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Cosmic Queries: Gravitational Waves & the Great Dust Debate · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:02
Andrew Dunkley: Hi there. Thanks again for joining us. This
0:03
is Space Nuts, a Q and A edition. My name is
0:06
Andrew Dunkley, your host. Uh, terrific to
0:08
have your company. Questions that we will be
0:11
answering on today's program include the Big
0:14
Crunch, gravitational waves,
0:16
shifting magnetic poles, uh,
0:19
the use of the term dust. Somebody's got
0:22
maybe an issue with that. And questions
0:25
about gas and ice giants and why do we
0:28
think they've got rocky cores. That's all
0:30
coming up on this episode of space nuts.
0:33
Voice Over Guy: 15 seconds. Guidance is internal.
0:35
10, 9. Ignition
0:38
sequence time. Space nuts. 5, 4, 3,
0:41
2. 1, 2, 3, 4, 5, 5, 4,
0:44
3, 2, 1. Space nuts. Astronauts It
0:47
feels good.
0:48
Andrew Dunkley: And joining us for what will be the last time
0:51
in a little while, because Fred's coming back
0:54
next week, Jonti Horner, professor of
0:56
astrophysics at the University of Southern
0:57
Queensland. Hi, Jonti.
0:59
Jonti Horner: Good afternoon. How are you going?
1:00
Andrew Dunkley: Ah, uh, pretty good. And you?
1:03
Jonti Horner: Uh, not too bad, you know, dealing with the
1:05
usual kind of too much work, not enough fun.
1:07
Looking forward to a trip to a conference
1:10
next week. I'm down to the Australian Space
1:11
Research Conference, which is always my
1:13
favorite meeting of the year. So it's perfect
1:16
timing for Fred to return because I wouldn't
1:17
have been easily available next week anyway.
1:19
And, um, time to hand over. And everybody
1:21
listening can breathe a huge sigh of relief
1:23
because normality has been restored.
1:26
Andrew Dunkley: Ah, no, it's not like that.
1:27
Uh, in fact, um, in fact, that's where we can
1:30
start because we, uh, do have some
1:32
comments from the audience. Uh, this came
1:35
from Sam in British Columbia. He says, I just
1:38
wanted to say how helpful I
1:41
found the answer to the Lagrange points in
1:43
Mass question
1:46
and how much I enjoy Johnny Horner's
1:48
explanations, musings and answers. I know
1:51
sometimes they seem a little more detailed
1:53
than chatty, but I really enjoy that
1:56
extra detail and context. I found the spatial
1:58
contours explanation extremely useful. Thank
2:01
you. So, um, you got a bit of a fan there.
2:04
And another comment that I came across
2:06
on our, um, podcast
2:09
group Facebook page. I appreciated all the
2:12
attention Andrew and Jonti devoted to the
2:14
government shutdown. My family suffered
2:16
personally. That came from Martin. Although,
2:19
uh, there was someone else who didn't
2:20
appreciate us going down the political line.
2:23
But because of the impact that had on NASA
2:26
particularly, uh, it was probably something,
2:29
uh, that was worth discussing.
2:31
Jonti Horner: Yeah, I think it is important. I understand
2:33
that people don't like it when you get into
2:36
politics too much and to your political
2:38
views. But I think in this case it's
2:40
something where colleagues of mine were being
2:42
directly affected. I know people
2:45
who had more than four weeks without pay. And
2:47
we're here to talk about what's happening
2:50
with space and um, exploration and
2:52
research. And when there's something that's
2:54
impeding that, it's important to discuss it.
2:56
And it's doubly important I think when people
2:59
are trying to use it for political capital to
3:02
perpetuate lies about alien
3:04
spacecraft, you know, um, you need to
3:07
set the record straight to correct other
3:09
people training into politics when they
3:10
shouldn't do so. You know, I appreciate the
3:12
comments. I love the positive feedback. I ah,
3:14
try and not get too political in terms of my
3:16
own views on stuff, but there are some topics
3:18
which we do need to cross. And you know, my
3:20
heart does go out to those who were directly
3:22
impacted by the shutdown for whatever the
3:24
reasons the shutdown was happening. It's not
3:26
good when you have to go m more than a month
3:27
without food, particularly for those families
3:29
who have two people who are both government
3:31
employees and have children with mouths to
3:33
feed.
3:34
Andrew Dunkley: Yeah, and we were talking, we're talking
3:35
thousands upon thousands of people. So it
3:37
wasn't just a handful.
3:39
Uh, let's move on to our first set of
3:41
questions. Beau in Melbourne has sent us two
3:44
questions, uh, via our audio stream.
3:47
Uh, let's see what he wants to find out.
3:50
Beau: Hello, Andrew and Professor, uh, Jonti
3:52
Horner. Is Beau here? Yes. Your second
3:55
favorite B.O. from Melbourne, Australia.
3:58
I have a question for you, but first I would
4:01
like to do a fact check please. Um,
4:04
a couple of episodes ago, um, Professor
4:07
Watson, uh, talked about the Gnab Gib or
4:10
the Big Crunch. And basically he said,
4:13
ah, at the end of the Gnab Gib, um, matter
4:16
will come closer to one another, uh, as the
4:18
effect of gravity takes over and we uh, will
4:21
end up in one giant singularity and
4:24
collapse. Uh, what he didn't say
4:27
was the uh, effect of that on
4:29
light. Now my understanding is that
4:32
um, obviously as stars and galaxies come
4:35
closer together, the sky will get brighter
4:37
and brighter and uh, as matter starts to
4:40
fuse, uh, will give out more heat and more
4:43
uh, light as well. So essentially
4:47
will end up in a reverse Big Bang, uh, and
4:50
then we will all come to a big blinding,
4:52
uh, end, um, both matter and uh,
4:55
light coming together in a reverse Big Bang.
4:58
So I just wanted to see if that is correct,
5:01
uh, regarding light. I'd love to hear
5:04
Jonty's view on that.
5:06
Um, now my question is related to
5:09
gravitational waves. Uh, we
5:12
know that gravitational waves, ah,
5:14
distort the fabric of space time.
5:18
Um, In a wave pattern. We also know
5:21
that multiple gravitational wave exist,
5:24
um, because there are, you know, black hole
5:26
collisions and black hole neutron star
5:28
collisions happening, um, throughout the
5:30
universe. Now what happens when
5:33
those two gravitational waves meet
5:36
each other? Um, particularly what would
5:38
happen to, um, I guess the interference
5:41
patterns as the waves, uh, starts overlapping
5:44
each other at the peaks and the troughs
5:46
during, do we see any
5:49
changes to space time itself?
