Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / Interstellar Inquiries: Hot Jupiters, Rocket Fuel Solutions & Debunking the Artemis Conspiracy

Transcript

Interstellar Inquiries: Hot Jupiters, Rocket Fuel Solutions & Debunking the Artemis Conspiracy · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Andrew Dunkley: Hello again. Thank you for joining us on
0:02
another episode of Space Nuts. This is a Q
0:04
and A edition where we take audience
0:06
questions, we write them on a piece of paper
0:08
and then we throw it in the bin. Or we
0:11
could answer them. We'll do the latter. Uh,
0:14
we got questions about ultra hot
0:17
Jupiters. We've also got questions about,
0:19
uh, reusing spent rocket fuel. How would
0:22
you do that? That is the question. And
0:26
wow, how about this one? Uh, some conspiracy
0:29
with the Artemis 2 mission
0:31
being fake. We'll deal with all of that on
0:34
this episode of space nuts.
0:36
Generic: 15 seconds. Guidance is internal.
0:39
10, 9. Ignition
0:42
sequence start.
0:43
Jonti Horner: Uh, space nuts.
0:44
Generic: 5, 4, 3, 2, 1. 3, 4, 5,
0:47
5, 4, 3, 2', 1.
0:49
Jonti Horner: Space nuts.
0:50
Generic: Astronauts report. It feels good.
0:53
Andrew Dunkley: And joining us to try and sort all that out
0:56
is Jonty Horner, professor of Astrophysics at
0:58
the University of Southern Queensland.
1:01
Jonty, hello.
1:02
Jonti Horner: Good afternoon. How are you?
1:04
Andrew Dunkley: I'm, um, all right. Um, please forgive me if
1:07
there's some background noise. There's a
1:09
gardener working, uh, just out the front, and
1:12
he's, uh, doing a fabulous job. But he's
1:13
using that kind of equipment that you would,
1:16
um, you know, demolish a building with.
1:19
So, uh, it's, um, it's making
1:22
quite a noise. But, um, I've got my filter
1:24
turned on, so hopefully it'll just keep it
1:26
blocked out.
1:27
Jonti Horner: Oh, it's amazing just how well these things
1:28
work. I use this microphone in front of me
1:31
for my teaching. I've had a number of
1:32
occasions where the dog has decided that I'm
1:35
painting too much attention to my students
1:36
and not enough to her. And it's got quite
1:38
vocal about that lying just behind me here
1:40
next to her fire at the minute, keeping her
1:41
really happy. And they say, no, we can't hear
1:44
anything. It's amazing how well it can filter
1:46
out the background noise.
1:47
Andrew Dunkley: Yeah, the technology is amazing today. It's
1:50
like the telescope technology that exists now
1:53
where you can filter out light pollution.
1:56
I don't know how that works, but, uh, it's
1:59
quite incredible these days. Works really
2:02
well. I want to answer some questions.
2:04
Jonti Horner: Of course.
2:05
Andrew Dunkley: All right, let's start with David, who's on
2:08
the Sunshine coast in Queensland, Australia.
2:12
David: G', day, David from the sunny coast again. I,
2:14
uh, just had a question regarding the, uh,
2:17
ultra hot Jupiter article from the latest,
2:20
uh, podcast. Um,
2:23
in the conversation, Fred Watson, uh,
2:25
mentioned that, uh, the belief is
2:28
that stars and their surrounding planets all
2:31
form from the same, uh, disc of material.
2:34
Um, I just had a question regarding the
2:37
material. Um, you know, we tend to
2:40
think of stars as Helium or hydrogen or both,
2:43
um, and everything else as metals. And we
2:46
believe those metals formed within stars,
2:49
uh, due to the
2:51
fusion burning. Um, where then
2:54
does this material come from in the disc to
2:57
form a star and its planets? Is that from
3:00
material from. Do we believe it's material
3:02
from another star or, um, is there some
3:05
other process going on? Thanks very much for
3:08
the show. Awesome. See you guys.
3:10
Andrew Dunkley: See you, David. Thank you very much. Um, that
3:12
sounds like it's right up your alley.
3:14
Jonti Horner: It is. It's a good film to start off with.
3:17
Sah. Uh, you're right. The
3:19
material that forms a star and its planets
3:23
has been contributed to by many previous
3:25
stars. If you imagine after the Big Bang, the
3:28
universe was hydrogen and helium and a tiny
3:31
little bit of other stuff, but it really was
3:32
barely any, which meant that a generation of
3:35
stars formed that were pretty much just
3:37
hydrogen and helium and very little else.
3:39
Those stars in the early universe, there's
3:41
some speculation that they may have been,
3:43
including mega megastars, much
3:46
bigger than something called the Eddington
3:48
Limit, which is a maximum size a
3:51
stable star can form, um, because of how
3:53
dense the universe was at the time, how much
3:55
material there was. So speculation of stars
3:57
up to several thousand solar mass. Those
4:00
stars lived fast, died young, put
4:02
material back out into the cosmos. So they,
4:05
when they died, they locked some of the stuff
4:07
up in the remnants to the left, whether
4:09
that's a black hole, a neutron star, a white
4:11
dwarf, whatever. But the material that was
4:14
flung outwards to form planetary nebulae,
4:16
supernova remnants, disperses into the
4:19
wider galaxy. So what's happening over
4:22
the aeons of time since the Milky Way formed
4:25
is that stars are born, live and
4:28
die. And when they die, they pollute the
4:31
cosmos. Stars of different masses throughout
4:33
different things. But what that means is that
4:35
you gradually get more and more heavy
4:37
elements introduced into the galaxy.
