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Navigating Time, Saturn's Mysteries & Planetary Favourites | A Q&A Episode · Space Nuts: Astronomy Insights & Cosmic Discoveries

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
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57:55
become a supporter, that's optional and
57:58
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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.