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Navigating Time, Saturn’s Mysteries & Planetary Favourites | A Q&A Episode | Space Nuts:... · Space News Today

• 0:00
  Hi there. Thanks again for joining us.
• 0:01
  This is a Q&A edition of Space Nuts,
• 0:04
  where we talk astronomy and space
• 0:06
  science. And in a Q&A edition, uh UQ and
• 0:09
  we a uh which means we'll answer
• 0:12
  audience questions. Uh today we're going
• 0:14
  to talk about uh moving through time.
• 0:17
  What does that mean? Uh also some stuff
• 0:20
  from Saturn's rings and a sort of
• 0:23
  hypothetical, not a hypothetical, but a
• 0:25
  you know, not even a what if question.
• 0:27
  And it's just a question asking our
• 0:30
  favorite planets and why. Well, you
• 0:32
  know, um that's Jonty's thing. So, we
• 0:35
  will talk about all of that on this
• 0:37
  episode of Space Nuts.
• 0:38
  >> 15 seconds. Guidance is internal. 10 9
• 0:43
  Ignition sequence start.
• 0:45
  >> Space Nuts.
• 0:46
  >> 5 4 3 2 1 2 3 4 5 5 4 3 2 1
• 0:51
  >> Space Nuts.
• 0:52
  >> Astronauts report. It feels good. And
• 0:55
  while Fred's away, Jonty is here to play
• 0:59
  and answer your questions. He is
• 1:01
  Professor Jotty her, professor of
• 1:03
  astrophysics at the University of
• 1:05
  Southern Queensland. Hello, Johnny.
• 1:07
  >> Hey, how are you going?
• 1:08
  >> I am very well. Good to see you again.
• 1:11
  >> Well, it's good. Yeah. Now, I've got
• 1:12
  interesting questions today.
• 1:14
  >> Yeah, we've got some beauties. Um, we
• 1:16
  might get straight into it. Our first
• 1:18
  question comes from Renie uh in Sunny
• 1:21
  West Hills, California. Hi, Renie. Renie
• 1:22
  is a a regular contributor, so u we hear
• 1:25
  from Renie semi-regularly.
• 1:27
  Uh can you please explain what it means
• 1:30
  to be moving through time? If I
• 1:33
  theoretically could sit in a chair from
• 1:36
  birth to death, will I die on a faster
• 1:38
  timeline than someone who lived a
• 1:41
  regular normal life? uh is what's aging
• 1:45
  me about the movement of the earth
• 1:47
  around the sun combined with the sun
• 1:49
  moving around the galaxy combined with
• 1:50
  the galaxies moving around each other
• 1:52
  and my own physical movement
• 1:56
  really that that's kind of a what if
• 1:58
  question we love what if questions uh
• 2:00
  thanks Renie um let's open that one up
• 2:02
  to a little bit of um investigation
• 2:06
  >> absolutely and I think the first thing
• 2:08
  I'd say here is this is such a fun
• 2:09
  question it may be well give it a couple
• 2:12
  of months and ask it again and see
• 2:14
  whether Fred gives a similar answer to
• 2:16
  me or not.
• 2:17
  >> Um, it it's a really interesting one.
• 2:21
  So, the idea of time being a dimension
• 2:25
  is something that I think makes all of
• 2:27
  our heads hurt a little bit when we
• 2:28
  first encounter it and for most of us
• 2:30
  continues to do so forever more. It's
• 2:33
  one of the fundamentals of the idea of
• 2:36
  what I guess is often described as
• 2:37
  space-time physics comes out of the work
• 2:41
  that people like Albert Einstein did
• 2:43
  with relativity.
• 2:46
  We're used to the three physical three
• 2:49
  spatial dimensions
• 2:51
  up, down, left, right, and forward and
• 2:53
  back. Although I I'm realizing more and
• 2:56
  more that we actually live in a two two
• 2:59
  plus one kind of existence really
• 3:01
  because we don't look up very often.
• 3:04
  Part of our common sense is about
• 3:05
  two-dimensional movement, not
• 3:06
  threedimensional cuz we think about
• 3:08
  moving around on the surface of the
• 3:09
  earth and there's all sorts of weird and
• 3:12
  fundamental things with that. Now, the
• 3:14
  idea that time is also a dimension is
• 3:17
  part of that whole thing of space-time
• 3:19
  physics built into the relativity twins,
• 3:22
  you know, special in general. And it's a
• 3:24
  very weird one because with the other
• 3:26
  dimensions,
• 3:27
  we choose where to move or we're carried
• 3:30
  along where we're aware of motion.
• 3:32
  Motion in a way that is changing
• 3:34
  direction. We can change speed. We feel
• 3:36
  agency. But with time, when you get told
• 3:39
  that time is a dimension, you think,
• 3:41
  "But I can't move. I can't choose my
• 3:43
  motion in it. We're all carried through
• 3:46
  time at 1 second per second. And so it's
• 3:50
  like a dimension without agency. It's
• 3:52
  all a little bit weird.
• 3:54
  >> Now, it does lead to that concept of
• 3:58
  time as a dimension is one of the things
• 3:59
  that's part of the underpinninging of
• 4:01
  all this stuff like with special and
• 4:03
  general relativity, things like time
• 4:05
  dilation, stuff like this. It's also
• 4:09
  tied into
• 4:11
  um events and consequences, the logical
• 4:14
  order of things. You know, a cause has
• 4:16
  to cause an effect. You don't get the
• 4:18
  effect before the cause. Things like
• 4:20
  this. Now,
• 4:22
  this rapidly gets very complicated. And
• 4:24
  I know at university when you study
• 4:26
  physics as a partner to astronomy or you
• 4:28
  study um relative relativity as part of
• 4:31
  an astronomy thing, I know a lot of
• 4:33
  people find it hugely challenging to get
• 4:36
  their head around it. And I will openly
• 4:38
  admit that when I did my relativity
• 4:40
  courses as an undergrad, my head hurt.
• 4:42
  It was really, really hard. And
• 4:44
  particularly in first year, special
• 4:45
  relativity didn't work for me. And it's
• 4:48
  something I always say to my students,
• 4:50
  something I'm very aware of, and
• 4:51
  something I'd say to listeners is that
• 4:53
  no one explanation will work for
• 4:55
  everybody. We all learn in different
• 4:58
  ways, and one source that is brilliant
• 4:59
  for me might not be brilliant for you.
• 5:01
  So if my explanation doesn't work,
• 5:03
  please go out and seek another one.
• 5:04
  That's no slight on me. It just means
• 5:06
  that your way of learning and my way of
• 5:07
  explaining didn't match in that case and
• 5:09
  another explanation is needed. And when
• 5:12
  it came to relativity, I was very much
• 5:14
  in that boat. I was sat in these
• 5:16
  lectures and this is old style education
• 5:18
  30 years ago and it actually is 29 and a
• 5:21
  half years ago that I was in these
• 5:22
  lectures cuz it was late 1996. Sat there
• 5:25
  taking notes on paper while somebody's
• 5:28
  talking at you and writing on a board.
• 5:29
  So a lot of the information was going
• 5:30
  through from my eyes to the page without
• 5:32
  going through my brain. I suspect, you
• 5:34
  know, that autonomous writing thing,
• 5:36
  >> but it just wasn't jelling for me. The
• 5:38
  whole the equations are written down so
• 5:41
  you can use them, but it wasn't making
• 5:43
  sense. And the course textbook we had
• 5:45
  was incredibly mathematical because
• 5:49
  the person who wrote the textbook
• 5:51
  understood it through the maths, so they
• 5:52
  explained it through the maths. And
• 5:53
  that's not the way that I learn. Some
• 5:56
  people learn brilliantly from maths. I
• 5:58
  don't. I'm much more of a visual form or
• 6:00
  a picture form or metaphor type thinker
• 6:02
  than an equation is a be all and end
• 6:04
  all. So about the only textbook I ever
• 6:07
  used in my undergrad days, I was
• 6:09
  terrible. I'd buy the textbooks, not
• 6:11
  open them, and then I'd sell them on at
• 6:12
  the end of the trimester, end of the
• 6:14
  term for someone else to take off me and
• 6:15
  probably do the same thing.
• 6:17
  >> But I found a textbook in the library
• 6:19
  that worked for me and ended up buying
• 6:21
  it. And I was going to recommend it
• 6:22
  because it was so foundation in helping
• 6:25
  me to overcome something I couldn't
• 6:28
  understand that I always think when
• 6:29
  people are struggling with the
• 6:30
  relativity stuff. Worth recommending it.
• 6:32
  It's a big book called Spacetime Physics
• 6:34
  by Edwin F. Taylor and John Archie Bald
• 6:37
  Wheeler. And to my shock, I looked it up
• 6:39
  just before this podcast and the first
• 6:41
  edition was published in 1965.
• 6:44
  So the first edition was born was
• 6:47
  launched closer to the publishing of the
• 6:50
  theory of general relativity and the
• 6:52
  theory of special relativity than my
• 6:54
  reading it
• 6:55
  >> or certainly than we are today should I
• 6:58
  say absolutely than we are today. Um it
• 7:00
  is still in print and what worked for me
• 7:02
  was that it didn't go straight to the
• 7:04
  maths instead it used drawings and
• 7:06
  figures and thought experiments and I
• 7:09
  read it voraciously. It was very
• 7:10
  readable. I remember it from 30 years
• 7:12
  ago and it had an impact. I'd really
• 7:13
  recommend that if you're struggling with
• 7:14
  the relativity stuff, um, go to your
• 7:17
  local library. The textbooks are
• 7:19
  punishingly expensive and um, therefore
• 7:22
  I'd always recommend people get them
• 7:23
  from library first and make absolutely
• 7:25
  sure. But if you're at all interested in
• 7:28
  those foundations of how relativity and
• 7:31
  everything works, I found that book
• 7:33
  astonishing. Okay,
• 7:35
  >> that's all getting a bit off the topic
• 7:36
  though. But that explains a lot better
• 7:38
  than I could do the concepts behind
• 7:40
  relativity that include time as a
• 7:43
  dimension. Includes space-time diagrams,
• 7:46
  which are these weird cone- shaped
• 7:48
  figures where if you're traveling at the
• 7:50
  speed of light, you move the same
• 7:53
  distance in X, which is distance as you
• 7:55
  do in time Y. So you get a cone opened
• 7:57
  out like this and everything inside that
• 7:59
  cone is moving slower than the speed of
• 8:01
  light because it's going up the y- axis
• 8:03
  quicker than it goes on the x- axis.
