Stellar Q&A: Rusty Moons, Space Stations & What If Earth Disappeared?

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Andrew Dunkley: Hi there. Thanks for joining us. This is a Q

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and A edition of Space Nuts. Not only do

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we talk astronomy and space science, we

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pretend to answer questions from our

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wonderful, uh, audience. We've got a bunch

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today. Bill, uh, is asking about small

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bodies in solar systems.

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I don't think that's got anything to do with

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weight loss, but we'll see. Uh, Peter is

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asking about, uh, leaving something behind

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that could survive the destruction of Earth.

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Wow, that's a what if question. Tiny moons

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and giant planets and issues with a

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giant space station. Those are, uh,

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questions we will endeavour to answer today

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on this edition of Space Nuts.

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Professor Fred Watson: 15 seconds. Guidance is internal.

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10, 9. Ignition

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sequence start. Space Nuts. 5, 4,

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3, 2. 1. 2, 3, 4, 5, 5,

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4, 3, 2, 1. Space Nuts

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astronauts report it feels good.

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Andrew Dunkley: And with us again is Professor Fred Watson

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Watson, um, astronomer at large. Hello,

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Fred Watson.

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Professor Fred Watson: Hello, Andrew. Uh, fancy seeing you here.

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Andrew Dunkley: Yes, unusual. Both wearing black.

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Professor Fred Watson: Is it black? Uh,

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it is, yeah.

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It's the, um, this is the, the shirt

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that if I have Jordy sitting on my lap, you,

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you can't see him at all because it's exactly

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the same colour as he is. Jet black.

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Andrew Dunkley: Uh, that'll make a good Instagram photo.

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Professor Fred Watson: Well, it might do. Just two eyes poking

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out.

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Andrew Dunkley: Now, um, we've got a lot to get through, so

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we'll start straight away with, uh, a

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question that comes from Bill

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and he asks if small bodies in the solar

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system formed by accretion of fine dust

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and gas, why are they not all

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fluffy, low gravity powder

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puffs? Um, we're

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all dense stony. Uh, or, uh, were

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all dense stony or metallic objects

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originally part of a larger body that could,

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could differentiate under, uh, decent

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gravity levels, then were smashed to small

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pieces in collisions. Uh, thanks for the

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great podcasts. Uh, that comes from Bill.

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Um, so, yeah, why isn't everything

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puffy?

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Professor Fred Watson: Um, I think it was to start with. Well, there

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you go. Yeah. So,

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um, people often say,

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people who should know better often say that

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if you want to know how planet formation

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starts, look under your bed because

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the bits of fluff that you tend to find under

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your bed are, uh, made of dust

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sticking together, uh, usually by

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electrostatic forces, which we think played a

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part in the early, uh, evolution of planets.

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Uh, these things stick together. You build

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up bigger and bigger fluff balls. Um,

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and eventually the

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fluff balls, because. Exactly,

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um, as Bill says, they do tend to collide

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with one another. We're now talking about a

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very, a very, very

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dense, dusty environment. We're talking about

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the protoplanetary disc that Surrounded the

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sun. Uh, very dusty place

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with lots of, um, basically

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lots of capacity for uh, dust

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fluff balls to build up to have bigger and

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bigger sizes. Eventually

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these various forces uh, will

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cause the dust balls to sort of

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collapse. Probably collisions will contribute

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to, um, by that I mean that they

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tend to lose their porosity. In other words,

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they become more solid.

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Um, now having said that, there are objects

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in space that we know are very

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porous.

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Andrew Dunkley: Um, well we've found powder puff planets,

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haven't we?

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Professor Fred Watson: Yes, that's right. Uh, yes, almost exactly

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a good description of them. I'm just thinking

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more nearer to home though. Um, uh,

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uh, Phobos, the larger moon of Mars,

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is thought to have a composition a bit like

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um. God, the word's gone.

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Uh, stuff that forms when

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eruptions, um, take place

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underwater.

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Andrew Dunkley: Like a honeycomb.

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Professor Fred Watson: Yes, um, but it's got a word. Oh, that's

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ridiculous. When you get to a certain age,

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words just disappear. It'll come to me

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in a minute. I know. Uh, but yeah,

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the stuff that floats on the water

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underground eruption. Pumice. The very word.

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That's what I was looking for. Thank you.

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Thank you, Andrew. So pumice is, you know,

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it's porous, it's a stony

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structure, uh, that's got a lot of gaps in it

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and I guess that might well be an

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intermediate structure of many of these

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objects. Ah, as I said, Phobos is like

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that, um, one of Saturn's moons and I

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can't remember which one it is, it's the one

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shaped like a potato. That'll probably come

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to me in a minute as well. Uh, it's also

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got that sort of structure. Um, so

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maybe, you know, when you get things like

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that colour colliding, uh, then

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and building up in size, then you're

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eventually going to get to this situation

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where gravity takes over, uh, and it

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pulls um, these low

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density materials into something

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more solid.

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Andrew Dunkley: Um, is it a malthea, A mouth?

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Professor Fred Watson: No, uh, it's one with a better known name.

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Ah. It's very highly cratered and

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potato shaped.

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Andrew Dunkley: Ah, okay.

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Professor Fred Watson: It's uh, yeah, it's one of the most cratered

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objects in the, in the solar system. I'm

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annoyed. I can't remember it. It's

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ridiculous. I was getting too

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old for this, Andrew.

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Andrew Dunkley: Oh no you're not.

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Professor Fred Watson: No, no, maybe I'm not.

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Andrew Dunkley: No, it keeps your brain active.

