Supercharged Neutrinos, Exploding Black Holes & Lunar Mysteries Uncovered | Q&A | Space Nuts:...

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Language: en

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Hi there. Thanks for joining us on a Q&A


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edition of Space Nuts. Andrew Dunley


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here, your host. Great to have your


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company. Coming up, we've got a few


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questions. Nick is going to ask about


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supercharged neutrinos. Andrea is making


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a return appearance. She's got a couple


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of questions about the dark side of the


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moon and shallow craters. And Eli is


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asking about elements and the speed of


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objects. And if we've got time, we'll


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chuck another question into the mix as


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well. All coming up on this edition of


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Space Nuts.


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>> 15 seconds. Guidance is internal. 10 9g


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Ignition sequence start.


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>> Space nuts.


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>> 5 4 3 2


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>> 1 2 3 4 5 5 4 3 2 1


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>> Space Nuts.


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>> Astronauts report. It feels good.


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>> And with Freda away Jonty can play. It's


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uh Professor Jonty her professor of


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astrophysics at the University of


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Southern Queensland. Jonty, hello again.


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>> Good afternoon. How are you going?


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>> I'm well. Great to see you. I think we


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should just go straight into it and uh


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hit you with our first question. It's a


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it's a topic I'm not overly familiar


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with, but uh this one comes from Nick.


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Uh I just read that a supercharged


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neutrino was detected by the Kilometer


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Cube Nutrino telescope and a theory was


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put forward that it came from an


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exploding black hole. Please explain how


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a black hole can explode. Love the show,


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Nick. Thank you, Nick. We love that you


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love the show. Thank Thank you for


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sending in a question. Um, exploding


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black holes. Um, I I seem to remember


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Fred might have written a book about


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something like that once. Um, but


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anyway, um, do they explode or do they


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merge or do they collapse? They they


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eventually disappear. I know that


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>> things now, you know, straight up. I'm


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not a cosmologist or a cosmetologist


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which I always used to joke about


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cosmologists being cosmetologist and


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then it turns out a cosmetologist is a


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real thing. So never mind. Um that's


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further from my area of expertise. So


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any answer I give take with a larger


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grain of salt. You know as is always the


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way you know you the further you go from


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your expertise the more out of date your


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knowledge is. My knowledge on exploding


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or rather evaporating black holes goes


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back to basically when I was in


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undergrad and I was doing lots of


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courses in lots of different things and


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this goes back to some of the work that


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made Steven Hawking so worldrenowned.


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Now obviously for a lot of people


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Stephven Hawking became a global name


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with the publication of a brief history


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of time which did a very good job of


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explaining very complicated things in a


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way that people could at least feel like


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they had a grasp of. Um, I remember


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reading it as a kid and it made my head


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hurt, but it in a good way. I could


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actually follow it. It was well


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explained. One of the things that


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Stephven Hawking did fairly early in his


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career, I think in like 1974 or


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something, was do some very theoretical


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work on black holes where he postulated


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that black holes could lose weight


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through a process called Hawking


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radiation. And the idea is that black


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holes can effectively be considered to


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have a temperature and to radiate energy


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and therefore mass away into space. And


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the smaller the black hole, the hotter


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it is, so the quicker it would radiate.


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And this is all backed up by


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ridiculously complex physics and


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mathematics that is way beyond my level


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of full understanding. But part of the


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idea behind it is that what we think of


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as the empty vacuum of space is actually


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not a true vacuum, but is instead


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constantly populated by pairs of matter


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and antimatter particles that


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spontaneously create and then collide


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with each other and disappear again. And


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if these if such an event happens near


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the event horizon of a black hole, one


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of the particles falls into the black


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hole, the other escapes and it seemed to


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lose mass, lose energy and radiation


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going along with that. Now the bigger


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the black hole, the colder it would be.


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So the slower it radiates anyway, but


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also the bigger it is, the more


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effectively it can feed from its


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environment. Even if that's little bits


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of dust falling in, or if it's near a


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star, it can feed off that star, get an


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accretion disc. So the black holes that


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form in the modern universe are formed


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by stars reaching the end of their lives


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and are massive. They're more massive


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than the sun by a long way. They're


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formed from stars much more massive than


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the sun. You get massive black holes,


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you get intermediate mass black holes,


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and you get super massive black holes.


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And they're all the big whopping ones.


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And the time scale, as I understand it,


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for those black holes to decay through


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Hawking radiation is ridiculously,


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ridiculously, ridiculously longer than


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the age of the universe.


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>> Yes.


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>> And they're probably not emitting


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Hawking radiation at a level that we


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could detect because they are very cold


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in his quantification of it. However, at


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the birth of the universe when the


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temperature and pressure was immense


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after the big bang, there were


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theoretically a class of black holes


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created called primordial black holes.


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So these were black holes that were not


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born from the fiery death of a star, but


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were instead born out of the big bang


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and the pressures and the temperatures.


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And these could be black holes down to


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the mass of a thumbnail or down really


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really tiny ones, planet mass black


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holes. Y


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>> the smaller you are as a black hole, the


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more quickly you radiate things away. So


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the shorter your lifetime and so you


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have this idea that these primordial


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black holes evaporate it over time and


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effectively none of them will survive to


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the current day. Those evaporating black


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holes would evaporate over time and give


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off radiation that we have never yet


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detected. But a black hole coming to the


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end of its life will evaporate faster


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and faster. There's a quote on an


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article I found recently which may be


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tied to this. Um, an article entitled,


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"An exploding black hole could reveal


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the foundations of the universe,


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published from September last year,


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talking about the predictions that as


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our technology gets better in the coming


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years, we may be able to detect this


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Hawking radiation in an event where the


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black hole reaches its critical phase


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and evaporates entirely within the next


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few years." So, not quite the neutrino


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discovery that we were talking about in


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the question, but a related thing. And


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there's a quote here from Andrea Tham


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who associate professor Andrea Tham. I I


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do hate it when articles don't give


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people's well- earned titles until later


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in the sentence or don't give them at


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all.


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>> Um which is another rant I could go on


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that's separate but it's particularly


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affects my um early career colleagues


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and affects colleagues from


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nontraditional backgrounds and stuff and


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it's a very dim demonizing


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thing diminishing thing. It lowers their


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expertise. Anyway, this is a quote from


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associate professor Andrea Tham from


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University of Massachusetts Amhurst


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says, "As primordial black holes


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evaporate, they become ever lighter, so


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hotter, they therefore emit even more


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radiation. It's a runaway process until


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they explode."


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>> It's that Hawking radiation that our


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telescopes can detect.


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>> Yeah.


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>> So, what's happening is you've got these


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primordial black holes that are really


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itty bitty diddy ones that are therefore


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evaporating quicker than they can gain


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mass. they'll be on this critical


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threshold. And so you get this runaway


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death where the more massive ones live


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longer before they get small enough to


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finally evaporate and then explode. And


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so I would guess that the observation of


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this super neutrino that has been linked


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potentially to an exploding black hole


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is not two black holes colliding. not a


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modern black hole formed from the death


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of stars but rather is a death of a


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primordial black hole as would be


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predicted by this research by Steven


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Hawking more than 50 years ago in the


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form of Hawking radiation. So that's my


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thinking on what's happening here. Now


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obviously I am not an expert. Um I've


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said previously on many places that in a


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lot of disciplines and when we're


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teaching our undergrads we often say


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avoid Wikipedia. Wikipedia is not a


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static resource. It's a fluid resource


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and it's often wrong and I know for


00:07:56.960 --> 00:07:58.309
journalists it's probably often


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something you cautioned don't get your


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facts from Wikipedia


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>> for astrophysics and particularly the


00:08:03.280 --> 00:08:05.749
more technical and hardcore ends of


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astrophysics. Wikipedia is actually very


00:08:08.560 --> 00:08:10.710
reliable because very few people will be


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interested in maliciously editing a web


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page because frankly they'll go after


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other topics that are more triggering.


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But also people who are interested in


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this stuff and have the knowledge tend


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to be very obsessive and if they spot


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something wrong they fix it very


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quickly. The result of that is if you


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Google Hawking radiation the Wikipedia


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page is very lengthy goes into a lot of


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detail includes some of the maths that


00:08:33.839 --> 00:08:35.430
makes my head hurt and makes me want to


00:08:35.440 --> 00:08:37.670
cry a little bit um talking about black


00:08:37.680 --> 00:08:40.149
hole evaporation and things like this.


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Now


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the equation for black hole evaporation


00:08:44.000 --> 00:08:45.509
that's on here which is based on the


00:08:45.519 --> 00:08:49.910
Hawking work gives a evaporation time


00:08:49.920 --> 00:08:55.670
for a black hole of 2.14 * 10 67 years.


00:08:55.680 --> 00:08:59.350
So that's 2.14 multiplied by 10 with 67


00:08:59.360 --> 00:09:01.350
zeros


00:09:01.360 --> 00:09:03.750
multiplied by the mass of the black hole


00:09:03.760 --> 00:09:05.670
divided the by the mass of the sun to


00:09:05.680 --> 00:09:08.630
the power three. So if you've got a


00:09:08.640 --> 00:09:11.350
black hole that is one solar mass, it


00:09:11.360 --> 00:09:14.389
will take 2.14 * 10 67 years to


00:09:14.399 --> 00:09:15.829
evaporate. And the more massive it is,


00:09:15.839 --> 00:09:17.430
the larger that number gets.


00:09:17.440 --> 00:09:17.750
>> Yeah.


00:09:17.760 --> 00:09:20.630
>> To the power 3. So the multiplier here


00:09:20.640 --> 00:09:22.310
is get the mass of the black hole as


00:09:22.320 --> 00:09:23.829
measured in units of the mass of the


00:09:23.839 --> 00:09:27.030
sun. Cube that number and then multiply


00:09:27.040 --> 00:09:31.190
it by 2.14 * 10 67 and you get a


00:09:31.200 --> 00:09:34.070
headache. But you get a number. Now the


00:09:34.080 --> 00:09:38.389
mass of the sun is what? 2 * 10 30


00:09:38.399 --> 00:09:39.670
kilos,


00:09:39.680 --> 00:09:45.030
>> right? Mass of the earth is 5.97 * 10 24


00:09:45.040 --> 00:09:48.550
kilos. So that is effectively


00:09:48.560 --> 00:09:51.269
um 2 * 10 - 6 solar mass. It's about a


00:09:51.279 --> 00:09:52.630
millionth of a solar mass. So we'll just


00:09:52.640 --> 00:09:55.590
say it's 1 millionth of a solar mass. 1


00:09:55.600 --> 00:09:57.430
millionth


00:09:57.440 --> 00:10:02.550
cubed is 1 * 10 - 18. That means a black


00:10:02.560 --> 00:10:04.949
hole the mass of the earth would decay


00:10:04.959 --> 00:10:06.470
much more quickly. it would decay in


00:10:06.480 --> 00:10:09.990
only 10^ the 49 years which is still


00:10:10.000 --> 00:10:12.070
much much much much longer than the age


00:10:12.080 --> 00:10:13.590
of the universe but you can play this


00:10:13.600 --> 00:10:16.710
game with everything. I am too fat. You


00:10:16.720 --> 00:10:17.910
know, we talk about health and


00:10:17.920 --> 00:10:20.470
everything on the show before. I am a


00:10:20.480 --> 00:10:22.230
fair bit more than 100 kilos, but let's


00:10:22.240 --> 00:10:25.110
assume I was 100 kilos. Um, just because


00:10:25.120 --> 00:10:26.870
that's an aspirational goal and it would


00:10:26.880 --> 00:10:28.710
be nice if it were true one day. In


00:10:28.720 --> 00:10:30.949
fact, I'm 100 kilos and you make me a


00:10:30.959 --> 00:10:32.949
black hole. Um, I would be sad but


00:10:32.959 --> 00:10:34.150
probably wouldn't have long to think


00:10:34.160 --> 00:10:38.550
about it. At 100 kilos, I would be 10


00:10:38.560 --> 00:10:42.310
the 28 times less massive than the sun


00:10:42.320 --> 00:10:45.030
roughly. The sun is 10 to the 30. I'm 10


00:10:45.040 --> 00:10:49.030
2 10 the 28 is a difference 10 28 cubed


00:10:49.040 --> 00:10:54.710
is 28 56 84 so that's 10 84


00:10:54.720 --> 00:10:57.430
so that means I would disintegrate in 2


00:10:57.440 --> 00:11:02.949
* 10 67 * 10 - 84 which is about 10 -17


00:11:02.959 --> 00:11:05.430
years so suddenly a jumpy mass black


00:11:05.440 --> 00:11:08.310
hole would disintegrate and evaporate in


00:11:08.320 --> 00:11:11.509
a tiny fraction of a millisecond


00:11:11.519 --> 00:11:13.750
so these primordial mass black holes


00:11:13.760 --> 00:11:15.590
that evaporate


00:11:15.600 --> 00:11:19.030
are doing so because they're very small.


00:11:19.040 --> 00:11:20.310
You could, if you wanted to, and I'll


00:11:20.320 --> 00:11:21.750
leave this as an exercise to the reader


00:11:21.760 --> 00:11:23.350
because me doing mental arithmetic is


00:11:23.360 --> 00:11:25.590
not the most exciting thing, you could


00:11:25.600 --> 00:11:27.350
work out what mass a black hole would


00:11:27.360 --> 00:11:31.190
have to be to evaporate after 13.8


00:11:31.200 --> 00:11:34.150
billion years, which is about how old


00:11:34.160 --> 00:11:36.389
the universe is. The reason that's an


00:11:36.399 --> 00:11:37.590
interesting one is if there were any


00:11:37.600 --> 00:11:40.870
primordial mass black holes of that mass


00:11:40.880 --> 00:11:43.269
>> and they were to evaporate, they would


00:11:43.279 --> 00:11:44.710
be evaporating in the very near


00:11:44.720 --> 00:11:46.230
universe.


00:11:46.240 --> 00:11:47.990
And that would make them much easier to


00:11:48.000 --> 00:11:49.509
detect because the intensity of


00:11:49.519 --> 00:11:52.150
radiation we detect is proportional to


00:11:52.160 --> 00:11:54.230
one over the square of the distance. So


00:11:54.240 --> 00:11:55.829
if something's twice as far away, it's


00:11:55.839 --> 00:11:57.509
four times fainter. If it's three times


00:11:57.519 --> 00:12:00.630
as far away, it's nine times fainter. So


00:12:00.640 --> 00:12:02.150
I don't know. I'm not a black hole


00:12:02.160 --> 00:12:04.310
expert by any means. I I say that all


00:12:04.320 --> 00:12:06.310
the time.


