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Jonti Horner: Hi there.

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Andrew Dunkley: Thanks for joining us yet again. This is

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Space Nuts. My name is Andrew Dunkley. Great

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to have your company one more time. Well,

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hopefully it's more than one more time, but

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on this occasion, uh, now with Fred Watson

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away, uh, we are doing a series of

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little specials and today the focus

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will be on exoplanets.

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We've known about them since the early 90s

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and since then we have found

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thousands of them. But what is there to

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know? I mean, we've got our own planets.

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Surely that just means everything else around

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the galaxy is the same. That's

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probably not true. And we're going to talk

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about all of it today on this, uh, episode of

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space nuts. 15 seconds. Guidance is

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internal. 10, 9,

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ignition sequence.

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Jonti Horner: Star. Space nuts. 5, 4, 3, 2.

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Andrew Dunkley: 1. 2, 3, 4, 5, 5, 4, 3,

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2, 1. Space nuts. Astronauts report

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at and with us while

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Fred Watson is away is Jonty Horner,

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professor of astrophysics at the University

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of Southern Queensland. Hi, Jonty.

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Jonti Horner: Good afternoon. How are you going?

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Andrew Dunkley: I am quite well. And you?

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Jonti Horner: I can't complain. I'm enjoying us having a

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public holiday today, which is great. I mean,

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I'm still off anyway, so it doesn't really

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matter, but it means I'm taking one day's

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less of sick leave, I guess. Uh, well, it's

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all good.

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Andrew Dunkley: I'm retired, so public holidays mean nothing

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to me now. I

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used to so look forward to having a few days

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off or, you know, an extra long weekend if

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they combined the two in April because we

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get, uh, east sometimes, get Easter and Anzac

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Day in April. And if, um, you jam them

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together, you get a nice free holiday. But,

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uh, it doesn't mean squat to me anymore.

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Jonti Horner: I keep finding it bizarre. At least in

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Toowoomba. I'm sure this is reproduced

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everywhere. If the shop shut for one day, the

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day after is absolutely feral. So

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last week we had Anzac Day, which tells you

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how long ago these were recorded, by the way.

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Um, but yeah, last week we had Anzac Day. And

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obviously, Franz, act quite rightly, the

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shops, the supermarkets and everything are

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shut. It's one of the biggest holidays in

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Australia of the lot of them. But we, we tend

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to do our shopping on a Sunday anyway, so it

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didn't really matter. Went to the shops on

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the Sunday and it was almost people fighting

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in the aisles because heaven forfend that one

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day you don't, you know, you don't get food

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for one day and the shops start running empty

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of bread. And it's like people buy more when

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they've had one day without the Shops being

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open, very, very strange phenomenon.

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Andrew Dunkley: They panic by and there's no toilet paper on

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the shelves. Is also.

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Jonti Horner: Well, the best thing about that. That led us

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to subscribing to who Gives a Crap which

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panel started online.

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Um, and they've been brilliant. We've

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recommended them to everyone because it works

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out cheaper than getting it from the

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supermarket and they're better quality. I

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mean it's, it feels like very much a no, uh,

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brainer. And we'd never have come across them

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if it wasn't for Covid and the

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incredibly smart people of Toowoomba going,

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oh my God, Covid's happening. We're going to

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run out of toilet paper. Of all the things

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for the shop to run out of, happened

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everywhere. Why toilet paper? Uh,

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I mean Covid affect my

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memory was that Covid was a, was something

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that made things come out of your head, not

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things that came out anywhere else. It's not

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like there will be an expectation it would

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make you use more. No, bread was

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fine, eggs were fine, perishables were fine.

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But toilet paper, I don't understand.

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Andrew Dunkley: I never, I never got it either. But uh, uh,

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our shelves were devoid of the stuff.

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We better get down to business.

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We're talking exoplanets today.

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And I did a little bit of research. Uh, the

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first exoplanets were confirmed in

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1992. In fact, they suspected they existed

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before that, but they couldn't prove it. But

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1992, uh, they

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found two planets that were later named

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Poltergeist and um, Phobitor

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Phoebe. Uh, so they were

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officially the first two exoplanets. And then

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the first one that was

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orbiting a sun like star was found in

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1995. That was

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um, 51 Pegasi B.

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Jonti Horner: Yes.

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Andrew Dunkley: So, uh, those were the first few. And of

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course now we've reached a point where

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as at 30

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April 2026,

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6278 confirmed

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exoplanets with another 8000

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waiting to be, um, officially

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catalogued. I suppose. So we've

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found a lot of them. And the other thing

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we've been discovering about, um, finding

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these things is how very different

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a lot of solar systems are and how very

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different some of the planets are. Ah,

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what we always thought was basically the

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standard for solar systems,

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which was ours. Doesn't appear to be very

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standard at all.

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Jonti Horner: No, it's an incredible time to live through.

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I think the way I always budge this is we've

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lived through one of the great scientific

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revolutions almost without noticing it.