• 8:05
  Anything that is nearer to the x-axis of
• 8:08
  that line is further away from the
• 8:10
  observer than they could observe it yet.
• 8:13
  So any light that left that would not
• 8:14
  have reached you yet. Now hard to
• 8:17
  visualize but if you look into the book
• 8:19
  that is what it means. Now moving in
• 8:22
  time is talking about our motion on the
• 8:26
  y-axis of that graph where we move up it
• 8:28
  by 1 second every second.
• 8:30
  >> Y
• 8:31
  >> that is something over which we do not
• 8:34
  really have control. Um I I suspect some
• 8:37
  people would argue that certain
• 8:39
  substances that can be ingested change
• 8:40
  your perception of how time loads. So
• 8:42
  you might be able to control the speed
• 8:43
  you fly through it there. But that's
• 8:46
  what we mean by moving in time. It's
• 8:48
  perceiving time moving forward so that
• 8:52
  from one second to the next change
• 8:54
  happens. You know, yesterday is a time
• 8:57
  in the past that's already happened.
• 8:59
  That's a cause. You'll see the effects
• 9:00
  today. Tomorrow hasn't happened yet. You
• 9:02
  can't see what is there tomorrow.
• 9:05
  >> That's what it means by moving in time.
• 9:07
  And it there's all sorts of wonderful
• 9:09
  ways people have described it or played
• 9:11
  with this. again. You know, I often come
• 9:13
  back to the Terry Pratt stuff and I was
• 9:15
  just looking at a thread the other day
• 9:16
  of people talking about their favorite
• 9:17
  Terry Pratt quotes. I'll just try and
• 9:19
  pull this one up. Um, it's from when the
• 9:23
  eternally surprised, uh, who was the
• 9:26
  founder of the history monks. Um,
• 9:29
  basically talking about his perception
• 9:30
  of time. So, you know, man looks a
• 9:32
  keyboard cuz I didn't think of doing
• 9:33
  this, but yeah, this is from Thief of
• 9:37
  Time, I think it was. Yes. um talking
• 9:40
  about how when viewed the universe and
• 9:42
  viewed moving through time as this
• 9:45
  ancient philosopher who set up the monks
• 9:48
  of history who are the people who run
• 9:50
  around unseen in the background fixing
• 9:52
  things when they go wrong because in the
• 9:53
  disc world they go wrong all the time.
• 9:55
  Yeah.
• 9:55
  >> But says when considered the nature of
• 9:57
  time
• 9:59
  >> and understood that the universe is
• 10:00
  instant by instant recreated a new.
• 10:03
  Therefore he understood there is in
• 10:05
  truth no past only a memory of the past.
• 10:08
  Blink your eyes and the world you see
• 10:09
  next did not exist when you closed them.
• 10:12
  Therefore, he said, the only appropriate
• 10:13
  state of the mind is surprise. The only
• 10:16
  appropriate state of the heart is joy.
• 10:19
  The sky you see now, you have never seen
• 10:21
  before. The perfect moment is now. Be
• 10:23
  glad of it.
• 10:25
  >> That's good.
• 10:25
  >> I talk about patchet a lot, but I always
• 10:27
  think that's really beautiful and it
• 10:29
  fits in with this concept of time moving
• 10:32
  irrevocably forward. You can never
• 10:34
  return to the past and change things.
• 10:36
  What you can change is the future. When
• 10:39
  you wake up every morning, it's as
• 10:41
  though you're newborn into the universe
• 10:43
  effectively because who is to say that
• 10:46
  you ever lived before? You know, it may
• 10:48
  well be that all of your memories were
• 10:50
  just implanted in you when you woke up
• 10:52
  this very instant. We don't know.
• 10:53
  Obviously,
• 10:55
  >> the Okam's razor argument is yes, you
• 10:57
  existed yesterday and we did do the
• 10:59
  record the other day. But it's
• 11:01
  interesting to think of that and it's
• 11:02
  the way that people perceive time. Now
• 11:06
  moving on to the motion side of it,
• 11:08
  Renie. Um the idea of sitting in a chair
• 11:10
  from birth to death and how that would
• 11:12
  affect your life. I'm not a medic, but I
• 11:15
  suspect if you ask your doctor that
• 11:16
  question, they will probably tell you
• 11:18
  that indeed if you sat in a chair from
• 11:21
  birth to death, your life would be
• 11:22
  shorter than if you lived a normal life
• 11:23
  as a person because of health reasons. I
• 11:26
  mean if nothing else if there's no one
• 11:27
  around to feed you it might lead to a
• 11:29
  relatively short existence. So there is
• 11:32
  that aspect of it as well. We can't see
• 11:35
  the future. So we can't predict what our
• 11:37
  choices are going to do in terms of
• 11:38
  lengthening or shortening our lives. But
• 11:40
  there is one way in which your motion
• 11:42
  can lead to you having a slightly
• 11:45
  different timeline. So from the point of
• 11:48
  view of your life or the number of beats
• 11:49
  of your heart or your perceived time,
• 11:51
  you live the time that you live.
• 11:53
  >> Yeah. The faster you're moving though,
• 11:56
  and this is an outcome of general
• 11:58
  relativity, motion causes time dilation,
• 12:02
  particularly motion with acceleration.
• 12:04
  You know, there's loads and loads of
• 12:06
  complexity to this.
• 12:08
  If you were moving faster,
• 12:11
  the time you perceive is very slightly
• 12:14
  slower. Now, you then get into rest
• 12:16
  frames and all that stuff makes my head
• 12:18
  hurt. So the only place this actually
• 12:20
  really becomes relevant particularly in
• 12:23
  our day-to-day lives in our lived
• 12:25
  experience is when you've got a moving
• 12:27
  platform that's changing direction. So
• 12:28
  it's undergoing acceleration.
• 12:31
  Think about satellites circling the
• 12:33
  earth. They are circling the earth. They
• 12:36
  are moving at a faster speed than we are
• 12:38
  here on the surface of the earth.
• 12:41
  >> We however slightly nearer the center of
• 12:43
  the earth. So we get a little bit of
• 12:44
  gravitational time dilation as I
• 12:46
  understand it. Our clock runs slightly
• 12:48
  slower because we're at the bottom of a
• 12:50
  gravity well, but that is hugely
• 12:51
  overcome by the fact of the high speed
• 12:53
  things are moving in orbit. You're
• 12:55
  talking several kilometers per second.
• 12:58
  Now, under general and special
• 13:01
  relativity, you can work out the number
• 13:04
  of seconds you experience per second
• 13:06
  that ticks in a certain rest frame using
• 13:08
  these equations to get the time
• 13:10
  dilation. And typically that is a
• 13:13
  vanishingly vanishingly small effect
• 13:14
  unless you get very near the speed of
• 13:16
  light and then it ramps up. But it is a
• 13:19
  large enough effect that both we need to
• 13:22
  understand it and we can measure it. Now
• 13:26
  to illustrate the level of this, it's
• 13:28
  not a huge effect. There's a fabulous
• 13:30
  stat that there are people who spent
• 13:33
  time on the International Space Station
• 13:35
  who therefore technically have
• 13:36
  experienced less time passing while they
• 13:38
  were up there than we did on the ground
• 13:40
  watching them. because of time dilation,
• 13:42
  because of their fast movement and their
• 13:43
  acceleration and all the rest of it.
• 13:45
  Space stations going around the earth
• 13:47
  what nearly 8 km/s
• 13:49
  roughly. A couple of Russian guys were
• 13:51
  up there for 6 months. Sergey Criclev
• 13:54
  and Sergey Avd, they did 6 months up
• 13:58
  there and as a result of time dilation,
• 14:01
  when they returned to the surface of the
• 14:03
  earth, they would have experienced less
• 14:05
  time passing than the people on the
• 14:07
  ground did while they were up there.
• 14:09
  >> Yeah. but not enough for them to
• 14:10
  perceive. It would have been 20
• 14:12
  milliseconds,
• 14:13
  >> right?
• 14:14
  >> So that's 0.02 seconds. Um 21,000th of a
• 14:18
  second. It's not very much, but it has a
• 14:20
  huge impact on our day-to-day life. And
• 14:23
  this means that that part of the
• 14:26
  theories of relativity are among the
• 14:29
  most tested theories ever to have been
• 14:31
  developed by humans. And the reason I
• 14:33
  say that is that every time you use your
• 14:35
  generic fruitbased device to navigate,
• 14:38
  anytime you use a satnav, you're using
• 14:41
  GPS satellites.
