Oceans, Space-Time Stiffness & Ganymede’s Hidden Crater: A Cosmic Q&A | Space Nuts: Astronomy...

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Hi there. Thanks for joining us again.


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This is Space Nuts, a Q&A edition. Uh my


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name is Andrew Dunley, your host. It's


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good to have your company. Uh questions


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today coming from Matt, who wants to


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talk about the oceans on Earth. Doug is


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asking about the stiffness of spaceime.


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We have talked about that before, but


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he's got a different idea. Uh John is


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asking questions about a new antenna


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array, and Rusty is honing in on


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something we talked about uh late last


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year. the largest impact crater, but he


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wants to go further than the surface of


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the Earth. So, we'll talk about all of


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that on this episode of Space Nuts. 15


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seconds. Guidance is internal. 10 9


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Ignition sequence start. Space Nuts. 5 4


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3 2 1 2 3 4 5 5 4 3 2 1 Space Nuts.


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Astronauts report. It feels good. And


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he's done all his homework. He's ready


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to go. It's Professor Fred Watson,


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astronomer at large. Hello, Fred. I've


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just um realized there was one bit of


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homework that I didn't do, which uh


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never mind. It'll be all right. There's


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this thing called guessing. We can do


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that. We can do that. Yeah, that'll


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solve it. Uh shall we just get straight


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into it? I think we ought to. Yes, I


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think that would be a very good uh thing


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to do. All right. Our first question is


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a text question from Matt. Hi, Andrew


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and Fred. I have a question for you.


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That's good because this is the Q&A


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segment. So, it's good that you've got a


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question. I was thinking about what the


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Earth's surface would look like as a


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rocky planet without any water. Imagine


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if you happen to live by the sea and


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could stand on the surface, how


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different your part of the world would


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suddenly look. You'd probably fall a


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long way too in some parts of um of the


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world. Uh that started me thinking uh


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what is it that determines how far our


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oceans got filled up? Uh why for


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instance aren't there much smaller and


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um or why aren't they much smaller and


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only a max of say a few hundred meters


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deep? What's the physics that governs


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how much total water we ended up having


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um on Earth? Uh and if you can share


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some wisdom on that it would be grand.


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Thank you. I love the podcast. been


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listening for a few years. Um, but this


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is my first question. Uh, keep up the


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good work. Thanks, Matt. Well, thanks


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for sending in the question. Uh, we


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we've talked about how water ended up on


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Earth and there are all sorts of


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initially the the thought was it's, you


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know, carried by asteroids, but then


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they started thinking no that they it


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wouldn't carry enough. And the latest


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theory is that um when the accretion of


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the planet happened, the water was


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already there, which would probably go a


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long way to answering Matt's question


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about how come there's this much. But


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yes, maybe that's right. Um in fact, you


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probably answered it in that regard.


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Although, uh I think the asteroid and


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comet theory still carries weight and


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yeah, holds water. It holds water. Yes.


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So I was avoiding that uh


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term. The the the thing that put doubt


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on that was the the mixture between


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heavy water and normal water, the the


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isotope ratio. Uh because the that


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mixture on in the Earth's oceans doesn't


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really match what we find in comets


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because we can analyze the vapors that


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they give off when when they get near


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the sun. Um and and in fact we we


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brought samples back from from certainly


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from asteroids. Uh so um but you're


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right. I think the the prevalent idea is


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that the water was intrinsic to the


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earth's formation and maybe it just got


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topped up a bit by asteroids and comets.


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Um so that does to some extent answer


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the question. It's uh to do with the uh


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you know with the inherent mix uh


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molecular mix of the constituents of the


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cloud of gas and dust from which the


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earth uh and the sun and the solar


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system were formed.


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Um I uh I think


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um it it it's not


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necessarily


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a a done deal though because


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uh we think about some of the ice moons


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of the solar system which are


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effectively covered in water. Uh they


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have far more water than the earth has


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in its oceans. And I'm talking now about


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places like Europa, like Titan, uh


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Saturn's moon Titan, Jupiter's moon


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Europa. Uh these are ice worlds. They've


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got a a liquid water ocean, uh with a


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covering of solid ice on top of that. So


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they're basically global water worlds,


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except they're covered with ice. Um so


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uh a bigger world of that kind could


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have a global ocean. And we when we're


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talking about um K218b that uh planet


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whose atmosphere has shown some possible


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biomarker chemicals uh one of the


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possible uh scenarios on K218b is a


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world that is actually covered in water


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that it's a global ocean that it's got a


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thick enough atmosphere that the


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atmospheric pressure balances out the


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water surface. So you've got a situation


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like we have on Earth where you've got


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equilibrium between the the liquid and


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the atmosphere. Um so it may be that you


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know uh our earth could have had more


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water. Uh maybe some of it's evaporated,


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maybe some of it has dissociated into


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its component chemicals um uh component


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elements hydrogen and oxygen uh and the


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and which have been lost into space as


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we think has happened on the planet


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Mars. Um so maybe you know um there is


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certainly snowball earth is one of the


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things that we think happened in the


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history of our planet that it was


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covered with ice with an icy surface. Uh


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it's a great question that Matt asks


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though uh about um you know what the


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earth would be like if you imagined it


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without the ocean oceans. Uh there'd be


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those trenches. What's the deepest one?