00:12:06.320 --> 00:12:08.230
But if there were a black hole of that


00:12:08.240 --> 00:12:12.470
mass formed at the big bang, then maybe


00:12:12.480 --> 00:12:13.750
they would be evaporating in the


00:12:13.760 --> 00:12:15.190
relatively local universe and they're


00:12:15.200 --> 00:12:16.629
the ones that have been most likely to


00:12:16.639 --> 00:12:20.310
detect. I do not, however, know what the


00:12:20.320 --> 00:12:23.990
distribution of masses for primordial


00:12:24.000 --> 00:12:25.509
black holes would be. It's possibly on


00:12:25.519 --> 00:12:28.870
this Wikipedia page, but have a look and


00:12:28.880 --> 00:12:30.710
find out if it's your kind of thing. But


00:12:30.720 --> 00:12:33.110
hopefully that explains why there's a


00:12:33.120 --> 00:12:34.710
turnover point where things will decay


00:12:34.720 --> 00:12:36.230
in less than the age of the universe or


00:12:36.240 --> 00:12:38.069
more than the edge of the universe. And


00:12:38.079 --> 00:12:39.670
that mass is somewhere between the mass


00:12:39.680 --> 00:12:42.230
of a Jonty and the mass of the Earth.


00:12:42.240 --> 00:12:44.629
Okay. Fascinating. Yeah. All right.


00:12:44.639 --> 00:12:46.710
Thank you, Nick. Uh and Nick uh you


00:12:46.720 --> 00:12:49.110
might have heard us talking a week or


00:12:49.120 --> 00:12:52.790
two or three or four back uh about uh


00:12:52.800 --> 00:12:55.030
what they think might be the discovery


00:12:55.040 --> 00:12:57.350
of a primordial black hole. So that's a


00:12:57.360 --> 00:12:59.190
story worth looking up as well. Thanks


00:12:59.200 --> 00:13:01.269
for your question. This is Space Nuts


00:13:01.279 --> 00:13:04.310
Q&A edition with Andrew Dunley and Jonty


00:13:04.320 --> 00:13:08.069
Horner.


00:13:08.079 --> 00:13:09.590
>> G and I feel fine.


00:13:09.600 --> 00:13:10.710
>> Space Nuts.


00:13:10.720 --> 00:13:12.790
>> Uh, now Jonty, we've got an audio


00:13:12.800 --> 00:13:14.949
question that comes from a repeat


00:13:14.959 --> 00:13:17.590
offender. Uh, her name's Andrea.


00:13:17.600 --> 00:13:19.910
>> Hi guys. Um, got a couple of questions


00:13:19.920 --> 00:13:22.470
I'm hoping you can help me with. Um, the


00:13:22.480 --> 00:13:26.310
first question I have is, um, why does


00:13:26.320 --> 00:13:29.269
the dark side of the moon not have


00:13:29.279 --> 00:13:31.750
anywhere near as much damage as the face


00:13:31.760 --> 00:13:35.030
of the moon? Um,


00:13:35.040 --> 00:13:39.750
my second question is, um,


00:13:39.760 --> 00:13:42.230
why are the craters so shallow on the


00:13:42.240 --> 00:13:43.990
moon? Considering


00:13:44.000 --> 00:13:47.110
the size of some of the impacts zones


00:13:47.120 --> 00:13:49.670
and craters, um they all seem to be the


00:13:49.680 --> 00:13:51.910
same depth and which is quite shallow.


00:13:51.920 --> 00:13:54.629
Um especially if you look at Teao, which


00:13:54.639 --> 00:13:58.310
is 3,000 mi wide, um with an incredibly


00:13:58.320 --> 00:14:02.150
shallow crater. Um if you could explain


00:14:02.160 --> 00:14:05.750
for me why that occurs, that would be


00:14:05.760 --> 00:14:07.910
absolutely amazing. Thank you very much.


00:14:07.920 --> 00:14:10.470
Oh, and this is Andrea from Wanoo. and


00:14:10.480 --> 00:14:14.069
Andrew uh wannoo is actually a nunga or


00:14:14.079 --> 00:14:18.150
wjak nunga uh people word um that


00:14:18.160 --> 00:14:22.790
actually means the area of the digging


00:14:22.800 --> 00:14:25.910
stick. Unfortunately not pet kangaroo


00:14:25.920 --> 00:14:27.269
although I have had one of those as


00:14:27.279 --> 00:14:29.750
well. Thanks guys. Take care.


00:14:29.760 --> 00:14:31.430
>> Thanks Andrea. Lovely to hear from you.


00:14:31.440 --> 00:14:33.030
I'm glad she explained that. Um, you


00:14:33.040 --> 00:14:33.990
probably don't know what she's talking


00:14:34.000 --> 00:14:36.230
about, Jonty, but um, when Andrea last


00:14:36.240 --> 00:14:38.629
sent us an audio question and she said


00:14:38.639 --> 00:14:40.949
she was from Woo, I translated that to


00:14:40.959 --> 00:14:43.110
an indigenous word meaning I want a pet


00:14:43.120 --> 00:14:44.629
kangaroo.


00:14:44.639 --> 00:14:47.189
So, yeah, I know I was being silly, but


00:14:47.199 --> 00:14:49.509
um, no, it's um, place of the digging


00:14:49.519 --> 00:14:52.069
stick. Didn't know that. So um of course


00:14:52.079 --> 00:14:53.910
a digging stick was one of the uh


00:14:53.920 --> 00:14:57.110
implements that the ancient indigenous


00:14:57.120 --> 00:14:59.350
peoples of Australia used to use to uh


00:14:59.360 --> 00:15:03.829
to dig up food um grubs and other other


00:15:03.839 --> 00:15:05.910
bush tucker as we call it these days.


00:15:05.920 --> 00:15:07.590
So, it's probably worth mentioning for


00:15:07.600 --> 00:15:09.110
the listeners who are not in Australia


00:15:09.120 --> 00:15:11.910
that many of the Australian places have


00:15:11.920 --> 00:15:14.870
names that derive from the languages of


00:15:14.880 --> 00:15:15.990
the traditional owners of the land of


00:15:16.000 --> 00:15:17.990
the indigenous people of Australia who


00:15:18.000 --> 00:15:19.910
had many different countries with many


00:15:19.920 --> 00:15:22.470
different language groups. And the


00:15:22.480 --> 00:15:24.389
origin of the names is not always that


00:15:24.399 --> 00:15:27.269
wellknown or understood because during


00:15:27.279 --> 00:15:29.189
the invasion of Australia and during the


00:15:29.199 --> 00:15:30.310
events that happened all the way through


00:15:30.320 --> 00:15:32.550
to the 1970s there was a fairly


00:15:32.560 --> 00:15:34.790
aggressive attempt to even if you


00:15:34.800 --> 00:15:36.310
weren't wiping out the people to get rid


00:15:36.320 --> 00:15:37.750
of the culture and to get rid of the


00:15:37.760 --> 00:15:39.670
knowledge. Now I've just looked up to


00:15:39.680 --> 00:15:43.110
Womba where I am to o wa


00:15:43.120 --> 00:15:46.069
I live about 20ks west of there. Toua is


00:15:46.079 --> 00:15:47.750
an indigenous name. It's a really


00:15:47.760 --> 00:15:49.829
interesting town because it's like the


00:15:49.839 --> 00:15:51.269
Florida of Queensland. All the old


00:15:51.279 --> 00:15:53.910
people come here to retire.


00:15:53.920 --> 00:15:55.269
>> It's a beautiful place because


00:15:55.279 --> 00:15:59.670
Queensland has a particular climate, but


00:15:59.680 --> 00:16:01.829
Touumba is a moderated version of that


00:16:01.839 --> 00:16:03.110
climate because it sits on the Great


00:16:03.120 --> 00:16:05.110
Dividing Range at about 700 meters above


00:16:05.120 --> 00:16:07.189
sea level. So, it's not as humid as the


00:16:07.199 --> 00:16:08.710
coast. It doesn't get as hot as the


00:16:08.720 --> 00:16:10.870
coast. It has very lovely dry winters.


00:16:10.880 --> 00:16:14.949
Anyway, the name of Toumba is probably


00:16:14.959 --> 00:16:18.790
based on a word from likely the Gable or


00:16:18.800 --> 00:16:21.590
Jawar peoples. Not entirely sure, but if


00:16:21.600 --> 00:16:23.590
you look around for the origin of


00:16:23.600 --> 00:16:26.150
Towumba as a word, there's lots of


00:16:26.160 --> 00:16:27.670
suggestions. There is a suggestion that


00:16:27.680 --> 00:16:29.910
it was a word for swamp because Toumba


00:16:29.920 --> 00:16:31.350
sits in this swampy area on top of the


00:16:31.360 --> 00:16:33.509
hills. According to the Touumba regional


00:16:33.519 --> 00:16:35.670
council, it may have been named after a


00:16:35.680 --> 00:16:38.710
property in the area in the 1850s.


00:16:38.720 --> 00:16:40.870
Or it may have come from an Aboriginal


00:16:40.880 --> 00:16:42.550
word meaning either place where water


00:16:42.560 --> 00:16:44.389
sits, which would be the swamp thing, or


00:16:44.399 --> 00:16:46.629
place of melon, or place where reeds


00:16:46.639 --> 00:16:49.350
grow, or berries place, or white man.


00:16:49.360 --> 00:16:50.949
There are other things saying meeting of


00:16:50.959 --> 00:16:53.670
the waters or saying the name of Touumba


00:16:53.680 --> 00:16:55.269
maybe an anglicized version of the word


00:16:55.279 --> 00:16:58.230
bua which meant thunder in the dialect


00:16:58.240 --> 00:17:00.949
of the upper bett and gander tribes. So


00:17:00.959 --> 00:17:03.189
we just don't know and does make me a


00:17:03.199 --> 00:17:04.789
little bit sad. We talk about indigenous


00:17:04.799 --> 00:17:06.470
astronomy a bit and the wonderful work


00:17:06.480 --> 00:17:08.789
that um professor Dwayne Hammer and his


00:17:08.799 --> 00:17:09.990
students have done over the years


00:17:10.000 --> 00:17:11.350
working with the indigenous people of


00:17:11.360 --> 00:17:13.029
Australia but it does make me sad how


00:17:13.039 --> 00:17:14.470
much of this knowledge is lost where you


00:17:14.480 --> 00:17:16.309
don't even know the origin of the name.


00:17:16.319 --> 00:17:18.549
So it's wonderful that in this case we


00:17:18.559 --> 00:17:20.630
actually know where the name comes from


00:17:20.640 --> 00:17:21.990
and we can tag that. So when you're


00:17:22.000 --> 00:17:23.189
looking at the map of Australia and


00:17:23.199 --> 00:17:25.270
think a lot of the places are unusual


00:17:25.280 --> 00:17:27.189
from the perspective of someone from an


00:17:27.199 --> 00:17:29.029
Anglo background or from a European


00:17:29.039 --> 00:17:31.430
background because even though it's a


00:17:31.440 --> 00:17:33.029
primarily English-speaking country


00:17:33.039 --> 00:17:37.029
nowadays with a with that you know Anglo


00:17:37.039 --> 00:17:38.789
heritage a lot of the names are actually


00:17:38.799 --> 00:17:41.190
from the traditional owners even if the


00:17:41.200 --> 00:17:43.669
heritage of that name itself is lost.


00:17:43.679 --> 00:17:47.190
>> Yes. Uh where I live, do is supposedly a


00:17:47.200 --> 00:17:49.590
wordy word for red earth because the


00:17:49.600 --> 00:17:53.270
soil here is red. Uh which might sound


00:17:53.280 --> 00:17:55.750
horrifying to people. Uh it is when you


00:17:55.760 --> 00:17:57.750
get a dust storm and everything turns


00:17:57.760 --> 00:17:59.029
red.


00:17:59.039 --> 00:18:01.510
>> And when it gets wet and your bring it


00:18:01.520 --> 00:18:04.470
in because the red soil marks everything


00:18:04.480 --> 00:18:05.830
up, you know,


00:18:05.840 --> 00:18:07.430
>> dog goes out and gets their paws muddy


00:18:07.440 --> 00:18:09.270
and brings in red footprints.


00:18:09.280 --> 00:18:11.590
>> Red footprints on a light colored


00:18:11.600 --> 00:18:14.150
carpet. No. Terrible stuff. And of


00:18:14.160 --> 00:18:17.029
course, one that relates to astronomy is


00:18:17.039 --> 00:18:20.230
warmer, which is an indigenous word for


00:18:20.240 --> 00:18:23.110
uh the the implement they used to launch


00:18:23.120 --> 00:18:25.430
a spear. Rather than just throw the


00:18:25.440 --> 00:18:28.150
spear, they used to have a speciallymade


00:18:28.160 --> 00:18:29.750
um


00:18:29.760 --> 00:18:31.590
I suppose you'd call it a like a


00:18:31.600 --> 00:18:35.270
handheld catapult and it um and it


00:18:35.280 --> 00:18:37.510
>> and and it Yeah. And it flung the spear


00:18:37.520 --> 00:18:39.350
at greater speed and distance. And


00:18:39.360 --> 00:18:41.270
that's uh yeah it was called a WMAR and


00:18:41.280 --> 00:18:43.270
of course WRA rocket range is where


00:18:43.280 --> 00:18:47.350
Australia's uh early space efforts were


00:18:47.360 --> 00:18:48.710
uh were launched from in South


00:18:48.720 --> 00:18:50.549
Australia. So yeah it's um yeah it's


00:18:50.559 --> 00:18:52.950
fascinating history really is and


00:18:52.960 --> 00:18:54.390
>> of course the atal that I mentioned


00:18:54.400 --> 00:18:55.669
there I just double checked because it's


00:18:55.679 --> 00:18:58.070
like I remember an atal being a thing


00:18:58.080 --> 00:18:59.590
that used for throwing space turns out


00:18:59.600 --> 00:19:01.029
that that was an Aztec implement that


00:19:01.039 --> 00:19:02.470
served the same kind of process. So the


00:19:02.480 --> 00:19:05.270
word atal apparently comes from Aztec.


00:19:05.280 --> 00:19:08.470
>> Oh wow. I didn't know that. Back to you,


00:19:08.480 --> 00:19:09.270
Andrea. Yes.


00:19:09.280 --> 00:19:11.669
>> Uh, now the dark Okay, two questions.


00:19:11.679 --> 00:19:14.230
Dark side of the moon, uh, smoother.