5:52
Do we see, for example, time speed up,
5:55
slow down or stop? Do we see gravity,
5:58
um, cease or increase
6:00
or decrease? Um, um,
6:04
just wanted to know what would happen to
6:05
space time and that interference patterns,
6:07
the peaks to troughs. Um, love to hear
6:09
Professor John de Horner's view on that. Um,
6:12
thank you very much and please.
6:13
Jonti Horner: Keep up your good work.
6:15
Andrew Dunkley: Thank you, Beau. Uh, great questions.
6:17
Uh, we'll probably start with the big crunch
6:20
and the effect on light. Now,
6:22
um, I suppose we have to consider
6:26
the timing of events because the universe
6:28
is still expanding, Although now they're
6:31
starting to think that acceleration is no
6:33
longer speeding up, it's slowing down
6:36
or that the expansion, um, but
6:38
it's still expanding. Far as we're aware at
6:41
this point in time. Uh, Fred has told us in
6:44
the past that it will expand to the point
6:46
where everything will move so far apart that
6:48
we will just be by ourselves in the universe,
6:51
in blackness. Um, so
6:54
the question is, is that still going to
6:55
happen? And even if it
6:58
does, and there is a big crunch,
7:01
what's going to happen to all the light
7:03
anyway? So it's a really
7:05
fascinating area.
7:07
Jonti Horner: It is, and it's really complicated. It's
7:10
dealing with things that are incredibly far
7:12
in the distant future.
7:13
Andrew Dunkley: Um, it is week or the week after, I think.
7:16
Jonti Horner: Absolutely. Um, well, with the way that time
7:18
seems to pass quicker and quicker as I get
7:20
older, it does probably mean that it will be
7:22
next week, but it's a difficult one.
7:25
So there is still some debate over whether
7:27
the universe will continue to expand forever
7:30
or whether it will turn around and begin to
7:32
collapse. And reminds me of the Arthur C.
7:34
Clarke quote about life elsewhere, which I'm
7:36
going to butcher and paraphrase in this case,
7:39
which is that two possibilities exist and
7:41
both are equally terrifying. You know,
7:44
either, you know, we expand forever or we
7:46
don't. And they're equally scary in many
7:48
ways. But assuming that we did collapse back
7:50
down to a point. Now that will likely happen
7:53
at the point when all the stars have died,
7:56
um, when everything has come to an end. And
7:59
so you'll probably have a universe full of
8:01
non luminous stuff and black holes. And
8:03
that's about it maybe so far away in the
8:05
future that even the biggest black holes have
8:07
evaporated from Hawking radiation. But
8:09
whatever will happen, whatever is left will
8:12
be squashed into an ever smaller place that
8:14
will include all of the radiation that's
8:16
going through the universe. Now we see the
8:19
cosmic microwave background, and we see it
8:21
at, uh, um, very long wavelengths, at
8:23
microwave wavelengths, with an approximate
8:26
temperature of like 2.9 Kelvin or something
8:28
like that. I can't remember the exact number.
8:30
That's because that light is redshifted,
8:32
because the universe has expanded and
8:34
stretched that energy out. If the universe
8:36
collapsed back in, you'd be going the
8:39
opposite. You'd be blue, shifting all the
8:40
radiation. So as you squash the universe into
8:42
an ever smaller space because of the quirk of
8:45
the fact that there is nothing outside the
8:47
universe, the universe is both infinite and
8:49
finite at the same time. So you can't be
8:52
outside the universe, because that's
8:53
meaningless. All of the light and all of the
8:56
energy in the universe will remain in the
8:57
universe as the universe gets smaller. So my
8:59
understanding is that as you get towards a
9:02
high, hypothetical Big Crunch, the
9:04
temperature, the pressure and the density
9:05
will just increase and increase and increase.
9:07
And, um, the universe will end in a very,
9:09
very hot mess, effectively. So it will be
9:11
like running the Big Bang backwards. There'll
9:13
be differences. We don't fully understand
9:15
what will happen and how it will all go. We
9:18
don't know whether that would trigger another
9:20
Big Bang, because, to be honest, we don't
9:22
know enough about that time of the universe.
9:24
And certainly I'm nowhere near, uh, the
9:26
forefront of researching that to give a more
9:28
educated opinion. But I know that the closer
9:30
you get to the Big Bang looking back, the
9:32
harder it is to be exactly sure what
9:34
happened. Because the less information we
9:35
have and the harder you're having to push our
9:38
understanding of physics to the point it
9:40
breaks down. And the same will be true going
9:42
the other way. You're just reaching
9:43
temperatures and pressures that make no
9:46
sense. You have periods when different
9:48
forces were combined into a single force. I
9:51
do not know with my level of knowledge
9:53
whether the expectation is that those
9:55
transitions would happen at the same point
9:57
going back as they did coming forward.
10:00
So I think that the exact details of
10:03
how the Big Crunch would go, uh, are still
10:06
very much up for debate if it were to happen.
10:08
But I think it's very fair to say that it
10:10
will be very bright, very hot, very
10:12
unpleasant, and we wouldn't be around to
10:14
enjoy it.
10:15
Andrew Dunkley: No, definitely. Well, yeah. It's like the
10:18
restaurant at the end of the universe in
10:19
hitchhikers. You know, if we're not going
10:22
to sit there and enjoy a wonderful dinner
10:25
while it all happens around us, it's um,
10:27
yeah, I'd say humanity be long gone by then
10:30
or transition into something else, I don't
10:32
know. But I certainly don't think it would be
10:34
like rewinding a film and watching it all
10:36
just happen in reverse. There'll be some
10:39
cataclysmic effect for sure.
10:42
Uh, the main question Beau wanted answered
10:44
was about gravitational waves. And they're
10:46
out there, they're happening, we're detecting
10:48
them all the time. Um,
10:51
but what happens when they cross each other?
10:53
What's the effect? I would equate it to
10:55
throwing two pebbles in a pond and the waves
10:58
just cross over and that'd be it.
11:00
Jonti Horner: Yeah, I've done a bit of reading around on
11:02
this one because honestly, I haven't got the
11:04
foggies coming into this. So my
11:07
default assumption is that, ah, the waves
11:10
would interfere in the same way that
11:11
electromagnetic waves interfere in that
11:13
they'd add, um, together. So you'd get a peak
11:15
and a trough would cancel out a peak and a
11:17
peak would lead to constructive interference.
11:20
So you'd get bigger and smaller
11:23
instantaneous amplitudes.
