Andrew Dunkley: Space Nuts is taking a bit of a break at the
moment, Fred. Uh, and I will be back, uh, in
the not too distant future with fresh
episodes. In the meantime, enjoy some of, uh,
the key episodes that we have presented over
the years. Major events in
astronomy and space science. And
we'll see you real soon.
Generic: Space Nuts.
Andrew Dunkley: Hi there. Thanks for joining us on a Q and A
edition of Space Nuts. I'm Andrew Dunkley,
your host. Once again. Uh, thanks for joining
us and, um, good to have your company. On
this edition, we're, uh, answering some
questions about light in space. Um, this
one comes from Lee. He's asked a very
interesting question. I've never actually
thought about this particular
concept, but, uh, it's a question that I
think is worth answering for sure. That's why
we included it. Fenton wants to know about,
um, shielding astronauts in the
outer reaches of the solar system. And he's
got an idea on how to do that. Uh,
Robert wants to, uh, talk about things we
learned from the moon. And what if our moon
wasn't the same as the moon is now?
Would our learnings be different? That's a
really interesting question. And Duncan wants
to talk about ice giants. And why are they
ice giants? Why don't we call them something
else? That's all coming up shortly on this
edition of Space Nuts.
Generic: 15 seconds. Guidance is internal.
10, 9. Ignition
sequence start.
Professor Fred Watson: Space Nuts.
Generic: 5, 4, 3, 2.
Duncan: 1.
Generic: 2, 3, 4, 5, 5, 4, 3, 2,
1.
Professor Fred Watson: Space Nuts astronauts report at Beales.
Good.
Andrew Dunkley: Once again we welcome the one and only Fred
Watson, astronomer at large. Hello, Fred.
Professor Fred Watson: Hello, Andrew. How have you been since we
last spoke?
Andrew Dunkley: I haven't moved from this seat in all that
time.
Professor Fred Watson: Well, it's. I know. It's, uh. I can see
you're glued to your chair there. Um,
very much so. Uh, yes.
Andrew Dunkley: Uh, shall we get, um, straight into it and
answer some questions from our audience?
Professor Fred Watson: Uh, that's a good idea.
Andrew Dunkley: Yeah, it is. That's what we're here for.
This first one, Fred, comes from Lee. He
lives in New York City. Uh,
he's asking how much light is in space.
He'll qualify that question. For example, if
you were to visit Voyager 1, where Voyager 1
is today, would you be able to see. See it?
Would you see just a silhouette? Would you be
able to make out, uh, details and colors, if
there are any colors on it? Uh, what about
if, uh, you and Voyager were midway between
the sun and Alpha Centauri? Uh, can we
know a reasonably accurate answer,
or is it pure speculation? Thanks. Love the
show. Lee, from New York. I've never
thought about that. I mean, we take for
granted light on Earth because we're
illuminated by the sun. But it's a bit
different in other parts of the solar system
and the universe in general. So, yeah, if we
could just go, snap, we're out there next to
Voyager 1. Could we actually see it? Is it
illuminated in any way? Is it being
illuminated by something? What would it be
like?
Professor Fred Watson: Uh, the answer is yes, you'd see it. Um, and
so we're talking really now about the
sensitivity of the human eye. Um, because,
uh, with a camera, uh, you know,
with long exposure settings and things you'd
be able to see in great detail
but thinking about the human eye. So,
um, I used
to work, as you know, at Siding Spring
Observatory. Uh, I spent
many hours, uh, outside at
night. There it is a place that is truly
dark. There's no interference from street
lights. Uh, there are a few blobs of
light on the horizon, but nothing that
affects the pristine darkness of the night
sky. And on a starry night
with the sun not in the sky, you can see
quite clearly. Um, there's enough
light from the stars themselves to let
you see where you're going. Uh, let
you, you know, walk around and be
quite confident that you're not going to fall
off the mountain, as I nearly did one night
when it was, uh, cloudy. I went out without
my torch. I thought, oh, yeah, I'll see by
the stars. But fortunately, unfortunately,
the cloud had come in, I couldn't see
anything and I nearly fell off the mountain.
Uh, I didn't in the end. But, um.
Andrew Dunkley: It's a long drop free.