00:19:14.240 --> 00:19:16.390
Now, I I've always been aware that the


00:19:16.400 --> 00:19:19.350
the side we can see is so rugged and and


00:19:19.360 --> 00:19:21.110
pockmarked and mountainous.


00:19:21.120 --> 00:19:21.830
>> Yes.


00:19:21.840 --> 00:19:24.070
>> But the side that we cannot see that


00:19:24.080 --> 00:19:26.789
Artemus 2 recently had a look at and


00:19:26.799 --> 00:19:28.310
where the Chinese have been running


00:19:28.320 --> 00:19:31.510
around on their little scooters, um,


00:19:31.520 --> 00:19:33.590
it's smoother. Why?


00:19:33.600 --> 00:19:38.150
>> Well, this is a weird one. So it looks


00:19:38.160 --> 00:19:39.990
more uniform when you look at it. And


00:19:40.000 --> 00:19:41.430
I'm I'm saying that very carefully


00:19:41.440 --> 00:19:43.909
rather than smoother because smoother


00:19:43.919 --> 00:19:46.310
invokes polished or smooth. Like your


00:19:46.320 --> 00:19:47.669
skin when you're a kid is a lot smoother


00:19:47.679 --> 00:19:48.789
than your skin when you get to my age


00:19:48.799 --> 00:19:50.549
and you've got all the wrinkles, right?


00:19:50.559 --> 00:19:50.870
>> Yeah.


00:19:50.880 --> 00:19:51.510
>> Um


00:19:51.520 --> 00:19:52.950
>> all the scars. See this one?


00:19:52.960 --> 00:19:53.750
>> Yeah.


00:19:53.760 --> 00:19:55.110
>> That's from a golf that's from a golf


00:19:55.120 --> 00:19:56.549
club. My neighbor hit me in the face


00:19:56.559 --> 00:19:57.990
with a seven iron.


00:19:58.000 --> 00:19:58.310
>> Yeah.


00:19:58.320 --> 00:19:59.830
>> It wasn't malicious. It was the back


00:19:59.840 --> 00:20:01.510
swing. I was standing too close. I was


00:20:01.520 --> 00:20:02.870
going to say about the adventures of


00:20:02.880 --> 00:20:04.310
having double, you know, they do


00:20:04.320 --> 00:20:06.390
something to pass the time. The reason


00:20:06.400 --> 00:20:07.909
that I'm being careful in my wording


00:20:07.919 --> 00:20:09.510
here and saying it looks more uniform


00:20:09.520 --> 00:20:11.909
rather than it's smoother is actually I


00:20:11.919 --> 00:20:13.270
don't think it is smoother, but I think


00:20:13.280 --> 00:20:15.590
it definitely does look more uniform. On


00:20:15.600 --> 00:20:17.669
the near side of the moon, it should be


00:20:17.679 --> 00:20:19.029
said that we're talking near side and


00:20:19.039 --> 00:20:20.630
far side. The dark side of the moon is


00:20:20.640 --> 00:20:22.150
simply the side of the moon pointed away


00:20:22.160 --> 00:20:24.710
from the sun and that rotates around as


00:20:24.720 --> 00:20:26.230
the moon goes around the earth, which is


00:20:26.240 --> 00:20:27.590
why we get the phases. Right? If you're


00:20:27.600 --> 00:20:29.430
stood on the moon, you'll get at a given


00:20:29.440 --> 00:20:31.270
location two weeks of daytime and two


00:20:31.280 --> 00:20:32.789
weeks of nighttime. And when it's


00:20:32.799 --> 00:20:34.310
nighttime for you, you'd be on the dark


00:20:34.320 --> 00:20:36.070
side of the moon. But when the moon's


00:20:36.080 --> 00:20:37.669
new, the dark side points towards us.


00:20:37.679 --> 00:20:39.669
The far side of the moon always points


00:20:39.679 --> 00:20:41.750
away from the Earth. Now, on the near


00:20:41.760 --> 00:20:43.270
side of the moon, which is a side we're


00:20:43.280 --> 00:20:47.029
familiar with, the view we get is very


00:20:47.039 --> 00:20:49.430
non-uniform because we've got the Mare


00:20:49.440 --> 00:20:51.669
and the non-mar regions. So the Mari are


00:20:51.679 --> 00:20:53.270
the seas which make up the man in the


00:20:53.280 --> 00:20:55.270
moon or whatever picture you have which


00:20:55.280 --> 00:20:57.830
are these flood bassalt areas. And then


00:20:57.840 --> 00:21:00.310
you've got the non-mari areas which are


00:21:00.320 --> 00:21:03.350
more traditionally rocky object looking.


00:21:03.360 --> 00:21:06.710
>> He's he's the drunk man in the moon uh


00:21:06.720 --> 00:21:08.230
here because he's upside down.


00:21:08.240 --> 00:21:11.350
>> Absolutely. Yeah. It's those areas that


00:21:11.360 --> 00:21:14.710
make the drunk man are flood bassalt


00:21:14.720 --> 00:21:16.710
outpourings on the near side of the moon


00:21:16.720 --> 00:21:18.310
that were formed early in the moon's


00:21:18.320 --> 00:21:20.549
formation. If you ascribe to the idea


00:21:20.559 --> 00:21:22.390
that there was a late heavy bombardment


00:21:22.400 --> 00:21:25.029
when the impact rate spiked, then they


00:21:25.039 --> 00:21:26.789
are thought to have formed there. But in


00:21:26.799 --> 00:21:28.310
actuality, evidence for the late heavy


00:21:28.320 --> 00:21:30.149
bombardment has pretty much dissipated.


00:21:30.159 --> 00:21:32.870
So the closer you are to impact studies


00:21:32.880 --> 00:21:34.630
and studies of the moon, the less


00:21:34.640 --> 00:21:35.909
strongly you hold to the idea of the


00:21:35.919 --> 00:21:37.590
late heavy bombardment was a thing. But


00:21:37.600 --> 00:21:39.669
as with all science, the further you get


00:21:39.679 --> 00:21:41.270
from certain expertise, the more out of


00:21:41.280 --> 00:21:43.029
date your knowledge is. So the late


00:21:43.039 --> 00:21:44.710
heavy bombardment is quite often still


00:21:44.720 --> 00:21:46.390
viewed as cannon in a lot of areas


00:21:46.400 --> 00:21:47.990
whereas those who were closest to the


00:21:48.000 --> 00:21:49.990
topic have a lot more doubt that it ever


00:21:50.000 --> 00:21:51.909
happened. But anyway on the near side of


00:21:51.919 --> 00:21:54.630
the moon you've got


00:21:54.640 --> 00:21:58.549
areas of the moon that didn't have a mar


00:21:58.559 --> 00:22:01.830
didn't have a flood bassalt outpouring


00:22:01.840 --> 00:22:03.510
and you've got areas that did. And then


00:22:03.520 --> 00:22:05.270
overlaid on that you've got some more


00:22:05.280 --> 00:22:06.870
recent impacts which are the rare


00:22:06.880 --> 00:22:09.110
craters where you've got weathered


00:22:09.120 --> 00:22:10.630
material on the surface that looks


00:22:10.640 --> 00:22:12.549
darker and an impact comes along digs


00:22:12.559 --> 00:22:13.830
through the darker material to the


00:22:13.840 --> 00:22:15.350
unweathered material below and splashes


00:22:15.360 --> 00:22:17.430
it across the surface. So the near side


00:22:17.440 --> 00:22:18.950
of the moon looks very non-uniform


00:22:18.960 --> 00:22:20.390
because you've got that disparity


00:22:20.400 --> 00:22:22.789
between the flood bassels and the non-


00:22:22.799 --> 00:22:25.270
flood basel. And the non- flood basel is


00:22:25.280 --> 00:22:27.350
an older surface because the flood basel


00:22:27.360 --> 00:22:28.789
erases the evidence of what happened


00:22:28.799 --> 00:22:31.430
before. So there are slightly fewer


00:22:31.440 --> 00:22:33.350
impacts on the MAR than there are on the


00:22:33.360 --> 00:22:36.870
non-mar because it's a younger surface.


00:22:36.880 --> 00:22:39.190
Prior to any spacecraft going to the


00:22:39.200 --> 00:22:40.549
moon, the assumption was the far side of


00:22:40.559 --> 00:22:42.630
the moon would look like the near side.


00:22:42.640 --> 00:22:43.990
>> But when we sent the spacecraft there,


00:22:44.000 --> 00:22:45.590
we realized it doesn't. And that was a


00:22:45.600 --> 00:22:47.190
big puzzle for astronomers for a very


00:22:47.200 --> 00:22:49.190
long time in that there are effectively


00:22:49.200 --> 00:22:51.350
no mare on the far side. There's little


00:22:51.360 --> 00:22:53.590
bits but not very much.


00:22:53.600 --> 00:22:56.950
Now the idea here is that when the moon


00:22:56.960 --> 00:22:58.710
formed, it formed as a result of a giant


00:22:58.720 --> 00:23:01.110
impact on the earth. The moon accreted


00:23:01.120 --> 00:23:02.789
and initially was fully molten and then


00:23:02.799 --> 00:23:05.110
it cooled from the outside in. So at a


00:23:05.120 --> 00:23:07.430
certain time in the moon's youth, the


00:23:07.440 --> 00:23:09.669
surface was very thin above a magma


00:23:09.679 --> 00:23:12.230
ocean, above a molten ocean. And at that


00:23:12.240 --> 00:23:14.630
time, small impacts wouldn't penetrate


00:23:14.640 --> 00:23:16.789
that crust and you get normal craters,


00:23:16.799 --> 00:23:18.310
you get mountain ranges and all the rest


00:23:18.320 --> 00:23:19.909
of it forming. But when you got a really


00:23:19.919 --> 00:23:21.990
big impact that would break through the


00:23:22.000 --> 00:23:24.390
crust, create a big impact basin that


00:23:24.400 --> 00:23:26.630
would then be flooded with flood bassel


00:23:26.640 --> 00:23:28.310
which gave you this incredibly flat


00:23:28.320 --> 00:23:30.950
smooth floor and erased all the evidence


00:23:30.960 --> 00:23:33.110
of the impacts before.


00:23:33.120 --> 00:23:34.789
Eventually the moon cooled enough that


00:23:34.799 --> 00:23:36.950
the that any molten material was


00:23:36.960 --> 00:23:38.710
sufficiently deep that even the biggest


00:23:38.720 --> 00:23:41.110
impacts would not cause these flood


00:23:41.120 --> 00:23:43.750
bassel outpourings. coupled with the


00:23:43.760 --> 00:23:46.310
fact that as the solar system aged it


00:23:46.320 --> 00:23:47.909
cleaned up very effectively and the big


00:23:47.919 --> 00:23:49.430
impactors were effectively gone. So the


00:23:49.440 --> 00:23:51.510
big impacts were early on. So the idea


00:23:51.520 --> 00:23:54.710
was that the mare are caused by the very


00:23:54.720 --> 00:23:57.430
biggest impacts that will create impact


00:23:57.440 --> 00:23:59.669
basins that are hundreds or thousands of


00:23:59.679 --> 00:24:02.950
kilometers across that are broadly


00:24:02.960 --> 00:24:04.950
circular in shape before other things


00:24:04.960 --> 00:24:07.029
happen and that they fill with molten


00:24:07.039 --> 00:24:09.510
material. And the areas on the near side


00:24:09.520 --> 00:24:11.590
that are not in the mar are the areas


00:24:11.600 --> 00:24:14.149
that were not induced into one of these


00:24:14.159 --> 00:24:15.830
flood basel output or rings. Effectively


00:24:15.840 --> 00:24:17.909
they escaped being in one of the craters


00:24:17.919 --> 00:24:20.390
from the very biggest impactors.


00:24:20.400 --> 00:24:22.549
We thought that prior to going to the


00:24:22.559 --> 00:24:23.990
far side of the moon you would have


00:24:24.000 --> 00:24:25.350
assumed that the far side would be the


00:24:25.360 --> 00:24:27.590
same but it turns out that it's not.


00:24:27.600 --> 00:24:29.190
That was a real problem because this


00:24:29.200 --> 00:24:31.029
idea that the impacts were big enough to


00:24:31.039 --> 00:24:35.510
punch through and flood to the surface


00:24:35.520 --> 00:24:38.310
should work all across the moon. So why


00:24:38.320 --> 00:24:39.590
then do you not get the flood bass


00:24:39.600 --> 00:24:41.510
outpourings on the far side of the moon?


00:24:41.520 --> 00:24:43.669
There are kind of three explanations


00:24:43.679 --> 00:24:45.909
that have been put forward for this. The


00:24:45.919 --> 00:24:48.630
first of which is frankly bunkam. The


00:24:48.640 --> 00:24:50.149
idea that the near side of the moon


00:24:50.159 --> 00:24:52.149
faced the earth and the earth shielded


00:24:52.159 --> 00:24:54.230
it and so therefore there'd be more


00:24:54.240 --> 00:24:55.990
impacts on the far side. Well that just


00:24:56.000 --> 00:24:57.909
kind of


00:24:57.919 --> 00:25:00.070
runs counterintuitive. You'd say the far


00:25:00.080 --> 00:25:01.669
side experienced more hits. It gets more


00:25:01.679 --> 00:25:03.430
cratering. Well I don't believe that


00:25:03.440 --> 00:25:04.950
from an earth is so small from the


00:25:04.960 --> 00:25:06.710
moon's point of view. barely a shield at


00:25:06.720 --> 00:25:09.590
all. But if that were the case, surely


00:25:09.600 --> 00:25:11.510
you'd expect more mar on the far side


00:25:11.520 --> 00:25:12.630
because you get more of these big


00:25:12.640 --> 00:25:14.710
impacts. So that to me doesn't work. So


00:25:14.720 --> 00:25:18.630
we can rule that out. The other answers


00:25:18.640 --> 00:25:21.830
are kind of tied together, but the idea


00:25:21.840 --> 00:25:26.230
is that the moon had a thicker layer


00:25:26.240 --> 00:25:28.310
above the molten layer on the far side


00:25:28.320 --> 00:25:31.350
of the moon to the near side. Two ways


00:25:31.360 --> 00:25:33.110
you can make that happen. One idea is


00:25:33.120 --> 00:25:36.149
that the heat from the young earth which


00:25:36.159 --> 00:25:37.669
would also have been molten at this time


00:25:37.679 --> 00:25:39.190
and being bigger will keep its heat


00:25:39.200 --> 00:25:41.430
longer. So will be molten for longer.


