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Supercharged Neutrinos, Exploding Black Holes & Lunar Mysteries Uncovered | Q&A | Space Nuts:... · Space News Today

• 0:00
  Hi there. Thanks for joining us on a Q&A
• 0:03
  edition of Space Nuts. Andrew Dunley
• 0:05
  here, your host. Great to have your
• 0:07
  company. Coming up, we've got a few
• 0:09
  questions. Nick is going to ask about
• 0:11
  supercharged neutrinos. Andrea is making
• 0:14
  a return appearance. She's got a couple
• 0:16
  of questions about the dark side of the
• 0:18
  moon and shallow craters. And Eli is
• 0:21
  asking about elements and the speed of
• 0:24
  objects. And if we've got time, we'll
• 0:26
  chuck another question into the mix as
• 0:27
  well. All coming up on this edition of
• 0:30
  Space Nuts.
• 0:31
  >> 15 seconds. Guidance is internal. 10 9g
• 0:36
  Ignition sequence start.
• 0:38
  >> Space nuts.
• 0:39
  >> 5 4 3 2
• 0:41
  >> 1 2 3 4 5 5 4 3 2 1
• 0:44
  >> Space Nuts.
• 0:45
  >> Astronauts report. It feels good.
• 0:48
  >> And with Freda away Jonty can play. It's
• 0:51
  uh Professor Jonty her professor of
• 0:54
  astrophysics at the University of
• 0:56
  Southern Queensland. Jonty, hello again.
• 0:58
  >> Good afternoon. How are you going?
• 0:59
  >> I'm well. Great to see you. I think we
• 1:02
  should just go straight into it and uh
• 1:05
  hit you with our first question. It's a
• 1:07
  it's a topic I'm not overly familiar
• 1:10
  with, but uh this one comes from Nick.
• 1:12
  Uh I just read that a supercharged
• 1:14
  neutrino was detected by the Kilometer
• 1:18
  Cube Nutrino telescope and a theory was
• 1:21
  put forward that it came from an
• 1:23
  exploding black hole. Please explain how
• 1:25
  a black hole can explode. Love the show,
• 1:28
  Nick. Thank you, Nick. We love that you
• 1:31
  love the show. Thank Thank you for
• 1:33
  sending in a question. Um, exploding
• 1:35
  black holes. Um, I I seem to remember
• 1:39
  Fred might have written a book about
• 1:40
  something like that once. Um, but
• 1:43
  anyway, um, do they explode or do they
• 1:45
  merge or do they collapse? They they
• 1:47
  eventually disappear. I know that
• 1:49
  >> things now, you know, straight up. I'm
• 1:51
  not a cosmologist or a cosmetologist
• 1:53
  which I always used to joke about
• 1:55
  cosmologists being cosmetologist and
• 1:57
  then it turns out a cosmetologist is a
• 1:58
  real thing. So never mind. Um that's
• 2:02
  further from my area of expertise. So
• 2:04
  any answer I give take with a larger
• 2:06
  grain of salt. You know as is always the
• 2:09
  way you know you the further you go from
• 2:10
  your expertise the more out of date your
• 2:12
  knowledge is. My knowledge on exploding
• 2:15
  or rather evaporating black holes goes
• 2:19
  back to basically when I was in
• 2:20
  undergrad and I was doing lots of
• 2:22
  courses in lots of different things and
• 2:24
  this goes back to some of the work that
• 2:27
  made Steven Hawking so worldrenowned.
• 2:29
  Now obviously for a lot of people
• 2:31
  Stephven Hawking became a global name
• 2:33
  with the publication of a brief history
• 2:34
  of time which did a very good job of
• 2:36
  explaining very complicated things in a
• 2:38
  way that people could at least feel like
• 2:40
  they had a grasp of. Um, I remember
• 2:42
  reading it as a kid and it made my head
• 2:44
  hurt, but it in a good way. I could
• 2:46
  actually follow it. It was well
• 2:47
  explained. One of the things that
• 2:49
  Stephven Hawking did fairly early in his
• 2:51
  career, I think in like 1974 or
• 2:53
  something, was do some very theoretical
• 2:55
  work on black holes where he postulated
• 2:58
  that black holes could lose weight
• 3:00
  through a process called Hawking
• 3:02
  radiation. And the idea is that black
• 3:05
  holes can effectively be considered to
• 3:08
  have a temperature and to radiate energy
• 3:11
  and therefore mass away into space. And
• 3:14
  the smaller the black hole, the hotter
• 3:15
  it is, so the quicker it would radiate.
• 3:17
  And this is all backed up by
• 3:19
  ridiculously complex physics and
• 3:20
  mathematics that is way beyond my level
• 3:22
  of full understanding. But part of the
• 3:25
  idea behind it is that what we think of
• 3:27
  as the empty vacuum of space is actually
• 3:28
  not a true vacuum, but is instead
• 3:31
  constantly populated by pairs of matter
• 3:34
  and antimatter particles that
• 3:35
  spontaneously create and then collide
• 3:37
  with each other and disappear again. And
• 3:39
  if these if such an event happens near
• 3:42
  the event horizon of a black hole, one
• 3:43
  of the particles falls into the black
• 3:44
  hole, the other escapes and it seemed to
• 3:46
  lose mass, lose energy and radiation
• 3:48
  going along with that. Now the bigger
• 3:51
  the black hole, the colder it would be.
• 3:54
  So the slower it radiates anyway, but
• 3:56
  also the bigger it is, the more
• 3:58
  effectively it can feed from its
• 4:00
  environment. Even if that's little bits
• 4:02
  of dust falling in, or if it's near a
• 4:04
  star, it can feed off that star, get an
• 4:05
  accretion disc. So the black holes that
• 4:08
  form in the modern universe are formed
• 4:11
  by stars reaching the end of their lives
• 4:13
  and are massive. They're more massive
• 4:15
  than the sun by a long way. They're
• 4:16
  formed from stars much more massive than
• 4:18
  the sun. You get massive black holes,
• 4:21
  you get intermediate mass black holes,
• 4:23
  and you get super massive black holes.
• 4:24
  And they're all the big whopping ones.
• 4:26
  And the time scale, as I understand it,
• 4:28
  for those black holes to decay through
• 4:29
  Hawking radiation is ridiculously,
• 4:33
  ridiculously, ridiculously longer than
• 4:35
  the age of the universe.
• 4:36
  >> Yes.
• 4:36
  >> And they're probably not emitting
• 4:38
  Hawking radiation at a level that we
• 4:40
  could detect because they are very cold
• 4:42
  in his quantification of it. However, at
• 4:45
  the birth of the universe when the
• 4:47
  temperature and pressure was immense
• 4:48
  after the big bang, there were
• 4:51
  theoretically a class of black holes
• 4:53
  created called primordial black holes.
• 4:56
  So these were black holes that were not
• 4:58
  born from the fiery death of a star, but
• 5:01
  were instead born out of the big bang
• 5:04
  and the pressures and the temperatures.
• 5:05
  And these could be black holes down to
• 5:07
  the mass of a thumbnail or down really
• 5:09
  really tiny ones, planet mass black
• 5:11
  holes. Y
• 5:12
  >> the smaller you are as a black hole, the
• 5:14
  more quickly you radiate things away. So
• 5:16
  the shorter your lifetime and so you
• 5:19
  have this idea that these primordial
• 5:20
  black holes evaporate it over time and
• 5:24
  effectively none of them will survive to
• 5:25
  the current day. Those evaporating black
• 5:28
  holes would evaporate over time and give
• 5:31
  off radiation that we have never yet
• 5:33
  detected. But a black hole coming to the
• 5:35
  end of its life will evaporate faster
• 5:37
  and faster. There's a quote on an
• 5:39
  article I found recently which may be
• 5:41
  tied to this. Um, an article entitled,
• 5:43
  "An exploding black hole could reveal
• 5:45
  the foundations of the universe,
• 5:47
  published from September last year,
• 5:49
  talking about the predictions that as
• 5:51
  our technology gets better in the coming
• 5:54
  years, we may be able to detect this
• 5:55
  Hawking radiation in an event where the
• 5:58
  black hole reaches its critical phase
• 6:00
  and evaporates entirely within the next
• 6:02
  few years." So, not quite the neutrino
• 6:04
  discovery that we were talking about in
• 6:05
  the question, but a related thing. And
• 6:07
  there's a quote here from Andrea Tham
• 6:10
  who associate professor Andrea Tham. I I
• 6:13
  do hate it when articles don't give
• 6:14
  people's well- earned titles until later
• 6:17
  in the sentence or don't give them at
• 6:18
  all.
• 6:19
  >> Um which is another rant I could go on
• 6:21
  that's separate but it's particularly
• 6:22
  affects my um early career colleagues
• 6:26
  and affects colleagues from
• 6:28
  nontraditional backgrounds and stuff and
• 6:30
  it's a very dim demonizing
• 6:33
  thing diminishing thing. It lowers their
• 6:35
  expertise. Anyway, this is a quote from
• 6:37
  associate professor Andrea Tham from
• 6:39
  University of Massachusetts Amhurst
• 6:42
  says, "As primordial black holes
• 6:43
  evaporate, they become ever lighter, so
• 6:46
  hotter, they therefore emit even more
• 6:48
  radiation. It's a runaway process until
• 6:50
  they explode."
• 6:52
  >> It's that Hawking radiation that our
• 6:54
  telescopes can detect.
• 6:56
  >> Yeah.