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8 kilometers or something like that.


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Yes. San Andreas I think which Yes.


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which would be pretty impressive. Yeah.


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Oh, can you imagine the Earth without


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water? Yes. San Andreas. Um, no, it's


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not San Andreas. The It's the um Oh,


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what's it called? Pacific Trench. Yes,


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it's a Pacific one.


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Um, can't remember either. Never mind.


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The Marinara trench. That's the one.


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Yeah, it's um it's incredibly deep. Uh


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it's about 8 kilometers. Yeah, I'm just


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trying to find it now. Check it out,


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Andrew. But uh yeah, if you imagine


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Earth without water, uh you could do


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some incredible skydiving there, I


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reckon, without having to catch a plane.


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Yeah. Yeah. Um but getting out, that


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would be the fun part, I imagine. But um


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yeah, it's Yeah. I can't find the depth


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of it, but it is it is something


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massive. But they have sent um


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submarines down deep into it. Yes.


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Without other people on board. Yeah.


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Here it is.


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26,850 ft or


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8,184 m deep. What I said. Yeah. Doing


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all right. You're doing very well. So,


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um, Matt, if if the Earth did not have


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oceans, uh, it would look very very


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different. It would be it'd be quite


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spectacular in places to say the least


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because there are mountain ranges under


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the Yes. The ocean which we can't see.


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Yeah. And I mean you got you got things


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like Hawaii which is a super volcano but


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you can only see the tip of it. Yes.


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Yes. I I I do wonder though um so you


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know there are significant differences.


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So plate tectonics is is the the key


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thing here. Uh the ocean plates are


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different from the continental plates


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and possibly a lot of that is the fact


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that they're being weighed down by the


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water on them. So so without the water


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they might bounce up a bit and you might


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get a much more level playing field


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compared with what um what it's like


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now. Well, you you see evidence of that


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uh around New Zealand where the you know


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Milford Sound and all the other and


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Dusty Sound and all those beautiful


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areas are uh they're still lifting after


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the ice age where where the glaciers


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compress the ground and you can see


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evidence of the of the the rebound


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effect. So, yeah, you're right. Uh


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because the water weighs


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I don't know how you'd measure it, but


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it's incredibly heavy. It's um and


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putting a lot of pressure on those uh on


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those areas. Uh yeah, the earth could


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look very different uh if all the water


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disappeared and it' probably bounce back


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pretty quickly. Yes, I think so. In the


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scheme of in geological time. That's


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right. Yes. Yes, absolutely. Uh thanks


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for the question, Matt. Hope we


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adequately answered that for you. Uh our


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next question is an audio question from


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Doug. Hi, this is Doug and Hazel the


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Wonder Doodle calling from Whippy,


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Ontario, Canada. Second time caller.


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Thanks very much for the show. Uh the


00:09:23.760 --> 00:09:26.790
question today from Hazel is we've heard


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people talk about the stiffness of


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spaceime being something like a 100


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billion billion times stiffer than steel


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and we're wondering how that can be when


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spacetime isn't matter so to speak. Uh,


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how can you measure the stiffness of


00:09:47.959 --> 00:09:50.389
spacetime and what exactly are you


00:09:50.399 --> 00:09:53.269
measuring? Thank you.


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Um, how long's a piece of string?


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Um, it's it's a great question and I


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appreciate that one because this is one


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that has always fascinated me. So what


00:10:03.839 --> 00:10:06.750
you do is


00:10:06.760 --> 00:10:12.910
you you look at the way matter distorts


00:10:12.920 --> 00:10:17.350
space and we know that very very well


00:10:17.360 --> 00:10:19.430
from Einstein's general theory of


00:10:19.440 --> 00:10:21.350
relativity. We we know what the


00:10:21.360 --> 00:10:23.910
distortion is for a given amount of mass


00:10:23.920 --> 00:10:26.630
and a given size. It's why we understand


00:10:26.640 --> 00:10:28.949
black holes because of the fact that the


00:10:28.959 --> 00:10:31.990
space is so highly distorted. So, so


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what you do, you look at the way matter


00:10:33.920 --> 00:10:37.150
distorts space and from that you can


00:10:37.160 --> 00:10:39.670
determine a property called the Young's


00:10:39.680 --> 00:10:42.750
modulus of space which is a kind of


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geometrical property. Um, it's usually


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applied to solids as uh exactly as Doug


00:10:49.040 --> 00:10:51.350
has said, you know, when how can you


00:10:51.360 --> 00:10:52.949
measure its stiffness when it's not a


00:10:52.959 --> 00:10:55.509
solid? Um, so what you do is you you


00:10:55.519 --> 00:10:57.590
know that it's flexible. You can see the


00:10:57.600 --> 00:11:01.350
way matter flexes it and you go from


00:11:01.360 --> 00:11:04.790
there to saying if it was a solid it


00:11:04.800 --> 00:11:06.150
would have this property and the


00:11:06.160 --> 00:11:07.430
property we measure is something called


00:11:07.440 --> 00:11:10.710
Young's modulus. Uh I remember doing


00:11:10.720 --> 00:11:12.630
Young's modulus as a physics experiment


00:11:12.640 --> 00:11:14.590
at school. You hang weights on a bit of


00:11:14.600 --> 00:11:17.509
wire and that gives you the amount of


00:11:17.519 --> 00:11:19.990
stretch the stiffness of the wire uh


00:11:20.000 --> 00:11:23.110
with the weights hanging on it. And so


00:11:23.120 --> 00:11:25.430
you can do an equivalent thing and it's


00:11:25.440 --> 00:11:27.269
exactly the number actually that uh that


00:11:27.279 --> 00:11:30.069
Doug has said. It's uh uh 100 billion


00:11:30.079 --> 00:11:33.430
billion times uh stiffer than steel. Uh


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10 to the^ 20. Uh there is a there's a