Professor Fred Watson: Yes, it is. Yes. It's quite a long drop
anyway, uh, if you, uh, you know,
normally on a starry night, you will see,
um, by the light of the stars. Now,
where voyager is Voyager 1, I
just looked it up. Uh, it is, uh,
at a distance from the sun
in astronomical units, which is
163 astronomical units. That's
163 times the number
of times the distance between the Earth and
the sun. So that's 150 million
kilometers. Multiply that by 163
and you will get,
uh. What do you get? I was looking for it in
kilometers, but it's not there. I'll have to
do the numbers anyway. It doesn't matter. The
bad thing is, um, Its distance is
22.55 light hours away.
That's how long it takes, uh, the signal to
get from Voyager to Earth. It's almost a day.
It's almost a light day away. Um,
so at that distance from the Sun,
160 odd astronomical units,
there's still significant light coming from
the sun, not to mention Venus,
uh, and um, you know, Jupiter and
uh, the other planets. Mostly the sun though,
you'd, you're being illuminated by the sun,
so that's certainly opposite, uh, as
compared with just being illuminated by the
starry sky, which is what I was just talking
about. So you'd see it really clearly. You
uh, wouldn't have any problem making it out,
assuming your eye was dark adapted.
Andrew Dunkley: So, um, it's fairly bright out
there.
We talked about the sensitivity of the human
eye as uh, you referred to
how sort of small amount of light can we see
as human beings?
Professor Fred Watson: Um, I think there were some
experiments. Let me think, was
it one photon.
Andrew Dunkley: Or one pixel like that?
Professor Fred Watson: There was. That's right. We might have talked
about this. There were experiments done that
showed that the human eye is capable of
detecting single photons. Uh, it was
under special circumstances, but uh,
and that is just extraordinary, um,
when you think that the human eye can also
cope with broad daylight. That's the
amazing thing about the human eye. It can,
you know, it's quite happy, uh, to see
light, uh, one brightness and then
a light that's only a millionth of as bright.
Um, it's fine. You can deal with that. Ah.
And that's a combination of what's called
retinal bleaching and the iris of
your eye opening and closing. It's all those
things come together to give you this
unbelievably versatile and sensitive
tool with which we can look at the uh, our
surroundings. Whether it's uh, the rock face
I'm looking at now because that's what our
backyard consists of, or whether it's uh,
you know, the night sky where you're looking
at faint objects, uh, in the sky.
It's quite amazing.
Andrew Dunkley: So even if you went deeper into space, way
beyond our solar system, you, you would
probably still see objects that you were
near.
Professor Fred Watson: There'd be enough light from the stars. The
Milky Way is bright. Uh, it
would, it would. You know, even if, as uh,
Lee says, even if you were halfway between
sun and Alpha Centauri, you'd still see it
because of the ambient light, um,
that's coming from, from the stars. Yeah.
Andrew Dunkley: And you'd still see color because that's
what. Well, it's dark enough, it might turn
into the grays, which happens.
Professor Fred Watson: That's right. Yeah. And I think that's
likely. I think, I don't Think you would see
color? Um, you. You would. Where it is now,
there's enough light coming from the sun that
you'd see color. But I think, uh, when you
got further out, you would start to just see
the. You know, as you said, that
sort of pale gray appearance. Where you're
looking at very low light. Low light levels
indeed. Where the color cells aren't
receptive.
Andrew Dunkley: There you go. Lee, uh, the answer to your
question's yes to all of the above,
Basically.
Duncan: Yeah.
Andrew Dunkley: Great question. Excellent question.
All right, let's move on. This is from
Fenton.
Duncan: Yeah. Hello, Fred and Andrew. This is
Fenton contacting you from St.
Paul, Minnesota, in the U.S.
um, I sort of have a different type of
astrophysical question for you.
And this is on how to
shield astronauts from
radiation outside of the Van Allen Belt.
Um, I was curious if you know of any pending
technologies. That would allow this
obvious choice would some people would say is
lead. But I can think of several reasons why
this is not a good idea. How about
a miniature Van Allen Belt
which could surround a
spacecraft? How does that sound? How
could this become, uh, reality?
Thank you very much. I hope you like the
question. Bye now.
Andrew Dunkley: Thanks, Fenton. Fenton always has these
intriguing thoughts. I've noticed in the
Times that we've heard from him. Um, maybe we
should start by explaining what the Van Allen
Belt is. For those of us who just can't
remember, like me.
Professor Fred Watson: Um, it's, uh.
So the Van Allen belts are the. Basically
the. You know, the magnetic shielding
around the Earth, uh, which is,
uh. Caused by
the magnetism of the Earth. It's caused by,
uh, the fact that we've got an iron core. And
basically, uh, it's in two parts. It's solid
and liquid. So it acts like a dynamo. It's
rotating. And that gives us this, uh.
