22:33 impacts on the MAR than there are on the
00:22:33 --> 00:22:36 non-mar because it's a younger surface.
00:22:36 --> 00:22:39 Prior to any spacecraft going to the
00:22:39 --> 00:22:40 moon, the assumption was the far side of
00:22:40 --> 00:22:42 the moon would look like the near side.
00:22:42 --> 00:22:43 >> But when we sent the spacecraft there,
00:22:44 --> 00:22:45 we realized it doesn't. And that was a
00:22:45 --> 00:22:47 big puzzle for astronomers for a very
00:22:47 --> 00:22:49 long time in that there are effectively
00:22:49 --> 00:22:51 no mare on the far side. There's little
00:22:51 --> 00:22:53 bits but not very much.
00:22:53 --> 00:22:56 Now the idea here is that when the moon
00:22:56 --> 00:22:58 formed, it formed as a result of a giant
00:22:58 --> 00:23:01 impact on the earth. The moon accreted
00:23:01 --> 00:23:02 and initially was fully molten and then
00:23:02 --> 00:23:05 it cooled from the outside in. So at a
00:23:05 --> 00:23:07 certain time in the moon's youth, the
00:23:07 --> 00:23:09 surface was very thin above a magma
00:23:09 --> 00:23:12 ocean, above a molten ocean. And at that
00:23:12 --> 00:23:14 time, small impacts wouldn't penetrate
00:23:14 --> 00:23:16 that crust and you get normal craters,
00:23:16 --> 00:23:18 you get mountain ranges and all the rest
00:23:18 --> 00:23:19 of it forming. But when you got a really
00:23:19 --> 00:23:21 big impact that would break through the
00:23:22 --> 00:23:24 crust, create a big impact basin that
00:23:24 --> 00:23:26 would then be flooded with flood bassel
00:23:26 --> 00:23:28 which gave you this incredibly flat
00:23:28 --> 00:23:30 smooth floor and erased all the evidence
00:23:30 --> 00:23:33 of the impacts before.
00:23:33 --> 00:23:34 Eventually the moon cooled enough that
00:23:34 --> 00:23:36 the that any molten material was
00:23:36 --> 00:23:38 sufficiently deep that even the biggest
00:23:38 --> 00:23:41 impacts would not cause these flood
00:23:41 --> 00:23:43 bassel outpourings. coupled with the
00:23:43 --> 00:23:46 fact that as the solar system aged it
00:23:46 --> 00:23:47 cleaned up very effectively and the big
00:23:47 --> 00:23:49 impactors were effectively gone. So the
00:23:49 --> 00:23:51 big impacts were early on. So the idea
00:23:51 --> 00:23:54 was that the mare are caused by the very
00:23:54 --> 00:23:57 biggest impacts that will create impact
00:23:57 --> 00:23:59 basins that are hundreds or thousands of
00:23:59 --> 00:24:02 kilometers across that are broadly
00:24:02 --> 00:24:04 circular in shape before other things
00:24:04 --> 00:24:07 happen and that they fill with molten
00:24:07 --> 00:24:09 material. And the areas on the near side
00:24:09 --> 00:24:11 that are not in the mar are the areas
00:24:11 --> 00:24:14 that were not induced into one of these
00:24:14 --> 00:24:15 flood basel output or rings. Effectively
00:24:15 --> 00:24:17 they escaped being in one of the craters
00:24:17 --> 00:24:20 from the very biggest impactors.
00:24:20 --> 00:24:22 We thought that prior to going to the
00:24:22 --> 00:24:23 far side of the moon you would have
00:24:24 --> 00:24:25 assumed that the far side would be the
00:24:25 --> 00:24:27 same but it turns out that it's not.
00:24:27 --> 00:24:29 That was a real problem because this
00:24:29 --> 00:24:31 idea that the impacts were big enough to
00:24:31 --> 00:24:35 punch through and flood to the surface
00:24:35 --> 00:24:38 should work all across the moon. So why
00:24:38 --> 00:24:39 then do you not get the flood bass
00:24:39 --> 00:24:41 outpourings on the far side of the moon?
00:24:41 --> 00:24:43 There are kind of three explanations
00:24:43 --> 00:24:45 that have been put forward for this. The
00:24:45 --> 00:24:48 first of which is frankly bunkam. The
00:24:48 --> 00:24:50 idea that the near side of the moon
00:24:50 --> 00:24:52 faced the earth and the earth shielded
00:24:52 --> 00:24:54 it and so therefore there'd be more
00:24:54 --> 00:24:55 impacts on the far side. Well that just
00:24:56 --> 00:24:57 kind of
00:24:57 --> 00:25:00 runs counterintuitive. You'd say the far
00:25:00 --> 00:25:01 side experienced more hits. It gets more
00:25:01 --> 00:25:03 cratering. Well I don't believe that
00:25:03 --> 00:25:04 from an earth is so small from the
00:25:04 --> 00:25:06 moon's point of view. barely a shield at
00:25:06 --> 00:25:09 all. But if that were the case, surely
00:25:09 --> 00:25:11 you'd expect more mar on the far side
00:25:11 --> 00:25:12 because you get more of these big
00:25:12 --> 00:25:14 impacts. So that to me doesn't work. So
00:25:14 --> 00:25:18 we can rule that out. The other answers
00:25:18 --> 00:25:21 are kind of tied together, but the idea
00:25:21 --> 00:25:26 is that the moon had a thicker layer
00:25:26 --> 00:25:28 above the molten layer on the far side
00:25:28 --> 00:25:31 of the moon to the near side. Two ways
00:25:31 --> 00:25:33 you can make that happen. One idea is
00:25:33 --> 00:25:36 that the heat from the young earth which
00:25:36 --> 00:25:37 would also have been molten at this time
00:25:37 --> 00:25:39 and being bigger will keep its heat
00:25:39 --> 00:25:41 longer. So will be molten for longer.
00:25:41 --> 00:25:43 The earth would be irradiating the moon.
00:25:43 --> 00:25:44 The moon would be close to the earth
00:25:44 --> 00:25:46 when they formed cuz it's moved away
00:25:46 --> 00:25:49 since. That radiative heat would have
00:25:49 --> 00:25:51 kept the near side of the moon hot for
00:25:51 --> 00:25:53 longer which the molten material on the
00:25:53 --> 00:25:55 surface would have stayed for longer but
00:25:55 --> 00:25:57 also it would have taken longer for the
00:25:57 --> 00:26:00 crust to thicken on that side. So
00:26:00 --> 00:26:01 therefore the crust on the far side of
00:26:01 --> 00:26:03 the moon would have formed quicker and
00:26:03 --> 00:26:06 thicker. The other idea is that you get
00:26:06 --> 00:26:07 the same kind of effect from tidal
00:26:08 --> 00:26:10 forces that the tidal influence of the
00:26:10 --> 00:26:11 earth on the moon is stronger on the
00:26:11 --> 00:26:12 near side than the far side because the
00:26:12 --> 00:26:15 strength of tides falls off as distance
00:26:15 --> 00:26:16 to the power four. So that's a very
00:26:16 --> 00:26:19 strong very rapid effect. Yeah. Possibly
00:26:19 --> 00:26:22 both of those things to com combine give
00:26:22 --> 00:26:24 you a crust around the moon that is
00:26:24 --> 00:26:25 thinner on the near side than the far
00:26:25 --> 00:26:28 side at all times as the moon cools on
00:26:28 --> 00:26:31 the interior which means that the far
00:26:31 --> 00:26:34 side of the moon the molten material was
00:26:34 --> 00:26:37 deeply enough buried quickly enough that
00:26:37 --> 00:26:39 no m forming impact happened. You've got
00:26:39 --> 00:26:40 the South Pole Lake Kim Basin which is
00:26:40 --> 00:26:43 the biggest impact scar on the moon
00:26:43 --> 00:26:44 doesn't really have much flood bassalt
00:26:44 --> 00:26:46 in it which either means that it is
00:26:46 --> 00:26:49 younger and therefore the interior had
00:26:49 --> 00:26:51 cooled enough that it didn't crack that
00:26:51 --> 00:26:56 egg or that it was an area where the
00:26:56 --> 00:26:58 crust was thicker anyway. You know, so
00:26:58 --> 00:27:00 the idea is that the difference between
00:27:00 --> 00:27:01 the near side and the far side of the
00:27:01 --> 00:27:02 moon is down to the thickness of the
00:27:02 --> 00:27:04 crust when the biggest impacts were
00:27:04 --> 00:27:06 happening. And the idea that probably
00:27:06 --> 00:27:08 due to a combination of tidal effects
00:27:08 --> 00:27:10 and radiative heating from the
00:27:10 --> 00:27:13 incredibly luminous molten earth, the
00:27:13 --> 00:27:15 near side of the moon stayed a thicker
00:27:15 --> 00:27:17 shell and therefore was more effectively
00:27:17 --> 00:27:19 punctured. And so the near side got the
00:27:19 --> 00:27:21 vare and the far side looks more like
00:27:21 --> 00:27:24 your typical rocky objects like Mercury
00:27:24 --> 00:27:25 like a lot of the rocky moons and stuff
00:27:25 --> 00:27:27 like that in the outer solar system.