• 14:43
  GPS satellites orbiting the Earth allow
• 14:46
  you to work out your position on a basic
• 14:48
  level because at any time your device
• 14:51
  can see signals from a number of those
• 14:54
  satellites
• 14:56
  and figure out where they are. There are
• 14:59
  clocks on board all of them. you know,
• 15:00
  it can figure out the like travel time
• 15:02
  to get to it. By seeing the time that
• 15:04
  they're broadcasting, knowing what your
• 15:06
  local time is, figuring out the
• 15:08
  difference between the two, you know,
• 15:09
  how far away the satellite is from one
• 15:11
  of them, that places you at any point on
• 15:13
  a sphere around that satellite that is
• 15:14
  that distance away. From a second
• 15:16
  satellite, you've got another sphere,
• 15:18
  and you're where they intersect, which
• 15:19
  gives you a line. And then a third one
• 15:22
  brings it down to a point. And the more
• 15:23
  you have, the more accurate you get. So
• 15:26
  this is all based on measurement of
• 15:28
  time, allowing you to measure distance
• 15:31
  for things that are at a known distance
• 15:33
  away. This only works so if you can take
• 15:36
  into account the way that the clocks are
• 15:38
  ticking at different speeds because the
• 15:40
  satellites are moving in orbit around
• 15:42
  the Earth.
• 15:43
  The difference including relativistic
• 15:47
  effects and time dilation into the
• 15:49
  calculations for GPS has my
• 15:52
  understanding is it's between a factor
• 15:53
  of 10 and a factor of 100 on the
• 15:56
  precision with which your location be
• 15:58
  can can be calculated and your GPS is
• 16:00
  usually good to probably about a meter.
• 16:02
  I think some of the modern ones are even
• 16:04
  more accurate than that. So if you
• 16:06
  imagine that let's take the really
• 16:08
  optimistic case that you're only getting
• 16:09
  a factor of 10 improvement by including
• 16:11
  relativity at the minute you've got an
• 16:13
  accuracy of 1 meter and that's good
• 16:15
  enough for you to navigate with 10 m it
• 16:16
  probably wouldn't be with 100 m it
• 16:19
  certainly wouldn't be. So our GPS
• 16:22
  systems only work because of our level
• 16:26
  of understanding of relativistic motion
• 16:28
  and of time dilation. So those
• 16:31
  satellites moving very very quickly
• 16:33
  around the earth
• 16:35
  are experiencing an infinite decimally
• 16:37
  small amount of time dilation compared
• 16:39
  to the things they're broadcasting to on
• 16:40
  the surface
• 16:41
  >> and we have to factor that in into our
• 16:43
  calculations to navigate. So your satnav
• 16:45
  wouldn't work without the theorems that
• 16:48
  Albert Einstein put together more than a
• 16:50
  century ago
• 16:52
  >> that are all about how things move
• 16:53
  through time.
• 16:54
  >> So hopefully that has answered that
• 16:56
  question. I think Renie, I would be very
• 16:59
  tempted to suggest that at some point
• 17:00
  you try and get friend to answer that as
• 17:02
  well, just to see where he took it. Um,
• 17:05
  but hopefully that at least is helpful.
• 17:06
  And like I say, if the relativistic
• 17:08
  stuff really interests you, spacetime
• 17:10
  physics, even though it's a book that
• 17:12
  was first published 60 years ago, I
• 17:14
  found invaluable in getting me through
• 17:16
  the exams and actually allowed me to get
• 17:18
  out of my first year and pass rather
• 17:20
  than being kicked out of uni. So, it was
• 17:21
  a great book. H uh Renie might also like
• 17:24
  to go on Wikipedia or any number of
• 17:26
  platforms and look up the twin paradox.
• 17:29
  That's a fun one. That's a great thought
• 17:30
  experiment. And I think there were twin
• 17:33
  astronauts that have uh had a little bit
• 17:36
  of a separation in age because one of
• 17:38
  them spent spent much more time in space
• 17:41
  than his brother. So um their age
• 17:44
  difference uh increased by 8.6
• 17:47
  milliseconds or something something like
• 17:49
  that.
• 17:50
  >> I've seen Yeah,
• 17:52
  >> there are a couple of well there are
• 17:54
  many science fiction books that play
• 17:56
  around this. I've spoken before about
• 17:58
  this series of science fiction books
• 17:59
  called the mass works of science fiction
• 18:01
  which was an attempt by a publisher to
• 18:03
  make money obviously but also to bring
• 18:05
  back some classic science fiction that
• 18:07
  is regarded as being very good and you
• 18:10
  know some of the things I read are very
• 18:12
  fun but they're not necessarily very
• 18:13
  good. You know, there's always that side
• 18:15
  of things. And I'd say the Chrysis books
• 18:16
  I'm reading at the minute, the guy
• 18:18
  incarnated into the body of an ant,
• 18:20
  that's very good fun. I'm really loving
• 18:22
  it, but I wouldn't necessarily say
• 18:23
  they're high literature. They're fun.
• 18:25
  Um, the practic stuff is a bit of both,
• 18:27
  but these mass works of science fiction
• 18:30
  are often fascinating because they are
• 18:34
  quite often hard sci-fi. So in other
• 18:36
  words, there science fiction that is
• 18:37
  grounded in our understanding of science
• 18:39
  at the time they were written and tries
• 18:41
  to use the laws of physics to help build
• 18:44
  the narrative rather than waving the
• 18:46
  laws of physics to allow the narrative.
• 18:48
  You know, there's a fundamental
• 18:49
  difference between the soft and woolly
• 18:50
  sci-fi and the hard scientific sci-fi.
• 18:53
  And two books in particular that leap to
• 18:56
  mind when we're talking about time
• 18:57
  dilation and relativity and things like
• 18:58
  that are The Forever War by Joe Heburn,
• 19:02
  I think his name was. I'll just put that
• 19:04
  name up. The Forever War um was
• 19:07
  basically yeah Joe Holderman. Um the
• 19:10
  idea that there is um it's written in
• 19:13
  1974. It's called military science
• 19:15
  fiction. And the idea is humans are
• 19:17
  fighting an interstellar war against
• 19:19
  these alien civilization. And they're
• 19:21
  sent off on missions on spacecraft that
• 19:23
  travel at relativistic speed because it
• 19:25
  takes a hell of a long time to get
• 19:26
  anywhere. And it's not really about what
• 19:28
  they do when they get there. It's about
• 19:30
  what they do when they come back.
• 19:31
  Because the time you've gone there and
• 19:32
  come back, the earth has moved on
• 19:34
  hugely. You know, you've been away for
• 19:36
  five years, but earth has skipped
• 19:38
  forward 100 years.
• 19:40
  >> Can you reintegrate? How has society
• 19:42
  changed? And I think it's fair to say
• 19:44
  that without a spoiler,
• 19:46
  >> the motivation is that you've more in
• 19:48
  common with the people you've lived that
• 19:50
  experience with than you do with
• 19:51
  everybody else.
• 19:52
  >> And it's all about that. grounded in
• 19:56
  this knowledge of time dilation. I have
• 19:59
  traveled there and back again and come
• 20:00
  back to a world that is changed. The
• 20:02
  other one that really stuck in my mind
• 20:04
  as a interesting way to get your head
• 20:07
  around time dilation is a book called
• 20:08
  Talzer by Paul Anderson and I think that
• 20:11
  was published even longer ago. I think
• 20:12
  it was probably in the 1950s and part of
• 20:15
  the reason I can say that is that that
• 20:17
  book I believe predates the Big Bang
• 20:20
  Theory um or it's around the time of the
• 20:23
  Big Bang Theory. It's um based on a
• 20:25
  short story published in 1967. The book
• 20:27
  itself was published in 1970. So it's a
• 20:30
  a fabulous exploration of it was
• 20:33
  actually post Big Bang, but it's a
• 20:35
  fabulous exploration of relativity in an
• 20:38
  unusual circumstance. In this case, it
• 20:39
  was people being the first humans to
• 20:42
  travel to the stars on a spaceship that
• 20:45
  was meant to go to a star and then come
• 20:48
  back and report. Um they were aiming to
• 20:50
  reach beta vaginis. It says crew of 50,
• 20:53
  25 men, 25 women using something called
• 20:56
  a busard ramjet. So you have basically a
• 20:59
  rocket that scoops up fuel and burns it
• 21:01
  to go faster and faster, right? Um, but
• 21:04
  there's a problem. They get up to high
• 21:05
  speed and then something breaks, but
• 21:07
  they're going so quick that they can't
• 21:08
  get outside the spacecraft to fix it.
• 21:11
  And so they just have to go quicker and
• 21:13
  quicker. And so it explores this captive
• 21:16
  group of 50 people on an island in the
• 21:19
  universe that cannot stop, can only go
• 21:21
  quicker and quicker as the universe
• 21:23
  moves around them. And of course, by
• 21:25
  continually accelerating, they get
• 21:26
  closer and closer to the speed of light.
• 21:28
  And time dilation impacts them more and
• 21:30
  more. So they see the universe to the
• 21:33
  end of the universe and beyond
• 21:36
  >> within a human lifetime. And you know,
• 21:39
  the cosmology in it has changed. It was
• 21:40
  at a time where the big bang a lot of
• 21:42
  people thought would end up in a big
• 21:43
  crunch that everything would stop
• 21:44
  expanding fall back together. But it's
• 21:47
  again this awesome way of demonstrating
• 21:52
  how relativistic terms work. And the
• 21:55
  crew on the mission before anything went
• 21:57
  wrong were aware that when they returned
• 21:58
  to Earth, something like 33 years would
• 22:02
  have passed before they get to their
• 22:03
  destination, this star. But for them,
• 22:06
  only 5 years would have passed. So when
• 22:07
  they turn around and come home, they'll
• 22:08
  have aged 10 years. But 66 years would
• 22:10
  have passed on Earth, give or take.
• 22:11
  >> Yeah, that that's
• 22:12
  >> In fact, that doesn't happen. Wonderful
• 22:14
  book.
• 22:15
  >> Yeah,
• 22:16
  >> it I love those sorts of stories. I I I
• 22:18
  love time, travel, sci-fi, and uh um all
• 22:22
  those relativistic uh concepts. I Yeah,
• 22:27
  I'm actually just finished writing a
• 22:29
  trilogy, and I'm just getting it proof
• 22:30
  read at the moment. Um Oh, fabulous.