• 6:56
  >> So, what's happening is you've got these
• 6:57
  primordial black holes that are really
• 6:59
  itty bitty diddy ones that are therefore
• 7:02
  evaporating quicker than they can gain
• 7:04
  mass. they'll be on this critical
• 7:05
  threshold. And so you get this runaway
• 7:07
  death where the more massive ones live
• 7:09
  longer before they get small enough to
• 7:12
  finally evaporate and then explode. And
• 7:15
  so I would guess that the observation of
• 7:18
  this super neutrino that has been linked
• 7:22
  potentially to an exploding black hole
• 7:23
  is not two black holes colliding. not a
• 7:26
  modern black hole formed from the death
• 7:28
  of stars but rather is a death of a
• 7:30
  primordial black hole as would be
• 7:33
  predicted by this research by Steven
• 7:35
  Hawking more than 50 years ago in the
• 7:37
  form of Hawking radiation. So that's my
• 7:40
  thinking on what's happening here. Now
• 7:42
  obviously I am not an expert. Um I've
• 7:45
  said previously on many places that in a
• 7:48
  lot of disciplines and when we're
• 7:49
  teaching our undergrads we often say
• 7:51
  avoid Wikipedia. Wikipedia is not a
• 7:53
  static resource. It's a fluid resource
• 7:54
  and it's often wrong and I know for
• 7:56
  journalists it's probably often
• 7:58
  something you cautioned don't get your
• 7:59
  facts from Wikipedia
• 8:01
  >> for astrophysics and particularly the
• 8:03
  more technical and hardcore ends of
• 8:05
  astrophysics. Wikipedia is actually very
• 8:08
  reliable because very few people will be
• 8:10
  interested in maliciously editing a web
• 8:12
  page because frankly they'll go after
• 8:15
  other topics that are more triggering.
• 8:17
  But also people who are interested in
• 8:19
  this stuff and have the knowledge tend
• 8:20
  to be very obsessive and if they spot
• 8:22
  something wrong they fix it very
• 8:23
  quickly. The result of that is if you
• 8:25
  Google Hawking radiation the Wikipedia
• 8:28
  page is very lengthy goes into a lot of
• 8:31
  detail includes some of the maths that
• 8:33
  makes my head hurt and makes me want to
• 8:35
  cry a little bit um talking about black
• 8:37
  hole evaporation and things like this.
• 8:40
  Now
• 8:41
  the equation for black hole evaporation
• 8:44
  that's on here which is based on the
• 8:45
  Hawking work gives a evaporation time
• 8:49
  for a black hole of 2.14 * 10 67 years.
• 8:55
  So that's 2.14 multiplied by 10 with 67
• 8:59
  zeros
• 9:01
  multiplied by the mass of the black hole
• 9:03
  divided the by the mass of the sun to
• 9:05
  the power three. So if you've got a
• 9:08
  black hole that is one solar mass, it
• 9:11
  will take 2.14 * 10 67 years to
• 9:14
  evaporate. And the more massive it is,
• 9:15
  the larger that number gets.
• 9:17
  >> Yeah.
• 9:17
  >> To the power 3. So the multiplier here
• 9:20
  is get the mass of the black hole as
• 9:22
  measured in units of the mass of the
• 9:23
  sun. Cube that number and then multiply
• 9:27
  it by 2.14 * 10 67 and you get a
• 9:31
  headache. But you get a number. Now the
• 9:34
  mass of the sun is what? 2 * 10 30
• 9:38
  kilos,
• 9:39
  >> right? Mass of the earth is 5.97 * 10 24
• 9:45
  kilos. So that is effectively
• 9:48
  um 2 * 10 - 6 solar mass. It's about a
• 9:51
  millionth of a solar mass. So we'll just
• 9:52
  say it's 1 millionth of a solar mass. 1
• 9:55
  millionth
• 9:57
  cubed is 1 * 10 - 18. That means a black
• 10:02
  hole the mass of the earth would decay
• 10:04
  much more quickly. it would decay in
• 10:06
  only 10^ the 49 years which is still
• 10:10
  much much much much longer than the age
• 10:12
  of the universe but you can play this
• 10:13
  game with everything. I am too fat. You
• 10:16
  know, we talk about health and
• 10:17
  everything on the show before. I am a
• 10:20
  fair bit more than 100 kilos, but let's
• 10:22
  assume I was 100 kilos. Um, just because
• 10:25
  that's an aspirational goal and it would
• 10:26
  be nice if it were true one day. In
• 10:28
  fact, I'm 100 kilos and you make me a
• 10:30
  black hole. Um, I would be sad but
• 10:32
  probably wouldn't have long to think
• 10:34
  about it. At 100 kilos, I would be 10
• 10:38
  the 28 times less massive than the sun
• 10:42
  roughly. The sun is 10 to the 30. I'm 10
• 10:45
  2 10 the 28 is a difference 10 28 cubed
• 10:49
  is 28 56 84 so that's 10 84
• 10:54
  so that means I would disintegrate in 2
• 10:57
  * 10 67 * 10 - 84 which is about 10 -17
• 11:02
  years so suddenly a jumpy mass black
• 11:05
  hole would disintegrate and evaporate in
• 11:08
  a tiny fraction of a millisecond
• 11:11
  so these primordial mass black holes
• 11:13
  that evaporate
• 11:15
  are doing so because they're very small.
• 11:19
  You could, if you wanted to, and I'll
• 11:20
  leave this as an exercise to the reader
• 11:21
  because me doing mental arithmetic is
• 11:23
  not the most exciting thing, you could
• 11:25
  work out what mass a black hole would
• 11:27
  have to be to evaporate after 13.8
• 11:31
  billion years, which is about how old
• 11:34
  the universe is. The reason that's an
• 11:36
  interesting one is if there were any
• 11:37
  primordial mass black holes of that mass
• 11:40
  >> and they were to evaporate, they would
• 11:43
  be evaporating in the very near
• 11:44
  universe.
• 11:46
  And that would make them much easier to
• 11:48
  detect because the intensity of
• 11:49
  radiation we detect is proportional to
• 11:52
  one over the square of the distance. So
• 11:54
  if something's twice as far away, it's
• 11:55
  four times fainter. If it's three times
• 11:57
  as far away, it's nine times fainter. So
• 12:00
  I don't know. I'm not a black hole
• 12:02
  expert by any means. I I say that all
• 12:04
  the time.
• 12:06
  But if there were a black hole of that
• 12:08
  mass formed at the big bang, then maybe
• 12:12
  they would be evaporating in the
• 12:13
  relatively local universe and they're
• 12:15
  the ones that have been most likely to
• 12:16
  detect. I do not, however, know what the
• 12:20
  distribution of masses for primordial
• 12:24
  black holes would be. It's possibly on
• 12:25
  this Wikipedia page, but have a look and
• 12:28
  find out if it's your kind of thing. But
• 12:30
  hopefully that explains why there's a
• 12:33
  turnover point where things will decay
• 12:34
  in less than the age of the universe or
• 12:36
  more than the edge of the universe. And
• 12:38
  that mass is somewhere between the mass
• 12:39
  of a Jonty and the mass of the Earth.
• 12:42
  Okay. Fascinating. Yeah. All right.
• 12:44
  Thank you, Nick. Uh and Nick uh you
• 12:46
  might have heard us talking a week or
• 12:49
  two or three or four back uh about uh
• 12:52
  what they think might be the discovery
• 12:55
  of a primordial black hole. So that's a
• 12:57
  story worth looking up as well. Thanks
• 12:59
  for your question. This is Space Nuts
• 13:01
  Q&A edition with Andrew Dunley and Jonty
• 13:04
  Horner.
• 13:08
  >> G and I feel fine.
• 13:09
  >> Space Nuts.
• 13:10
  >> Uh, now Jonty, we've got an audio
• 13:12
  question that comes from a repeat
• 13:14
  offender. Uh, her name's Andrea.
• 13:17
  >> Hi guys. Um, got a couple of questions
• 13:19
  I'm hoping you can help me with. Um, the
• 13:22
  first question I have is, um, why does
• 13:26
  the dark side of the moon not have
• 13:29
  anywhere near as much damage as the face
• 13:31
  of the moon? Um,
• 13:35
  my second question is, um,
• 13:39
  why are the craters so shallow on the
• 13:42
  moon? Considering
• 13:44
  the size of some of the impacts zones
• 13:47
  and craters, um they all seem to be the
• 13:49
  same depth and which is quite shallow.
• 13:51
  Um especially if you look at Teao, which
• 13:54
  is 3,000 mi wide, um with an incredibly
• 13:58
  shallow crater. Um if you could explain
• 14:02
  for me why that occurs, that would be
• 14:05
  absolutely amazing. Thank you very much.
• 14:07
  Oh, and this is Andrea from Wanoo. and
• 14:10
  Andrew uh wannoo is actually a nunga or
• 14:14
  wjak nunga uh people word um that
• 14:18
  actually means the area of the digging
• 14:22
  stick. Unfortunately not pet kangaroo
• 14:25
  although I have had one of those as
• 14:27
  well. Thanks guys. Take care.
• 14:29
  >> Thanks Andrea. Lovely to hear from you.
• 14:31
  I'm glad she explained that. Um, you
• 14:33
  probably don't know what she's talking
• 14:34
  about, Jonty, but um, when Andrea last
• 14:36
  sent us an audio question and she said
• 14:38
  she was from Woo, I translated that to
• 14:40
  an indigenous word meaning I want a pet
• 14:43
  kangaroo.
• 14:44
  So, yeah, I know I was being silly, but
• 14:47
  um, no, it's um, place of the digging
• 14:49
  stick. Didn't know that. So um of course
• 14:52
  a digging stick was one of the uh
• 14:53
  implements that the ancient indigenous
• 14:57
  peoples of Australia used to use to uh
• 14:59
  to dig up food um grubs and other other
• 15:03
  bush tucker as we call it these days.