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Professor Fred Watson: Well, except it's demonstrating quite

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clearly, uh, that the memory banks are

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disappearing. Anyway, um, it'll come to me,

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as I said, in a minute. It's not Enceladus,

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but it's something like that. Uh, so, uh,

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if you've got, you know, gravity taking over,

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then you' to get basically solid rock

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emerging from that. Uh, uh,

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as Bill says, dense, stony or metallic

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objects, that's basically what they turn

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into. And then they collide. Uh,

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um, the larger objects are differentiated.

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That means the heavy stuff sinks to the

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middle. Uh, exactly as Bill says, but they

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collide. And that's how you can get stony

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meteorites or metallic

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meteorites because the metal tends to sink

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mostly, uh, to the middle. So I

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think, um, it is a natural process, but it's

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one in a way it's counterintuitive to us. You

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know, how do you get from a dust, a fluff

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ball under your bed. How do you get from that

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to a stone to a rock?

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Andrew Dunkley: Gravity.

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Professor Fred Watson: Yes, that's right, gravity. But over a long

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period of time. Uh, and probably heat as

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well. You know, you've got heat processes

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coming into this too. So, um,

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uh, I, uh,

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think uh, what um,

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Bill's saying is right. If the small bodies

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in the solar system formed by accretion of

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fine dust and gas, why are they not all

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fluffy, low gravity powder puffs? Well, some

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of them are and that's. Perhaps you could

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describe them like um,

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Phobos. Uh, perhaps he could describe them as

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unevolved. They haven't evolved much.

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I think it might be Hyperion, the one I'm

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thinking of.

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Andrew Dunkley: Okay.

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Professor Fred Watson: I think it might be Hyperion. I'll have a

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look, Have a look, See if it's um, shaped

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like a potato and got lots of graters on it.

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Andrew Dunkley: Yeah. Well, there's got to be a photo of it

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somewhere. Yes, it is.

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Professor Fred Watson: Yeah.

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Andrew Dunkley: Yeah.

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Professor Fred Watson: Okay, good.

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Andrew Dunkley: It's got, it's got that big, um.

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It's got a massive crater in it actually.

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Professor Fred Watson: Yeah. Yes, yes. Yeah, yeah.

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So, um, so these are you got

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Andrew Dunkley: there in the end, Fred Watson.

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Professor Fred Watson: In the end? Yeah, it's. Yes. It's just the

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processing speeds down a bit. I must be

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offline or something like that. Probably need

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a reboot. God, don't say that. Might

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never come back.

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Andrew Dunkley: Well, that's happened. My car did that while

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we were away. Uh, came home

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and to, uh, to, to stop falling asleep. We

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decided we'd go and do the groceries straight

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after getting off a long haul flight.

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Professor Fred Watson: Oh, yes. Yeah.

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Andrew Dunkley: And the car wouldn't start.

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Yeah, the battery died, so.

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Professor Fred Watson: Oh, the battery died.

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Andrew Dunkley: Yeah. That's another 315 bucks. Thank you

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very much.

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Professor Fred Watson: Yes.

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Andrew Dunkley: Anyway, it happens. It was four years. It

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lasted four years.

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Professor Fred Watson: Oh, that's all right. That's about as long as

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you get from a battery.

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Andrew Dunkley: Yes, it is indeed. But thanks, Bill, for the

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question. Uh, I think you answered it

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yourself, but, um, y, uh, although

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if you're, um, someone like me,

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um, and you don't clean under the bed, uh,

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you can watch planets evolve.

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That's what's happening.

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Professor Fred Watson: Yep, you can.

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Andrew Dunkley: All right, uh, thanks, Bill.

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Our next question, uh, is

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coming from Peter.

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Speaker C: Hello, this is Peter in Lamington

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Spa. And I want to know

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what would it take for

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humans to

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make something that will survive

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the destruction of Earth

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and then potentially be incorporated

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into a new planet when all the bits of Earth

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become a different planet and sometime in the

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future, Is it possible?

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Andrew Dunkley: Have a good evening. Thank you, Peter. That's

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a what if question. Uh, yeah, I wonder.

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That's a very. It's a long haul science

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fiction situation. You build something

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that will survive the destruction of Earth

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and then somehow the planet reconstitutes

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itself and billions of years later there's an

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intelligent race living on the planet and

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they go, oh, hello. What's all this then?

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Professor Fred Watson: This is some leftover of humankind? Yeah,

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whatever they were.

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Andrew Dunkley: There was a TV series that I watched many

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years ago called Childhood's End, and

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it was about the destruction of Earth. And

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before it, before it was destroyed,

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um, the humans asked the aliens

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that rescued the children, basically, um,

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can we just leave something behind so they

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know we were here? So they left. Music.

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Professor Fred Watson: Lovely. I like that. Yes, I like that very

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much.

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Andrew Dunkley: I just spoiled the whole thing too, by the

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way.

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Professor Fred Watson: Um, I don't think you did really, uh,

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because. Yes, that's a kind of concept, isn't

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it, that you're leaving behind? Uh, and

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my mind, when I read Peter's question or

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heard Peter's question, went to

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more concrete things, not necessarily made of

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concrete.

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Andrew Dunkley: I was about to say that.