• 22:32
  >> And there's a little bit of that in it,
• 22:33
  >> but I'm not giving anything away. So, so
• 22:36
  maybe without without any spoilers at
• 22:38
  all that in a few years time maybe I'll
• 22:40
  be picking up your books as part of the
• 22:42
  mass works of science fiction.
• 22:43
  >> You might.
• 22:45
  >> That'd be nice, wouldn't it?
• 22:46
  >> No pressure.
• 22:46
  >> No. Well, okay.
• 22:49
  Uh, thanks Randy. Um, enjoyed that
• 22:51
  question. It's a It's a fun one to talk
• 22:53
  about. This is Space Nuts with Andrew
• 22:55
  Dunley and Professor Jonty Horner.
• 22:58
  Let's take a short break from the show
• 22:59
  to tell you about our sponsor, NordVPN.
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• 24:46
  Think
• 24:47
  >> we need to do a little more all weather
• 24:49
  testing.
• 24:50
  >> Amen. Space nets.
• 24:52
  >> Our next question, Jonty, comes from
• 24:54
  Paul in Brisbane, although uh he doesn't
• 24:57
  call it Brisbane. You've probably heard
• 24:58
  this term because um you live so close
• 25:01
  to Brisbane, but overseas people might
• 25:03
  think, what on earth is he talking
• 25:04
  about? Good day, Space Nuts. Paul uh
• 25:07
  from sunny Bris Vegas uh here and he's
• 25:11
  thrown a challenge at me. Before I ask
• 25:13
  my question, could you read it in a
• 25:15
  Queensland accent to make it sound
• 25:18
  authentic? Andrew T,
• 25:21
  I'll give it a go, Paul. But, you know,
• 25:22
  it's been a long time since I lived in
• 25:24
  Queensland. I was thinking just
• 25:27
  listening in episode 681 when you and
• 25:31
  Fred started talking uh about the
• 25:34
  possibility of Titan and Hypernian
• 25:37
  Hyperion Collidon, uh, thus creating
• 25:39
  Saturn's rings 100 million years ago. Uh
• 25:43
  what do you reckon the odds are of some
• 25:46
  of the bigger blocks of the collision
• 25:48
  spinning off into space uh getting
• 25:51
  closer to the sun? I don't know.
• 25:53
  Colliding with the Earth, say 65 million
• 25:56
  years ago. Is that a possibility? Or
• 25:59
  does the chemical residue from on here
• 26:02
  on Earth suggest there's more likely to
• 26:06
  have been a comet? Curious to get your
• 26:08
  thoughts on this, eh? Uh, as always,
• 26:11
  keep up the great work and thank you.
• 26:15
  Was that Queenslandish enough?
• 26:17
  >> Uh, theatrical. So, the accent thing and
• 26:19
  again, we're very good at getting off
• 26:21
  topic or I am.
• 26:22
  >> Depends what part of Queensland because
• 26:23
  it's a big state.
• 26:25
  >> For people listening
• 26:26
  >> and you got to you got to chuck in an A
• 26:28
  on the end of every sentence.
• 26:30
  >> One of the things that's always made my
• 26:33
  head hurt a little bit since I moved to
• 26:34
  Australia in 2010 and I am officially
• 26:36
  Australian, you know.
• 26:37
  >> Yeah. is a lack of diversity in the
• 26:39
  accents. I I grew up in the UK where
• 26:43
  accents are very very varied to the
• 26:45
  extent that you could tell within my
• 26:46
  school which estate people grew up in
• 26:47
  because of subtleties in their accent
• 26:49
  locally. And the variation on the larger
• 26:52
  scale is astonishing. It's part of why I
• 26:55
  I think British actors have so much
• 26:57
  success, partly because they get very
• 27:00
  good training, of course, but if you're
• 27:01
  an actor in the UK, you have to have a
• 27:03
  fluidity with accents because there's
• 27:05
  such a diversity just within the UK.
• 27:07
  >> Yeah.
• 27:08
  >> And I came to Australia and I do not
• 27:11
  I've lost some of my ear for the UK
• 27:12
  accents. I used to be really good
• 27:14
  because you grow up there, it's a
• 27:15
  natural thing. I've lost a bit of that,
• 27:17
  >> but over here it seems to be there isn't
• 27:20
  a very strong regional diversity.
• 27:22
  There's just a little bit of town versus
• 27:24
  country and a very little bit of north
• 27:26
  south, but it's very smooth, although
• 27:30
  very little variety.
• 27:31
  >> I'll tell you, when I got into radio, I
• 27:34
  um did a demo tape and I had a friend
• 27:37
  listen to it who'd been in radio a very
• 27:39
  long time and I was only just starting
• 27:40
  out and he listened to it and he said,
• 27:42
  "You know, you've got to get rid of rid
• 27:44
  of your Newcastle twang." Cuz I grew up
• 27:46
  in the Hunter Valley um in that
• 27:48
  Newcastle district. And I said, "What?"
• 27:50
  He said, "You've got a Newcastle twang.
• 27:52
  There's a certain sound that comes out
• 27:55
  of the mouths of Navicestrians. You got"
• 27:58
  And I had to get I had to train that out
• 28:00
  of myself
• 28:01
  >> and and it it it can be no disrespect,
• 28:04
  but it can be a bit grating.
• 28:06
  >> Um but there there is there are
• 28:10
  diversities in in accent across
• 28:13
  Australia that when I worked for the
• 28:15
  ABC, they actually published a map of
• 28:17
  accents.
• 28:18
  >> Yeah. Yeah.
• 28:19
  >> And I think the most prominent variation
• 28:21
  is South Australia, particularly
• 28:23
  Adelaide. Much more posh,
• 28:26
  >> but it's also to me it's much more
• 28:29
  evidence because I just don't quite have
• 28:30
  the air for it cuz in the UK the accents
• 28:32
  are very much more val. So Newcastle
• 28:34
  accent to me is very different to what
• 28:36
  you think of a Newcastle accent.
• 28:37
  >> But where I see it is in language. So
• 28:39
  there's the the perennial argument among
• 28:42
  Australians of whether it's a potato
• 28:44
  cape or a potato scholar is a good
• 28:46
  example. you got regional things like
• 28:47
  that and for
• 28:49
  >> from my side of things I worked in
• 28:51
  Switzerland for 3 years
• 28:52
  >> and shared an office with Haga who was
• 28:55
  this young woman from I think Iran or
• 28:58
  somewhere Persian I'm not sure exactly
• 29:00
  where but we communicated in English
• 29:02
  which was her sixth language
• 29:04
  >> wow
• 29:05
  >> which was astonishing to me but there
• 29:07
  was one time I've been on the phone to
• 29:09
  my parents and I finished and she said
• 29:10
  so Johny what does a mean up and yeah a
• 29:14
  up um and It reminds me of the wonderful
• 29:17
  >> Isn't that Liverpoolian that
• 29:19
  >> no aopsy Yorkshire as well? Not far.
• 29:22
  >> If you want to see the accent of roughly
• 29:24
  where I grew up incidentally, it's worth
• 29:26
  people looking up the fabulous song Ilk
• 29:29
  Batat which is a cultural treasure from
• 29:31
  my part of the world and we all learned
• 29:33
  when we were in Scouts and at school and
• 29:35
  it's um basically group of group of
• 29:37
  fellas at the pub saying where where
• 29:39
  have you been since I saw you last? been
• 29:41
  you've been caught in Mary Jane and it
• 29:42
  goes on about how he's not been dressed
• 29:45
  appropriately and he's going to die in
• 29:46
  the laughter burium and but it's all in
• 29:48
  very strong dialect so you can see that
• 29:50
  but what that resulted in is everybody
• 29:53
  in burn communicated in English at the
• 29:56
  physical institute I had speak German
• 29:58
  when I was out in the town but English
• 30:01
  has become this kind of lingua frana
• 30:03
  lingua lingua frana there because
• 30:06
  Switzerland is a country with four
• 30:07
  different languages it's got French
• 30:08
  German Italian and romance
• 30:10
  But everybody's proud of their language.
• 30:12
  The French speakers will not silly
• 30:14
  themselves by speaking German to the
• 30:16
  German speakers. The German speakers
• 30:18
  therefore will not silly themselves by
• 30:20
  speaking the foul French to the French
• 30:22
  speakers.
• 30:22
  >> Yeah.
• 30:23
  >> So they speak English.
• 30:25
  Um but that means people have very good
• 30:28
  English, but they've learned a lot of
• 30:29
  their English from watching American TV
• 30:31
  rather than British TV. But even the
• 30:33
  British TV is a little bit denuded in
• 30:35
  terms of accent and um in terms
• 30:40
  particularly of dialect terms
• 30:43
  and it was to an extent we were talking
• 30:44
  about the accents the news presenters
• 30:46
  until about 20 or 30 years ago on the
• 30:48
  BBC had to use received pronunciation
• 30:50
  which is the Queen's English and you
• 30:52
  have to speak very properly and they got
• 30:54
  rid of that because people realize that
• 30:55
  actually diversity in accents represents
• 30:57
  the diversity of people and that's
• 30:58
  great. What that meant though was uh my
• 31:02
  accent I've reliably been told is
• 31:03
  relatively strong. But I don't really
• 31:06
  use any dialect terms anymore other than
• 31:08
  the o bit of Aussie stuff I've picked up
• 31:10
  because what was really throwing people
• 31:11
  in Switzerland was the dialect terms,
• 31:14
  not the accents, things like a up. And
• 31:17
  so my language has shifted. I've lost a
• 31:19
  bit of an A for the UK stuff, but I
• 31:20
  don't hear much variety in the
• 31:23
  Australian accent. Now, part of that is
• 31:25
  because I'm not from here, but I I
• 31:29
  always find that kind of stuff really
• 31:30
  really interesting. So, I mean, I could
• 31:32
  tell you were getting a stronger
• 31:33
  Australian accent. Um, but it wasn't
• 31:36
  necessarily I couldn't have told you
• 31:37
  where it was from. Other thing is,
• 31:40
  again, saw an interesting discussion
• 31:42
  online about the Australian accent
• 31:43
  changing over time, asking why when you
• 31:45
  watch Aussie films and TVs from 30, 40,
• 31:49
  50 years ago, everybody almost sounds
• 31:51
  like they're a pastiche of the
• 31:52
  Australian accent. It's so full on and
• 31:54
  there's so many terms and insults and
• 31:57
  stuff that aren't used today. Yeah.
