# Navigating Time, Saturn's Mysteries & Planetary Favourites | A Q&A Episode

An episode of [Space Nuts: Astronomy Insights & Cosmic Discoveries](https://invisiblenetwork.ai/podcast/1080090608), 25 May 2026, 1 h 01 min.

Audio: https://dts.podtrac.com/redirect.mp3/pscrb.fm/rss/p/op3.dev/e/api.spreaker.com/download/episode/72149313/navigating_time_saturn_s_mysteries_planetary_favourites_a_q_a_episode_nordvpn.mp3

Sponsor Link: This episode of Space Nuts is brouht to with the support of NordVPN. When it's time to upgrade your online securiy, get NordVPN. We did! To check out our special money saving deal - Click Here Time Travel, Saturn's Rings, and Favourite Planets In this engaging Q&A edition of Space Nuts, hosts Andrew Dunkley and Professor Jonti Horner dive into a series of thought-provoking questions from listeners. From the complexities of moving through time to the intriguing origins of Saturn's rings, this episode is packed with cosmic insights. Episode Highlights: - Understanding Time Travel: Rennie from California poses a fascinating question about the nature of time and whether one's lifespan could differ based on their movement through time. Jonty unpacks the concept of time as a dimension, exploring relativity and time dilation. - The Mystery of Saturn's Rings: Paul from Brisbane asks about the potential for debris from a collision between Saturn’s moons to have impacted Earth 65 million years ago. The discussion delves into the origins of Saturn's rings and the dynamics of celestial collisions. - Favourite Planets: Dan from the Gold Coast wonders about the hosts' favourite planets in the solar system. Andrew shares his admiration for Mars and its geological wonders, while Jonty contemplates the complexity of Earth and the awe of Jupiter. For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. Follow us on social media at SpaceNutsPod on Facebook, Instagram, and more. We love engaging with our community, so be sure to drop us a message or comment on your favourite platform. If you’d like to help support Space Nuts and join our growing family of insiders for commercial-free episodes and more, visit spacenutspodcast.com/about. Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing. Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support. - Introduction to Time Travel - The Nature of Time and Relativity - Saturn's Rings and Cosmic Collisions - The Search for Debris and Impacts - Favourite Planets: Mars vs. Earth vs. Jupiter

## Transcript

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

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