00:27:27 --> 00:27:29 That's the thinking there. But it is
00:27:29 --> 00:27:31 really strikingly obvious when you see
00:27:31 --> 00:27:34 photos of the far side of the moon and
00:27:34 --> 00:27:35 you're not told it's the far side of the
00:27:35 --> 00:27:36 moon, you assume you're looking at an
00:27:36 --> 00:27:39 object that is not the moon because no
00:27:39 --> 00:27:41 different to our experience of the moon.
00:27:41 --> 00:27:43 >> Indeed. So, so part two of your question
00:27:43 --> 00:27:45 you basically covered because of the
00:27:45 --> 00:27:46 deep impact
00:27:46 --> 00:27:48 >> a little bit.
00:27:48 --> 00:27:50 >> Part two is a bit more complex.
00:27:50 --> 00:27:51 >> So, this is about this is the one about
00:27:51 --> 00:27:52 shallow craters.
00:27:52 --> 00:27:55 >> Crater shallow and craters are shallow
00:27:55 --> 00:27:57 not just on the moon but everywhere.
00:27:57 --> 00:27:58 There is a boundary between what
00:27:58 --> 00:28:00 researchers describe as a simple crater
00:28:00 --> 00:28:02 and a complex crater. And
00:28:02 --> 00:28:05 >> the size at which you get that boundary
00:28:05 --> 00:28:06 varies dependent on the strength of
00:28:06 --> 00:28:09 material that's impacted and also the
00:28:09 --> 00:28:10 mass of the planet and therefore the
00:28:10 --> 00:28:12 strength of gravity. So I believe on the
00:28:12 --> 00:28:15 earth it's about 8 or 9 km. For the moon
00:28:15 --> 00:28:18 it's about 18 km.
00:28:18 --> 00:28:20 Smaller than that you get a simple
00:28:20 --> 00:28:21 crater that forms which looks very
00:28:21 --> 00:28:23 similar to what you get if you almost
00:28:23 --> 00:28:26 just threw a rock really hard into sand
00:28:26 --> 00:28:27 or something. You get the typical
00:28:27 --> 00:28:29 B-shaped crater like meteor crater in
00:28:29 --> 00:28:32 Arizona. Really nice example. Yeah.
00:28:32 --> 00:28:36 >> At a size above about like say 8 or 9 km
00:28:36 --> 00:28:38 on Earth or above about 20 km on the
00:28:38 --> 00:28:40 moon, you get to the domain where you
00:28:40 --> 00:28:42 get a complex crater. And complex
00:28:42 --> 00:28:44 craters are characterized by having
00:28:44 --> 00:28:48 quite often central impact peaks but
00:28:48 --> 00:28:50 also having these much shallower depths
00:28:50 --> 00:28:53 compared to their width. You know, and
00:28:53 --> 00:28:55 it's particularly true for the Mar where
00:28:55 --> 00:28:56 they're flood basults where you have a
00:28:56 --> 00:28:59 very shallow crater for the width of the
00:28:59 --> 00:29:01 crater. But it's true even if you look
00:29:01 --> 00:29:04 at 20 km craters on the moon and there's
00:29:04 --> 00:29:05 a beautiful photo incidentally if you
00:29:05 --> 00:29:07 look on some of the NASA images there's
00:29:07 --> 00:29:09 a beautiful photo of the crater Arisus
00:29:09 --> 00:29:11 taken by the lunar reconnaissance
00:29:11 --> 00:29:13 orbiter and that shows this kind of
00:29:13 --> 00:29:15 terracing around the walls the central
00:29:15 --> 00:29:17 peaks and so there's a few things going
00:29:17 --> 00:29:20 on here that contribute to why what we
00:29:20 --> 00:29:22 describe as being
00:29:22 --> 00:29:25 um what I say complex craters are
00:29:25 --> 00:29:27 actually
00:29:27 --> 00:29:28 um
00:29:28 --> 00:29:30 shallower compared to their width than
00:29:30 --> 00:29:32 the simple ones. And there's a few
00:29:32 --> 00:29:33 things that have been suggested to this.
00:29:33 --> 00:29:36 So complex craters have depths that can
00:29:36 --> 00:29:39 be a 15th or 25th or even less of the
00:29:39 --> 00:29:41 crater width which looks very very
00:29:41 --> 00:29:43 shallow. Now there's a few things
00:29:43 --> 00:29:46 proposed in for this. Firstly, when you
00:29:46 --> 00:29:48 form a bigger crater, the walls can
00:29:48 --> 00:29:51 slump in. So material slides and
00:29:51 --> 00:29:53 gradually you get this material from the
00:29:53 --> 00:29:55 edges sliding into the middle. And if
00:29:55 --> 00:29:56 you look at that photo of Verisarchus,
00:29:56 --> 00:29:59 it looks very much like that's happened.
00:29:59 --> 00:30:01 evidence of landslides that have filled
00:30:01 --> 00:30:04 in the crater and made it shallower.
00:30:04 --> 00:30:07 >> The other thing is craters that big are
00:30:07 --> 00:30:09 large enough to render the material
00:30:09 --> 00:30:12 where the impact happens molten. And in
00:30:12 --> 00:30:14 other words, the material can flow like
00:30:14 --> 00:30:16 a liquid rather than behaving like a
00:30:16 --> 00:30:17 solid material of your desk.
00:30:17 --> 00:30:19 >> Well, you can you can still see a
00:30:19 --> 00:30:20 rebound point in the middle of the
00:30:20 --> 00:30:21 crater too.
00:30:21 --> 00:30:23 >> So that's it. So the stuff at the
00:30:23 --> 00:30:24 middle, the central peaks are thought to
00:30:24 --> 00:30:26 be rebound of this fluid activ fluid
00:30:26 --> 00:30:28 material springing back before it
00:30:28 --> 00:30:30 freezes solid again effectively. And
00:30:30 --> 00:30:32 then the flat base of these craters that
00:30:32 --> 00:30:34 makes them shallower is because you make
00:30:34 --> 00:30:36 a pool of liquid that spreads out and
00:30:36 --> 00:30:38 settles
00:30:38 --> 00:30:39 and so therefore you get these shallower
00:30:40 --> 00:30:42 things. Whereas with smaller craters you
00:30:42 --> 00:30:44 don't get to that point. So you get much
00:30:44 --> 00:30:46 more material behaving more as a solid
00:30:46 --> 00:30:49 than a liquid effectively. So the
00:30:49 --> 00:30:50 thinking is for these complex craters
00:30:50 --> 00:30:52 and like I say for the moon I think the
00:30:52 --> 00:30:54 size scale is what 18 to 20 km something
00:30:54 --> 00:30:57 like that it's a point at which you
00:30:57 --> 00:30:58 transition from simply behaving as a
00:30:58 --> 00:31:01 solid to the surface behaving in more of
00:31:01 --> 00:31:03 a liquid fashion. You get complex
00:31:03 --> 00:31:05 craters having central peaks they have
00:31:05 --> 00:31:08 terraces. They've got flat flows. The
00:31:08 --> 00:31:10 more massive the object the smaller the
00:31:10 --> 00:31:14 boundary is because gravity has a role
00:31:14 --> 00:31:15 in this.