Exactly the protection that, um.
Um. Um. Fenton is talking about.
Andrew Dunkley: Um.
Professor Fred Watson: Yeah, I was gonna refer.
I'm a bit annoyed actually, because I've lost
it. Uh, there is a very
nice article on, um.
Uh, it's actually on the, um.
BBC's website. Uh,
their sky at Night website. There's a lovely
article on exactly this. Here it is. I found
it. I hadn't lost it. How astronauts can hide
from radiation on Mars. And it goes into,
uh. Exactly the problem that,
uh, Fenton's talking about. How do you
present. How do you prevent, um, astronauts
basically becoming irradiated.
Uh, and over time it's
basically lethal. Uh, because
of the cosmic radiation that's coming down
through space. Uh, and
the cell damage, uh, in your
body. Uh, and it can actually trigger cancer.
So, um, the whole study of
this is. Sorry,
the thrust of this article, BBC sky at
Night magazine, uh, is to
discuss how you might protect astronauts,
uh, from the radiation. Uh, and that's not
just on Mars, but on route. Uh,
okay, uh, the
solution that Fenton has suggested
is covered in a paragraph. I'm going to read
it because we quoted where the source is. Uh,
for example. All right,
let me go back a paragraph. One method of
helping astronauts to avoid the radiation on
Mars is active shielding. For
example, superconducting electromagnets could
be used to create a powerful magnetic field
to deflect the incoming charged radiation
particles away, just as the Earth's field
does. That's the Van Allen Belt. The problem
is that such solutions can demand a lot of
power to run, and the technology is a long
way from being fully developed. An easier
alternative is passive shielding. Simply
placing a thick bulk of shielding material
between the crew habitat and the sky.
Uh, and then they go on to consider different
materials. Aluminium, AKA
aluminum, the metal that spacecraft are
constructed from is actually a pretty bad
radiation shield. Um, and
they say when hit by an energetic cosmic
ray, its atoms can shatter and fly onwards to
create even more radiation particles.
And Martian soil, the regolith, uh, which if
you're on Mars, you might think about digging
a hole there. Uh, it's got the same problem,
but it's actually, uh, you know,
abundant. Um, and so you
could use that to dig a pole. If you
put a 2 to 3 meter layer on top of
your habitat, uh, then you'll,
you'll get some protection. But, uh, the
thing that surprised me, Andrew, uh, is once
again, it comes from this same article. Uh,
hydrogen is the best shielding material
as it's light atoms. Yeah, it's light
atoms. Uh, and by light I mean
not heavy. Its light atoms don't create as
much secondary radiation. And so tanks of
rocket fuel or water, which is
rich in hydrogen, placed over crew quarters
could double up as effective radiation
shields. I've heard that before that, um,
one way of protecting your spacecraft as it
flies to Mars is put it in a tank of water.
Uh, it's the last thing you'd expect to do,
but water is a good shielding material.
And they also, uh, point out the
alternative of hydrogen rich plastics like
polyethylene could be used to cement
regolith grains together. This is on Mars.
And improve their shielding effect. Um,
so, uh, if you want to read more about this,
it's an article that originally appeared in
the August 2022 issue of BBC
sky at Night magazine. And it covers pretty
well most of the ideas, uh, that have been,
that have been suggested for this radiation
issue. It's one that's got to, you know, it's
got to find an answer soon because, uh,
good old Elon and his starship, uh,
is getting nearer to thinking about going to
Mars. I don't think it's ever going to
happen, but, uh, that's something he'll
definitely be thinking about.
Andrew Dunkley: Yes, indeed. He's too busy dealing with the
Australian government at the moment.
Professor Fred Watson: That's right.
Andrew Dunkley: Some of the content on Twitter that the
government wants to get rid of simply because
of its, um, volatility. But anyway, that's a
different story. Um, but there's plenty of
water on Mars, so maybe, maybe creating those
water barriers is probably the simplest thing
to do. You've already got the material there.
Professor Fred Watson: If you've landed in the right spot where
you've got permafrost or whatever.
Andrew Dunkley: That's the question. Yes, indeed. Uh, well
done, Fenton. You actually happened across
some of, uh, the answers too in, uh, asking
your question. Uh, this is Space
Nuts Andrew Dunkley here with Professor Fred
Watson.
Generic: Three, two, one.
Andrew Dunkley: Space Nuts.
