Sunlight Satellites, Near-Earth Asteroids & the 6,000th Exoplanet Revelation

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Andrew Dunkley: Hi there. Thanks for joining us on another

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edition of Space Nuts, where we talk

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astronomy and space science. My name is

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Andrew Dunkley, your host. It's good to have

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your company as always. Today,

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we're going to start off with something quite

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controversial. And in some

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parts of the world they probably call this

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dumb. But, a proposal to create

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a sunlight service. Yes. Using

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mirrors in orbit. It's a thing.

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also a near miss for Earth involving asteroid

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20, 2025 TF, the

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6,000th exoplanet has

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been discovered. And another potential

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subsurface ocean, this one

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involving the moon Mimas. That's all coming

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up on this edition of Space Nuts.

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Jonti Horner: 15 seconds. Guidance is internal.

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10, 9. Ignition

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sequence. Star. Space Nuts. 5, 4,

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

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3, 2, 1. Space Nuts astronauts,

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report.

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Andrew Dunkley: It feels good.

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And joining us, in the stead of Fred

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Watson, we are, joined by Jonti Horner,

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professor of astrophysics at the University

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of Southern Queensland. Hello again, Jonti.

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Jonti Horner: good morning. How are you going?

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Andrew Dunkley: I am well. And we should, just put a

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caveat to this episode. There might be noise

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because you're getting work done at the

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house.

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Jonti Horner: Yes. And of course we organized to record at

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this time prior to the trade is getting in

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touch and saying, you know what, we'll be

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there at 7am on Monday morning. It's like

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great, you know, want this done. Hopefully

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the wonders of the microphone will filter it

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all out. But given that some of the banging I

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can feel through my feet, I suspect the

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vibrations might go all the way through the

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desk and all the way up the microphone and

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we'll occasionally get bang, bang, bang,

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drill, drill, drill. So, yeah, I know.

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Consider it like we've got a craft work gig

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going on or something like that.

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Andrew Dunkley: Well, I can tell you we've, we've heard worse

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from Fred's house. So, yeah, it should, it

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shouldn't sound out of the ordinary, to be

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honest.

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All right, let's get, stuck into these

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stories because we've got a lot to talk

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about. This first one, I know you sent me

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the, information initially that came from, I

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believe, one of your students who's overseas.

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But this is, an idea of a Californian company

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who is applying to the federal,

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communications commission in the United

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States, the fcc, for permission to launch a

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satellite into space to reflect

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sunlight back down on Earth and

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charge people for the privilege.

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Jonti Horner: Yeah. Now I try very hard to be

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even handed and to not be too critical even

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when I'm talking About the people who shall

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not be named. You know, the ones who are

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putting up, Starlink satellites and abusing

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colleagues of mine, or people who are

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claiming that things that are not aliens are

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aliens in order to sell books. You know, I

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try and be even handed and it's very

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hard to talk about this one without getting a

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bit caustic. it reminds me

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of the late, great Terry Pratchett, who,

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in one of the books was talking about a

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certain subset of the landed gentry.

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You know, there's, political things going on

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and this is a time when the city's under

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siege and they're reforming the regiments and

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things like this. And it's talking about the

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boys who were dropped on their heads as

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babies, as this kind of subset of,

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you know, nice but dim gentry. Yeah, they're

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nice, but they're not all there. And this,

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to me, seems like an idea that was dropped on

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its head as a baby. It's so

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overwhelmingly dumb that you think it must be

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April 1st and it isn't. So the idea

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that this company called Reflector Orbital

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have. And it's an idea that has

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led to them getting tens of millions of

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dollars of funding. So it's not like,

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yeah, this is. It's

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not like these are people in the pub saying,

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we've had a few. You know what'd be funny?

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This is a company taking it seriously.

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They're getting interns in, they've got a

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very active social media presence and their

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whole business is. Isn't it sad that it's

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dark at nighttime? Wouldn't it be great if

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you could pay somebody and get sunshine

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delivered to you at night? And that could

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power your solar panels or it could help you

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grow your crops or, you know, help you

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illuminate your sporting event or your

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concert. And the idea that

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they've got is that they will launch

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satellites into low Earth orbit, maybe 400

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kilometers up, that will go around the Earth

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every 90 minutes. So they're going to be

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fleetingly above any given location, above

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the horizon for a few minutes. And if you

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send them a few of your dollary dues, they

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will make their satellite reflect light down

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to your location and deliver

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sunlight to you. Now, there's all sorts of

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problems with this. Firstly, you know, I

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live, in Toowoomba. I'm 27 degrees south and

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I can see satellites that are about 400 km up

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in about the first hour after sunset, the

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first hour before sunrise, the rest of the

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night, those satellites are in shadow too. So

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there isn't any sun to reflect. Oh.

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Andrew Dunkley: So, you know, fair point.

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Jonti Horner: Nobody seems to be really mentioning that in

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the narrative of how this will work. But even

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ignoring that, think about the International

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Space Station going overhead. And you can get

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predictions of this from wonderful websites

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like heavensabove.com and the space

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station becomes visible,

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passes over, and then goes into the shadow.

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And you might get five, six minutes of it

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going overhead, if you're lucky. Yeah. And

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then it's gone. So you have this idea that

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these mirrors, that they're going to launch

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at about that altitude, and

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if you want them to illuminate a single point

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on the ground, they've got to be turning. So

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they keep rotating the light to that point as

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they pass overhead. Mm. When they're

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passed overhead, what do they do? They can't

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just turn off the mirror. So is that

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suggesting that you're gonna have a beam of

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light sweeping across the countryside at

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orbital speed? Like when you're trying

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to entertain a cat and you're shining a laser

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pointer on the floor and the cat's chasing

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it, you've got a beam going across the Earth.

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yeah. Going across the skies of all these

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people who didn't pay for the service. Not

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just that, how do you get enough sunlight

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down to be functional? So

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these satellites are going to be small enough

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to launch. So you're talking about a mirror a

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few meters across, 400 kilometers away,

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trying to reflect sunlight down, and they,

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they talk about how the diameter of the

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beam will be about 5km across.

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So that means if I pay for them to deliver

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light to my backyard, anybody in a five

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kilometer diameter area around me also get

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illuminated as well, for free, whether they

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want to or not.

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Andrew Dunkley: Yeah, but not just that.

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Jonti Horner: The light's not going to be that bright,

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because if you've got a 1 meter sized mirror

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reflecting sunlight, and then you spread that

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light over an area that is 5km in diameter,

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you're spreading that light awfully thin. So

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any area on the ground there is not going to

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see broad daylight. They're going to see

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something that is comparable in brightness or

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a few times brighter than the full moon,

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which is. Okay, that's enough light for you

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to go out and do something in the backyard

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by. But it's not particularly enough light to

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get really effective solar power from. So if

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you want to make this effective, you're going

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to have to launch hundreds of thousands

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of these mirrors, all to work in

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concert to beam towards a given location,

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which doesn't sound that feasible. Add to

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that the fact that these are Big floating

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targets in space that space debris can hit

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and smash, which means that a, you could

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get all this debris scattered off in all

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sorts of different directions, but also that

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it's going to be hard for them to control the

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direction the mirror's pointing. So you've

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got all sorts of problems here. I mean, I

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think there's growing and

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demonstrated evidence, and Fred's talked

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about this to death, about all the negative

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effects artificial light at night has. We've

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got effects on people. You've got increased

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cancer rates, a very bizarre but

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very significant link between light at night

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and an increased risk of breast cancer for

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women. Believe it or not, just as one

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example, you've got the impact in our

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circadian rhythms, the fact that we need it

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to be dark to sleep, then you've got all the

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impact on flora and fauna. Now, I've visited

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some wonderful places on the coast of

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Queensland to do outreach sessions, you know,

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some kind of night sky observing. And a lot

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of these places are places where turtles

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nest. In fact, I'm going next weekend to the

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wonderful Lady Elliot island on the reef to

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do some outreach. And I go there several

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times a year. And all of their resort is

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designed to keep light down and pointed at

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the ground and have lights that get turned

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off because baby turtles, when they hatch,

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they navigate to the ocean by looking at the

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very faint light on the horizon, light

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reflecting off the ocean. And, that's what

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sets their internal compass as they start

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their lives. And if you have stray light,

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they go the wrong way and they end up under

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the buildings and on the road and things like

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this. Yeah, so there's huge impacts on life.

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But I think the biggest concern about this is

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the safety aspect. You know, you're driving

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around and I know here in regional Australia,

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most of our roads don't have street lights

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and that's perfectly fine. It's safer. As

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such, you drive along with your full beam on

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and any kangaroo that you see, you've got

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room to do something about it. So you're

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driving along on this pitch black road and,

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suddenly from nowhere, something brighter

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than the full moon shines full head on in

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your view. You're dazzled. That's

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hugely dangerous. Odd enough, if you're

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driving on the ground, if you're a pilot

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coming in to land, and suddenly somebody's

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trying to spotlight in your face, that's not

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going to be a particularly pleasant outcome

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for you and the passengers in your plane. And

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so there's all these issues there that

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any one of them will be enough for you to

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say, this is a really foolish idea. It

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is not something that is likely to work

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anyway, but it's a really foolish

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idea from the ground up. It's only going to

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work near twilight. You're going to have to

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launch thousands of satellites to make it

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work, but it isn't stopping people funding

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them. And, this company, like I say, has

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applied to the FCC in the US for

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permission to launch the first of these

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satellites, which they've named Earundel 1

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after the light from Lord of the Rings.

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Earundel 1. They're hoping to launch April,

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May time next year, 2026, to

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demonstrate that their wonderful great idea

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can work. And it's just yet another example

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of this kind of Wild west scenario we've got

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with the use of space around the Earth, where

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the use of space is really outstripping our

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ability to regulate and control that use.

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And, people are doing things because it

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seemed like a good idea at the time without

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any real thought about the practicality of

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it, whether it could work. And, normally you

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just think like, say you think this is an

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April Fool's Day kind of prank. But the

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fact that this company has raised tens of

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millions of dollars in kind of venture

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capital, it's supported by A M

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multibillionaire, is really, really

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concerning. And that's why a group of

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astronomers, including Jessica Heim, who's

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doing a PhD with me at UNISQ, have put

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out this fact sheet with lots of information,

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loads of links, number of astronomers in the

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US who people in the media can contact for

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more information and suggestions about what

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people can do to flag up how catastrophically

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dumb this is. And that includes submit

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comments on the application to the Federal

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Communications Commission in the US to demand

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an environmental review of reflected light

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from orbit. Contact government

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representatives, particularly in the US but

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also locally where you live, to try and raise

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noise about this, but also tell people about

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it and point out how dumb it is. Because I

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can understand that if you don't really think

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about this too much, you can think, yeah,

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there are times it'd be really nice to have a

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bit of extra light at night.

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I didn't get round to doing the gardening.

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It'd be good to mow the lawn tonight.

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Wouldn't it be great if I could just turn on

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the spotlight and have half an hour of my

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backyard being daily, at night for me to do

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that job? And you need to talk about it and

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you need to think about it to see why this is

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just so catastrophically dumb. In

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so, so many ways that you would have thought

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it'd be an unstarter, but yet they're getting

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money.