00:31:15 --> 00:31:17 >> Yeah. Um and then you get the basins
00:31:18 --> 00:31:19 which are even bigger and they're where
00:31:19 --> 00:31:21 you get the flooding from bassalts which
00:31:21 --> 00:31:23 makes them even shallower compared to
00:31:23 --> 00:31:26 their width. So there is some beautiful
00:31:26 --> 00:31:29 complexity of this where it's all to do
00:31:29 --> 00:31:32 with the physical behavior of material
00:31:32 --> 00:31:34 and how that changes as an impact gets
00:31:34 --> 00:31:36 larger and larger and therefore more and
00:31:36 --> 00:31:39 more damaging and energetic. Now NASA
00:31:39 --> 00:31:42 have a Marsded website um where they
00:31:42 --> 00:31:44 actually explicitly say if you Google
00:31:44 --> 00:31:48 for this it's marked.asu.edu
00:31:48 --> 00:31:49 and then a really long string
00:31:49 --> 00:31:51 afterwards. It's a Mars education thing
00:31:51 --> 00:31:53 at Arizona State University. And I'll
00:31:53 --> 00:31:55 just quote here
00:31:55 --> 00:31:57 compared to simple craters complex
00:31:57 --> 00:32:00 craters also generate a lot more impact
00:32:00 --> 00:32:03 melted rock. This typically flows and
00:32:03 --> 00:32:04 pools like lava to form a sheet that
00:32:04 --> 00:32:07 covers a shattered rock known as breia
00:32:07 --> 00:32:09 on the crater floor. The crater's inner
00:32:09 --> 00:32:11 walls may slump downwards rotating
00:32:11 --> 00:32:13 backwards in blocks which can widen the
00:32:13 --> 00:32:15 crater's rim and line the inner walls
00:32:15 --> 00:32:18 with terraces. But as a result, complex
00:32:18 --> 00:32:19 craters look shallow. They have rim
00:32:19 --> 00:32:21 diameters about 30 times greater than
00:32:21 --> 00:32:23 their depths. By comparison, simple
00:32:23 --> 00:32:25 craters are about five times wider than
00:32:25 --> 00:32:27 they are deep. Um earlier on it said the
00:32:28 --> 00:32:29 more energy an impact delivers, the
00:32:29 --> 00:32:31 bigger the cavity on the ground. But
00:32:31 --> 00:32:32 immediately after the blast, the center
00:32:32 --> 00:32:34 of the cavity begins to rise as rocks
00:32:34 --> 00:32:35 rebound from the shock. That's what
00:32:35 --> 00:32:37 gives you the mountains. This uplift
00:32:37 --> 00:32:39 gives you a central peak or cluster of
00:32:39 --> 00:32:41 peaks. So that's a really nice way of
00:32:41 --> 00:32:44 condensing my lengthy waffly answer into
00:32:44 --> 00:32:45 something a bit more simple and
00:32:45 --> 00:32:47 straightforward.
00:32:47 --> 00:32:49 >> Fair enough. Okay. Uh now Andrea, you
00:32:49 --> 00:32:51 can believe all of that or you can go
00:32:51 --> 00:32:53 with my theory that the Luna City
00:32:53 --> 00:32:55 Council were on strike and they didn't
00:32:55 --> 00:32:58 finish filling the potholes.
00:32:58 --> 00:33:02 I go with option two. Um, Andrea, thanks
00:33:02 --> 00:33:03 for your question. Great to hear from
00:33:03 --> 00:33:05 you. Thanks for explaining Woo. This is
00:33:05 --> 00:33:08 Space Nuts, a Q&A edition with Professor
00:33:08 --> 00:33:13 Jonty Horner and Andrew Dunley.
00:33:13 --> 00:33:15 >> Okay, we've had a problem here.
00:33:15 --> 00:33:17 >> This is Houston. Say again, please.
00:33:17 --> 00:33:19 >> Houston, we've had a main undervolt.
00:33:19 --> 00:33:22 >> Roger. Main. Okay, stand by 13. We're
00:33:22 --> 00:33:23 looking at it.
00:33:23 --> 00:33:25 >> Space Muts.
00:33:25 --> 00:33:27 Our last question uh comes in two parts
00:33:27 --> 00:33:31 and it uh comes from Eli. Uh hello from
00:33:31 --> 00:33:33 Coachella Valley in California. Wasn't
00:33:33 --> 00:33:36 Coachella in the news recently for some
00:33:36 --> 00:33:39 big suare that happened there? Yeah.
00:33:39 --> 00:33:41 >> Uh big event. Uh anyway, he says the
00:33:41 --> 00:33:43 grasshoppers have decided to invade.
00:33:43 --> 00:33:45 Believe it or not, Eli, exactly the same
00:33:45 --> 00:33:48 thing is happening where I am. We have
00:33:48 --> 00:33:50 uh locust plagues once in a blue moon
00:33:50 --> 00:33:52 and we we had a little one recently.
00:33:52 --> 00:33:54 wasn't uh too significant. But I I have
00:33:54 --> 00:33:56 discovered with with locusts or
00:33:56 --> 00:33:58 grasshoppers or whatever you call them
00:33:58 --> 00:34:01 wherever you are that if you drive over
00:34:01 --> 00:34:04 50 kilometers an hour they splatter. Uh
00:34:04 --> 00:34:07 if you drive under 50 km an hour they
00:34:07 --> 00:34:09 bounce off. Important safety tip
00:34:09 --> 00:34:11 especially because when they splatter
00:34:11 --> 00:34:13 they stink
00:34:13 --> 00:34:14 >> and it's very hard to get off when
00:34:14 --> 00:34:15 they're dry.
00:34:15 --> 00:34:17 >> I'd love to have a swap toy wear. We've
00:34:17 --> 00:34:19 had an incredibly dry last few months
00:34:19 --> 00:34:20 here. It's been our wet season. And
00:34:20 --> 00:34:22 we've had 40 mil of rain in 4 months.
00:34:22 --> 00:34:23 >> Wow.
00:34:23 --> 00:34:25 >> Which is hooray. You know, that's really
00:34:25 --> 00:34:26 what you want in your wet season when
00:34:26 --> 00:34:28 the dry season's about to start. But
00:34:28 --> 00:34:29 what that means is that we're probably
00:34:29 --> 00:34:31 going to see yet another mouse plague.
00:34:31 --> 00:34:33 And mouse plagues are sad because in the
00:34:33 --> 00:34:35 times that are good, mice reproduce like
00:34:35 --> 00:34:36 crazy, but then you get the boom
00:34:36 --> 00:34:38 busting. And so you start getting lots
00:34:38 --> 00:34:40 of them coming to your house. And I'm
00:34:40 --> 00:34:41 soft-hearted. I don't want to hurt them
00:34:41 --> 00:34:43 or do anything, but at the same time, I
00:34:43 --> 00:34:44 don't want them pooing on everything in
00:34:44 --> 00:34:46 my kitchen.
00:34:46 --> 00:34:48 >> So we're getting mouse plague time. So,
00:34:48 --> 00:34:50 I I I suspect that locust plagues are
00:34:50 --> 00:34:52 horrible, but mouse plague is an
00:34:52 --> 00:34:53 entirely different horror. And
00:34:53 --> 00:34:55 >> mouse plagues are worse. Yeah.
00:34:55 --> 00:34:57 >> Because the mice try to find somewhere
00:34:57 --> 00:35:00 to hide inside. Locusts only get in if
00:35:00 --> 00:35:02 they've got an open avenue. Otherwise,
00:35:02 --> 00:35:04 they just stay outside and
00:35:04 --> 00:35:06 >> you know, and they also are very
00:35:06 --> 00:35:08 disturbing when you're trying to putt on
00:35:08 --> 00:35:09 a golf.
00:35:09 --> 00:35:10 >> Oh, absolutely.
00:35:10 --> 00:35:13 >> They get in the way.
00:35:13 --> 00:35:14 >> Sorry. You walk into the kitchen at
00:35:14 --> 00:35:16 night or you walk somewhere and you just
00:35:16 --> 00:35:17 see something move in the periphery of
00:35:17 --> 00:35:18 unit and that's always a little
00:35:18 --> 00:35:19 disturbing.
00:35:19 --> 00:35:20 >> Yeah.
00:35:20 --> 00:35:21 >> Yeah. Well, we
00:35:21 --> 00:35:21 >> Yeah,
00:35:21 --> 00:35:23 >> we're talk we're talking mouse plague
00:35:23 --> 00:35:25 here as well. So, we could have we could
00:35:25 --> 00:35:28 have both. But our last big locust
00:35:28 --> 00:35:30 plague, uh it was so big the birds just
00:35:30 --> 00:35:32 got fed up with eating them. So, they
00:35:32 --> 00:35:35 gave up as well. It's very weird. Um
00:35:35 --> 00:35:37 Eli, what are you asking us? Uh since
00:35:37 --> 00:35:40 you mentioned a pority of questions, I
00:35:40 --> 00:35:44 hope you don't mind. Um, a twofer. Okay,
00:35:44 --> 00:35:46 we well we've got two questions then.
00:35:46 --> 00:35:48 Uh, when the solar system formed, I
00:35:48 --> 00:35:50 always imagined the inner rockier
00:35:50 --> 00:35:52 planets as having more heavier elements
00:35:52 --> 00:35:54 due to their greater mass and gravity
00:35:54 --> 00:35:57 and with lighter elements collecting
00:35:57 --> 00:35:59 more in the outer gas giants. But then I
00:35:59 --> 00:36:02 realized, isn't the sun mostly hydrogen,
00:36:02 --> 00:36:05 the lightest element? Now I'm confused.
00:36:05 --> 00:36:06 That's his first question.
00:36:06 --> 00:36:07 >> Yeah. So,
00:36:07 --> 00:36:10 >> and this is this is your bullpen, isn't
00:36:10 --> 00:36:11 it? This is your area of expertise.