00:11:36.160 --> 00:11:38.389
paper it's pretty easy to find it on the


00:11:38.399 --> 00:11:42.230
web. Uh it was um written by let me see


00:11:42.240 --> 00:11:46.630
if I can bring it up. Uh it is by Kirk


00:11:46.640 --> 00:11:49.269
T. Macdonald who's uh at Princeton


00:11:49.279 --> 00:11:51.750
University. So this is probably the you


00:11:51.760 --> 00:11:53.590
know the almost the headquarters of


00:11:53.600 --> 00:11:55.509
gravity because that's where where


00:11:55.519 --> 00:11:59.190
Einstein did a lot of his work. Um he's


00:11:59.200 --> 00:12:01.110
uh he's got a little paper that you can


00:12:01.120 --> 00:12:03.030
find online. What is the stiffness of


00:12:03.040 --> 00:12:05.430
space time? And the answer I've given is


00:12:05.440 --> 00:12:09.190
the the classical answer the 10 the^ 20.


00:12:09.200 --> 00:12:12.470
Uh he's got a quantum answer as well. Uh


00:12:12.480 --> 00:12:15.190
and uh you can throw in something about


00:12:15.200 --> 00:12:16.790
cosmological sound waves and


00:12:16.800 --> 00:12:19.110
electromagnetic waves. uh and enjoy


00:12:19.120 --> 00:12:20.389
yourself with some of the equations


00:12:20.399 --> 00:12:22.310
there. But that's basically uh where


00:12:22.320 --> 00:12:23.750
that number comes from. It comes from


00:12:23.760 --> 00:12:25.829
that paper. Yeah. And it's not so much


00:12:25.839 --> 00:12:29.110
about the physical attributes of the


00:12:29.120 --> 00:12:31.190
universe. It's about the fabric of space


00:12:31.200 --> 00:12:34.230
time itself and and and the way it


00:12:34.240 --> 00:12:37.509
behaves. Yeah. Yes. Yeah. Cuz we have


00:12:37.519 --> 00:12:40.230
talked about it before and um I think


00:12:40.240 --> 00:12:42.710
when we first talked about it, I was


00:12:42.720 --> 00:12:45.350
quite astonished by how


00:12:45.360 --> 00:12:49.590
um stiff space is. Yes, in the scheme of


00:12:49.600 --> 00:12:51.269
things. But when you compare it to


00:12:51.279 --> 00:12:54.629
steel, um I I guess it puts you in a


00:12:54.639 --> 00:12:57.829
mindset of a physical thing. Yeah,


00:12:57.839 --> 00:12:59.670
that's right. Like an object, but that's


00:12:59.680 --> 00:13:03.829
not really what it's about. Yeah.


00:13:03.839 --> 00:13:06.949
All right. Um short answer, but there's


00:13:06.959 --> 00:13:09.590
Yeah, that it's pretty well documented


00:13:09.600 --> 00:13:11.509
and uh yeah, go you can you can


00:13:11.519 --> 00:13:13.910
certainly look that um that article up,


00:13:13.920 --> 00:13:16.550
Doug, and and learn more about it. And


00:13:16.560 --> 00:13:18.310
thanks for the question. and thanks for


00:13:18.320 --> 00:13:20.790
introducing us to your puppy dog. This


00:13:20.800 --> 00:13:23.190
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SY here. Also Spacenuts. Our next


