Space Light, Cosmic Shields & Moon Mysteries

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Andrew Dunkley: Space Nuts is taking a bit of a break at the

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moment, Fred. Uh, and I will be back, uh, in

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the not too distant future with fresh

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episodes. In the meantime, enjoy some of, uh,

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the key episodes that we have presented over

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the years. Major events in

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astronomy and space science. And

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we'll see you real soon.

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Generic: Space Nuts.

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Andrew Dunkley: Hi there. Thanks for joining us on a Q and A

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edition of Space Nuts. I'm Andrew Dunkley,

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your host. Once again. Uh, thanks for joining

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us and, um, good to have your company. On

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this edition, we're, uh, answering some

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questions about light in space. Um, this

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one comes from Lee. He's asked a very

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interesting question. I've never actually

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thought about this particular

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concept, but, uh, it's a question that I

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think is worth answering for sure. That's why

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we included it. Fenton wants to know about,

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um, shielding astronauts in the

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outer reaches of the solar system. And he's

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got an idea on how to do that. Uh,

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Robert wants to, uh, talk about things we

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learned from the moon. And what if our moon

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wasn't the same as the moon is now?

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Would our learnings be different? That's a

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really interesting question. And Duncan wants

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to talk about ice giants. And why are they

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ice giants? Why don't we call them something

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else? That's all coming up shortly on this

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edition of Space Nuts.

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Generic: 15 seconds. Guidance is internal.

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10, 9. Ignition

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sequence start.

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Professor Fred Watson: Space Nuts.

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Generic: 5, 4, 3, 2.

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Duncan: 1.

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Generic: 2, 3, 4, 5, 5, 4, 3, 2,

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1.

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Professor Fred Watson: Space Nuts astronauts report at Beales.

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Good.

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Andrew Dunkley: Once again we welcome the one and only Fred

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Watson, astronomer at large. Hello, Fred.

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Professor Fred Watson: Hello, Andrew. How have you been since we

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last spoke?

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Andrew Dunkley: I haven't moved from this seat in all that

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time.

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Professor Fred Watson: Well, it's. I know. It's, uh. I can see

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you're glued to your chair there. Um,

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very much so. Uh, yes.

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Andrew Dunkley: Uh, shall we get, um, straight into it and

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answer some questions from our audience?

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Professor Fred Watson: Uh, that's a good idea.

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Andrew Dunkley: Yeah, it is. That's what we're here for.

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This first one, Fred, comes from Lee. He

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lives in New York City. Uh,

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he's asking how much light is in space.

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He'll qualify that question. For example, if

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you were to visit Voyager 1, where Voyager 1

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is today, would you be able to see. See it?

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Would you see just a silhouette? Would you be

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able to make out, uh, details and colors, if

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there are any colors on it? Uh, what about

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if, uh, you and Voyager were midway between

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the sun and Alpha Centauri? Uh, can we

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know a reasonably accurate answer,

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or is it pure speculation? Thanks. Love the

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show. Lee, from New York. I've never

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thought about that. I mean, we take for

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granted light on Earth because we're

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illuminated by the sun. But it's a bit

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different in other parts of the solar system

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and the universe in general. So, yeah, if we

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could just go, snap, we're out there next to

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Voyager 1. Could we actually see it? Is it

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illuminated in any way? Is it being

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illuminated by something? What would it be

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like?

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Professor Fred Watson: Uh, the answer is yes, you'd see it. Um, and

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so we're talking really now about the

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sensitivity of the human eye. Um, because,

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uh, with a camera, uh, you know,

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with long exposure settings and things you'd

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be able to see in great detail

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but thinking about the human eye. So,

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um, I used

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to work, as you know, at Siding Spring

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Observatory. Uh, I spent

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many hours, uh, outside at

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night. There it is a place that is truly

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dark. There's no interference from street

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lights. Uh, there are a few blobs of

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light on the horizon, but nothing that

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affects the pristine darkness of the night

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sky. And on a starry night

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with the sun not in the sky, you can see

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quite clearly. Um, there's enough

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light from the stars themselves to let

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you see where you're going. Uh, let

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you, you know, walk around and be

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quite confident that you're not going to fall

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off the mountain, as I nearly did one night

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when it was, uh, cloudy. I went out without

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my torch. I thought, oh, yeah, I'll see by

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the stars. But fortunately, unfortunately,

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the cloud had come in, I couldn't see

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anything and I nearly fell off the mountain.

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Uh, I didn't in the end. But, um.

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Andrew Dunkley: It's a long drop free.