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Professor Fred Watson: But in a sense we've already done it, Andrew,

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because there are five

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little spacecraft which are,

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ah, absolute, um,

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uh, monuments to humanity leaving the

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solar system, um, way, way beyond

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the orbit of Earth. Voyager 1 is

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probably beyond. Actually,

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that's not quite true. I, uh, was going to

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say beyond the limits of the sun. When it

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turns into a red giant star, um,

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Voyager 1 will probably survive,

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um, the red giant phase of

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our sun, uh, which will take place in

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a few billion years, three or four

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billion years. Um, it'll survive that,

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but might not survive the formation of

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a planetary nebula when you've got hot gas

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coming off the, uh, being puffed off the

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surface of the red Giant. It might actually

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melt in that because it's because planetary

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nebulae get to be light years in diameter.

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Uh, our Voyager, uh, is only, well, it's

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nearly a light day away. Um, on the other

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hand, we've got 3 or 4 billion years to play

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with because the sun's not going to do

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anything really nasty, um, within that

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time. So yes, Voyager 1 will be well out of

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the way, probably will survive the

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eventual evolution, um, and

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uh, final evolutionary stages of the sun when

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it actually turns into a white dwarf star. So

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yes, uh, those spacecraft, Voyager

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1, Voyager 2, Pioneer 10, Pioneer 11,

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is that right? And New Horizons,

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they're the five that are leaving the solar

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system which will probably outlive humanity.

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Andrew Dunkley: They probably won't. They probably won't be

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the last.

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Professor Fred Watson: They won't be the last. No, I think that's

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right. Uh, but,

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um, I mean

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the idea of, um, the Earth, uh,

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being destroyed, the

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kinds of things that might destroy the Earth,

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ah, are first of all, that eventual

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evolution of the sun to a red giant star that

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will almost certainly melt the Earth because

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the Sun's, um, surface, put

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it that way, will be, um, a quarter of a

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mile from the Earth. And we might be on the

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inside of, uh, could even,

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uh, overtake the planet Mars. Uh,

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so it's hard to imagine how you'd rebuild

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the Earth, uh, from the debris that is really

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just molecules, uh, because it'll have been

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vaporised. Um, so I think, uh,

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in addressing this question, you've really

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got to think about things that uh, have

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left the Earth. And that really basically

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pushes your mind to spacecraft. There are

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some spacecraft which are, uh, in orbit

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around the sun, uh, which

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are spacecraft that have been sent

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exploring the inner solar system. Mostly

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these days we try and get rid of them. We

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plunge them, uh, into either, uh, Jupiter or

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Saturn. Jupiter in the case of Galileo,

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Saturn in the case of Cassini. Uh, those

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spacecraft were destroyed purposely so that

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they didn't accidentally land on one of the

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moons of Jupiter or Saturn and leave microbes

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behind. Um, so you're really talking about

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something that's left the solar system. And

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that leaves those five spacecraft

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I've mentioned. And they definitely will

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outlast humankind.

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Andrew Dunkley: Okay, there you have it, Peter. Um, so we've

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already done it kind of, uh, I don't think

344
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you could probably build some kind

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of monolith or something that would survive

346
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the red giant phase of

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the sun and, and overwhelm Earth. That would

348
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all get destroyed, um, unless you did

349
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it deep down inside. But I don't even Know,

350
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if you could do that, I think a

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red giant phase would be pretty cataclysmic,

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wouldn't it?

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Professor Fred Watson: Yeah. Uh, yes. If your planet's being

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vaporised. Your planet's being vaporised. It

355
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is, yeah.

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Andrew Dunkley: Indeed. Thank you, Peter. Great to hear from

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you. I love what if questions. So, um, thanks

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for serving it up. This is Space Nuts with

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00:14:55.000 --> 00:14:57.200
Andrew Dunkley and Professor Fred Watson

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Watson.

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Professor Fred Watson: Swiften Tranquilly Base here.

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00:15:03.760 --> 00:15:06.160
The eagle has landed. Space Nuts.

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Andrew Dunkley: Our next question, Fred Watson, comes from

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00:15:08.559 --> 00:15:11.520
Martin in Heswall. Heswall, is that right?

365
00:15:11.840 --> 00:15:13.200
Professor Fred Watson: Yes, Heswall. Yeah.

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Andrew Dunkley: Where's that? I'm going to guess it's the UK

367
00:15:15.160 --> 00:15:15.680
somewhere.

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00:15:16.160 --> 00:15:19.120
Professor Fred Watson: It is indeed. It's, um, uh, on the Wirral

369
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Peninsula. So if you think of Liverpool,

370
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you've been to Liverpool? I have. And done

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the Beatles experience.

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Andrew Dunkley: Yes.

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Professor Fred Watson: Is that right? Yes. Yeah. Well, across the

374
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River Mersey from Liverpool is the Wirral

375
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Peninsula and Heswall is

376
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one of the towns on that, um, I've said

377
00:15:35.750 --> 00:15:38.070
before, and in fact we've had listener

378
00:15:38.070 --> 00:15:40.630
comments about this, I had a girlfriend once

379
00:15:40.630 --> 00:15:43.190
who lived on the Wirral Peninsula and so I

380
00:15:43.190 --> 00:15:45.190
used to be a very regular visitor there to a

381
00:15:45.190 --> 00:15:46.950
village called Barnston, which was not that

382
00:15:46.950 --> 00:15:49.190
far from Heswall. There you are. All right.

383
00:15:49.510 --> 00:15:51.500
It's very pretty too. It's a pretty village.

384
00:15:51.810 --> 00:15:52.210
Hmm.

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00:15:52.290 --> 00:15:55.210
Andrew Dunkley: Okay. Just wanted to know where you

386
00:15:55.210 --> 00:15:57.210
were, Martin. So thank you for that. Uh, I

387
00:15:57.210 --> 00:15:58.970
hope, uh, you'll answer this question.