• 15:05
  So, it's probably worth mentioning for
• 15:07
  the listeners who are not in Australia
• 15:09
  that many of the Australian places have
• 15:11
  names that derive from the languages of
• 15:14
  the traditional owners of the land of
• 15:16
  the indigenous people of Australia who
• 15:18
  had many different countries with many
• 15:19
  different language groups. And the
• 15:22
  origin of the names is not always that
• 15:24
  wellknown or understood because during
• 15:27
  the invasion of Australia and during the
• 15:29
  events that happened all the way through
• 15:30
  to the 1970s there was a fairly
• 15:32
  aggressive attempt to even if you
• 15:34
  weren't wiping out the people to get rid
• 15:36
  of the culture and to get rid of the
• 15:37
  knowledge. Now I've just looked up to
• 15:39
  Womba where I am to o wa
• 15:43
  I live about 20ks west of there. Toua is
• 15:46
  an indigenous name. It's a really
• 15:47
  interesting town because it's like the
• 15:49
  Florida of Queensland. All the old
• 15:51
  people come here to retire.
• 15:53
  >> It's a beautiful place because
• 15:55
  Queensland has a particular climate, but
• 15:59
  Touumba is a moderated version of that
• 16:01
  climate because it sits on the Great
• 16:03
  Dividing Range at about 700 meters above
• 16:05
  sea level. So, it's not as humid as the
• 16:07
  coast. It doesn't get as hot as the
• 16:08
  coast. It has very lovely dry winters.
• 16:10
  Anyway, the name of Toumba is probably
• 16:14
  based on a word from likely the Gable or
• 16:18
  Jawar peoples. Not entirely sure, but if
• 16:21
  you look around for the origin of
• 16:23
  Towumba as a word, there's lots of
• 16:26
  suggestions. There is a suggestion that
• 16:27
  it was a word for swamp because Toumba
• 16:29
  sits in this swampy area on top of the
• 16:31
  hills. According to the Touumba regional
• 16:33
  council, it may have been named after a
• 16:35
  property in the area in the 1850s.
• 16:38
  Or it may have come from an Aboriginal
• 16:40
  word meaning either place where water
• 16:42
  sits, which would be the swamp thing, or
• 16:44
  place of melon, or place where reeds
• 16:46
  grow, or berries place, or white man.
• 16:49
  There are other things saying meeting of
• 16:50
  the waters or saying the name of Touumba
• 16:53
  maybe an anglicized version of the word
• 16:55
  bua which meant thunder in the dialect
• 16:58
  of the upper bett and gander tribes. So
• 17:00
  we just don't know and does make me a
• 17:03
  little bit sad. We talk about indigenous
• 17:04
  astronomy a bit and the wonderful work
• 17:06
  that um professor Dwayne Hammer and his
• 17:08
  students have done over the years
• 17:10
  working with the indigenous people of
• 17:11
  Australia but it does make me sad how
• 17:13
  much of this knowledge is lost where you
• 17:14
  don't even know the origin of the name.
• 17:16
  So it's wonderful that in this case we
• 17:18
  actually know where the name comes from
• 17:20
  and we can tag that. So when you're
• 17:22
  looking at the map of Australia and
• 17:23
  think a lot of the places are unusual
• 17:25
  from the perspective of someone from an
• 17:27
  Anglo background or from a European
• 17:29
  background because even though it's a
• 17:31
  primarily English-speaking country
• 17:33
  nowadays with a with that you know Anglo
• 17:37
  heritage a lot of the names are actually
• 17:38
  from the traditional owners even if the
• 17:41
  heritage of that name itself is lost.
• 17:43
  >> Yes. Uh where I live, do is supposedly a
• 17:47
  wordy word for red earth because the
• 17:49
  soil here is red. Uh which might sound
• 17:53
  horrifying to people. Uh it is when you
• 17:55
  get a dust storm and everything turns
• 17:57
  red.
• 17:59
  >> And when it gets wet and your bring it
• 18:01
  in because the red soil marks everything
• 18:04
  up, you know,
• 18:05
  >> dog goes out and gets their paws muddy
• 18:07
  and brings in red footprints.
• 18:09
  >> Red footprints on a light colored
• 18:11
  carpet. No. Terrible stuff. And of
• 18:14
  course, one that relates to astronomy is
• 18:17
  warmer, which is an indigenous word for
• 18:20
  uh the the implement they used to launch
• 18:23
  a spear. Rather than just throw the
• 18:25
  spear, they used to have a speciallymade
• 18:28
  um
• 18:29
  I suppose you'd call it a like a
• 18:31
  handheld catapult and it um and it
• 18:35
  >> and and it Yeah. And it flung the spear
• 18:37
  at greater speed and distance. And
• 18:39
  that's uh yeah it was called a WMAR and
• 18:41
  of course WRA rocket range is where
• 18:43
  Australia's uh early space efforts were
• 18:47
  uh were launched from in South
• 18:48
  Australia. So yeah it's um yeah it's
• 18:50
  fascinating history really is and
• 18:52
  >> of course the atal that I mentioned
• 18:54
  there I just double checked because it's
• 18:55
  like I remember an atal being a thing
• 18:58
  that used for throwing space turns out
• 18:59
  that that was an Aztec implement that
• 19:01
  served the same kind of process. So the
• 19:02
  word atal apparently comes from Aztec.
• 19:05
  >> Oh wow. I didn't know that. Back to you,
• 19:08
  Andrea. Yes.
• 19:09
  >> Uh, now the dark Okay, two questions.
• 19:11
  Dark side of the moon, uh, smoother.
• 19:14
  Now, I I've always been aware that the
• 19:16
  the side we can see is so rugged and and
• 19:19
  pockmarked and mountainous.
• 19:21
  >> Yes.
• 19:21
  >> But the side that we cannot see that
• 19:24
  Artemus 2 recently had a look at and
• 19:26
  where the Chinese have been running
• 19:28
  around on their little scooters, um,
• 19:31
  it's smoother. Why?
• 19:33
  >> Well, this is a weird one. So it looks
• 19:38
  more uniform when you look at it. And
• 19:40
  I'm I'm saying that very carefully
• 19:41
  rather than smoother because smoother
• 19:43
  invokes polished or smooth. Like your
• 19:46
  skin when you're a kid is a lot smoother
• 19:47
  than your skin when you get to my age
• 19:48
  and you've got all the wrinkles, right?
• 19:50
  >> Yeah.
• 19:50
  >> Um
• 19:51
  >> all the scars. See this one?
• 19:52
  >> Yeah.
• 19:53
  >> That's from a golf that's from a golf
• 19:55
  club. My neighbor hit me in the face
• 19:56
  with a seven iron.
• 19:58
  >> Yeah.
• 19:58
  >> It wasn't malicious. It was the back
• 19:59
  swing. I was standing too close. I was
• 20:01
  going to say about the adventures of
• 20:02
  having double, you know, they do
• 20:04
  something to pass the time. The reason
• 20:06
  that I'm being careful in my wording
• 20:07
  here and saying it looks more uniform
• 20:09
  rather than it's smoother is actually I
• 20:11
  don't think it is smoother, but I think
• 20:13
  it definitely does look more uniform. On
• 20:15
  the near side of the moon, it should be
• 20:17
  said that we're talking near side and
• 20:19
  far side. The dark side of the moon is
• 20:20
  simply the side of the moon pointed away
• 20:22
  from the sun and that rotates around as
• 20:24
  the moon goes around the earth, which is
• 20:26
  why we get the phases. Right? If you're
• 20:27
  stood on the moon, you'll get at a given
• 20:29
  location two weeks of daytime and two
• 20:31
  weeks of nighttime. And when it's
• 20:32
  nighttime for you, you'd be on the dark
• 20:34
  side of the moon. But when the moon's
• 20:36
  new, the dark side points towards us.
• 20:37
  The far side of the moon always points
• 20:39
  away from the Earth. Now, on the near
• 20:41
  side of the moon, which is a side we're
• 20:43
  familiar with, the view we get is very
• 20:47
  non-uniform because we've got the Mare
• 20:49
  and the non-mar regions. So the Mari are
• 20:51
  the seas which make up the man in the
• 20:53
  moon or whatever picture you have which
• 20:55
  are these flood bassalt areas. And then
• 20:57
  you've got the non-mari areas which are
• 21:00
  more traditionally rocky object looking.
• 21:03
  >> He's he's the drunk man in the moon uh
• 21:06
  here because he's upside down.
• 21:08
  >> Absolutely. Yeah. It's those areas that
• 21:11
  make the drunk man are flood bassalt
• 21:14
  outpourings on the near side of the moon
• 21:16
  that were formed early in the moon's
• 21:18
  formation. If you ascribe to the idea
• 21:20
  that there was a late heavy bombardment
• 21:22
  when the impact rate spiked, then they
• 21:25
  are thought to have formed there. But in
• 21:26
  actuality, evidence for the late heavy
• 21:28
  bombardment has pretty much dissipated.
• 21:30
  So the closer you are to impact studies
• 21:32
  and studies of the moon, the less
• 21:34
  strongly you hold to the idea of the
• 21:35
  late heavy bombardment was a thing. But
• 21:37
  as with all science, the further you get
• 21:39
  from certain expertise, the more out of
• 21:41
  date your knowledge is. So the late
• 21:43
  heavy bombardment is quite often still
• 21:44
  viewed as cannon in a lot of areas
• 21:46
  whereas those who were closest to the
• 21:48
  topic have a lot more doubt that it ever
• 21:50
  happened. But anyway on the near side of
• 21:51
  the moon you've got
• 21:54
  areas of the moon that didn't have a mar
• 21:58
  didn't have a flood bassalt outpouring
• 22:01
  and you've got areas that did. And then
• 22:03
  overlaid on that you've got some more
• 22:05
  recent impacts which are the rare
• 22:06
  craters where you've got weathered
• 22:09
  material on the surface that looks
• 22:10
  darker and an impact comes along digs
• 22:12
  through the darker material to the
• 22:13
  unweathered material below and splashes
• 22:15
  it across the surface. So the near side
• 22:17
  of the moon looks very non-uniform
• 22:18
  because you've got that disparity
• 22:20
  between the flood bassels and the non-
• 22:22
  flood basel. And the non- flood basel is
• 22:25
  an older surface because the flood basel
• 22:27
  erases the evidence of what happened
• 22:28
  before. So there are slightly fewer
• 22:31
  impacts on the MAR than there are on the
• 22:33
  non-mar because it's a younger surface.