Now, Fred, uh, our next question comes from
Robert. Hi guys. Love your show. Sorry for
the long question, but feel free to
paraphrase, uh, or shorten it. Our
moon is heavily crated and has given
us a lot of insight into the history of the
solar system and perhaps how the planets
formed. But what if we had a moon
like the icy moon Europa or the
shrouded in, uh, haze Titan, both of
which don't show immediate evidence of
cratering? Would our theory about, uh, how
the planets developed would, uh, be
different? What other insights about our
solar system would be missing or would
we be missing? And lastly, uh, would we have
spent, uh, or would we have sent people to
land on such moons, that is, uh,
would they be more dangerous for
astronauts? Cheers.
Robert in Vienna, Austria. Wow. I don't think
we've had a question from Vienna before, have
we? Lovely to hear from you, Robert.
Professor Fred Watson: I think, I think Robert might have been in
touch once before.
Andrew Dunkley: Oh, I might have been too. It's very rare to
hear from Vienna.
Professor Fred Watson: Yeah, I was in Vienna at the beginning of
last year and I think, I think we got
something around about the same time. And I
was waxing lyrical about being in Vienna at
the UN when I was at, uh, the copywritten
meeting. Anyway, that's another, another
issue. Uh, what if we had a. Yeah, it's a
really interesting question. Um,
what would we not know about
the solar system. If our moon
was basically one
that had been resurfaced in recent years
or even millennia, because that's what makes
the surface smooth. That's how we
recognize, um, the
fact that the universe. Sorry, that the.
It's how we recognize the age of a surface is
by how many craters it's got. The older, the
older the surface, the more craters it has.
And so the Moon's southern region, which is
heavily cratered, as is the backside, tell
uh, us that, uh, early on in the solar
system's history, it was a very, um, wild and
woolly place with things charging about all
over and causing these craters. Now if we
had a moon that was like Europa, that had,
um, you know, icy, uh,
geysers on it that basically covered up the
craters, would we have known about that? My
guess is yes, we would, because we'd
see other bodies within the solar solar
system, uh, like, you know, other moons,
like, um, places like,
um, Ceres, um, the biggest of the
asteroids, the dwarf planet that dominates
the asteroid belt that's heavily cratered.
Uh, parts of Pluto are heavily cratered.
Duncan: Um.
Professor Fred Watson: Uh, Mimas, uh, one of Saturn's
moons is heavily cratered too. So we'd
know about it by looking at other objects.
Even if our own moon was smoothly, uh,
surfaced, um, it's, it's, uh.
But the. Robert's last point, uh, on,
um, this would, uh. We have sent
people to land on such a moon. I,
uh, think, um. I don't know. That's a really
good question. I mean, we have sent people to
land on our moon as it stands, uh, with an
ancient surface. In fact, where they landed
were more recent, uh, than the heavily
cratered surfaces because they were
principally in the maria, the basalt plains.
Yeah, so maybe that
suggests that we would have landed people on
Europa as well, uh, because I think we
probably.
Andrew Dunkley: Yeah, we probably would because it would have
a solid surface. There'd be places because it
would be so close to us, we'd be able to
examine and find the right landing points.
Might be a bit more difficult with a moon
that's shrouded in land gas.
Professor Fred Watson: Yeah, yeah, that's right. And
especially in places, um, like Titan.
Uh, I still think
we'd have done it actually. I think, um, you
know, the JFK's, uh, promise
to put astronauts on the moon would have
still held good even if it had been a very
different place. If it had been like IO, uh,
it might have been a different story where,
you know, you've got the most volcanically
active body in the entire solar system with
stuff going off all over the place, I think
we might have been a bit more reluctant to
land on eo.
Andrew Dunkley: Uh, yes, possibly. So, uh,
it would be interesting to have something
different. But then if we'd always
had an ice moon, we probably would have
caught a question from, uh, Robert asking,
what if we had a rocky moon now.
Professor Fred Watson: Would we look, would we have
a.
Andrew Dunkley: Different interpretation of the formations of
the planets if there was a rocky moon next to
us instead of an ice moon? Yes. Um, in an
alternative universe, Robert, you would have
flipped your question. Good to hear from you.
Hope all is well in Austria.
Our final question for this episode comes
from Duncan.
Duncan: Hello, Duncan here from
Weymouth in the uk.
Again, a quick question.
Just looking was doing some reading and I
noticed that Uranus and Neptune
are often referred to as ice
giants. Now
given that ice is
basically just sort of like a rock form of
water or CO2
or whatever else, but basically just
a solid form of it, why are they not just
called rock giants? Why do we
make the definition of ice rather than just
calling them rock? It just seems
odd because the little planets in the
inner solar system are referred to as rocky
planets. So given that they're also
apparently rocky, why are they not called
rocky giants? Okay,
thank you, Bye.