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According to Wikipedia, there are, uh, now

389
00:16:02.130 --> 00:16:04.930
known to be 292 satellites,

390
00:16:05.500 --> 00:16:07.970
uh, with confirmed orbits around Saturn.

391
00:16:07.970 --> 00:16:10.370
Presumably, many of these moons are very

392
00:16:10.370 --> 00:16:13.370
small. So is there a minimum size for

393
00:16:13.370 --> 00:16:16.250
an object to be called a moon? And is

394
00:16:16.250 --> 00:16:18.210
there a minimum size for an object to

395
00:16:18.210 --> 00:16:20.850
maintain a stable orbit around a planet?

396
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Uh, as all the giant plan have ring

397
00:16:24.550 --> 00:16:27.550
systems, would the smaller particles just

398
00:16:27.550 --> 00:16:30.390
be absorbed into the rings? Conversely, I

399
00:16:30.390 --> 00:16:32.950
suppose that many objects could be knocked

400
00:16:32.950 --> 00:16:34.670
out of the rings to form independent

401
00:16:34.670 --> 00:16:36.430
satellites that may become permanently

402
00:16:36.430 --> 00:16:39.070
separated from the rings. Will Saturn get,

403
00:16:39.770 --> 00:16:42.190
uh, to 1,000 moons or more?

404
00:16:42.590 --> 00:16:44.990
Also, uh, can you recommend a website

405
00:16:45.310 --> 00:16:47.830
which has the latest data about, uh, the

406
00:16:47.830 --> 00:16:50.790
solar system, as the numbers vary from one

407
00:16:50.790 --> 00:16:53.630
site to the next, no doubt due to how recent

408
00:16:53.630 --> 00:16:56.450
the information is. Keep up the work. Thanks,

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00:16:56.450 --> 00:16:58.890
Martin. Um, that's a good question because,

410
00:16:58.970 --> 00:17:01.930
yeah, we know that the ring systems,

411
00:17:02.530 --> 00:17:04.770
um, are full of dust and ice, but they've

412
00:17:04.770 --> 00:17:07.210
also got larger objects that are referred to

413
00:17:07.290 --> 00:17:08.970
regularly as moons.

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00:17:10.470 --> 00:17:12.170
Professor Fred Watson: Um, it's interesting, this was one of the

415
00:17:12.170 --> 00:17:14.890
exact questions that came up in the Q and

416
00:17:14.890 --> 00:17:17.490
A night, the science in the pub night that we

417
00:17:17.490 --> 00:17:20.450
had on Lord Howe island at the Dark Sky

418
00:17:20.450 --> 00:17:20.890
Festival.

419
00:17:21.290 --> 00:17:23.210
Andrew Dunkley: That was Martin. He was, he was there.

420
00:17:24.610 --> 00:17:25.570
No he probably wasn't.

421
00:17:26.050 --> 00:17:28.970
Professor Fred Watson: Carry on. There was a Martin

422
00:17:28.970 --> 00:17:29.250
there.

423
00:17:30.370 --> 00:17:31.810
Andrew Dunkley: Did he have a British accent?

424
00:17:32.570 --> 00:17:35.330
Professor Fred Watson: Uh no, he's quite Australian but

425
00:17:35.330 --> 00:17:38.330
he's not from Haswell. But yeah, uh,

426
00:17:38.610 --> 00:17:41.330
but interesting coincidence to get the two

427
00:17:41.410 --> 00:17:44.290
and I don't think at the moment there is

428
00:17:45.410 --> 00:17:47.810
a uh limiting size

429
00:17:48.530 --> 00:17:51.170
to differentiate between a ring particle

430
00:17:52.380 --> 00:17:54.390
and a moon. Um

431
00:17:55.340 --> 00:17:58.260
so uh, it

432
00:17:58.260 --> 00:18:01.260
is a great question um how

433
00:18:01.260 --> 00:18:03.820
do you define a moon around a planet which is

434
00:18:03.900 --> 00:18:06.380
festooned with objects orbiting around it

435
00:18:07.259 --> 00:18:09.620
in the form of rings. So we think the rings

436
00:18:09.620 --> 00:18:12.460
of Saturn are uh the debris

437
00:18:12.540 --> 00:18:14.940
of uh probably a satellite

438
00:18:15.500 --> 00:18:18.220
that came within the Roche limit

439
00:18:18.540 --> 00:18:21.350
of the the planet. The Roche limit

440
00:18:21.350 --> 00:18:24.230
being the point at which uh a solid

441
00:18:24.230 --> 00:18:27.150
object can't actually survive within

442
00:18:27.230 --> 00:18:30.030
that distance. In other words that close to

443
00:18:30.030 --> 00:18:32.910
the planet. Um and so

444
00:18:32.910 --> 00:18:35.550
it broke up into lots of small particles.

445
00:18:36.670 --> 00:18:39.630
Probably the biggest ring sized

446
00:18:40.190 --> 00:18:42.830
sorry the biggest ring particles

447
00:18:43.690 --> 00:18:46.590
uh, uh in the region of 10 metres

448
00:18:47.830 --> 00:18:49.590
because the rings themselves are only about

449
00:18:49.590 --> 00:18:52.190
100 metres thick. Yeah it's quite

450
00:18:52.190 --> 00:18:52.950
staggering.

451
00:18:54.390 --> 00:18:57.350
Um and 250,000 kilometres

452
00:18:57.350 --> 00:19:00.230
in diameter. So yes it's quite a contrast.