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Andrew Dunkley: I can't see or understand

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any logic in this. And,

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the way in low Earth orbit, as you said,

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there's only going to be a few minutes of

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light. It's not like they can light a stadium

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for four hours straight. Not yet, any. But,

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even if they could, that's going to take a

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lot of hardware up in space. And there's more

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light pollution on Earth.

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Jonti Horner: Which is a big problem.

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Andrew Dunkley: Fred and Marnie are so heavily involved in

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the Dark Skies project. This would just blow

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that out of the water.

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Jonti Horner: Well, it would. And I mean, to light that

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stadium for four hours, you would need

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mirrors going overhead continuously in a

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parade. You'd need that stadium to be near

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enough to the pole on it to be summertime

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that those satellites were always in sunlight

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or you'd need to put them further from the

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Earth. The further you move them from the

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Earth, the more spread out the light will be,

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and so therefore the more satellites you'll

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need, you know. And if you get

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to that stage, if you've got that many

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satellites in orbit around the Earth, you may

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as well build a mirror that

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is held in geostationary orbit that covers

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half of the size of the Earth, and bears the

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entirety of that side of the Earth in

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sunlight. And, you know, while you're at it,

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you're increasing the amount of heat coming

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to the Earth and we'll just speed up global

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warming and kill everybody.

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Andrew Dunkley: Yeah, there is a groundswell of discontent,

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as you mentioned. So people are starting to

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make some noise about this. I hope the fcc,

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you know, looks at both sides of the story.

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how, just quickly, how likely are they

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to get their license and start testing

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this?

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Jonti Horner: I mean, a pessimist would say it's almost

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certain to happen because, you know, the FCC

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are quite happy for sailing to be putting up

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the number of satellites. They are looking at

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42,000 long term. So it

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doesn't seem like there's much thought of

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that. And there's the added concern. I think

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one of the things that is hindering

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legislation is the fact that you can launch

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the space from many, many countries. And so

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companies can quite rightly say to, a given

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legislating body, if you don't give us this,

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we'll just take our business elsewhere and

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someone else will. And, you know, once you're

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launched from a given country, you're above

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all of the countries of the world as you move

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over them in your orbit. So it isn't like

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this thing is just going to affect people in

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the U.S. because it's been launched from the

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U.S. it's going to be going around the Earth,

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like say, running a five kilometer size beam

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of light across the surface of the earth,

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every 90 minutes as it goes round and round

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and round and round.

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Andrew Dunkley: It just doesn't, doesn't make much sense

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really. It sounds like pie in the sky. But,

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yeah, they're actually seriously considering

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doing this. And yeah, hopefully

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common sense will prevail, but, time will

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tell, I suppose we'll know next year whether

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or not they start testing these things.

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I know they did do this some years ago

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with a mirror array up in space and they,

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they lit up a spot on Siberia or something.

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yeah, I don't know why they did that then. I

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can't remember. But, it was, somewhat

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successful, although quite dim. But, This,

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this just. Yeah, I mean, I don't know where

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it stops. there seems to be this,

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this constant tug of war between what

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we need up there and what we don't need up

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there. And the. Yeah,

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it's swinging the wrong way at the moment, I

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suppose, would be the way to describe it.

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But, I dare say this will get a lot more

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press and a lot more pushback and maybe the

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fcc, will look at the

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problems associated with this.

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Jonti Horner: Really hope so. I mean, it reminds me, and

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I'm probably paraphrasing terribly, but

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there's a famous science fiction quote,

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something along the lines of, you know, they

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spent so much time and effort trying to show

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that they could, that they never put any

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thought into whether they should. It feels

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like all of those.

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Andrew Dunkley: Yes, yes, indeed. All right. yeah, it's

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a project, you might find online. It's only

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just sort of starting to emerge. I don't know

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how much press it's got yet, but, it will

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grow. Because it's one of those stories that,

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is also fascinating and they're the ones that

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generally get a lot of attention.

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Jonti Horner: Looking at the website, the company seems to

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have been around for quite a while and I

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think it's probably getting attention now

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because previously everybody thought, well,

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no, this will never fly. This is clearly not

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something we should be worried about. And now

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it's very clear that actually it is, because

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they're in for licenses and they've got a lot

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of money invested.

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Andrew Dunkley: Yeah.

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Jonti Horner: Yeah.

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Andrew Dunkley: And one wonders who's really going to pay

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them to shed a little light on their

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whatever. I mean, what would you use it for?

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Solar panels. You said they won't work.

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Football, matches. Well, we've got lights for

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that. I don't know. I don't know.

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Jonti Horner: We can do a bit of quick mental arithmetic to

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cheer everybody up. I mean, the brightness of

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the full moon to first order very roughly, is

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about magnitude -12 in the wonderful

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complex magnitude system astronomers are so

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fond of. The brightness of the noonday sun's

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about magnitude -27. So that's a 15

435
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magnitude difference. Now, that magnitude

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system is a logarithmic scale.

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So every five magnitudes you're brighter off

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enter than something is equivalent to a

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factor of 100 influx. So if you're

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15 magnitudes, that's three lots of 100. So

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100 times 100 times 100, that's 100

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becomes 10,000 becomes a million.

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So if the light from this thing is about the

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brightness of the full moon, it's a million

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times fainter than the sun is.

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So if you've got your solar panels that are

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generating in full sunlight, you know, a few

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hundred watts of power, right. they're

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generating a few hundred watts. Divide that

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by a million and you're not

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generating enough to register. Yeah,

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yeah.

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Andrew Dunkley: It would be like putting up a solar panel to

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power a light and using that light to

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generate the power to power that light.

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Jonti Horner: It's just absolutely. Or just holding a

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match, a lit match near your solar panels and

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expecting it to run your entire house. Yeah,

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yeah.

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Andrew Dunkley: Ah, it's crazy stuff. All right, yeah, keep

461
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an eye out for that story and if you feel

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strongly enough about it, maybe, get

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involved.

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let's move on to our next story. this

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involves a near miss for Earth with asteroid,

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2025 TF just skimming us,

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and we didn't see it till it was too late,

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technically speaking. And, it kind of

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dovetails into the previous story because if

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there's going to be more light up there, it's

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going to make us harder, make things harder

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for us in terms of, you know, getting these

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ready alerts for potential objects that could

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strike Earth. this one wasn't huge,

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but, yeah, it was, it was there and

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it was a detectable object and we didn't see

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it.

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Jonti Horner: Yes. And that's the issue. Now, this

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thing, you know, quite happy to say, straight

480
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up the size of this thing is such that it

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would have put on a nice light show as it,

482
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you know, was quite harmlessly destroyed in

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the atmosphere. It was probably about 1 to 3

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meters across.

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Andrew Dunkley: Yeah.

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Jonti Horner: But of the things that have not entered the

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Earth's atmosphere, but have come close, this

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is the second closest on record. Now,

489
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back in. I'm trying to remember exactly when

490
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the great daylight fireball was. But in the

491
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early 1970s, there was a fireball

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observed widely over, North America, which

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was what we call an earth grazing object, and

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it actually hit the atmosphere and skimmed

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back out. That is not counted when people

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talk about these two closest encounters that

497
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didn't hit Earth because technically that did

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hit the atmosphere. The fact that it skipped

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back out again is beside the point.

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And that was a daylight fireball. It created

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sonic booms over a couple of the US States

502
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and was really the first kind of fireball

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event that was widely captured because it was

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early in the era of modern holiday

505
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snaps. And this was a time when people were

506
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taking photos on holiday, then boring their

507
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friends when they came home.

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Andrew Dunkley: Yeah, yeah, 1972 it was.

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Jonti Horner: That's the one. Yeah, I thought it was. It

510
00:19:32.590 --> 00:19:35.040
was, probably something smaller than a house

511
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that came within about 57 km

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of the surface of the Earth. And put that in

513
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perspective, that's like, you know, the old

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William Tell thing of shooting an apple off

515
00:19:43.740 --> 00:19:45.780
somebody's head. That's like shooting the

516
00:19:45.780 --> 00:19:47.780
arrow at the apple and touching the skin of

517
00:19:47.780 --> 00:19:50.300
the apple without breaking it. It's coming

518
00:19:50.300 --> 00:19:52.740
within less than 1% of the diameter of the

519
00:19:52.740 --> 00:19:54.900
Earth of actually hitting our planet. This

520
00:19:54.900 --> 00:19:57.660
one wasn't quite that close. But it's an

521
00:19:57.660 --> 00:19:59.980
object that was discovered by the Catalina

522
00:19:59.980 --> 00:20:02.780
Sky Survey a few hours after

523
00:20:02.780 --> 00:20:04.500
its closest approach to the Earth,

524
00:20:05.550 --> 00:20:08.470
basically whizzed over Antarctica. So I think

525
00:20:08.470 --> 00:20:10.190
it's one of those that even if it had hit the

526
00:20:10.190 --> 00:20:11.790
atmosphere and burned up, very few people

527
00:20:11.790 --> 00:20:13.350
would have seen it, but a lot of penguins

528
00:20:13.350 --> 00:20:16.160
would have been impressed. at

529
00:20:16.160 --> 00:20:19.160
its closest, it was 428km above the

530
00:20:19.160 --> 00:20:21.400
Earth's surface. So that's slightly closer

531
00:20:21.640 --> 00:20:23.760
than reflector orbital. Want to put their

532
00:20:23.760 --> 00:20:25.990
mirrors. so if it had come through a few

533
00:20:25.990 --> 00:20:27.270
years later, we could have hoped it would

534
00:20:27.270 --> 00:20:28.670
have knocked a few of them out of the way.

535
00:20:28.670 --> 00:20:31.450
But it's a really close approach.

536
00:20:31.690 --> 00:20:33.880
And, yes, it's an object that in this case

537
00:20:33.880 --> 00:20:35.680
wouldn't have been big enough to cause any

538
00:20:35.760 --> 00:20:38.600
damage, wouldn't have had any impacts felt at

539
00:20:38.600 --> 00:20:41.240
ground level. It may have, if it was made of

540
00:20:41.240 --> 00:20:42.840
the right stuff, dropped a few little bits of

541
00:20:42.840 --> 00:20:45.240
meteorite on the surface, but that's about

542
00:20:45.240 --> 00:20:47.320
it. But it's a reminder,

543
00:20:48.070 --> 00:20:50.230
of the fact that as we're looking for things

544
00:20:50.310 --> 00:20:52.040
that come close enough to the Earth, to pose

545
00:20:52.040 --> 00:20:54.840
a threat. We haven't found them all yet.