• 31:59
  >> And apparently part of it is language
• 32:02
  evolves. We've got all these
• 32:03
  multicultural influence. We've got all
• 32:05
  that stuff. But also apparently the
• 32:06
  actors were trained to ham it up.
• 32:09
  >> Oh, absolutely. That's exactly what it
• 32:12
  was. And and uh see what you started,
• 32:14
  Paul. But uh I understand because I did
• 32:17
  some research on it. The Australian
• 32:18
  accent came about because we were
• 32:23
  a colony of convicts brought over from
• 32:25
  the UK, but the convicts were all from
• 32:28
  different walks of life, but they were
• 32:30
  conglomerated into a new community and
• 32:33
  all their accents merged into what is
• 32:36
  now the Australian accent. So you know
• 32:39
  you you you had Welsh, you had Irish,
• 32:42
  you had Scottish, you had English or
• 32:44
  with all the variations all coming
• 32:46
  together and creating the Australian
• 32:48
  accent. So that's why it is what it is.
• 32:51
  >> Yes.
• 32:51
  >> But it's ever evolving too.
• 32:53
  >> And it's a wonderful thing. It does
• 32:54
  change over time which I found
• 32:56
  interesting. Anyway, sorry about that.
• 32:58
  We get off topic wonderfully,
• 32:59
  wonderfully. Well, Saturn,
• 33:00
  >> we're good at that. So Fred started
• 33:02
  talking about the possibility of Titan
• 33:03
  and a Hyperion colliding and what
• 33:06
  happened to the stuff. Could a big rock
• 33:08
  from that event have hit Earth 65
• 33:10
  million years ago and you know what he's
• 33:12
  talking about there or did it all just
• 33:13
  go flying off into space or did it do
• 33:15
  something else etc etc.
• 33:18
  >> All all sorts of ways we can go with
• 33:20
  this. So the origin of Saturn's rings
• 33:23
  first and foremost is not yet
• 33:25
  definitively known. We know that there
• 33:27
  are ring systems around Jupiter, Uranus
• 33:29
  and Neptune as well. We suspect strongly
• 33:31
  that in the past and in the future Mars
• 33:34
  has had and will have ring rings. I
• 33:37
  think red dwarfy has will have possibly
• 33:40
  going to have whatever it it may have
• 33:42
  had episodic rings in the past. We've
• 33:44
  found rings around a few of the solstice
• 33:45
  from smaller objects like um the
• 33:47
  centaurs Chiron and Currico. Um rings
• 33:50
  are a thing. We've also found
• 33:52
  potentially rings around exoplanets.
• 33:54
  Some debate about that. We find rings
• 33:55
  around stars in the form of debris discs
• 33:58
  and all the rest of it. Yeah,
• 34:00
  ever since Saturn's rings were known,
• 34:03
  there's been ongoing how did they get
• 34:05
  there? And there is an ongoing not only
• 34:08
  how did they get there, but are they
• 34:09
  transient or permanent? And there are a
• 34:12
  wide variety of opinions on this and
• 34:14
  modeling has not yet come down strongly
• 34:16
  one way or the other. Currently, the
• 34:19
  best thinking about Saturn's rings is
• 34:20
  that they are more likely to be new than
• 34:23
  old. So we're probably seeing a ring
• 34:26
  system that has in bulk not existed
• 34:29
  since the birth of the solar system and
• 34:32
  estimates of the age range from 10 to
• 34:35
  100 to 300 million years. These
• 34:38
  estimates on the which the rings are
• 34:40
  being depleted suggest that they may
• 34:43
  well return to the level of Neptune,
• 34:45
  Uranus, Jupiter type rings within about
• 34:48
  300 million years from now. Those
• 34:52
  theories, those arguments
• 34:54
  would suggest that if the ring system is
• 34:56
  younger than the edge of the solar
• 34:57
  system, there had to be an event to
• 34:59
  bring it into being. Obviously, and
• 35:01
  there have been a number of different
• 35:03
  suggestions to cause this. One is that,
• 35:06
  and this was commonly argued when I was
• 35:08
  a kid learning about it, that Saturn had
• 35:10
  a comet or asteroid that got too close,
• 35:12
  was torn us under creating the rings.
• 35:14
  Now this invokes a part of planetary
• 35:16
  science knowledge and physics called the
• 35:19
  ro limit which is essentially if you
• 35:22
  have two massive objects and you bring
• 35:24
  them close enough together tidal effects
• 35:26
  will disrupt the smaller of them due to
• 35:29
  the gravity of the bigger of them. And
• 35:31
  the point there is if you think that the
• 35:33
  strength of the gravitational pull falls
• 35:35
  off as a square of the distance and
• 35:37
  you've got an object that's 100 km
• 35:39
  across, the side that is nearer a planet
• 35:41
  will be feeling a stronger pull than the
• 35:43
  side that's further away. Now depending
• 35:45
  on the strength of the object, that
• 35:47
  distance will vary. The stronger the
• 35:49
  object is, the closer it can get to a
• 35:51
  planet before disruption. But we have
• 35:53
  this concept of the ro limit. And
• 35:54
  Saturn's rings are within the ro limit,
• 35:57
  which is why they've been disrupted. And
• 35:58
  the largest objects in them are probably
• 36:01
  to be honest the shepherd moons that are
• 36:03
  kilometer scale objects which are
• 36:06
  probably due to the nature of the ro
• 36:08
  limit and stuff they're probably fairly
• 36:11
  rubbish rather than rubble panels
• 36:12
  because if they were rubble panels
• 36:13
  they'd get disintegrated. Um, so they're
• 36:16
  probably at a distance where they are
• 36:18
  within the ro limit for a fluid object
• 36:20
  that has no strength, but they are
• 36:22
  strong enough that the ro limit for them
• 36:23
  will be closer in. Anyway, a bit off
• 36:24
  topic there, but that's the physics
• 36:26
  behind it. And you can work out that ro
• 36:28
  limit either as a ratio of the mass of
• 36:30
  the object to the mass of the thing it's
• 36:32
  the bigger thing that it's coming near
• 36:34
  or as a ratio of the densities. It works
• 36:36
  either way, which is kind of cool. Um,
• 36:40
  that's what
• 36:43
  the physics is behind why you don't have
• 36:45
  a single object there. It can't form a
• 36:46
  single object. It's got to be broken up
• 36:48
  into debris. The rings are decaying.
• 36:51
  Dust is lost to Saturn all the time.
• 36:53
  They're also being slightly replenished
• 36:55
  by the activity particularly of
• 36:56
  Enceladus
• 36:58
  um, which is repopulating the earrings.
• 37:00
  So, there are system in flux and it's
• 37:03
  not clear exactly where they formed.
• 37:05
  There was the idea when I was a kid that
• 37:07
  it was a comed asteroid that was
• 37:08
  disrupted to make that much material. I
• 37:11
  think that has gone probably by the
• 37:13
  wayside because you need a way to
• 37:16
  dissipate the energy for an object to be
• 37:18
  captured. So if you have a comet or an
• 37:21
  asteroid get close enough to Saturn to
• 37:22
  be torn apart, that material is still
• 37:25
  moving faster than Saturn's escape
• 37:27
  velocity. So we just fly away, albeit
• 37:29
  torn apart.
• 37:29
  >> Right? If you have something that is
• 37:31
  temporarily captured as a satellite,
• 37:34
  it'll be on a fairly elongated orbit if
• 37:36
  it's going to get close enough to be
• 37:37
  disrupted and it will continue to follow
• 37:39
  that. So if you look at comet Schumac
• 37:41
  119 back in the 1990s, it came very
• 37:44
  close to Jupiter in 1992, I think, was
• 37:46
  torn apart so that we had many smaller
• 37:48
  comets that all followed essentially the
• 37:50
  same art orbit in a lengthy chain and
• 37:53
  fell apart, crashed into Jupiter one
• 37:56
  after the other over the space of a
• 37:57
  couple of weeks in 1994.
• 37:58
  >> That's right. They didn't form a ring
• 38:01
  system.
• 38:02
  >> No.
• 38:02
  >> When that had its first approach to
• 38:04
  Jupiter, it was torn apart, but it
• 38:06
  didn't make a new ring system. So, you
• 38:08
  need some way to dissipate the energy to
• 38:10
  trap all the debris onto a circular
• 38:11
  orbit near the planet. And it's very
• 38:13
  hard to visualize how you do that from
• 38:15
  an asteroid or comet passing through.