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Professor Fred Watson: Yes, it is. Yes. It's quite a long drop

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anyway, uh, if you, uh, you know,

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normally on a starry night, you will see,

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um, by the light of the stars. Now,

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where voyager is Voyager 1, I

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just looked it up. Uh, it is, uh,

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at a distance from the sun

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in astronomical units, which is

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163 astronomical units. That's

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163 times the number

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of times the distance between the Earth and

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the sun. So that's 150 million

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kilometers. Multiply that by 163

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and you will get,

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uh. What do you get? I was looking for it in

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kilometers, but it's not there. I'll have to

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do the numbers anyway. It doesn't matter. The

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bad thing is, um, Its distance is

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22.55 light hours away.

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That's how long it takes, uh, the signal to

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get from Voyager to Earth. It's almost a day.

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It's almost a light day away. Um,

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so at that distance from the Sun,

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160 odd astronomical units,

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there's still significant light coming from

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the sun, not to mention Venus,

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uh, and um, you know, Jupiter and

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uh, the other planets. Mostly the sun though,

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you'd, you're being illuminated by the sun,

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so that's certainly opposite, uh, as

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compared with just being illuminated by the

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starry sky, which is what I was just talking

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about. So you'd see it really clearly. You

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uh, wouldn't have any problem making it out,

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assuming your eye was dark adapted.

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Andrew Dunkley: So, um, it's fairly bright out

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there.

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We talked about the sensitivity of the human

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eye as uh, you referred to

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how sort of small amount of light can we see

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as human beings?

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Professor Fred Watson: Um, I think there were some

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experiments. Let me think, was

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it one photon.

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Andrew Dunkley: Or one pixel like that?

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Professor Fred Watson: There was. That's right. We might have talked

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about this. There were experiments done that

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showed that the human eye is capable of

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detecting single photons. Uh, it was

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under special circumstances, but uh,

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and that is just extraordinary, um,

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when you think that the human eye can also

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cope with broad daylight. That's the

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amazing thing about the human eye. It can,

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you know, it's quite happy, uh, to see

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light, uh, one brightness and then

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a light that's only a millionth of as bright.

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Um, it's fine. You can deal with that. Ah.

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And that's a combination of what's called

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retinal bleaching and the iris of

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your eye opening and closing. It's all those

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things come together to give you this

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unbelievably versatile and sensitive

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tool with which we can look at the uh, our

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surroundings. Whether it's uh, the rock face

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I'm looking at now because that's what our

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backyard consists of, or whether it's uh,

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you know, the night sky where you're looking

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at faint objects, uh, in the sky.

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It's quite amazing.

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Andrew Dunkley: So even if you went deeper into space, way

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beyond our solar system, you, you would

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probably still see objects that you were

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near.

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Professor Fred Watson: There'd be enough light from the stars. The

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Milky Way is bright. Uh, it

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would, it would. You know, even if, as uh,

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Lee says, even if you were halfway between

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sun and Alpha Centauri, you'd still see it

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because of the ambient light, um,

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that's coming from, from the stars. Yeah.

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Andrew Dunkley: And you'd still see color because that's

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what. Well, it's dark enough, it might turn

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into the grays, which happens.

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Professor Fred Watson: That's right. Yeah. And I think that's

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likely. I think, I don't Think you would see

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color? Um, you. You would. Where it is now,

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there's enough light coming from the sun that

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you'd see color. But I think, uh, when you

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got further out, you would start to just see

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the. You know, as you said, that

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sort of pale gray appearance. Where you're

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looking at very low light. Low light levels

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indeed. Where the color cells aren't

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receptive.

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Andrew Dunkley: There you go. Lee, uh, the answer to your

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question's yes to all of the above,

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Basically.

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Duncan: Yeah.

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Andrew Dunkley: Great question. Excellent question.

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All right, let's move on. This is from

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Fenton.

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Duncan: Yeah. Hello, Fred and Andrew. This is

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Fenton contacting you from St.

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Paul, Minnesota, in the U.S.

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um, I sort of have a different type of

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astrophysical question for you.

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And this is on how to

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shield astronauts from

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radiation outside of the Van Allen Belt.

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Um, I was curious if you know of any pending

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technologies. That would allow this

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obvious choice would some people would say is

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lead. But I can think of several reasons why

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this is not a good idea. How about

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a miniature Van Allen Belt

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which could surround a

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spacecraft? How does that sound? How

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could this become, uh, reality?

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Thank you very much. I hope you like the

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question. Bye now.

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Andrew Dunkley: Thanks, Fenton. Fenton always has these

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intriguing thoughts. I've noticed in the

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Times that we've heard from him. Um, maybe we

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should start by explaining what the Van Allen

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Belt is. For those of us who just can't

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remember, like me.

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Professor Fred Watson: Um, it's, uh.

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So the Van Allen belts are the. Basically

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the. You know, the magnetic shielding

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around the Earth, uh, which is,

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uh. Caused by

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the magnetism of the Earth. It's caused by,

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uh, the fact that we've got an iron core. And

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basically, uh, it's in two parts. It's solid

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and liquid. So it acts like a dynamo. It's

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rotating. And that gives us this, uh.