00:16:06.399 --> 00:16:09.269
question comes from John. I live in


00:16:09.279 --> 00:16:11.509
Cloudcraftoft, New Mexico in the United


00:16:11.519 --> 00:16:14.150
States. Today's Albuquerque, New Mexico


00:16:14.160 --> 00:16:16.430
newspaper reported on


00:16:16.440 --> 00:16:20.710
NGVLA. Uh it will replace an existing 27


00:16:20.720 --> 00:16:24.389
antenna array with 192. Each new


00:16:24.399 --> 00:16:27.670
foundation 430 tons. Each new antenna


00:16:27.680 --> 00:16:31.990
generating 1.5 terabytes per second. And


00:16:32.000 --> 00:16:36.150
each 18 m tall uh uh structure weighing


00:16:36.160 --> 00:16:39.829
130 tons. How will this new antenna fit


00:16:39.839 --> 00:16:43.110
into the astronomy community? uh and he


00:16:43.120 --> 00:16:46.710
he makes a reference to um the square


00:16:46.720 --> 00:16:49.189
kilometer array and mircat arrays that


00:16:49.199 --> 00:16:50.790
are being set up in Australia and South


00:16:50.800 --> 00:16:52.790
Africa. Thank you, John. Uh I didn't


00:16:52.800 --> 00:16:55.189
know about this one. Yeah, it's been in


00:16:55.199 --> 00:16:58.470
the pipeline quite a while. So the VA is


00:16:58.480 --> 00:17:02.069
uh the very large array. It's uh in New


00:17:02.079 --> 00:17:04.470
Mexico. We visited it a few years ago. A


00:17:04.480 --> 00:17:08.069
very impressive set of antennas. Uh and


00:17:08.079 --> 00:17:13.110
um um essentially uh it's been a really


00:17:13.120 --> 00:17:16.789
productive um uh machine for research,


00:17:16.799 --> 00:17:20.150
the VA back to going back to the 1970s.


00:17:20.160 --> 00:17:22.150
Uh and there's a note on their website


00:17:22.160 --> 00:17:23.829
that says it's been used for more than


00:17:23.839 --> 00:17:27.189
11,000 different observing projects. Um


00:17:27.199 --> 00:17:28.950
and had an impact on nearly every branch


00:17:28.960 --> 00:17:32.870
of astronomy. So uh what has happening


00:17:32.880 --> 00:17:35.830
what is happening now is an upgrade uh


00:17:35.840 --> 00:17:38.150
to make it the next generation very


00:17:38.160 --> 00:17:40.470
large array the NGVLA


00:17:40.480 --> 00:17:45.150
uh and um exactly as John says it's got


00:17:45.160 --> 00:17:48.789
similarities to uh actually to the mid


00:17:48.799 --> 00:17:50.630
frequency component of the square


00:17:50.640 --> 00:17:52.870
kilometer array which is a in South


00:17:52.880 --> 00:17:55.350
Africa and is a basically an extension


00:17:55.360 --> 00:17:57.990
of Mircat which is an existing array in


00:17:58.000 --> 00:18:02.070
in South Africa. Um, so, uh, that also


00:18:02.080 --> 00:18:05.350
will have, uh, antennas about 200, much


00:18:05.360 --> 00:18:08.549
the same as the, uh, NGVLA will have.


00:18:08.559 --> 00:18:10.230
Uh, what I was looking for, and this is


00:18:10.240 --> 00:18:11.430
the bit of homework that I didn't


00:18:11.440 --> 00:18:15.270
actually do, uh, it's, um, it's it's


00:18:15.280 --> 00:18:19.669
going to have uh, a frequency range,


00:18:19.679 --> 00:18:22.789
which uh, I I'm not sure about. It's


00:18:22.799 --> 00:18:27.029
probably quite similar. 1.2 2 GHz or 21


00:18:27.039 --> 00:18:32.070
cm to 116 GHz. Okay. Uh that's uh rather


00:18:32.080 --> 00:18:34.669
more I think than the um than the


00:18:34.679 --> 00:18:38.150
mid-frequency of the uh of the square


00:18:38.160 --> 00:18:41.430
kilometer observatory. Um I think though


00:18:41.440 --> 00:18:46.310
the other thing is that the NG VALA will


00:18:46.320 --> 00:18:53.510
have uh a much wider spacing of the


00:18:53.520 --> 00:18:56.390
antennas. They're talking about over


00:18:56.400 --> 00:18:59.270
nearly 9,000 kilometers. So this is


00:18:59.280 --> 00:19:01.990
continentwide stuff. Uh and that's


00:19:02.000 --> 00:19:05.350
certainly bigger than the array uh in


00:19:05.360 --> 00:19:08.150
South Africa. Uh and so it will probably


00:19:08.160 --> 00:19:09.669
be used for different science. So the


00:19:09.679 --> 00:19:11.990
answer to to John's question is that yes


00:19:12.000 --> 00:19:15.190
these things dovetail together uh m


00:19:15.200 --> 00:19:19.350
maybe in frequency and in um and in in


00:19:19.360 --> 00:19:23.110
spacing in antenna spacing. Uh it's the


00:19:23.120 --> 00:19:26.070
sort of thing that astronomers you know


00:19:26.080 --> 00:19:28.190
you they don't tend to work in


00:19:28.200 --> 00:19:30.950
isolation. Uh they have complimentary


00:19:30.960 --> 00:19:32.950
things and it's a bit like the three


00:19:32.960 --> 00:19:35.510
ELTs that are currently being planned or


00:19:35.520 --> 00:19:37.909
built extremely large telescopes. These


00:19:37.919 --> 00:19:40.470
are optical telescopes in the 20 to 30


00:19:40.480 --> 00:19:43.750
meter class. Uh and um well there's only


00:19:43.760 --> 00:19:45.190
one of them that's anywhere near


00:19:45.200 --> 00:19:46.870
completion and that's the European


00:19:46.880 --> 00:19:49.430
extremely large telescope 39 m


00:19:49.440 --> 00:19:50.789
instrument. But there are two others


00:19:50.799 --> 00:19:53.029
that are still on the stocks. I don't


00:19:53.039 --> 00:19:55.270
know how the current funding situation


00:19:55.280 --> 00:19:56.789
in the US will affect them because


00:19:56.799 --> 00:19:59.990
they've they require a huge component of


00:20:00.000 --> 00:20:01.270
US funding even though they're


00:20:01.280 --> 00:20:03.350
international projects. there the the


00:20:03.360 --> 00:20:05.909
giant Mellan telescope and the and the


00:20:05.919 --> 00:20:09.270
TMT the 30 meter telescope in Hawaii. So


00:20:09.280 --> 00:20:11.510
that that it's it's a similar situation.