00:36:11 --> 00:36:13 >> This is much more my comfort zone. So,
00:36:13 --> 00:36:15 this is um
00:36:15 --> 00:36:16 >> I hope you realize I did try to find
00:36:16 --> 00:36:18 questions that worked for you.
00:36:18 --> 00:36:20 >> No, no, that's all good. And it it means
00:36:20 --> 00:36:21 you can leave the cosmology ones for
00:36:21 --> 00:36:23 when Fred gets back as well, which is
00:36:23 --> 00:36:25 great. This is a lovely question and it
00:36:25 --> 00:36:28 speaks to how our understanding of how
00:36:28 --> 00:36:29 planets form has changed over time. And
00:36:30 --> 00:36:32 we've now got quite a high level of
00:36:32 --> 00:36:34 complexity in the ideas we have behind
00:36:34 --> 00:36:36 planet formation. But a really
00:36:36 --> 00:36:38 fundamental part of it is that
00:36:38 --> 00:36:41 everything in the solar system to first
00:36:41 --> 00:36:43 order has the same composition as the
00:36:43 --> 00:36:46 sun because we all form from the same
00:36:46 --> 00:36:47 material. We formed from an enormous
00:36:47 --> 00:36:48 cloud of gas and dust called a giant
00:36:48 --> 00:36:51 molecular cloud that collapsed under its
00:36:51 --> 00:36:53 own gravity. You you got effectively the
00:36:53 --> 00:36:55 protostar sun forming in the middle with
00:36:55 --> 00:36:56 a dis of material around it we call a
00:36:56 --> 00:36:59 protolanetary disc. And in that disc you
00:36:59 --> 00:37:03 have solid material and gaseous material
00:37:03 --> 00:37:05 going around the sun orbiting the sun
00:37:05 --> 00:37:06 collapsing to a disc because of the
00:37:06 --> 00:37:08 conservation of angular momentum. So
00:37:08 --> 00:37:10 kind of where the earth is material was
00:37:10 --> 00:37:13 whizzing around at about 30 km a second
00:37:13 --> 00:37:15 but individual dust grains that were
00:37:15 --> 00:37:17 next to each other were both moving at
00:37:17 --> 00:37:19 about the same speed. So very little
00:37:19 --> 00:37:21 difference in speed between the
00:37:21 --> 00:37:22 particles even though they're going
00:37:22 --> 00:37:25 really quickly. Now the further you are
00:37:25 --> 00:37:26 from the sun, the colder the temperature
00:37:26 --> 00:37:29 is in that disc. And every single
00:37:29 --> 00:37:32 material you can think of has a
00:37:32 --> 00:37:34 sublimation temperature. Below that
00:37:34 --> 00:37:36 temperature it will be solid and above
00:37:36 --> 00:37:39 that temperature it will be gas. Reason
00:37:39 --> 00:37:40 I'm not talking about liquid is in order
00:37:40 --> 00:37:42 to have liquid you need pressure. And in
00:37:42 --> 00:37:44 this case you don't have or you don't
00:37:44 --> 00:37:46 have enough. So you either have solid or
00:37:46 --> 00:37:47 gas.
00:37:47 --> 00:37:47 >> Yep.
00:37:47 --> 00:37:51 >> If you are gas then you don't form
00:37:51 --> 00:37:53 planets initially. If you're solid, you
00:37:53 --> 00:37:55 can do so. What happens all through this
00:37:55 --> 00:37:58 disc for a variety of different bits of
00:37:58 --> 00:38:00 physics going on, you get whatever solid
00:38:00 --> 00:38:02 material you have at that distance
00:38:02 --> 00:38:04 colliding,
00:38:04 --> 00:38:06 sticking together, forming bigger bits.
00:38:06 --> 00:38:08 And so you get from millimeter to meter
00:38:08 --> 00:38:11 to kilometer to planet size bits of
00:38:11 --> 00:38:14 debris. As you get bigger, gravity can
00:38:14 --> 00:38:16 start taking on a role and start pulling
00:38:16 --> 00:38:17 in a bit of extra stuff so you can feed
00:38:18 --> 00:38:19 quicker. Plus, if you're bigger, you've
00:38:19 --> 00:38:21 got a bigger cross-section, so you hit
00:38:21 --> 00:38:23 more things to devour them. So, you get
00:38:23 --> 00:38:24 this process where you get lots of small
00:38:24 --> 00:38:26 things making a few bigger things and
00:38:26 --> 00:38:29 the big ones tend to dominate. Um, so a
00:38:29 --> 00:38:31 thing called oligarchic growth is the
00:38:31 --> 00:38:33 idea. And you form planetessimals and
00:38:33 --> 00:38:35 then oligarchs, which are protolanets,
00:38:35 --> 00:38:37 and a few of them collide all the rest
00:38:37 --> 00:38:40 of it. If you are far enough from the
00:38:40 --> 00:38:43 sun, you're beyond what's known as the
00:38:43 --> 00:38:45 water ice line. Now that's a point at
00:38:45 --> 00:38:47 which the temperature is below the
00:38:47 --> 00:38:49 sublimation point of water. So instead
00:38:49 --> 00:38:51 of water being a gas or vapor, it's a
00:38:51 --> 00:38:54 solid. Now we always imagine water being
00:38:54 --> 00:38:55 quite scarce. And I just said we've had
00:38:55 --> 00:38:58 40 mm of rain in the last 4 months. So
00:38:58 --> 00:39:00 water is very scarce here. But in terms
00:39:00 --> 00:39:02 of compounds in the universe, water is
00:39:02 --> 00:39:05 one of the most abundant things there is
00:39:05 --> 00:39:06 because it's a combination of hydrogen
00:39:06 --> 00:39:09 which is the most common atom with 74
00:39:09 --> 00:39:11 75% of all atoms and oxygen which is the
00:39:11 --> 00:39:13 second most common atom with about 1% of
00:39:14 --> 00:39:16 all atoms. Put hydrogen oxygen together
00:39:16 --> 00:39:18 and you get water. So in the
00:39:18 --> 00:39:21 protolanetary disc around the sun, water
00:39:21 --> 00:39:23 was probably about the most common
00:39:23 --> 00:39:25 species other than molecular hydrogen
00:39:25 --> 00:39:28 molecular and helium atoms. Lots and
00:39:28 --> 00:39:29 lots of water. Now where the earth
00:39:29 --> 00:39:32 formed it was too hot. So you don't have
00:39:32 --> 00:39:35 water as a solid. So you form the earth
00:39:35 --> 00:39:37 dry. There's no solid water to accrete.
00:39:37 --> 00:39:39 You might get a little bit of water as a
00:39:40 --> 00:39:41 gas that is trapped in the solid
00:39:41 --> 00:39:44 material. Which is why people think most
00:39:44 --> 00:39:45 of the earth's water was delivered from
00:39:45 --> 00:39:47 further out because if far enough out
00:39:48 --> 00:39:50 you form from primarily water with
00:39:50 --> 00:39:52 everything else added in. So the inner
00:39:52 --> 00:39:54 solar system you don't have that water
00:39:54 --> 00:39:56 to accrete. So you're limited to the
00:39:56 --> 00:39:58 things that are solid at higher
00:39:58 --> 00:40:00 temperatures. So you're limited to
00:40:00 --> 00:40:02 accreting from rock and metal. So you
00:40:02 --> 00:40:05 get turmeric planets or is the archaic
00:40:05 --> 00:40:07 way of saying it or terrestrial planets.
00:40:08 --> 00:40:10 Beyond the ice line, water ice dominates
00:40:10 --> 00:40:12 the solid material. So you've got a lot
00:40:12 --> 00:40:14 more to feed from. So you grow more
00:40:14 --> 00:40:16 quickly and you can get more massive
00:40:16 --> 00:40:18 planets more quickly which where Jupiter
00:40:18 --> 00:40:20 and Saturn come in. Now, there's a lot
00:40:20 --> 00:40:21 of discussion about how they may have
00:40:22 --> 00:40:23 migrated through the nebula, all the
00:40:23 --> 00:40:25 rest of it, and the subtleties of the
00:40:25 --> 00:40:27 formation. In other planetary systems,
00:40:27 --> 00:40:29 we have planets like Jupiter orbiting
00:40:29 --> 00:40:30 their stars every four or five hours
00:40:30 --> 00:40:32 even, but we don't think they formed
00:40:32 --> 00:40:34 there. We think they migrated in. So,
00:40:34 --> 00:40:37 you form beyond the ice line more
00:40:37 --> 00:40:39 quickly because you've got more food.