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Exactly the protection that, um.

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Um. Um. Fenton is talking about.

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Andrew Dunkley: Um.

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Professor Fred Watson: Yeah, I was gonna refer.

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I'm a bit annoyed actually, because I've lost

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it. Uh, there is a very

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nice article on, um.

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Uh, it's actually on the, um.

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BBC's website. Uh,

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their sky at Night website. There's a lovely

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article on exactly this. Here it is. I found

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it. I hadn't lost it. How astronauts can hide

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from radiation on Mars. And it goes into,

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uh. Exactly the problem that,

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uh, Fenton's talking about. How do you

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present. How do you prevent, um, astronauts

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basically becoming irradiated.

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Uh, and over time it's

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basically lethal. Uh, because

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of the cosmic radiation that's coming down

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through space. Uh, and

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the cell damage, uh, in your

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body. Uh, and it can actually trigger cancer.

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So, um, the whole study of

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this is. Sorry,

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the thrust of this article, BBC sky at

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Night magazine, uh, is to

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discuss how you might protect astronauts,

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uh, from the radiation. Uh, and that's not

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just on Mars, but on route. Uh,

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okay, uh, the

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solution that Fenton has suggested

280
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is covered in a paragraph. I'm going to read

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it because we quoted where the source is. Uh,

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for example. All right,

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let me go back a paragraph. One method of

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helping astronauts to avoid the radiation on

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Mars is active shielding. For

286
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example, superconducting electromagnets could

287
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be used to create a powerful magnetic field

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to deflect the incoming charged radiation

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particles away, just as the Earth's field

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does. That's the Van Allen Belt. The problem

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is that such solutions can demand a lot of

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power to run, and the technology is a long

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way from being fully developed. An easier

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alternative is passive shielding. Simply

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placing a thick bulk of shielding material

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between the crew habitat and the sky.

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Uh, and then they go on to consider different

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materials. Aluminium, AKA

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aluminum, the metal that spacecraft are

300
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constructed from is actually a pretty bad

301
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radiation shield. Um, and

302
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they say when hit by an energetic cosmic

303
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ray, its atoms can shatter and fly onwards to

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create even more radiation particles.

305
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And Martian soil, the regolith, uh, which if

306
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you're on Mars, you might think about digging

307
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a hole there. Uh, it's got the same problem,

308
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but it's actually, uh, you know,

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abundant. Um, and so you

310
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could use that to dig a pole. If you

311
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put a 2 to 3 meter layer on top of

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your habitat, uh, then you'll,

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you'll get some protection. But, uh, the

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thing that surprised me, Andrew, uh, is once

315
00:13:20.530 --> 00:13:23.160
again, it comes from this same article. Uh,

316
00:13:23.370 --> 00:13:25.850
hydrogen is the best shielding material

317
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as it's light atoms. Yeah, it's light

318
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atoms. Uh, and by light I mean

319
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not heavy. Its light atoms don't create as

320
00:13:34.300 --> 00:13:37.180
much secondary radiation. And so tanks of

321
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rocket fuel or water, which is

322
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rich in hydrogen, placed over crew quarters

323
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could double up as effective radiation

324
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shields. I've heard that before that, um,

325
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one way of protecting your spacecraft as it

326
00:13:49.900 --> 00:13:52.340
flies to Mars is put it in a tank of water.

327
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Uh, it's the last thing you'd expect to do,

328
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but water is a good shielding material.

329
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And they also, uh, point out the

330
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alternative of hydrogen rich plastics like

331
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polyethylene could be used to cement

332
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regolith grains together. This is on Mars.

333
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And improve their shielding effect. Um,

334
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so, uh, if you want to read more about this,

335
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it's an article that originally appeared in

336
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the August 2022 issue of BBC

337
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sky at Night magazine. And it covers pretty

338
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well most of the ideas, uh, that have been,

339
00:14:23.810 --> 00:14:26.370
that have been suggested for this radiation

340
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issue. It's one that's got to, you know, it's

341
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got to find an answer soon because, uh,

342
00:14:31.650 --> 00:14:34.440
good old Elon and his starship, uh,

343
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is getting nearer to thinking about going to

344
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Mars. I don't think it's ever going to

345
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happen, but, uh, that's something he'll

346
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definitely be thinking about.

347
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Andrew Dunkley: Yes, indeed. He's too busy dealing with the

348
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Australian government at the moment.

349
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Professor Fred Watson: That's right.

350
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Andrew Dunkley: Some of the content on Twitter that the

351
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government wants to get rid of simply because

352
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of its, um, volatility. But anyway, that's a

353
00:14:55.530 --> 00:14:57.530
different story. Um, but there's plenty of

354
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water on Mars, so maybe, maybe creating those

355
00:15:00.410 --> 00:15:03.290
water barriers is probably the simplest thing

356
00:15:03.290 --> 00:15:05.050
to do. You've already got the material there.