00:20:11.520 --> 00:20:13.270
I think you've got differences. There


00:20:13.280 --> 00:20:15.190
are nuances of differences between them.


00:20:15.200 --> 00:20:18.230
They will um have different strengths um


00:20:18.240 --> 00:20:20.710
in terms of their capabilities. Uh and


00:20:20.720 --> 00:20:22.549
the astronomical community throughout


00:20:22.559 --> 00:20:24.549
the world will be glad to have them. Uh


00:20:24.559 --> 00:20:25.990
because the one thing that we're always


00:20:26.000 --> 00:20:29.390
short of is is astronomical facilities.


00:20:29.400 --> 00:20:32.950
uh telescopes are rare things when it


00:20:32.960 --> 00:20:34.870
comes to this you know things of this


00:20:34.880 --> 00:20:37.750
size of this stature. So uh great to to


00:20:37.760 --> 00:20:41.110
welcome the NG VALA into the uh you know


00:20:41.120 --> 00:20:43.590
into the mix. Yeah. They say the array


00:20:43.600 --> 00:20:46.149
will achieve uh high surface brightness


00:20:46.159 --> 00:20:48.549
sensitivity and high fidelity imaging on


00:20:48.559 --> 00:20:51.909
angular scales down to the uh mill arc


00:20:51.919 --> 00:20:55.669
second. Yeah. Um and it will uh extend


00:20:55.679 --> 00:20:58.870
out to 1,000 kilometers and uh it'll


00:20:58.880 --> 00:21:00.470
have longer baselines reaching across


00:21:00.480 --> 00:21:03.669
North America and Hawaii. Yeah. It's


00:21:03.679 --> 00:21:05.909
pretty long comes from. Yeah. Yeah.


00:21:05.919 --> 00:21:07.830
Yeah. Incredible. I mean we we've seen


00:21:07.840 --> 00:21:09.510
this already with the you know the event


00:21:09.520 --> 00:21:12.070
horizon telescope which goes over


00:21:12.080 --> 00:21:14.230
basically the diameter of the earth is


00:21:14.240 --> 00:21:17.029
the is the baseline for that but it's


00:21:17.039 --> 00:21:19.029
it's only that I think that's only nine


00:21:19.039 --> 00:21:20.390
telescopes or something like that or


00:21:20.400 --> 00:21:23.270
nine observatories. Yeah. I mean, I


00:21:23.280 --> 00:21:25.029
think it's great that they can integrate


00:21:25.039 --> 00:21:27.350
so much hardware over such vast


00:21:27.360 --> 00:21:29.909
distances to make them, you know, super


00:21:29.919 --> 00:21:32.789
telescopes basically. And y they're so


00:21:32.799 --> 00:21:35.110
much more powerful and uh yeah, the data


00:21:35.120 --> 00:21:36.950
will um be very interesting. I'm sure


00:21:36.960 --> 00:21:38.870
we'll be talking about it uh at some


00:21:38.880 --> 00:21:42.230
stage, John. So, keep your ear to the


00:21:42.240 --> 00:21:45.110
podcast platform that you use and there


00:21:45.120 --> 00:21:47.909
will be more. Thanks for the question.


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space nuts. Now, back to the show. Okay,


00:24:23.440 --> 00:24:25.430
we checked all four systems and being


00:24:25.440 --> 00:24:27.750
with the girls. Space nuts. One final


00:24:27.760 --> 00:24:30.310
question. This one comes from, you'll


00:24:30.320 --> 00:24:33.909
never guess, Rusty and Donny Brook.


00:24:33.919 --> 00:24:35.830
Hi Fred and Andrew. It's Rusty and Donny


00:24:35.840 --> 00:24:37.750
Brook. Andrew, it's good to have you


00:24:37.760 --> 00:24:39.590
back, but didn't Heidi do a great job in


00:24:39.600 --> 00:24:42.110
your absence. How did you find


00:24:42.120 --> 00:24:45.149
her? Questions about


00:24:45.159 --> 00:24:48.310
uh the largest


00:24:48.320 --> 00:24:51.750
uh crater in the solar system. I presume


00:24:51.760 --> 00:24:53.870
that the one you spoke about last


00:24:53.880 --> 00:24:57.830
September on Ganymede at 1600 kilometer


00:24:57.840 --> 00:25:00.070
diameter is larger than the one on the


00:25:00.080 --> 00:25:03.750
moon, the Aken basin. So the the title


00:25:03.760 --> 00:25:06.390
of largest would then change to the one


00:25:06.400 --> 00:25:09.230
on Ganymede. Does it have a name yet?