00:25:41.440 --> 00:25:43.350
The earth would be irradiating the moon.


00:25:43.360 --> 00:25:44.870
The moon would be close to the earth


00:25:44.880 --> 00:25:46.549
when they formed cuz it's moved away


00:25:46.559 --> 00:25:49.590
since. That radiative heat would have


00:25:49.600 --> 00:25:51.350
kept the near side of the moon hot for


00:25:51.360 --> 00:25:53.830
longer which the molten material on the


00:25:53.840 --> 00:25:55.110
surface would have stayed for longer but


00:25:55.120 --> 00:25:57.669
also it would have taken longer for the


00:25:57.679 --> 00:26:00.070
crust to thicken on that side. So


00:26:00.080 --> 00:26:01.669
therefore the crust on the far side of


00:26:01.679 --> 00:26:03.510
the moon would have formed quicker and


00:26:03.520 --> 00:26:06.470
thicker. The other idea is that you get


00:26:06.480 --> 00:26:07.990
the same kind of effect from tidal


00:26:08.000 --> 00:26:10.149
forces that the tidal influence of the


00:26:10.159 --> 00:26:11.350
earth on the moon is stronger on the


00:26:11.360 --> 00:26:12.950
near side than the far side because the


00:26:12.960 --> 00:26:15.269
strength of tides falls off as distance


00:26:15.279 --> 00:26:16.870
to the power four. So that's a very


00:26:16.880 --> 00:26:19.830
strong very rapid effect. Yeah. Possibly


00:26:19.840 --> 00:26:22.630
both of those things to com combine give


00:26:22.640 --> 00:26:24.310
you a crust around the moon that is


00:26:24.320 --> 00:26:25.830
thinner on the near side than the far


00:26:25.840 --> 00:26:28.230
side at all times as the moon cools on


00:26:28.240 --> 00:26:31.669
the interior which means that the far


00:26:31.679 --> 00:26:34.470
side of the moon the molten material was


00:26:34.480 --> 00:26:37.350
deeply enough buried quickly enough that


00:26:37.360 --> 00:26:39.269
no m forming impact happened. You've got


00:26:39.279 --> 00:26:40.950
the South Pole Lake Kim Basin which is


00:26:40.960 --> 00:26:43.190
the biggest impact scar on the moon


00:26:43.200 --> 00:26:44.710
doesn't really have much flood bassalt


00:26:44.720 --> 00:26:46.230
in it which either means that it is


00:26:46.240 --> 00:26:49.590
younger and therefore the interior had


00:26:49.600 --> 00:26:51.909
cooled enough that it didn't crack that


00:26:51.919 --> 00:26:56.149
egg or that it was an area where the


00:26:56.159 --> 00:26:58.230
crust was thicker anyway. You know, so


00:26:58.240 --> 00:27:00.149
the idea is that the difference between


00:27:00.159 --> 00:27:01.510
the near side and the far side of the


00:27:01.520 --> 00:27:02.950
moon is down to the thickness of the


00:27:02.960 --> 00:27:04.549
crust when the biggest impacts were


00:27:04.559 --> 00:27:06.870
happening. And the idea that probably


00:27:06.880 --> 00:27:08.950
due to a combination of tidal effects


00:27:08.960 --> 00:27:10.630
and radiative heating from the


00:27:10.640 --> 00:27:13.430
incredibly luminous molten earth, the


00:27:13.440 --> 00:27:15.190
near side of the moon stayed a thicker


00:27:15.200 --> 00:27:17.350
shell and therefore was more effectively


00:27:17.360 --> 00:27:19.590
punctured. And so the near side got the


00:27:19.600 --> 00:27:21.430
vare and the far side looks more like


00:27:21.440 --> 00:27:24.149
your typical rocky objects like Mercury


00:27:24.159 --> 00:27:25.830
like a lot of the rocky moons and stuff


00:27:25.840 --> 00:27:27.750
like that in the outer solar system.


00:27:27.760 --> 00:27:29.909
That's the thinking there. But it is


00:27:29.919 --> 00:27:31.750
really strikingly obvious when you see


00:27:31.760 --> 00:27:34.070
photos of the far side of the moon and


00:27:34.080 --> 00:27:35.350
you're not told it's the far side of the


00:27:35.360 --> 00:27:36.870
moon, you assume you're looking at an


00:27:36.880 --> 00:27:39.190
object that is not the moon because no


00:27:39.200 --> 00:27:41.350
different to our experience of the moon.


00:27:41.360 --> 00:27:43.830
>> Indeed. So, so part two of your question


00:27:43.840 --> 00:27:45.830
you basically covered because of the


00:27:45.840 --> 00:27:46.789
deep impact


00:27:46.799 --> 00:27:48.230
>> a little bit.


00:27:48.240 --> 00:27:50.070
>> Part two is a bit more complex.


00:27:50.080 --> 00:27:51.510
>> So, this is about this is the one about


00:27:51.520 --> 00:27:52.870
shallow craters.


00:27:52.880 --> 00:27:55.590
>> Crater shallow and craters are shallow


00:27:55.600 --> 00:27:57.110
not just on the moon but everywhere.


00:27:57.120 --> 00:27:58.870
There is a boundary between what


00:27:58.880 --> 00:28:00.710
researchers describe as a simple crater


00:28:00.720 --> 00:28:02.789
and a complex crater. And


00:28:02.799 --> 00:28:05.190
>> the size at which you get that boundary


00:28:05.200 --> 00:28:06.950
varies dependent on the strength of


00:28:06.960 --> 00:28:09.510
material that's impacted and also the


00:28:09.520 --> 00:28:10.950
mass of the planet and therefore the


00:28:10.960 --> 00:28:12.950
strength of gravity. So I believe on the


00:28:12.960 --> 00:28:15.909
earth it's about 8 or 9 km. For the moon


00:28:15.919 --> 00:28:18.470
it's about 18 km.


00:28:18.480 --> 00:28:20.070
Smaller than that you get a simple


00:28:20.080 --> 00:28:21.510
crater that forms which looks very


00:28:21.520 --> 00:28:23.029
similar to what you get if you almost


00:28:23.039 --> 00:28:26.149
just threw a rock really hard into sand


00:28:26.159 --> 00:28:27.510
or something. You get the typical


00:28:27.520 --> 00:28:29.590
B-shaped crater like meteor crater in


00:28:29.600 --> 00:28:32.389
Arizona. Really nice example. Yeah.


00:28:32.399 --> 00:28:36.070
>> At a size above about like say 8 or 9 km


00:28:36.080 --> 00:28:38.710
on Earth or above about 20 km on the


00:28:38.720 --> 00:28:40.630
moon, you get to the domain where you


00:28:40.640 --> 00:28:42.230
get a complex crater. And complex


00:28:42.240 --> 00:28:44.470
craters are characterized by having


00:28:44.480 --> 00:28:48.070
quite often central impact peaks but


00:28:48.080 --> 00:28:50.950
also having these much shallower depths


00:28:50.960 --> 00:28:53.590
compared to their width. You know, and


00:28:53.600 --> 00:28:55.350
it's particularly true for the Mar where


00:28:55.360 --> 00:28:56.789
they're flood basults where you have a


00:28:56.799 --> 00:28:59.590
very shallow crater for the width of the


00:28:59.600 --> 00:29:01.430
crater. But it's true even if you look


00:29:01.440 --> 00:29:04.149
at 20 km craters on the moon and there's


00:29:04.159 --> 00:29:05.590
a beautiful photo incidentally if you


00:29:05.600 --> 00:29:07.029
look on some of the NASA images there's


00:29:07.039 --> 00:29:09.830
a beautiful photo of the crater Arisus


00:29:09.840 --> 00:29:11.430
taken by the lunar reconnaissance


00:29:11.440 --> 00:29:13.190
orbiter and that shows this kind of


00:29:13.200 --> 00:29:15.590
terracing around the walls the central


00:29:15.600 --> 00:29:17.190
peaks and so there's a few things going


00:29:17.200 --> 00:29:20.070
on here that contribute to why what we


00:29:20.080 --> 00:29:22.789
describe as being


00:29:22.799 --> 00:29:25.590
um what I say complex craters are


00:29:25.600 --> 00:29:27.190
actually


00:29:27.200 --> 00:29:28.710
um


00:29:28.720 --> 00:29:30.470
shallower compared to their width than


00:29:30.480 --> 00:29:32.389
the simple ones. And there's a few


00:29:32.399 --> 00:29:33.590
things that have been suggested to this.


00:29:33.600 --> 00:29:36.230
So complex craters have depths that can


00:29:36.240 --> 00:29:39.350
be a 15th or 25th or even less of the


00:29:39.360 --> 00:29:41.510
crater width which looks very very


00:29:41.520 --> 00:29:43.750
shallow. Now there's a few things


00:29:43.760 --> 00:29:46.470
proposed in for this. Firstly, when you


00:29:46.480 --> 00:29:48.870
form a bigger crater, the walls can


00:29:48.880 --> 00:29:51.350
slump in. So material slides and


00:29:51.360 --> 00:29:53.830
gradually you get this material from the


00:29:53.840 --> 00:29:55.269
edges sliding into the middle. And if


00:29:55.279 --> 00:29:56.870
you look at that photo of Verisarchus,


00:29:56.880 --> 00:29:59.269
it looks very much like that's happened.


00:29:59.279 --> 00:30:01.669
evidence of landslides that have filled


00:30:01.679 --> 00:30:04.470
in the crater and made it shallower.


00:30:04.480 --> 00:30:07.269
>> The other thing is craters that big are


00:30:07.279 --> 00:30:09.909
large enough to render the material


00:30:09.919 --> 00:30:12.549
where the impact happens molten. And in


00:30:12.559 --> 00:30:14.310
other words, the material can flow like


00:30:14.320 --> 00:30:16.070
a liquid rather than behaving like a


00:30:16.080 --> 00:30:17.750
solid material of your desk.


00:30:17.760 --> 00:30:19.190
>> Well, you can you can still see a


00:30:19.200 --> 00:30:20.710
rebound point in the middle of the


00:30:20.720 --> 00:30:21.269
crater too.


00:30:21.279 --> 00:30:23.269
>> So that's it. So the stuff at the


00:30:23.279 --> 00:30:24.549
middle, the central peaks are thought to


00:30:24.559 --> 00:30:26.630
be rebound of this fluid activ fluid


00:30:26.640 --> 00:30:28.070
material springing back before it


00:30:28.080 --> 00:30:30.389
freezes solid again effectively. And


00:30:30.399 --> 00:30:32.549
then the flat base of these craters that


00:30:32.559 --> 00:30:34.549
makes them shallower is because you make


00:30:34.559 --> 00:30:36.789
a pool of liquid that spreads out and


00:30:36.799 --> 00:30:38.470
settles


00:30:38.480 --> 00:30:39.990
and so therefore you get these shallower


00:30:40.000 --> 00:30:42.630
things. Whereas with smaller craters you


00:30:42.640 --> 00:30:44.310
don't get to that point. So you get much


00:30:44.320 --> 00:30:46.950
more material behaving more as a solid


00:30:46.960 --> 00:30:49.190
than a liquid effectively. So the


00:30:49.200 --> 00:30:50.789
thinking is for these complex craters


00:30:50.799 --> 00:30:52.149
and like I say for the moon I think the


00:30:52.159 --> 00:30:54.870
size scale is what 18 to 20 km something


00:30:54.880 --> 00:30:57.029
like that it's a point at which you


00:30:57.039 --> 00:30:58.789
transition from simply behaving as a


00:30:58.799 --> 00:31:01.190
solid to the surface behaving in more of


00:31:01.200 --> 00:31:03.909
a liquid fashion. You get complex


00:31:03.919 --> 00:31:05.830
craters having central peaks they have


00:31:05.840 --> 00:31:08.549
terraces. They've got flat flows. The


00:31:08.559 --> 00:31:10.950
more massive the object the smaller the


00:31:10.960 --> 00:31:14.070
boundary is because gravity has a role


00:31:14.080 --> 00:31:15.190
in this.


00:31:15.200 --> 00:31:17.990
>> Yeah. Um and then you get the basins


00:31:18.000 --> 00:31:19.269
which are even bigger and they're where


00:31:19.279 --> 00:31:21.510
you get the flooding from bassalts which


00:31:21.520 --> 00:31:23.190
makes them even shallower compared to


00:31:23.200 --> 00:31:26.230
their width. So there is some beautiful


00:31:26.240 --> 00:31:29.190
complexity of this where it's all to do


00:31:29.200 --> 00:31:32.630
with the physical behavior of material


00:31:32.640 --> 00:31:34.549
and how that changes as an impact gets


00:31:34.559 --> 00:31:36.310
larger and larger and therefore more and


00:31:36.320 --> 00:31:39.590
more damaging and energetic. Now NASA


00:31:39.600 --> 00:31:42.870
have a Marsded website um where they


00:31:42.880 --> 00:31:44.870
actually explicitly say if you Google


00:31:44.880 --> 00:31:48.070
for this it's marked.asu.edu


00:31:48.080 --> 00:31:49.269
and then a really long string


00:31:49.279 --> 00:31:51.110
afterwards. It's a Mars education thing


00:31:51.120 --> 00:31:53.430
at Arizona State University. And I'll


00:31:53.440 --> 00:31:55.750
just quote here


00:31:55.760 --> 00:31:57.830
compared to simple craters complex


00:31:57.840 --> 00:32:00.470
craters also generate a lot more impact


00:32:00.480 --> 00:32:03.110
melted rock. This typically flows and


00:32:03.120 --> 00:32:04.870
pools like lava to form a sheet that


00:32:04.880 --> 00:32:07.269
covers a shattered rock known as breia


00:32:07.279 --> 00:32:09.830
on the crater floor. The crater's inner


00:32:09.840 --> 00:32:11.909
walls may slump downwards rotating


00:32:11.919 --> 00:32:13.750
backwards in blocks which can widen the


00:32:13.760 --> 00:32:15.669
crater's rim and line the inner walls


00:32:15.679 --> 00:32:18.149
with terraces. But as a result, complex


00:32:18.159 --> 00:32:19.750
craters look shallow. They have rim


00:32:19.760 --> 00:32:21.590
diameters about 30 times greater than


00:32:21.600 --> 00:32:23.830
their depths. By comparison, simple


00:32:23.840 --> 00:32:25.590
craters are about five times wider than


00:32:25.600 --> 00:32:27.990
they are deep. Um earlier on it said the


00:32:28.000 --> 00:32:29.350
more energy an impact delivers, the


00:32:29.360 --> 00:32:31.269
bigger the cavity on the ground. But


00:32:31.279 --> 00:32:32.630
immediately after the blast, the center


00:32:32.640 --> 00:32:34.630
of the cavity begins to rise as rocks


00:32:34.640 --> 00:32:35.909
rebound from the shock. That's what


00:32:35.919 --> 00:32:37.830
gives you the mountains. This uplift


00:32:37.840 --> 00:32:39.350
gives you a central peak or cluster of


00:32:39.360 --> 00:32:41.350
peaks. So that's a really nice way of


00:32:41.360 --> 00:32:44.470
condensing my lengthy waffly answer into


00:32:44.480 --> 00:32:45.750
something a bit more simple and


00:32:45.760 --> 00:32:47.269
straightforward.