11:26
You'd get an interference pattern reading
11:28
around online. Um, it seems that that is
11:31
broadly the consensus, so long as you
11:34
are a long way away from a strong
11:36
gravitational field, so you're a long way
11:38
away from the source of these things, or
11:40
you're a long way away from something like a
11:42
black hole. And apparently the physics of
11:45
the general relativistic treatment of
11:48
this gets incredibly gnarly. When you get
11:51
to those kind of situations and nobody's
11:53
really sure what happened, the maths gets
11:55
difficult. And the point is you're pushing
11:57
the boundaries of what we know and what we
11:58
can observe into the unknown. So what you
12:01
have to do is you have to develop possible
12:04
answers and um, test them, build
12:07
theories, make predictions, see what happens.
12:09
But I think in general, if, for example,
12:12
one of our big gravitational wave detectors,
12:14
two waves came in at once, you would
12:17
probably, at that instantaneous location, you
12:20
get an extra large peak or an extra large
12:21
trough, or they'd cancel out. But because you
12:24
might have more than one detector around the
12:26
earth, thanks to the directions of motion,
12:28
you'd only have that specific type of
12:30
interference at that specific detector. So it
12:33
will probably give us a signal that, if
12:35
you've got multiple gravitational wave
12:36
detectors around the globe, would be distinct
12:39
and identifiable and would allow you to test
12:41
that interference, if that makes sense.
12:44
Now my understanding of the typical
12:46
gravitational wave events that we see is that
12:48
you've, ah, got these waves that are building
12:50
up from inspiraling neutron stars or black
12:53
holes, or a neutron star and a black hole
12:54
about to collide, where you get
12:57
very low frequency, very low amplitude waves
13:00
that build to a sharp crescendo, which is why
13:02
you get these attempts to sonify the data,
13:05
where you get this rising whistle, rising in
13:07
pitch and rising in volume. So the idea is
13:10
that you get a lot of small waves first and
13:12
then you get a really big build to a
13:13
crescendo and then fall off. So typically you
13:16
probably wouldn't observe this happening with
13:17
our current technology unless you have the
13:20
incredible good fortune to have two events
13:23
where you get the peak arriving at the same
13:25
time. And that'll be the interesting test.
13:28
So, yeah, to summarize, I don't think anybody
13:30
fully knows, but because you're pushing the
13:32
bounds of what is known. But it seems to be
13:34
that the consensus is that in open space,
13:36
away from really significant masses or away
13:39
from the sources of the waves, they would
13:42
just have normal kind of constructive and
13:43
destructive interference as the peaks and
13:46
troughs go across each other.
13:48
Andrew Dunkley: Okie dokie. There you are. Uh, thank you, Bo.
13:51
Great question.
13:54
Jonti Horner: 0G and I feel fine. Space nuts.
13:58
Andrew Dunkley: Uh, our next question comes from Paddy,
14:01
uh, reflecting on the discussion around the
14:04
shifting of the magnetic poles. If they were
14:06
to flip, how would the field
14:09
behave as it transitioned? Uh,
14:12
the equator, uh, would it
14:15
spin with the Earth's, uh, rotation? Would it
14:17
let in more debris, solar radiation and
14:20
or, uh, uh, cosmic particles?
14:23
And to go full Hollywood disaster
14:26
movie, given the, uh, visual representation
14:29
of the mega magnetic field suggests an apple
14:31
shape. Uh, could the funnel of the
14:34
magnetic field become like a magnifying glass
14:37
scorching the earth as it crosses the
14:39
equator?
14:40
Jonti Horner: Love, uh, the show.
14:40
Andrew Dunkley: Keep up the great work. That's from Paddy.
14:42
He's put a bit of thought into this and I
14:44
love the sci fi component. But, um,
14:47
yeah, is this in your
14:50
ballpark, this kind of thing?
14:52
Jonti Horner: Uh, as an astrophysicist, it's
14:55
closer to my ballpark than the gnabs and the
14:57
dark energy stuff. I mean, I'm still not, I
15:00
would argue, an expert, but I'm close to it
15:02
and I have done a bit of reading. Now what I
15:03
would say here is actually, um, the
15:06
Wikipedia page for geomagnetic reversal
15:09
is a really interesting read. It's very in
15:11
depth and contains a lot of good historical
15:13
information. So while I acknowledge Wikipedia
15:16
is very much secondary rather than primary
15:17
Resource, I think for topics like this and
15:20
topics in astronomy, the articles tend to
15:22
stay fairly on task and fairly accurate
15:24
because people will fix them if they break
15:26
very quickly. Um, and that
15:29
reading that should, to some degree,
15:30
immediately put Paddy's mind at rest in terms
15:32
of the Earth getting baked or scorched or
15:34
Hollywood disaster movie type things
15:36
happening at the time of a field reversal.
15:38
Because we've had at least
15:40
183reversals in the last 83 million
15:43
years, which means that these things have
15:45
happened regularly through the period of
15:48
the Earth being inhabited and have not caused
15:51
any mass extinctions. There have been some
15:53
suggestions that periods where
15:56
you get magnetic field locked in one
15:58
direction for very long periods of time,
16:01
which last happened during the Cretaceous
16:03
period, where you had something like a 50
16:06
million year period where the magnetic field
16:08
didn't flip. There have been some suggestions
16:10
that when those very long periods of time
16:13
come to an end, that it could trigger a
16:16
certain amount of added volcanic
16:18
activity and stuff like this. And that may
16:21
lead to some traumas for life, but never
16:23
quite at the level of a mass extinction. And
16:26
there's a couple of beautiful, um, figures
16:29
plotting out the
16:31
flips that have happened going back about
16:34
180 million years,
16:37
talking about these periods where the
16:39
magnetic field gets locked into a single
16:41
orientation. Nothing much happens for a long
16:43
time, which is known as a superchron. And
16:46
then you get other times when you get more
16:48
flips in a short period than typical. There's
16:51
one here, 51 reversals occurred during a 12
16:53
million period centered on, I think it's 15
16:56
million years ago. So you get periods where
16:59
there's a lot more of them happening. You
17:01
also get periods where it tries to flip and
17:03
then goes back to how it was. Uh, so the idea
17:05
that you had from school that the Earth's
17:07
magnetic field is essentially, we have a
17:09
giant bar magnet in the middle of the Earth,
17:10
and it's very controlled and static. As we
17:12
said on the podcast a few weeks ago, that has
17:14
fallen by the wayside. Now, the magnetic
17:17
field being generated by wibbly wobbliness
17:20
and convection currents and all sorts in the
17:22
Earth's outer core through a dynamo effect is
17:24
fairly well understood. And, um, these field
17:27
reversals are something that falls out
17:30
naturally in modeling. So people have not had
17:32
to hugely increase the capacity of their
17:34
modeling ability when modeling the behavior
17:36
of the outer core to make them happen. They
17:39
happen naturally from the way the models are
17:41
set up, which is really interesting. What
17:43
seems to happen is that, uh, unlike the sun,
17:46
where you get the magnetic field reversals at
17:48
about the time when the Sun's magnetic field
17:50
gets the strongest. And that's all down to
17:52
the tangling up of the magnetic field lines
17:55
as the sun rotates as a fluid body, not a
17:57
solid body. On the Earth, the magnetic
18:00
field reversals tend to occur at times of low
18:02
magnetic field. So what tends to happen is
18:05
that the dynamo becomes less effective.