546
00:20:54.840 --> 00:20:57.730
Now probably about 75% of the threat

547
00:20:57.730 --> 00:20:59.140
to the Earth, from impacts comes from the

548
00:20:59.140 --> 00:21:01.540
near Earth asteroids. And they're objects at

549
00:21:01.540 --> 00:21:04.140
the bottom of the asteroid belt, typically

550
00:21:04.140 --> 00:21:06.820
rocky or metallic objects moving on orbits at

551
00:21:06.820 --> 00:21:08.820
a relatively short period in the inner solar

552
00:21:08.820 --> 00:21:10.580
system. And they're short lived. You know, if

553
00:21:10.580 --> 00:21:12.380
you come back in a million years, most of the

554
00:21:12.380 --> 00:21:14.300
ones we currently know will have been

555
00:21:14.300 --> 00:21:15.820
removed. They'll have been ejected from the

556
00:21:15.820 --> 00:21:17.740
solar system or collided with a planet or

557
00:21:17.740 --> 00:21:20.020
fallen apart or fallen into the sun. But

558
00:21:20.020 --> 00:21:21.980
they're continually being repopulated from

559
00:21:21.980 --> 00:21:24.780
the asteroid belt. Some of them hide

560
00:21:24.780 --> 00:21:26.660
closer to the sun than we are and then pop

561
00:21:26.660 --> 00:21:28.420
out to say hello. We were talking about that

562
00:21:28.420 --> 00:21:30.300
last week with the objects near Venus.

563
00:21:31.500 --> 00:21:33.460
But there's this effort to try and find all

564
00:21:33.460 --> 00:21:36.460
of them. And the earlier you can find them,

565
00:21:36.460 --> 00:21:38.859
and the earlier you can figure out if there's

566
00:21:38.859 --> 00:21:40.980
going to be an encounter with the Earth that

567
00:21:40.980 --> 00:21:43.300
poses a threat, the better the odds of you

568
00:21:43.300 --> 00:21:45.700
doing something about it. And we saw this

569
00:21:46.100 --> 00:21:48.100
kind of a bright light shone on this back at

570
00:21:48.100 --> 00:21:50.180
the start of 2025 with the object

571
00:21:50.960 --> 00:21:53.280
2024 yr 4. I think the name M was

572
00:21:53.680 --> 00:21:55.440
that for a while we thought had a

573
00:21:56.080 --> 00:21:58.080
substantial possibility of hitting the Earth

574
00:21:58.080 --> 00:22:01.040
in 2032 that we now know is not going to

575
00:22:01.040 --> 00:22:02.440
hit the Earth, but might hit the moon in

576
00:22:02.440 --> 00:22:04.680
2032. And that was a big success because we

577
00:22:04.680 --> 00:22:06.480
found it early enough to get a lot of data.

578
00:22:06.490 --> 00:22:07.830
and over the course of about a month

579
00:22:07.830 --> 00:22:10.550
astronomers observed it repeatedly until

580
00:22:10.550 --> 00:22:12.190
eventually we showed that it definitely

581
00:22:12.190 --> 00:22:13.790
wasn't going to hit the Earth in eight year

582
00:22:13.790 --> 00:22:15.910
time. And everybody kind of basically jumped

583
00:22:15.910 --> 00:22:17.270
up and down and said hooray. And there was

584
00:22:17.270 --> 00:22:19.720
much rejoicing. So that's like the ideal

585
00:22:19.720 --> 00:22:22.320
scenario. We find something when it passes

586
00:22:22.320 --> 00:22:25.280
relatively nearby on one apparition a

587
00:22:25.280 --> 00:22:27.600
few years before it would realistically pose

588
00:22:27.600 --> 00:22:30.200
a threat. And that's what we want to achieve.

589
00:22:30.280 --> 00:22:32.920
And the stated goal of a lot of the agencies

590
00:22:32.920 --> 00:22:34.520
looking for these things is to find all the

591
00:22:34.520 --> 00:22:36.600
objects bigger than about 100 meters across

592
00:22:37.160 --> 00:22:38.650
that could pose a threat to the Earth, and

593
00:22:38.650 --> 00:22:41.570
catalog them. And we haven't managed

594
00:22:41.570 --> 00:22:44.330
that yet. We even more haven't managed that

595
00:22:44.330 --> 00:22:45.930
when you take into account things like

596
00:22:45.930 --> 00:22:47.700
comets. You know we were talking about, about

597
00:22:47.700 --> 00:22:50.260
Comet Swan last week, which appeared from

598
00:22:50.580 --> 00:22:52.820
hiding behind the sun and came and was

599
00:22:52.820 --> 00:22:54.500
suddenly the brightest comet in the sky.

600
00:22:54.980 --> 00:22:56.940
Comets are coming in on orbits that take

601
00:22:56.940 --> 00:22:59.020
hundreds, thousands, sometimes even tens of

602
00:22:59.020 --> 00:23:00.900
thousands or millions of years to complete.

603
00:23:01.220 --> 00:23:02.740
So even if we find all the near Earth

604
00:23:02.740 --> 00:23:05.020
asteroids, we're still going to have comets

605
00:23:05.020 --> 00:23:06.940
coming in. So we'll have to stay vigilant and

606
00:23:06.940 --> 00:23:09.820
keep watching forevermore. But this

607
00:23:09.820 --> 00:23:12.300
is a really good reminder that despite how

608
00:23:12.300 --> 00:23:15.070
you feel, we're not there yet. We are still

609
00:23:15.070 --> 00:23:17.910
in a position where these things are

610
00:23:17.910 --> 00:23:20.030
catching us by surprise. And the worst case

611
00:23:20.030 --> 00:23:22.270
scenario is what happened in 2013 with the

612
00:23:22.270 --> 00:23:24.750
Chelyabinsk impactor to a similar

613
00:23:24.990 --> 00:23:27.070
level of what happened with comets 1 earlier

614
00:23:27.070 --> 00:23:28.829
this year in that as, ah, the object

615
00:23:28.829 --> 00:23:30.510
approaches the Earth and eventually gets

616
00:23:30.510 --> 00:23:32.310
close enough that it was visible in the

617
00:23:32.310 --> 00:23:34.190
nighttime sky, would be able to detect it.

618
00:23:34.590 --> 00:23:36.470
It's coming from the sunward side of the

619
00:23:36.470 --> 00:23:37.770
Earth, so it's hidden in the glare of

620
00:23:37.770 --> 00:23:40.540
daylight. And so that's why you

621
00:23:40.540 --> 00:23:42.340
don't want to try and detect something the

622
00:23:42.500 --> 00:23:44.820
moment it's on an approach to hit you. You

623
00:23:44.820 --> 00:23:47.020
want to find it well in advance. And with

624
00:23:47.020 --> 00:23:48.740
Charlie Abinsky, it demonstrated something

625
00:23:48.740 --> 00:23:51.060
big enough to injure people, damage a city

626
00:23:51.780 --> 00:23:53.420
we didn't find until it was in the

627
00:23:53.420 --> 00:23:55.540
atmosphere. And it was kind of too late. It

628
00:23:55.540 --> 00:23:56.660
was seconds from disaster.

629
00:23:57.060 --> 00:23:57.620
Andrew Dunkley: Indeed.

630
00:23:58.020 --> 00:24:00.940
Jonti Horner: Now there's hope. We've got Vera Rubin

631
00:24:00.940 --> 00:24:02.700
coming online. We saw a beautiful picture

632
00:24:02.700 --> 00:24:05.080
from that earlier this year. Vera Rubin's

633
00:24:05.080 --> 00:24:06.750
going to start getting data regularly,

634
00:24:07.340 --> 00:24:09.500
continuously later this year, early next

635
00:24:09.500 --> 00:24:11.500
year, that's when the Mayan mission starts.

636
00:24:11.500 --> 00:24:13.420
And Vera Rubin is going to be an exceptional

637
00:24:13.900 --> 00:24:16.420
thing finding tool no matter what. The thing

638
00:24:16.420 --> 00:24:18.340
is, it will find more of them than anybody's

639
00:24:18.340 --> 00:24:20.620
found before. From a solar system point of

640
00:24:20.620 --> 00:24:22.300
view. We're really excited because it will

641
00:24:22.620 --> 00:24:24.820
increase the number of objects we know by a

642
00:24:24.820 --> 00:24:27.020
factor of several to an order of magnitude

643
00:24:27.020 --> 00:24:29.380
within a year or two. And it'll be great at

644
00:24:29.380 --> 00:24:32.360
finding these things, but it'll be less

645
00:24:32.360 --> 00:24:34.360
great than it would have been thanks to all

646
00:24:34.360 --> 00:24:35.280
the stuff we keep watching.

647
00:24:35.280 --> 00:24:36.960
Then this is where it ties into the previous

648
00:24:37.120 --> 00:24:40.000
story. Also ties in again to the wonderful

649
00:24:40.000 --> 00:24:42.400
student who sent me the information about the

650
00:24:42.400 --> 00:24:44.480
reflector orbital stuff. Jessica Heim

651
00:24:45.360 --> 00:24:47.920
is finishing up her PhD with us at UNESCO.

652
00:24:47.920 --> 00:24:50.560
She's based in North America and she's

653
00:24:50.800 --> 00:24:53.200
done a lot of her work about light pollution

654
00:24:53.440 --> 00:24:55.710
and artificial, light at night and things

655
00:24:55.710 --> 00:24:57.750
like this. And one of her papers early in a

656
00:24:57.750 --> 00:25:00.740
PhD that she was a co author on was in

657
00:25:00.740 --> 00:25:02.860
Nature Astronomy. And they actually did a

658
00:25:02.860 --> 00:25:05.500
study looking at just the starlink satellites

659
00:25:05.500 --> 00:25:07.140
that were in orbit at that time, so not the

660
00:25:07.140 --> 00:25:10.060
predicted number in the future, and tried to

661
00:25:10.060 --> 00:25:13.020
quantify how much harder they would make

662
00:25:13.020 --> 00:25:14.700
life for Vera Rubin, and particularly how

663
00:25:14.700 --> 00:25:16.620
much harder they make it for Vera Rubin to

664
00:25:16.620 --> 00:25:18.100
find objects like the one we're just talking

665
00:25:18.100 --> 00:25:20.380
about that was over Antarctica.

666
00:25:21.180 --> 00:25:23.780
And what they found was the Starlink

667
00:25:23.780 --> 00:25:25.710
satellites that were in orbit at the time. So

668
00:25:25.710 --> 00:25:27.590
not the constellation we have now, which is

669
00:25:27.590 --> 00:25:30.190
big and not the final constellation would

670
00:25:30.190 --> 00:25:32.550
make it 10% harder for Vera Rubin to do its

671
00:25:32.550 --> 00:25:33.830
job. So in other words, it would have to

672
00:25:33.830 --> 00:25:36.030
observe for 10% longer. Roughly. I think the

673
00:25:36.030 --> 00:25:37.630
number was actually slightly higher than that

674
00:25:38.510 --> 00:25:40.630
in order to achieve the same results. Now

675
00:25:40.630 --> 00:25:42.390
when you're talking about a facility that's a

676
00:25:42.390 --> 00:25:45.190
billion dollar level facility, hundreds of

677
00:25:45.190 --> 00:25:47.950
millions of dollars to build, having to take

678
00:25:47.950 --> 00:25:50.150
10% longer to do something is a cost measured

679
00:25:50.150 --> 00:25:52.710
in tens of millions of dollars. Yeah, that's

680
00:25:52.710 --> 00:25:54.980
real impact in this. And what it means is

681
00:25:54.980 --> 00:25:56.540
that things like this are going to be harder

682
00:25:56.540 --> 00:25:58.620
to find. And our ability to

683
00:25:59.420 --> 00:26:02.300
detect potential threats is really

684
00:26:02.300 --> 00:26:05.300
kind of confused and obfuscated by the

685
00:26:05.300 --> 00:26:07.300
stuff we're putting to hang around in the

686
00:26:07.300 --> 00:26:09.540
foreground. It's like, I guess it's really

687
00:26:09.540 --> 00:26:11.500
easy to see a road sign on a clear day, but

688
00:26:11.500 --> 00:26:13.740
when it's foggy, it's a lot harder to spot it

689
00:26:13.740 --> 00:26:14.940
until you're right on that side.