00:32:47.279 --> 00:32:49.669
>> Fair enough. Okay. Uh now Andrea, you


00:32:49.679 --> 00:32:51.509
can believe all of that or you can go


00:32:51.519 --> 00:32:53.430
with my theory that the Luna City


00:32:53.440 --> 00:32:55.350
Council were on strike and they didn't


00:32:55.360 --> 00:32:58.789
finish filling the potholes.


00:32:58.799 --> 00:33:02.230
I go with option two. Um, Andrea, thanks


00:33:02.240 --> 00:33:03.430
for your question. Great to hear from


00:33:03.440 --> 00:33:05.909
you. Thanks for explaining Woo. This is


00:33:05.919 --> 00:33:08.230
Space Nuts, a Q&A edition with Professor


00:33:08.240 --> 00:33:13.509
Jonty Horner and Andrew Dunley.


00:33:13.519 --> 00:33:15.190
>> Okay, we've had a problem here.


00:33:15.200 --> 00:33:17.190
>> This is Houston. Say again, please.


00:33:17.200 --> 00:33:19.830
>> Houston, we've had a main undervolt.


00:33:19.840 --> 00:33:22.389
>> Roger. Main. Okay, stand by 13. We're


00:33:22.399 --> 00:33:23.029
looking at it.


00:33:23.039 --> 00:33:25.029
>> Space Muts.


00:33:25.039 --> 00:33:27.909
Our last question uh comes in two parts


00:33:27.919 --> 00:33:31.590
and it uh comes from Eli. Uh hello from


00:33:31.600 --> 00:33:33.909
Coachella Valley in California. Wasn't


00:33:33.919 --> 00:33:36.389
Coachella in the news recently for some


00:33:36.399 --> 00:33:39.269
big suare that happened there? Yeah.


00:33:39.279 --> 00:33:41.269
>> Uh big event. Uh anyway, he says the


00:33:41.279 --> 00:33:43.190
grasshoppers have decided to invade.


00:33:43.200 --> 00:33:45.590
Believe it or not, Eli, exactly the same


00:33:45.600 --> 00:33:48.310
thing is happening where I am. We have


00:33:48.320 --> 00:33:50.389
uh locust plagues once in a blue moon


00:33:50.399 --> 00:33:52.310
and we we had a little one recently.


00:33:52.320 --> 00:33:54.950
wasn't uh too significant. But I I have


00:33:54.960 --> 00:33:56.710
discovered with with locusts or


00:33:56.720 --> 00:33:58.149
grasshoppers or whatever you call them


00:33:58.159 --> 00:34:01.509
wherever you are that if you drive over


00:34:01.519 --> 00:34:04.549
50 kilometers an hour they splatter. Uh


00:34:04.559 --> 00:34:07.269
if you drive under 50 km an hour they


00:34:07.279 --> 00:34:09.589
bounce off. Important safety tip


00:34:09.599 --> 00:34:11.909
especially because when they splatter


00:34:11.919 --> 00:34:13.109
they stink


00:34:13.119 --> 00:34:14.629
>> and it's very hard to get off when


00:34:14.639 --> 00:34:15.190
they're dry.


00:34:15.200 --> 00:34:17.270
>> I'd love to have a swap toy wear. We've


00:34:17.280 --> 00:34:19.190
had an incredibly dry last few months


00:34:19.200 --> 00:34:20.470
here. It's been our wet season. And


00:34:20.480 --> 00:34:22.790
we've had 40 mil of rain in 4 months.


00:34:22.800 --> 00:34:23.270
>> Wow.


00:34:23.280 --> 00:34:25.270
>> Which is hooray. You know, that's really


00:34:25.280 --> 00:34:26.550
what you want in your wet season when


00:34:26.560 --> 00:34:28.310
the dry season's about to start. But


00:34:28.320 --> 00:34:29.750
what that means is that we're probably


00:34:29.760 --> 00:34:31.510
going to see yet another mouse plague.


00:34:31.520 --> 00:34:33.270
And mouse plagues are sad because in the


00:34:33.280 --> 00:34:35.030
times that are good, mice reproduce like


00:34:35.040 --> 00:34:36.550
crazy, but then you get the boom


00:34:36.560 --> 00:34:38.389
busting. And so you start getting lots


00:34:38.399 --> 00:34:40.310
of them coming to your house. And I'm


00:34:40.320 --> 00:34:41.829
soft-hearted. I don't want to hurt them


00:34:41.839 --> 00:34:43.510
or do anything, but at the same time, I


00:34:43.520 --> 00:34:44.869
don't want them pooing on everything in


00:34:44.879 --> 00:34:46.069
my kitchen.


00:34:46.079 --> 00:34:48.149
>> So we're getting mouse plague time. So,


00:34:48.159 --> 00:34:50.869
I I I suspect that locust plagues are


00:34:50.879 --> 00:34:52.230
horrible, but mouse plague is an


00:34:52.240 --> 00:34:53.589
entirely different horror. And


00:34:53.599 --> 00:34:55.349
>> mouse plagues are worse. Yeah.


00:34:55.359 --> 00:34:57.670
>> Because the mice try to find somewhere


00:34:57.680 --> 00:35:00.310
to hide inside. Locusts only get in if


00:35:00.320 --> 00:35:02.550
they've got an open avenue. Otherwise,


00:35:02.560 --> 00:35:04.710
they just stay outside and


00:35:04.720 --> 00:35:06.470
>> you know, and they also are very


00:35:06.480 --> 00:35:08.790
disturbing when you're trying to putt on


00:35:08.800 --> 00:35:09.349
a golf.


00:35:09.359 --> 00:35:10.710
>> Oh, absolutely.


00:35:10.720 --> 00:35:13.109
>> They get in the way.


00:35:13.119 --> 00:35:14.950
>> Sorry. You walk into the kitchen at


00:35:14.960 --> 00:35:16.150
night or you walk somewhere and you just


00:35:16.160 --> 00:35:17.510
see something move in the periphery of


00:35:17.520 --> 00:35:18.950
unit and that's always a little


00:35:18.960 --> 00:35:19.750
disturbing.


00:35:19.760 --> 00:35:20.230
>> Yeah.


00:35:20.240 --> 00:35:21.270
>> Yeah. Well, we


00:35:21.280 --> 00:35:21.589
>> Yeah,


00:35:21.599 --> 00:35:23.190
>> we're talk we're talking mouse plague


00:35:23.200 --> 00:35:25.270
here as well. So, we could have we could


00:35:25.280 --> 00:35:28.230
have both. But our last big locust


00:35:28.240 --> 00:35:30.390
plague, uh it was so big the birds just


00:35:30.400 --> 00:35:32.390
got fed up with eating them. So, they


00:35:32.400 --> 00:35:35.510
gave up as well. It's very weird. Um


00:35:35.520 --> 00:35:37.589
Eli, what are you asking us? Uh since


00:35:37.599 --> 00:35:40.950
you mentioned a pority of questions, I


00:35:40.960 --> 00:35:44.230
hope you don't mind. Um, a twofer. Okay,


00:35:44.240 --> 00:35:46.150
we well we've got two questions then.


00:35:46.160 --> 00:35:48.230
Uh, when the solar system formed, I


00:35:48.240 --> 00:35:50.310
always imagined the inner rockier


00:35:50.320 --> 00:35:52.470
planets as having more heavier elements


00:35:52.480 --> 00:35:54.390
due to their greater mass and gravity


00:35:54.400 --> 00:35:57.109
and with lighter elements collecting


00:35:57.119 --> 00:35:59.750
more in the outer gas giants. But then I


00:35:59.760 --> 00:36:02.870
realized, isn't the sun mostly hydrogen,


00:36:02.880 --> 00:36:05.589
the lightest element? Now I'm confused.


00:36:05.599 --> 00:36:06.950
That's his first question.


00:36:06.960 --> 00:36:07.750
>> Yeah. So,


00:36:07.760 --> 00:36:10.150
>> and this is this is your bullpen, isn't


00:36:10.160 --> 00:36:11.910
it? This is your area of expertise.


00:36:11.920 --> 00:36:13.670
>> This is much more my comfort zone. So,


00:36:13.680 --> 00:36:15.109
this is um


00:36:15.119 --> 00:36:16.950
>> I hope you realize I did try to find


00:36:16.960 --> 00:36:18.470
questions that worked for you.


00:36:18.480 --> 00:36:20.310
>> No, no, that's all good. And it it means


00:36:20.320 --> 00:36:21.750
you can leave the cosmology ones for


00:36:21.760 --> 00:36:23.190
when Fred gets back as well, which is


00:36:23.200 --> 00:36:25.910
great. This is a lovely question and it


00:36:25.920 --> 00:36:28.230
speaks to how our understanding of how


00:36:28.240 --> 00:36:29.990
planets form has changed over time. And


00:36:30.000 --> 00:36:32.150
we've now got quite a high level of


00:36:32.160 --> 00:36:34.710
complexity in the ideas we have behind


00:36:34.720 --> 00:36:36.230
planet formation. But a really


00:36:36.240 --> 00:36:38.710
fundamental part of it is that


00:36:38.720 --> 00:36:41.589
everything in the solar system to first


00:36:41.599 --> 00:36:43.829
order has the same composition as the


00:36:43.839 --> 00:36:46.069
sun because we all form from the same


00:36:46.079 --> 00:36:47.349
material. We formed from an enormous


00:36:47.359 --> 00:36:48.790
cloud of gas and dust called a giant


00:36:48.800 --> 00:36:51.109
molecular cloud that collapsed under its


00:36:51.119 --> 00:36:53.270
own gravity. You you got effectively the


00:36:53.280 --> 00:36:55.030
protostar sun forming in the middle with


00:36:55.040 --> 00:36:56.790
a dis of material around it we call a


00:36:56.800 --> 00:36:59.670
protolanetary disc. And in that disc you


00:36:59.680 --> 00:37:03.109
have solid material and gaseous material


00:37:03.119 --> 00:37:05.430
going around the sun orbiting the sun


00:37:05.440 --> 00:37:06.710
collapsing to a disc because of the


00:37:06.720 --> 00:37:08.310
conservation of angular momentum. So


00:37:08.320 --> 00:37:10.390
kind of where the earth is material was


00:37:10.400 --> 00:37:13.270
whizzing around at about 30 km a second


00:37:13.280 --> 00:37:15.109
but individual dust grains that were


00:37:15.119 --> 00:37:17.109
next to each other were both moving at


00:37:17.119 --> 00:37:19.750
about the same speed. So very little


00:37:19.760 --> 00:37:21.109
difference in speed between the


00:37:21.119 --> 00:37:22.230
particles even though they're going


00:37:22.240 --> 00:37:25.030
really quickly. Now the further you are


00:37:25.040 --> 00:37:26.870
from the sun, the colder the temperature


00:37:26.880 --> 00:37:29.349
is in that disc. And every single


00:37:29.359 --> 00:37:32.230
material you can think of has a


00:37:32.240 --> 00:37:34.950
sublimation temperature. Below that


00:37:34.960 --> 00:37:36.950
temperature it will be solid and above


00:37:36.960 --> 00:37:39.109
that temperature it will be gas. Reason


00:37:39.119 --> 00:37:40.790
I'm not talking about liquid is in order


00:37:40.800 --> 00:37:42.870
to have liquid you need pressure. And in


00:37:42.880 --> 00:37:44.630
this case you don't have or you don't


00:37:44.640 --> 00:37:46.310
have enough. So you either have solid or


00:37:46.320 --> 00:37:47.190
gas.


00:37:47.200 --> 00:37:47.910
>> Yep.


00:37:47.920 --> 00:37:51.270
>> If you are gas then you don't form


00:37:51.280 --> 00:37:53.349
planets initially. If you're solid, you


00:37:53.359 --> 00:37:55.829
can do so. What happens all through this


00:37:55.839 --> 00:37:58.069
disc for a variety of different bits of


00:37:58.079 --> 00:38:00.390
physics going on, you get whatever solid


00:38:00.400 --> 00:38:02.470
material you have at that distance


00:38:02.480 --> 00:38:04.069
colliding,


00:38:04.079 --> 00:38:06.710
sticking together, forming bigger bits.


00:38:06.720 --> 00:38:08.710
And so you get from millimeter to meter


00:38:08.720 --> 00:38:11.270
to kilometer to planet size bits of


00:38:11.280 --> 00:38:14.150
debris. As you get bigger, gravity can


00:38:14.160 --> 00:38:16.470
start taking on a role and start pulling


00:38:16.480 --> 00:38:17.990
in a bit of extra stuff so you can feed


00:38:18.000 --> 00:38:19.510
quicker. Plus, if you're bigger, you've


00:38:19.520 --> 00:38:21.030
got a bigger cross-section, so you hit


00:38:21.040 --> 00:38:23.109
more things to devour them. So, you get


00:38:23.119 --> 00:38:24.870
this process where you get lots of small


00:38:24.880 --> 00:38:26.310
things making a few bigger things and


00:38:26.320 --> 00:38:29.349
the big ones tend to dominate. Um, so a


00:38:29.359 --> 00:38:31.109
thing called oligarchic growth is the


00:38:31.119 --> 00:38:33.270
idea. And you form planetessimals and


00:38:33.280 --> 00:38:35.829
then oligarchs, which are protolanets,


00:38:35.839 --> 00:38:37.829
and a few of them collide all the rest


00:38:37.839 --> 00:38:40.710
of it. If you are far enough from the


00:38:40.720 --> 00:38:43.109
sun, you're beyond what's known as the


00:38:43.119 --> 00:38:45.510
water ice line. Now that's a point at


00:38:45.520 --> 00:38:47.589
which the temperature is below the


00:38:47.599 --> 00:38:49.670
sublimation point of water. So instead


00:38:49.680 --> 00:38:51.829
of water being a gas or vapor, it's a


00:38:51.839 --> 00:38:54.390
solid. Now we always imagine water being


00:38:54.400 --> 00:38:55.829
quite scarce. And I just said we've had


00:38:55.839 --> 00:38:58.390
40 mm of rain in the last 4 months. So


00:38:58.400 --> 00:39:00.950
water is very scarce here. But in terms


00:39:00.960 --> 00:39:02.790
of compounds in the universe, water is


00:39:02.800 --> 00:39:05.190
one of the most abundant things there is


00:39:05.200 --> 00:39:06.870
because it's a combination of hydrogen


00:39:06.880 --> 00:39:09.030
which is the most common atom with 74


00:39:09.040 --> 00:39:11.910
75% of all atoms and oxygen which is the


00:39:11.920 --> 00:39:13.990
second most common atom with about 1% of


00:39:14.000 --> 00:39:16.390
all atoms. Put hydrogen oxygen together


00:39:16.400 --> 00:39:18.390
and you get water. So in the


00:39:18.400 --> 00:39:21.349
protolanetary disc around the sun, water


00:39:21.359 --> 00:39:23.510
was probably about the most common


00:39:23.520 --> 00:39:25.190
species other than molecular hydrogen


00:39:25.200 --> 00:39:28.470
molecular and helium atoms. Lots and


00:39:28.480 --> 00:39:29.750
lots of water. Now where the earth


00:39:29.760 --> 00:39:32.950
formed it was too hot. So you don't have


00:39:32.960 --> 00:39:35.109
water as a solid. So you form the earth


00:39:35.119 --> 00:39:37.829
dry. There's no solid water to accrete.