18:07
Things become confused in the inner core. You
18:09
can even get periods where you get multiple
18:11
north and south poles while the magnetic
18:14
field in the dynamo breaks down and reasserts
18:16
itself, and then it flips over. There is some
18:18
discussion over how quick this can happen
18:20
with most studies seem to suggest it can take
18:23
anything from 2,000 to 12,000 years.
18:26
But sometimes it could be quicker, sometimes
18:28
it could be slower. It's all complex, and
18:30
it's because it's all tied to this turbulent
18:33
roiling of the liquid metal in the outer
18:35
core. What this means is that,
18:38
uh, firstly, if you shift where the north and
18:40
south magnetic poles of the Earth are, they
18:42
will rotate with the Earth. Uh, that's in
18:44
fact what we see with pulsars. Why we get the
18:47
pulsars is that the magnetic fields and the
18:49
rotation axis are not lined up. So you get a
18:52
magnetic hotspot on the surface of the
18:54
pulsar, uh, where you get the magnetic polis,
18:56
where any material around will be funneled
18:58
down the magnetic field to hit there. You get
19:00
this hot spot. You get lots of radiation
19:02
emitted from the poles. And as, uh,
19:05
the pulsar rotates, those poles sweep
19:08
like lighthouse beams, and we get pulses of
19:10
radio waves when that beam sweeps across us.
19:13
So it's fairly well understood that the
19:15
magnetic field rotates with the Earth. And
19:17
therefore, if the
19:20
magnetic pole was in Kenya or somewhere like
19:23
that, it was somewhere near the equator, it
19:25
will be rotating with the Earth. That's kind
19:27
of how it would work. And, um, that will
19:28
probably happen if the flip was the north
19:31
pole wandering to the Earth's south pole. In
19:34
reality, though, it seems that these
19:35
reversals are more almost like the Earth's
19:38
magnetic fields weaken. They become
19:40
disestablished, you get all this confusion,
19:43
and then a new field establishes itself,
19:45
which I think is probably part of the
19:48
reason that the flips are even less periodic
19:51
than you think. They're talked about as being
19:53
totally random. But I suspect that's added to
19:55
by the fact that, that if you wipe out the
19:57
Earth's magnetic field and turn it on again,
19:59
if you imagine you had a 50, 50 chance of it
20:02
being north south, and a 50, 50 transmit
20:04
being south north, then only half of the Time
20:06
it weakened, would you get it flipped to the
20:08
other polarity. And so that might be part of
20:10
what's going on there. So it's all really,
20:13
really complex. What would happen is that we
20:16
would get to some degree a greater flux of
20:18
radiation hitting the top of the Earth's
20:20
atmosphere. The charged particles that get
20:22
diverted around us by the magnetic field, it
20:24
will get less effective. But it's worth
20:27
noting that our atmosphere is incredibly
20:29
effective protection for us anyway. I saw one
20:32
article saying our atmosphere is as effective
20:34
at protecting against the solar wind and
20:36
charged particles as a 3 meter layer of
20:38
concrete would be. So the atmosphere does a
20:40
very, very good job. Uh, which is why it
20:43
seems that these magnetic field weakenings
20:46
don't lead to m mass extinctions and things.
20:48
They will have a bit of an effect on the
20:50
upper atmosphere stuff will happen. There
20:53
are suggestions that maybe you could get a
20:55
little bit of additional atmospheric
20:56
stripping happening during these times from
20:58
solar radiation, but effectively the impact
21:01
would not be that great on the surface of the
21:03
Earth. It would probably play merry havoc
21:06
with scouts who are doing orienteering and
21:08
people doing the Duke of Edinburgh Reward and
21:10
things like this where you follow a map and
21:12
you've got to use a map and a compass.
21:13
Because if the North Pole is in a different
21:15
place every year and weaker, uh, that's going
21:17
to be a pain for navigation. There would
21:20
doubtless be significant effects on
21:21
technology, obviously, and we
21:24
saw last week with a really good solar storm
21:26
and Aurora again, that we are to some degree
21:28
at the mercy of big solar storms. We
21:31
discussed in the past the likelihood of
21:32
events like the Carrington event being a
21:34
problem for satellites and for unshielded
21:36
electronics on the surface of the Earth. And
21:38
if the Earth's magnetic field were weaker or
21:40
were in the process of reversing, then an
21:43
equal strength solar storm would do more
21:44
damage because less of it would be deflected.
21:48
Um, but you wouldn't end up with the kind of
21:49
giant lens baking strip along the Earth.
21:52
Um, fortunately or unfortunately, depending
21:54
on your point of view and your love of
21:55
Hollywood dramatics, that should be fine.
21:59
It would be an interesting event.
22:00
There are people who keep suggesting that
22:03
this kind of thing is imminent. The problem
22:05
there is imminent in geological timescales
22:08
doesn't mean imminent on a human timescale.
22:10
So the last reversal, I believe, was about
22:12
780,000 years ago. The
22:15
average timing of them seems to be out every
22:17
half a million years. So people say we're
22:19
overdue. That skips the fact
22:22
that actually the timings are very random.
22:23
It's A bit like waiting for a bus. I use this
22:25
analogy all the time. You know, if you've got
22:26
a bus due every five minutes, you may wait
22:28
half an hour and five come along at once. You
22:31
did? No. And, um, with these kind of
22:33
reversals, that's exacerbated by the fact
22:35
that we tend to get long blocks and short
22:37
blocks. So I'm looking just at the last 5
22:39
million years. And if you go from 5 million
22:41
years ago, um, black on this
22:44
plot is the polarity we have now on white is
22:46
the other one. 5.01 million years ago, it
22:49
flipped so that south was at the top. Then
22:51
4.89 million years ago, we had, what
22:54
is it, 80,000 years of our current polarity.
22:57
Then it flipped back and we had 17,000 years.
22:59
Then it flipped back for 17,000 years, back
23:02
for 18,000 years, back for 8,000
23:05
years, and then there was a 60,000
23:08
600,000 year gap.
23:11
And so it's very, very spotty. The last flip
23:13
was 780,000 years ago. Before
23:16
that it was only a 12,000 year gap.