• 22:36
  Prior to any spacecraft going to the
• 22:39
  moon, the assumption was the far side of
• 22:40
  the moon would look like the near side.
• 22:42
  >> But when we sent the spacecraft there,
• 22:44
  we realized it doesn't. And that was a
• 22:45
  big puzzle for astronomers for a very
• 22:47
  long time in that there are effectively
• 22:49
  no mare on the far side. There's little
• 22:51
  bits but not very much.
• 22:53
  Now the idea here is that when the moon
• 22:56
  formed, it formed as a result of a giant
• 22:58
  impact on the earth. The moon accreted
• 23:01
  and initially was fully molten and then
• 23:02
  it cooled from the outside in. So at a
• 23:05
  certain time in the moon's youth, the
• 23:07
  surface was very thin above a magma
• 23:09
  ocean, above a molten ocean. And at that
• 23:12
  time, small impacts wouldn't penetrate
• 23:14
  that crust and you get normal craters,
• 23:16
  you get mountain ranges and all the rest
• 23:18
  of it forming. But when you got a really
• 23:19
  big impact that would break through the
• 23:22
  crust, create a big impact basin that
• 23:24
  would then be flooded with flood bassel
• 23:26
  which gave you this incredibly flat
• 23:28
  smooth floor and erased all the evidence
• 23:30
  of the impacts before.
• 23:33
  Eventually the moon cooled enough that
• 23:34
  the that any molten material was
• 23:36
  sufficiently deep that even the biggest
• 23:38
  impacts would not cause these flood
• 23:41
  bassel outpourings. coupled with the
• 23:43
  fact that as the solar system aged it
• 23:46
  cleaned up very effectively and the big
• 23:47
  impactors were effectively gone. So the
• 23:49
  big impacts were early on. So the idea
• 23:51
  was that the mare are caused by the very
• 23:54
  biggest impacts that will create impact
• 23:57
  basins that are hundreds or thousands of
• 23:59
  kilometers across that are broadly
• 24:02
  circular in shape before other things
• 24:04
  happen and that they fill with molten
• 24:07
  material. And the areas on the near side
• 24:09
  that are not in the mar are the areas
• 24:11
  that were not induced into one of these
• 24:14
  flood basel output or rings. Effectively
• 24:15
  they escaped being in one of the craters
• 24:17
  from the very biggest impactors.
• 24:20
  We thought that prior to going to the
• 24:22
  far side of the moon you would have
• 24:24
  assumed that the far side would be the
• 24:25
  same but it turns out that it's not.
• 24:27
  That was a real problem because this
• 24:29
  idea that the impacts were big enough to
• 24:31
  punch through and flood to the surface
• 24:35
  should work all across the moon. So why
• 24:38
  then do you not get the flood bass
• 24:39
  outpourings on the far side of the moon?
• 24:41
  There are kind of three explanations
• 24:43
  that have been put forward for this. The
• 24:45
  first of which is frankly bunkam. The
• 24:48
  idea that the near side of the moon
• 24:50
  faced the earth and the earth shielded
• 24:52
  it and so therefore there'd be more
• 24:54
  impacts on the far side. Well that just
• 24:56
  kind of
• 24:57
  runs counterintuitive. You'd say the far
• 25:00
  side experienced more hits. It gets more
• 25:01
  cratering. Well I don't believe that
• 25:03
  from an earth is so small from the
• 25:04
  moon's point of view. barely a shield at
• 25:06
  all. But if that were the case, surely
• 25:09
  you'd expect more mar on the far side
• 25:11
  because you get more of these big
• 25:12
  impacts. So that to me doesn't work. So
• 25:14
  we can rule that out. The other answers
• 25:18
  are kind of tied together, but the idea
• 25:21
  is that the moon had a thicker layer
• 25:26
  above the molten layer on the far side
• 25:28
  of the moon to the near side. Two ways
• 25:31
  you can make that happen. One idea is
• 25:33
  that the heat from the young earth which
• 25:36
  would also have been molten at this time
• 25:37
  and being bigger will keep its heat
• 25:39
  longer. So will be molten for longer.
• 25:41
  The earth would be irradiating the moon.
• 25:43
  The moon would be close to the earth
• 25:44
  when they formed cuz it's moved away
• 25:46
  since. That radiative heat would have
• 25:49
  kept the near side of the moon hot for
• 25:51
  longer which the molten material on the
• 25:53
  surface would have stayed for longer but
• 25:55
  also it would have taken longer for the
• 25:57
  crust to thicken on that side. So
• 26:00
  therefore the crust on the far side of
• 26:01
  the moon would have formed quicker and
• 26:03
  thicker. The other idea is that you get
• 26:06
  the same kind of effect from tidal
• 26:08
  forces that the tidal influence of the
• 26:10
  earth on the moon is stronger on the
• 26:11
  near side than the far side because the
• 26:12
  strength of tides falls off as distance
• 26:15
  to the power four. So that's a very
• 26:16
  strong very rapid effect. Yeah. Possibly
• 26:19
  both of those things to com combine give
• 26:22
  you a crust around the moon that is
• 26:24
  thinner on the near side than the far
• 26:25
  side at all times as the moon cools on
• 26:28
  the interior which means that the far
• 26:31
  side of the moon the molten material was
• 26:34
  deeply enough buried quickly enough that
• 26:37
  no m forming impact happened. You've got
• 26:39
  the South Pole Lake Kim Basin which is
• 26:40
  the biggest impact scar on the moon
• 26:43
  doesn't really have much flood bassalt
• 26:44
  in it which either means that it is
• 26:46
  younger and therefore the interior had
• 26:49
  cooled enough that it didn't crack that
• 26:51
  egg or that it was an area where the
• 26:56
  crust was thicker anyway. You know, so
• 26:58
  the idea is that the difference between
• 27:00
  the near side and the far side of the
• 27:01
  moon is down to the thickness of the
• 27:02
  crust when the biggest impacts were
• 27:04
  happening. And the idea that probably
• 27:06
  due to a combination of tidal effects
• 27:08
  and radiative heating from the
• 27:10
  incredibly luminous molten earth, the
• 27:13
  near side of the moon stayed a thicker
• 27:15
  shell and therefore was more effectively
• 27:17
  punctured. And so the near side got the
• 27:19
  vare and the far side looks more like
• 27:21
  your typical rocky objects like Mercury
• 27:24
  like a lot of the rocky moons and stuff
• 27:25
  like that in the outer solar system.
• 27:27
  That's the thinking there. But it is
• 27:29
  really strikingly obvious when you see
• 27:31
  photos of the far side of the moon and
• 27:34
  you're not told it's the far side of the
• 27:35
  moon, you assume you're looking at an
• 27:36
  object that is not the moon because no
• 27:39
  different to our experience of the moon.
• 27:41
  >> Indeed. So, so part two of your question
• 27:43
  you basically covered because of the
• 27:45
  deep impact
• 27:46
  >> a little bit.
• 27:48
  >> Part two is a bit more complex.
• 27:50
  >> So, this is about this is the one about
• 27:51
  shallow craters.
• 27:52
  >> Crater shallow and craters are shallow
• 27:55
  not just on the moon but everywhere.
• 27:57
  There is a boundary between what
• 27:58
  researchers describe as a simple crater
• 28:00
  and a complex crater. And
• 28:02
  >> the size at which you get that boundary
• 28:05
  varies dependent on the strength of
• 28:06
  material that's impacted and also the
• 28:09
  mass of the planet and therefore the
• 28:10
  strength of gravity. So I believe on the
• 28:12
  earth it's about 8 or 9 km. For the moon
• 28:15
  it's about 18 km.
• 28:18
  Smaller than that you get a simple
• 28:20
  crater that forms which looks very
• 28:21
  similar to what you get if you almost
• 28:23
  just threw a rock really hard into sand
• 28:26
  or something. You get the typical
• 28:27
  B-shaped crater like meteor crater in
• 28:29
  Arizona. Really nice example. Yeah.
• 28:32
  >> At a size above about like say 8 or 9 km
• 28:36
  on Earth or above about 20 km on the
• 28:38
  moon, you get to the domain where you
• 28:40
  get a complex crater. And complex
• 28:42
  craters are characterized by having
• 28:44
  quite often central impact peaks but
• 28:48
  also having these much shallower depths
• 28:50
  compared to their width. You know, and
• 28:53
  it's particularly true for the Mar where
• 28:55
  they're flood basults where you have a
• 28:56
  very shallow crater for the width of the
• 28:59
  crater. But it's true even if you look
• 29:01
  at 20 km craters on the moon and there's
• 29:04
  a beautiful photo incidentally if you
• 29:05
  look on some of the NASA images there's
• 29:07
  a beautiful photo of the crater Arisus
• 29:09
  taken by the lunar reconnaissance
• 29:11
  orbiter and that shows this kind of
• 29:13
  terracing around the walls the central
• 29:15
  peaks and so there's a few things going
• 29:17
  on here that contribute to why what we
• 29:20
  describe as being
• 29:22
  um what I say complex craters are
• 29:25
  actually
• 29:27
  um
• 29:28
  shallower compared to their width than
• 29:30
  the simple ones. And there's a few
• 29:32
  things that have been suggested to this.
• 29:33
  So complex craters have depths that can
• 29:36
  be a 15th or 25th or even less of the
• 29:39
  crater width which looks very very
• 29:41
  shallow. Now there's a few things
• 29:43
  proposed in for this. Firstly, when you
• 29:46
  form a bigger crater, the walls can
• 29:48
  slump in. So material slides and
• 29:51
  gradually you get this material from the
• 29:53
  edges sliding into the middle. And if
• 29:55
  you look at that photo of Verisarchus,
• 29:56
  it looks very much like that's happened.