4:41
And, um, that goes to basically contributing
4:44
to the composition of the gas and dust that
4:46
floats around in our galaxy. If you go out,
4:48
particularly this time of year in the
4:50
Southern Hemisphere. But if you go out on any
4:52
night of the year where you can see the Milky
4:54
Way, you'll see that in the band of the Milky
4:56
Way, there are dark patches as well as
4:58
glowing bits. The dark patches are not
5:00
places where there is a lack of stars, but
5:02
rather they're places where you've got huge
5:04
clouds of gas and dust that are opaque, that
5:07
are blocking the light from stars that are
5:09
more distant from reaching us. So they look
5:11
dark in the same way that a cloud blocking
5:14
the sun will look dark in the daytime. It's
5:16
blocking light from beyond. These clouds
5:19
can be vast and they're made of gas and dust
5:21
and ice, mainly hydrogen and
5:24
helium, but lots of other stuff. And that
5:26
other stuff will vary from one cloud to the
5:29
next to some degree, based on what it has
5:32
been polluted with. You'll have to some
5:34
degree a stirring, a pollution of the galaxy
5:36
that gives you a background increase in the
5:37
amount of metals. But you'll also get local
5:40
variation. We see all of this
5:42
incidentally in the Earth and the solar
5:44
system. There are suggestions that the solar
5:47
system, when it was young, when it was
5:49
forming, was polluted by a nearby supernova
5:51
that injected a lot of very short lived
5:53
radioactive aluminium isotopes that
5:56
accelerated the degree of melting you got in
5:58
the rocky objects. There's a signature there
6:01
of a radioisotope that is so short
6:04
lived, there shouldn't really have been any
6:05
of it around, unless a supernova exploded
6:07
nearby to pollute our disc, giving us a
6:10
slightly unusual composition. There is also
6:12
an argument that the Earth is richer
6:15
in gold than it should be, because
6:18
sometime between 10 and 100 million years
6:20
before the formation of the Earth, 10,000
6:22
light years from where we formed, two neutron
6:25
stars collided, polluting the universe with
6:27
gold. And some of that gold made its way into
6:30
the disc that formed the solar system, got
6:32
incorporated into the Earth. And that's why
6:33
we are a particularly good place for
6:35
Goldfinger to, uh, have his little layer.
6:38
We've got more gold than normal.
6:40
Andrew Dunkley: Yeah.
6:40
Jonti Horner: What this all means is that those giant
6:42
clouds of gas and dust in space can be truly
6:45
vast. When they get nudged and start to
6:47
collapse, they'll fragment in their interiors
6:50
to form a cluster of stars, a number of
6:52
stars, which form from the little denser
6:54
bits. It's like driving through a fog bank.
6:56
Fog banks are never one uniform density.
6:58
There's denser patches and less dense
6:59
patches. A denser patch in one of these
7:02
clouds will collapse under its own gravity.
7:04
And so you'll get lots of stars forming. As
7:07
that material collapses in, it collapses down
7:09
to form a disc around that young protostar
7:11
that's forming. And the star and the
7:13
disc are made of the same material. They're
7:16
forming from the same material. All that
7:18
material that was in the cloud from which
7:20
they're formed, which has been polluted over
7:22
many generations of stars, cooking the
7:24
books to give the composition that is uniform
7:27
across that star system. What happens then is
7:30
that the star forms from everything, so it
7:32
ends up very rich in hydrogen and helium.
7:35
Because even after all that pollution and all
7:37
that evolution, hydrogen and helium still
7:40
make up something like between 98 and 99% of
7:43
all atoms in the universe. So the star is
7:45
going to be primarily hydrogen and helium
7:47
with a thin veneer of everything else. In
7:50
other words, the abundance of material in the
7:52
star is going to be very nearly
7:54
identical to the disc. Star will end
7:57
up being very, very, very slightly enriched
8:00
in the heavier elements, because from
8:03
the disc, particularly when the disc is
8:04
cleared, there will be some infall of rocky
8:07
and icy objects like the Kreutz sun, grazing
8:09
comets, we see that fall into the star and
8:11
pollute it further. But that' very, very
8:13
small effect compared to the overall mass of
8:16
the star. The planets form in the
8:18
disc in the main
8:21
form through a process we call core
8:23
accretion. There are some suggestions that
8:24
some of the most massive stars can form
8:26
through a process of instability. And those
8:29
planets and binary stars would form with a
8:32
more stellar composition, I.e. lots of
8:34
hydrogen, helium. But most planets
8:37
will form by initially growing a core of
8:39
solid material, because when you have a low,
8:42
uh, mass, you can't capture gas,
8:44
and so therefore your composition will be
8:47
dominated by the solid material, not the
8:49
gases. So that's why the Earth doesn't have
8:51
free hydrogen and helium. We simply don't
8:54
have enough mass to capture those gases and
8:56
hold onto them. So even though 99% of all
8:59
atoms in the protoplanetary disc were
9:01
hydrogen and helium, we didn't get any of
9:02
them, other than the old tiny little atom
9:05
that was captured in a cage of other
9:07
compounds called clathrate,
9:10
that was captured in a mineral effectively.
9:13
So we barely got any of those materials
9:15
because we couldn't hold onto them. We formed
9:17
out of the solid stuff. The further you are
9:19
from the star, the colder it is, so the more
9:21
different things can be solid rather than
9:23
gas, which is where we get the idea of the
9:24
ice line. If you're far enough from the star,
9:27
water can be solid, can be ice, and then
9:30
suddenly you've got a lot more solid material
9:32
because water's about the most common
9:34
compound there is, almost it's the most
9:36
common atom, hydrogen, and the third most
9:38
common atom, oxygen. And you put them
9:39
together and you've got water. So beyond the
9:42
ice line, you've got a lot more solid, and
9:43
you can form planets much quicker, which is
9:46
why we think Jupiter and Saturn got so big so
9:48
quickly. They had a lot to feed on. And
9:50
eventually they got massive enough that their
9:52
gravity was strong enough to hold onto the
9:54
hydrogen and helium around them and devour
9:56
it. So they are
9:59
in composition much more similar to the sun
10:01
than the, uh, Earth. Is because they have all
10:03
that hydrogen and helium, but they are still
10:05
richer in solid material than the sun
10:08
because at their core, there was all the
10:11
solid material needed to build up before they
10:13
could gather the hydrogen and helium. So they
10:16
started with more solids. Effectively.
10:19
The Earth doesn't really have the hydrogen
10:21
and helium. So all of the objects in our
10:23
solar system will have the same composition
10:25
as the sun in terms of the balance between
10:28
carbon and nitrogen and iron and all these
10:30
elements, except for where they weren't able
10:33
to capture those elements because they
10:36
weren't massive enough. So the Earth doesn't
10:38
have the same composition as the sun in terms
10:39
of hydrogen and helium, but it does in terms
10:42
of iron, nickel, all those things,
10:45
the balance between iron and nickel and
10:47
carbon and all the rest of it are all in the
10:48
same ratios as the sun, um, to an
10:51
incredibly high precision. And that's because
10:54
we all formed from the same material that
10:56
quite rightly was mentioned in the question
10:58
was delivered by past generation of stars
11:00
that had lived and died. And that's where the
11:02
whole concept that we are stardust comes
11:03
from. It's the idea that all the atoms that
11:05
we need to make us, us, other than the
11:07
hydrogen atoms, were cooked in the furnaces
11:10
of stars long de. All the carbon, the
11:12
nitrogen, the oxygen, the phosphorus, all
11:15
those wonderful things, calcium, that
11:16
contributes to our bones are all stardust
11:18
from stars that died long before the solar
11:20
system formed.