00:40:39 --> 00:40:42 And you can grow to masses like 10 or 12
00:40:42 --> 00:40:44 Earth masses while there is still an
00:40:44 --> 00:40:47 abundance of gas around. that gas
00:40:47 --> 00:40:48 doesn't hang around long because once
00:40:48 --> 00:40:50 the sun fully turns on after a few
00:40:50 --> 00:40:52 million years it blows the dust and the
00:40:52 --> 00:40:54 gas away and you're left with what
00:40:54 --> 00:40:57 whatever's left over. But if you form to
00:40:57 --> 00:41:00 be 10 or 12 Earth masses before the gas
00:41:00 --> 00:41:02 is blown away, suddenly your
00:41:02 --> 00:41:04 gravitational pull is strong enough to
00:41:04 --> 00:41:06 hold on to hydrogen and helium. If
00:41:06 --> 00:41:08 you're less massive than that, then the
00:41:08 --> 00:41:10 escape velocity of a hydrogen or helium
00:41:10 --> 00:41:13 atom will be higher. Sorry. The escape
00:41:13 --> 00:41:16 velocity of your object with that mass
00:41:16 --> 00:41:18 will be lower than the speed at which
00:41:18 --> 00:41:20 hydrogen and helium atoms move at that
00:41:20 --> 00:41:21 temperature. So, you can't hold on to
00:41:21 --> 00:41:23 them. They just escape because of their
00:41:23 --> 00:41:25 motion, because of the temperature
00:41:25 --> 00:41:27 they're at. When you get to 10 or 12
00:41:27 --> 00:41:29 Earth masses, the escape velocity from
00:41:29 --> 00:41:31 your core is higher than the speed at
00:41:31 --> 00:41:33 which hydrogen and helium is moving. So,
00:41:33 --> 00:41:35 you can start to capture that. And like
00:41:35 --> 00:41:37 I said, 75% of all atoms are hydrogen.
00:41:38 --> 00:41:41 24% of all atoms are helium. 99% of the
00:41:41 --> 00:41:44 mass of the protolantry disc or 98%
00:41:44 --> 00:41:46 maybe is unaccessible till you get to
00:41:46 --> 00:41:47 that mass and suddenly you've got this
00:41:47 --> 00:41:50 whole new food food source. So you
00:41:50 --> 00:41:51 quickly devour all the gas around you
00:41:51 --> 00:41:54 until you open a gap in the disc and
00:41:54 --> 00:41:55 that's how you get the gas giant planet
00:41:55 --> 00:41:57 Jupiter and Saturn. With Uranus and
00:41:57 --> 00:41:59 Neptune, they formed further out. They
00:41:59 --> 00:42:01 had a lot of abundant volatile material
00:42:01 --> 00:42:03 but they didn't really get massive
00:42:03 --> 00:42:06 enough to devour the gas before the gas
00:42:06 --> 00:42:08 was blown away. So that's why you get
00:42:08 --> 00:42:11 the ice giants and that is partially
00:42:11 --> 00:42:12 because they're further away they form
00:42:12 --> 00:42:14 slower. There are some arguments that
00:42:14 --> 00:42:15 Uranus and Neptune may have formed
00:42:15 --> 00:42:17 between Jupiter and Saturn and been
00:42:17 --> 00:42:20 scattered out. But on a broad brush
00:42:20 --> 00:42:23 sense in our solar system we don't think
00:42:23 --> 00:42:25 a huge amount of migration happened
00:42:25 --> 00:42:26 which probably down to the mass of the
00:42:26 --> 00:42:29 protolantry discared
00:42:29 --> 00:42:31 to the hot Jupiter systems we find
00:42:31 --> 00:42:34 elsewhere. So the planets we see today
00:42:34 --> 00:42:37 are within a factor of two or three
00:42:37 --> 00:42:38 times the same distance they were when
00:42:38 --> 00:42:40 they formed. Jupiter might have migrated
00:42:40 --> 00:42:43 in and back out. Uranus and Neptune
00:42:43 --> 00:42:44 probably formed significantly closer to
00:42:44 --> 00:42:46 the sun and migrated outwards. But
00:42:46 --> 00:42:49 you've got Jupiter and outwards forming
00:42:49 --> 00:42:51 in the ice dominated area. The
00:42:51 --> 00:42:53 terrestrial planets forming in the in
00:42:53 --> 00:42:56 the area without ice and therefore
00:42:56 --> 00:42:57 they're dominated by the rock and the
00:42:57 --> 00:42:59 metal. So you've like got this filter.
00:42:59 --> 00:43:01 So if you look at the fraction of iron
00:43:02 --> 00:43:05 compared to carbon in the earth or pick
00:43:05 --> 00:43:06 any two things that would have been
00:43:06 --> 00:43:10 solid, silicon versus iron, phosphorus,
00:43:10 --> 00:43:11 whatever, you know, things that were
00:43:11 --> 00:43:15 solid, the abundances of those things in
00:43:15 --> 00:43:16 all of the planets relative to one
00:43:16 --> 00:43:18 another will be effectively the same as
00:43:18 --> 00:43:20 the abundance in the sun. But the
00:43:20 --> 00:43:22 terrestrial planets weren't able to
00:43:22 --> 00:43:23 capture the things that would have been
00:43:23 --> 00:43:26 gas at their distances other than that
00:43:26 --> 00:43:28 what was delivered later on and weren't
00:43:28 --> 00:43:30 able to hold on to hydrogen and helium.
00:43:30 --> 00:43:33 So you get that chemical differentiation
00:43:33 --> 00:43:35 as a result of the location of the solar
00:43:35 --> 00:43:36 system. There's a bit of added
00:43:36 --> 00:43:38 complexity because chemistry happens and
00:43:38 --> 00:43:40 you'll get isotopic variations and
00:43:40 --> 00:43:42 stuff. But in broad brush strokes, the
00:43:42 --> 00:43:44 reason the terrestrial planets are
00:43:44 --> 00:43:46 dominated by rocky and metallic material
00:43:46 --> 00:43:47 is they never got massive enough to
00:43:47 --> 00:43:50 capture the gas and they formed close in
00:43:50 --> 00:43:52 where ice wasn't around. That's
00:43:52 --> 00:43:54 effectively how it happened. So what
00:43:54 --> 00:43:56 this question from Eli is doing is
00:43:56 --> 00:43:59 actually effectively describing the
00:43:59 --> 00:44:02 logic process that went into how we
00:44:02 --> 00:44:04 first began to understand planet
00:44:04 --> 00:44:06 formation. Because I've I said before, I
00:44:06 --> 00:44:08 think um on a previous episode,
00:44:08 --> 00:44:10 astronomy is not an experimental science
00:44:10 --> 00:44:12 in the way that every other science is.
00:44:12 --> 00:44:14 You know, biology, chemistry, physics,
00:44:14 --> 00:44:15 you want to figure out how something
00:44:15 --> 00:44:17 works, you can do experiments. Astronomy
00:44:17 --> 00:44:18 is an observational science.
00:44:18 --> 00:44:20 Everything's so big and so far away, we
00:44:20 --> 00:44:22 can't put it in a lab and smash it. We
00:44:22 --> 00:44:24 instead play detective. We look out at
00:44:24 --> 00:44:25 the universe and we gather clues and we
00:44:26 --> 00:44:27 ask questions. Exactly like the question
00:44:27 --> 00:44:29 Neo has asked here, which in its
00:44:29 --> 00:44:30 fundamental sense is why do we have
00:44:30 --> 00:44:33 rocky planets close in and gaseous ones
00:44:33 --> 00:44:34 further out? Why are there different
00:44:34 --> 00:44:36 compositions when we should be the same
00:44:36 --> 00:44:38 composition of the sun? We then come up
00:44:38 --> 00:44:40 with explanations for that that are our
00:44:40 --> 00:44:42 theories. And to be a good theory, you
00:44:42 --> 00:44:44 can't just say, I explain everything we
00:44:44 --> 00:44:47 see. You've got to make predictions. As
00:44:47 --> 00:44:49 we find more things, we will observe
00:44:49 --> 00:44:50 this. And that's how we test that
00:44:50 --> 00:44:52 theory. And we test it by this interplay
00:44:52 --> 00:44:54 between observation on the one hand,
00:44:54 --> 00:44:56 theory on the other. And what Eli's
00:44:56 --> 00:44:59 asked here is essentially the questions
00:44:59 --> 00:45:00 that people are asking that led to our
00:45:00 --> 00:45:01 current understanding of planet
00:45:01 --> 00:45:03 formation.
00:45:03 --> 00:45:06 And yet
00:45:06 --> 00:45:08 uh we see other solar systems with
00:45:08 --> 00:45:11 exoplanets that defy what we think is
00:45:11 --> 00:45:13 normal. Uh you have gas giants close to
00:45:13 --> 00:45:15 the parent star and rocky planets
00:45:15 --> 00:45:17 further out.