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And I think it sheds A light into how people

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would have reacted in previous scientific

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revolutions, which is that when it's

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happening in your lifetime, it just happens.

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So we look back and think that was such a

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fundamental change. And at the time it was

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just Tuesday, you know. And

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yes, it's like that with exoplanets. I

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grew up in a world where one of the big

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science questions was, is a solar system

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unique? Are there planets around other stars?

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Or are we alone? And there were good

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reasons for some people to suspect that we

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might be the only planetary system in the

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universe. There were kind of, at that time,

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two broadly competing models of planet

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formation that could both explain the solar

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system as we see it to a fair degree. And one

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was what's almost described as the

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Laplace model, the disc model, which is now

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what we favour, that has developed a lot

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since then. But the other was this idea that

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you had a close encounter between the sun and

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a protostar. Ah, that was close enough that

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the two stars almost collided and a tongue of

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material was pulled out of the sun, which

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went on to condense from the planets. And

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that was championed by people like Martin

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Wolfson of York University, among others.

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At, uh, this time we're talking in the late

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80s, it was kind of widely held that, uh,

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Wolfson's suggestion had problems.

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It was probably not the right solution, but

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it potentially could be. We'd found a few

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debris discs, debris around stars, a bit like

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the asteroid belt around the sun, but much

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more massive in the early 80s. And that

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was kind of hinting that planets could be

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common, that the disc model could be the one.

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But at the time I was growing up, and at the

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time, going into the early 90s, you have

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these two models of planet formation that

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predicted vastly different outcomes. If

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the disc model was right, planets would be

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ubiquitous, planets would just be the

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leftovers from star formation, and

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effectively every star would have planets or

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close to it. If the encounter

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model was right, then planetary systems would

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be exceedingly rare, because to get two stars

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to come sufficiently close together at just

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the right speed for that to draw a tongue out

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and form a planetary system is vanishingly

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unlikely. So that was arguing that we were

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effectively the result of a freak encounter.

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And if that prediction was right, then if

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that method was right, sorry, it would

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predict that planetary systems were

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exceedingly rare and that we wouldn't find

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them. So going into the 90s, you had these

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two theories that could both explain in broad

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brushstrokes, what we see at home, but that

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predicted very, very, very different

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outcomes. And as I say, The Wolfson idea was

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already losing a bit of seam. But in the time

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since we found that planets are under the

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stars and, um, that they are ubiquitous,

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basically every star you see in the night

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sky, no matter how complex system, no

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matter what's that, there are going to be

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planetary objects around it, pretty much all

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cases. And that's a death knell, of course,

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for the Wolfson model of freak planetary

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system formation and its support for the

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model we now know and love, which has been

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refined over the years because of all the

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oddities we found. Now, it's really

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interesting, storey, but it goes way back

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before that. We've got a long history of

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the things that led to finding the first

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planets. What we take it a bit for granted

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now. We're finding so many planets and I have

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the good fortune of getting to be involved

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peripherally in some of the discoveries. I'

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have the very entertaining job of killing

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some planetary systems. So it should be said

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that the number you gave at the start can go

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down as well as going up. Some of

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the planets that get confirmed later on get

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redacted, get killed. And I've probably,

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certainly as lead author, I've never led a

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planet discovery, but I've been involved with

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them. But I've led a number of research

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projects that killed planets that other

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people claimed. So I've probably been net

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responsible as an individual for a negative

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number of planet discoveries that can happen.

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But it's really important that we do that

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kind of work. I've always been really

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passionate about that because all of the

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things that we do to talk about how common

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planets are, to look into how they form and,

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um, further down the line to try and find

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planets that could be like the Earth and to

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try and look for life on them. All of that is

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based on the catalogue of the known. What do

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we know? What's the variety? And so if you've

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got planets that are in that catalogue that

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don't exist, they're polluting that catalogue

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and confusing and obscuring the truth. So

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it's really important to not just accept that

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when a planet is claimed and marked as

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confirmed, that's the end of the storey. But

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we need to follow it up and say, does it make

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sense? Could there be something else going

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on? And in those cases we do learn more about

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it. So it's a fascinating field. I'm really

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fortunate to have gone from being a kid who

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wondered to an adult who gets to be involved

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in the process. That's incredibly

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wonderful for me, but it's a fabulous Storey

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we have lived through a great scientific

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revolution in many ways. One that's as big as

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the acceptance of continental drift or uh,

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the origin of species and Darwin or general

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relativity and Einstein. It's one of those

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revolutions. And when you talk about the

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other ones, you think about how epochal

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and incredible and how they change the world

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and we've just lived through one. Um, it's

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amazing.

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Andrew Dunkley: Yeah, it's incredible. And, and

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will it never end? I mean the thought of

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looking up into the night sky and seeing

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billions of stars and knowing that there

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are probably multi, billions of planets is

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just, it's mind blowing.