23:19
Um, and then there was a very long period
23:21
between 1.0, uh, 6 and 1.78 million years
23:23
ago, when it was the opposite polarity,
23:26
except for a single measurement at 1.19
23:29
million years ago, when it was the other way
23:30
around. So that was a very short flip. So, in
23:33
all honesty, saying that we're overdue for it
23:35
is a bit like bumping into somebody grumpy at
23:37
the bus stop because the bus is 30 seconds
23:39
late. In all honesty, you've got no clue when
23:41
that bus is going to arrive. And looking at
23:43
the time periods in the Cretaceous, there's
23:46
two or three of these megalong breaks, these
23:49
superchrons that have been identified. Two
23:51
are very confident ones, a bit more
23:52
controversial, but the most recent one in the
23:54
Cretaceous was more than 50 million years
23:57
with a single polarity. And that's the
23:59
equivalent of being at the bus stop. But the
24:01
buses are on strike.
24:02
Andrew Dunkley: Yes, yes. Wouldn't be a problem in
24:05
Japan. They are very strict about their
24:07
timing. In fact, I remember a story a couple
24:09
of years ago about a train driver who lost
24:11
his job for being two minutes late.
24:13
Jonti Horner: Yeah. So I remember that in Switzerland. One
24:15
of the bizarre experiences when I first moved
24:17
to Switzerland for my first postdoc, kind of,
24:20
um, 20 years ago, 22 years ago, was being on
24:22
the train platform and the train was slightly
24:24
late and, um, people were checking their
24:26
watches and correcting their watches because
24:28
they thought that their watch was wrong
24:30
rather than the train being late.
24:31
Andrew Dunkley: Wow.
24:32
Jonti Horner: And it's like, I'm used to British trends,
24:34
where if they come on the correct week,
24:36
you're lucky, you know? Yes.
24:39
Andrew Dunkley: The. Australia's a bit like that. Although
24:40
they're pretty good most of the time. You
24:42
only ever hear about them when the press has
24:44
decided to stick the knife in.
24:45
Jonti Horner: Absolutely. Yeah.
24:47
Andrew Dunkley: Ah, nine times out of ten that'll be okay.
24:49
Jonti Horner: At least most places have trains. I don't
24:50
know if I've told this story before, but my
24:52
understanding of the reason that we don't
24:53
have a fast train from Toowoomba to Brisbane
24:56
is that there used to be a train service. And
24:57
in the 1950s, the family that ran the coach
25:00
service on the roads from Toowoomba to
25:03
Brisbane got elected to the Toowoomba Council
25:05
and shut down the railway, because it was.
25:08
And so 70 years later, we still have no fast
25:10
rail to Brisbane. And it comes up every few
25:12
years that we should have it. And it just
25:13
never got going again.
25:16
Andrew Dunkley: Yeah, I'm sure there's a lot of that going
25:18
on. Um, but. Great question, Patty. And
25:21
it sort of throws a curveball, um,
25:24
into, um, you know, if it happens, if
25:26
there is a magnetic pole flip,
25:30
um, does that mean we are no longer down
25:32
under, but up over?
25:34
Jonti Horner: Absolutely.
25:36
Andrew Dunkley: Yes, that could be the case.
25:39
Oh, uh, gosh, no. We don't want to cause any
25:41
trouble. Let's just leave things as they, uh,
25:43
are. Thanks, Paddy. This is Space Nuts with
25:45
Andrew Dunkley and John Dee Horner.
25:50
Okay, we checked all four systems, and.
25:52
Jonti Horner: Being with a go, Space Nuts, our.
25:55
Andrew Dunkley: Next question comes from Howard Bennett.
25:57
Howard is in Penang in Malaysia.
26:00
Uh, I have a question about the term
26:03
dust.
26:04
Jonti Horner: Dust.
26:05
Andrew Dunkley: Dust. The word is used indiscriminately
26:08
throughout astrophysics with no real
26:10
definition. I don't know. Um,
26:14
uh, I know it's not the same as the dust
26:17
bunnies under my bed, but what exactly is the
26:20
space dust that obscures our heart
26:23
of, uh, galaxies and inhabits the empty space
26:26
between galaxies, not to mention moon dust
26:28
and deadly dust storms on Mars? Most
26:31
confusing. Uh, maybe we need a new word.
26:35
So when we refer to dust in space,
26:38
what are we talking about? And is it all the
26:40
same stuff?
26:41
Jonti Horner: It's all sorts of stuff, basically, but the
26:44
commonality is that it's small pieces of
26:47
solid material. So that's effectively what
26:49
you're talking about. It becomes
26:53
confusing occasionally in the solar system,
26:54
for example, when we draw the line between
26:56
meteoroids, which are, uh, particles of,
26:59
effectively, dust going around the sun, and
27:00
asteroids, which are bigger things going
27:02
around the sun. And typically, people place A
27:04
division there at about a meter diameter. So
27:07
the same object that's 1.1 meters across,
27:09
you'd call a small asteroid at uh, 0.9 meters
27:12
would be a meteoroid. And that's just because
27:14
we have to have a boundary somewhere. Um,
27:17
and materials that are considered dust in
27:19
space will include things that at home you'd
27:22
consider ice. If it's solid, it's
27:25
dust. And um, the hodred is the lessings can
27:28
be solid. When it comes to the stuff on the
27:30
moon then you're talking about the dust being
27:33
surface rocks that have been pulverized by
27:35
impacts. So you have these tiny
27:38
particles of martian, of lunar regoliths,
27:41
sorry, which are uh, small pieces of dust
27:43
because they're small pieces of solid
27:45
material. Lunar dust is pretty brutal
27:48
because there's no moisture and no weathering
27:49
there. So it's incredibly sharp edged and
27:52
abrasive. And that's why it's such a problem
27:54
for future astronauts. It's why it's a
27:57
problem technologically. It's why when they
27:58
came back they had to clean the astronauts
28:01
vacuum them.
28:02
Andrew Dunkley: I think they did. Ah, I remember Buzz Aldrin
28:05
described walking on the moon as walking on
28:07
talcum powder.
28:08
Jonti Horner: Yeah, very, very slippery, lots of very fine
28:10
dust particles. With the exception that
28:12
talcum powder is a lot less abrasive. Um,
28:15
I think a better analogy, although it's not
28:17
perfect, to the kind of things you get that
28:20
cause miner's lung and things like that,
28:21
where you've got particles of dust being
28:23
created by explosions or digging underground
28:26
that haven't had time to be rounded off by
28:29
moisture and weathering yet. And they cause
28:31
huge problems for people who inhale them. I
28:34
believe that was a part of the problem with
28:35
asbestos when you inhale it actually it's to
28:37
do with the sharpness of the particles and
28:38
the damage that they do. So that's the kind
28:41
of mundus stuff. Similarly when we talk about
28:43
dust zones on Mars, the dust there are those
28:46
particles of solid material that are small
28:49
enough that they can be lofted into the
28:50
atmosphere through a variety of processes.