00:39:37.839 --> 00:39:39.990
You might get a little bit of water as a


00:39:40.000 --> 00:39:41.750
gas that is trapped in the solid


00:39:41.760 --> 00:39:44.470
material. Which is why people think most


00:39:44.480 --> 00:39:45.829
of the earth's water was delivered from


00:39:45.839 --> 00:39:47.990
further out because if far enough out


00:39:48.000 --> 00:39:50.069
you form from primarily water with


00:39:50.079 --> 00:39:52.550
everything else added in. So the inner


00:39:52.560 --> 00:39:54.870
solar system you don't have that water


00:39:54.880 --> 00:39:56.710
to accrete. So you're limited to the


00:39:56.720 --> 00:39:58.630
things that are solid at higher


00:39:58.640 --> 00:40:00.470
temperatures. So you're limited to


00:40:00.480 --> 00:40:02.870
accreting from rock and metal. So you


00:40:02.880 --> 00:40:05.750
get turmeric planets or is the archaic


00:40:05.760 --> 00:40:07.990
way of saying it or terrestrial planets.


00:40:08.000 --> 00:40:10.550
Beyond the ice line, water ice dominates


00:40:10.560 --> 00:40:12.790
the solid material. So you've got a lot


00:40:12.800 --> 00:40:14.470
more to feed from. So you grow more


00:40:14.480 --> 00:40:16.790
quickly and you can get more massive


00:40:16.800 --> 00:40:18.150
planets more quickly which where Jupiter


00:40:18.160 --> 00:40:20.390
and Saturn come in. Now, there's a lot


00:40:20.400 --> 00:40:21.990
of discussion about how they may have


00:40:22.000 --> 00:40:23.670
migrated through the nebula, all the


00:40:23.680 --> 00:40:25.670
rest of it, and the subtleties of the


00:40:25.680 --> 00:40:27.190
formation. In other planetary systems,


00:40:27.200 --> 00:40:29.190
we have planets like Jupiter orbiting


00:40:29.200 --> 00:40:30.710
their stars every four or five hours


00:40:30.720 --> 00:40:32.390
even, but we don't think they formed


00:40:32.400 --> 00:40:34.470
there. We think they migrated in. So,


00:40:34.480 --> 00:40:37.589
you form beyond the ice line more


00:40:37.599 --> 00:40:39.910
quickly because you've got more food.


00:40:39.920 --> 00:40:42.310
And you can grow to masses like 10 or 12


00:40:42.320 --> 00:40:44.870
Earth masses while there is still an


00:40:44.880 --> 00:40:47.510
abundance of gas around. that gas


00:40:47.520 --> 00:40:48.790
doesn't hang around long because once


00:40:48.800 --> 00:40:50.870
the sun fully turns on after a few


00:40:50.880 --> 00:40:52.470
million years it blows the dust and the


00:40:52.480 --> 00:40:54.470
gas away and you're left with what


00:40:54.480 --> 00:40:57.190
whatever's left over. But if you form to


00:40:57.200 --> 00:41:00.550
be 10 or 12 Earth masses before the gas


00:41:00.560 --> 00:41:02.150
is blown away, suddenly your


00:41:02.160 --> 00:41:04.550
gravitational pull is strong enough to


00:41:04.560 --> 00:41:06.630
hold on to hydrogen and helium. If


00:41:06.640 --> 00:41:08.870
you're less massive than that, then the


00:41:08.880 --> 00:41:10.710
escape velocity of a hydrogen or helium


00:41:10.720 --> 00:41:13.589
atom will be higher. Sorry. The escape


00:41:13.599 --> 00:41:16.230
velocity of your object with that mass


00:41:16.240 --> 00:41:18.069
will be lower than the speed at which


00:41:18.079 --> 00:41:20.069
hydrogen and helium atoms move at that


00:41:20.079 --> 00:41:21.910
temperature. So, you can't hold on to


00:41:21.920 --> 00:41:23.910
them. They just escape because of their


00:41:23.920 --> 00:41:25.349
motion, because of the temperature


00:41:25.359 --> 00:41:27.030
they're at. When you get to 10 or 12


00:41:27.040 --> 00:41:29.270
Earth masses, the escape velocity from


00:41:29.280 --> 00:41:31.910
your core is higher than the speed at


00:41:31.920 --> 00:41:33.589
which hydrogen and helium is moving. So,


00:41:33.599 --> 00:41:35.670
you can start to capture that. And like


00:41:35.680 --> 00:41:37.990
I said, 75% of all atoms are hydrogen.


00:41:38.000 --> 00:41:41.510
24% of all atoms are helium. 99% of the


00:41:41.520 --> 00:41:44.630
mass of the protolantry disc or 98%


00:41:44.640 --> 00:41:46.710
maybe is unaccessible till you get to


00:41:46.720 --> 00:41:47.910
that mass and suddenly you've got this


00:41:47.920 --> 00:41:50.230
whole new food food source. So you


00:41:50.240 --> 00:41:51.910
quickly devour all the gas around you


00:41:51.920 --> 00:41:54.069
until you open a gap in the disc and


00:41:54.079 --> 00:41:55.829
that's how you get the gas giant planet


00:41:55.839 --> 00:41:57.910
Jupiter and Saturn. With Uranus and


00:41:57.920 --> 00:41:59.349
Neptune, they formed further out. They


00:41:59.359 --> 00:42:01.910
had a lot of abundant volatile material


00:42:01.920 --> 00:42:03.510
but they didn't really get massive


00:42:03.520 --> 00:42:06.710
enough to devour the gas before the gas


00:42:06.720 --> 00:42:08.069
was blown away. So that's why you get


00:42:08.079 --> 00:42:11.030
the ice giants and that is partially


00:42:11.040 --> 00:42:12.390
because they're further away they form


00:42:12.400 --> 00:42:14.390
slower. There are some arguments that


00:42:14.400 --> 00:42:15.829
Uranus and Neptune may have formed


00:42:15.839 --> 00:42:17.190
between Jupiter and Saturn and been


00:42:17.200 --> 00:42:20.630
scattered out. But on a broad brush


00:42:20.640 --> 00:42:23.589
sense in our solar system we don't think


00:42:23.599 --> 00:42:25.349
a huge amount of migration happened


00:42:25.359 --> 00:42:26.710
which probably down to the mass of the


00:42:26.720 --> 00:42:29.430
protolantry discared


00:42:29.440 --> 00:42:31.910
to the hot Jupiter systems we find


00:42:31.920 --> 00:42:34.550
elsewhere. So the planets we see today


00:42:34.560 --> 00:42:37.109
are within a factor of two or three


00:42:37.119 --> 00:42:38.870
times the same distance they were when


00:42:38.880 --> 00:42:40.870
they formed. Jupiter might have migrated


00:42:40.880 --> 00:42:43.030
in and back out. Uranus and Neptune


00:42:43.040 --> 00:42:44.550
probably formed significantly closer to


00:42:44.560 --> 00:42:46.710
the sun and migrated outwards. But


00:42:46.720 --> 00:42:49.109
you've got Jupiter and outwards forming


00:42:49.119 --> 00:42:51.670
in the ice dominated area. The


00:42:51.680 --> 00:42:53.750
terrestrial planets forming in the in


00:42:53.760 --> 00:42:56.309
the area without ice and therefore


00:42:56.319 --> 00:42:57.589
they're dominated by the rock and the


00:42:57.599 --> 00:42:59.589
metal. So you've like got this filter.


00:42:59.599 --> 00:43:01.990
So if you look at the fraction of iron


00:43:02.000 --> 00:43:05.510
compared to carbon in the earth or pick


00:43:05.520 --> 00:43:06.870
any two things that would have been


00:43:06.880 --> 00:43:10.069
solid, silicon versus iron, phosphorus,


00:43:10.079 --> 00:43:11.670
whatever, you know, things that were


00:43:11.680 --> 00:43:15.349
solid, the abundances of those things in


00:43:15.359 --> 00:43:16.950
all of the planets relative to one


00:43:16.960 --> 00:43:18.710
another will be effectively the same as


00:43:18.720 --> 00:43:20.710
the abundance in the sun. But the


00:43:20.720 --> 00:43:22.309
terrestrial planets weren't able to


00:43:22.319 --> 00:43:23.670
capture the things that would have been


00:43:23.680 --> 00:43:26.150
gas at their distances other than that


00:43:26.160 --> 00:43:28.470
what was delivered later on and weren't


00:43:28.480 --> 00:43:30.069
able to hold on to hydrogen and helium.


00:43:30.079 --> 00:43:33.270
So you get that chemical differentiation


00:43:33.280 --> 00:43:35.030
as a result of the location of the solar


00:43:35.040 --> 00:43:36.150
system. There's a bit of added


00:43:36.160 --> 00:43:38.630
complexity because chemistry happens and


00:43:38.640 --> 00:43:40.390
you'll get isotopic variations and


00:43:40.400 --> 00:43:42.710
stuff. But in broad brush strokes, the


00:43:42.720 --> 00:43:44.150
reason the terrestrial planets are


00:43:44.160 --> 00:43:46.150
dominated by rocky and metallic material


00:43:46.160 --> 00:43:47.589
is they never got massive enough to


00:43:47.599 --> 00:43:50.069
capture the gas and they formed close in


00:43:50.079 --> 00:43:52.710
where ice wasn't around. That's


00:43:52.720 --> 00:43:54.710
effectively how it happened. So what


00:43:54.720 --> 00:43:56.309
this question from Eli is doing is


00:43:56.319 --> 00:43:59.510
actually effectively describing the


00:43:59.520 --> 00:44:02.710
logic process that went into how we


00:44:02.720 --> 00:44:04.150
first began to understand planet


00:44:04.160 --> 00:44:06.870
formation. Because I've I said before, I


00:44:06.880 --> 00:44:08.470
think um on a previous episode,


00:44:08.480 --> 00:44:10.390
astronomy is not an experimental science


00:44:10.400 --> 00:44:12.150
in the way that every other science is.


00:44:12.160 --> 00:44:14.390
You know, biology, chemistry, physics,


00:44:14.400 --> 00:44:15.589
you want to figure out how something


00:44:15.599 --> 00:44:17.670
works, you can do experiments. Astronomy


00:44:17.680 --> 00:44:18.870
is an observational science.


00:44:18.880 --> 00:44:20.630
Everything's so big and so far away, we


00:44:20.640 --> 00:44:22.870
can't put it in a lab and smash it. We


00:44:22.880 --> 00:44:24.470
instead play detective. We look out at


00:44:24.480 --> 00:44:25.990
the universe and we gather clues and we


00:44:26.000 --> 00:44:27.589
ask questions. Exactly like the question


00:44:27.599 --> 00:44:29.510
Neo has asked here, which in its


00:44:29.520 --> 00:44:30.950
fundamental sense is why do we have


00:44:30.960 --> 00:44:33.030
rocky planets close in and gaseous ones


00:44:33.040 --> 00:44:34.870
further out? Why are there different


00:44:34.880 --> 00:44:36.309
compositions when we should be the same


00:44:36.319 --> 00:44:38.390
composition of the sun? We then come up


00:44:38.400 --> 00:44:40.470
with explanations for that that are our


00:44:40.480 --> 00:44:42.790
theories. And to be a good theory, you


00:44:42.800 --> 00:44:44.550
can't just say, I explain everything we


00:44:44.560 --> 00:44:47.270
see. You've got to make predictions. As


00:44:47.280 --> 00:44:49.190
we find more things, we will observe


00:44:49.200 --> 00:44:50.870
this. And that's how we test that


00:44:50.880 --> 00:44:52.550
theory. And we test it by this interplay


00:44:52.560 --> 00:44:54.390
between observation on the one hand,


00:44:54.400 --> 00:44:56.710
theory on the other. And what Eli's


00:44:56.720 --> 00:44:59.030
asked here is essentially the questions


00:44:59.040 --> 00:45:00.630
that people are asking that led to our


00:45:00.640 --> 00:45:01.670
current understanding of planet


00:45:01.680 --> 00:45:03.670
formation.


00:45:03.680 --> 00:45:06.069
And yet


00:45:06.079 --> 00:45:08.309
uh we see other solar systems with


00:45:08.319 --> 00:45:11.270
exoplanets that defy what we think is


00:45:11.280 --> 00:45:13.910
normal. Uh you have gas giants close to


00:45:13.920 --> 00:45:15.910
the parent star and rocky planets


00:45:15.920 --> 00:45:17.510
further out.


00:45:17.520 --> 00:45:20.470
>> Um and that's how we is that because


00:45:20.480 --> 00:45:22.390
they've just drifted that way.