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Jonti Horner: And the rest, I mean to me it's a numbers

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game and we talk about this when we talk

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about life elsewhere, but the numbers get

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ridiculous really, really quickly. Now we've

269
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been heavily biassing what we found to

270
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finding planets closer to their stars than

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the Earth is to the sun. The overwhelming

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majority of planets. We found a very close

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end, but there will be planets further out as

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well. You're not going to have a situation

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very often where you've got a few planets

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near the star and nothing further out. So a

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lot of the very tentative estimates you get

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of the number of planets in the universe say,

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well, imagine there's just one planet per I.

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Based on what we found so far, I think it's

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fairer to say there are probably nearer to 10

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planets per star. And depending on whether

283
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Jared Isaacson, the guy who's taken

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over NASA who is not an astronomer, gets his

285
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way and restores Pluto. If he restores

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Pluto, then you have to argue that Ceres,

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Makemake, Haumea, Eris, all these other

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things are planets in the solar system. You

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could have 20 planets in the solar system. So

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let's assume 10 per star. You

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know whether Pluto is arisen. Leave that for

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aside. I have strong opinions on that. Other

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opinions are available. They're wrong, but

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they're available. As Matt come out always

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says, um, ignoring

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that though, if you assume 10 planets per

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star, because it's going to be nearer to 10

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than when an astronomer's working factors of

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10. In our galaxy alone, um, we have

300
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somewhere around 400,000 million

301
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stars. Now that number also is only accurate

302
00:11:39.440 --> 00:11:41.480
to a factor of 2 or 3. So it could be 200, it

303
00:11:41.480 --> 00:11:44.120
could be 600, but call it 400,000

304
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million stars means 10 planets per star.

305
00:11:46.980 --> 00:11:49.820
You'd have 4 trillion planets in our

306
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galaxy, ignoring the free floating ones that

307
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don't have a star to call their own. 4

308
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trillion planets in our galaxy.

309
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There are more galaxies in the observable

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universe than there are stars in our galaxy

311
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by orders of magnitude. Which means you start

312
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getting to the point which, in the observable

313
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universe alone, um, ignoring the part of the

314
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universe that we can't see because that's

315
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utterly unquantifiable, but just in the part

316
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we can see, you'll have planets numbered in

317
00:12:14.100 --> 00:12:16.100
the sextillions of septillions.

318
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So a trillion is 10 to the 12, a trillion is

319
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a thousand billion, a quadrillion is 10 to

320
00:12:22.720 --> 00:12:25.400
the 15, which is a thousand trillion, and so

321
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on. So these numbers are utterly,

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astonishingly, overwhelmingly, mind boggling.

323
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And that's where I come to with this thing,

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that if we're the only place with life in the

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universe, then there's something very unusual

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going on.

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Andrew Dunkley: Absolutely, yeah. Um, and

328
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it was the movie Contact where they said, uh,

329
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space is really big. So if it's just stuff,

330
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just us, it seems like an awful waste of

331
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space.

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Jonti Horner: It is.

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Andrew Dunkley: I always like that line.

334
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Jonti Horner: Yeah, well, the question of life elsewhere is

335
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one that really polarises people. I mean,

336
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everybody's interested to know the answer.

337
00:12:58.410 --> 00:13:00.570
Arthur C Clarke said something along the

338
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lines of, there are two possibilities. Either

339
00:13:02.450 --> 00:13:04.490
we're alone in the universe or we are not.

340
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Both equally terrifying. Um,

341
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a lot of people. Stephen Hawking was very

342
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adamantly, we shouldn't try and contact

343
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aliens because they will kill us in the face.

344
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I don't tend to agree with them, but

345
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it is one of those discussions that really

346
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fires people up, gets people energised. And

347
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for me, it would be actually far more

348
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terrifying to know we're alone in the

349
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universe, because that means life is such an

350
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impossible fluke that given planets

351
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numbering in the sextillions or septillions,

352
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in the known universe, we're the only one

353
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with life. Which means that only one planet

354
00:13:38.240 --> 00:13:41.040
in 10 followed by 20 zeros or more

355
00:13:41.040 --> 00:13:43.960
gets life on it. And that seems infeasible to

356
00:13:43.960 --> 00:13:46.780
me, but m. We won't really know until

357
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we move forward and we actually proceed with

358
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the search for life elsewhere. And as I've

359
00:13:51.940 --> 00:13:54.740
said in a previous episode, absence of

360
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evidence is not evidence of absence. So if we

361
00:13:56.780 --> 00:13:58.900
find life, then we'll know we're not alone.

362
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We'll know that life's common in the

363
00:14:00.060 --> 00:14:02.940
universe. The longer it takes us to find life

364
00:14:03.660 --> 00:14:05.460
doesn't mean that there is nothing to be

365
00:14:05.460 --> 00:14:08.140
found, it just means that life is scarcer,

366
00:14:08.460 --> 00:14:10.860
basically. So the longer we take to find it,

367
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the better we'll get at doing it. The further

368
00:14:12.460 --> 00:14:14.340
we'll be able to look, the more planets we

369
00:14:14.340 --> 00:14:16.460
can Sample. And that will then give us a

370
00:14:16.460 --> 00:14:18.050
handle for the commonality of life.

