Space Light, Cosmic Shields & Moon Mysteries

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.

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. 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. 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. 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.

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. 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. There you go. Lee, uh, the answer to your question's yes to all of the above, Basically.

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.

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. 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. Yes, indeed. He's too busy dealing with the Australian government at the moment. Professor Fred Watson: That's right. 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. 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.

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. 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.

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.

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.

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. 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.

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.

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. 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.

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.

Professor Fred Watson: Thanks, Duncan. 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 your question. That's audio questions only. Uh, or you can send us text and audio questions via the AMA M tab up the top. It's

your choice. Don't forget to tell us who you are and where you're from and have a look around while you're on our website or join our media social, uh, media platforms, Facebook, Instagram, YouTube Music, where you can subscribe just by pressing the subscribe 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.

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.