11:23
Andrew Dunkley: There you are, David. Um, a very
11:26
good, uh, answer. That pretty m. Well, nails
11:28
it. I like the bit about there being more
11:30
gold on Earth than there probably would be in
11:33
other places.
11:33
So that's. That was a lucky break for us.
11:35
Jonti Horner: Absolutely. So useful for a
11:38
lot of the technology we use. Not just for
11:40
those who are sparkly, bangly things, but,
11:42
you know, there's a lot of those rarer type
11:45
things that are so vital to our technological
11:48
growth that are all linked to our ancient
11:50
heritage.
11:52
Andrew Dunkley: Yeah, yeah. Um, well,
11:54
there's gold, there's lithium.
11:57
There's just so many of them. But we've got a
11:59
lithium mine just down the road from us,
12:00
actually.
12:01
Jonti Horner: And that lithium, probably all primordial,
12:03
the lithium in the universe, is almost
12:05
certainly, almost all leftovers from the Big
12:07
Bang.
12:09
Andrew Dunkley: Wow, that's interesting. There you go,
12:12
David, thanks for the question. Lovely to
12:14
hear from you. Hope all is well on the
12:15
Sunshine Coast. This is Space Nuts with
12:18
Andrew Dunkley and Jonty Horner, A
12:21
Q and A Edition.
12:25
Generic: Roger, your lab is right here.
12:26
David: Also Space Nuts.
12:28
Andrew Dunkley: And we're with Professor Jonty Horner today
12:31
with Fred Watson away. Uh, let's Go to our,
12:34
uh, next question. Jonty, this one comes from
12:37
Mark.
12:38
Mark: Hi, it's Mark from Sunny Siddlesham in the
12:40
uk. I've eventually plugged up the courage to
12:42
send in an audio question, so here goes. You
12:45
quite often mention water ice and the
12:48
possibility of turning this into rocket fuel.
12:50
So my what do you think? Sort of question is,
12:53
when you use hydrogen and oxygen as a rocket
12:55
fuel, it must turn back into water ice in
12:57
space. So do you think it would be possible
13:00
to collect it and reuse it through the rocket
13:02
engine, again massively reducing the amount
13:05
of fuel you would need to carry for an
13:07
extended journey, say, to Mars? I've sort of
13:09
drawn up an idea, but what do you think? Once
13:12
again, keep up the great work, Mark from the
13:15
uk.
13:16
Andrew Dunkley: Thank you, Mark. It's an interesting idea.
13:18
My, uh, first thought when I
13:21
first heard the question was, um,
13:24
how would you collect it? That
13:27
might be the first challenge.
13:29
Jonti Horner: That would be a bit of a challenge. I mean,
13:30
the thing is, your exhaust is being pushed
13:32
out of the bucket, the rocket, at very high
13:34
speed in a very dispersed form. Now the
13:36
rocket's going forward because you're
13:38
throwing the things out the back. You've got
13:40
the momentum, um, being transferred and it's
13:43
equivalent, I guess, to you. The way I'd
13:46
visualise this is imagining, again, sitting
13:48
on an ice rink on a wheelie chair. So you've
13:50
got no friction whatsoever, really slippy and
13:53
you're holding, Normally, I'd just say one
13:55
medicine ball, but instead imagine that
13:56
you're holding a big bag of short puts. You
13:59
throw a short put away from you and you'll
14:01
recall in the other direction. You throw
14:03
another short put and you'll speed up and
14:04
you'll move in the opposite direction to the
14:06
direction your short puts are going. So
14:08
that's how you'll work. And that's
14:10
essentially what you're doing with the
14:11
rocket. You're pushing material out of the
14:13
back and you're moving the opposite way,
14:15
because overall, the momentum is conserved
14:17
between the stuff going one way and you going
14:19
the other. The problem with the
14:21
rocket itself capturing its own exhaust,
14:24
pumping it back in and reusing it, is
14:27
then you're taking that momentum and bringing
14:29
it back to you, which means you're getting
14:30
pulled back towards it and you'll end up
14:31
having gone nowhere to some degree.
14:34
So imagine now that situation with the short
14:36
puts on the I shrink, but
14:39
instead you've got a really efficient bungee
14:42
cord, so that when you throw them away, they
14:43
bounce back and you catch them again. What'll
14:45
Happen is as they're moving away from you,
14:47
you'll wheel away from them. And then as they
14:49
get pulled back towards you, you get pulled
14:50
back towards them and you end up where you
14:51
started from. Here will know a little bit of
14:54
change due to friction and loss of energy and
14:56
stuff like that. So the problem I'd have
14:59
with this suggestion is not actually the idea
15:01
of capturing and reusing the fuel.
15:04
Um, I think that will be hard because the
15:06
fuel will get so dispersed, so water will be
15:08
scattered out there. It's just easier to go
15:09
get a big lump of ice from somewhere than try
15:12
and pick up individual water molecules or
15:14
small grains of ice disperse over a large
15:16
area. But the idea of being able to capture
15:19
it from the same rocket and reuse it would
15:21
get you into this problem of having to pull
15:23
back material that you've pushed away, which
15:25
means you'd be pulling yourself back to where
15:27
you started from. So you can't get away, I
15:29
think, from that momentum issue there.
15:32
So I think it's two different things. I think
15:34
if you had the ability to, instead of using
15:37
hydrogen and oxygen as a fuel and burning
15:39
them to be water, you can instead have a
15:42
rocket fired powered by firing
15:44
pellets of water out of the back. You could
15:47
fire them at a target that captures them, um,
15:50
collect them and reuse those pellets for
15:52
something else. But that target will get
15:53
pushed around by the arriving water pellets.