371
00:14:18.120 --> 00:14:18.360
Andrew Dunkley: Life.

372
00:14:18.680 --> 00:14:20.720
Jonti Horner: So we find life in our lifetime. All well and

373
00:14:20.720 --> 00:14:22.440
good. If we're still looking in a thousand

374
00:14:22.440 --> 00:14:25.160
years. I'd be gobsmacked, but that just tells

375
00:14:25.160 --> 00:14:26.760
you life is a lot rarer than we thought.

376
00:14:27.720 --> 00:14:30.120
Andrew Dunkley: Indeed. And we will talk about that more in

377
00:14:30.440 --> 00:14:32.680
another, uh, special episode when we do part

378
00:14:32.680 --> 00:14:35.400
two of Astrobiology. Uh, we kind

379
00:14:35.400 --> 00:14:38.360
of had, we didn't have enough time to

380
00:14:38.360 --> 00:14:39.960
talk about it last time, so we're going to do

381
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a part two.

382
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Jonti Horner: But uh, I can talk too much.

383
00:14:43.160 --> 00:14:45.990
Andrew Dunkley: It's also an area that um, uh, makes

384
00:14:45.990 --> 00:14:48.710
your brain hurt. So we, we decided to,

385
00:14:49.190 --> 00:14:51.430
you know, give it a miss this week and go

386
00:14:51.430 --> 00:14:52.710
back, uh, next week.

387
00:14:53.490 --> 00:14:56.430
Um, so where do you want to go with this?

388
00:14:56.430 --> 00:14:58.710
Like, um, everyone knows there's

389
00:14:58.710 --> 00:15:01.229
exoplanets. Everyone knows there are, um, you

390
00:15:01.229 --> 00:15:03.910
know, powder puff planets. And um,

391
00:15:04.630 --> 00:15:06.870
they've actually got names for them. I've got

392
00:15:07.270 --> 00:15:10.110
named, um. So you know, we can

393
00:15:10.110 --> 00:15:13.110
officially say that uh, as far as

394
00:15:13.110 --> 00:15:14.870
planets are concerned, we have

395
00:15:15.050 --> 00:15:17.690
um, specific types of

396
00:15:17.690 --> 00:15:19.970
planets in our solar system, and that is

397
00:15:20.130 --> 00:15:22.530
rocky planets, gas giants, and

398
00:15:23.570 --> 00:15:25.850
for want of a better term, ice giants. But in

399
00:15:25.850 --> 00:15:28.610
the exoplanet world there are

400
00:15:28.690 --> 00:15:31.430
several other types. Um,

401
00:15:31.430 --> 00:15:34.370
you've got um, uh, Neptunian,

402
00:15:34.530 --> 00:15:37.450
like planets, super Earths, uh, you've

403
00:15:37.450 --> 00:15:40.450
got uh, hot Jupiters, you've got super cold

404
00:15:40.450 --> 00:15:42.460
worlds, you've got pulsar planets, and

405
00:15:42.460 --> 00:15:44.830
there's even uh, uh,

406
00:15:44.900 --> 00:15:47.300
circumbinary planets where they're

407
00:15:47.540 --> 00:15:49.460
orbiting two stars. We don't have that

408
00:15:49.460 --> 00:15:51.940
thankfully. Uh, that could be messy,

409
00:15:51.940 --> 00:15:53.820
especially when it comes to trying to predict

410
00:15:53.820 --> 00:15:56.780
the tides. But um, it's, you know, there's so

411
00:15:56.780 --> 00:15:58.180
much more going on out there.

412
00:15:58.420 --> 00:16:00.620
Jonti Horner: There is, and it reflects something that's

413
00:16:00.620 --> 00:16:03.580
incredibly human. And it again goes back to

414
00:16:03.580 --> 00:16:06.340
that discussion about Pluto and many other

415
00:16:06.340 --> 00:16:08.980
things in human experience. What we find

416
00:16:09.710 --> 00:16:11.910
in every field of study, but you know, in

417
00:16:11.910 --> 00:16:14.190
astronomy in particular, is you have a

418
00:16:14.190 --> 00:16:16.030
continuum of things you've got from the very

419
00:16:16.030 --> 00:16:18.990
small to the very big with no obvious sharp

420
00:16:18.990 --> 00:16:21.550
gaps. You know, you'll find everything in

421
00:16:21.630 --> 00:16:23.590
planetary systems from stuff the size of a

422
00:16:23.590 --> 00:16:25.910
grain of dust to things more massive than the

423
00:16:25.910 --> 00:16:27.750
sun, depending on the planetary system you're

424
00:16:27.750 --> 00:16:30.630
in. What we tend to do as humans is we tend

425
00:16:30.630 --> 00:16:33.550
to break down that which we

426
00:16:33.550 --> 00:16:36.150
see as a continuum into manageable bite sized

427
00:16:36.150 --> 00:16:38.820
chunks by grouping like with like in order

428
00:16:38.820 --> 00:16:41.540
that we can then better study objects.