• 38:17
  So, that's led to instead the idea of
• 38:21
  the collision between two moons. Now,
• 38:23
  the most recent version I've seen
• 38:25
  discussed of this is that there was a
• 38:28
  moon that was possibly as large as
• 38:31
  Hyperion or even bigger
• 38:34
  that collided that sorry, whose orbit
• 38:37
  spiraled inwards to the point it crossed
• 38:39
  the ro limit. Now, we're seeing this
• 38:41
  happen with Phoebe, the innermost of
• 38:44
  Mars's two moons. Phoebe is closer to
• 38:46
  Mars than what we call the co- rotation
• 38:49
  altitude, which means its orbit around
• 38:51
  Mars takes less time than Mars takes to
• 38:53
  spin. And when you're closer than that
• 38:55
  co- rotation place, tidal forces will
• 38:57
  make you spiral inwards rather than
• 38:59
  spiraling outwards. Our moon's further
• 39:00
  out. It takes longer to orbit the Earth
• 39:02
  than the Earth takes to spin. So, it
• 39:04
  moves away.
• 39:05
  >> Yeah. Imagine then that you had a moon
• 39:09
  few hundred km across 200 300 400 km
• 39:12
  across close in that spiraled inwards
• 39:16
  and cross the ro limit it would be
• 39:17
  disrupted forming system that's one
• 39:19
  theory another is that you had a moon
• 39:21
  that was pretty close in that was then
• 39:24
  struck by an object large enough to
• 39:26
  shatter and disrupt it. that collisions
• 39:30
  of that size would be relatively rare
• 39:33
  these days because projectiles big
• 39:34
  enough to shatter a moon of that size
• 39:37
  are relatively scarce. Um, a more more
• 39:40
  recent version that's been proposed is
• 39:42
  that you had a much larger object,
• 39:44
  something more like the size of Titan
• 39:46
  and that was stripped off during the
• 39:49
  formation period of Saturn. There's all
• 39:50
  sorts of theories here, but like I say,
• 39:53
  we're not fully there yet. We're still
• 39:54
  exploring. That's where future missions
• 39:57
  to Saturn are going to teach us a lot
• 39:59
  more. Um, we've got an age here. Um,
• 40:02
  observations based on the KEK telescope
• 40:05
  suggests that the rings will be gone in
• 40:07
  292
• 40:09
  plus 818US 124 million years, which
• 40:12
  illustrates that as astronomers, we are
• 40:14
  terrible at choosing significant
• 40:16
  figures. And I tell my students this all
• 40:18
  the time because if you talk to a
• 40:19
  physicist, they'd see those numbers and
• 40:21
  weep because they'd say, "Well, that
• 40:23
  should just be 300 plus 800 minus 100
• 40:25
  because the other numbers are
• 40:26
  meaningless anyway." Um, but it's a very
• 40:29
  large uncertainty on how long they will
• 40:31
  take till they're gone. We don't know
• 40:33
  how massive they were initially, and how
• 40:36
  massive they are initially will be part
• 40:39
  of what determines
• 40:41
  how long they've been around.
• 40:43
  >> Uhhuh. Anyway, so that's why there's
• 40:45
  still a lot of misunderstanding and a
• 40:47
  lot of confusion there. And it may well
• 40:49
  be that rings of the scale of the rings
• 40:51
  of Saturn around the giant planets are
• 40:53
  an episodic thing. It may well be that
• 40:55
  planets like Saturn, Jupiter, Uranus,
• 40:58
  and Neptune have minor ring systems all
• 41:00
  the time, but occasionally they'll get a
• 41:02
  really good one. And it could be that in
• 41:03
  the past Jupiter had a massive ring
• 41:05
  system like this. And in the future,
• 41:07
  Uranus might, for example, Mars will
• 41:10
  probably get a ring system when um
• 41:12
  Phobos gets close enough and is
• 41:13
  disrupted.
• 41:15
  >> All that now to aside, the next part was
• 41:17
  about debris reaching us from the
• 41:20
  collision and reaching the Earth.
• 41:23
  >> Yeah.
• 41:24
  >> Um two parts to this. The first is that
• 41:28
  some material from that collision could
• 41:31
  potentially have reached Earth. I don't
• 41:32
  doubt that. I did work while I was at
• 41:35
  the University of Burn, which we talked
• 41:36
  about earlier, with a PhD student at the
• 41:39
  time called Augustine Anich, who was
• 41:41
  doing simulations of the giant collision
• 41:44
  that made Mercury the planet we know it
• 41:46
  is today. Mercury is over dense. It has
• 41:49
  an oversized core. And the thinking is
• 41:51
  it was probably once a planet twice the
• 41:53
  diameter of the current Mercury. And it
• 41:56
  had this massive collision that stripped
• 41:58
  it of its mantle and crust, leaving
• 41:59
  behind a core with a little bit of
• 42:00
  rubble on top. and he was doing
• 42:02
  simulations of that impact.
• 42:05
  And my contribution was I ran orbital
• 42:07
  mechanics simulations. This is kind of
• 42:09
  core to my day-to-day work. This is what
• 42:11
  I've done all through my career. And I
• 42:14
  said, where would the ejector go? If you
• 42:16
  have a collision like that, some of the
• 42:18
  material ejected will be traveling at
• 42:20
  less than the escape velocity for all of
• 42:22
  the mass that's around. So that material
• 42:23
  won't be lost and it would either in the
• 42:26
  case of the earth moon collision form a
• 42:27
  satellite like the moon or fall back and
• 42:29
  contribute to the reacion.
• 42:32
  >> Material traveling above the escape
• 42:34
  velocity will escape and go into orbit
• 42:37
  around the sun. And at that point it is
• 42:39
  subject to all of the dynamics that goes
• 42:41
  on the grav gravitational interactions
• 42:42
  with all the other planets. And I ran
• 42:45
  simulations of the ejector to see what
• 42:47
  their eventual fates would be where they
• 42:49
  would wind up. The majority of the
• 42:51
  ejector from the mercury forming
• 42:52
  collision hit the sun or was flung from
• 42:55
  the solar system never to return as a as
• 42:57
  a final fate. That's where it ended up.
• 42:59
  But about 2% of the material ejected
• 43:01
  from Mercury would have landed on Earth.
• 43:04
  >> Oh.
• 43:04
  >> So we will have been polluted by the
• 43:06
  Mercury forming impact by what you
• 43:08
  describe as herian material. If if we
• 43:11
  were talking about Venus being venerial
• 43:14
  material which then became Venian
• 43:16
  material, Mars being Martian, Jupiter
• 43:18
  being Jovian for Mercury, Mercurian
• 43:22
  never quite worked. So a lot of people
• 43:23
  used to call it herian um the
• 43:25
  traditional name for but anyway the
• 43:27
  material from Mercury about 2% of it
• 43:28
  would have rained down on the earth. Now
• 43:31
  this ties into the work that I've talked
• 43:34
  about before about panspermia as well.
• 43:36
  Material ejected from one planet becomes
• 43:39
  objects moving freely within the solar
• 43:41
  system subject to the gravitational
• 43:44
  pinball that goes on. If you have a
• 43:47
  collision in orbit around Saturn, if it
• 43:50
  is a collision between two of Saturn's
• 43:52
  moons, the overwhelmingly vast majority
• 43:55
  of ejector will stay bound in the Saturn
• 43:57
  system because the moons are both
• 43:58
  themselves very deep in Saturn's gravity
• 44:00
  while very tightly held. So the vast
• 44:04
  majority of ejector from two moons
• 44:05
  colliding with each other will be kept
• 44:07
  in house.
• 44:09
  But that's not all of it. Also some of
• 44:12
  that ejector that ejector in the Saturn
• 44:14
  system will be like ejector in the solar
• 44:16
  system. It'll be bounced around and
• 44:17
  moved around by the gravity of the
• 44:18
  moons. So a small tiny fraction of it
• 44:21
  could eventually be ejected that way as
• 44:22
  well. If you have a collision that
• 44:25
  instead involves or invokes an object
• 44:27
  that is not currently orbiting Saturn
• 44:29
  but is a comet or an asteroid passing
• 44:31
  through that object itself is moving
• 44:33
  faster than the escape velocity of
• 44:35
  Saturn. So a significant amount of the
• 44:36
  ejector also will be that case you'll
• 44:39
  get more material put into orbit around
• 44:41
  the sun. Once the material has escaped
• 44:44
  from Saturn it is moving on an orbit
• 44:46
  that makes it one of the centaurs. And
• 44:48
  the centaurs are one of my favorite
• 44:49
  populations of objects anyway because
• 44:52
  they're what I studied for my PhD and I
• 44:53
  did the same dynamic simulations of
• 44:55
  them. Where do they come from? Where are
• 44:56
  they going? How will they get there? The
• 44:59
  centaurs are the parent population of
• 45:01
  the short period comets. The centaurs
• 45:03
  themselves are daughters, sons, children
• 45:08
  of the transep union objects moving
• 45:10
  around in the out solar system being
• 45:11
  scattered inwards. In my simulations of
• 45:14
  the Centaurs, about onethird of Centos,
• 45:17
  which is about onethird of those objects
• 45:19
  between the orbits of Jupiter and
• 45:21
  Neptune that are on unstable orbits,
• 45:22
  about onethird of them will eventually
• 45:24
  become a Jupiter family comet, will be
• 45:25
  flung into the inner solar system,
• 45:27
  usually by Jupiter, which means it'll be
• 45:29
  put onto an Earth crossing orbit, which
• 45:31
  means that if you eject enough material
• 45:34
  from the Saturn system,
• 45:37
  some of it will hit the Earthh.
• 45:38
  >> It'll be a vanishingly small amount. It
• 45:41
  is unlikely though that you'll get a
• 45:44
  chunk big enough to cause a mass
• 45:45
  extinction making it all that far. You
• 45:49
  the thing that killed the dinosaurs was
• 45:51
  about 10 km across. We think maybe even
• 45:53
  a little bit bigger. That's a very very
• 45:55
  very big bit of stuff. Now obviously
• 45:58
  there's a small chance it could have
• 45:59
  been the result of something like that.