00:45:22.400 --> 00:45:27.030
>> It's complicated. So our ideas planet


00:45:27.040 --> 00:45:29.349
formation happened have undergone quite


00:45:29.359 --> 00:45:30.950
a few major evolutions as we found


00:45:30.960 --> 00:45:33.829
planets around other stars. So in the


00:45:33.839 --> 00:45:36.470
early 1990s


00:45:36.480 --> 00:45:37.750
had a couple of talks at my local


00:45:37.760 --> 00:45:40.150
astronomy society in the UK from um


00:45:40.160 --> 00:45:43.349
Professor Wolfson of York University and


00:45:43.359 --> 00:45:45.190
Professor Wolson was an advocate of an


00:45:45.200 --> 00:45:47.670
entirely different formation scenario


00:45:47.680 --> 00:45:49.270
for the solar system. I think he was


00:45:49.280 --> 00:45:51.349
someone who argued that the solar system


00:45:51.359 --> 00:45:53.270
formed through an encounter between the


00:45:53.280 --> 00:45:55.190
sun and a young protoar where materials


00:45:55.200 --> 00:45:56.710
pulled out of the sun into a massive


00:45:56.720 --> 00:45:58.710
tongue and that tongue condensed into


00:45:58.720 --> 00:46:00.230
planets.


00:46:00.240 --> 00:46:04.230
Um back then


00:46:04.240 --> 00:46:06.230
um that idea was going out of fashion


00:46:06.240 --> 00:46:07.829
because we'd found a few debris discs


00:46:07.839 --> 00:46:10.069
around stars like Vega formal hotbe. But


00:46:10.079 --> 00:46:11.829
it was still considered possible.


00:46:11.839 --> 00:46:14.390
>> Yeah. Such an event would be incredibly


00:46:14.400 --> 00:46:17.030
vanishingly rare because stars getting


00:46:17.040 --> 00:46:19.270
that close together within one another's


00:46:19.280 --> 00:46:22.950
hills sphere is incredibly unusual. Very


00:46:22.960 --> 00:46:26.390
very rare. And so what that would


00:46:26.400 --> 00:46:29.030
predict is if that theory were correct,


00:46:29.040 --> 00:46:31.589
we would be almost unique. There would


00:46:31.599 --> 00:46:33.829
be vanishingly few planets around other


00:46:33.839 --> 00:46:35.510
stars because the scenario you need to


00:46:35.520 --> 00:46:37.670
form planets would only happen very


00:46:37.680 --> 00:46:39.829
rarely. On the other hand, there was the


00:46:39.839 --> 00:46:42.069
idea which data back to initially the


00:46:42.079 --> 00:46:44.870
1700s and beyond. um the lelassian


00:46:44.880 --> 00:46:47.430
model, the circum solar disc model,


00:46:47.440 --> 00:46:49.670
which has evolved into what we have now,


00:46:49.680 --> 00:46:51.670
which suggested that as part of star


00:46:51.680 --> 00:46:52.950
formation, you get a disc of material


00:46:52.960 --> 00:46:54.550
around a star and planets form from that


00:46:54.560 --> 00:46:56.950
disc. Discs are a natural byproduct to


00:46:56.960 --> 00:46:58.470
the formation of stars. Therefore,


00:46:58.480 --> 00:47:01.190
planetary systems should be common. Both


00:47:01.200 --> 00:47:02.870
scenarios with a bit of fudging and


00:47:02.880 --> 00:47:04.630
fiddling could perfectly explain how the


00:47:04.640 --> 00:47:05.750
solar system looked and have been


00:47:05.760 --> 00:47:08.390
finessed to reproduce the solar system.


00:47:08.400 --> 00:47:09.829
But the test was always going to be


00:47:09.839 --> 00:47:12.150
which of these series is correct will


00:47:12.160 --> 00:47:13.430
depend on how many planets we find


00:47:13.440 --> 00:47:16.390
around other stars. If planets are rare,


00:47:16.400 --> 00:47:17.910
then maybe the solar system is the


00:47:17.920 --> 00:47:19.190
result of a tongue being pulled out of


00:47:19.200 --> 00:47:21.750
the sun. If planetary systems are


00:47:21.760 --> 00:47:24.309
common, that cannot be the case. So that


00:47:24.319 --> 00:47:26.630
was a test that was done there. So when


00:47:26.640 --> 00:47:27.990
we found the first planetary systems


00:47:28.000 --> 00:47:29.270
around other stars and we found that


00:47:29.280 --> 00:47:31.670
planets are ubiquitous, that was kind of


00:47:31.680 --> 00:47:33.430
the death nail for the Wolfson type


00:47:33.440 --> 00:47:35.510
model of a tongue being sucked out of


00:47:35.520 --> 00:47:38.069
the sun and forming planets.


00:47:38.079 --> 00:47:40.470
But it kind of confirmed the LLAS model.


00:47:40.480 --> 00:47:41.829
But it also threw a spanner into the


00:47:41.839 --> 00:47:44.309
work in that the variation of planet


00:47:44.319 --> 00:47:46.950
formation of that disc model suggested


00:47:46.960 --> 00:47:48.230
that you would always form planetary


00:47:48.240 --> 00:47:49.589
systems with rocky planets in the middle


00:47:49.599 --> 00:47:50.950
and gas planets on the outside because


00:47:50.960 --> 00:47:52.950
it had been developed to explain the


00:47:52.960 --> 00:47:55.670
solar system. When you found planets


00:47:55.680 --> 00:47:57.270
that were hot Jupiters, they don't fit


00:47:57.280 --> 00:47:58.950
their planets and massive Jupiter close


00:47:58.960 --> 00:48:01.270
to their star which brought in the


00:48:01.280 --> 00:48:03.430
concept of inward migration. Now it's an


00:48:03.440 --> 00:48:05.990
interesting time because in the same few


00:48:06.000 --> 00:48:08.390
years people had started to realize that


00:48:08.400 --> 00:48:09.829
in the solar system there was clear


00:48:09.839 --> 00:48:11.589
evidence of planetary migration for the


00:48:11.599 --> 00:48:14.309
giant planets primarily that Neptune had


00:48:14.319 --> 00:48:16.790
migrated outwards carrying Pluto with it


00:48:16.800 --> 00:48:18.950
to form the Plutinos. So you've got


00:48:18.960 --> 00:48:21.750
these seminal papers by Renu Malhotra


00:48:21.760 --> 00:48:23.349
talking about the outward migration of


00:48:23.359 --> 00:48:26.069
Neptune being evidenced in Pluto and the


00:48:26.079 --> 00:48:28.470
Plutinos predating the discovery of the


00:48:28.480 --> 00:48:30.630
first exoplanet. And one of my gripes


00:48:30.640 --> 00:48:32.230
through my career has been that the


00:48:32.240 --> 00:48:34.950
exoplanet community primarily came from


00:48:34.960 --> 00:48:36.790
binary star astronomers, not from solar


00:48:36.800 --> 00:48:38.630
system astronomers. So reinvented


00:48:38.640 --> 00:48:40.950
migration to some degree and assumed


00:48:40.960 --> 00:48:42.309
that we had no evidence for it in the


00:48:42.319 --> 00:48:44.069
solar system. And in parallel, the solar


00:48:44.079 --> 00:48:45.349
system community was working on


00:48:45.359 --> 00:48:48.309
migration separately. But the


00:48:48.319 --> 00:48:49.750
discoveries of planets around other


00:48:49.760 --> 00:48:53.349
stars over the last 30 years and more,


00:48:53.359 --> 00:48:54.950
which is a great scientific revolution


00:48:54.960 --> 00:48:56.309
we've lived through. You know, you and I


00:48:56.319 --> 00:48:57.349
grew up in a world where the only


00:48:57.359 --> 00:48:59.510
planetary system we knew was our own.


00:48:59.520 --> 00:49:00.950
>> And kids today grew up in a world where


00:49:00.960 --> 00:49:02.790
we know planets are ubiquitous. That's a


00:49:02.800 --> 00:49:05.510
cataclysmic shift to have lived through.


00:49:05.520 --> 00:49:08.150
>> That living through that has proven an


00:49:08.160 --> 00:49:09.750
incredibly fertile testing ground for


00:49:09.760 --> 00:49:12.230
our theories of planet formation. Turns


00:49:12.240 --> 00:49:14.069
out that that lelass theory, the disc


00:49:14.079 --> 00:49:17.589
theory was a good way of the way there.


00:49:17.599 --> 00:49:19.109
So, it hasn't been totally discarded,


00:49:19.119 --> 00:49:20.549
but it's been refined and we've learned


00:49:20.559 --> 00:49:22.150
more about it. And that continues to the


00:49:22.160 --> 00:49:24.390
current day. The refinements are leading


00:49:24.400 --> 00:49:26.230
to all sorts of complexities like


00:49:26.240 --> 00:49:28.150
invoking streaming instabilities to


00:49:28.160 --> 00:49:30.230
concentrate pebbles at certain distances


00:49:30.240 --> 00:49:33.109
and all sorts of subtleties to try and


00:49:33.119 --> 00:49:35.030
address some of the pitfalls of how on


00:49:35.040 --> 00:49:37.030
earth do you get from millimeter size to


00:49:37.040 --> 00:49:38.630
meter sized objects when collisions


00:49:38.640 --> 00:49:40.790
should become destructive.


00:49:40.800 --> 00:49:42.470
>> All sorts of things like this. And it's


00:49:42.480 --> 00:49:44.790
through those observations that we get


00:49:44.800 --> 00:49:47.670
to improve and refine our models.


00:49:47.680 --> 00:49:49.030
We're not going to end up throwing out


00:49:49.040 --> 00:49:50.549
the disc model now because we can see


00:49:50.559 --> 00:49:52.470
the discs that form planets around other


00:49:52.480 --> 00:49:53.990
stars because our telescopes have got


00:49:54.000 --> 00:49:55.670
that good. Yeah. And one of the


00:49:55.680 --> 00:49:57.750
predictions would have been prior to


00:49:57.760 --> 00:49:59.270
them getting that good. If the disc


00:49:59.280 --> 00:50:00.549
model is right, when we look at places


00:50:00.559 --> 00:50:01.829
like the Orion Nebula with a


00:50:01.839 --> 00:50:03.829
sufficiently good telescope, we should


00:50:03.839 --> 00:50:06.549
see protolanetary discs propelled then


00:50:06.559 --> 00:50:07.990
the telescope's got good enough and we


00:50:08.000 --> 00:50:10.069
can see them. Now, we've even got to the


00:50:10.079 --> 00:50:12.549
point now where we can actually even


00:50:12.559 --> 00:50:14.950
observe fine structure within them to


00:50:14.960 --> 00:50:16.870
see the gaps that giant planets open up


00:50:16.880 --> 00:50:18.870
to see the spiral waves that are


00:50:18.880 --> 00:50:20.390
sometimes induced by a massive planet


00:50:20.400 --> 00:50:22.950
being born. So, we're now not only


00:50:22.960 --> 00:50:25.270
inferring planet formation from the


00:50:25.280 --> 00:50:26.470
plethora of planets that we're


00:50:26.480 --> 00:50:28.630
discovering around other stars and from


00:50:28.640 --> 00:50:30.069
the fine details of what we know about


00:50:30.079 --> 00:50:31.190
the solar system, but we're actually


00:50:31.200 --> 00:50:32.790
also getting observations of the discs


00:50:32.800 --> 00:50:34.470
in which it's happening that are


00:50:34.480 --> 00:50:36.150
providing extra information to improve


00:50:36.160 --> 00:50:38.790
those models. It's fascinating.


00:50:38.800 --> 00:50:41.030
>> So just so you can simply say there's no


00:50:41.040 --> 00:50:43.270
onesizefits-all


00:50:43.280 --> 00:50:45.589
way of this happening. It's it's


00:50:45.599 --> 00:50:46.390
circumstantial.


00:50:46.400 --> 00:50:48.710
>> It's a broad thing versus a narrow


00:50:48.720 --> 00:50:50.710
thing. So in a broad sense, planets


00:50:50.720 --> 00:50:52.549
forming a disc around a star natural


00:50:52.559 --> 00:50:55.190
product star formation. There may be


00:50:55.200 --> 00:50:57.750
occasional ways other planet formation


00:50:57.760 --> 00:50:59.190
mechanisms happen like the planets


00:50:59.200 --> 00:51:03.190
around um neutron stars are thought to


00:51:03.200 --> 00:51:05.030
probably be second generation planets.


00:51:05.040 --> 00:51:06.710
uh probably material formed from a disc


00:51:06.720 --> 00:51:07.990
that formed around the neutron star


00:51:08.000 --> 00:51:09.990
after the supernova and formed a new


00:51:10.000 --> 00:51:12.549
generation of planets. You might


00:51:12.559 --> 00:51:14.710
eventually one day possibly find planets


00:51:14.720 --> 00:51:18.150
formed from material pulled off a star.


00:51:18.160 --> 00:51:19.829
The very most massive planets, some of


00:51:19.839 --> 00:51:21.829
them will probably have been formed more


00:51:21.839 --> 00:51:24.230
like binary stars than actual planets


00:51:24.240 --> 00:51:26.710
which we talked in the past about when


00:51:26.720 --> 00:51:29.109
is a brown dwarf not a brown dwarf.


00:51:29.119 --> 00:51:30.870
>> Yes, but the broad brushstroke thing is


00:51:30.880 --> 00:51:33.430
fairly well established. that and every


00:51:33.440 --> 00:51:35.910
single planetary system is unique.


00:51:35.920 --> 00:51:38.230
Everyone has unique circumstances. Some


00:51:38.240 --> 00:51:39.910
discs around stars are more massive than


00:51:39.920 --> 00:51:41.589
others. Not every star will have an


00:51:41.599 --> 00:51:44.390
identical disc. Some discs get truncated


00:51:44.400 --> 00:51:46.790
because passing starships material away.


00:51:46.800 --> 00:51:48.549
Some discs get ablated away because


00:51:48.559 --> 00:51:49.990
there's a massive star nearby whose


00:51:50.000 --> 00:51:52.710
radiation pushes material away. You then


00:51:52.720 --> 00:51:54.309
even get impacts on the chemistry. So


00:51:54.319 --> 00:51:56.390
there's really fascinating studies


00:51:56.400 --> 00:51:58.630
looking at the solar system that suggest


00:51:58.640 --> 00:52:00.790
there was a nearby so supernova when the


00:52:00.800 --> 00:52:02.710
planets were forming that injected


00:52:02.720 --> 00:52:04.950
highly radioactive short-lived aluminium


00:52:04.960 --> 00:52:07.670
23 I think it is that gave an extra


00:52:07.680 --> 00:52:10.710
spike to the melting of planet decimals


00:52:10.720 --> 00:52:12.870
that led to some of the subtleties of


00:52:12.880 --> 00:52:14.870
how the solar system looks. There are


00:52:14.880 --> 00:52:16.549
indications even I think that the amount


00:52:16.559 --> 00:52:18.549
of gold in the solar system is unusually


00:52:18.559 --> 00:52:21.190
high compared to the standard metalicity


00:52:21.200 --> 00:52:23.270
the amounts of everything else which


00:52:23.280 --> 00:52:25.270
indication of pollution from two neutron


00:52:25.280 --> 00:52:27.829
stars colliding within 10,000 light


00:52:27.839 --> 00:52:29.349
years of where the solar system would


00:52:29.359 --> 00:52:31.910
form about a 100 million years before we


00:52:31.920 --> 00:52:34.870
formed. So even that level of injection


00:52:34.880 --> 00:52:37.670
of material is unique from one system to


00:52:37.680 --> 00:52:39.589
the next. And that's why every planetary


00:52:39.599 --> 00:52:41.990
system like every person is unique.