453
00:19:00.830 --> 00:19:03.470
Um a sort of blade of material in space is

454
00:19:03.470 --> 00:19:05.530
the way I've always described it. Uh

455
00:19:07.190 --> 00:19:09.950
but some of the smaller satellites of

456
00:19:09.950 --> 00:19:12.910
Saturn and some of them are actually embedded

457
00:19:12.910 --> 00:19:15.710
in the ring system. Uh some of them

458
00:19:15.710 --> 00:19:17.670
are measured in

459
00:19:18.470 --> 00:19:20.790
single digit kilometres so they're not that

460
00:19:21.190 --> 00:19:23.590
much more than

461
00:19:24.310 --> 00:19:27.310
the biggest ring particles and I'm not sure

462
00:19:27.310 --> 00:19:30.150
that there is a definition between the two.

463
00:19:30.750 --> 00:19:33.030
Uh and in a sense you could say that every

464
00:19:33.590 --> 00:19:36.070
solid object within Saturn's rings is a

465
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satellite and so you're then talking about

466
00:19:38.750 --> 00:19:41.110
millions or maybe even billions of

467
00:19:41.510 --> 00:19:44.430
moons of Saturn. Uh it's a great

468
00:19:44.430 --> 00:19:46.510
question and one that I don't have an answer

469
00:19:46.510 --> 00:19:49.210
for and I perhaps ough who have checked it

470
00:19:49.210 --> 00:19:51.890
out in the wake of the question that came uh

471
00:19:52.290 --> 00:19:55.090
at the science in the pub science in the bolo

472
00:19:55.330 --> 00:19:58.090
on Lord Howe island the week before last when

473
00:19:58.090 --> 00:19:59.730
we did the Dark Sky Festival there.

474
00:19:59.890 --> 00:20:02.770
Andrew Dunkley: Yeah, yeah he also

475
00:20:02.770 --> 00:20:05.750
asked about uh website. Yeah ah

476
00:20:05.850 --> 00:20:08.770
well I just did a quick cheque and top uh of

477
00:20:08.770 --> 00:20:11.770
the tree is NASA for up

478
00:20:11.770 --> 00:20:14.050
to date solar system information.

479
00:20:15.250 --> 00:20:17.610
Uh yeah, uh but the other ones that you could

480
00:20:17.610 --> 00:20:19.800
try uh the sky

481
00:20:19.950 --> 00:20:22.670
mylive.com apparently is

482
00:20:22.670 --> 00:20:25.630
very highly rated um says

483
00:20:25.630 --> 00:20:27.750
it offers comprehensive information about the

484
00:20:27.750 --> 00:20:29.870
most interesting celestial objects and sets

485
00:20:29.870 --> 00:20:32.270
tools designed to support the exploration et

486
00:20:32.270 --> 00:20:34.590
cetera. Uh the planets today

487
00:20:35.790 --> 00:20:38.630
uh is also there and there's a specific uh

488
00:20:38.910 --> 00:20:41.590
NASA page that you can look up

489
00:20:41.590 --> 00:20:44.490
called Eyes on the Solar System. Um,

490
00:20:44.670 --> 00:20:47.670
and it provides a 3D solar

491
00:20:47.670 --> 00:20:50.590
scape if you like. So there's a few

492
00:20:50.590 --> 00:20:53.290
ideas if you uh, want to um, chase them

493
00:20:53.290 --> 00:20:56.010
up, Martin. But um, there'd be plenty more

494
00:20:56.010 --> 00:20:58.490
out there. There's um, just to name a few

495
00:20:58.490 --> 00:21:00.090
more, Global Solar Atlas,

496
00:21:00.790 --> 00:21:03.690
um, the NOAA homepage,

497
00:21:03.850 --> 00:21:06.330
the Space Weather Prediction homepage, um,

498
00:21:06.730 --> 00:21:09.450
and Planet Labs just to name a few. So

499
00:21:10.030 --> 00:21:13.010
um, and they're constantly being updated as

500
00:21:13.010 --> 00:21:15.930
far as I'm aware, as things change or as

501
00:21:15.930 --> 00:21:18.210
new things come to light. So might be worth

502
00:21:18.210 --> 00:21:21.000
chasing all of those up because they do seem

503
00:21:21.000 --> 00:21:23.400
to be, um, highly credentialed. Fred Watson?

504
00:21:24.280 --> 00:21:27.200
Professor Fred Watson: Yeah, I was going to say I usually go

505
00:21:27.200 --> 00:21:29.720
to NASA when I want the latest figures on

506
00:21:30.120 --> 00:21:33.000
this sort of thing. M. So,

507
00:21:33.190 --> 00:21:35.640
uh, you've confirmed that and also given a

508
00:21:35.640 --> 00:21:37.160
few other options as well, which is good.

509
00:21:37.160 --> 00:21:38.960
Andrew Dunkley: Yep, plenty to look at. There's lots of great

510
00:21:38.960 --> 00:21:41.360
sites out there. Just don't go to the ones

511
00:21:41.360 --> 00:21:43.960
that start with um, words

512
00:21:43.960 --> 00:21:45.460
starting with F and e.

513
00:21:51.370 --> 00:21:53.050
Professor Fred Watson: I was thought you were going to say don't go

514
00:21:53.050 --> 00:21:55.450
to ones that start with space and have knots

515
00:21:55.450 --> 00:21:55.930
in the.

516
00:21:57.610 --> 00:21:59.210
Andrew Dunkley: That's, that's good advice too.