357
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Professor Fred Watson: If you've landed in the right spot where

358
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you've got permafrost or whatever.

359
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Andrew Dunkley: That's the question. Yes, indeed. Uh, well

360
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done, Fenton. You actually happened across

361
00:15:14.050 --> 00:15:16.810
some of, uh, the answers too in, uh, asking

362
00:15:16.810 --> 00:15:19.410
your question. Uh, this is Space

363
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Nuts Andrew Dunkley here with Professor Fred

364
00:15:21.930 --> 00:15:22.570
Watson.

365
00:15:25.590 --> 00:15:27.670
Generic: Three, two, one.

366
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Andrew Dunkley: Space Nuts.

367
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Now, Fred, uh, our next question comes from

368
00:15:32.470 --> 00:15:34.790
Robert. Hi guys. Love your show. Sorry for

369
00:15:34.790 --> 00:15:36.590
the long question, but feel free to

370
00:15:36.590 --> 00:15:39.230
paraphrase, uh, or shorten it. Our

371
00:15:39.230 --> 00:15:42.150
moon is heavily crated and has given

372
00:15:42.150 --> 00:15:44.110
us a lot of insight into the history of the

373
00:15:44.110 --> 00:15:46.190
solar system and perhaps how the planets

374
00:15:46.190 --> 00:15:48.710
formed. But what if we had a moon

375
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like the icy moon Europa or the

376
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shrouded in, uh, haze Titan, both of

377
00:15:54.430 --> 00:15:56.730
which don't show immediate evidence of

378
00:15:56.730 --> 00:15:59.730
cratering? Would our theory about, uh, how

379
00:15:59.730 --> 00:16:02.090
the planets developed would, uh, be

380
00:16:02.090 --> 00:16:04.450
different? What other insights about our

381
00:16:04.450 --> 00:16:07.410
solar system would be missing or would

382
00:16:07.410 --> 00:16:10.010
we be missing? And lastly, uh, would we have

383
00:16:10.010 --> 00:16:12.610
spent, uh, or would we have sent people to

384
00:16:12.610 --> 00:16:14.960
land on such moons, that is, uh,

385
00:16:15.570 --> 00:16:18.410
would they be more dangerous for

386
00:16:18.410 --> 00:16:19.930
astronauts? Cheers.

387
00:16:19.930 --> 00:16:22.530
Robert in Vienna, Austria. Wow. I don't think

388
00:16:22.530 --> 00:16:24.250
we've had a question from Vienna before, have

389
00:16:24.250 --> 00:16:26.720
we? Lovely to hear from you, Robert.

390
00:16:27.120 --> 00:16:28.840
Professor Fred Watson: I think, I think Robert might have been in

391
00:16:28.840 --> 00:16:29.600
touch once before.

392
00:16:29.920 --> 00:16:32.600
Andrew Dunkley: Oh, I might have been too. It's very rare to

393
00:16:32.600 --> 00:16:33.600
hear from Vienna.

394
00:16:34.000 --> 00:16:35.560
Professor Fred Watson: Yeah, I was in Vienna at the beginning of

395
00:16:35.560 --> 00:16:37.360
last year and I think, I think we got

396
00:16:37.360 --> 00:16:39.040
something around about the same time. And I

397
00:16:39.040 --> 00:16:41.840
was waxing lyrical about being in Vienna at

398
00:16:41.840 --> 00:16:44.160
the UN when I was at, uh, the copywritten

399
00:16:44.160 --> 00:16:46.440
meeting. Anyway, that's another, another

400
00:16:46.440 --> 00:16:49.320
issue. Uh, what if we had a. Yeah, it's a

401
00:16:49.320 --> 00:16:51.730
really interesting question. Um,

402
00:16:52.310 --> 00:16:55.190
what would we not know about

403
00:16:55.590 --> 00:16:57.750
the solar system. If our moon

404
00:16:58.230 --> 00:17:00.950
was basically one

405
00:17:01.030 --> 00:17:03.670
that had been resurfaced in recent years

406
00:17:03.990 --> 00:17:06.830
or even millennia, because that's what makes

407
00:17:06.830 --> 00:17:09.110
the surface smooth. That's how we

408
00:17:09.110 --> 00:17:11.830
recognize, um, the

409
00:17:11.910 --> 00:17:14.230
fact that the universe. Sorry, that the.

410
00:17:15.350 --> 00:17:17.990
It's how we recognize the age of a surface is

411
00:17:17.990 --> 00:17:20.510
by how many craters it's got. The older, the

412
00:17:20.510 --> 00:17:22.809
older the surface, the more craters it has.