• 46:01
  There are suggestions that the thing
• 46:03
  that killed off the dinosaurs might have
• 46:04
  been an asteroid that was probably
• 46:07
  produced in a collision in the asteroid
• 46:08
  belt and been a member of one of the
• 46:10
  collisional families that feed material
• 46:11
  to the inner solar system. Others have
• 46:13
  suggested it could be a comet.
• 46:15
  >> It could potentially have been a
• 46:17
  fragment of a a smashed moon like Paul
• 46:20
  is suggesting. It could have been a very
• 46:22
  ancient fragment of the Mercury
• 46:24
  collision that had managed to survive 4
• 46:26
  billion years. But that's vanishingly
• 46:27
  unlikely because things are rejected on
• 46:29
  a much shorter time scale. So there'll
• 46:31
  be nothing left effectively. But we
• 46:33
  don't know. That's a fundamental thing.
• 46:36
  What drives the understanding that the
• 46:38
  impact itself was extraterrestrial was
• 46:41
  initially the iridium layer that was
• 46:43
  found globally. That was kind of a bit
• 46:44
  of a smoking gun at the point of the
• 46:46
  mass extinction in the fossil record.
• 46:48
  They found the crater. You cannot tell
• 46:51
  from the crater's size alone what the
• 46:54
  nature of the impactor was or the impact
• 46:56
  speed. Now for a crater that old it's a
• 46:59
  bit bit impossible to do anyway. I've
• 47:01
  been really interested and we've never
• 47:03
  got round to doing this as research to
• 47:05
  talk with people like the create
• 47:07
  accounting people to see if there is any
• 47:09
  way for bodies like the moon or Mars
• 47:10
  where there's much less weathering to
• 47:13
  distinguish between a cometary or
• 47:14
  asteroidal impact on the basis of
• 47:18
  whether the speeds influence on the
• 47:21
  kinetic energy of the impact can modify
• 47:24
  the crater formation process. probably
• 47:26
  it can't because effectively you're
• 47:28
  dumping X energy into the surface and
• 47:30
  that's what makes the crater but I've
• 47:32
  been interested in that but what that
• 47:34
  means from the Earth's point of view is
• 47:35
  that from the morphology of the crater
• 47:37
  from what's left from that impact we
• 47:40
  cannot tell what the impact was or how
• 47:41
  fast it's traveling had to be faster
• 47:43
  than the escape velocity of the earth
• 47:45
  because it came from beyond the earth so
• 47:47
  the minimum speed is 12 km a second it
• 47:49
  is almost guaranteed that it was a solar
• 47:52
  system object not an interstellar comet
• 47:54
  like comet Atlas Which means that the
• 47:56
  maximum speed it could have hit us is 72
• 47:58
  km a second which is you get that number
• 48:02
  by combining the orbital speed of the
• 48:04
  earth which is 30 km a second going
• 48:06
  forward with the maximum speed that
• 48:08
  something could be traveling at one
• 48:09
  astronomical unit at our location and
• 48:12
  still be bound to the sun which if you
• 48:13
  work out the velocity if you're going at
• 48:16
  42 km a second at the location of the
• 48:19
  earth's orbit you're right on the
• 48:20
  boundary between the solar systems
• 48:22
  escape velocity and not so anything
• 48:24
  faster than that will escape. Take those
• 48:26
  two numbers and say, "Right, you've got
• 48:28
  an op object coming head on at the
• 48:30
  fastest speed it could have and stay
• 48:32
  bound to the solar system. 42 km a
• 48:35
  second one way, 30 km a second the other
• 48:37
  way gives you 72 km a second. So we know
• 48:40
  the velocity with which the signal was
• 48:43
  coming in within a factor of six. Most
• 48:45
  likely at the lower end because we get
• 48:46
  more asteroidal impactors and cometry
• 48:48
  ones, but we don't really have much more
• 48:51
  than that on the composition of it.
• 48:53
  There is a lot of debate over whether it
• 48:55
  was cometry, whether it was asteroidal.
• 48:58
  An object from from part of one of the
• 49:02
  moons of Saturn would be iceer rich and
• 49:05
  so it would look like a cometary
• 49:07
  impactor. So I'm not sure for an impact
• 49:10
  65 million years old whether we would
• 49:13
  ever be able to distinguish be between a
• 49:15
  fragment of one of the moons of Saturn
• 49:17
  as the impactor and a comet as the
• 49:20
  impactor. Um, I I just have no idea how
• 49:24
  we would do that. What we would probably
• 49:26
  be able to do is if we went to a
• 49:28
  near-Earth object, whether it's a comet
• 49:30
  or an asteroid, and took samples, there
• 49:33
  is a potential that then maybe through
• 49:36
  isotopic analysis, we could tell that
• 49:38
  something was a fragment of a Saturnian
• 49:41
  moon, but we need things to compare that
• 49:43
  to. That is very much on the very
• 49:45
  fringes of what we can do. But we do
• 49:47
  that a little bit with some meteorites.
• 49:49
  There's a couple of families of
• 49:51
  meteorites where we think we know the
• 49:52
  parent object. And these meteorites are
• 49:55
  compositionally grouped together with
• 49:58
  such tightness that they are
• 49:59
  distinguishable against the compositions
• 50:01
  of everything as a background. It's like
• 50:03
  if you measure the composition of
• 50:04
  everything and they're points on a wall,
• 50:06
  these ones all group together. So they
• 50:08
  come from the same parent. But I don't
• 50:10
  know how we could
• 50:13
  figure out whether it was a fragment of
• 50:15
  a Saturnian moon versus a comet. If we
• 50:19
  got to the point where we could
• 50:20
  distinguish comet versus asteroid, I
• 50:22
  think the argument will be it's a
• 50:24
  commentary body probably um but we
• 50:26
  couldn't tell you whether it's short or
• 50:28
  a long period comet. But people will
• 50:29
  probably come down on the cometry
• 50:31
  explanation rather than the fragment of
• 50:33
  a moon explanation because of the Okam's
• 50:35
  razor thing. So if you've got two
• 50:38
  explanations that are equally good at
• 50:39
  explaining the story, take the one
• 50:41
  that's simpler. Yeah,
• 50:42
  >> that might not be AM's razor, but that's
• 50:43
  one of those philosophical constructs
• 50:45
  that, you know, it's a more complex and
• 50:49
  challenging route to get a fragment of a
• 50:51
  Saturnian satellite to kill the
• 50:52
  dinosaurs than it is to have it just be
• 50:54
  a normal comet.
• 50:55
  >> Yeah, fair enough. All right, very good.
• 50:58
  Um, thank you, Paul. I think we covered
• 51:01
  that uh topic very, very well. And hope
• 51:04
  all's well in Queensland. Hey, uh we're
• 51:08
  going to take a breath and then uh we'll
• 51:10
  quickly go into our final question here
• 51:12
  on Space Nuts
• 51:17
  and I feel fine.
• 51:18
  >> Space Nuts
• 51:20
  >> and we're with Professor Jyer today with
• 51:23
  Fred away. Uh a Q&A edition. Uh one last
• 51:27
  question. Uh we'll have to make it quick
• 51:28
  because I think we've really burnt the
• 51:30
  clock today. Too much talking about
• 51:31
  accents. I think uh I have a question.
• 51:33
  Talking. I was just going to say talking
• 51:35
  accents. Get Fred to single climb
• 51:39
  >> cuz he's from my neck of the woods
• 51:41
  originally.
• 51:41
  >> Okay. Uh I have a question that might
• 51:44
  come across as lame or childish. Yes, it
• 51:47
  did. No. No, it didn't. Uh, but I'm
• 51:49
  hoping that a professor and a genuine
• 51:52
  space nut uh or I'm hoping that asking a
• 51:57
  professor and a genuine space nut this
• 51:59
  question, it might prompt uh for much
• 52:01
  more interesting answer than the average
• 52:03
  Joe. What is your favorite planet in our
• 52:06
  solar system and why? I wish I could
• 52:08
  give you an interesting answer myself. I
• 52:10
  do find Jupiter fascinating and Europa.
• 52:12
  Okay, you know, I know it's a moon, but
• 52:15
  I'm intrigued by what could be under all
• 52:17
  that ice. Hopefully, um, we'll find out
• 52:19
  in my lifetime. So, yeah, childish
• 52:21
  question from a 40-year-old, but
• 52:22
  hopefully you can turn it into a more
• 52:25
  deep and meaningful answer. That's Dan
• 52:27
  from the Gold Coast, also a
• 52:28
  Queenslander.
• 52:30
  Um, I can go first and be very quick.
• 52:32
  I'm fascinated by Mars. I just find the
• 52:35
  geography
• 52:37
  um outstanding. a smaller planet than
• 52:40
  Earth uh with geographic
• 52:44
  um highlights that are just
• 52:46
  mind-bogglingly huge like the Olympus
• 52:50
  Mons for example that that is a volcano
• 52:52
  that is it's the biggest in the solar
• 52:54
  system and um I think it is so high that
• 52:58
  it's actually sticking out of Earth's
• 53:00
  out of Mars's atmosphere.
• 53:02
  um the the the canyons on Mars and
• 53:05
  there's more than one but there's the
• 53:07
  the biggest one dwarfs the Grand Canyon
• 53:10
  on Earth like I think you can fit the
• 53:12
  Grand Canyon in one of one of its
• 53:13
  tributaries
• 53:15
  um and the list goes on. It is a f a
• 53:19
  fascinating planet. I always like to
• 53:20
  think of it as um that was God's first
• 53:22
  attempt and he stuffed it up and then we
• 53:25
  came next.