517
00:21:59.210 --> 00:21:59.690
Professor Fred Watson: Yeah.

518
00:22:00.730 --> 00:22:02.210
Andrew Dunkley: Okay, thank you, Martin.

519
00:22:02.210 --> 00:22:05.210
Our final question today comes from

520
00:22:05.370 --> 00:22:06.010
Finn.

521
00:22:06.410 --> 00:22:08.770
Speaker C: Hello, Andrew and Fred Watson. It's Finn from

522
00:22:08.770 --> 00:22:11.570
NAN in the Adelaide Hills in South

523
00:22:11.570 --> 00:22:14.010
Australia. And a happy May 4th to you as

524
00:22:14.010 --> 00:22:16.540
well. I was watching a 40 year old

525
00:22:16.540 --> 00:22:18.500
documentary the other day about a space

526
00:22:18.500 --> 00:22:21.220
station orbiting a planet. And this

527
00:22:21.220 --> 00:22:24.220
space station, um, if it was to orbit

528
00:22:24.220 --> 00:22:26.180
the Earth, I would like to know how that

529
00:22:26.180 --> 00:22:28.620
would affect the orbit of our

530
00:22:28.700 --> 00:22:31.540
moon and maybe the orbit of the Earth

531
00:22:31.540 --> 00:22:34.460
around the sun. This space station being 150

532
00:22:34.460 --> 00:22:36.980
kilometres diameter with a mass of about 10

533
00:22:36.980 --> 00:22:39.980
to the 15 tonne. Um, I'd

534
00:22:39.980 --> 00:22:42.860
like to know, and if for whatever reason this

535
00:22:42.860 --> 00:22:45.500
space station happened to destroy our planet,

536
00:22:46.100 --> 00:22:48.140
how would the rest of the planets in the

537
00:22:48.140 --> 00:22:50.500
solar system be affected by that

538
00:22:50.500 --> 00:22:53.220
destruction? One last question,

539
00:22:53.640 --> 00:22:56.500
um, to you both is, um, what was the first

540
00:22:56.580 --> 00:22:57.700
animal in space?

541
00:22:58.260 --> 00:22:59.220
Andrew Dunkley: It was a dog.

542
00:22:59.540 --> 00:23:02.380
Speaker C: Ah, ah, don't think it was that. It was

543
00:23:02.380 --> 00:23:04.700
actually the cow because it jumped over the

544
00:23:04.700 --> 00:23:06.180
moon. Thank you.

545
00:23:06.980 --> 00:23:07.780
Professor Fred Watson: Dear, oh dear.

546
00:23:07.780 --> 00:23:09.900
Andrew Dunkley: Finn. That was probably one of the worst dad

547
00:23:09.900 --> 00:23:12.820
jokes I've ever heard. So,

548
00:23:13.220 --> 00:23:15.740
but you know, most welcome on this show.

549
00:23:19.340 --> 00:23:20.940
Professor Fred Watson: Yeah, it was good. It wasn't, wasn't even

550
00:23:20.940 --> 00:23:21.940
adequate that one, was it?

551
00:23:21.940 --> 00:23:22.500
Andrew Dunkley: No, it wasn't.

552
00:23:22.500 --> 00:23:23.260
Professor Fred Watson: No, no.

553
00:23:23.340 --> 00:23:26.060
Andrew Dunkley: We strive for adequacy and we didn't even

554
00:23:26.060 --> 00:23:28.860
achieve that. Thank you, Finn.

555
00:23:28.880 --> 00:23:31.500
Uh, so the substance of his question was,

556
00:23:31.760 --> 00:23:34.580
uh, you got a space Station orbiting Earth

557
00:23:34.580 --> 00:23:36.860
at 150 kilometres in

558
00:23:37.260 --> 00:23:40.260
diameter or whatever. Uh what kind

559
00:23:40.260 --> 00:23:42.900
of effect could that have on the orbit of the

560
00:23:42.900 --> 00:23:45.740
Moon? And ye

561
00:23:46.040 --> 00:23:47.520
get to the next part of the question after

562
00:23:47.520 --> 00:23:49.400
that. Could it have, would that have any.

563
00:23:49.560 --> 00:23:50.520
That's pretty big.

564
00:23:52.040 --> 00:23:54.560
Professor Fred Watson: It's well the critical thing was the mass

565
00:23:54.560 --> 00:23:57.080
which um Fin actually

566
00:23:57.640 --> 00:24:00.560
mentioned as being 10 to

567
00:24:00.560 --> 00:24:03.240
the 15 tonnes I think is what he said

568
00:24:04.330 --> 00:24:07.000
uh which is 10 to the 18

569
00:24:07.000 --> 00:24:09.480
kilogrammes. Um and

570
00:24:10.840 --> 00:24:12.920
so the bottom line is that's not enough

571
00:24:14.410 --> 00:24:17.240
uh the Earth just. Yeah, nah, ah forget it.

572
00:24:17.400 --> 00:24:20.280
So the earth's uh six times 10 to the

573
00:24:20.280 --> 00:24:22.920
24 kilogrammes. So it's

574
00:24:23.270 --> 00:24:25.960
um, what is it? It's

575
00:24:26.680 --> 00:24:29.640
six uh orders of magnitude bigger in

576
00:24:29.640 --> 00:24:32.600
mass than uh this space station

577
00:24:33.240 --> 00:24:35.320
and so the other. So

578
00:24:37.240 --> 00:24:39.600
it's certainly not going to affect the orbit

579
00:24:39.600 --> 00:24:42.530
of the ah Earth. It might perturb

580
00:24:42.530 --> 00:24:44.450
the orbit of the Moon a bit.