413
00:17:23.129 --> 00:17:25.809
And so the Moon's southern region, which is

414
00:17:25.809 --> 00:17:28.670
heavily cratered, as is the backside, tell

415
00:17:28.670 --> 00:17:31.089
uh, us that, uh, early on in the solar

416
00:17:31.089 --> 00:17:33.809
system's history, it was a very, um, wild and

417
00:17:33.809 --> 00:17:36.049
woolly place with things charging about all

418
00:17:36.049 --> 00:17:38.969
over and causing these craters. Now if we

419
00:17:38.969 --> 00:17:41.130
had a moon that was like Europa, that had,

420
00:17:41.130 --> 00:17:43.230
um, you know, icy, uh,

421
00:17:43.649 --> 00:17:46.369
geysers on it that basically covered up the

422
00:17:46.369 --> 00:17:49.289
craters, would we have known about that? My

423
00:17:49.369 --> 00:17:52.369
guess is yes, we would, because we'd

424
00:17:52.369 --> 00:17:54.030
see other bodies within the solar solar

425
00:17:54.030 --> 00:17:56.790
system, uh, like, you know, other moons,

426
00:17:56.950 --> 00:17:59.190
like, um, places like,

427
00:18:00.040 --> 00:18:02.630
um, Ceres, um, the biggest of the

428
00:18:02.630 --> 00:18:04.390
asteroids, the dwarf planet that dominates

429
00:18:04.390 --> 00:18:06.950
the asteroid belt that's heavily cratered.

430
00:18:07.260 --> 00:18:09.750
Uh, parts of Pluto are heavily cratered.

431
00:18:10.000 --> 00:18:10.140
Duncan: Um.

432
00:18:11.940 --> 00:18:14.790
Professor Fred Watson: Uh, Mimas, uh, one of Saturn's

433
00:18:15.190 --> 00:18:18.190
moons is heavily cratered too. So we'd

434
00:18:18.190 --> 00:18:20.270
know about it by looking at other objects.

435
00:18:20.270 --> 00:18:23.000
Even if our own moon was smoothly, uh,

436
00:18:23.570 --> 00:18:26.210
surfaced, um, it's, it's, uh.

437
00:18:26.370 --> 00:18:29.260
But the. Robert's last point, uh, on,

438
00:18:29.260 --> 00:18:31.730
um, this would, uh. We have sent

439
00:18:31.970 --> 00:18:34.970
people to land on such a moon. I,

440
00:18:34.970 --> 00:18:37.649
uh, think, um. I don't know. That's a really

441
00:18:37.649 --> 00:18:39.770
good question. I mean, we have sent people to

442
00:18:39.770 --> 00:18:42.610
land on our moon as it stands, uh, with an

443
00:18:42.610 --> 00:18:45.250
ancient surface. In fact, where they landed

444
00:18:45.250 --> 00:18:48.050
were more recent, uh, than the heavily

445
00:18:48.050 --> 00:18:49.450
cratered surfaces because they were

446
00:18:49.450 --> 00:18:52.210
principally in the maria, the basalt plains.

447
00:18:52.770 --> 00:18:55.010
Yeah, so maybe that

448
00:18:55.570 --> 00:18:58.090
suggests that we would have landed people on

449
00:18:58.090 --> 00:19:00.690
Europa as well, uh, because I think we

450
00:19:00.690 --> 00:19:01.130
probably.

451
00:19:01.130 --> 00:19:03.930
Andrew Dunkley: Yeah, we probably would because it would have

452
00:19:03.930 --> 00:19:06.730
a solid surface. There'd be places because it

453
00:19:06.730 --> 00:19:08.569
would be so close to us, we'd be able to

454
00:19:08.569 --> 00:19:11.410
examine and find the right landing points.

455
00:19:12.130 --> 00:19:15.010
Might be a bit more difficult with a moon

456
00:19:15.010 --> 00:19:17.730
that's shrouded in land gas.

457
00:19:17.890 --> 00:19:20.590
Professor Fred Watson: Yeah, yeah, that's right. And

458
00:19:20.590 --> 00:19:22.830
especially in places, um, like Titan.

459
00:19:23.320 --> 00:19:26.110
Uh, I still think

460
00:19:26.110 --> 00:19:28.550
we'd have done it actually. I think, um, you

461
00:19:28.550 --> 00:19:31.510
know, the JFK's, uh, promise

462
00:19:31.510 --> 00:19:33.590
to put astronauts on the moon would have

463
00:19:33.590 --> 00:19:35.710
still held good even if it had been a very

464
00:19:35.710 --> 00:19:38.570
different place. If it had been like IO, uh,

465
00:19:38.590 --> 00:19:40.870
it might have been a different story where,

466
00:19:40.870 --> 00:19:42.510
you know, you've got the most volcanically

467
00:19:42.510 --> 00:19:45.150
active body in the entire solar system with

468
00:19:45.150 --> 00:19:47.270
stuff going off all over the place, I think

469
00:19:47.270 --> 00:19:48.990
we might have been a bit more reluctant to

470
00:19:49.230 --> 00:19:49.900
land on eo.