15:56
So you'd want to be clever with that and
15:57
you'd need to continually change its orbit
15:59
and stuff. So in theory, potentially, you
16:02
could gather the fuel for use on another
16:04
rocket without it being the rocket you're
16:06
flying that gathers that fuel. But in
16:09
reality, you're dispersing over such a large
16:11
area that unfortunately, it wouldn't be that
16:14
practical anyway. Especially when we've got
16:15
just huge lumps of ice floating around
16:17
anyway. I mean, you and I have both been
16:19
photographing a beautiful lump of ice flying
16:21
through the solar system. There we go in the
16:23
background. That's enough fuel for
16:26
missions forevermore. If we were to go and
16:28
mine there, and that's a lot more efficient
16:30
to mine one big comet or
16:33
asteroid for water ice or mine the moon for
16:36
water ice, then try and catch it when it's
16:38
dispersed, I think. So it's a really good
16:40
idea. It's really good thinking. But it's
16:43
something that wouldn't work. I think that's
16:44
the way I'd view it.
16:47
Andrew Dunkley: It'd be very complicated. And as you said,
16:49
um, trying to capture it in the ship, you're
16:51
actually propelling would be
16:53
counterproductive. Using another
16:56
spaceship to capture the ice after it's been
16:59
expelled, uh, would be difficult because it
17:02
would spread out too far. But then you're
17:04
using the same technology
17:07
to chase the ice that's been spent already
17:10
and spending more to get the ice back. So it,
17:13
yeah, It's a catch 22. It's just going to
17:15
keep going around and around. So um,
17:19
it makes it a little bit difficult. Uh, Mark,
17:21
but, uh, thanks for your question, that
17:24
was a fun one actually. But, uh, yeah,
17:26
um, yeah, I like the way people
17:29
think. But I, uh, suppose just to expand on
17:32
it a bit, um, there's going to come a
17:35
time where using those kinds of fuels
17:37
probably won't be necessary. They're
17:39
developing all sorts of different kinds of
17:41
engine technology, uh, everything
17:44
from solar sails to scramjets, and
17:48
they don't use that kind of fuel.
17:50
Jonti Horner: There's all sorts of things you could do. I
17:52
mean again, going back to the Bobiverse,
17:54
which I mentioned before, the Van Neumann
17:55
probes going through, they used kind of um,
17:58
ram scoots essentially initially in the book
18:01
set. They then move on to other kind of
18:03
speculative sci fi things. But initially the
18:05
idea of having a fusion drive where you scoop
18:08
up hydrogen atoms and turn them into helium
18:10
and push them out the back where in front of
18:12
you you deploy a big thing that gathers the
18:14
hydrogen you're moving through. This is also
18:16
what they did in Tau Zero by Poole Anderson
18:18
is you know, you're moving really quickly,
18:20
you gather hydrogen from in front of you and
18:22
compress it like a ramjet effectively.
18:25
There's all these kind of things, but they
18:26
will all, unless we get to truly sci fi
18:29
type things like warp driver albatier drives
18:32
or whatever, which require physics to be
18:34
somewhat different than how we can only
18:36
understand it. You still have
18:39
either a source of propellant which you
18:42
then get rid of out the back one way or the
18:44
other, or with solar sails you're using
18:47
the stellar wind and that pushes you away.
18:51
Um, people who are sailors can probably tell
18:54
you a lot more about the complexity of how
18:55
you can tack into the wind and move across
18:57
the wind. But the wind, the solar wind is
18:59
incredibly tenuous compared to the wind in
19:02
the Earth's atmosphere. So you need a very,
19:03
very big sail. And I think that will be
19:06
somewhat limiting. If you were wanting to do,
19:09
I guess, Star wars style dogfight manoeuvres,
19:11
you wouldn't do that with a solar sail. So
19:13
people will pick the right technology for the
19:15
kind of mission that they want. And that was
19:17
where the dawn mission which went to Ceres
19:20
and um, Juno in the asteroid belt was really
19:22
interesting because it used an ion drive
19:25
where it was using I think ionised xenon. And
19:27
um, that kind of drive achieves a much,
19:30
much lower thrust but can operate for much
19:33
much longer time. So it's very energy
19:35
efficient um, but it wouldn't be any good for
19:38
getting off the surface of the Earth. But
19:39
it's very, very good for cruising around the
19:41
solar system when you're not in a rush. And
19:43
so what will happen is I think different
19:45
people will have different types of drives
19:48
for different types of scenario
19:51
and choose the one that works best.
19:53
Andrew Dunkley: Yeah but to get off the planet at the moment
19:56
you need rockets. There's no real
19:59
other technology that will get you out there.
20:01
I know they've been trying um, sort
20:04
of catapult technology uh, which
20:08
um, could deploy satellites in the
20:11
future. I um, think
20:13
you'd need to be in the right place on the
20:15
planet to take advantage of the um, rotation
20:18
of the Earth so that you don't have to like
20:20
you couldn't do it too far away from the
20:22
equator, that kind of thing. But um,
20:25
at the moment uh, yeah the um, standard
20:27
old rocket engine is uh, the best option at
20:30
the moment.
20:31
Jonti Horner: Um, part of where the refuelling station idea
20:33
around uh, the moon comes from which is if
20:36
you have to take your fuel with you, you're
20:38
carrying a lot of extra weight so you've got
20:39
to burn extra fuel to carry that fuel which
20:41
means you're carrying extra weight so you've
20:43
got to take even more fuel to burn um, to
20:44
carry the weight of the fuel you're carrying
20:46
to carry the extra fuel. And so uh, it
20:48
becomes very inefficient very quickly. So if
20:50
instead you can small launches from Earth and
20:52
then refuel once you're beyond the Earth,
20:54
that's a lot more effective. And the other
20:57
thing that people have suggested long term
20:58
um, as a solution to get things off the Earth
21:01
more cheaply are things like space elevators
21:04
which are ah, probably still far science
21:06
fiction. I don't, don't think we have the
21:08
material science to do that nor the political
21:10
will. I mean putting that in perspective,
21:12
just saw the announcement this week that the
21:14
vast inland rail project that was happening
21:17
in Australia is no longer happening because
21:20
it got too expensive and it's taken too long.
21:22
And if we can't build a railway between
21:24
Melbourne and Brisbane, it's going to be
21:26
really hard to build an elevator between low
21:29
Earth orbit, well between the Earth's surface
21:31
geostationary orbit and the same distance
21:33
beyond for the counterweight. Yeah,
21:36
So I don't see it happening anytime soon.
21:39
Andrew Dunkley: We can't even get a tunnel under the Blue
21:41
Mountains between the west and Sydney.