581
00:24:45.100 --> 00:24:47.770
Uh one of the considerations will be how far

582
00:24:47.770 --> 00:24:50.490
away is it from the

583
00:24:50.490 --> 00:24:53.410
Earth? And uh, our last question

584
00:24:53.730 --> 00:24:56.130
actually pointed to an answer to that

585
00:24:56.609 --> 00:24:59.370
and that is that if it's 150

586
00:24:59.370 --> 00:25:02.290
kilometres in diameter it has to be a long

587
00:25:02.290 --> 00:25:04.850
way away or else it's within the Roche limit

588
00:25:06.050 --> 00:25:08.050
of the Earth uh and it would just break up

589
00:25:08.130 --> 00:25:10.650
straight away. So I'm not going to guess how

590
00:25:10.650 --> 00:25:12.530
far away it has to be but it'll be a long way

591
00:25:12.830 --> 00:25:15.230
the earth if it's 150 kilometres in diameter.

592
00:25:16.020 --> 00:25:18.870
Um so that again um, basically

593
00:25:18.870 --> 00:25:21.750
mitigates any effects it might have

594
00:25:21.750 --> 00:25:23.750
on the orbital dynamics of the Earth. It

595
00:25:23.750 --> 00:25:25.230
certainly wouldn't affect the Earth's orbit

596
00:25:25.230 --> 00:25:28.150
around the Sun. Might just tweak the

597
00:25:28.150 --> 00:25:30.110
Moon's orbit around the Earth a bit.

598
00:25:30.820 --> 00:25:33.670
Uh wouldn't cause the demolition of the

599
00:25:33.670 --> 00:25:36.510
Earth. The orbits of the other planets

600
00:25:36.990 --> 00:25:39.940
wouldn't even bother to, to take any

601
00:25:39.940 --> 00:25:42.860
notice of it. Uh they are too

602
00:25:42.860 --> 00:25:45.740
stable compared with uh, a

603
00:25:45.740 --> 00:25:48.140
thing of that mass and that far away from the

604
00:25:48.140 --> 00:25:50.900
Earth. So ah it's an interesting

605
00:25:50.900 --> 00:25:53.660
thought uh and one that I

606
00:25:53.660 --> 00:25:56.380
think um we can say yes you could have a

607
00:25:56.380 --> 00:25:58.980
space station 150 kilometres in diameter

608
00:25:58.980 --> 00:26:01.900
weighing 10 to the 15 tonnes uh and it

609
00:26:01.900 --> 00:26:04.740
probably would not affect the status quo

610
00:26:04.740 --> 00:26:05.490
terribly badly.

611
00:26:06.200 --> 00:26:08.560
Andrew Dunkley: Okay, there you go. Uh and I just did a quick

612
00:26:08.560 --> 00:26:11.240
cheque but um, there's not much information

613
00:26:11.240 --> 00:26:13.520
about how fast space stations have to be away

614
00:26:13.520 --> 00:26:16.120
to avoid the Roche limit. But a solid object

615
00:26:16.920 --> 00:26:19.240
such as a Rocky body

616
00:26:20.040 --> 00:26:22.640
with 150 kilometre diameter would have to be

617
00:26:22.640 --> 00:26:25.480
at least 141,000 kilometres

618
00:26:25.480 --> 00:26:28.480
away from Earth. Um probably better off being

619
00:26:28.480 --> 00:26:30.200
over 200,000 kilometres away.

620
00:26:30.200 --> 00:26:32.480
Professor Fred Watson: Yes that's the sort of distance I had in

621
00:26:32.480 --> 00:26:35.360
mind. Something like that. Three times as

622
00:26:35.360 --> 00:26:37.760
far away as the, the geostationary

623
00:26:37.760 --> 00:26:38.400
satellites. Huh.

624
00:26:38.400 --> 00:26:39.760
Andrew Dunkley: Are. There you are now.

625
00:26:39.760 --> 00:26:42.160
He had a second question as to what would

626
00:26:42.160 --> 00:26:44.520
happen to the other planets if Earth was

627
00:26:44.520 --> 00:26:46.800
destroyed, no longer existed. I think we've

628
00:26:46.800 --> 00:26:48.480
been down this road before and I can't

629
00:26:48.480 --> 00:26:49.400
remember the answer.

630
00:26:50.040 --> 00:26:52.920
Professor Fred Watson: Yeah, so, um, the other planets

631
00:26:52.920 --> 00:26:55.680
would more or less stay in the present

632
00:26:55.680 --> 00:26:58.160
orbits. Those orbits would be

633
00:26:58.160 --> 00:27:00.920
perturbed, uh, differently from what they are

634
00:27:00.920 --> 00:27:03.600
now. So perturbations are the gravitational

635
00:27:03.600 --> 00:27:05.720
effects of other bodies in the solar system.