690
00:26:15.180 --> 00:26:18.060
Andrew Dunkley: Yeah, yeah, indeed. And

691
00:26:18.220 --> 00:26:20.630
if you want to read up on that story, about

692
00:26:20.630 --> 00:26:23.101
the near miss, you can do so@space

693
00:26:23.319 --> 00:26:25.860
space.com. this is Space Nuts with Andrew

694
00:26:25.860 --> 00:26:27.980
Dunkley and John T. Horner.

695
00:26:28.620 --> 00:26:30.860
Jonti Horner: Three, two, one.

696
00:26:31.500 --> 00:26:32.700
Andrew Dunkley: Space nuts.

697
00:26:33.100 --> 00:26:35.590
Now, Johnny, we have found the

698
00:26:35.590 --> 00:26:38.270
6,000th exoplanet.

699
00:26:38.350 --> 00:26:40.910
It took us 30 years, which is,

700
00:26:41.470 --> 00:26:43.940
you know, if you, if you look back at when we

701
00:26:43.940 --> 00:26:46.460
found the first one, it was quite a surprise

702
00:26:46.460 --> 00:26:49.310
for a bunch of reasons. mostly because

703
00:26:49.310 --> 00:26:51.550
we didn't even know they could have existed

704
00:26:51.550 --> 00:26:53.830
beyond our solar system. Logic suggests, you

705
00:26:53.830 --> 00:26:56.270
know, if it's. We've got planets around our

706
00:26:56.270 --> 00:26:59.110
sun, other stars must have planets too.

707
00:26:59.750 --> 00:27:02.500
And 30 years ago, that was proven. Well, now

708
00:27:02.500 --> 00:27:04.620
we're up to number 6,000. When are we going

709
00:27:04.620 --> 00:27:06.700
to stop counting? Because it's going to reach

710
00:27:06.700 --> 00:27:08.340
a point where we're going to find millions

711
00:27:08.340 --> 00:27:10.140
upon millions of these things, isn't it?

712
00:27:10.460 --> 00:27:12.370
Jonti Horner: It is. And even the counting's a little bit

713
00:27:12.370 --> 00:27:15.330
confused because the resource I

714
00:27:15.330 --> 00:27:18.130
trust as kind of being the authoritative word

715
00:27:18.130 --> 00:27:20.690
on this is the NASA exoplanet archive, which

716
00:27:20.690 --> 00:27:22.610
is a wonderful resource. And they've got a

717
00:27:22.610 --> 00:27:25.610
certain threshold for what they consider a

718
00:27:25.610 --> 00:27:27.810
confirmed planet. And we've got all these

719
00:27:27.810 --> 00:27:29.970
candidate planets as well, of which there are

720
00:27:29.970 --> 00:27:31.730
thousands more where we're fairly Confident

721
00:27:31.730 --> 00:27:33.410
there's a planet there, but it doesn't meet

722
00:27:33.410 --> 00:27:36.250
that rigorous criterion. There is a

723
00:27:36.250 --> 00:27:38.530
different exoplanet catalog run out of Europe

724
00:27:38.610 --> 00:27:40.490
that has a number higher because they are

725
00:27:40.490 --> 00:27:42.930
less strict on their criterion for

726
00:27:43.330 --> 00:27:45.740
confirmation. part of the reason I'm more

727
00:27:45.740 --> 00:27:47.660
skeptical about that catalog is that there's

728
00:27:47.660 --> 00:27:49.660
a number of planetary systems I've helped to

729
00:27:49.660 --> 00:27:52.020
kill and they've left them in their catalog.

730
00:27:52.180 --> 00:27:53.900
So we know for a fact those planets aren't

731
00:27:53.900 --> 00:27:55.950
there. I did some of that work and they still

732
00:27:55.950 --> 00:27:57.510
include them in their catalog, which puts

733
00:27:57.510 --> 00:27:59.470
them m on my naughty list. So I prefer the

734
00:27:59.470 --> 00:28:02.150
NASA one and the NASA one is the more

735
00:28:02.150 --> 00:28:04.670
cautious of them. It's really

736
00:28:04.670 --> 00:28:06.230
interesting how this has come though. You

737
00:28:06.230 --> 00:28:08.590
know, I'm, I'm 47 now. I don't feel it, but

738
00:28:08.590 --> 00:28:11.410
I'm getting on a little bit. I was a kid who

739
00:28:11.410 --> 00:28:13.370
was mad about astronomy. You know, like some

740
00:28:13.370 --> 00:28:14.850
of the people who send in their questions,

741
00:28:14.850 --> 00:28:16.490
some of the youngsters who send in questions.

742
00:28:16.970 --> 00:28:18.240
And when I was growing up, one of the

743
00:28:18.240 --> 00:28:19.920
questions I'd have been asking is do you

744
00:28:19.920 --> 00:28:21.680
think there are planets around other stars?

745
00:28:22.080 --> 00:28:24.760
We'd had observations from satellites like

746
00:28:24.760 --> 00:28:27.480
IRAS in the 1980s that indicated there was

747
00:28:27.480 --> 00:28:30.480
dust and debris around some stars. But at

748
00:28:30.480 --> 00:28:33.210
the time our models of planet formation fell

749
00:28:33.210 --> 00:28:35.480
into kind of two camps. So whereas what's now

750
00:28:35.480 --> 00:28:37.800
become kind of the standard baseline with

751
00:28:37.800 --> 00:28:39.680
some tweaks, which was that you get a disc of

752
00:28:39.680 --> 00:28:42.340
material around every young star and planets

753
00:28:42.340 --> 00:28:44.500
forming it. So most stars will have planets.

754
00:28:44.900 --> 00:28:47.220
But there was a competing theory that said

755
00:28:47.220 --> 00:28:49.340
that the planets were formed by a very close

756
00:28:49.340 --> 00:28:51.540
encounter between the sun and a passing star

757
00:28:51.940 --> 00:28:54.140
that pulled material out of the sun like a

758
00:28:54.140 --> 00:28:56.700
tongue of material, and the planets formed

759
00:28:56.700 --> 00:28:59.430
from that. and there are people who were

760
00:28:59.430 --> 00:29:02.090
very strong advocates of that. Now

761
00:29:02.090 --> 00:29:04.050
the test of those theories

762
00:29:05.250 --> 00:29:07.530
it would have been, are, ah, there planets

763
00:29:07.530 --> 00:29:09.050
around other stars, Are they common? Because

764
00:29:09.050 --> 00:29:10.930
the idea that two stars get close enough

765
00:29:10.930 --> 00:29:13.410
together to have this tidal interaction pull

766
00:29:13.410 --> 00:29:15.370
out a ton of material and planets form from

767
00:29:15.370 --> 00:29:17.730
that would suggest that planets would be

768
00:29:17.810 --> 00:29:20.010
overwhelmingly rare in the cosmos. So

769
00:29:20.010 --> 00:29:21.650
likelihood of 2 stars getting that close

770
00:29:21.650 --> 00:29:23.090
together and having exactly the right

771
00:29:23.090 --> 00:29:25.850
conditions would mean that planets were

772
00:29:25.850 --> 00:29:28.440
pretty much non existent, that they were a

773
00:29:28.440 --> 00:29:31.320
fluke of nature. The other model

774
00:29:31.320 --> 00:29:33.680
suggested that planets are common. And so one

775
00:29:33.680 --> 00:29:36.400
of the goals in the early 1990s with the

776
00:29:36.400 --> 00:29:39.040
search for planets elsewhere was to see

777
00:29:39.040 --> 00:29:40.720
whether there were any at all. And we just

778
00:29:40.720 --> 00:29:43.560
didn't know. The discovery of

779
00:29:43.640 --> 00:29:45.720
three planets around a pulsar in the early

780
00:29:45.720 --> 00:29:48.640
1990s broke everybody's heads. Those

781
00:29:48.640 --> 00:29:50.280
planets have now, incidentally, been called

782
00:29:50.280 --> 00:29:53.160
drow, Phoebeta and poltergeist, which are

783
00:29:53.160 --> 00:29:54.800
names of different types of undead from

784
00:29:54.800 --> 00:29:56.120
different cultures around the world. And I

785
00:29:56.120 --> 00:29:57.560
think that's kind of cute because you've got

786
00:29:57.560 --> 00:30:00.480
zombie planets around a dead star. That's all

787
00:30:00.480 --> 00:30:03.200
good. But 30 years ago, and actually 30 years

788
00:30:03.200 --> 00:30:05.546
ago last week on the 6th of October

789
00:30:05.694 --> 00:30:08.640
1995, we saw the announcement

790
00:30:08.640 --> 00:30:10.960
of the first confirmed planet around a star

791
00:30:10.960 --> 00:30:13.920
like the sun. And that planet was 51 Pegasi

792
00:30:13.920 --> 00:30:16.480
b. So it's a planet going around the south 51

793
00:30:16.480 --> 00:30:19.090
Pegasi. And it immediately broke

794
00:30:19.090 --> 00:30:20.850
everybody's heads because it was not what we

795
00:30:20.850 --> 00:30:23.010
expected. So both our models of planet

796
00:30:23.010 --> 00:30:26.010
formation that were based on a grand total of

797
00:30:26.010 --> 00:30:28.730
one planetary system, our own, predicted

798
00:30:28.730 --> 00:30:30.610
you'd have rocky planets close to the star

799
00:30:30.690 --> 00:30:33.010
and big gas giants a long way from the star,

800
00:30:33.010 --> 00:30:34.490
because that's what we see at home. And that

801
00:30:34.490 --> 00:30:37.010
makes sense. So to find a planet

802
00:30:37.170 --> 00:30:39.410
similar to Jupiter, but going around its star

803
00:30:39.410 --> 00:30:41.770
every four days with a surface temperature in

804
00:30:41.770 --> 00:30:44.690
excess of a thousand degrees C was not

805
00:30:44.690 --> 00:30:46.450
what was expected, I think would be the

806
00:30:46.450 --> 00:30:48.970
polite way to put it. Now, that forced people

807
00:30:48.970 --> 00:30:51.050
to immediately go back and start revisiting

808
00:30:51.050 --> 00:30:53.490
and improving that disk model of planet

809
00:30:53.490 --> 00:30:55.250
formation, which has kind of led us to where

810
00:30:55.250 --> 00:30:57.810
we are now. But that was kind of

811
00:30:57.810 --> 00:31:00.650
fundamental and foundational. For the first

812
00:31:01.290 --> 00:31:03.650
decade or so after that

813
00:31:03.650 --> 00:31:06.650
discovery, new planets were found in dribs

814
00:31:06.650 --> 00:31:08.130
and drabs, and the rate at which they were

815
00:31:08.130 --> 00:31:10.010
discovered gradually increased. And in that

816
00:31:10.010 --> 00:31:12.960
first decade, the best technique for finding

817
00:31:12.960 --> 00:31:14.640
planets, the one that was most successful,

818
00:31:14.640 --> 00:31:16.800
was what we call the radial velocity method,

819
00:31:17.040 --> 00:31:19.280
which Australia really played a leading role

820
00:31:19.280 --> 00:31:21.320
in with the Anglo Australian Planet Search.