429
00:16:42.180 --> 00:16:44.300
And so for example, you'd say that the Earth

430
00:16:44.300 --> 00:16:46.300
is more like Venus or Mars than it is Like

431
00:16:46.300 --> 00:16:47.980
Jupiter. So you categorise them into

432
00:16:47.980 --> 00:16:50.740
different subgroups. For humans, we do this

433
00:16:50.820 --> 00:16:53.100
all around the world. You've got babies and

434
00:16:53.100 --> 00:16:55.940
toddlers, children, teenagers, adults,

435
00:16:55.940 --> 00:16:58.700
retirees, pensioners, and you set boundaries.

436
00:16:58.700 --> 00:17:00.660
And those boundaries don't always agree from

437
00:17:00.660 --> 00:17:02.180
country to country. You know, you remember

438
00:17:02.180 --> 00:17:04.460
the incredible day that you suddenly wake up

439
00:17:04.460 --> 00:17:06.220
and you're able to drive legally when the day

440
00:17:06.220 --> 00:17:08.340
before you weren't. And fundamentally you'

441
00:17:08.640 --> 00:17:11.440
changed as a human. You're one day older out

442
00:17:11.440 --> 00:17:14.120
of what, you know, several thousand days at

443
00:17:14.120 --> 00:17:16.840
that point, about 5,000, 6,000 days. But

444
00:17:16.840 --> 00:17:18.640
miraculously you've crossed this arbitrary

445
00:17:18.640 --> 00:17:21.120
threshold which we've put there to separate

446
00:17:21.280 --> 00:17:23.640
people who can't drive and people who can but

447
00:17:23.640 --> 00:17:25.120
maybe shouldn't. You know, that's kind of

448
00:17:25.120 --> 00:17:26.000
where the division is.

449
00:17:28.000 --> 00:17:29.960
We do this as humans all the time to

450
00:17:29.960 --> 00:17:32.000
categorise things. And that's kind of where

451
00:17:32.000 --> 00:17:34.440
Pluto fallafal and it's where all these

452
00:17:34.440 --> 00:17:36.120
groups of different types of planets come

453
00:17:36.120 --> 00:17:37.960
from. You've got hot Jupiters and warm

454
00:17:37.960 --> 00:17:40.830
Jupiters, super puff planets and all

455
00:17:40.830 --> 00:17:43.590
sorts of quirky things. And those terms

456
00:17:43.670 --> 00:17:46.630
are taking the broad spectrum of planets that

457
00:17:46.630 --> 00:17:48.990
we've got and trying to group apples with

458
00:17:48.990 --> 00:17:50.830
apples and oranges with oranges, things that

459
00:17:50.830 --> 00:17:53.830
are similar to one another. And the diversity

460
00:17:53.830 --> 00:17:55.630
just continues to ascend, as every time we

461
00:17:55.630 --> 00:17:57.150
think we've found the most extreme of

462
00:17:57.150 --> 00:17:58.950
whatever, we find something that's even more

463
00:17:58.950 --> 00:18:01.950
so. Like I said, we found planets who we

464
00:18:01.950 --> 00:18:04.070
can calculate their size by how much light of

465
00:18:04.070 --> 00:18:05.950
their star they block. We can calculate their

466
00:18:05.950 --> 00:18:07.990
mass by how much they pull their star around.