636
00:27:06.440 --> 00:27:09.240
Uh, when you look at the way

637
00:27:09.240 --> 00:27:11.240
things are in orbit, you start off with a two

638
00:27:11.240 --> 00:27:14.240
body problem with the sun and your object in

639
00:27:14.240 --> 00:27:16.760
orbit. But then you modify it by

640
00:27:17.400 --> 00:27:19.080
taking into account the gravitational

641
00:27:19.080 --> 00:27:20.960
attraction of other bodies and it becomes a

642
00:27:20.960 --> 00:27:22.680
three body problem and then four body problem

643
00:27:22.680 --> 00:27:25.080
and all the rest of it. Now,

644
00:27:25.480 --> 00:27:27.760
that three body problem would change if the

645
00:27:27.760 --> 00:27:30.720
Earth wasn't there. Um, or the N body

646
00:27:30.720 --> 00:27:32.720
problem, I suppose it would be a solar system

647
00:27:32.720 --> 00:27:34.980
with seven planets rather than eight. Uh,

648
00:27:35.000 --> 00:27:37.320
that would change the dynamics of the planets

649
00:27:37.320 --> 00:27:40.030
a little bit, but they would basically

650
00:27:40.030 --> 00:27:42.830
remain in their present orbits, uh, with

651
00:27:42.830 --> 00:27:45.670
just changes to the orbit rather than the

652
00:27:45.670 --> 00:27:46.630
orbits being destroyed.

653
00:27:46.630 --> 00:27:48.750
Andrew Dunkley: So, uh, in other words, if Earth disappeared,

654
00:27:48.750 --> 00:27:49.710
no great loss.

655
00:27:50.190 --> 00:27:53.150
Professor Fred Watson: No, not really. I mean, uh, you know, Douglas

656
00:27:53.150 --> 00:27:55.430
Adams had it in one. Mostly harmless. Mostly

657
00:27:55.430 --> 00:27:57.230
harmless, that's right.

658
00:27:57.230 --> 00:27:58.510
Andrew Dunkley: Thanks to the white mice.

659
00:27:59.150 --> 00:28:00.110
Professor Fred Watson: Yes, that's right.

660
00:28:01.710 --> 00:28:03.590
Andrew Dunkley: I wonder how all the other mice felt about

661
00:28:03.590 --> 00:28:06.430
that. You know, it was

662
00:28:06.430 --> 00:28:08.910
musculus. Racism. That's what it was.

663
00:28:08.990 --> 00:28:11.800
Professor Fred Watson: It is, yes. Mass racism. Exactly. So,

664
00:28:12.520 --> 00:28:14.030
yeah, thanks.

665
00:28:14.030 --> 00:28:16.200
Andrew Dunkley: Uh, Finn, great question. We always love

666
00:28:16.200 --> 00:28:18.440
these what ifs. So, um, if you'd like to keep

667
00:28:18.440 --> 00:28:20.200
sending in questions like that, or if you've

668
00:28:20.200 --> 00:28:22.800
got something deadly serious to discuss with

669
00:28:22.800 --> 00:28:25.440
us, like, uh, I don't know, exploding

670
00:28:25.440 --> 00:28:27.960
rockets and whatever else, uh, you can send

671
00:28:27.960 --> 00:28:30.600
them in to us. Uh, just go to spacenuts

672
00:28:30.680 --> 00:28:33.320
IO or spacenutspodcast.com,

673
00:28:33.400 --> 00:28:35.800
click on the Ask me anything button.

674
00:28:36.280 --> 00:28:38.840
You won't be asking me, you'll be asking him.

675
00:28:39.400 --> 00:28:41.710
But, uh, I'll read it out or you can send us

676
00:28:41.940 --> 00:28:43.220
audio question. As long as you've got a

677
00:28:43.220 --> 00:28:45.250
device with a microphone, you're all set. Uh,

678
00:28:45.250 --> 00:28:46.580
and while you're there, have a look around.

679
00:28:47.250 --> 00:28:48.820
Uh, that brings us to the end. Fred Watson,

680
00:28:48.820 --> 00:28:49.540
thank you very much.

681
00:28:50.260 --> 00:28:52.700
Professor Fred Watson: Great pleasure, Andrew. Always good to chew

682
00:28:52.700 --> 00:28:54.500
the fat. And, uh, I, uh, hope we'll do it

683
00:28:54.500 --> 00:28:54.940
again soon.

684
00:28:54.940 --> 00:28:55.460
Andrew Dunkley: We will.

685
00:28:55.540 --> 00:28:56.860
That's Professor Fred Watson Watson,

686
00:28:56.860 --> 00:28:58.700
astronomer at large, part of the team here at

687
00:28:58.700 --> 00:29:00.900
Space Nuts and thanks to Huw in the studio.

688
00:29:01.110 --> 00:29:02.620
Uh, who couldn't be with us today. He was

689
00:29:02.620 --> 00:29:04.780
seeing his dietitian after he reached 10 to

690
00:29:04.780 --> 00:29:05.780
the 15 tonnes.

691
00:29:08.190 --> 00:29:10.470
I'm surprised he survived. And from me,

692
00:29:10.470 --> 00:29:12.030
Andrew Dunkley. Thanks for your company.

693
00:29:12.110 --> 00:29:14.790
We'll be back again soon with another episode

694
00:29:14.790 --> 00:29:16.430
of Space Nuts. See you then.

695
00:29:16.430 --> 00:29:17.150
Professor Fred Watson: Bye. Bye.

696
00:29:18.350 --> 00:29:20.630
Andrew Dunkley: You've been listening to the Space Nuts

697
00:29:20.630 --> 00:29:23.590
podcast, available at

698
00:29:23.590 --> 00:29:25.550
Apple Podcasts, Spotify,

699
00:29:25.790 --> 00:29:28.470
iHeartRadio or your favourite podcast

700
00:29:28.470 --> 00:29:30.270
player. You can also stream on

701
00:29:30.270 --> 00:29:33.230
demand@bytes.com. this has been another

702
00:29:33.230 --> 00:29:35.230
quality podcast production from

703
00:29:35.230 --> 00:29:36.430
bytes.com.