• 29:59
  evidence of landslides that have filled
• 30:01
  in the crater and made it shallower.
• 30:04
  >> The other thing is craters that big are
• 30:07
  large enough to render the material
• 30:09
  where the impact happens molten. And in
• 30:12
  other words, the material can flow like
• 30:14
  a liquid rather than behaving like a
• 30:16
  solid material of your desk.
• 30:17
  >> Well, you can you can still see a
• 30:19
  rebound point in the middle of the
• 30:20
  crater too.
• 30:21
  >> So that's it. So the stuff at the
• 30:23
  middle, the central peaks are thought to
• 30:24
  be rebound of this fluid activ fluid
• 30:26
  material springing back before it
• 30:28
  freezes solid again effectively. And
• 30:30
  then the flat base of these craters that
• 30:32
  makes them shallower is because you make
• 30:34
  a pool of liquid that spreads out and
• 30:36
  settles
• 30:38
  and so therefore you get these shallower
• 30:40
  things. Whereas with smaller craters you
• 30:42
  don't get to that point. So you get much
• 30:44
  more material behaving more as a solid
• 30:46
  than a liquid effectively. So the
• 30:49
  thinking is for these complex craters
• 30:50
  and like I say for the moon I think the
• 30:52
  size scale is what 18 to 20 km something
• 30:54
  like that it's a point at which you
• 30:57
  transition from simply behaving as a
• 30:58
  solid to the surface behaving in more of
• 31:01
  a liquid fashion. You get complex
• 31:03
  craters having central peaks they have
• 31:05
  terraces. They've got flat flows. The
• 31:08
  more massive the object the smaller the
• 31:10
  boundary is because gravity has a role
• 31:14
  in this.
• 31:15
  >> Yeah. Um and then you get the basins
• 31:18
  which are even bigger and they're where
• 31:19
  you get the flooding from bassalts which
• 31:21
  makes them even shallower compared to
• 31:23
  their width. So there is some beautiful
• 31:26
  complexity of this where it's all to do
• 31:29
  with the physical behavior of material
• 31:32
  and how that changes as an impact gets
• 31:34
  larger and larger and therefore more and
• 31:36
  more damaging and energetic. Now NASA
• 31:39
  have a Marsded website um where they
• 31:42
  actually explicitly say if you Google
• 31:44
  for this it's marked.asu.edu
• 31:48
  and then a really long string
• 31:49
  afterwards. It's a Mars education thing
• 31:51
  at Arizona State University. And I'll
• 31:53
  just quote here
• 31:55
  compared to simple craters complex
• 31:57
  craters also generate a lot more impact
• 32:00
  melted rock. This typically flows and
• 32:03
  pools like lava to form a sheet that
• 32:04
  covers a shattered rock known as breia
• 32:07
  on the crater floor. The crater's inner
• 32:09
  walls may slump downwards rotating
• 32:11
  backwards in blocks which can widen the
• 32:13
  crater's rim and line the inner walls
• 32:15
  with terraces. But as a result, complex
• 32:18
  craters look shallow. They have rim
• 32:19
  diameters about 30 times greater than
• 32:21
  their depths. By comparison, simple
• 32:23
  craters are about five times wider than
• 32:25
  they are deep. Um earlier on it said the
• 32:28
  more energy an impact delivers, the
• 32:29
  bigger the cavity on the ground. But
• 32:31
  immediately after the blast, the center
• 32:32
  of the cavity begins to rise as rocks
• 32:34
  rebound from the shock. That's what
• 32:35
  gives you the mountains. This uplift
• 32:37
  gives you a central peak or cluster of
• 32:39
  peaks. So that's a really nice way of
• 32:41
  condensing my lengthy waffly answer into
• 32:44
  something a bit more simple and
• 32:45
  straightforward.
• 32:47
  >> Fair enough. Okay. Uh now Andrea, you
• 32:49
  can believe all of that or you can go
• 32:51
  with my theory that the Luna City
• 32:53
  Council were on strike and they didn't
• 32:55
  finish filling the potholes.
• 32:58
  I go with option two. Um, Andrea, thanks
• 33:02
  for your question. Great to hear from
• 33:03
  you. Thanks for explaining Woo. This is
• 33:05
  Space Nuts, a Q&A edition with Professor
• 33:08
  Jonty Horner and Andrew Dunley.
• 33:13
  >> Okay, we've had a problem here.
• 33:15
  >> This is Houston. Say again, please.
• 33:17
  >> Houston, we've had a main undervolt.
• 33:19
  >> Roger. Main. Okay, stand by 13. We're
• 33:22
  looking at it.
• 33:23
  >> Space Muts.
• 33:25
  Our last question uh comes in two parts
• 33:27
  and it uh comes from Eli. Uh hello from
• 33:31
  Coachella Valley in California. Wasn't
• 33:33
  Coachella in the news recently for some
• 33:36
  big suare that happened there? Yeah.
• 33:39
  >> Uh big event. Uh anyway, he says the
• 33:41
  grasshoppers have decided to invade.
• 33:43
  Believe it or not, Eli, exactly the same
• 33:45
  thing is happening where I am. We have
• 33:48
  uh locust plagues once in a blue moon
• 33:50
  and we we had a little one recently.
• 33:52
  wasn't uh too significant. But I I have
• 33:54
  discovered with with locusts or
• 33:56
  grasshoppers or whatever you call them
• 33:58
  wherever you are that if you drive over
• 34:01
  50 kilometers an hour they splatter. Uh
• 34:04
  if you drive under 50 km an hour they
• 34:07
  bounce off. Important safety tip
• 34:09
  especially because when they splatter
• 34:11
  they stink
• 34:13
  >> and it's very hard to get off when
• 34:14
  they're dry.
• 34:15
  >> I'd love to have a swap toy wear. We've
• 34:17
  had an incredibly dry last few months
• 34:19
  here. It's been our wet season. And
• 34:20
  we've had 40 mil of rain in 4 months.
• 34:22
  >> Wow.
• 34:23
  >> Which is hooray. You know, that's really
• 34:25
  what you want in your wet season when
• 34:26
  the dry season's about to start. But
• 34:28
  what that means is that we're probably
• 34:29
  going to see yet another mouse plague.
• 34:31
  And mouse plagues are sad because in the
• 34:33
  times that are good, mice reproduce like
• 34:35
  crazy, but then you get the boom
• 34:36
  busting. And so you start getting lots
• 34:38
  of them coming to your house. And I'm
• 34:40
  soft-hearted. I don't want to hurt them
• 34:41
  or do anything, but at the same time, I
• 34:43
  don't want them pooing on everything in
• 34:44
  my kitchen.
• 34:46
  >> So we're getting mouse plague time. So,
• 34:48
  I I I suspect that locust plagues are
• 34:50
  horrible, but mouse plague is an
• 34:52
  entirely different horror. And
• 34:53
  >> mouse plagues are worse. Yeah.
• 34:55
  >> Because the mice try to find somewhere
• 34:57
  to hide inside. Locusts only get in if
• 35:00
  they've got an open avenue. Otherwise,
• 35:02
  they just stay outside and
• 35:04
  >> you know, and they also are very
• 35:06
  disturbing when you're trying to putt on
• 35:08
  a golf.
• 35:09
  >> Oh, absolutely.
• 35:10
  >> They get in the way.
• 35:13
  >> Sorry. You walk into the kitchen at
• 35:14
  night or you walk somewhere and you just
• 35:16
  see something move in the periphery of
• 35:17
  unit and that's always a little
• 35:18
  disturbing.
• 35:19
  >> Yeah.
• 35:20
  >> Yeah. Well, we
• 35:21
  >> Yeah,
• 35:21
  >> we're talk we're talking mouse plague
• 35:23
  here as well. So, we could have we could
• 35:25
  have both. But our last big locust
• 35:28
  plague, uh it was so big the birds just
• 35:30
  got fed up with eating them. So, they
• 35:32
  gave up as well. It's very weird. Um
• 35:35
  Eli, what are you asking us? Uh since
• 35:37
  you mentioned a pority of questions, I
• 35:40
  hope you don't mind. Um, a twofer. Okay,
• 35:44
  we well we've got two questions then.
• 35:46
  Uh, when the solar system formed, I
• 35:48
  always imagined the inner rockier
• 35:50
  planets as having more heavier elements
• 35:52
  due to their greater mass and gravity
• 35:54
  and with lighter elements collecting
• 35:57
  more in the outer gas giants. But then I
• 35:59
  realized, isn't the sun mostly hydrogen,
• 36:02
  the lightest element? Now I'm confused.
• 36:05
  That's his first question.
• 36:06
  >> Yeah. So,
• 36:07
  >> and this is this is your bullpen, isn't
• 36:10
  it? This is your area of expertise.
• 36:11
  >> This is much more my comfort zone. So,
• 36:13
  this is um
• 36:15
  >> I hope you realize I did try to find
• 36:16
  questions that worked for you.