471
00:19:49.900 --> 00:19:52.550
Andrew Dunkley: Uh, yes, possibly. So, uh,

472
00:19:52.750 --> 00:19:54.390
it would be interesting to have something

473
00:19:54.390 --> 00:19:57.390
different. But then if we'd always

474
00:19:57.390 --> 00:19:59.990
had an ice moon, we probably would have

475
00:19:59.990 --> 00:20:02.590
caught a question from, uh, Robert asking,

476
00:20:02.590 --> 00:20:04.910
what if we had a rocky moon now.

477
00:20:04.910 --> 00:20:07.830
Professor Fred Watson: Would we look, would we have

478
00:20:07.830 --> 00:20:07.950
a.

479
00:20:07.950 --> 00:20:10.110
Andrew Dunkley: Different interpretation of the formations of

480
00:20:10.110 --> 00:20:11.950
the planets if there was a rocky moon next to

481
00:20:11.950 --> 00:20:14.860
us instead of an ice moon? Yes. Um, in an

482
00:20:14.860 --> 00:20:16.660
alternative universe, Robert, you would have

483
00:20:16.660 --> 00:20:18.700
flipped your question. Good to hear from you.

484
00:20:18.700 --> 00:20:21.100
Hope all is well in Austria.

485
00:20:21.100 --> 00:20:23.380
Our final question for this episode comes

486
00:20:23.380 --> 00:20:24.660
from Duncan.

487
00:20:25.220 --> 00:20:27.620
Duncan: Hello, Duncan here from

488
00:20:27.620 --> 00:20:29.460
Weymouth in the uk.

489
00:20:30.340 --> 00:20:32.260
Again, a quick question.

490
00:20:34.260 --> 00:20:37.100
Just looking was doing some reading and I

491
00:20:37.100 --> 00:20:39.980
noticed that Uranus and Neptune

492
00:20:39.980 --> 00:20:42.410
are often referred to as ice

493
00:20:42.410 --> 00:20:44.450
giants. Now

494
00:20:45.090 --> 00:20:47.330
given that ice is

495
00:20:48.050 --> 00:20:50.530
basically just sort of like a rock form of

496
00:20:50.690 --> 00:20:53.450
water or CO2

497
00:20:53.450 --> 00:20:56.370
or whatever else, but basically just

498
00:20:56.370 --> 00:20:59.010
a solid form of it, why are they not just

499
00:20:59.010 --> 00:21:01.730
called rock giants? Why do we

500
00:21:02.610 --> 00:21:05.610
make the definition of ice rather than just

501
00:21:05.610 --> 00:21:08.310
calling them rock? It just seems

502
00:21:08.310 --> 00:21:11.110
odd because the little planets in the

503
00:21:11.110 --> 00:21:13.790
inner solar system are referred to as rocky

504
00:21:13.790 --> 00:21:16.590
planets. So given that they're also

505
00:21:17.230 --> 00:21:19.390
apparently rocky, why are they not called

506
00:21:19.390 --> 00:21:22.110
rocky giants? Okay,

507
00:21:22.510 --> 00:21:24.270
thank you, Bye.

508
00:21:24.990 --> 00:21:27.590
Andrew Dunkley: Thanks, Duncan. Appreciate your questions as

509
00:21:27.590 --> 00:21:30.190
always. Uh, yeah, why do we call them ice

510
00:21:30.190 --> 00:21:32.350
giants? Just for the sake of the exercise?

511
00:21:32.590 --> 00:21:35.550
Because there's gas giants and ice giants.

512
00:21:36.270 --> 00:21:39.150
Professor Fred Watson: Yeah, except one is a subset of the other.

513
00:21:39.390 --> 00:21:42.150
And so all four of the outer

514
00:21:42.150 --> 00:21:44.670
planets, Jupiter, Saturn, Neptune, sorry,

515
00:21:44.670 --> 00:21:47.390
Uranus, Neptune, they're all gas giants

516
00:21:47.710 --> 00:21:50.510
because they have, uh, high mass.

517
00:21:51.180 --> 00:21:54.140
Uh, um, you know, much more,

518
00:21:54.140 --> 00:21:56.670
um, in the case of Jupiter certainly, than,

519
00:21:56.700 --> 00:21:59.000
uh, our own planet. Um,

520
00:21:59.390 --> 00:22:02.150
the. They've got their giants, they're big,

521
00:22:02.230 --> 00:22:05.030
they've got high mass, and they don't

522
00:22:05.030 --> 00:22:07.910
have a visible surface,

523
00:22:08.070 --> 00:22:10.030
which is why they call gas giants, because

524
00:22:10.030 --> 00:22:12.150
all we see is a gassy envelope.