00:52:42.000 --> 00:52:43.750
>> Fascinating. Fascinating. Aren't you


00:52:43.760 --> 00:52:46.309
glad you asked, Eli? And Eli's second


00:52:46.319 --> 00:52:48.870
question. I recently read that some star


00:52:48.880 --> 00:52:51.190
systems are zipping through their galaxy


00:52:51.200 --> 00:52:54.390
orbits at incredible speeds of 1,200,


00:52:54.400 --> 00:52:57.190
I'm assuming that is kilometers/s.


00:52:57.200 --> 00:52:59.589
Uh that's4%


00:52:59.599 --> 00:53:01.430
the speed of light. That got me


00:53:01.440 --> 00:53:03.589
wondering how fast could our solar


00:53:03.599 --> 00:53:06.630
system get going before we started


00:53:06.640 --> 00:53:08.710
noticing things going wrong. You know,


00:53:08.720 --> 00:53:11.670
the windows rattling and such.


00:53:11.680 --> 00:53:15.510
Um, yeah, I I I think we've had


00:53:15.520 --> 00:53:17.589
questions similar to this. I think we


00:53:17.599 --> 00:53:19.510
did one recently where we talked about


00:53:19.520 --> 00:53:21.190
how fast the Earth would spin before


00:53:21.200 --> 00:53:24.390
things started to go horribly wrong. Um,


00:53:24.400 --> 00:53:27.109
this is a a question of similar ilk. I I


00:53:27.119 --> 00:53:29.190
hadn't heard about those sorts of speeds


00:53:29.200 --> 00:53:33.030
being detected by um


00:53:33.040 --> 00:53:34.549
there'd be stars very near the super


00:53:34.559 --> 00:53:35.829
massive black holes at centers of


00:53:35.839 --> 00:53:37.589
galaxies and that kind of speed doesn't


00:53:37.599 --> 00:53:39.990
surprise me. Now my immediate take on


00:53:40.000 --> 00:53:43.510
this is that we wouldn't notice


00:53:43.520 --> 00:53:45.990
effectively. So the reason that I'm


00:53:46.000 --> 00:53:47.990
saying that and I I stand to be proved


00:53:48.000 --> 00:53:49.829
wrong when you get up to relativistic


00:53:49.839 --> 00:53:51.190
speeds because my knowledge of


00:53:51.200 --> 00:53:53.030
relativity is not sufficiently good to


00:53:53.040 --> 00:53:55.430
be absolutely certain on this. If you


00:53:55.440 --> 00:53:58.390
were moving at a substantial fraction of


00:53:58.400 --> 00:54:00.549
the speed of light, I don't think we'd


00:54:00.559 --> 00:54:01.910
notice anything wrong in terms of the


00:54:01.920 --> 00:54:03.109
Earth moving around the Sun because we'd


00:54:03.119 --> 00:54:05.670
still be going around the Sun at 30 km/s


00:54:05.680 --> 00:54:07.030
while we're both moving around the


00:54:07.040 --> 00:54:08.630
galaxy at relativistic speed and


00:54:08.640 --> 00:54:10.870
accelerating. What we might notice then


00:54:10.880 --> 00:54:13.750
is time dilation in the fact that the


00:54:13.760 --> 00:54:16.549
external universe appears to be moving


00:54:16.559 --> 00:54:18.470
quicker than it should do. So we might


00:54:18.480 --> 00:54:20.069
see the effect of the fact that our time


00:54:20.079 --> 00:54:21.910
is slowed


00:54:21.920 --> 00:54:23.510
>> if we were going around just the same as


00:54:23.520 --> 00:54:24.870
you know you see the stuff about people


00:54:24.880 --> 00:54:26.390
orbiting a black hole at high speed or


00:54:26.400 --> 00:54:28.549
whatever or falling into a black hole.


00:54:28.559 --> 00:54:31.910
But in terms of us noticing in terms of


00:54:31.920 --> 00:54:34.950
physical phenomena on Earth that we're


00:54:34.960 --> 00:54:36.630
traveling at a certain speed around the


00:54:36.640 --> 00:54:39.190
galaxy I don't see a way that that would


00:54:39.200 --> 00:54:41.589
work. And the reason for that is that


00:54:41.599 --> 00:54:43.270
there's no resistive medium. We think


00:54:43.280 --> 00:54:44.630
about this thing happening because when


00:54:44.640 --> 00:54:45.990
you're driving in your car, the quicker


00:54:46.000 --> 00:54:47.589
you get, the more obvious your speed is


00:54:47.599 --> 00:54:48.870
because of the rattling and the wind


00:54:48.880 --> 00:54:51.190
resistance and the noise. But that's all


00:54:51.200 --> 00:54:52.630
down to your interaction with something


00:54:52.640 --> 00:54:54.710
that isn't moving at the same speed you


00:54:54.720 --> 00:54:56.710
are. If you're in the International


00:54:56.720 --> 00:54:58.150
Space Station, you're orbiting the Earth


00:54:58.160 --> 00:55:00.549
at several kilometers a second, you


00:55:00.559 --> 00:55:02.069
don't feel the space station rattling


00:55:02.079 --> 00:55:04.309
cuz it's going really quick because it's


00:55:04.319 --> 00:55:05.910
moving through the vacuum of space. So,


00:55:05.920 --> 00:55:07.829
it's not interacting with anything. If


00:55:07.839 --> 00:55:09.109
you're coming back into the atmosphere,


00:55:09.119 --> 00:55:10.470
you rattle and rumble and all the rest


00:55:10.480 --> 00:55:12.790
of it. saw this with Optimus 2 because


00:55:12.800 --> 00:55:14.309
you're slowing down. You're experiencing


00:55:14.319 --> 00:55:15.750
acceleration and you're experiencing


00:55:15.760 --> 00:55:17.190
buffering.


00:55:17.200 --> 00:55:20.230
>> So to me, if we are moving as a


00:55:20.240 --> 00:55:22.230
planetary system around the middle of


00:55:22.240 --> 00:55:24.630
the galaxy at very high speed, our


00:55:24.640 --> 00:55:27.270
planets would still be orbiting the sun


00:55:27.280 --> 00:55:28.549
in the same way and we wouldn't notice


00:55:28.559 --> 00:55:30.870
any difference. What would happen though


00:55:30.880 --> 00:55:32.470
is we'd be moving through a much much


00:55:32.480 --> 00:55:34.870
denser stellar neighborhood. The sky


00:55:34.880 --> 00:55:37.109
would be immeasurably beautiful but


00:55:37.119 --> 00:55:39.109
challenged. But also close encounters


00:55:39.119 --> 00:55:41.990
between stars would be very common and


00:55:42.000 --> 00:55:43.670
so it may well be that the stars would


00:55:43.680 --> 00:55:45.109
be so densely packed that eventually


00:55:45.119 --> 00:55:47.109
we'd have a stellar approach that will


00:55:47.119 --> 00:55:48.630
be so close to solar system would be


00:55:48.640 --> 00:55:50.549
disrupted and we'd certainly notice


00:55:50.559 --> 00:55:54.549
that. Also if we were injected to there


00:55:54.559 --> 00:55:56.870
from where we are now there will be a


00:55:56.880 --> 00:55:58.470
period of adjustment where the or cloud


00:55:58.480 --> 00:56:00.230
would be heavily destabilized and we'd


00:56:00.240 --> 00:56:01.990
have catastrophic levels of impacts from


00:56:02.000 --> 00:56:03.750
the comets being scattered. But


00:56:03.760 --> 00:56:05.190
eventually they'd all be gone so it


00:56:05.200 --> 00:56:07.910
wouldn't be a problem. So we'd notice it


00:56:07.920 --> 00:56:08.789
from the point of view.


00:56:08.799 --> 00:56:10.150
>> You tell that to the dinosaurs.


00:56:10.160 --> 00:56:13.349
>> Oh, absolutely. Um, long may they rest.


00:56:13.359 --> 00:56:16.390
But it's one of those things where if we


00:56:16.400 --> 00:56:18.150
were there and we were transported there


00:56:18.160 --> 00:56:20.390
from now, what we'd notice is that the


00:56:20.400 --> 00:56:21.990
sky looked very different. If we were


00:56:22.000 --> 00:56:24.710
moving at that kind of speed in that


00:56:24.720 --> 00:56:26.470
denser stellar neighborhood, the proper


00:56:26.480 --> 00:56:28.309
motion of stars would be apparent to the


00:56:28.319 --> 00:56:30.630
naked eye over human time scales, which


00:56:30.640 --> 00:56:32.950
it's not for us. Barard star which is


00:56:32.960 --> 00:56:34.870
the fastest moving star across the night


00:56:34.880 --> 00:56:36.870
sky will cross the diameter of the full


00:56:36.880 --> 00:56:39.990
moon in a century very roughly that


00:56:40.000 --> 00:56:41.829
means if Barard star was bright enough


00:56:41.839 --> 00:56:44.230
to see with a naked eye we'd have known


00:56:44.240 --> 00:56:46.230
about proper motion earlier because it


00:56:46.240 --> 00:56:48.230
would be obvious but it wouldn't be the


00:56:48.240 --> 00:56:49.589
kind of thing you'd notice from one year


00:56:49.599 --> 00:56:51.030
to the next. Whereas if we were in the


00:56:51.040 --> 00:56:52.309
middle of the galaxy going around the


00:56:52.319 --> 00:56:53.670
super massive black hole at that


00:56:53.680 --> 00:56:56.390
ridiculous speed. stars will be closer


00:56:56.400 --> 00:56:59.030
together which magnifies the effect of


00:56:59.040 --> 00:57:00.789
motion


00:57:00.799 --> 00:57:03.109
from our perspective. Also, they'd be


00:57:03.119 --> 00:57:04.549
moving quicker which means that the


00:57:04.559 --> 00:57:06.470
motion is quicker from our perspective


00:57:06.480 --> 00:57:07.910
and you probably have proper motion


00:57:07.920 --> 00:57:10.230
being visible on human time scales to


00:57:10.240 --> 00:57:11.829
the point that the constellations would


00:57:11.839 --> 00:57:14.789
move rather than being fixed patterns


00:57:14.799 --> 00:57:16.950
that you'd notice.


00:57:16.960 --> 00:57:19.109
You wouldn't feel the acceleration. you


00:57:19.119 --> 00:57:21.030
wouldn't notice anything's wrong, but we


00:57:21.040 --> 00:57:22.630
we probably wouldn't be there if the sun


00:57:22.640 --> 00:57:23.829
had been there for a long time because


00:57:23.839 --> 00:57:31.589
it's a very ineviably


00:57:31.599 --> 00:57:33.910
a bit of a dead zone.


00:57:33.920 --> 00:57:37.829
>> Aha. Okay. All right. Um, thanks for


00:57:37.839 --> 00:57:40.470
your questions, Eli. And, uh, yeah, I


00:57:40.480 --> 00:57:42.470
love that second one. I love what if


00:57:42.480 --> 00:57:44.950
questions. Uh, so yeah, we've been


00:57:44.960 --> 00:57:46.710
getting a few of those lately.


00:57:46.720 --> 00:57:49.109
They're just such great fun. Uh, thanks


00:57:49.119 --> 00:57:50.710
to Nick and Andrea as well for


00:57:50.720 --> 00:57:52.230
contributing. And if you would like to


00:57:52.240 --> 00:57:54.470
send us a question, please do on our


00:57:54.480 --> 00:57:56.630
website, spaceenutspodcast.com.


00:57:56.640 --> 00:57:58.230
spacenuts.io.


00:57:58.240 --> 00:58:00.309
Click on the AMA button at the top. Ask


00:58:00.319 --> 00:58:02.789
me anything is what that stands for. And


00:58:02.799 --> 00:58:04.710
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00:58:04.720 --> 00:58:06.230
Don't forget to tell us who you are and


00:58:06.240 --> 00:58:07.670
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00:58:07.680 --> 00:58:08.950
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00:58:08.960 --> 00:58:10.950
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00:58:14.640 --> 00:58:16.789
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00:58:16.799 --> 00:58:19.589
please leave reviews wherever you listen


00:58:19.599 --> 00:58:22.710
to Space Nuts. We appreciate that as


00:58:22.720 --> 00:58:24.549
well. And we appreciate you, Jonty.


00:58:24.559 --> 00:58:26.789
Thanks so much for uh your input today.


00:58:26.799 --> 00:58:27.430
Fantastic.


00:58:27.440 --> 00:58:28.950
>> Oh, it's always a pleasure. And yeah,


00:58:28.960 --> 00:58:31.589
fabulous questions. Really enjoy them.


00:58:31.599 --> 00:58:33.349
>> Me too. And we'll catch up with you uh


00:58:33.359 --> 00:58:34.470
with you very, very soon.


00:58:34.480 --> 00:58:36.630
>> Yeah, I look forward to it. Thank you.


00:58:36.640 --> 00:58:39.190
>> Professor Jonty her from the University


00:58:39.200 --> 00:58:41.190
of Southern Queensland where he is a


00:58:41.200 --> 00:58:43.430
professor of astrophysics. And thanks to


00:58:43.440 --> 00:58:45.030
Hugh in the studio who couldn't be with


00:58:45.040 --> 00:58:47.190
us today because time moves slower for


00:58:47.200 --> 00:58:49.990
Hugh. So, uh, he'll be joining us in


00:58:50.000 --> 00:58:52.069
couple of thousand years. And from me,


00:58:52.079 --> 00:58:53.589
Andrew Dunley, thanks for your company.


00:58:53.599 --> 00:58:54.870
We'll see you on the next episode of


00:58:54.880 --> 00:58:56.630
Space Nuts. Bye-bye.


00:58:56.640 --> 00:58:57.589
>> Space Nuts.


00:58:57.599 --> 00:58:59.750
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00:59:02.000 --> 00:59:04.950
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