• 36:18
  >> No, no, that's all good. And it it means
• 36:20
  you can leave the cosmology ones for
• 36:21
  when Fred gets back as well, which is
• 36:23
  great. This is a lovely question and it
• 36:25
  speaks to how our understanding of how
• 36:28
  planets form has changed over time. And
• 36:30
  we've now got quite a high level of
• 36:32
  complexity in the ideas we have behind
• 36:34
  planet formation. But a really
• 36:36
  fundamental part of it is that
• 36:38
  everything in the solar system to first
• 36:41
  order has the same composition as the
• 36:43
  sun because we all form from the same
• 36:46
  material. We formed from an enormous
• 36:47
  cloud of gas and dust called a giant
• 36:48
  molecular cloud that collapsed under its
• 36:51
  own gravity. You you got effectively the
• 36:53
  protostar sun forming in the middle with
• 36:55
  a dis of material around it we call a
• 36:56
  protolanetary disc. And in that disc you
• 36:59
  have solid material and gaseous material
• 37:03
  going around the sun orbiting the sun
• 37:05
  collapsing to a disc because of the
• 37:06
  conservation of angular momentum. So
• 37:08
  kind of where the earth is material was
• 37:10
  whizzing around at about 30 km a second
• 37:13
  but individual dust grains that were
• 37:15
  next to each other were both moving at
• 37:17
  about the same speed. So very little
• 37:19
  difference in speed between the
• 37:21
  particles even though they're going
• 37:22
  really quickly. Now the further you are
• 37:25
  from the sun, the colder the temperature
• 37:26
  is in that disc. And every single
• 37:29
  material you can think of has a
• 37:32
  sublimation temperature. Below that
• 37:34
  temperature it will be solid and above
• 37:36
  that temperature it will be gas. Reason
• 37:39
  I'm not talking about liquid is in order
• 37:40
  to have liquid you need pressure. And in
• 37:42
  this case you don't have or you don't
• 37:44
  have enough. So you either have solid or
• 37:46
  gas.
• 37:47
  >> Yep.
• 37:47
  >> If you are gas then you don't form
• 37:51
  planets initially. If you're solid, you
• 37:53
  can do so. What happens all through this
• 37:55
  disc for a variety of different bits of
• 37:58
  physics going on, you get whatever solid
• 38:00
  material you have at that distance
• 38:02
  colliding,
• 38:04
  sticking together, forming bigger bits.
• 38:06
  And so you get from millimeter to meter
• 38:08
  to kilometer to planet size bits of
• 38:11
  debris. As you get bigger, gravity can
• 38:14
  start taking on a role and start pulling
• 38:16
  in a bit of extra stuff so you can feed
• 38:18
  quicker. Plus, if you're bigger, you've
• 38:19
  got a bigger cross-section, so you hit
• 38:21
  more things to devour them. So, you get
• 38:23
  this process where you get lots of small
• 38:24
  things making a few bigger things and
• 38:26
  the big ones tend to dominate. Um, so a
• 38:29
  thing called oligarchic growth is the
• 38:31
  idea. And you form planetessimals and
• 38:33
  then oligarchs, which are protolanets,
• 38:35
  and a few of them collide all the rest
• 38:37
  of it. If you are far enough from the
• 38:40
  sun, you're beyond what's known as the
• 38:43
  water ice line. Now that's a point at
• 38:45
  which the temperature is below the
• 38:47
  sublimation point of water. So instead
• 38:49
  of water being a gas or vapor, it's a
• 38:51
  solid. Now we always imagine water being
• 38:54
  quite scarce. And I just said we've had
• 38:55
  40 mm of rain in the last 4 months. So
• 38:58
  water is very scarce here. But in terms
• 39:00
  of compounds in the universe, water is
• 39:02
  one of the most abundant things there is
• 39:05
  because it's a combination of hydrogen
• 39:06
  which is the most common atom with 74
• 39:09
  75% of all atoms and oxygen which is the
• 39:11
  second most common atom with about 1% of
• 39:14
  all atoms. Put hydrogen oxygen together
• 39:16
  and you get water. So in the
• 39:18
  protolanetary disc around the sun, water
• 39:21
  was probably about the most common
• 39:23
  species other than molecular hydrogen
• 39:25
  molecular and helium atoms. Lots and
• 39:28
  lots of water. Now where the earth
• 39:29
  formed it was too hot. So you don't have
• 39:32
  water as a solid. So you form the earth
• 39:35
  dry. There's no solid water to accrete.
• 39:37
  You might get a little bit of water as a
• 39:40
  gas that is trapped in the solid
• 39:41
  material. Which is why people think most
• 39:44
  of the earth's water was delivered from
• 39:45
  further out because if far enough out
• 39:48
  you form from primarily water with
• 39:50
  everything else added in. So the inner
• 39:52
  solar system you don't have that water
• 39:54
  to accrete. So you're limited to the
• 39:56
  things that are solid at higher
• 39:58
  temperatures. So you're limited to
• 40:00
  accreting from rock and metal. So you
• 40:02
  get turmeric planets or is the archaic
• 40:05
  way of saying it or terrestrial planets.
• 40:08
  Beyond the ice line, water ice dominates
• 40:10
  the solid material. So you've got a lot
• 40:12
  more to feed from. So you grow more
• 40:14
  quickly and you can get more massive
• 40:16
  planets more quickly which where Jupiter
• 40:18
  and Saturn come in. Now, there's a lot
• 40:20
  of discussion about how they may have
• 40:22
  migrated through the nebula, all the
• 40:23
  rest of it, and the subtleties of the
• 40:25
  formation. In other planetary systems,
• 40:27
  we have planets like Jupiter orbiting
• 40:29
  their stars every four or five hours
• 40:30
  even, but we don't think they formed
• 40:32
  there. We think they migrated in. So,
• 40:34
  you form beyond the ice line more
• 40:37
  quickly because you've got more food.
• 40:39
  And you can grow to masses like 10 or 12
• 40:42
  Earth masses while there is still an
• 40:44
  abundance of gas around. that gas
• 40:47
  doesn't hang around long because once
• 40:48
  the sun fully turns on after a few
• 40:50
  million years it blows the dust and the
• 40:52
  gas away and you're left with what
• 40:54
  whatever's left over. But if you form to
• 40:57
  be 10 or 12 Earth masses before the gas
• 41:00
  is blown away, suddenly your
• 41:02
  gravitational pull is strong enough to
• 41:04
  hold on to hydrogen and helium. If
• 41:06
  you're less massive than that, then the
• 41:08
  escape velocity of a hydrogen or helium
• 41:10
  atom will be higher. Sorry. The escape
• 41:13
  velocity of your object with that mass
• 41:16
  will be lower than the speed at which
• 41:18
  hydrogen and helium atoms move at that
• 41:20
  temperature. So, you can't hold on to
• 41:21
  them. They just escape because of their
• 41:23
  motion, because of the temperature
• 41:25
  they're at. When you get to 10 or 12
• 41:27
  Earth masses, the escape velocity from
• 41:29
  your core is higher than the speed at
• 41:31
  which hydrogen and helium is moving. So,
• 41:33
  you can start to capture that. And like
• 41:35
  I said, 75% of all atoms are hydrogen.
• 41:38
  24% of all atoms are helium. 99% of the
• 41:41
  mass of the protolantry disc or 98%
• 41:44
  maybe is unaccessible till you get to
• 41:46
  that mass and suddenly you've got this
• 41:47
  whole new food food source. So you
• 41:50
  quickly devour all the gas around you
• 41:51
  until you open a gap in the disc and
• 41:54
  that's how you get the gas giant planet
• 41:55
  Jupiter and Saturn. With Uranus and
• 41:57
  Neptune, they formed further out. They
• 41:59
  had a lot of abundant volatile material
• 42:01
  but they didn't really get massive
• 42:03
  enough to devour the gas before the gas
• 42:06
  was blown away. So that's why you get
• 42:08
  the ice giants and that is partially
• 42:11
  because they're further away they form
• 42:12
  slower. There are some arguments that
• 42:14
  Uranus and Neptune may have formed
• 42:15
  between Jupiter and Saturn and been
• 42:17
  scattered out. But on a broad brush
• 42:20
  sense in our solar system we don't think
• 42:23
  a huge amount of migration happened
• 42:25
  which probably down to the mass of the
• 42:26
  protolantry discared
• 42:29
  to the hot Jupiter systems we find
• 42:31
  elsewhere. So the planets we see today
• 42:34
  are within a factor of two or three
• 42:37
  times the same distance they were when
• 42:38
  they formed. Jupiter might have migrated
• 42:40
  in and back out. Uranus and Neptune
• 42:43
  probably formed significantly closer to
• 42:44
  the sun and migrated outwards. But
• 42:46
  you've got Jupiter and outwards forming
• 42:49
  in the ice dominated area. The
• 42:51
  terrestrial planets forming in the in
• 42:53
  the area without ice and therefore
• 42:56
  they're dominated by the rock and the
• 42:57
  metal. So you've like got this filter.
• 42:59
  So if you look at the fraction of iron
• 43:02
  compared to carbon in the earth or pick
• 43:05
  any two things that would have been
• 43:06
  solid, silicon versus iron, phosphorus,
• 43:10
  whatever, you know, things that were
• 43:11
  solid, the abundances of those things in
• 43:15
  all of the planets relative to one
• 43:16
  another will be effectively the same as
• 43:18
  the abundance in the sun. But the
• 43:20
  terrestrial planets weren't able to
• 43:22
  capture the things that would have been
• 43:23
  gas at their distances other than that
• 43:26
  what was delivered later on and weren't
• 43:28
  able to hold on to hydrogen and helium.
• 43:30
  So you get that chemical differentiation
• 43:33
  as a result of the location of the solar
• 43:35
  system. There's a bit of added
• 43:36
  complexity because chemistry happens and
• 43:38
  you'll get isotopic variations and
• 43:40
  stuff. But in broad brush strokes, the
• 43:42
  reason the terrestrial planets are
• 43:44
  dominated by rocky and metallic material
• 43:46
  is they never got massive enough to
• 43:47
  capture the gas and they formed close in
• 43:50
  where ice wasn't around. That's
• 43:52
  effectively how it happened. So what
• 43:54
  this question from Eli is doing is
• 43:56
  actually effectively describing the
• 43:59
  logic process that went into how we
• 44:02
  first began to understand planet
• 44:04
  formation. Because I've I said before, I
• 44:06
  think um on a previous episode,
• 44:08
  astronomy is not an experimental science
• 44:10
  in the way that every other science is.