467
00:18:09.100 --> 00:18:11.220
We've got a subset of stars and planets where

468
00:18:11.220 --> 00:18:12.620
we can do both those, uh, things which lets

469
00:18:12.620 --> 00:18:15.180
us figure out the density. And from them we

470
00:18:15.180 --> 00:18:18.060
found planets that are less dense than cotton

471
00:18:18.060 --> 00:18:20.660
candy, which are the super puffs,

472
00:18:20.660 --> 00:18:22.580
fluffy ones, probably coming towards the end

473
00:18:22.580 --> 00:18:24.460
of their lives because they're so low density

474
00:18:24.699 --> 00:18:26.820
that they are probably being stripped away by

475
00:18:26.820 --> 00:18:28.660
their star stellar winds. We found planets

476
00:18:28.660 --> 00:18:31.180
that are effectively like comets with tails

477
00:18:31.180 --> 00:18:33.660
as their atmosphere stripped off. I mean, to

478
00:18:33.660 --> 00:18:35.300
some degree, actually, the planet Mercury in

479
00:18:35.300 --> 00:18:37.540
the solar system is a comet. It's got a

480
00:18:37.540 --> 00:18:39.980
beautiful long sodium tail. One of my

481
00:18:39.980 --> 00:18:42.190
favourite astrophotos I've ever seen is a

482
00:18:42.190 --> 00:18:44.470
picture of Mercury near the Pleiades, where

483
00:18:44.470 --> 00:18:46.190
somebody's done some imaging in a sodium

484
00:18:46.190 --> 00:18:48.510
filter and you can see Mercury's tail

485
00:18:48.990 --> 00:18:51.230
visible on the image. It's an astonishing

486
00:18:51.230 --> 00:18:53.750
thing. So we found planets like comets. We've

487
00:18:53.750 --> 00:18:55.830
even found planets around pulsars and they

488
00:18:55.830 --> 00:18:57.950
were the first three planets we found around

489
00:18:57.950 --> 00:19:00.910
other stars. There were um, Phoebe Toe,

490
00:19:00.910 --> 00:19:03.590
Poltergeist and Rao, these stars orbiting a

491
00:19:03.590 --> 00:19:05.430
pulsar named after three kinds of the, um,

492
00:19:05.430 --> 00:19:07.770
undead. So there's this huge variety that

493
00:19:07.930 --> 00:19:09.730
worth mentioning actually from the names. The

494
00:19:09.730 --> 00:19:12.210
names are being allocated by the

495
00:19:12.210 --> 00:19:13.930
International Astronomical Union, just as

496
00:19:13.930 --> 00:19:16.090
names of asteroids and names of satellites

497
00:19:16.090 --> 00:19:18.650
and things like that are. What they're trying

498
00:19:18.650 --> 00:19:20.890
to do with them is to be very

499
00:19:21.130 --> 00:19:24.090
democratic globally, to try and represent

500
00:19:24.250 --> 00:19:26.530
multiple cultures rather than just have all

501
00:19:26.530 --> 00:19:29.250
the planets draw from a single cultural base,

502
00:19:29.250 --> 00:19:31.370
a single kind of background. And so they've

503
00:19:31.370 --> 00:19:33.810
been running a series of competitions over

504
00:19:33.810 --> 00:19:36.410
the years for the general public where a

505
00:19:36.410 --> 00:19:39.190
given planetary system is to a given country.

506
00:19:39.830 --> 00:19:41.830
And, um, then people from that country get to

507
00:19:41.830 --> 00:19:43.670
nominate names, and then people from that

508
00:19:43.670 --> 00:19:46.070
country get to vote on it. And I think we've

509
00:19:46.070 --> 00:19:47.950
now got more than 100 planets named. We've

510
00:19:47.950 --> 00:19:49.590
had a few of them from Australia named. And

511
00:19:49.590 --> 00:19:52.030
I'm actually just trying to look up, um, the

512
00:19:52.030 --> 00:19:54.630
planet names from the iau. They're the

513
00:19:54.630 --> 00:19:56.470
official ones. Now, what's interesting is

514
00:19:56.470 --> 00:19:59.390
these are, uh, official names. They're

515
00:19:59.390 --> 00:20:01.790
the IAU's official names. I

516
00:20:01.790 --> 00:20:04.390
therefore try to use them in my purpose.

517
00:20:04.710 --> 00:20:06.580
Um, and I've had pushback from astronomers

518
00:20:06.580 --> 00:20:08.140
because everyone's so used to the catalogue

519
00:20:08.140 --> 00:20:10.620
numbers. So what I've been trying to do

520
00:20:10.940 --> 00:20:12.700
is you give both names, you give the

521
00:20:12.700 --> 00:20:14.620
catalogue name on the proper now. And I think

522
00:20:14.620 --> 00:20:16.300
where it will go long term is it'll become a

523
00:20:16.300 --> 00:20:18.380
bit like comets. You know, I've been trying

524
00:20:18.380 --> 00:20:20.780
to get images through the cloud and cursing

525
00:20:20.780 --> 00:20:22.500
the weather of Comet Pan Stars at the minute.

526
00:20:22.500 --> 00:20:24.460
And we talk about Comet Pan Stars, but it's

527
00:20:24.460 --> 00:20:26.540
real name that I'd write down, if I'm writing

528
00:20:26.540 --> 00:20:29.260
it is C20, 26 R3

529
00:20:29.260 --> 00:20:31.930
brackets, pan stars. And I think

530
00:20:32.090 --> 00:20:34.130
in the long term, I can see exoplanet names

531
00:20:34.130 --> 00:20:36.010
going that kind of way once people get used

532
00:20:36.010 --> 00:20:38.810
to it. So 51 Pegasi B,

533
00:20:39.050 --> 00:20:41.610
for example, is dimidium. That's the name

534
00:20:41.610 --> 00:20:44.210
that's been given there. And you can use both

535
00:20:44.210 --> 00:20:46.050
interchangeably. But because astronomers are

536
00:20:46.050 --> 00:20:49.010
used to 51 Pegasi B, that's where it

537
00:20:49.010 --> 00:20:51.850
sticks. Now, the names come from lots of

538
00:20:51.850 --> 00:20:53.530
different cultures. They come from lots of

539
00:20:53.530 --> 00:20:55.530
different groups. There are planets that have

540
00:20:55.530 --> 00:20:57.770
been discovered by Australians that are named

541
00:20:57.770 --> 00:20:59.370
after Australians. There are planets that are

542
00:20:59.370 --> 00:21:01.450
named after people. You know, you've got the

543
00:21:01.450 --> 00:21:03.990
planet Galileo going around 55 Cancri.