21:44
Uh, and that's despite the fact
21:47
that that road is currently closed due to
21:50
a structural failure in Victoria Pass.
21:52
The old convict bridge, that's, uh, 200
21:55
years old or something, or 150 years old. And
21:58
it's finally given up the ghost. And so
22:01
they've closed the road.
22:02
It's. You know, people have been screaming
22:05
for a tunnel for decades. And,
22:08
um, no politicians willing to spend the
22:11
money because there aren't enough people.
22:13
Bottom line is there aren't enough people
22:14
living west of the mountains to make it worth
22:17
your vote.
22:18
Jonti Horner: Really. What it comes down.
22:20
Andrew Dunkley: That's what it comes down to.
22:21
Jonti Horner: Reminds me of the old episode of the Simpsons
22:23
when I was a kid with the kind of argument
22:24
about books for the kids or something.
22:26
There's the two people at the front room
22:28
basically shouting, but our children, but
22:30
taxes. But our children, but taxes. And it's
22:33
this whole thing of everybody wants it, but
22:35
nobody wants to pay for it.
22:36
Andrew Dunkley: Exactly, yes. Uh, a tunnel under the Blue
22:39
Mounds would be wonderful, though. Although,
22:41
um, some. Some of the arguments against it
22:44
are, uh. Well, it'll only save you 15
22:46
minutes. I think it'd probably save you more.
22:48
Gets pretty log jammed up over that mountain.
22:50
Jonti Horner: We have those arguments about the Toowoomba
22:52
bypass, and that's been a godsend.
22:54
Andrew Dunkley: I mean, yeah, I used it last, uh, year. Yeah,
22:57
it's fantastic.
22:58
Jonti Horner: It fell apart and bits fell onto it because
22:59
they contracted fairly cheaply.
23:02
Um, but that has saved about half an hour
23:04
from my trip down to Brisbane when I go to
23:06
the airport and stuff because I don't have to
23:08
go through Toowoomba and all the freight
23:10
companies use it even though the tolls are
23:12
quite high. Because the tolls being high is a
23:15
lot better than the wear and tear on their
23:16
vehicles coming up the old road into
23:18
Toowoomba and having to stop at all the
23:19
traffic lights and stuff. So it works out
23:21
deeper for them. It's better for the
23:23
Toowoomba council because they're having to
23:25
repair less potholes and they have less
23:26
accidents. And it's one of those things where
23:28
it was a little controversial when it was
23:29
being built, but since it's there, it's been
23:32
a godsend. And I'd like to think that some of
23:34
these big infrastructure projects would be
23:36
the same. And I mean, a space elevator would
23:38
be wonderful, but, you know, gonna be hard to
23:40
persuade people to commit to building it,
23:42
even when we get the technology.
23:43
Andrew Dunkley: I think, uh, wait till there are
23:46
orbiting hotels that'll change everything.
23:49
You wait and see. Might be
23:52
waiting a while. Um, thanks, Mark. Lovely to
23:54
hear from you.
23:55
This is Space Nuts with Andrew Dunkley and
23:58
Professor Jonty Horner.
24:04
Jonti Horner: Space Nuts.
24:05
Andrew Dunkley: One more question, uh, Jonty. And this one
24:08
comes from Paul.
24:10
Joe: G', day, Fred Watson and Andrew. Paul here
24:12
from Sunnybridge, Vegas. I have
24:15
a question and a dirty secret that
24:18
I need to confess.
24:21
So I was on this Flat Earth group on
24:24
Facebook. Yes, I know, I know. Uh, anyway,
24:27
this guy provided some AI information
24:30
which was absolutely correct to
24:33
contend that there is no way that the Artemis
24:36
mission could have ever caught up to the
24:38
Earth because the Earth travels a hell of a
24:40
lot faster than that little spaceship.
24:43
I pointed out that they didn't need to
24:47
catch up to the Earth at all. They just
24:49
needed to point themselves to where it was
24:51
going to be and then splash down,
24:54
land safely, and be
24:57
applauded by everybody except for the Flat
24:59
Earthers like him, uh, who are absolutely
25:02
incensed at the moment about
25:05
how it's all fake, as per, uh, usual.
25:08
Anyway, I told him
25:11
that if he really wanted a better answer,
25:13
exact answer, he really needed to talk to an
25:15
astrophysicist. So my second question
25:18
is. Well, my first question is, was I on the
25:21
right track? And my second question is,
25:24
are there any astrophysicists or any websites
25:26
out there that can give us an animation
25:30
of the Earth going around
25:32
the sun that also has, uh, the
25:35
animated version of the Artemis going around
25:38
the moon so that we can see the whole thing
25:40
in context in terms of the solar system, or
25:43
at least our area of the solar system system.
25:45
Uh, it's not going to convince him, I'm sure,
25:48
but I think it'd be pretty cool to see
25:51
something like that. Anyway, thanks very
25:54
much, gentlemen, for the show, as always. Um,
25:56
look forward to it every week and catch you
25:59
later.
26:00
Jonti Horner: Have a good one.
26:01
Andrew Dunkley: You too, Paul. Thank you. If only we had
26:04
an astrophysicist somewhere nearby.
26:07
Jonty, any I know
26:10
was directing the question to Fred Watson,
26:12
but he asked for an
26:13
astrophysicist.
26:15
Jonti Horner: Yeah. We are legion, for we are many. There's
26:17
plenty of us around. It, uh, was always a
26:19
thing when I was at uni of what title you use
26:22
for what you're studying would depend on how
26:23
bothered you were about the conversation.
26:25
Because if, you know, if I told someone I was
26:27
studying physics, said very quickly, exit
26:30
stage left, if I told them I was doing
26:31
astronomy, they'd stay and chat. And if I
26:33
told them I was doing astrophysics, they'd
26:34
just look a little bit scared. Um, but I was
26:37
doing all three.
26:39
This is an interesting one. I mean,
26:42
people like the flat Earthers are difficult.
26:45
David: Ah.