525
00:22:12.670 --> 00:22:15.470
Um, just to go to the last of

526
00:22:15.470 --> 00:22:17.510
Duncan's questions there, we wouldn't call

527
00:22:17.910 --> 00:22:20.230
the inner planets rocky giants because

528
00:22:20.230 --> 00:22:22.030
they're not giants. They're, uh, kind of

529
00:22:22.030 --> 00:22:23.790
normal planet size. You know, if you, if you

530
00:22:23.790 --> 00:22:25.430
think of the Earth as being your standard

531
00:22:25.430 --> 00:22:27.890
planet, then, uh, Mercury,

532
00:22:28.290 --> 00:22:31.130
Venus and Mars are similar, ah, in size.

533
00:22:31.130 --> 00:22:33.730
They're, uh, all smaller. Venus is about the

534
00:22:33.730 --> 00:22:35.730
same size, but Mercury and Mars of course are

535
00:22:35.730 --> 00:22:38.570
smaller. Uh, so it's only when you

536
00:22:38.570 --> 00:22:40.970
compare with the size of Earth that you'd

537
00:22:40.970 --> 00:22:42.850
start talking about giants because they are

538
00:22:42.850 --> 00:22:45.010
much, much bigger than Earth. And so that's

539
00:22:45.010 --> 00:22:47.670
the gas giants. So why Are, uh,

540
00:22:48.290 --> 00:22:50.610
Uranus and Neptune called ice giants

541
00:22:51.170 --> 00:22:53.380
because they have

542
00:22:53.620 --> 00:22:56.580
hazes of ice in their atmosphere.

543
00:22:57.220 --> 00:23:00.220
So. And that's the trick. It's not

544
00:23:00.220 --> 00:23:02.340
a solid surface. It's not rock.

545
00:23:03.220 --> 00:23:06.060
It's a haze. It's kind of like, uh, a dust

546
00:23:06.060 --> 00:23:08.860
of ice which permeates their atmosphere.

547
00:23:08.860 --> 00:23:11.830
And it's water ice, in fact, uh,

548
00:23:11.830 --> 00:23:14.740
mostly. Uh, so that's why they

549
00:23:14.740 --> 00:23:17.420
called ice giants, because unlike Saturn and

550
00:23:17.420 --> 00:23:20.060
Jupiter, which don't have these hazes,

551
00:23:20.190 --> 00:23:20.510
uh,

552
00:23:23.020 --> 00:23:25.820
the two outer planets, Uranus and

553
00:23:25.820 --> 00:23:28.340
Neptune, do they have ice hazes in their

554
00:23:28.340 --> 00:23:29.580
atmosphere. Hence the name.

555
00:23:30.780 --> 00:23:33.180
Andrew Dunkley: Okay. Yeah. And of course, the last episode

556
00:23:33.180 --> 00:23:35.620
we learned there wasn't much water in

557
00:23:35.620 --> 00:23:36.500
Jupiter's atmosphere.

558
00:23:36.500 --> 00:23:37.020
Professor Fred Watson: That's right.

559
00:23:38.620 --> 00:23:41.620
Andrew Dunkley: In the two outer gas giants. Yeah,

560
00:23:41.620 --> 00:23:43.140
it sounds like there is. Is that why they're

561
00:23:43.140 --> 00:23:43.900
a different color?

562
00:23:44.800 --> 00:23:47.790
Professor Fred Watson: Yes, yes, I think that's right. Um,

563
00:23:48.000 --> 00:23:50.490
and also their atmospheric constituents are,

564
00:23:50.490 --> 00:23:53.160
uh, different. They don't have the same belt

565
00:23:53.160 --> 00:23:56.000
structure that Saturn and Jupiter do. It may

566
00:23:56.000 --> 00:23:58.480
be that that's because any belts that exist

567
00:23:58.480 --> 00:24:00.320
are, uh, much lower in the atmosphere, and so

568
00:24:00.320 --> 00:24:03.160
you don't see them. Um, yeah, I

569
00:24:03.160 --> 00:24:06.000
mean, uh, there's a strong body of,

570
00:24:07.930 --> 00:24:10.160
uh, advocacy within the space

571
00:24:10.320 --> 00:24:12.130
fraternity to get

572
00:24:14.050 --> 00:24:16.890
more spacecraft out to Uranus and

573
00:24:16.890 --> 00:24:19.730
Neptune because they're the two planets about

574
00:24:19.730 --> 00:24:22.730
which we know least. Um, and, uh, will

575
00:24:22.730 --> 00:24:23.890
be good to know more.