821
00:31:21.320 --> 00:31:23.280
There was this beautiful spectrograph

822
00:31:23.280 --> 00:31:25.960
attached to the 3.9 meter telescope at Siding

823
00:31:25.960 --> 00:31:28.400
Spring, which I know Fred loves daily. It's a

824
00:31:28.400 --> 00:31:31.150
real icon of Australian astronomy. And, that

825
00:31:31.150 --> 00:31:33.270
telescope was used to point at one star,

826
00:31:33.510 --> 00:31:35.590
measure that star speed, then point at

827
00:31:35.590 --> 00:31:38.500
another, and gradually survey this collection

828
00:31:38.500 --> 00:31:40.100
of stars and then keep coming back to them

829
00:31:40.100 --> 00:31:41.660
every now and again and measure their speed

830
00:31:41.660 --> 00:31:43.990
again. And, by measuring the speed of these

831
00:31:43.990 --> 00:31:46.630
stars to the level that you can see them

832
00:31:46.630 --> 00:31:49.550
wobbling with changes of

833
00:31:49.550 --> 00:31:51.550
speed measured in a few meters per second. So

834
00:31:51.550 --> 00:31:53.549
comparable to speed, people walk or jog

835
00:31:53.549 --> 00:31:56.110
around stars that are trillions or

836
00:31:56.110 --> 00:31:57.790
quadrillions of kilometers away, measuring

837
00:31:57.790 --> 00:31:59.950
their wobbles to a precision of meters per

838
00:31:59.950 --> 00:32:02.350
second. That just makes my head hurt. But by

839
00:32:02.350 --> 00:32:04.900
doing that, you can spot the telltale wobble

840
00:32:04.900 --> 00:32:07.020
of a star rocking back and forward in space

841
00:32:07.020 --> 00:32:09.860
and infer the presence of a planet. But it's

842
00:32:09.860 --> 00:32:12.820
a really time consuming, challenging

843
00:32:12.820 --> 00:32:14.740
method where you can only observe a few stars

844
00:32:14.740 --> 00:32:15.980
at once, because you've got to gather light

845
00:32:15.980 --> 00:32:18.899
for an hour or more to get enough

846
00:32:18.899 --> 00:32:20.740
light, to get an accurate enough spectrum to

847
00:32:20.740 --> 00:32:22.140
get a single measurement. And you can only

848
00:32:22.140 --> 00:32:24.900
point at one star at once. By

849
00:32:25.140 --> 00:32:27.980
the late part of the first decade of the

850
00:32:27.980 --> 00:32:30.800
21st century, the transit method started to

851
00:32:30.800 --> 00:32:32.560
take over. And this is where we look at a lot

852
00:32:32.560 --> 00:32:35.480
of stars all at once and look for the

853
00:32:35.480 --> 00:32:37.560
few of them that are winking at us. So

854
00:32:37.560 --> 00:32:39.160
they've got a planet going around them that's

855
00:32:39.160 --> 00:32:40.770
lined, up just right that every time it goes

856
00:32:40.770 --> 00:32:42.450
around that star, it will block a bit of that

857
00:32:42.450 --> 00:32:44.490
star's light and the star will dim and then

858
00:32:44.490 --> 00:32:47.450
brighten again. And that started to

859
00:32:47.450 --> 00:32:49.290
take over from the radial velocity method

860
00:32:49.290 --> 00:32:51.330
purely because of the numbers. Again, because

861
00:32:51.330 --> 00:32:53.210
you can look at a large number of stars at

862
00:32:53.210 --> 00:32:56.020
the same time. And even if only

863
00:32:56.020 --> 00:32:58.620
1% of those stars have a planet oriented in

864
00:32:58.620 --> 00:33:00.980
the right direction for you to have it line

865
00:33:00.980 --> 00:33:03.540
up and give us a dip by looking at 100,000

866
00:33:03.540 --> 00:33:05.060
stars at once, you'll have plenty of

867
00:33:05.060 --> 00:33:07.820
candidates. The Kepler spacecraft

868
00:33:07.820 --> 00:33:10.619
launched in about 2008 and became

869
00:33:10.619 --> 00:33:13.380
this first census of the night sky. And

870
00:33:13.380 --> 00:33:15.500
it discovered on its own more than 3,000

871
00:33:15.500 --> 00:33:17.740
planets around other stars using this transit

872
00:33:17.740 --> 00:33:20.060
method. So we've got better and better at

873
00:33:20.060 --> 00:33:22.380
doing it. And over time what's happened is

874
00:33:22.990 --> 00:33:24.830
we've not only found the low hanging fruit,

875
00:33:24.830 --> 00:33:26.670
the really big planets close to their stars

876
00:33:26.670 --> 00:33:28.310
that give a whopping great signal that you

877
00:33:28.310 --> 00:33:30.670
can find, but with each generation of new

878
00:33:30.670 --> 00:33:31.990
instrument that's gone up there, we've got

879
00:33:31.990 --> 00:33:33.550
better at finding planets that are further

880
00:33:33.550 --> 00:33:35.710
from their stars, better at finding planets

881
00:33:35.710 --> 00:33:37.990
that are ever smaller, finding planets that

882
00:33:37.990 --> 00:33:40.270
are weird, or other techniques are coming

883
00:33:40.270 --> 00:33:41.830
online that allow us to do things another

884
00:33:41.830 --> 00:33:43.630
way. And I still think one of the greatest

885
00:33:43.630 --> 00:33:45.990
movies that never won an Oscar are, ah, the

886
00:33:45.990 --> 00:33:48.950
wonderful Images of the SAHR 8799 that

887
00:33:48.950 --> 00:33:51.320
shows four planets going around it. And we've

888
00:33:51.320 --> 00:33:53.280
got kind of a live movie of those planets

889
00:33:53.280 --> 00:33:56.160
orbiting that star that runs back more than a

890
00:33:56.160 --> 00:33:57.880
decade now. It's just breathtaking.

891
00:33:57.960 --> 00:33:59.160
Andrew Dunkley: Yeah, I saw it.

892
00:33:59.640 --> 00:34:02.330
Jonti Horner: Yeah, it's awesome. And we've basically lived

893
00:34:02.330 --> 00:34:04.690
through this awesome scientific

894
00:34:04.690 --> 00:34:07.490
revolution without really realizing it. You

895
00:34:07.490 --> 00:34:09.010
know, we've gone from a world where nobody

896
00:34:09.010 --> 00:34:10.930
knew if there were planets around other stars

897
00:34:11.250 --> 00:34:13.290
to a fact that there is nobody younger than

898
00:34:13.290 --> 00:34:15.490
the age of 30 now who grew up in that world

899
00:34:15.490 --> 00:34:18.110
that you and I grew up in, where we wondered

900
00:34:18.110 --> 00:34:19.510
if there were planets around other stars.

901
00:34:19.510 --> 00:34:22.270
It's absolutely breathtaking. We've had

902
00:34:22.750 --> 00:34:24.390
real big involvement with this here in

903
00:34:24.390 --> 00:34:26.390
Australia. The Anglo Australian Planet Search

904
00:34:26.390 --> 00:34:29.110
was one of the leaders for the first 10 or 15

905
00:34:29.110 --> 00:34:31.270
years of this exoplanet era. We've got a

906
00:34:31.270 --> 00:34:33.630
facility here in Queensland that is now

907
00:34:33.630 --> 00:34:34.990
leading the way, one of the leading

908
00:34:34.990 --> 00:34:37.750
facilities in the entire planet. You

909
00:34:37.750 --> 00:34:40.150
know, the only dedicated exoplanet search

910
00:34:40.150 --> 00:34:41.910
facility in the Southern hemisphere. And we

911
00:34:41.910 --> 00:34:44.170
work with NASA to do this. We've been

912
00:34:44.170 --> 00:34:47.090
directly involved with 41 planet discoveries

913
00:34:47.090 --> 00:34:49.890
in the last couple of years, using NASA's

914
00:34:49.890 --> 00:34:52.370
test mission and working with them. But it's

915
00:34:52.370 --> 00:34:54.850
this kind of ongoing exploration, this

916
00:34:54.850 --> 00:34:57.230
ongoing search. And, you know, what will the

917
00:34:57.230 --> 00:34:59.550
next 30 years bring? That's kind of what I

918
00:34:59.550 --> 00:35:02.190
wonder. Where will we go with it? And

919
00:35:02.830 --> 00:35:05.070
it's not so much when will we stop counting,

920
00:35:05.470 --> 00:35:07.870
but when will we start to get things that

921
00:35:08.270 --> 00:35:10.270
really potentially could be like the Earth?

922
00:35:10.270 --> 00:35:12.070
And I've said this before, I don't think

923
00:35:12.070 --> 00:35:13.550
we've found an Earth like planet yet. We

924
00:35:13.550 --> 00:35:15.710
found things about as big as the Earth that

925
00:35:15.710 --> 00:35:18.110
are very different. Like saying, I went

926
00:35:18.110 --> 00:35:19.910
swimming last week and I saw the most human

927
00:35:19.910 --> 00:35:21.670
like creature I've ever seen. And it was a

928
00:35:21.670 --> 00:35:23.310
dolphin. It was about the same size and

929
00:35:23.310 --> 00:35:25.110
weight as a human, but it's fundamentally not

930
00:35:25.110 --> 00:35:27.310
a human being. Yeah, but we're going to be

931
00:35:27.310 --> 00:35:29.030
moving forward and we're going to be moving

932
00:35:29.030 --> 00:35:30.870
from just finding these things to learning

933
00:35:30.870 --> 00:35:32.430
more about them. We're moving into this era

934
00:35:32.430 --> 00:35:35.030
of characterization and I think the number's

935
00:35:35.030 --> 00:35:36.670
going to gradually lose importance.

936
00:35:36.670 --> 00:35:39.510
You know, when we find 10,000 or 100,000,

937
00:35:40.540 --> 00:35:42.220
the difference will be a lot less significant

938
00:35:42.220 --> 00:35:44.980
than the difference between 0 and 1. But

939
00:35:44.980 --> 00:35:46.980
it'll start being which of the planets we

940
00:35:46.980 --> 00:35:49.660
know the most about. What are they like? What

941
00:35:49.660 --> 00:35:52.020
can we learn about them? And that's, I think,

942
00:35:52.020 --> 00:35:53.580
the journey for the next 30 years.