26:46
Jonti Horner: Because there is no amount of truth, no
26:48
amount of evidence that you can put before
26:51
people who are convinced that they've been
26:52
lied to, um, other than talking to
26:55
them gently about it. And it's like
26:58
discussions of climate change I've had in the
26:59
past with people who argue climate change
27:02
isn't real. Arguing and fighting with people
27:05
over this doesn't win hearts and minds. It
27:07
just gets them more entrenched. But talking
27:09
to them about it and talking about why we
27:11
think something is the case, this is our
27:14
evidence, this is what it is. That can
27:17
be a little bit more fruitful, I guess, but
27:18
it is really challenging. I mean, especially
27:19
given that we had a beautiful eclipse of the
27:21
moon just a few months ago, where you can see
27:23
that the shadow of the Earth is round.
27:27
Andrew Dunkley: And that's the big argument. If the Earth was
27:30
flat, the shadow at some stage would be
27:33
just a line across the Moon.
27:35
Jonti Horner: We'd see the elephants in the turtle. Um,
27:38
the other thing is, if the Earth was flat,
27:40
the cats would have pushed everything off the
27:41
edge by now. Yes, yes,
27:44
that's the other one. But, uh, in terms of
27:47
Artemis, at the end of the day,
27:50
we know it happened because we saw it. You
27:53
know, I was over in Europe at the
27:56
time, and, um, my colleagues at UNISQ were
27:58
happily sharing their own little footage of
28:00
the spacecraft that they got from our
28:02
telescopes. They have no reason to lie.
28:05
They have no vested interest in this. It's
28:08
not like they're secretly on the payroll of
28:09
NASA, ignoring the fact that if it was faked,
28:13
Russia and China will be racing to tell
28:15
everybody because that will be the best PR
28:17
victory ever. You know, I mean, it's the same
28:20
with the Moon landings in, uh, 1969.
28:23
Did anybody really, really think that the
28:25
Russians would have stayed quiet if there was
28:26
a sniff of it being faked?
28:28
Andrew Dunkley: In fact, my great grandmother
28:32
always thought the Apollo landings were
28:34
faked. Uh, she absolutely refused
28:37
to believe it. But she grew up in an era
28:40
before flight, so
28:43
I can understand why she would
28:46
think that, but she just thought it was all
28:47
just some sort of publicity stunt. But I
28:50
don't remember what they might have been
28:52
trying to get publicity for,
28:53
Jonti Horner: because they beat the Russians. I mean,
28:54
that's what it was to them. I'll beat the
28:56
Soviets as it was then, have been pulled up
28:58
on that a couple of times.
28:58
Andrew Dunkley: It was definitely a big PR, um,
29:00
Jonti Horner: exercise in that regard. Uh, a former
29:03
PhD student who worked with me, Jake Clark,
29:05
Dr. Jack Clark, now M, gave a wonderful talk
29:08
a couple of times about the
29:10
moon landings in 1969 and why they couldn't
29:13
have been faked because we couldn't afford
29:14
it. Talking about faking it with the
29:17
technology we had at the time would have
29:19
actually been more expensive than going
29:20
there. Um, which is fairly compelling
29:23
for me. I mean, there's always a joke that,
29:25
you know, yeah, the moon landings were always
29:26
going to be faked, but they hired Stanley
29:28
Kubrick to direct and he was such a
29:29
perfectionist that they demanded that they do
29:31
it on site. Um,
29:34
um, with Artemis 2, there
29:38
is abundant evidence that it really happened.
29:41
You could, with a small telescope or
29:43
binoculars, go outside and see the
29:44
spacecraft. And I mean, you can't fake that.
29:46
It's not like we're beaming thoughts into
29:48
your head. And if you think we are, you can
29:49
wear some tinfoil. That's all good.
29:52
Um, in terms of the
29:54
argument that the Earth is going too quick
29:56
for this thing to catch up, that is
30:00
in the kindest interpretation of it, that
30:03
is allowing common sense
30:06
based on your understanding of how day to day
30:08
life works, interfere with
30:11
looking at how things would move through
30:13
space. I can see why you would get to that.
30:15
If you think about a small child running
30:18
along with a model of Artemis in the hand and
30:20
a Ferrari driving down the motorway, or
30:22
insert the make of car driving down the
30:23
motorway at 100 kilometres an hour, the child
30:26
is not going to catch the thing because
30:27
they're not quick enough. And there are, uh,
30:30
limits on how fast a child can run and how
30:32
fast the car can move to do with air
30:33
resistance. It's
30:36
however, almost similar to saying, you know,
30:39
I can't throw a ball up in the air and catch
30:41
it because I'm Moving at over 1000 kilometres
30:43
an hour around the Earth. So I'm moving too
30:45
fast to catch up with that ball. Doesn't work
30:48
like that because me and the ball are both
30:49
moving at 1000 kilometres per hour. And so
30:52
it's a relative speed between us that
30:54
matters. So the Earth is going around the sun
30:57
at about 30 kilometres a second. That's
30:59
demonstrably true. Artemis moving
31:02
in orbit around the Earth is moving around
31:05
the sun at 30 kilometres a second with the
31:07
Earth. It's falling with the Earth. Uh, so
31:09
it's a relative speed that matters.
31:12
Andrew Dunkley: Yeah.
31:12
Jonti Horner: Now, if I went above the Earth, onto the
31:14
space station, but instead of orbiting the,
31:17
uh, Earth and falling with things, I was able
31:19
to use rockets to stand still. Or I had
31:22
an imaginary hovering platform of doom that
31:24
wasn't moving. I'm, um, out of the
31:26
atmosphere. If I threw a ball up in the air,
31:29
it would move away from the Earth and the
31:30
Earth's gravity would slow it down and pull
31:31
it back, and it'd fall back down to me just
31:33
the same as how it does on the ground.
31:36
Now, if I was in orbit around the Earth and
31:39
I was stood on the International Space
31:40
Station and I tossed the ball upward, it
31:42
would actually start moving on a different
31:44
orbit around the Earth. So while it would
31:45
move up, away from me and it would move down,
31:47
it'd be going around the Earth on an orbit
31:49
that takes slightly longer to go around the
31:51
Earth than I do. So it also fall behind,
31:53
behind. And that would look like wind
31:54
resistance. But it's actually just a quirk of
31:57
orbital mechanics in that I've put it onto a
31:59
different orbit, um, because we are both
32:02
falling at the time I let go of it. So if we
32:05
imagine our flat Earther jumped off a cliff,
32:07
and I'm not encouraging them to please do not
32:09
do this, but imagine one jumps off a cliff
32:11
while holding one of the shot puts from the
32:14
previous answer without it being on a bungee
32:16
cord. And they let go of the shot put, but
32:18
the shot put will fall with them at the same
32:20
speed. It won't move away from them and come
32:23
back. It will accelerate downwards in exactly
32:26
the same way that they do. And, uh, they'll
32:28
only diverge once air resistance takes
32:30
effect, depending on which of them feels more
32:33
air resistance.