28:52
Not just the wind, but there are solar, ah,
28:55
radiation processes that can levitate dust
28:58
off the surface of Mars, um, including
29:02
um, one that is really fascinating that I did
29:04
some research on with colleagues again 20
29:06
years ago now, which is this weird
29:09
photo, um, with light
29:12
based effect. We're familiar with kind of
29:15
radiation pressure and the Ponting Robertson
29:17
effect. These are things we talk about a lot.
29:19
But there's also something called
29:20
photophoresis which is
29:23
to do with the Absorption and re emission
29:26
of light from very small dust grains
29:29
that when you're at a, ah, very specific size
29:32
range, can exert a really intense force.
29:35
So what happens is, uh, when your dust
29:37
grain absorbs some light, it
29:40
temporarily has a temperature gradient on it.
29:43
That temperature gradient depends on how big
29:45
the dust grain is. Whether the near side or
29:47
the far side of the dust grain gets hot.
29:48
Because if the light penetrates most of the
29:50
way through, the far side is a bit that
29:52
absorbs it and gets hot. So you get a dust
29:54
grain that's hotter on one side than another.
29:56
If that dust is in an atmosphere that is not
29:58
too dense and not too low density,
30:01
the gas particles from the point of
30:04
view of the dust grain will be perceived as
30:06
single impactors, single billiard
30:09
balls. And when they hit the dust
30:11
grain, they stick briefly and then leave
30:13
again. And if they hit the hot side, they'll
30:15
leave with more energy than when they leave
30:17
the cool side. So you get a
30:20
force. Now, this is a really
30:22
quirky force I'd never come across until I
30:24
saw talk from a couple of physicists who were
30:26
talking about dust grains on Mars. Um, we
30:29
looked into it in the form of what this would
30:31
have as an effect for planet formation disks
30:33
and stuff like this. But what's really quirky
30:36
is that this is only effective over a
30:38
relatively small range of gas pressures.
30:40
If the gas is too thin, doesn't happen. M if
30:43
the gas is too dense or that individual
30:46
probabilistic single gas molecules adhering
30:48
and leaving doesn't happen. But in those
30:51
range of pressures, it can be up to 10 or 100
30:54
times stronger than all the other forces.
30:56
And, um, can Mars atmosphere, particularly in
30:58
the highlands, is the right pressure that
31:00
this can actually levitate dust grains off
31:02
the surface of Mars and is viewed as
31:04
potentially been helping to trigger those
31:05
dust zones to start the dust getting kicked
31:07
up into the atmosphere. So all sorts of
31:10
really cool stuff there. The other thing that
31:12
I found out from those physicists that we
31:14
worked with, um, way back then is that
31:17
when you buy the little light windmills that
31:19
you can get in an evacuated shell that are
31:21
meant to show radiation pressure, they're
31:23
actually not there using photophoresis
31:25
because there is some atmosphere in that
31:27
bubble still. And, um, the Havel's one is
31:29
colored white, one is colored black, the
31:31
black side gets hotter and you get this
31:33
photophoresis force happening rather than
31:36
radiation pressure, which is interesting and
31:39
quirky. Coming back to the question, all the
31:42
way to the question is whenever astronomers
31:44
use the term dust, then what they're meaning
31:47
is particles of solid material
31:49
that are too small to be considered asteroids
31:52
or planets or things like this. That gets
31:55
a catch all of dust. And it behaves very much
31:57
like dust in the Earth's atmosphere. Red
32:00
light penetrates it more easily than yellow
32:01
light, which penetrates more easily than blue
32:03
light. Because the longer the wavelength, the
32:05
better you can pass through. Which is why if
32:07
you look at photographs of some of the
32:10
wonderful dark nebulae in the night sky, like
32:12
the Coalsack Nebula, which is ahead of the
32:14
EMU in the sky to the traditional owners of
32:16
the M land here in Australia. Like many of
32:18
the Barnard Nebulas, Barnard did a big study
32:20
of finding dark nebulae all across the sky.
32:23
If you look at photographs of those that have
32:25
been taken in full color and you zoom in
32:27
around the peripheries of those clouds,
32:29
you'll see that the stars right at the edge
32:31
look red. And that's because he's seeing them
32:33
through the outer edge of the dust cloud. And
32:35
the blue and the yellow light is scattered
32:37
away. The red light penetrates through. And
32:39
you can see this very well. If you look at
32:41
some of the famous photos of the Coalsack
32:42
Nebula, it's really, really distinct and
32:45
noticeable. And it's because dust is dust is
32:47
dust. I appreciate it gets confusing because
32:50
we use the term in so very many contexts
32:53
as a throwaway thing and
32:55
to our experience on Earth because it's warm
32:58
here. You don't consider flakes of ice and
33:01
snowflakes as dust, but if you were.
33:03
Andrew Dunkley: Or smoke, you don't think about smoke as
33:05
dust, but that's exactly what it is. Can you
33:08
see that photo I took during the bushfires a
33:10
few years ago?
33:11
Jonti Horner: Yeah. What's spooky about that is that I've
33:14
seen the sky diminished and denuded
33:17
by bushfire smoke. And I've
33:19
also seen it from, um,
33:23
dust storms. Dust that's been kicked up and
33:25
alligated off the surface of the Earth. And I
33:26
would have never expected this. But when it's
33:29
really, really bad, they both lead to a very
33:32
red sky. But when it's not that
33:34
intense, you can actually tell the
33:35
difference. Because the sky looks different
33:37
between lofted dust and smoke, you actually
33:40
get a very different kind of reddening that
33:43
makes the particles of different sizes. But
33:45
if I took a bucket of smoke or a bucket of
33:47
snowflakes into space and scattered them into
33:50
the solar system, they'd just be considered
33:52
dust. Yeah. Small pieces of solid
33:54
material.
33:55
Andrew Dunkley: There you go. Um, Howard, if you can think
33:58
of a set of names to cover
34:01
the Various categories let, uh, us know.
34:04
But, um, I think just using the term dust
34:07
is probably the easiest way to deal with
34:10
it, by the sound of things. Thanks for your
34:12
question. Hope all is well in Malaysia.
34:17
Jonti Horner: Three, two, one.
34:20
Space. No.
34:21
Andrew Dunkley: Uh, our final question today comes from
34:23
Martin.