943
00:35:53.740 --> 00:35:56.099
Andrew Dunkley: Yes. And finding, and as you said, finding

944
00:35:56.099 --> 00:35:59.010
that, one planet that is so

945
00:35:59.010 --> 00:36:01.970
like ours in size and proximity,

946
00:36:02.600 --> 00:36:04.440
orbiting a sun like ours,

947
00:36:05.940 --> 00:36:08.210
maybe with liquid water, et cetera, et

948
00:36:08.210 --> 00:36:08.490
cetera.

949
00:36:08.490 --> 00:36:08.890
Jonti Horner: Yeah.

950
00:36:09.520 --> 00:36:11.320
Andrew Dunkley: that's the golden goose, isn't it, really?

951
00:36:11.960 --> 00:36:12.560
Jonti Horner: Absolutely.

952
00:36:12.560 --> 00:36:14.920
And we've got this really interesting

953
00:36:14.920 --> 00:36:17.560
question about how long has the

954
00:36:17.560 --> 00:36:20.440
Earth being in a condition that if we looked

955
00:36:20.440 --> 00:36:22.800
at it, it would look like the Earth. So in

956
00:36:22.800 --> 00:36:24.560
other words, how long has the Earth been an

957
00:36:24.560 --> 00:36:26.200
Earth like planet? Because when we're talking

958
00:36:26.200 --> 00:36:29.050
about a planet like the Earth, when it's

959
00:36:29.050 --> 00:36:30.650
something like the Earth is today, with, you

960
00:36:30.650 --> 00:36:32.650
know, beautiful blue sparkling oceans and A

961
00:36:32.650 --> 00:36:35.210
thin oxygen rich atmosphere and life

962
00:36:35.210 --> 00:36:37.130
teeming in abundant continents that are

963
00:36:37.130 --> 00:36:39.890
mottled brown and green and icy polar

964
00:36:39.890 --> 00:36:41.610
caps. But for the vast majority of the

965
00:36:41.610 --> 00:36:44.170
Earth's history it has looked nothing like it

966
00:36:44.170 --> 00:36:45.850
does now. It's had an entirely different

967
00:36:45.850 --> 00:36:48.650
atmosphere. It's not had free

968
00:36:48.650 --> 00:36:50.370
oxygen in the atmosphere. It's had periods

969
00:36:50.370 --> 00:36:52.850
when it was an enormous snowball, you know,

970
00:36:52.850 --> 00:36:55.460
snowball Earth episodes. So it's quite likely

971
00:36:55.460 --> 00:36:57.540
that for the majority of the Earth's history

972
00:36:58.500 --> 00:37:00.580
we wouldn't recognize it as an Earth like

973
00:37:00.580 --> 00:37:02.780
planet because it would look totally, totally

974
00:37:02.780 --> 00:37:03.060
different.

975
00:37:03.780 --> 00:37:05.740
Andrew Dunkley: Yeah, that's an interesting point. And that

976
00:37:05.740 --> 00:37:08.700
could exist elsewhere in the

977
00:37:08.700 --> 00:37:10.740
universe. And we may have seen a planet

978
00:37:10.820 --> 00:37:13.700
already that could one day be like

979
00:37:13.700 --> 00:37:15.900
ours, but it might be tens of thousands or

980
00:37:15.900 --> 00:37:17.740
hundreds of thousands of years before it

981
00:37:17.740 --> 00:37:19.700
reaches that point. So

982
00:37:20.500 --> 00:37:23.500
that's a really interesting factor to bring

983
00:37:23.500 --> 00:37:24.800
into the equation.

984
00:37:24.940 --> 00:37:27.180
you said some odd planets. I thought I'd do a

985
00:37:27.180 --> 00:37:29.310
bit of a search. these exoplanets that we've

986
00:37:29.310 --> 00:37:31.488
discovered in the last 30 years. Wasp

987
00:37:31.652 --> 00:37:34.390
76B. It's a hot

988
00:37:34.390 --> 00:37:37.230
Jupiter which rains molten iron. I think Fred

989
00:37:37.230 --> 00:37:38.880
and I talked about that one. Wasp,

990
00:37:39.270 --> 00:37:42.140
107B. A gas giant, with

991
00:37:42.140 --> 00:37:44.540
a density so low it's been described as a

992
00:37:44.540 --> 00:37:45.780
marshmallow planet.

993
00:37:47.230 --> 00:37:47.790
HD,

994
00:37:48.380 --> 00:37:51.380
189773B. It's a planet

995
00:37:51.380 --> 00:37:53.220
with an atmosphere that contains clouds of

996
00:37:53.220 --> 00:37:54.260
molten glass.

997
00:37:54.740 --> 00:37:57.540
Jonti Horner: Yeah, that's often described as a blue marble

998
00:37:57.540 --> 00:37:58.140
planet, I think.

999
00:37:58.140 --> 00:38:01.139
Andrew Dunkley: Yeah, yeah. Hat P7B is an ultra

1000
00:38:01.139 --> 00:38:03.100
hot Jupiter that's so dark it's nearly

1001
00:38:03.100 --> 00:38:05.990
charcoal and 5,

1002
00:38:06.070 --> 00:38:08.790
5 Cancri E I think it's

1003
00:38:08.790 --> 00:38:11.700
pronounced a, super Earth with a lava world,

1004
00:38:11.970 --> 00:38:14.790
and sparkling skies. And there's probably

1005
00:38:14.790 --> 00:38:17.030
more weird ones out there. We yet defined

1006
00:38:17.030 --> 00:38:19.500
that, defy explanation. It's a really

1007
00:38:19.500 --> 00:38:21.090
fascinating part of astronomy.

1008
00:38:21.090 --> 00:38:23.450
Jonti Horner: it is. And it's that realization that the

1009
00:38:23.450 --> 00:38:25.369
diversity of things that are out there is far

1010
00:38:25.369 --> 00:38:26.930
greater than we could have possibly imagined.

1011
00:38:26.930 --> 00:38:29.850
And it really forces us to revisit

1012
00:38:29.850 --> 00:38:31.690
and refine our definitions of what a planet

1013
00:38:31.690 --> 00:38:34.450
is. So we historically people have this

1014
00:38:34.850 --> 00:38:37.810
idealized boundary at 13 Jupiter masses where

1015
00:38:38.100 --> 00:38:39.460
if you're more massive than that, you're a

1016
00:38:39.460 --> 00:38:41.540
brown dwarf and you're a fail star. And if

1017
00:38:41.540 --> 00:38:42.940
you're less massive than that, you're a

1018
00:38:42.940 --> 00:38:43.380
planet.

1019
00:38:43.380 --> 00:38:43.780
Andrew Dunkley: Yeah.

1020
00:38:43.780 --> 00:38:45.380
Jonti Horner: And we're now finding things that people are

1021
00:38:45.380 --> 00:38:47.180
claiming a brown dwarfs that are only twice

1022
00:38:47.180 --> 00:38:49.220
the mass of Jupiter and things people are

1023
00:38:49.220 --> 00:38:50.980
claiming are planets that are 20 Jupiter

1024
00:38:50.980 --> 00:38:53.580
masses. You know, there's a real blurring of

1025
00:38:53.580 --> 00:38:56.300
that Boundary. You've then got one weird

1026
00:38:56.300 --> 00:38:58.460
object. If you look at what the most dense

1027
00:38:58.460 --> 00:39:00.860
planet we found is, there's one planet that

1028
00:39:00.860 --> 00:39:03.660
has a density that is something like

1029
00:39:03.660 --> 00:39:06.500
150 times the density of water or something

1030
00:39:06.500 --> 00:39:09.050
like this. And it's a few Jupiter

1031
00:39:09.050 --> 00:39:11.770
masses. And we know the density, we know the

1032
00:39:11.770 --> 00:39:13.650
size because of transits and we know the mass

1033
00:39:13.650 --> 00:39:15.250
because of radial velocity. And if you've got

1034
00:39:15.250 --> 00:39:16.930
the size and the mass, you get the density.

1035
00:39:18.210 --> 00:39:20.100
This thing is so dense so that it doesn't

1036
00:39:20.100 --> 00:39:22.780
confirm with any known material.

1037
00:39:23.260 --> 00:39:25.500
You know, it's many times denser than the

1038
00:39:25.500 --> 00:39:27.540
densest metal. Gravity pulling things in

1039
00:39:27.540 --> 00:39:30.220
can't explain it. And so

1040
00:39:30.460 --> 00:39:32.180
is it really a planet? There is some

1041
00:39:32.180 --> 00:39:34.790
speculation that it's actually something that

1042
00:39:34.790 --> 00:39:36.910
was probably a white dwarf that has somehow

1043
00:39:36.910 --> 00:39:39.150
been bombarded and fractured. So there's only

1044
00:39:39.550 --> 00:39:41.310
a few Jupiter masses left.

1045
00:39:42.910 --> 00:39:45.550
So it's not a planet. You know,

1046
00:39:46.190 --> 00:39:47.070
if it was a white.

1047
00:39:47.070 --> 00:39:49.710
Andrew Dunkley: Dwarf that's been culver, I would say no, but

1048
00:39:49.710 --> 00:39:51.210
gosh, yeah, there's.

1049
00:39:51.210 --> 00:39:53.410
Jonti Horner: All these other things. Planets that are less

1050
00:39:53.410 --> 00:39:56.410
dense than cotton candy and yeah, it's

1051
00:39:56.410 --> 00:39:58.650
awesome from a speculation point of view. And

1052
00:39:58.650 --> 00:40:00.810
it's a, a lot of the planets we've found are

1053
00:40:00.810 --> 00:40:02.530
things that if you saw them in an episode of

1054
00:40:02.530 --> 00:40:05.490
Star Trek or you know, any of these sci fi

1055
00:40:05.490 --> 00:40:08.010
series, you'd think that they jumped the

1056
00:40:08.010 --> 00:40:09.970
shark, that that kind of thing just wasn't

1057
00:40:09.970 --> 00:40:12.210
possible anymore. They'd obviously been

1058
00:40:12.370 --> 00:40:14.250
enjoying themselves a little bit too much in

1059
00:40:14.250 --> 00:40:17.010
the pre writing session. And yet we're

1060
00:40:17.010 --> 00:40:19.890
finding these objects are just so diverse

1061
00:40:19.890 --> 00:40:21.930
and bonkers. It's untrue. That's part of the

1062
00:40:21.930 --> 00:40:23.250
fun of it. You never know what we're going to

1063
00:40:23.250 --> 00:40:23.730
find next.

1064
00:40:23.890 --> 00:40:24.930
Andrew Dunkley: Absolutely not.

1065
00:40:25.080 --> 00:40:27.040
and that sort of takes us into our final

1066
00:40:27.040 --> 00:40:30.000
story because this is an object that

1067
00:40:30.390 --> 00:40:32.470
a little bit weird in our solar system.