544
00:21:04.150 --> 00:21:06.670
So 55 Cancer's five named planets are all

545
00:21:06.670 --> 00:21:08.510
named after astronomers. You've got Galileo,

546
00:21:08.510 --> 00:21:11.110
Brahe, Lipper, Hay Janssen,

547
00:21:11.270 --> 00:21:13.990
Harriet, and, um, that's it. So Five

548
00:21:13.990 --> 00:21:16.670
planets, five names. Lots of different names

549
00:21:16.670 --> 00:21:19.630
from different cultures. We've got names that

550
00:21:19.630 --> 00:21:21.590
are controversial, names from different

551
00:21:21.590 --> 00:21:24.230
folklore, names from different cultures all

552
00:21:24.230 --> 00:21:26.670
around. That list is growing. But you don't

553
00:21:26.670 --> 00:21:28.710
say, see used all that much yet because a

554
00:21:28.710 --> 00:21:31.480
planet needs to be confirmed and

555
00:21:31.480 --> 00:21:34.160
then very confidently there and well studied

556
00:21:34.160 --> 00:21:36.040
for it to get onto the list for the name. So

557
00:21:36.040 --> 00:21:37.280
I think like I said, we've got a bit more

558
00:21:37.280 --> 00:21:39.840
than 100 names and a bit more than 6,000

559
00:21:39.920 --> 00:21:42.920
planets. Those 6,000 planets, that

560
00:21:42.920 --> 00:21:44.520
number will go up as well as down, but it's

561
00:21:44.520 --> 00:21:45.999
not going to be too long until we're 10,000

562
00:21:45.999 --> 00:21:46.480
plus.

563
00:21:46.960 --> 00:21:49.760
Andrew Dunkley: Yeah, I figured out why, uh, some of these,

564
00:21:49.850 --> 00:21:52.320
um, sometimes the number goes down. They're

565
00:21:52.320 --> 00:21:54.080
the ones that have been discovered by Monty

566
00:21:54.080 --> 00:21:55.320
Python. It's a planet.

567
00:21:55.320 --> 00:21:56.400
Jonti Horner: No it's not, it's not.

568
00:21:56.890 --> 00:21:59.610
Um, so that's why we'll also lose

569
00:21:59.690 --> 00:22:02.370
some with Gaia. So Gaia has been this

570
00:22:02.370 --> 00:22:04.730
amazing satellite measuring positions of

571
00:22:04.730 --> 00:22:07.290
stars and it can measure the

572
00:22:07.290 --> 00:22:10.170
wobble on the sky side to side of

573
00:22:10.170 --> 00:22:12.330
stars as a result of their planets. Now

574
00:22:12.410 --> 00:22:15.130
historically, the two, by far the two most

575
00:22:15.130 --> 00:22:16.970
successful methods of finding planets are the

576
00:22:16.970 --> 00:22:19.170
radial velocity method where we measure the

577
00:22:19.170 --> 00:22:21.010
star speed towards our away from us and see

578
00:22:21.010 --> 00:22:23.090
it wobbling along the line of sight, and the

579
00:22:23.090 --> 00:22:24.730
transit method where we see it pass between

580
00:22:24.730 --> 00:22:26.450
us and the star. And that means the orbit is

581
00:22:26.450 --> 00:22:28.800
edge on to us. And but for those radial

582
00:22:28.800 --> 00:22:30.720
velocity planets, we're measuring the

583
00:22:30.720 --> 00:22:32.560
fraction of the wobble towards or away from

584
00:22:32.560 --> 00:22:35.280
the observer. And um, the orbit could be

585
00:22:35.280 --> 00:22:37.480
tilted almost edge on or almost face on to

586
00:22:37.480 --> 00:22:39.440
give that same amount of wobble along our

587
00:22:39.440 --> 00:22:41.880
line of sight. Gaia will give us the other

588
00:22:41.880 --> 00:22:43.559
dimension. It'll give us a side by side,

589
00:22:43.559 --> 00:22:45.920
which means it'll find us the tilts of all

590
00:22:45.920 --> 00:22:48.360
those planets. Some of those planets will be

591
00:22:48.360 --> 00:22:51.120
on orbits very tilted to ours and therefore

592
00:22:51.120 --> 00:22:52.840
the mass that they have will be much higher

593
00:22:52.840 --> 00:22:55.240
than that we think they probably have. And

594
00:22:55.240 --> 00:22:56.920
that there'll be certain amount of attrition

595
00:22:56.920 --> 00:22:58.880
where planets that we think are planets are

596
00:22:58.880 --> 00:23:01.180
actually brown water dwarfs. And that is

597
00:23:01.180 --> 00:23:02.740
another of these arbitrary boundaries which

598
00:23:02.740 --> 00:23:05.660
we set roughly at 13 Jupiter masses. But we

599
00:23:05.660 --> 00:23:07.620
will have planets falling off at the top end.