00:45:17 --> 00:45:20 >> Um and that's how we is that because
00:45:20 --> 00:45:22 they've just drifted that way.
00:45:22 --> 00:45:27 >> It's complicated. So our ideas planet
00:45:27 --> 00:45:29 formation happened have undergone quite
00:45:29 --> 00:45:30 a few major evolutions as we found
00:45:30 --> 00:45:33 planets around other stars. So in the
00:45:33 --> 00:45:36 early 1990s
00:45:36 --> 00:45:37 had a couple of talks at my local
00:45:37 --> 00:45:40 astronomy society in the UK from um
00:45:40 --> 00:45:43 Professor Wolfson of York University and
00:45:43 --> 00:45:45 Professor Wolson was an advocate of an
00:45:45 --> 00:45:47 entirely different formation scenario
00:45:47 --> 00:45:49 for the solar system. I think he was
00:45:49 --> 00:45:51 someone who argued that the solar system
00:45:51 --> 00:45:53 formed through an encounter between the
00:45:53 --> 00:45:55 sun and a young protoar where materials
00:45:55 --> 00:45:56 pulled out of the sun into a massive
00:45:56 --> 00:45:58 tongue and that tongue condensed into
00:45:58 --> 00:46:00 planets.
00:46:00 --> 00:46:04 Um back then
00:46:04 --> 00:46:06 um that idea was going out of fashion
00:46:06 --> 00:46:07 because we'd found a few debris discs
00:46:07 --> 00:46:10 around stars like Vega formal hotbe. But
00:46:10 --> 00:46:11 it was still considered possible.
00:46:11 --> 00:46:14 >> Yeah. Such an event would be incredibly
00:46:14 --> 00:46:17 vanishingly rare because stars getting
00:46:17 --> 00:46:19 that close together within one another's
00:46:19 --> 00:46:22 hills sphere is incredibly unusual. Very
00:46:22 --> 00:46:26 very rare. And so what that would
00:46:26 --> 00:46:29 predict is if that theory were correct,
00:46:29 --> 00:46:31 we would be almost unique. There would
00:46:31 --> 00:46:33 be vanishingly few planets around other
00:46:33 --> 00:46:35 stars because the scenario you need to
00:46:35 --> 00:46:37 form planets would only happen very
00:46:37 --> 00:46:39 rarely. On the other hand, there was the
00:46:39 --> 00:46:42 idea which data back to initially the
00:46:42 --> 00:46:44 1700s and beyond. um the lelassian
00:46:44 --> 00:46:47 model, the circum solar disc model,
00:46:47 --> 00:46:49 which has evolved into what we have now,
00:46:49 --> 00:46:51 which suggested that as part of star
00:46:51 --> 00:46:52 formation, you get a disc of material
00:46:52 --> 00:46:54 around a star and planets form from that
00:46:54 --> 00:46:56 disc. Discs are a natural byproduct to
00:46:56 --> 00:46:58 the formation of stars. Therefore,
00:46:58 --> 00:47:01 planetary systems should be common. Both
00:47:01 --> 00:47:02 scenarios with a bit of fudging and
00:47:02 --> 00:47:04 fiddling could perfectly explain how the
00:47:04 --> 00:47:05 solar system looked and have been
00:47:05 --> 00:47:08 finessed to reproduce the solar system.
00:47:08 --> 00:47:09 But the test was always going to be
00:47:09 --> 00:47:12 which of these series is correct will
00:47:12 --> 00:47:13 depend on how many planets we find
00:47:13 --> 00:47:16 around other stars. If planets are rare,
00:47:16 --> 00:47:17 then maybe the solar system is the
00:47:17 --> 00:47:19 result of a tongue being pulled out of
00:47:19 --> 00:47:21 the sun. If planetary systems are
00:47:21 --> 00:47:24 common, that cannot be the case. So that
00:47:24 --> 00:47:26 was a test that was done there. So when
00:47:26 --> 00:47:27 we found the first planetary systems
00:47:28 --> 00:47:29 around other stars and we found that
00:47:29 --> 00:47:31 planets are ubiquitous, that was kind of
00:47:31 --> 00:47:33 the death nail for the Wolfson type
00:47:33 --> 00:47:35 model of a tongue being sucked out of
00:47:35 --> 00:47:38 the sun and forming planets.
00:47:38 --> 00:47:40 But it kind of confirmed the LLAS model.
00:47:40 --> 00:47:41 But it also threw a spanner into the
00:47:41 --> 00:47:44 work in that the variation of planet
00:47:44 --> 00:47:46 formation of that disc model suggested
00:47:46 --> 00:47:48 that you would always form planetary
00:47:48 --> 00:47:49 systems with rocky planets in the middle
00:47:49 --> 00:47:50 and gas planets on the outside because
00:47:50 --> 00:47:52 it had been developed to explain the
00:47:52 --> 00:47:55 solar system. When you found planets
00:47:55 --> 00:47:57 that were hot Jupiters, they don't fit
00:47:57 --> 00:47:58 their planets and massive Jupiter close
00:47:58 --> 00:48:01 to their star which brought in the
00:48:01 --> 00:48:03 concept of inward migration. Now it's an
00:48:03 --> 00:48:05 interesting time because in the same few
00:48:06 --> 00:48:08 years people had started to realize that
00:48:08 --> 00:48:09 in the solar system there was clear
00:48:09 --> 00:48:11 evidence of planetary migration for the
00:48:11 --> 00:48:14 giant planets primarily that Neptune had
00:48:14 --> 00:48:16 migrated outwards carrying Pluto with it
00:48:16 --> 00:48:18 to form the Plutinos. So you've got
00:48:18 --> 00:48:21 these seminal papers by Renu Malhotra
00:48:21 --> 00:48:23 talking about the outward migration of
00:48:23 --> 00:48:26 Neptune being evidenced in Pluto and the
00:48:26 --> 00:48:28 Plutinos predating the discovery of the
00:48:28 --> 00:48:30 first exoplanet. And one of my gripes
00:48:30 --> 00:48:32 through my career has been that the
00:48:32 --> 00:48:34 exoplanet community primarily came from
00:48:34 --> 00:48:36 binary star astronomers, not from solar
00:48:36 --> 00:48:38 system astronomers. So reinvented
00:48:38 --> 00:48:40 migration to some degree and assumed
00:48:40 --> 00:48:42 that we had no evidence for it in the
00:48:42 --> 00:48:44 solar system. And in parallel, the solar
00:48:44 --> 00:48:45 system community was working on
00:48:45 --> 00:48:48 migration separately. But the
00:48:48 --> 00:48:49 discoveries of planets around other
00:48:49 --> 00:48:53 stars over the last 30 years and more,
00:48:53 --> 00:48:54 which is a great scientific revolution
00:48:54 --> 00:48:56 we've lived through. You know, you and I
00:48:56 --> 00:48:57 grew up in a world where the only
00:48:57 --> 00:48:59 planetary system we knew was our own.
00:48:59 --> 00:49:00 >> And kids today grew up in a world where
00:49:00 --> 00:49:02 we know planets are ubiquitous. That's a
00:49:02 --> 00:49:05 cataclysmic shift to have lived through.
00:49:05 --> 00:49:08 >> That living through that has proven an
00:49:08 --> 00:49:09 incredibly fertile testing ground for
00:49:09 --> 00:49:12 our theories of planet formation. Turns
00:49:12 --> 00:49:14 out that that lelass theory, the disc
00:49:14 --> 00:49:17 theory was a good way of the way there.
00:49:17 --> 00:49:19 So, it hasn't been totally discarded,
00:49:19 --> 00:49:20 but it's been refined and we've learned
00:49:20 --> 00:49:22 more about it. And that continues to the
00:49:22 --> 00:49:24 current day. The refinements are leading
00:49:24 --> 00:49:26 to all sorts of complexities like
00:49:26 --> 00:49:28 invoking streaming instabilities to
00:49:28 --> 00:49:30 concentrate pebbles at certain distances
00:49:30 --> 00:49:33 and all sorts of subtleties to try and
00:49:33 --> 00:49:35 address some of the pitfalls of how on
00:49:35 --> 00:49:37 earth do you get from millimeter size to
00:49:37 --> 00:49:38 meter sized objects when collisions
00:49:38 --> 00:49:40 should become destructive.
00:49:40 --> 00:49:42 >> All sorts of things like this. And it's
00:49:42 --> 00:49:44 through those observations that we get
00:49:44 --> 00:49:47 to improve and refine our models.