1068
00:40:33.030 --> 00:40:35.760
It's the moon Mimas. But it's also been

1069
00:40:35.760 --> 00:40:38.760
called the Death Star because it does have

1070
00:40:38.760 --> 00:40:40.880
that Death Star look about it. It's got a

1071
00:40:40.880 --> 00:40:43.670
dish like depression, in it where it

1072
00:40:43.750 --> 00:40:46.390
must have got hit at some stage. But the

1073
00:40:46.390 --> 00:40:49.150
reason it's in the news now is because it

1074
00:40:49.150 --> 00:40:51.910
is yet another object in our solar system

1075
00:40:52.070 --> 00:40:54.750
that may contain a subsurface

1076
00:40:54.750 --> 00:40:55.190
ocean.

1077
00:40:56.000 --> 00:40:58.310
Jonti Horner: Yes. And it's probably of all the moons where

1078
00:40:58.310 --> 00:41:01.110
subsurface oceans have been suspected or

1079
00:41:01.110 --> 00:41:03.990
detected, it is the smallest of them and

1080
00:41:03.990 --> 00:41:06.270
it's probably the most surprising of the lot.

1081
00:41:07.230 --> 00:41:10.190
The evidence for this has built up over

1082
00:41:10.160 --> 00:41:12.100
a bit more than a decade and comes from the

1083
00:41:12.100 --> 00:41:14.140
Cassini mission that Spent all that time

1084
00:41:14.140 --> 00:41:16.980
orbiting Saturn making wonderful discoveries,

1085
00:41:16.980 --> 00:41:19.540
most famously, of course, being the geysers

1086
00:41:19.540 --> 00:41:21.460
of liquid water erupting from the south pole

1087
00:41:21.460 --> 00:41:23.640
of another of the small icy moons, Enceladus,

1088
00:41:24.030 --> 00:41:26.110
which was a shock because Enceladus is so

1089
00:41:26.110 --> 00:41:28.030
small that it should be frozen to the core.

1090
00:41:28.190 --> 00:41:29.950
So it's a bit of a surprise there's liquid

1091
00:41:29.950 --> 00:41:32.830
water there. Mimas is even smaller.

1092
00:41:32.830 --> 00:41:35.390
It's the smallest object in the solar system

1093
00:41:36.350 --> 00:41:39.030
that is spherical because its gravity has

1094
00:41:39.030 --> 00:41:40.790
overcome the strength of the material it's

1095
00:41:40.790 --> 00:41:43.470
made from. And when you look at the

1096
00:41:43.550 --> 00:41:45.510
calculations people have made at what the

1097
00:41:45.510 --> 00:41:48.470
minimum size something would have to be to be

1098
00:41:48.470 --> 00:41:51.130
in hydrostatic equilibrium to be an object

1099
00:41:51.130 --> 00:41:53.010
where gravity overcomes the strength. Mimas

1100
00:41:53.010 --> 00:41:55.010
is actually a little bit smaller than that,

1101
00:41:55.490 --> 00:41:58.450
which is interesting. It's a real edge case.

1102
00:41:59.250 --> 00:42:01.890
And, you know, the fact that it is spherical

1103
00:42:01.890 --> 00:42:03.650
like it is would suggest that at some point

1104
00:42:03.650 --> 00:42:05.330
it has not been that strong in the past. So

1105
00:42:05.330 --> 00:42:07.930
it was probably fairly liquid early on in its

1106
00:42:07.930 --> 00:42:10.930
formation. But any ocean it had when it was

1107
00:42:10.930 --> 00:42:13.490
born should have frozen out

1108
00:42:13.650 --> 00:42:16.180
long, long, long, long, long ago. And, that's

1109
00:42:16.180 --> 00:42:18.300
kind of borne out when you see the photos

1110
00:42:18.300 --> 00:42:20.100
that are taken of Mimas. It doesn't look like

1111
00:42:20.100 --> 00:42:22.440
Enceladus. It doesn't look like AR were

1112
00:42:22.440 --> 00:42:24.240
talking about last week. It doesn't look like

1113
00:42:24.240 --> 00:42:26.680
Europa. They're all places that have

1114
00:42:26.680 --> 00:42:29.200
obviously been resurfaced, that have flat

1115
00:42:29.200 --> 00:42:31.560
areas with cracks that look like ice that has

1116
00:42:31.560 --> 00:42:33.520
been broken by plate tectonics. Because it's

1117
00:42:33.520 --> 00:42:36.200
floating on an ocean, Mimas just looks like

1118
00:42:36.200 --> 00:42:37.680
another cratered ice ball.

1119
00:42:37.840 --> 00:42:38.279
Andrew Dunkley: Yes.

1120
00:42:38.279 --> 00:42:40.120
Jonti Horner: So there's a few oddities that have built up.

1121
00:42:40.120 --> 00:42:41.760
One of them is that, enormous crater,

1122
00:42:41.760 --> 00:42:44.760
Herschel. Now, Herschel, as a crater, is

1123
00:42:44.760 --> 00:42:46.840
almost big enough that the impactor could

1124
00:42:46.840 --> 00:42:48.970
have shattered me. And if it had been only

1125
00:42:48.970 --> 00:42:50.450
slightly larger, Mimas would have been

1126
00:42:50.450 --> 00:42:53.330
destroyed. So it's right at the limit of

1127
00:42:53.330 --> 00:42:56.010
how big a crater can be before things get

1128
00:42:56.010 --> 00:42:58.930
seriously bad. But a lot of calculations

1129
00:42:58.930 --> 00:43:01.570
have shown that if the Herschel crater had

1130
00:43:01.570 --> 00:43:04.450
formed when the Moon was frozen solid to its

1131
00:43:04.450 --> 00:43:07.130
core, it shouldn't have a central peak.

1132
00:43:07.850 --> 00:43:10.290
But it has a central peak. Now, that suggests

1133
00:43:10.290 --> 00:43:13.010
that Mimas was a bit slushy. But if you do

1134
00:43:13.010 --> 00:43:15.370
the calculations and assume Mimas had a very,

1135
00:43:15.370 --> 00:43:18.320
very well developed ocean, that

1136
00:43:18.320 --> 00:43:19.760
crater wouldn't look like it did either,

1137
00:43:19.760 --> 00:43:21.680
because it would have dug down into the ocean

1138
00:43:21.680 --> 00:43:24.120
and splashed liquid water everywhere. So

1139
00:43:24.120 --> 00:43:25.680
there are suggestions that the Herschel

1140
00:43:25.680 --> 00:43:28.560
crater formed when Mimas was slushy rather

1141
00:43:28.560 --> 00:43:30.680
than ocean, when it was fluid enough to get

1142
00:43:30.680 --> 00:43:33.440
this central peak form, but not so fluid that

1143
00:43:33.440 --> 00:43:35.200
an ocean was breached. And with the size of

1144
00:43:35.200 --> 00:43:36.640
that M impact, it would have breached one if

1145
00:43:36.640 --> 00:43:39.240
one was there. Now I've seen some suggestions

1146
00:43:39.240 --> 00:43:41.080
from that saying that Herschel must therefore

1147
00:43:41.080 --> 00:43:44.050
be a young crater because it's tied

1148
00:43:44.050 --> 00:43:45.890
to this young ocean that is thought to be

1149
00:43:45.890 --> 00:43:48.490
there on Mimas. Now that's one of the

1150
00:43:48.490 --> 00:43:50.050
suggestions. I'm not necessarily sure that's

1151
00:43:50.050 --> 00:43:51.570
the case. It may be that Herschel may be

1152
00:43:51.570 --> 00:43:53.250
older than there was an ocean in the past.

1153
00:43:53.730 --> 00:43:56.650
That's still to be sorted. But aside from

1154
00:43:56.650 --> 00:43:58.690
that, there's been a lot of the data from

1155
00:43:58.690 --> 00:44:01.410
Cassini linked to how Mimas is

1156
00:44:01.410 --> 00:44:04.050
rotating and wobbling, suggested that

1157
00:44:04.130 --> 00:44:07.050
it couldn't be solid to the core unless the

1158
00:44:07.050 --> 00:44:09.170
core was not in her static equilibrium. The

1159
00:44:09.170 --> 00:44:11.660
core was elongated and pancake shaped. and

1160
00:44:11.660 --> 00:44:13.460
that just doesn't make sense. And as they got

1161
00:44:13.460 --> 00:44:14.780
more and more data, more and more

1162
00:44:14.780 --> 00:44:17.620
observations, that just doesn't work. And

1163
00:44:17.620 --> 00:44:19.540
so from the rotation and the wobble of this

1164
00:44:19.540 --> 00:44:22.140
moon, it suggests that as much as

1165
00:44:22.140 --> 00:44:24.900
50% of its volume is liquid water.

1166
00:44:25.140 --> 00:44:27.580
Wow. Which is an enormous subsurface ocean.

1167
00:44:27.580 --> 00:44:30.340
That's an absolutely incredible ocean. But

1168
00:44:30.340 --> 00:44:32.500
because of the thermodynamics of it, that

1169
00:44:32.500 --> 00:44:34.980
ocean can't be old because if it was old, it

1170
00:44:34.980 --> 00:44:37.950
would have frozen out already. Now, part of

1171
00:44:37.950 --> 00:44:39.590
the supporting evidence for this is that the

1172
00:44:39.590 --> 00:44:42.030
orbit of Mimas around Saturn is not perfectly

1173
00:44:42.030 --> 00:44:44.790
circular. It's actually a little bit more

1174
00:44:44.790 --> 00:44:46.430
eccentric than the orbit of the Earth around

1175
00:44:46.430 --> 00:44:49.030
the Sun. That is not a

1176
00:44:49.030 --> 00:44:51.270
situation that's tenable long term. The orbit

1177
00:44:51.270 --> 00:44:53.990
should be circularized by tidal

1178
00:44:53.990 --> 00:44:56.590
effects with Saturn. And so the suggestion

1179
00:44:56.590 --> 00:44:58.990
seems to be that at some point, probably in

1180
00:44:58.990 --> 00:45:01.710
the last 15 million years, something

1181
00:45:01.790 --> 00:45:04.190
happened to stir, Mimas's orbit upper Mechi

1182
00:45:04.660 --> 00:45:06.860
more eccentric, to actually make it a bit

1183
00:45:06.860 --> 00:45:09.420
more elongated. That increased

1184
00:45:09.420 --> 00:45:11.780
eccentricity means that Mimas now experience

1185
00:45:11.860 --> 00:45:13.780
a significant tidal heating

1186
00:45:14.500 --> 00:45:16.980
from being squashed and squeezed effectively

1187
00:45:18.020 --> 00:45:20.100
by the gravity of Saturn and also by the

1188
00:45:20.100 --> 00:45:21.900
other moons. It's in mean motion resonance

1189
00:45:21.900 --> 00:45:23.860
with a couple of the other saturnian moons.