• 44:12
  You know, biology, chemistry, physics,
• 44:14
  you want to figure out how something
• 44:15
  works, you can do experiments. Astronomy
• 44:17
  is an observational science.
• 44:18
  Everything's so big and so far away, we
• 44:20
  can't put it in a lab and smash it. We
• 44:22
  instead play detective. We look out at
• 44:24
  the universe and we gather clues and we
• 44:26
  ask questions. Exactly like the question
• 44:27
  Neo has asked here, which in its
• 44:29
  fundamental sense is why do we have
• 44:30
  rocky planets close in and gaseous ones
• 44:33
  further out? Why are there different
• 44:34
  compositions when we should be the same
• 44:36
  composition of the sun? We then come up
• 44:38
  with explanations for that that are our
• 44:40
  theories. And to be a good theory, you
• 44:42
  can't just say, I explain everything we
• 44:44
  see. You've got to make predictions. As
• 44:47
  we find more things, we will observe
• 44:49
  this. And that's how we test that
• 44:50
  theory. And we test it by this interplay
• 44:52
  between observation on the one hand,
• 44:54
  theory on the other. And what Eli's
• 44:56
  asked here is essentially the questions
• 44:59
  that people are asking that led to our
• 45:00
  current understanding of planet
• 45:01
  formation.
• 45:03
  And yet
• 45:06
  uh we see other solar systems with
• 45:08
  exoplanets that defy what we think is
• 45:11
  normal. Uh you have gas giants close to
• 45:13
  the parent star and rocky planets
• 45:15
  further out.
• 45:17
  >> Um and that's how we is that because
• 45:20
  they've just drifted that way.
• 45:22
  >> It's complicated. So our ideas planet
• 45:27
  formation happened have undergone quite
• 45:29
  a few major evolutions as we found
• 45:30
  planets around other stars. So in the
• 45:33
  early 1990s
• 45:36
  had a couple of talks at my local
• 45:37
  astronomy society in the UK from um
• 45:40
  Professor Wolfson of York University and
• 45:43
  Professor Wolson was an advocate of an
• 45:45
  entirely different formation scenario
• 45:47
  for the solar system. I think he was
• 45:49
  someone who argued that the solar system
• 45:51
  formed through an encounter between the
• 45:53
  sun and a young protoar where materials
• 45:55
  pulled out of the sun into a massive
• 45:56
  tongue and that tongue condensed into
• 45:58
  planets.
• 46:00
  Um back then
• 46:04
  um that idea was going out of fashion
• 46:06
  because we'd found a few debris discs
• 46:07
  around stars like Vega formal hotbe. But
• 46:10
  it was still considered possible.
• 46:11
  >> Yeah. Such an event would be incredibly
• 46:14
  vanishingly rare because stars getting
• 46:17
  that close together within one another's
• 46:19
  hills sphere is incredibly unusual. Very
• 46:22
  very rare. And so what that would
• 46:26
  predict is if that theory were correct,
• 46:29
  we would be almost unique. There would
• 46:31
  be vanishingly few planets around other
• 46:33
  stars because the scenario you need to
• 46:35
  form planets would only happen very
• 46:37
  rarely. On the other hand, there was the
• 46:39
  idea which data back to initially the
• 46:42
  1700s and beyond. um the lelassian
• 46:44
  model, the circum solar disc model,
• 46:47
  which has evolved into what we have now,
• 46:49
  which suggested that as part of star
• 46:51
  formation, you get a disc of material
• 46:52
  around a star and planets form from that
• 46:54
  disc. Discs are a natural byproduct to
• 46:56
  the formation of stars. Therefore,
• 46:58
  planetary systems should be common. Both
• 47:01
  scenarios with a bit of fudging and
• 47:02
  fiddling could perfectly explain how the
• 47:04
  solar system looked and have been
• 47:05
  finessed to reproduce the solar system.
• 47:08
  But the test was always going to be
• 47:09
  which of these series is correct will
• 47:12
  depend on how many planets we find
• 47:13
  around other stars. If planets are rare,
• 47:16
  then maybe the solar system is the
• 47:17
  result of a tongue being pulled out of
• 47:19
  the sun. If planetary systems are
• 47:21
  common, that cannot be the case. So that
• 47:24
  was a test that was done there. So when
• 47:26
  we found the first planetary systems
• 47:28
  around other stars and we found that
• 47:29
  planets are ubiquitous, that was kind of
• 47:31
  the death nail for the Wolfson type
• 47:33
  model of a tongue being sucked out of
• 47:35
  the sun and forming planets.
• 47:38
  But it kind of confirmed the LLAS model.
• 47:40
  But it also threw a spanner into the
• 47:41
  work in that the variation of planet
• 47:44
  formation of that disc model suggested
• 47:46
  that you would always form planetary
• 47:48
  systems with rocky planets in the middle
• 47:49
  and gas planets on the outside because
• 47:50
  it had been developed to explain the
• 47:52
  solar system. When you found planets
• 47:55
  that were hot Jupiters, they don't fit
• 47:57
  their planets and massive Jupiter close
• 47:58
  to their star which brought in the
• 48:01
  concept of inward migration. Now it's an
• 48:03
  interesting time because in the same few
• 48:06
  years people had started to realize that
• 48:08
  in the solar system there was clear
• 48:09
  evidence of planetary migration for the
• 48:11
  giant planets primarily that Neptune had
• 48:14
  migrated outwards carrying Pluto with it
• 48:16
  to form the Plutinos. So you've got
• 48:18
  these seminal papers by Renu Malhotra
• 48:21
  talking about the outward migration of
• 48:23
  Neptune being evidenced in Pluto and the
• 48:26
  Plutinos predating the discovery of the
• 48:28
  first exoplanet. And one of my gripes
• 48:30
  through my career has been that the
• 48:32
  exoplanet community primarily came from
• 48:34
  binary star astronomers, not from solar
• 48:36
  system astronomers. So reinvented
• 48:38
  migration to some degree and assumed
• 48:40
  that we had no evidence for it in the
• 48:42
  solar system. And in parallel, the solar
• 48:44
  system community was working on
• 48:45
  migration separately. But the
• 48:48
  discoveries of planets around other
• 48:49
  stars over the last 30 years and more,
• 48:53
  which is a great scientific revolution
• 48:54
  we've lived through. You know, you and I
• 48:56
  grew up in a world where the only
• 48:57
  planetary system we knew was our own.
• 48:59
  >> And kids today grew up in a world where
• 49:00
  we know planets are ubiquitous. That's a
• 49:02
  cataclysmic shift to have lived through.
• 49:05
  >> That living through that has proven an
• 49:08
  incredibly fertile testing ground for
• 49:09
  our theories of planet formation. Turns
• 49:12
  out that that lelass theory, the disc
• 49:14
  theory was a good way of the way there.
• 49:17
  So, it hasn't been totally discarded,
• 49:19
  but it's been refined and we've learned
• 49:20
  more about it. And that continues to the
• 49:22
  current day. The refinements are leading
• 49:24
  to all sorts of complexities like
• 49:26
  invoking streaming instabilities to
• 49:28
  concentrate pebbles at certain distances
• 49:30
  and all sorts of subtleties to try and
• 49:33
  address some of the pitfalls of how on
• 49:35
  earth do you get from millimeter size to
• 49:37
  meter sized objects when collisions
• 49:38
  should become destructive.
• 49:40
  >> All sorts of things like this. And it's
• 49:42
  through those observations that we get
• 49:44
  to improve and refine our models.
• 49:47
  We're not going to end up throwing out
• 49:49
  the disc model now because we can see
• 49:50
  the discs that form planets around other
• 49:52
  stars because our telescopes have got
• 49:54
  that good. Yeah. And one of the
• 49:55
  predictions would have been prior to
• 49:57
  them getting that good. If the disc
• 49:59
  model is right, when we look at places
• 50:00
  like the Orion Nebula with a
• 50:01
  sufficiently good telescope, we should
• 50:03
  see protolanetary discs propelled then
• 50:06
  the telescope's got good enough and we
• 50:08
  can see them. Now, we've even got to the
• 50:10
  point now where we can actually even
• 50:12
  observe fine structure within them to
• 50:14
  see the gaps that giant planets open up
• 50:16
  to see the spiral waves that are
• 50:18
  sometimes induced by a massive planet
• 50:20
  being born. So, we're now not only
• 50:22
  inferring planet formation from the
• 50:25
  plethora of planets that we're
• 50:26
  discovering around other stars and from
• 50:28
  the fine details of what we know about
• 50:30
  the solar system, but we're actually
• 50:31
  also getting observations of the discs
• 50:32
  in which it's happening that are
• 50:34
  providing extra information to improve
• 50:36
  those models. It's fascinating.
• 50:38
  >> So just so you can simply say there's no
• 50:41
  onesizefits-all
• 50:43
  way of this happening. It's it's
• 50:45
  circumstantial.
• 50:46
  >> It's a broad thing versus a narrow
• 50:48
  thing. So in a broad sense, planets
• 50:50
  forming a disc around a star natural
• 50:52
  product star formation. There may be
• 50:55
  occasional ways other planet formation
• 50:57
  mechanisms happen like the planets
• 50:59
  around um neutron stars are thought to
• 51:03
  probably be second generation planets.
• 51:05
  uh probably material formed from a disc
• 51:06
  that formed around the neutron star
• 51:08
  after the supernova and formed a new
• 51:10
  generation of planets. You might
• 51:12
  eventually one day possibly find planets
• 51:14
  formed from material pulled off a star.
• 51:18
  The very most massive planets, some of
• 51:19
  them will probably have been formed more
• 51:21
  like binary stars than actual planets
• 51:24
  which we talked in the past about when
• 51:26
  is a brown dwarf not a brown dwarf.
• 51:29
  >> Yes, but the broad brushstroke thing is
• 51:30
  fairly well established. that and every
• 51:33
  single planetary system is unique.