00:49:47 --> 00:49:49 We're not going to end up throwing out
00:49:49 --> 00:49:50 the disc model now because we can see
00:49:50 --> 00:49:52 the discs that form planets around other
00:49:52 --> 00:49:53 stars because our telescopes have got
00:49:54 --> 00:49:55 that good. Yeah. And one of the
00:49:55 --> 00:49:57 predictions would have been prior to
00:49:57 --> 00:49:59 them getting that good. If the disc
00:49:59 --> 00:50:00 model is right, when we look at places
00:50:00 --> 00:50:01 like the Orion Nebula with a
00:50:01 --> 00:50:03 sufficiently good telescope, we should
00:50:03 --> 00:50:06 see protolanetary discs propelled then
00:50:06 --> 00:50:07 the telescope's got good enough and we
00:50:08 --> 00:50:10 can see them. Now, we've even got to the
00:50:10 --> 00:50:12 point now where we can actually even
00:50:12 --> 00:50:14 observe fine structure within them to
00:50:14 --> 00:50:16 see the gaps that giant planets open up
00:50:16 --> 00:50:18 to see the spiral waves that are
00:50:18 --> 00:50:20 sometimes induced by a massive planet
00:50:20 --> 00:50:22 being born. So, we're now not only
00:50:22 --> 00:50:25 inferring planet formation from the
00:50:25 --> 00:50:26 plethora of planets that we're
00:50:26 --> 00:50:28 discovering around other stars and from
00:50:28 --> 00:50:30 the fine details of what we know about
00:50:30 --> 00:50:31 the solar system, but we're actually
00:50:31 --> 00:50:32 also getting observations of the discs
00:50:32 --> 00:50:34 in which it's happening that are
00:50:34 --> 00:50:36 providing extra information to improve
00:50:36 --> 00:50:38 those models. It's fascinating.
00:50:38 --> 00:50:41 >> So just so you can simply say there's no
00:50:41 --> 00:50:43 onesizefits-all
00:50:43 --> 00:50:45 way of this happening. It's it's
00:50:45 --> 00:50:46 circumstantial.
00:50:46 --> 00:50:48 >> It's a broad thing versus a narrow
00:50:48 --> 00:50:50 thing. So in a broad sense, planets
00:50:50 --> 00:50:52 forming a disc around a star natural
00:50:52 --> 00:50:55 product star formation. There may be
00:50:55 --> 00:50:57 occasional ways other planet formation
00:50:57 --> 00:50:59 mechanisms happen like the planets
00:50:59 --> 00:51:03 around um neutron stars are thought to
00:51:03 --> 00:51:05 probably be second generation planets.
00:51:05 --> 00:51:06 uh probably material formed from a disc
00:51:06 --> 00:51:07 that formed around the neutron star
00:51:08 --> 00:51:09 after the supernova and formed a new
00:51:10 --> 00:51:12 generation of planets. You might
00:51:12 --> 00:51:14 eventually one day possibly find planets
00:51:14 --> 00:51:18 formed from material pulled off a star.
00:51:18 --> 00:51:19 The very most massive planets, some of
00:51:19 --> 00:51:21 them will probably have been formed more
00:51:21 --> 00:51:24 like binary stars than actual planets
00:51:24 --> 00:51:26 which we talked in the past about when
00:51:26 --> 00:51:29 is a brown dwarf not a brown dwarf.
00:51:29 --> 00:51:30 >> Yes, but the broad brushstroke thing is
00:51:30 --> 00:51:33 fairly well established. that and every
00:51:33 --> 00:51:35 single planetary system is unique.
00:51:35 --> 00:51:38 Everyone has unique circumstances. Some
00:51:38 --> 00:51:39 discs around stars are more massive than
00:51:39 --> 00:51:41 others. Not every star will have an
00:51:41 --> 00:51:44 identical disc. Some discs get truncated
00:51:44 --> 00:51:46 because passing starships material away.
00:51:46 --> 00:51:48 Some discs get ablated away because
00:51:48 --> 00:51:49 there's a massive star nearby whose
00:51:50 --> 00:51:52 radiation pushes material away. You then
00:51:52 --> 00:51:54 even get impacts on the chemistry. So
00:51:54 --> 00:51:56 there's really fascinating studies
00:51:56 --> 00:51:58 looking at the solar system that suggest
00:51:58 --> 00:52:00 there was a nearby so supernova when the
00:52:00 --> 00:52:02 planets were forming that injected
00:52:02 --> 00:52:04 highly radioactive short-lived aluminium
00:52:04 --> 00:52:07 23 I think it is that gave an extra
00:52:07 --> 00:52:10 spike to the melting of planet decimals
00:52:10 --> 00:52:12 that led to some of the subtleties of
00:52:12 --> 00:52:14 how the solar system looks. There are
00:52:14 --> 00:52:16 indications even I think that the amount
00:52:16 --> 00:52:18 of gold in the solar system is unusually
00:52:18 --> 00:52:21 high compared to the standard metalicity
00:52:21 --> 00:52:23 the amounts of everything else which
00:52:23 --> 00:52:25 indication of pollution from two neutron
00:52:25 --> 00:52:27 stars colliding within 10 light
00:52:27 --> 00:52:29 years of where the solar system would
00:52:29 --> 00:52:31 form about a 100 million years before we
00:52:31 --> 00:52:34 formed. So even that level of injection
00:52:34 --> 00:52:37 of material is unique from one system to
00:52:37 --> 00:52:39 the next. And that's why every planetary
00:52:39 --> 00:52:41 system like every person is unique.
00:52:42 --> 00:52:43 >> Fascinating. Fascinating. Aren't you
00:52:43 --> 00:52:46 glad you asked, Eli? And Eli's second
00:52:46 --> 00:52:48 question. I recently read that some star
00:52:48 --> 00:52:51 systems are zipping through their galaxy
00:52:51 --> 00:52:54 orbits at incredible speeds of 1,
00:52:54 --> 00:52:57 I'm assuming that is kilometers/s.
00:52:57 --> 00:52:59 Uh that's4%
00:52:59 --> 00:53:01 the speed of light. That got me
00:53:01 --> 00:53:03 wondering how fast could our solar
00:53:03 --> 00:53:06 system get going before we started
00:53:06 --> 00:53:08 noticing things going wrong. You know,
00:53:08 --> 00:53:11 the windows rattling and such.
00:53:11 --> 00:53:15 Um, yeah, I I I think we've had
00:53:15 --> 00:53:17 questions similar to this. I think we
00:53:17 --> 00:53:19 did one recently where we talked about
00:53:19 --> 00:53:21 how fast the Earth would spin before
00:53:21 --> 00:53:24 things started to go horribly wrong. Um,
00:53:24 --> 00:53:27 this is a a question of similar ilk. I I
00:53:27 --> 00:53:29 hadn't heard about those sorts of speeds
00:53:29 --> 00:53:33 being detected by um
00:53:33 --> 00:53:34 there'd be stars very near the super
00:53:34 --> 00:53:35 massive black holes at centers of
00:53:35 --> 00:53:37 galaxies and that kind of speed doesn't
00:53:37 --> 00:53:39 surprise me. Now my immediate take on
00:53:40 --> 00:53:43 this is that we wouldn't notice
00:53:43 --> 00:53:45 effectively. So the reason that I'm
00:53:46 --> 00:53:47 saying that and I I stand to be proved
00:53:48 --> 00:53:49 wrong when you get up to relativistic
00:53:49 --> 00:53:51 speeds because my knowledge of
00:53:51 --> 00:53:53 relativity is not sufficiently good to
00:53:53 --> 00:53:55 be absolutely certain on this. If you
00:53:55 --> 00:53:58 were moving at a substantial fraction of
00:53:58 --> 00:54:00 the speed of light, I don't think we'd
00:54:00 --> 00:54:01 notice anything wrong in terms of the
00:54:01 --> 00:54:03 Earth moving around the Sun because we'd
00:54:03 --> 00:54:05 still be going around the Sun at 30 km/s
00:54:05 --> 00:54:07 while we're both moving around the
00:54:07 --> 00:54:08 galaxy at relativistic speed and
00:54:08 --> 00:54:10 accelerating. What we might notice then
00:54:10 --> 00:54:13 is time dilation in the fact that the
00:54:13 --> 00:54:16 external universe appears to be moving
00:54:16 --> 00:54:18 quicker than it should do. So we might
00:54:18 --> 00:54:20 see the effect of the fact that our time
00:54:20 --> 00:54:21 is slowed
00:54:21 --> 00:54:23 >> if we were going around just the same as
00:54:23 --> 00:54:24 you know you see the stuff about people
00:54:24 --> 00:54:26 orbiting a black hole at high speed or
00:54:26 --> 00:54:28 whatever or falling into a black hole.