34:25
Berman Gorvine: Hello, space nuts.
34:28
Martin Berman Gorvine here,
34:30
writer extraordinaire, uh, in many
34:33
genres, with yet another question.
34:36
How do we determine whether the gas
34:39
giants and. Or the ice
34:42
giants have rocky
34:44
cores? And if they do not
34:47
have rocky cores, what might they
34:50
have inside?
34:52
Possibly of tangential relevance.
34:56
I saw an article that
34:59
appeared earlier this year in
35:01
scitech Daily saying
35:04
that
35:07
analysis of Hubble data shows that
35:09
methane has been depleted at
35:12
Uranus poles in recent
35:15
decades, which begs the question,
35:19
is Uranus outgassing methane?
35:22
Oh, sorry, sorry. I shouldn't have said that.
35:25
I don't know what came over me. Uh,
35:27
I will, uh, do penance immediately.
35:31
Berman Gorvine, over and
35:34
out.
35:35
Andrew Dunkley: Thanks, Martin. I did wonder where
35:38
he was going with that. I shouldn't have been
35:40
surprised. Um, so to
35:42
gas and ice giants, um,
35:46
if they don't have rocky cores, what do they
35:48
have? I mean, there's been some suggestions
35:51
that some of them just have a liquid center,
35:53
like a nice, you know, chocolate you get at
35:56
Christmas. Um, could they all
35:59
be different? I mean, did they all have to
36:01
have the same kind of thing? It's not, you
36:03
know, we're not talking about dust here.
36:05
Jonti Horner: Well, there's a couple of different things
36:06
that lead into this and should make the
36:09
distinction between the planets we have in
36:11
the solar system and objects elsewhere. Um,
36:14
because the only planets that we can get up
36:15
close and personal to are the ones here at,
36:17
um, Home.
36:17
Andrew Dunkley: Yeah.
36:18
Jonti Horner: The background here is that traditional views
36:20
of planet formation involve a process called
36:23
core accretion. So this is where you take the
36:26
solid material, the dust from the
36:27
protoplanetary disk. And if you're out beyond
36:30
the ice line, that dust includes a lot of icy
36:32
material, solid material, agglomerates,
36:34
forming bigger and bigger objects until
36:36
eventually get something massive enough to
36:38
start gathering the gases and hold onto them.
36:40
Because whether you keep hold of an
36:41
atmosphere or not depends on your mass and
36:43
the strength of your gravity. The more
36:45
massive you are, the more gas you can hold
36:47
onto, but also the more capable you'll be of
36:49
capturing hydrogen and helium, which are the
36:51
main gases in the universe.
36:55
So the idea is that Jupiter and Saturn got
36:58
to 10 or 12 earth masses, which is kind of
37:00
viewed as being the threshold for gathering
37:02
up the hydrogen and helium gas
37:05
fairly quickly. Hoovered up a lot of hydrogen
37:07
and helium. And they became the gas giants.
37:09
And that's why the name gas giants has been
37:11
used for Uranus and Neptune. They
37:14
never really got big enough to gather
37:15
hydrogen and helium before the hydrogen and
37:17
helium had been blown away. But they gathered
37:19
huge mantles of methane,
37:22
ethane, ammonia, things that are
37:25
typically ice at that kind of distance
37:28
under gas phase, depending exactly how far
37:30
away you are. And so you've got these objects
37:32
that are uh, significantly composed of
37:35
material that could be considered ices or
37:39
gases that are more massive, so therefore
37:41
have a lower, a higher escape velocity
37:44
and therefore are easier to hold onto with a
37:47
lower mass. So the distinction between the
37:49
ice giants and the gas giants is a
37:51
compositional one. And it's to do with how
37:53
they formed. They always used to just all be
37:56
called gas giants. The ice giants idea came
37:59
in with different models of planet formation.
38:01
Because what we tend to do with planet name
38:04
classification with things like
38:07
whether Ceres is an asteroid or a dwarf
38:09
planet, or both, whether Pluto's a planet or
38:11
a dwarf planet. What we tend to do is we tend
38:13
to place boundaries as humans to allow us to
38:16
group like with like and separate things that
38:19
are functionally different in origin or have
38:21
a different history. And we do this in our
38:23
day to day lives. We have children and
38:25
pensioners, we have adults, we have
38:28
people who suddenly wake up one morning and
38:30
they can drive a car the day before. They
38:32
were legally not allowed to do so because
38:33
they've crossed this magic threshold. It's a
38:35
very human thing. The nature of them
38:38
in terms of having cores is therefore
38:41
initially an outcome of our best
38:43
understanding of how these things could form.
38:45
The idea is that you need to form a kernel of
38:47
solid material to get enough mass
38:49
in order to accrete the gas. Now there's an
38:52
alternate model which probably ties into the
38:55
formation of objects in binary star systems,
38:57
where when you've got a much more massive
38:59
disk of material around a star, you can get
39:02
an instantaneous gravitational instability
39:05
where you get a, ah, very gas heavy object
39:08
formed very, very quickly that
39:10
wouldn't need a core as a nucleus around
39:12
which it forms. It would have solid material
39:15
in it. But that solid material would just be
39:17
at the level that the background material
39:20
would have. So the composition of an object
39:22
formed in this way from this gravitational
39:24
instability would be the same as a bulk
39:27
composition of the disk. The composition of
39:29
an object that forms from core accretion
39:31
would be richer in the solid material because
39:33
they form a big amount of solids before they
39:35
gather any gas. Once they're at the point of
39:37
gathering the gas, they gather everything in
39:40
the same amounts as they're in the disk. So
39:42
you end up with something that has a large
39:44
amount of disk like composition, plus
39:47
a chunk of solids added in. But the thing is,
39:50
the bulk of those solids are down at the
39:51
bottom, so you can't really measure that
39:53
remotely. So how do you tell them apart?
39:55
Well, to be honest, for things around other
39:58
stars, we can't yet. So what we need to do
40:01
instead is look at their orbits and the
40:03
structures of the system and um, see how they
40:06
fit with these different formation
40:09
models. Um, and this is, I think going to,
40:12
in the next few years lead to a shift in how
40:13
we define what a brown dwarf is. Where
40:16
historically a brown dwarf was something
40:18
between 13 Jupiter masses and about 80
40:20
Jupiter masses, was something that was a
40:23
failed star rather than a giant planet. But
40:25
we're finding objects that blur that boundary
40:27
more and more. And I think we'll probably
40:29
shift to a different definition which looks
40:31
at, uh, the formation mechanism and the
40:33
presence of a core. So if you've got
40:35
something twice the mass of Jupiter bit
40:36
formed through this gravitational instability
40:38
method, that will be a very low mass brown
40:41
dwarf. Whereas if you've got something 20
40:43
Jupiter masses, that has a solid core, that
40:45
will be a very massive planet because it
40:48
formed through core accretion. I think that's
40:49
probably where we're going. That means
40:52
then that you can draw inferences on this
40:54
based on the structure of the planetary
40:56
system you've got, based on the orbits of the
40:58
objects, because these different formation
41:00
mechanisms would form very different systems.