32:35
Andrew Dunkley: It's the Galileo experiment, isn't it?
32:37
Jonti Horner: So if you're on the space station, you throw
32:39
a tennis ball up in the air. Ah, you're both
32:40
actually falling, but you've changed the
32:42
speed the tennis ball's falling, so it'll
32:43
move away from you and not appear to come
32:45
back because you're both still falling.
32:48
The reason all this is relevant to Artemis is
32:50
Artemis boosted off towards the Moon at, uh,
32:53
a speed that was not greater than the escape
32:55
velocity from the Earth. It was a speed that
32:57
was high enough to get to the Moon. And, uh,
33:00
the moon steered it around and flung it back
33:01
towards the Earth. But then it fell towards
33:04
the Earth under Earth's gravity, moving
33:06
with insufficient sideward speed that as
33:09
it fell towards the Earth, it would miss us.
33:12
It instead was going to hit us. And they
33:13
controlled it with rockets and stuff so that
33:15
it entered in a controlled rather than
33:16
uncontrolled fashion. What matters is
33:19
not the speed the Earth's moving around the
33:21
sun, or the speed the sun's moving around our
33:23
galaxy, or the speed that the galaxy is
33:25
moving through space. All that matters is the
33:27
difference in speed between the Earth and the
33:29
object, because they're moving together. This
33:32
thing's speed was at no time greater than the
33:34
escape velocity of the Earth, so it could
33:36
never fall away from the Earth and never come
33:38
back. It was always going to go up and then
33:40
come down again. Unless they use rockets to
33:43
boost it into an orbit around the moon to
33:44
shed some of that energy, which they didn't.
33:46
They instead slingshot it around the moon to
33:48
come back. All of that is perfectly
33:51
rational and straightforward given our
33:53
understanding of physics. But it doesn't
33:55
necessarily fit your common sense, because
33:58
you think about throwing a ball out of the
34:00
window of your car while your car's doing 100
34:02
kilometres an hour and the ball will fall
34:03
behind you and never catch you up. And so
34:06
a lot of the arguments that
34:09
flat Earth, uh, believers or other people in
34:11
that kind of situation are making good faith
34:14
are, uh, built on a faulty groundwork
34:17
where the common sense of how they understand
34:20
the world to work is not applicable to the
34:22
situation they're applying it in. Um,
34:25
and that's true of things like, you know, the
34:27
oceans are flat. If you put a spirit level on
34:30
them, they're flat. Well, it's actually that
34:32
they're curved, but they're curved at such
34:33
small level that locally they look flat.
34:36
It's a subtle difference, but it's one that's
34:37
easy to miss because it's hard to get your
34:39
head around those distances.
34:41
In terms of the animations. I just did a
34:43
quick Google search for Artemis animation of
34:45
orbit, and there's some beautiful. The first
34:48
hit is a NASA flight with an annotated and
34:51
animated path. There's a few YouTube videos,
34:53
there is a Reddit link with an interactive 3D
34:56
animation. There's a lot of
34:59
little YouTube short videos that pop up
35:02
which are not to scale, because if you make
35:04
things to scale, the sun and the Earth and
35:06
the Moon are points that are one pixel
35:08
across. And, um, the spaceship is a point
35:11
that is a pixel across as well, because
35:12
nothing can be smaller than a pixel. Um,
35:15
there is a fabulous thing, incidentally, and,
35:17
um, I'm gonna see if I can find it, see if
35:18
it's still there.
35:21
There's this great thing called if the Moon
35:23
were Only One Pixel. Um,
35:26
it is. I'm gonna see if the website still
35:29
works, because this is one of the great
35:30
things on the Internet. Here we go. I'm gonna
35:32
Drop it into the chat window. This, um,
35:35
was an effort somebody made many, many, long,
35:37
long years ago. I'll put this into the public
35:39
chat, which never gets used. There we go. To
35:41
visualise the scale of the solar system,
35:44
if you made the moon one pixel across,
35:47
so the Earth will then be two or three pixels
35:49
across, you can, when you get bored of
35:52
scrolling, you can click Play. But if you
35:54
open that up and then you scroll to the right
35:55
to explore, you move along
35:58
and then you've got the scale. One pixel is
36:00
3,500 kilometres, so the sun is a fairly big
36:03
blob. And you scroll to the right from the
36:06
sun and you've got a distance at the bottom.
36:08
Scroll to the right a long way. We've gone 10
36:10
million kilometres. This is this fabulous
36:12
visualisation to let you see how big
36:15
things are.
36:16
Andrew Dunkley: Oh, isn't that clever?
36:17
Jonti Horner: How fast light travels. You can click, um.
36:20
That's slow. It's fabulous. Now what
36:23
you can do is you can skip through.
36:26
I need to find where there was a way to skip
36:29
to the Earth. Yes, at the top. Skip to the
36:31
Earth, goes whiz, whiz, whiz, whiz, whiz.
36:33
Really quick, goes past Venus, comes to the
36:34
Earth and the Moon. If the moon is one pixel,
36:37
the earth is only two or three and you get
36:39
the scale of them 8.3 light minutes out from
36:42
the sun. And think how far you've got to
36:44
scroll to get there. Think with that moon
36:47
being a single pixel, how far it is from the
36:49
Earth. This is why none of those animations
36:52
have things to scale, because you wouldn't
36:55
see the spacecraft, you wouldn't see the
36:56
Earth and the moon, they wouldn't look
36:57
pretty. So the caution there is that, uh, the
37:00
animations that you see, even the beautiful
37:02
NASA ones that show the flight path, are,
37:05
ah, not to scale. And, um, that can be
37:07
misleading. That can also
37:10
add to some of the arguments that this is
37:12
fake, because people say, well, the Earth and
37:14
the Moon are much smaller than that and
37:15
they're much further apart. Uh, that looks
37:16
wrong. Um, so it's worth being explicit
37:19
that these are, these visualisations are, um,
37:22
definitively not to scale. Um, the one,
37:25
incidentally, that was linked on the Reddit
37:26
page looks like the dots for Earth and Moon
37:29
actually are more to scale. So I'll just drop
37:30
that one in as well. Not sure how this works,
37:33
I've not really played with it. But you can
37:34
drag the orbits around, you can move them
37:36
back and forward in time, you can see the in
37:38
and out of plane stuff and you can move the
37:41
visualisation around even with the background
37:43
stars, which is quite nice. Um, so that's
37:45
worth a play as well. And that looks a bit
37:47
more to scale. And there's lots of things you
37:49
can play with, but fundamentally we
37:52
could see it. The hardest part for me, about
37:55
the small number of people who have argued
37:57
that the Artemis mission didn't happen,
38:00
is that it's something that anybody on the
38:02
planet could see, so long as they owned a
38:03
binoculars or a telescope. You could have
38:06
pointed somewhere and you could see the
38:07
capsule moving there if you really wanted. At
38:10
any time when the moon was above the horizon,
38:12
you could track it round.