1190
00:45:24.340 --> 00:45:25.780
And all of that means that you're going to

1191
00:45:25.780 --> 00:45:27.820
get a significant amount of heat dumped into

1192
00:45:27.820 --> 00:45:30.740
the interior of Mimas, melting that interior

1193
00:45:30.740 --> 00:45:33.630
and creating this ocean. And the argument

1194
00:45:33.630 --> 00:45:35.510
for the fact that the surface is not yet

1195
00:45:35.510 --> 00:45:38.470
smooth and resurfaced is that a, that

1196
00:45:38.470 --> 00:45:41.190
ocean is young and it's a still developing

1197
00:45:41.190 --> 00:45:44.150
situation. But also that the crust of

1198
00:45:44.150 --> 00:45:46.950
Mimas is 20 or 30 kilometers thick and

1199
00:45:46.950 --> 00:45:48.670
that's thick enough that it hasn't yet

1200
00:45:48.670 --> 00:45:51.310
responded to the liquid underneath

1201
00:45:51.710 --> 00:45:53.910
and so you've almost got this hidden ocean in

1202
00:45:53.910 --> 00:45:56.710
a place you wouldn't expect, but where all

1203
00:45:56.710 --> 00:45:59.540
our observations, all our data is suggesting

1204
00:45:59.540 --> 00:46:01.540
that the only explanation that works for all

1205
00:46:01.540 --> 00:46:03.340
of the different things we've observed for it

1206
00:46:03.660 --> 00:46:05.780
is that this is yet another of this growing

1207
00:46:05.780 --> 00:46:08.500
catalog of places where there's a huge volume

1208
00:46:08.500 --> 00:46:10.580
of liquid water buried beneath an icy

1209
00:46:10.580 --> 00:46:12.900
surface. It's absolutely breathtaking work

1210
00:46:12.900 --> 00:46:14.900
and it's a really good example of the

1211
00:46:14.900 --> 00:46:17.780
iterative nature of science because it's not

1212
00:46:17.780 --> 00:46:19.580
like this is a new discovery this week.

1213
00:46:20.060 --> 00:46:21.740
There've been whispers about this for years

1214
00:46:21.740 --> 00:46:23.900
and papers published about it for years and

1215
00:46:24.630 --> 00:46:26.910
alternative hypotheses proposed and

1216
00:46:26.910 --> 00:46:29.910
disproved and all the rest of it. And all

1217
00:46:29.910 --> 00:46:31.590
the way through we're getting more and more

1218
00:46:31.590 --> 00:46:33.710
certain that this ocean's there. We're

1219
00:46:33.710 --> 00:46:36.670
learning more about the history. And I guess

1220
00:46:36.670 --> 00:46:38.120
again, not only are we learning that liquid

1221
00:46:38.120 --> 00:46:39.799
water is more common than the solar system,

1222
00:46:39.799 --> 00:46:41.840
but we're getting reminded once again that

1223
00:46:42.000 --> 00:46:44.320
the solar system's a very dynamic place. And

1224
00:46:44.320 --> 00:46:47.000
it's not like everything of interest happened

1225
00:46:47.000 --> 00:46:48.720
four and a half thousand million years ago.

1226
00:46:48.720 --> 00:46:50.520
And now we're in the kind of mop up phase

1227
00:46:50.520 --> 00:46:52.830
where nothing interesting happens. There's

1228
00:46:52.830 --> 00:46:55.180
still a lot going on. And the solar system's

1229
00:46:55.180 --> 00:46:57.580
dynamic in a way that if we were around when

1230
00:46:57.580 --> 00:47:00.020
the dinosaurs walked the Earth, it would have

1231
00:47:00.020 --> 00:47:01.540
looked like a very different place than the

1232
00:47:01.540 --> 00:47:03.380
place we see today. It's that changeable.

1233
00:47:03.620 --> 00:47:05.940
Andrew Dunkley: Yeah, absolutely. Yeah. And

1234
00:47:06.430 --> 00:47:07.550
Mimas is also,

1235
00:47:09.510 --> 00:47:11.190
if indeed it is another,

1236
00:47:13.330 --> 00:47:15.490
water moon, let's say ice moon, whatever you

1237
00:47:15.490 --> 00:47:17.920
want to call it, it's starting to show that

1238
00:47:17.920 --> 00:47:20.390
it's probably more normal than we ever

1239
00:47:20.390 --> 00:47:23.310
thought. You've got so many others that are

1240
00:47:23.310 --> 00:47:26.030
starting to be found. obviously

1241
00:47:26.030 --> 00:47:28.350
Europa Enceladus would be the top two, but

1242
00:47:28.900 --> 00:47:30.360
Ganymede's now in there.

1243
00:47:32.630 --> 00:47:35.030
Andrew Dunkley: Most of the dwarf moons,

1244
00:47:35.490 --> 00:47:37.450
or dwarf planets in the outer solar system

1245
00:47:37.450 --> 00:47:40.250
are starting to show these signs. So

1246
00:47:40.730 --> 00:47:43.650
it could be quite normal here. And

1247
00:47:43.650 --> 00:47:46.350
as we've already discussed, you know, there

1248
00:47:46.350 --> 00:47:47.990
was a time where we weren't sure whether or

1249
00:47:47.990 --> 00:47:50.630
not there were other planets in other solar

1250
00:47:50.630 --> 00:47:53.510
systems in the universe. Well, it's

1251
00:47:53.510 --> 00:47:55.630
probably going to be discovered that there

1252
00:47:55.630 --> 00:47:58.370
are probably a lot more ice moons out there

1253
00:47:58.370 --> 00:48:00.810
than we could possibly imagine. So.

1254
00:48:00.890 --> 00:48:02.690
Jonti Horner: Absolutely. And the other interesting thing

1255
00:48:02.690 --> 00:48:04.370
about this to me is it's not just suggesting

1256
00:48:04.370 --> 00:48:06.330
that you get oceans and the oceans go away.

1257
00:48:06.810 --> 00:48:09.290
It's suggesting you can get episodic oceans

1258
00:48:10.170 --> 00:48:12.330
because m. If this Ocean is only 10 or 15

1259
00:48:12.330 --> 00:48:15.080
million years old. We've had a lot of 10 and

1260
00:48:15.080 --> 00:48:17.360
15 million year old windows

1261
00:48:17.840 --> 00:48:20.240
in four and a half thousand million years of

1262
00:48:20.240 --> 00:48:23.150
time. And, what is the likelihood that we

1263
00:48:23.150 --> 00:48:24.830
just happen to be in the only one of those

1264
00:48:24.830 --> 00:48:26.990
windows where you've got two temporary oceans

1265
00:48:26.990 --> 00:48:29.790
at the same time, Where Enceladus and

1266
00:48:29.790 --> 00:48:32.750
Mimas have temporary transient oceans that

1267
00:48:32.750 --> 00:48:35.270
have only formed in recent times. And for

1268
00:48:35.270 --> 00:48:37.150
both of them, the logic is the same. They're

1269
00:48:37.150 --> 00:48:38.590
too small to have had this ocean since

1270
00:48:38.590 --> 00:48:39.840
they're formed. It's got to be a recent

1271
00:48:40.230 --> 00:48:42.470
thing. What is the likelihood that we catch

1272
00:48:42.470 --> 00:48:44.230
two of them going off at once, just by

1273
00:48:44.230 --> 00:48:46.070
random, when there have never been any

1274
00:48:46.070 --> 00:48:48.190
others? So that's suggesting that these

1275
00:48:48.190 --> 00:48:50.190
subsurface oceans on the smaller moons come

1276
00:48:50.190 --> 00:48:52.950
and go and come again, which means

1277
00:48:52.950 --> 00:48:55.150
that again, from the point of view of life

1278
00:48:55.150 --> 00:48:57.830
elsewhere, life that can

1279
00:48:57.830 --> 00:49:00.430
survive the long freeze is ready to take over

1280
00:49:00.430 --> 00:49:03.070
during the short summer. And we see that on

1281
00:49:03.070 --> 00:49:05.730
Earth. It's a really interesting thing that

1282
00:49:06.040 --> 00:49:08.680
if this is a temporary transient ocean now,

1283
00:49:09.080 --> 00:49:11.200
it's possibly been there multiple times in

1284
00:49:11.200 --> 00:49:13.160
the past. And that's why I

1285
00:49:13.800 --> 00:49:15.720
suspect that the Herschel Crater may not have

1286
00:49:15.720 --> 00:49:18.640
formed with the latest recent ocean. But

1287
00:49:18.640 --> 00:49:20.960
maybe it's a previous episode of it. We will

1288
00:49:20.960 --> 00:49:22.720
only know when we get more studies. And of

1289
00:49:22.720 --> 00:49:24.640
course, it's a really good reason to go back

1290
00:49:24.640 --> 00:49:25.720
to Saturn to find out.

1291
00:49:25.800 --> 00:49:28.270
Andrew Dunkley: Absolutely true. Yes, indeed. All right, if

1292
00:49:28.270 --> 00:49:30.190
you want to read about that story and the,

1293
00:49:30.200 --> 00:49:33.170
previous story, about exoplanets, you

1294
00:49:33.170 --> 00:49:35.450
can go to space.com

1295
00:49:36.330 --> 00:49:38.970
and we are done. Jonti, thank you so much.

1296
00:49:39.610 --> 00:49:41.330
Jonti Horner: It's a pleasure. It's a lot to talk about.

1297
00:49:41.330 --> 00:49:42.250
It's always good fun.

1298
00:49:42.330 --> 00:49:44.190
Andrew Dunkley: It is great fun. Good, to see you. that's

1299
00:49:44.190 --> 00:49:46.230
Jonti Horner, professor of Astrophysics at

1300
00:49:46.230 --> 00:49:48.910
the University of Southern Queensland. And

1301
00:49:48.910 --> 00:49:50.630
don't forget to visit our website while

1302
00:49:50.630 --> 00:49:53.370
you're online and check us out. you can do

1303
00:49:53.370 --> 00:49:56.130
that@spacenutspodcast.com or spacenuts.

1304
00:49:57.560 --> 00:49:59.560
And if you'd like to become a supporter of

1305
00:49:59.560 --> 00:50:02.040
Space Nuts, it's really simple. Just, click

1306
00:50:02.040 --> 00:50:04.370
on the supporter tab. you can become a

1307
00:50:04.370 --> 00:50:06.410
patron, or if you'd prefer to use another

1308
00:50:06.410 --> 00:50:08.490
platform, you can do that through Supercast.

1309
00:50:08.490 --> 00:50:09.970
And there are plenty of different options

1310
00:50:09.970 --> 00:50:12.210
there, but as I always say, it's not

1311
00:50:12.210 --> 00:50:15.140
mandatory. if you only want to

1312
00:50:15.140 --> 00:50:17.500
buy us a cup of coffee, that's fine as well.

1313
00:50:17.670 --> 00:50:20.110
in fact, some people have literally sent us

1314
00:50:20.190 --> 00:50:22.190
coffee vouchers over the years.

1315
00:50:22.960 --> 00:50:24.710
check it all out on our, space,

1316
00:50:24.710 --> 00:50:27.640
nutspodcast.com, website.

1317
00:50:28.050 --> 00:50:30.970
and I would say thanks to Huw in the studio.

1318
00:50:30.970 --> 00:50:33.820
But he's out counting, exoplanets. And he got

1319
00:50:33.820 --> 00:50:36.259
to 10, and you can't count any higher.

1320
00:50:36.660 --> 00:50:38.260
And from me, Andrew Dunkley, thanks for your

1321
00:50:38.260 --> 00:50:39.660
company. We'll see you on the next episode of

1322
00:50:39.660 --> 00:50:41.620
Space Nuts real soon. Bye. Bye.