576
00:24:24.610 --> 00:24:25.090
Duncan: Yeah.

577
00:24:25.890 --> 00:24:27.690
Andrew Dunkley: Well, if you sit down in snow for long

578
00:24:27.690 --> 00:24:30.130
enough, Uranus turns into a nice giant.

579
00:24:32.050 --> 00:24:33.170
I couldn't help it.

580
00:24:33.170 --> 00:24:35.010
Professor Fred Watson: Sorry. Uh, yeah,

581
00:24:36.610 --> 00:24:39.170
which is why we call it Uranus in politics.

582
00:24:39.570 --> 00:24:40.610
I know, I know.

583
00:24:41.010 --> 00:24:43.170
Andrew Dunkley: Yeah. But it's just a joke.

584
00:24:43.390 --> 00:24:43.950
Duncan: Got to tell.

585
00:24:43.950 --> 00:24:44.590
Professor Fred Watson: It's just.

586
00:24:44.670 --> 00:24:45.550
Andrew Dunkley: You have to.

587
00:24:46.510 --> 00:24:49.350
Professor Fred Watson: Yes, I. I blame Johannes Boda, who is

588
00:24:49.350 --> 00:24:52.070
the person who chose the name. He's fine in

589
00:24:52.070 --> 00:24:54.910
German. There's nothing wrong with

590
00:24:55.070 --> 00:24:57.990
German ruins. All the jokes

591
00:24:57.990 --> 00:24:58.270
there.

592
00:24:59.790 --> 00:25:01.830
Andrew Dunkley: All right, so, yes, uh, they're ice giants

593
00:25:01.830 --> 00:25:03.270
for a very good reason, Duncan. Because

594
00:25:03.270 --> 00:25:05.310
they've got ice in them in, uh, the

595
00:25:05.310 --> 00:25:07.070
atmosphere. But, uh, technically speaking,

596
00:25:07.070 --> 00:25:09.710
they are, in fact, gas giants. But, yes,

597
00:25:10.130 --> 00:25:11.890
you differentiate them because of their

598
00:25:12.210 --> 00:25:14.490
substantially different atmospheres. There

599
00:25:14.490 --> 00:25:14.930
you are.

600
00:25:15.010 --> 00:25:15.850
Professor Fred Watson: Thanks, Duncan.

601
00:25:15.850 --> 00:25:17.370
Andrew Dunkley: Great to hear from you. Great to, uh, hear

602
00:25:17.370 --> 00:25:18.970
from everybody. Thanks for sending in your

603
00:25:18.970 --> 00:25:20.570
questions. Don't forget, you can send in

604
00:25:20.570 --> 00:25:22.410
questions via our website, spacenuts

605
00:25:22.410 --> 00:25:25.410
podcast.com spacenuts IO

606
00:25:25.410 --> 00:25:26.970
and all you have to do is click on the

607
00:25:26.970 --> 00:25:29.290
various links on the right hand side, send us

608
00:25:29.290 --> 00:25:31.250
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609
00:25:31.810 --> 00:25:33.850
Uh, or you can send us text and audio

610
00:25:33.850 --> 00:25:36.730
questions via the AMA M tab up the top. It's

611
00:25:36.730 --> 00:25:38.450
your choice. Don't forget to tell us who you

612
00:25:38.450 --> 00:25:39.610
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613
00:25:39.610 --> 00:25:42.110
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614
00:25:42.110 --> 00:25:44.350
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615
00:25:44.350 --> 00:25:46.630
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616
00:25:46.630 --> 00:25:49.430
can subscribe just by pressing the subscribe

617
00:25:49.430 --> 00:25:52.390
button below. Which, yes, it's down

618
00:25:52.390 --> 00:25:55.030
there somewhere. I don't know one of those

619
00:25:55.030 --> 00:25:57.630
places. Fred, as always, thank you so much.

620
00:25:58.270 --> 00:25:59.950
Professor Fred Watson: Pleasure, Andrew. See you soon.

621
00:26:00.270 --> 00:26:03.150
Andrew Dunkley: Okay. Fred Watson, astronomer at large. We'll

622
00:26:03.150 --> 00:26:04.950
catch him on the next episode of Space Nuts.

623
00:26:04.950 --> 00:26:07.190
We might catch Huw then as well because, um,

624
00:26:09.310 --> 00:26:11.830
not here today. Didn't even call in sick. I

625
00:26:11.830 --> 00:26:14.270
need a note. And from me, Andrew Dunkley.

626
00:26:14.270 --> 00:26:16.150
Thanks very much for your company. We'll see

627
00:26:16.150 --> 00:26:18.230
you again soon on the next episode of Space

628
00:26:18.230 --> 00:26:19.390
Nuts. Bye. Bye.

629
00:26:20.590 --> 00:26:22.790
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630
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