• 51:35
  Everyone has unique circumstances. Some
• 51:38
  discs around stars are more massive than
• 51:39
  others. Not every star will have an
• 51:41
  identical disc. Some discs get truncated
• 51:44
  because passing starships material away.
• 51:46
  Some discs get ablated away because
• 51:48
  there's a massive star nearby whose
• 51:50
  radiation pushes material away. You then
• 51:52
  even get impacts on the chemistry. So
• 51:54
  there's really fascinating studies
• 51:56
  looking at the solar system that suggest
• 51:58
  there was a nearby so supernova when the
• 52:00
  planets were forming that injected
• 52:02
  highly radioactive short-lived aluminium
• 52:04
  23 I think it is that gave an extra
• 52:07
  spike to the melting of planet decimals
• 52:10
  that led to some of the subtleties of
• 52:12
  how the solar system looks. There are
• 52:14
  indications even I think that the amount
• 52:16
  of gold in the solar system is unusually
• 52:18
  high compared to the standard metalicity
• 52:21
  the amounts of everything else which
• 52:23
  indication of pollution from two neutron
• 52:25
  stars colliding within 10,000 light
• 52:27
  years of where the solar system would
• 52:29
  form about a 100 million years before we
• 52:31
  formed. So even that level of injection
• 52:34
  of material is unique from one system to
• 52:37
  the next. And that's why every planetary
• 52:39
  system like every person is unique.
• 52:42
  >> Fascinating. Fascinating. Aren't you
• 52:43
  glad you asked, Eli? And Eli's second
• 52:46
  question. I recently read that some star
• 52:48
  systems are zipping through their galaxy
• 52:51
  orbits at incredible speeds of 1,200,
• 52:54
  I'm assuming that is kilometers/s.
• 52:57
  Uh that's4%
• 52:59
  the speed of light. That got me
• 53:01
  wondering how fast could our solar
• 53:03
  system get going before we started
• 53:06
  noticing things going wrong. You know,
• 53:08
  the windows rattling and such.
• 53:11
  Um, yeah, I I I think we've had
• 53:15
  questions similar to this. I think we
• 53:17
  did one recently where we talked about
• 53:19
  how fast the Earth would spin before
• 53:21
  things started to go horribly wrong. Um,
• 53:24
  this is a a question of similar ilk. I I
• 53:27
  hadn't heard about those sorts of speeds
• 53:29
  being detected by um
• 53:33
  there'd be stars very near the super
• 53:34
  massive black holes at centers of
• 53:35
  galaxies and that kind of speed doesn't
• 53:37
  surprise me. Now my immediate take on
• 53:40
  this is that we wouldn't notice
• 53:43
  effectively. So the reason that I'm
• 53:46
  saying that and I I stand to be proved
• 53:48
  wrong when you get up to relativistic
• 53:49
  speeds because my knowledge of
• 53:51
  relativity is not sufficiently good to
• 53:53
  be absolutely certain on this. If you
• 53:55
  were moving at a substantial fraction of
• 53:58
  the speed of light, I don't think we'd
• 54:00
  notice anything wrong in terms of the
• 54:01
  Earth moving around the Sun because we'd
• 54:03
  still be going around the Sun at 30 km/s
• 54:05
  while we're both moving around the
• 54:07
  galaxy at relativistic speed and
• 54:08
  accelerating. What we might notice then
• 54:10
  is time dilation in the fact that the
• 54:13
  external universe appears to be moving
• 54:16
  quicker than it should do. So we might
• 54:18
  see the effect of the fact that our time
• 54:20
  is slowed
• 54:21
  >> if we were going around just the same as
• 54:23
  you know you see the stuff about people
• 54:24
  orbiting a black hole at high speed or
• 54:26
  whatever or falling into a black hole.
• 54:28
  But in terms of us noticing in terms of
• 54:31
  physical phenomena on Earth that we're
• 54:34
  traveling at a certain speed around the
• 54:36
  galaxy I don't see a way that that would
• 54:39
  work. And the reason for that is that
• 54:41
  there's no resistive medium. We think
• 54:43
  about this thing happening because when
• 54:44
  you're driving in your car, the quicker
• 54:46
  you get, the more obvious your speed is
• 54:47
  because of the rattling and the wind
• 54:48
  resistance and the noise. But that's all
• 54:51
  down to your interaction with something
• 54:52
  that isn't moving at the same speed you
• 54:54
  are. If you're in the International
• 54:56
  Space Station, you're orbiting the Earth
• 54:58
  at several kilometers a second, you
• 55:00
  don't feel the space station rattling
• 55:02
  cuz it's going really quick because it's
• 55:04
  moving through the vacuum of space. So,
• 55:05
  it's not interacting with anything. If
• 55:07
  you're coming back into the atmosphere,
• 55:09
  you rattle and rumble and all the rest
• 55:10
  of it. saw this with Optimus 2 because
• 55:12
  you're slowing down. You're experiencing
• 55:14
  acceleration and you're experiencing
• 55:15
  buffering.
• 55:17
  >> So to me, if we are moving as a
• 55:20
  planetary system around the middle of
• 55:22
  the galaxy at very high speed, our
• 55:24
  planets would still be orbiting the sun
• 55:27
  in the same way and we wouldn't notice
• 55:28
  any difference. What would happen though
• 55:30
  is we'd be moving through a much much
• 55:32
  denser stellar neighborhood. The sky
• 55:34
  would be immeasurably beautiful but
• 55:37
  challenged. But also close encounters
• 55:39
  between stars would be very common and
• 55:42
  so it may well be that the stars would
• 55:43
  be so densely packed that eventually
• 55:45
  we'd have a stellar approach that will
• 55:47
  be so close to solar system would be
• 55:48
  disrupted and we'd certainly notice
• 55:50
  that. Also if we were injected to there
• 55:54
  from where we are now there will be a
• 55:56
  period of adjustment where the or cloud
• 55:58
  would be heavily destabilized and we'd
• 56:00
  have catastrophic levels of impacts from
• 56:02
  the comets being scattered. But
• 56:03
  eventually they'd all be gone so it
• 56:05
  wouldn't be a problem. So we'd notice it
• 56:07
  from the point of view.
• 56:08
  >> You tell that to the dinosaurs.
• 56:10
  >> Oh, absolutely. Um, long may they rest.
• 56:13
  But it's one of those things where if we
• 56:16
  were there and we were transported there
• 56:18
  from now, what we'd notice is that the
• 56:20
  sky looked very different. If we were
• 56:22
  moving at that kind of speed in that
• 56:24
  denser stellar neighborhood, the proper
• 56:26
  motion of stars would be apparent to the
• 56:28
  naked eye over human time scales, which
• 56:30
  it's not for us. Barard star which is
• 56:32
  the fastest moving star across the night
• 56:34
  sky will cross the diameter of the full
• 56:36
  moon in a century very roughly that
• 56:40
  means if Barard star was bright enough
• 56:41
  to see with a naked eye we'd have known
• 56:44
  about proper motion earlier because it
• 56:46
  would be obvious but it wouldn't be the
• 56:48
  kind of thing you'd notice from one year
• 56:49
  to the next. Whereas if we were in the
• 56:51
  middle of the galaxy going around the
• 56:52
  super massive black hole at that
• 56:53
  ridiculous speed. stars will be closer
• 56:56
  together which magnifies the effect of
• 56:59
  motion
• 57:00
  from our perspective. Also, they'd be
• 57:03
  moving quicker which means that the
• 57:04
  motion is quicker from our perspective
• 57:06
  and you probably have proper motion
• 57:07
  being visible on human time scales to
• 57:10
  the point that the constellations would
• 57:11
  move rather than being fixed patterns
• 57:14
  that you'd notice.
• 57:16
  You wouldn't feel the acceleration. you
• 57:19
  wouldn't notice anything's wrong, but we
• 57:21
  we probably wouldn't be there if the sun
• 57:22
  had been there for a long time because
• 57:23
  it's a very ineviably
• 57:31
  a bit of a dead zone.
• 57:33
  >> Aha. Okay. All right. Um, thanks for
• 57:37
  your questions, Eli. And, uh, yeah, I
• 57:40
  love that second one. I love what if
• 57:42
  questions. Uh, so yeah, we've been
• 57:44
  getting a few of those lately.
• 57:46
  They're just such great fun. Uh, thanks
• 57:49
  to Nick and Andrea as well for
• 57:50
  contributing. And if you would like to
• 57:52
  send us a question, please do on our
• 57:54
  website, spaceenutspodcast.com.
• 57:56
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• 57:58
  Click on the AMA button at the top. Ask
• 58:00
  me anything is what that stands for. And
• 58:02
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• 58:04
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• 58:16
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• 58:19
  to Space Nuts. We appreciate that as
• 58:22
  well. And we appreciate you, Jonty.
• 58:24
  Thanks so much for uh your input today.
• 58:26
  Fantastic.
• 58:27
  >> Oh, it's always a pleasure. And yeah,
• 58:28
  fabulous questions. Really enjoy them.
• 58:31
  >> Me too. And we'll catch up with you uh
• 58:33
  with you very, very soon.
• 58:34
  >> Yeah, I look forward to it. Thank you.
• 58:36
  >> Professor Jonty her from the University
• 58:39
  of Southern Queensland where he is a
• 58:41
  professor of astrophysics. And thanks to
• 58:43
  Hugh in the studio who couldn't be with
• 58:45
  us today because time moves slower for
• 58:47
  Hugh. So, uh, he'll be joining us in
• 58:50
  couple of thousand years. And from me,
• 58:52
  Andrew Dunley, thanks for your company.
• 58:53
  We'll see you on the next episode of
• 58:54
  Space Nuts. Bye-bye.
• 58:56
  >> Space Nuts.
• 58:57
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• 58:59
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• 59:02
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