Andrew Dunkley: Thanks, Duncan. Appreciate your questions as
always. Uh, yeah, why do we call them ice
giants? Just for the sake of the exercise?
Because there's gas giants and ice giants.
Professor Fred Watson: Yeah, except one is a subset of the other.
And so all four of the outer
planets, Jupiter, Saturn, Neptune, sorry,
Uranus, Neptune, they're all gas giants
because they have, uh, high mass.
Uh, um, you know, much more,
um, in the case of Jupiter certainly, than,
uh, our own planet. Um,
the. They've got their giants, they're big,
they've got high mass, and they don't
have a visible surface,
which is why they call gas giants, because
all we see is a gassy envelope.
Um, just to go to the last of
Duncan's questions there, we wouldn't call
the inner planets rocky giants because
they're not giants. They're, uh, kind of
normal planet size. You know, if you, if you
think of the Earth as being your standard
planet, then, uh, Mercury,
Venus and Mars are similar, ah, in size.
They're, uh, all smaller. Venus is about the
same size, but Mercury and Mars of course are
smaller. Uh, so it's only when you
compare with the size of Earth that you'd
start talking about giants because they are
much, much bigger than Earth. And so that's
the gas giants. So why Are, uh,
Uranus and Neptune called ice giants
because they have
hazes of ice in their atmosphere.
So. And that's the trick. It's not
a solid surface. It's not rock.
It's a haze. It's kind of like, uh, a dust
of ice which permeates their atmosphere.
And it's water ice, in fact, uh,
mostly. Uh, so that's why they
called ice giants, because unlike Saturn and
Jupiter, which don't have these hazes,
uh,
the two outer planets, Uranus and
Neptune, do they have ice hazes in their
atmosphere. Hence the name.
Andrew Dunkley: Okay. Yeah. And of course, the last episode
we learned there wasn't much water in
Jupiter's atmosphere.
Professor Fred Watson: That's right.
Andrew Dunkley: In the two outer gas giants. Yeah,
it sounds like there is. Is that why they're
a different color?
Professor Fred Watson: Yes, yes, I think that's right. Um,
and also their atmospheric constituents are,
uh, different. They don't have the same belt
structure that Saturn and Jupiter do. It may
be that that's because any belts that exist
are, uh, much lower in the atmosphere, and so
you don't see them. Um, yeah, I
mean, uh, there's a strong body of,
uh, advocacy within the space
fraternity to get
more spacecraft out to Uranus and
Neptune because they're the two planets about
which we know least. Um, and, uh, will
be good to know more.
Duncan: Yeah.
Andrew Dunkley: Well, if you sit down in snow for long
enough, Uranus turns into a nice giant.
I couldn't help it.
Professor Fred Watson: Sorry. Uh, yeah,
which is why we call it Uranus in politics.
I know, I know.
Andrew Dunkley: Yeah. But it's just a joke.
Duncan: Got to tell.
Professor Fred Watson: It's just.
Andrew Dunkley: You have to.
Professor Fred Watson: Yes, I. I blame Johannes Boda, who is
the person who chose the name. He's fine in
German. There's nothing wrong with
German ruins. All the jokes
there.
Andrew Dunkley: All right, so, yes, uh, they're ice giants
for a very good reason, Duncan. Because
they've got ice in them in, uh, the
atmosphere. But, uh, technically speaking,
they are, in fact, gas giants. But, yes,
you differentiate them because of their
substantially different atmospheres. There
you are.
Professor Fred Watson: Thanks, Duncan.
Andrew Dunkley: Great to hear from you. Great to, uh, hear
from everybody. Thanks for sending in your
questions. Don't forget, you can send in
questions via our website, spacenuts
podcast.com spacenuts IO
and all you have to do is click on the
various links on the right hand side, send us
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Uh, or you can send us text and audio
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button below. Which, yes, it's down
there somewhere. I don't know one of those
places. Fred, as always, thank you so much.
Professor Fred Watson: Pleasure, Andrew. See you soon.
Andrew Dunkley: Okay. Fred Watson, astronomer at large. We'll
catch him on the next episode of Space Nuts.
We might catch Huw then as well because, um,
not here today. Didn't even call in sick. I
need a note. And from me, Andrew Dunkley.
Thanks very much for your company. We'll see
you again soon on the next episode of Space
Nuts. Bye. Bye.
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