00:25:09.240 --> 00:25:12.029
And I'm just wondering about


00:25:12.039 --> 00:25:17.350
Triton. Um it's its odd shape would have


00:25:17.360 --> 00:25:20.909
to have come from an impact decision uh


00:25:20.919 --> 00:25:23.190
collision. And uh I'm wondering if that


00:25:23.200 --> 00:25:26.230
qualifies as a crater. It's about it


00:25:26.240 --> 00:25:28.390
took away about a third of the moon uh


00:25:28.400 --> 00:25:33.590
that impact. And uh was that impact with


00:25:33.600 --> 00:25:37.029
the planet or did it acquire its odd


00:25:37.039 --> 00:25:40.789
shape by hitting something else? Thanks


00:25:40.799 --> 00:25:44.070
guys. Cheers. Thanks Rusty. Always good


00:25:44.080 --> 00:25:46.630
to hear from you chucking us curve


00:25:46.640 --> 00:25:49.269
balls. Uh yeah, I'll answer his first


00:25:49.279 --> 00:25:51.269
question. How did we find Heidi? Heidi


00:25:51.279 --> 00:25:55.230
found us. Um, Heidi was a Space Nuts


00:25:55.240 --> 00:25:58.070
listener and she came to us to say,


00:25:58.080 --> 00:26:01.110
"Look, I got an idea and I just want to


00:26:01.120 --> 00:26:03.350
sort of go to school off you guys to


00:26:03.360 --> 00:26:05.590
find out how I can get my idea out


00:26:05.600 --> 00:26:08.310
there." And her idea was a podcast about


00:26:08.320 --> 00:26:11.110
the relationship between real life and


00:26:11.120 --> 00:26:14.710
science fiction. And I said, "Well, why


00:26:14.720 --> 00:26:16.470
don't I introduce you to Hugh in the


00:26:16.480 --> 00:26:19.750
studio, if you can find him, and see


00:26:19.760 --> 00:26:22.390
what happens?" And voila, uh Heidi's


00:26:22.400 --> 00:26:26.149
podcast became one of the byes.com


00:26:26.159 --> 00:26:29.269
stable, uh reality check, the science of


00:26:29.279 --> 00:26:31.430
fiction podcast. So that's how it


00:26:31.440 --> 00:26:33.510
happened. Uh Heidi just sort of wanted


00:26:33.520 --> 00:26:35.430
to find out how she could get her idea


00:26:35.440 --> 00:26:39.590
out there and we um we took her on.


00:26:39.600 --> 00:26:41.510
Simple as that. So, uh, yeah, it turned


00:26:41.520 --> 00:26:43.269
out to be a really great podcast series,


00:26:43.279 --> 00:26:45.669
too, if you want to look it up, uh, and


00:26:45.679 --> 00:26:47.990
and listen to some of the great, uh,


00:26:48.000 --> 00:26:51.190
concepts that science fiction can give


00:26:51.200 --> 00:26:54.310
to real life situations or vice versa.