41:02
But here in the solar system, we actually
41:05
can eventually figure out whether
41:08
giant planets have got a solid core or not.
41:10
In order to do that, we need spacecraft to be
41:13
orbiting those planets for a lengthy period
41:15
of time, preferably on highly elongated
41:17
orbits like Juno. This was one of the key
41:19
points of the Juno mission, where you've got
41:22
a spacecraft going round on highly
41:24
elongated orbit which is
41:27
experiencing the gravitational pull from the
41:29
planet. And when you're very close to the
41:31
planet, your orbit is not just sensitive
41:34
to the mass of the planet, as if all of the
41:36
mass was at a single point in the middle of
41:37
the planet, you actually become sensitive to
41:40
the distribution of mass within the planet.
41:43
Fundamentally, a planet that has a lot of gas
41:45
on top and a small dense core that has a
41:47
varying density throughout will affect the
41:50
spacecraft differently to how a planet that
41:53
was uniform in density throughout would do.
41:55
Now, to some degree, we do this on Earth,
41:57
where people map the density variations at a
42:00
very local scale for, um, GPS
42:03
satellites and things like that. And you've
42:04
seen beautiful gravitational maps of the
42:06
Earth where it looks like a deformed potato
42:09
effect. Yes. So same kind of idea with
42:11
Jupiter and Saturn. By using the data from
42:14
Juno, by using Cassini data from around
42:17
Saturn, we have a fairly good idea that those
42:19
planets do actually have
42:22
cores of solid and liquid material deep
42:25
within them that would have formed through
42:27
this core accretion process. So that's why we
42:29
can be fairly confident that they have rocky
42:31
cores here, where rocky is basically meaning
42:34
anything solid. There'll be iron and nickel,
42:36
there'll be water ice, and there'll also be
42:38
liquid metallic hydrogen and things like
42:40
this. But there will be a solid kernel at the
42:42
core from which those planets form. There is
42:46
some interest that comes from this because I
42:48
think Jupiter's core, I think it was
42:50
Jupiter's rather than Saturn's, the data has
42:53
revealed is there, uh, it's a bit more
42:55
massive than expected, but also more spread
42:57
out and slushy. And that is thought to be
43:00
potentially evidence of a late giant impact
43:02
on Jupiter, where there was a late addition
43:04
of a big chunk of solid material in much same
43:07
way that there was a giant impact that formed
43:10
the Earth and the moon, A giant impact that
43:12
stripped the surface of Mercury away, leaving
43:14
Mercury denuded. Giant impacts were a huge
43:16
part of planet formation. But in order to be
43:19
absolutely definitively sure that you have a
43:22
solid core, you need those close up
43:24
spacecraft measurements to be able to
43:26
distinguish the
43:28
subtleties in the gravitational field that
43:30
result from something that is not uniformly
43:32
dense but has a varying density and has a,
43:35
I guess, significant internal structure. We
43:38
can do that in the solar system. We haven't
43:40
yet done that for Uranus and Neptune because
43:42
we've never had orbiters go to those planets.
43:44
And I look forward to the day that we manage
43:46
that. But even if those missions start being
43:48
planned now, they probably won't launch till
43:49
the 2000-40s. I will be retired by the time
43:52
they get there, but I'll still be watching on
43:53
eagerly for the planets round of the stars.
43:56
We have to draw on the nature of the
43:59
planetary system. They're moving the orbits
44:01
and draw inferences then on which of the
44:02
formation mechanisms that they had. And
44:05
that's where the complexity about brown dwarf
44:07
versus giant planet comes from as well.
44:10
So it's a wonderfully deep and complex
44:12
question. In terms of the methane on
44:14
Uranus, I think that is not that Uranus
44:17
is outgassing the methane, it's keeping the
44:19
methane to itself. A bit like when I put the
44:21
dogs in a locked room um, they keep their
44:23
methane to themselves, and it's sometimes not
44:25
that pleasant when I go back in there. Um,
44:27
but rather the methane levels varying because
44:29
of the time of year and the seasonality of
44:32
weather on Uranus. I think that's probably
44:34
what's happening there.
44:36
Andrew Dunkley: Okay. Uh, it's a great question. Uh, Martin
44:38
always comes up with a ripper or two from
44:41
time to time. And some good questions as
44:42
well. And, uh, yeah, that was.
44:45
That was a good one. Thank you, Martin. And
44:48
thanks. Thanks for the joke. Loved it.
44:51
Um, and that's where we are going to
44:54
finish up. And, Jonti, thank you for filling
44:56
in for the last seven weeks or so while
44:59
Fred took a vacay. Uh, we really
45:02
do appreciate it, and, uh, we'll certainly
45:04
have you back down the track. Thank you.
45:06
Jonti Horner: It's always a pleasure. And in the meantime,
45:07
I'll keep my eye on the Facebook group and
45:09
cheer on people sharing Nightwish videos. Uh,
45:12
I saw that. That made me happy.
45:13
Berman Gorvine: Yeah.
45:13
Andrew Dunkley: Yeah, I knew someone would.
45:15
Jonti Horner: Yeah.
45:15
Andrew Dunkley: Uh, fantastic than Jonti. Thank you very
45:18
much.
45:18
Jonti Horner: That's a pleasure. I'll catch you next time.
45:20
Andrew Dunkley: Okay, Bye. Bye. Uh, Jonti Horner, professor
45:22
of astrophysics at the university University
45:25
of Southern Queensland, uh, filling in for
45:27
Fred for the last several weeks. And we will,
45:30
uh, get him back on in the not too distant
45:32
future. And thanks to Huw in the studio. Huw
45:35
couldn't be with us today because, um, he's
45:38
been having trouble sitting. Uh, and he went
45:40
to the doctor, and the doctor said, you've
45:42
got a ring around your anus. Oh, I couldn't
45:44
help it. Thanks, Martin.
45:45
Jonti Horner: You inspired me. I'm done being
45:48
locked in a room with my dog.
45:51
Yes. Yes, indeed.
45:53
Andrew Dunkley: All right, we're done. Thanks for your
45:55
company. We'll catch you on the next episode
45:56
of Space Nuts. Bye. Bye.
45:59
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