38:15
Andrew Dunkley: And if you've got good enough gear, you can
38:17
actually look at the moon and see
38:20
the landing positions of some
38:23
of the Apollos. If you've got the gear.
38:25
Jonti Horner: If you've got the gear, I mean, that's kind
38:26
of spice athlete level. But what you can do
38:28
if you've got slightly less of the gear is
38:31
bounce laser pulses
38:34
off the retroreflectors that the astronauts
38:36
left at those sites and measure the distance
38:38
to the moon and measure its recession to an
38:41
incredible precision. And we can only do that
38:43
because people went to the moon.
38:46
Andrew Dunkley: Yeah, absolutely.
38:50
I remember the day that Neil
38:53
Armstrong stepped on the moon. I was, um,
38:55
sent home from school.
38:59
It's one of the strongest memories of my
39:01
childhood. I was seven years old and, uh,
39:03
I'll never forget it. It was, um, quite
39:06
an extraordinary thing in human history.
39:09
Inspirational.
39:09
Jonti Horner: I mean, I, I'm not old enough to have ever
39:12
seen anybody walk on the moon. I'm hoping
39:14
that'll change. But the generation of
39:16
astronomers who are 15,
39:19
20 years older than me, who were old enough
39:21
to see the moon landings and take them in,
39:24
so many people were inspired to become
39:25
scientists and engineers by that. We got a
39:28
whole generation of people across
39:31
the sciences, across the engineering subjects
39:34
that changed the world, who were all inspired
39:37
by seeing people walk on the moon.
39:40
And, um, it's kind of exciting to me, even
39:42
ignoring the signs, even ignoring the
39:43
technology, that we're going to get that
39:45
experience again in the coming years. If we
39:46
go back there, there'll be a whole new
39:48
generation who will change the world. All
39:50
inspired by those people touching down and
39:52
seeing it happen.
39:54
Andrew Dunkley: Yes, yes. I was very lucky to meet one
39:57
of them. Uh, Buzz Aldrin, um, some years ago,
40:00
came here because they built a Reutt
40:03
Flyer at a place called Narrowmine, just up
40:05
the road from here, 40 kilomet, and they took
40:08
it out for a fly and he came for the
40:10
occasion and, uh, gave A wonderful
40:13
speech and a, uh, handful of us in the media
40:16
got to interview him afterwards in a, in a
40:18
hangar at the same time as a helicopter
40:21
decided to take off.
40:23
Jonti Horner: That sounds about right.
40:24
Andrew Dunkley: He famously, you know what? You just, you
40:26
just go with it.
40:27
Jonti Horner: Oh, he very famously gave very short shrift
40:30
to people who told him that he'd not been to
40:31
the moon.
40:32
Andrew Dunkley: Oh, I know. Uh, Ah, yeah, I did
40:35
actually raise that question, but gee, it was
40:38
such an interesting answer.
40:41
Yeah, fabulous.
40:42
Um, Paul, great question, really
40:44
enjoyed that one and I,
40:48
I can understand your frustration, but, um,
40:51
maybe just avoid those Facebook pages,
40:54
um, because you can't, you just can't save
40:56
them, my friend. Uh, but good to hear from
40:58
you. Uh, if you've got questions for us,
41:00
please send them in. Uh, you can do that via
41:02
our website, space nutspodcast.com or
41:04
spacenut. You can also
41:08
visit us on social media. We've got the
41:09
official Space Nuts Facebook page and the
41:11
official. What's, uh, the
41:14
Instagram page. Uh, we've also got the
41:17
user group on Facebook, um, the
41:19
podcast group, uh, uh, which is
41:22
all. It's a lot of fun. It's where people who
41:25
listen get together, swap photos of stuff
41:28
they've taken in space and ask, uh,
41:31
questions. And, uh, it is a really good
41:34
group. So the Space Nuts podcast group on
41:37
Facebook book very much worth, uh, joining
41:39
that one as well and hope you'll join us
41:42
again real soon. And thank you to Johnny
41:44
Horner for filling in for Fred Watson for the
41:46
last month or so. It's been fantastic and
41:49
hopefully we can get that photography, uh,
41:51
special off the ground and get you back and
41:53
have a chat about astrophotography. Jonty,
41:56
that would be a real good one.
41:57
Jonti Horner: Fingers crossed. That would be awesome.
41:59
Andrew Dunkley: Yeah. All right, catch you soon. Thank you so
42:01
much.
42:01
Jonti Horner: M m. Take care. Thank you very much.
42:04
Andrew Dunkley: Professor Johnty Horner, professor of
42:05
Astrophysics at the University of Southern
42:07
Queensland, filling, uh, in for Fred Watson.
42:09
Fred Watson should be back, uh, next week
42:12
or later this week. I can't get my head
42:15
around when it'll be. It's a time slip thing.
42:18
Uh, but, uh, yeah, thanks to Jonty for
42:20
filling in and thanks to Huw in the studio,
42:22
who couldn't be with us today because he's
42:25
fake. Boom, boom. And from me, Andrew
42:28
Dunkley. Thanks for your company. We'll see
42:30
you on the next episode of Space Nuts.
42:32
Jonti Horner: Bye.
42:32
Andrew Dunkley: Bye.
42:34
Jonti Horner: You've been listening to the Space Nuts
42:36
podcast, available at
42:39
Apple Podcasts, Spotify,
42:41
iHeartRadio or your favourite podcast
42:44
player. You can also stream on
42:45
demand@bytes.um com
42:47
Andrew Dunkley: this has been another quality podcast
42:50
production from bytes.com
42:51
um.