00:26:54.320 --> 00:26:55.669
Sometimes they're a little bit out there


00:26:55.679 --> 00:26:58.070
and it would never be real, but uh, it's


00:26:58.080 --> 00:27:00.870
a and she speaks to experts in the field


00:27:00.880 --> 00:27:03.110
uh, about the ideas of science fiction


00:27:03.120 --> 00:27:04.470
and whether or not they're feasible in


00:27:04.480 --> 00:27:06.789
real life. Brilliant. Brilliant. But


00:27:06.799 --> 00:27:08.390
yes, she did a fabulous job while I was


00:27:08.400 --> 00:27:11.269
away. very pleased to uh be able to take


00:27:11.279 --> 00:27:13.430
a break and not have to have any worries


00:27:13.440 --> 00:27:19.590
at all about um Fred's behavior. Uh now


00:27:19.600 --> 00:27:22.230
um now the largest impact crater, we did


00:27:22.240 --> 00:27:25.669
talk about that recently and um I I've


00:27:25.679 --> 00:27:27.669
forgotten the nuts and bolts of Rusty's


00:27:27.679 --> 00:27:29.590
question now, but u I'm sure you've done


00:27:29.600 --> 00:27:32.470
your homework, Fred. I have. Two two


00:27:32.480 --> 00:27:35.750
parts to Rusty's question. one is uh he


00:27:35.760 --> 00:27:37.909
talks about and I had to go back to our


00:27:37.919 --> 00:27:41.510
um uh our podcast of the 4th of


00:27:41.520 --> 00:27:44.310
September last year to to find out what


00:27:44.320 --> 00:27:47.430
we actually said. Uh but yes it was a


00:27:47.440 --> 00:27:50.950
story uh that there is evidence on uh


00:27:50.960 --> 00:27:52.789
Jupiter's moon Ganymede the biggest moon


00:27:52.799 --> 00:27:56.149
in the solar system uh that uh sometime


00:27:56.159 --> 00:27:58.870
in the past it was hit by an asteroid


00:27:58.880 --> 00:28:01.029
probably a big one 300 kilometers in


00:28:01.039 --> 00:28:04.430
diameter uh which would have created a


00:28:04.440 --> 00:28:07.590
crater about somewhere between 1,400


00:28:07.600 --> 00:28:10.710
and600 kilometers wide on Ganymede


00:28:10.720 --> 00:28:13.990
that's a very very big chunk of Ganymede


00:28:14.000 --> 00:28:16.230
now that crater doesn't no longer


00:28:16.240 --> 00:28:19.110
exists. It's long gone. Uh Ganymede has


00:28:19.120 --> 00:28:21.669
a surface that's probably icy and is


00:28:21.679 --> 00:28:25.590
being renewed uh all the time um by


00:28:25.600 --> 00:28:29.350
probably you know the the the activity


00:28:29.360 --> 00:28:32.149
maybe even geysers of ice as we see on


00:28:32.159 --> 00:28:36.549
um on Europa and Enceladus. Uh so that


00:28:36.559 --> 00:28:38.470
crater isn't there anymore. And the


00:28:38.480 --> 00:28:41.350
reason why we did that story and what


00:28:41.360 --> 00:28:43.830
what has led to the idea that there was


00:28:43.840 --> 00:28:46.950
this clout of of Ganymede back in the in


00:28:46.960 --> 00:28:48.870
in the distant past about 4 billion


00:28:48.880 --> 00:28:51.269
years ago was what they were saying um


00:28:51.279 --> 00:28:55.669
was concentric circles uh which are in


00:28:55.679 --> 00:28:59.430
the surface of Ganymede. So the these


00:28:59.440 --> 00:29:01.750
concentric circles which are all


00:29:01.760 --> 00:29:04.470
centered on a point which is where that


00:29:04.480 --> 00:29:06.149
impact is thought to have taken place.


00:29:06.159 --> 00:29:09.190
So there's no crater but there are these


00:29:09.200 --> 00:29:12.149
uh ancient pieces of evidence of uh


00:29:12.159 --> 00:29:15.190
there having been uh an impact these


00:29:15.200 --> 00:29:17.830
concentric circular features which have


00:29:17.840 --> 00:29:19.750
which which are quite prominent on


00:29:19.760 --> 00:29:25.190
Ganymede's surface. Um so so I I think


00:29:25.200 --> 00:29:27.430
the Aken South Pole basin still has the


00:29:27.440 --> 00:29:31.510
record uh for the biggest crater


00:29:31.520 --> 00:29:33.990
certainly one of the biggest craters uh


00:29:34.000 --> 00:29:35.830
in the solar system. It's 2 and a half


00:29:35.840 --> 00:29:38.549
thousand kilometers in diameter. So it's


00:29:38.559 --> 00:29:40.710
actually bigger than what the Ganymede


00:29:40.720 --> 00:29:42.470
crater would have been had it still been


00:29:42.480 --> 00:29:46.310
there. Yeah, that's amazing. Yes. So, so


00:29:46.320 --> 00:29:48.789
it's a big a big dip in the southern


00:29:48.799 --> 00:29:52.070
polar region of the moon. Uh and again


00:29:52.080 --> 00:29:53.909
thought to be due to an asteroid impact


00:29:53.919 --> 00:29:56.630
perhaps in the very earliest history of


00:29:56.640 --> 00:30:00.389
the moon 4 billion years ago or so. Now,


00:30:00.399 --> 00:30:03.750
um, can they can they glean as to how


00:30:03.760 --> 00:30:05.510
large that asteroid would have been that


00:30:05.520 --> 00:30:08.470
hit the moon? Uh, yes. I I can't


00:30:08.480 --> 00:30:09.909
remember what the figure is, though.


00:30:09.919 --> 00:30:12.389
It's it's uh it's a sort of almost like


00:30:12.399 --> 00:30:14.710
a planetary body. It's almost a


00:30:14.720 --> 00:30:16.549
protolanet or something like that. So,


00:30:16.559 --> 00:30:18.710
several hundred kilometers across


00:30:18.720 --> 00:30:21.750
probably. Yeah. Okay.