• 53:27
  I I I just uh I just and because we've
• 53:30
  we've been able to send so many probes
• 53:32
  and and rovers and satellites to Mars,
• 53:36
  we've been able to document it, get some
• 53:39
  incredible high res pictures of it. It's
• 53:42
  I I just find it a a beautiful,
• 53:44
  beautiful world. And I mentioned my
• 53:47
  sci-fi trilogy um earlier. Um Mars is in
• 53:51
  it. I couldn't I couldn't leave it out.
• 53:54
  So Mars for me, that was a quick answer.
• 53:56
  What's yours? It's got to be in the
• 53:58
  solar system. It's a really tough one.
• 54:01
  And these kind of questions throw throw
• 54:03
  me because the it might be a childish
• 54:05
  question because it's the kind of
• 54:06
  questions kids ask, but it's entirely a
• 54:09
  good question to ask.
• 54:11
  >> I'm not as broken by this. While I was
• 54:12
  over in Switzerland, um met up with an
• 54:15
  ex of mine whose daughter's now 9 or 10
• 54:18
  years old and her daughter's doing
• 54:20
  English at school and all well and good
• 54:23
  and she wanted to practice her English
• 54:25
  and was talking to us a bit in English
• 54:27
  and kids ask you what's your favorite
• 54:28
  color, things like that. She asked me
• 54:30
  what my favorite fruit was and I was
• 54:32
  just broken cuz I've never really
• 54:34
  thought of that and it took me like two
• 54:36
  or three minutes to kind of it just put
• 54:37
  me into this head jam and I didn't know
• 54:40
  an answer. This one's a little bit like
• 54:42
  this. And to me, this question is a bit
• 54:45
  like asking somebody with a large family
• 54:47
  who their favorite child is or asking
• 54:49
  someone who their favorite pet is. Now,
• 54:50
  I suspect I don't have kids, but I think
• 54:53
  the favorite kid varies from time to
• 54:55
  time with people who've got parents and
• 54:56
  they'd never say they have a favorite,
• 54:57
  but there's a little ranking scale. It's
• 55:00
  nanny and her extended family in the
• 55:02
  discorld series where you could tell how
• 55:03
  in favor people were where where the
• 55:04
  trinkets that they bought her were in
• 55:06
  the house. and you know, heaven for fend
• 55:08
  that the little thing you brought back
• 55:09
  from holiday ended up on the coffee
• 55:10
  table outside in the hallway cuz that
• 55:12
  meant you were really in the bad books.
• 55:14
  I really struggle to answer questions
• 55:17
  like this because they're all
• 55:19
  fascinating in different ways. You know,
• 55:21
  there are things that we can really get
• 55:23
  from them. Mars from an astrobiology
• 55:25
  point of view is really the obvious
• 55:27
  answer because it's the place that we'll
• 55:28
  look for life elsewhere. Jupiter is the
• 55:31
  obvious answer because it's been
• 55:32
  fundamental to a lot of the research
• 55:34
  I've done in terms of the question of
• 55:35
  Jupiter friend or foe. It throws a lot
• 55:38
  of comments our way. It's the source of
• 55:40
  therefore indirectly the cause of many
• 55:42
  of the meteor showers and many of the
• 55:44
  meteor storms and stuff we see. I they
• 55:46
  they would be contenders as would the
• 55:49
  others to a certain degree. Neptune
• 55:51
  because it's a fabulous insight into how
• 55:54
  science can change over time and how we
• 55:56
  can discover things without seeing them.
• 55:58
  Neptune kind of preaged the exoplanet
• 56:01
  era because we discovered Neptune not by
• 56:04
  seeing Neptune but by observing Uranus
• 56:06
  misbehaving and inferring that Neptune
• 56:08
  had to be there to cause that
• 56:10
  misbehavior.
• 56:11
  >> Although there are some suggestions that
• 56:12
  Galileo actually saw Neptune in 1610 and
• 56:16
  should be credited as the discoverer but
• 56:18
  didn't realize what he had. There's a
• 56:20
  background star marked on one of his
• 56:22
  drawings I think of the Galilean moons,
• 56:24
  the moons of Jupiter where there is no
• 56:27
  star and people think it was actually
• 56:28
  Neptune.
• 56:29
  >> So there are some suggestions Galileo
• 56:31
  was a discover of Neptune.
• 56:32
  >> Interesting.
• 56:33
  >> But for me, Neptune's fascinating
• 56:34
  because of that indirect discovery. But
• 56:36
  I think for me, if you really push it, I
• 56:38
  probably have to say the Earth
• 56:40
  >> and a it's the Earth because we is here.
• 56:44
  >> But the Earth is a place that's driven
• 56:45
  all that complexity in terms of life.
• 56:47
  And if you think about Mars being a
• 56:48
  complex place, the Earth is even more so
• 56:51
  because of the influence of the water
• 56:53
  and the atmosphere, the weathering and
• 56:54
  the plate tectonics, you know. So, it's
• 56:57
  my favorite from the point of view of
• 56:58
  it's the only place I can sit around
• 57:00
  comfortably in shorts and t-shirt and
• 57:01
  chat like this. Also, because it is the
• 57:05
  window into the future of our knowledge
• 57:08
  of life elsewhere, and it's the cradle
• 57:10
  of everything we know and everything
• 57:11
  we've experienced. I do have a deep and
• 57:14
  abiding love of the earth from that
• 57:16
  point of view. But also as a scientist,
• 57:18
  the earth is fascinatingly complex
• 57:20
  compared to the other planets. It's the
• 57:23
  only planet on which we observe plate
• 57:26
  tectonics.
• 57:27
  >> Yeah.
• 57:28
  >> Therefore, it's the only planet whose
• 57:30
  surface on longtime scales is that
• 57:32
  degree of changeable and mutable. You
• 57:34
  know, if I brought you back, say we did
• 57:38
  um play with Ren's question from the
• 57:40
  start a bit more. We built the
• 57:41
  spacecraft from tow zero. We
• 57:43
  accelerated. Had a problem. Couldn't
• 57:46
  slow down. Eventually managed to fix it.
• 57:48
  Came back and we came back in a billion
• 57:49
  years time. Mars would still look like
• 57:52
  it does today. Unless humanity
• 57:54
  terraforms Mars. Mars would look like it
• 57:56
  does today. Venus would look like it
• 57:58
  does today. All of the planets would
• 57:59
  look like they do today. Saturn's rings
• 58:01
  may have gone. Peripheral things like
• 58:03
  that will have gone, but the Earth would
• 58:04
  be unrecognizable.
• 58:06
  >> With continental drift, the Earth
• 58:07
  wouldn't look like home. And even with
• 58:10
  the change in the atmosphere, the earth
• 58:11
  may have changed. I've seen some
• 58:13
  suggestions that when the earth was
• 58:14
  young, the oceans weren't blue, they
• 58:16
  were green.
• 58:17
  >> Yeah, I've heard that.
• 58:18
  >> That's how much the earth has changed.
• 58:20
  The mountain ranges will have shifted. I
• 58:21
  always find it fascinating to wonder
• 58:23
  what is the biggest mountain that the
• 58:25
  Earth has ever had. And you Google that,
• 58:27
  that's been asked a lot. Nobody's really
• 58:29
  got a strong answer because a lot of it
• 58:32
  depends on the elasticity of the Earth's
• 58:34
  interior and the energy available for
• 58:36
  plate tectonics because a limiting
• 58:38
  factor on the height of a mountain on
• 58:39
  Earth is the sinking that you get as a
• 58:42
  result of the mass of the mountain and
• 58:44
  the weathering that we get that wears it
• 58:45
  away. On Mars, you don't have that with
• 58:47
  Olympus Mons. There's no weathering.
• 58:50
  >> So, it could just get bigger and bigger
• 58:51
  even though it will have a very deep
• 58:53
  route. It could keep getting bigger
• 58:55
  because there was nothing wearing it
• 58:56
  down again. So I think for me because of
• 58:59
  the complexity and because it gives me a
• 59:01
  place to do my astrophotography and live
• 59:03
  my life and all the rest of it, the
• 59:06
  earth would have to be the top of the
• 59:07
  list. But trying to pick a planet other
• 59:09
  than the earth is a bit like trying to
• 59:11
  fi pick your favorite pet or your
• 59:13
  favorite child. And it might be that you
• 59:14
  have one internally, but heaven offend
• 59:16
  you tell them.
• 59:18
  Very good answer. Very good answer. I
• 59:20
  love the question. So uh not childish at
• 59:22
  all and appreciate you sending it in.
• 59:25
  And if you'd like to send questions into
• 59:26
  us at Spacenuts, jump on our website,
• 59:29
  spacenuts.io
• 59:31
  or spacenutspodcast.com
• 59:34
  and click on the ask me anything button
• 59:36
  at the top. It's just labeled AMA. And
• 59:38
  while you're there, have a look around,
• 59:39
  check out the shop, sign up for the
• 59:41
  newsletter, um see if you want to become
• 59:43
  a supporter. That's optional. And please
• 59:46
  leave reviews wherever you listen to us.
• 59:48
  And that'll wrap us up for another
• 59:50
  episode. Jonty, thank you so much.
• 59:52
  >> That's a pleasure. Thank you for having
• 59:53
  me. Always a pleasure. Uh, Professor
• 59:55
  Jonty her prof professor of astrophysics
• 59:58
  at the University of Southern
• 59:59
  Queensland. Hey, and uh, Hugh in the
• 1:00:02
  studio um, couldn't be with us today. He
• 1:00:04
  realized that Earth wasn't his favorite
• 1:00:06
  planet, so he left. And from me, Andrew
• 1:00:09
  Dunley, thanks for your company. Catch
• 1:00:11
  you on the next episode of Space Nuts.
• 1:00:13
  Bye-bye.
• 1:00:14
  >> Space Nuts. You'll be listening to the
• 1:00:16
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• 1:00:19
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• 1:00:22
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• 1:00:25
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