00:54:28 --> 00:54:31 But in terms of us noticing in terms of
00:54:31 --> 00:54:34 physical phenomena on Earth that we're
00:54:34 --> 00:54:36 traveling at a certain speed around the
00:54:36 --> 00:54:39 galaxy I don't see a way that that would
00:54:39 --> 00:54:41 work. And the reason for that is that
00:54:41 --> 00:54:43 there's no resistive medium. We think
00:54:43 --> 00:54:44 about this thing happening because when
00:54:44 --> 00:54:45 you're driving in your car, the quicker
00:54:46 --> 00:54:47 you get, the more obvious your speed is
00:54:47 --> 00:54:48 because of the rattling and the wind
00:54:48 --> 00:54:51 resistance and the noise. But that's all
00:54:51 --> 00:54:52 down to your interaction with something
00:54:52 --> 00:54:54 that isn't moving at the same speed you
00:54:54 --> 00:54:56 are. If you're in the International
00:54:56 --> 00:54:58 Space Station, you're orbiting the Earth
00:54:58 --> 00:55:00 at several kilometers a second, you
00:55:00 --> 00:55:02 don't feel the space station rattling
00:55:02 --> 00:55:04 cuz it's going really quick because it's
00:55:04 --> 00:55:05 moving through the vacuum of space. So,
00:55:05 --> 00:55:07 it's not interacting with anything. If
00:55:07 --> 00:55:09 you're coming back into the atmosphere,
00:55:09 --> 00:55:10 you rattle and rumble and all the rest
00:55:10 --> 00:55:12 of it. saw this with Optimus 2 because
00:55:12 --> 00:55:14 you're slowing down. You're experiencing
00:55:14 --> 00:55:15 acceleration and you're experiencing
00:55:15 --> 00:55:17 buffering.
00:55:17 --> 00:55:20 >> So to me, if we are moving as a
00:55:20 --> 00:55:22 planetary system around the middle of
00:55:22 --> 00:55:24 the galaxy at very high speed, our
00:55:24 --> 00:55:27 planets would still be orbiting the sun
00:55:27 --> 00:55:28 in the same way and we wouldn't notice
00:55:28 --> 00:55:30 any difference. What would happen though
00:55:30 --> 00:55:32 is we'd be moving through a much much
00:55:32 --> 00:55:34 denser stellar neighborhood. The sky
00:55:34 --> 00:55:37 would be immeasurably beautiful but
00:55:37 --> 00:55:39 challenged. But also close encounters
00:55:39 --> 00:55:41 between stars would be very common and
00:55:42 --> 00:55:43 so it may well be that the stars would
00:55:43 --> 00:55:45 be so densely packed that eventually
00:55:45 --> 00:55:47 we'd have a stellar approach that will
00:55:47 --> 00:55:48 be so close to solar system would be
00:55:48 --> 00:55:50 disrupted and we'd certainly notice
00:55:50 --> 00:55:54 that. Also if we were injected to there
00:55:54 --> 00:55:56 from where we are now there will be a
00:55:56 --> 00:55:58 period of adjustment where the or cloud
00:55:58 --> 00:56:00 would be heavily destabilized and we'd
00:56:00 --> 00:56:01 have catastrophic levels of impacts from
00:56:02 --> 00:56:03 the comets being scattered. But
00:56:03 --> 00:56:05 eventually they'd all be gone so it
00:56:05 --> 00:56:07 wouldn't be a problem. So we'd notice it
00:56:07 --> 00:56:08 from the point of view.
00:56:08 --> 00:56:10 >> You tell that to the dinosaurs.
00:56:10 --> 00:56:13 >> Oh, absolutely. Um, long may they rest.
00:56:13 --> 00:56:16 But it's one of those things where if we
00:56:16 --> 00:56:18 were there and we were transported there
00:56:18 --> 00:56:20 from now, what we'd notice is that the
00:56:20 --> 00:56:21 sky looked very different. If we were
00:56:22 --> 00:56:24 moving at that kind of speed in that
00:56:24 --> 00:56:26 denser stellar neighborhood, the proper
00:56:26 --> 00:56:28 motion of stars would be apparent to the
00:56:28 --> 00:56:30 naked eye over human time scales, which
00:56:30 --> 00:56:32 it's not for us. Barard star which is
00:56:32 --> 00:56:34 the fastest moving star across the night
00:56:34 --> 00:56:36 sky will cross the diameter of the full
00:56:36 --> 00:56:39 moon in a century very roughly that
00:56:40 --> 00:56:41 means if Barard star was bright enough
00:56:41 --> 00:56:44 to see with a naked eye we'd have known
00:56:44 --> 00:56:46 about proper motion earlier because it
00:56:46 --> 00:56:48 would be obvious but it wouldn't be the
00:56:48 --> 00:56:49 kind of thing you'd notice from one year
00:56:49 --> 00:56:51 to the next. Whereas if we were in the
00:56:51 --> 00:56:52 middle of the galaxy going around the
00:56:52 --> 00:56:53 super massive black hole at that
00:56:53 --> 00:56:56 ridiculous speed. stars will be closer
00:56:56 --> 00:56:59 together which magnifies the effect of
00:56:59 --> 00:57:00 motion
00:57:00 --> 00:57:03 from our perspective. Also, they'd be
00:57:03 --> 00:57:04 moving quicker which means that the
00:57:04 --> 00:57:06 motion is quicker from our perspective
00:57:06 --> 00:57:07 and you probably have proper motion
00:57:07 --> 00:57:10 being visible on human time scales to
00:57:10 --> 00:57:11 the point that the constellations would
00:57:11 --> 00:57:14 move rather than being fixed patterns
00:57:14 --> 00:57:16 that you'd notice.
00:57:16 --> 00:57:19 You wouldn't feel the acceleration. you
00:57:19 --> 00:57:21 wouldn't notice anything's wrong, but we
00:57:21 --> 00:57:22 we probably wouldn't be there if the sun
00:57:22 --> 00:57:23 had been there for a long time because
00:57:23 --> 00:57:31 it's a very ineviably
00:57:31 --> 00:57:33 a bit of a dead zone.
00:57:33 --> 00:57:37 >> Aha. Okay. All right. Um, thanks for
00:57:37 --> 00:57:40 your questions, Eli. And, uh, yeah, I
00:57:40 --> 00:57:42 love that second one. I love what if
00:57:42 --> 00:57:44 questions. Uh, so yeah, we've been
00:57:44 --> 00:57:46 getting a few of those lately.
00:57:46 --> 00:57:49 They're just such great fun. Uh, thanks
00:57:49 --> 00:57:50 to Nick and Andrea as well for
00:57:50 --> 00:57:52 contributing. And if you would like to
00:57:52 --> 00:57:54 send us a question, please do on our
00:57:54 --> 00:57:56 website, spaceenutspodcast.com.
00:57:56 --> 00:57:58 spacenuts.io.
00:57:58 --> 00:58:00 Click on the AMA button at the top. Ask
00:58:00 --> 00:58:02 me anything is what that stands for. And
00:58:02 --> 00:58:04 you can send text and audio questions.
00:58:04 --> 00:58:06 Don't forget to tell us who you are and
00:58:06 --> 00:58:07 where you're from. And while you're
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00:58:14 --> 00:58:16 things to see and do on our website. And
00:58:16 --> 00:58:19 please leave reviews wherever you listen
00:58:19 --> 00:58:22 to Space Nuts. We appreciate that as
00:58:22 --> 00:58:24 well. And we appreciate you, Jonty.
00:58:24 --> 00:58:26 Thanks so much for uh your input today.
00:58:26 --> 00:58:27 Fantastic.
00:58:27 --> 00:58:28 >> Oh, it's always a pleasure. And yeah,
00:58:28 --> 00:58:31 fabulous questions. Really enjoy them.
00:58:31 --> 00:58:33 >> Me too. And we'll catch up with you uh
00:58:33 --> 00:58:34 with you very, very soon.
00:58:34 --> 00:58:36 >> Yeah, I look forward to it. Thank you.
00:58:36 --> 00:58:39 >> Professor Jonty her from the University
00:58:39 --> 00:58:41 of Southern Queensland where he is a
00:58:41 --> 00:58:43 professor of astrophysics. And thanks to
00:58:43 --> 00:58:45 Hugh in the studio who couldn't be with
00:58:45 --> 00:58:47 us today because time moves slower for
00:58:47 --> 00:58:49 Hugh. So, uh, he'll be joining us in
00:58:50 --> 00:58:52 couple of thousand years. And from me,
00:58:52 --> 00:58:53 Andrew Dunley, thanks for your company.
00:58:53 --> 00:58:54 We'll see you on the next episode of
00:58:54 --> 00:58:56 Space Nuts. Bye-bye.
00:58:56 --> 00:58:57 >> Space Nuts.
00:58:57 --> 00:58:59 >> You'll be listening to the Space Nuts
00:58:59 --> 00:59:01 podcast
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