00:30:21.760 --> 00:30:24.950
Uh the second part of uh of Russ's


00:30:24.960 --> 00:30:26.950
question has me very puzzled because he


00:30:26.960 --> 00:30:31.269
talks about Triton uh which is uh the


00:30:31.279 --> 00:30:34.950
biggest moon of Neptune


00:30:34.960 --> 00:30:40.110
uh and it um it is


00:30:40.120 --> 00:30:42.669
uh


00:30:42.679 --> 00:30:47.269
it's it's just well what the the the


00:30:47.279 --> 00:30:49.669
what what um Rossy is saying is that


00:30:49.679 --> 00:30:50.789
it's got a


00:30:50.799 --> 00:30:52.710
impact crater on it to make it a very


00:30:52.720 --> 00:30:55.269
odd shape. But actually, Triton's almost


00:30:55.279 --> 00:30:57.510
perfectly spherical. So, I'm not quite


00:30:57.520 --> 00:31:00.630
sure where what he's thinking of here


00:31:00.640 --> 00:31:02.950
and whether he and I are cross purposes


00:31:02.960 --> 00:31:04.389
here, whether he's thinking of another


00:31:04.399 --> 00:31:07.269
object, but Triton is a very well-


00:31:07.279 --> 00:31:09.430
behaved moon. It's in terms of its


00:31:09.440 --> 00:31:11.510
shape, it's pretty spherical. It's a


00:31:11.520 --> 00:31:14.870
large moon. It It's unusual in that it


00:31:14.880 --> 00:31:18.389
orbits uh Neptune backwards. It's what's


00:31:18.399 --> 00:31:19.909
called a retrograde orbit. It's


00:31:19.919 --> 00:31:22.070
clockwise as seen from above the north


00:31:22.080 --> 00:31:23.830
pole which is backwards compared with


00:31:23.840 --> 00:31:25.590
the rest of the solar system. And so


00:31:25.600 --> 00:31:29.830
it's it's probably uh was once a dwarf


00:31:29.840 --> 00:31:31.510
planet in the Kyper belt. So it's


00:31:31.520 --> 00:31:34.389
something that's been captured uh by the


00:31:34.399 --> 00:31:37.909
gravity of Neptune. U but it is nicely


00:31:37.919 --> 00:31:41.110
circular, nicely spherical. So not sure


00:31:41.120 --> 00:31:43.190
about the impact crater. We might talk


00:31:43.200 --> 00:31:46.389
to Rusty again about that. Yeah. Oh, he


00:31:46.399 --> 00:31:49.190
he he's not I I'm not sure he'll ever


00:31:49.200 --> 00:31:50.630
send a question in again, but if he


00:31:50.640 --> 00:31:52.110
does, he


00:31:52.120 --> 00:31:56.669
can he can uh he can follow us up and


00:31:56.679 --> 00:31:59.669
um provide more clarity, I think we'll


00:31:59.679 --> 00:32:01.669
say. Uh I just looked it up. Uh the


00:32:01.679 --> 00:32:04.669
South Pole Aken Basin on the moon impact


00:32:04.679 --> 00:32:07.990
crater. Um yeah, you said 2 and a half


00:32:08.000 --> 00:32:09.750
thousand kilometers, so biggest in the


00:32:09.760 --> 00:32:11.909
solar system. Uh the object they think


00:32:11.919 --> 00:32:14.470
was about 200 km in diameter. Okay.


00:32:14.480 --> 00:32:16.630
Right. Yeah, that's a big hit on a small


00:32:16.640 --> 00:32:19.350
moon type of situation.


00:32:19.360 --> 00:32:21.590
Yeah, made a bit of a mess by the sound


00:32:21.600 --> 00:32:24.310
of it. Rusty, thank you. If you want to


00:32:24.320 --> 00:32:26.630
um kind of come back to us, uh yeah, by


00:32:26.640 --> 00:32:29.190
all means um send us a bit more info so


00:32:29.200 --> 00:32:32.950
that we can um uh revisit that question.


00:32:32.960 --> 00:32:34.230
And don't forget, if you've got a


00:32:34.240 --> 00:32:35.830
question for us, send us in because we


00:32:35.840 --> 00:32:37.990
are a bit short because I I did a bit of


00:32:38.000 --> 00:32:41.269
a clean out when I got back and uh we um


00:32:41.279 --> 00:32:44.310
we need some fresh material. So send the


00:32:44.320 --> 00:32:47.230
questions into us via our website


00:32:47.240 --> 00:32:50.149
spacenutspodcast.com or spacenuts.io and


00:32:50.159 --> 00:32:53.350
just that little um AMA link at the top


00:32:53.360 --> 00:32:55.430
is where you can send text and audio


00:32:55.440 --> 00:32:57.430
questions. Uh which is pretty easy if


00:32:57.440 --> 00:33:00.230
you've got a device with a microphone um


00:33:00.240 --> 00:33:02.389
whether that's a smartphone or a tablet


00:33:02.399 --> 00:33:05.190
or or a computer. Um send it into us.


00:33:05.200 --> 00:33:07.430
Don't forget forget as always to tell us


00:33:07.440 --> 00:33:09.750
who you are and where you're from. We're


00:33:09.760 --> 00:33:12.149
all done, Fred. Thank you so much. Oh,


00:33:12.159 --> 00:33:14.470
it's uh been a pleasure as always and


00:33:14.480 --> 00:33:16.230
it's always stimulating and good to


00:33:16.240 --> 00:33:18.950
chat. It is. I love it. All right, we'll


00:33:18.960 --> 00:33:20.789
see you soon. Professor Fred Watson,


00:33:20.799 --> 00:33:22.549
astronomer at large and thanks to Hugh


00:33:22.559 --> 00:33:25.430
in the studio who couldn't be with us


00:33:25.440 --> 00:33:27.230
today because that's his preferred


00:33:27.240 --> 00:33:30.430
state. He just doesn't want to be with


00:33:30.440 --> 00:33:33.110
us. Thanks, Hugh. Uh, and from me,


00:33:33.120 --> 00:33:34.470
Andrew Dunley, thanks for your company.


00:33:34.480 --> 00:33:35.990
See you on the very next episode of


00:33:36.000 --> 00:33:39.190
Space Nuts. Bye-bye. Space Nuts. You've


00:33:39.200 --> 00:33:43.269
been listening to the Space Nuts podcast


00:33:43.279 --> 00:33:46.230
available at Apple Podcasts, Spotify,


00:33:46.240 --> 00:33:48.870
iHeart Radio, or your favorite podcast


00:33:48.880 --> 00:33:51.710
player. You can also stream on demand at


00:33:51.720 --> 00:33:54.149
byes.com. This has been another quality


00:33:54.159 --> 00:33:58.679
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