600
00:23:08.340 --> 00:23:11.340
When Gaia comes out. I suspect he won't see

601
00:23:11.340 --> 00:23:12.900
the number drop though, because Gaia will

602
00:23:12.900 --> 00:23:14.580
also lead to so many new discoveries that,

603
00:23:14.580 --> 00:23:16.390
that will overwhelm the ones that fall, uh,

604
00:23:16.580 --> 00:23:17.460
off the top end.

605
00:23:18.180 --> 00:23:20.450
Andrew Dunkley: I, yes, that's a fair point. So, um,

606
00:23:20.980 --> 00:23:23.940
it's, it's going to be one of those waveforms

607
00:23:24.020 --> 00:23:26.190
that goes up and down

608
00:23:26.830 --> 00:23:29.070
as, as situations change. Yeah,

609
00:23:29.710 --> 00:23:31.390
let's take a. I was going

610
00:23:31.390 --> 00:23:33.590
Jonti Horner: to say I've been responsible for a number of

611
00:23:33.590 --> 00:23:35.750
systems getting killed because people propose

612
00:23:35.750 --> 00:23:38.350
planets in places that they seemed unlikely

613
00:23:38.350 --> 00:23:40.150
and they didn't make sense from orbital

614
00:23:40.150 --> 00:23:42.070
mechanics point of view. So I ran simulations

615
00:23:42.070 --> 00:23:44.350
and showed that if these planetary systems

616
00:23:44.350 --> 00:23:46.110
are real, wetting them in the last 10 years

617
00:23:46.110 --> 00:23:49.070
of a 4 billion year lifetime before

618
00:23:49.070 --> 00:23:50.830
the planets crash into each other or reject

619
00:23:50.830 --> 00:23:52.550
each other. And that's not feasible. So there

620
00:23:52.550 --> 00:23:53.950
must be something else going on. So on the

621
00:23:53.950 --> 00:23:55.770
one hand, hand, boohoo, you've killed a

622
00:23:55.770 --> 00:23:57.900
planet. That's not good, you naughty boy. Um,

623
00:23:57.930 --> 00:23:59.490
on the flip side though, it's really cool

624
00:23:59.490 --> 00:24:01.330
because there's something there creating the

625
00:24:01.330 --> 00:24:04.050
signal that people have measured and it

626
00:24:04.050 --> 00:24:06.610
isn't planets, so what is it? So there's

627
00:24:06.610 --> 00:24:08.490
always. Science always gives you more

628
00:24:08.490 --> 00:24:09.050
questions.

629
00:24:09.690 --> 00:24:12.570
Andrew Dunkley: Indeed it does. And you're listening to Space

630
00:24:12.570 --> 00:24:15.290
Nuts with Andrew Dunkley. Andrew Dunkley, I

631
00:24:15.290 --> 00:24:17.850
do know my name. And Professor Johnty Horner.

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00:24:19.290 --> 00:24:21.090
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Jonti Horner: Space Nuts.

674
00:26:11.070 --> 00:26:12.710
Andrew Dunkley: I'm gonna have to write it down so I can read

675
00:26:12.710 --> 00:26:13.310
it properly.

676
00:26:13.840 --> 00:26:16.470
Um, Jonty, where do you want to go next? I

677
00:26:16.470 --> 00:26:19.150
mean, we've found so many, uh, I don't think

678
00:26:19.150 --> 00:26:21.370
we will ever, never stop finding

679
00:26:21.370 --> 00:26:24.170
exoplanets, uh, because as

680
00:26:24.170 --> 00:26:25.690
technology improves they're just going to

681
00:26:25.690 --> 00:26:26.850
keep stacking up, aren't they?

682
00:26:26.850 --> 00:26:29.370
Jonti Horner: Yeah. I mean, if we talk about the 6000ish we

683
00:26:29.370 --> 00:26:32.210
found so far, uh, 6278

684
00:26:32.210 --> 00:26:34.890
I think it was. We said earlier on there are

685
00:26:34.890 --> 00:26:37.490
probably 4 trillion give or take in our

686
00:26:37.490 --> 00:26:40.090
galaxy, which means we've only found about

687
00:26:40.890 --> 00:26:43.770
one planet for every billion planets

688
00:26:43.850 --> 00:26:46.130
that are in our galaxy. We've barely

689
00:26:46.130 --> 00:26:48.890
scratched the surface in doing that. We've

690
00:26:48.890 --> 00:26:51.370
utterly revolutionised our knowledge of the,

691
00:26:51.470 --> 00:26:53.350
the variety of planets that'll be out there,

692
00:26:53.350 --> 00:26:56.230
of how planets form. We have still for

693
00:26:56.230 --> 00:26:58.350
me, not found something truly Earth like. I

694
00:26:58.350 --> 00:27:00.030
think that's the next hurdle. Now you'll see

695
00:27:00.430 --> 00:27:02.310
a number of media articles over the years

696
00:27:02.310 --> 00:27:04.150
saying the most Earth like planet yet has

697
00:27:04.150 --> 00:27:06.190
been found. All the bloody.

698
00:27:06.190 --> 00:27:08.990
Andrew Dunkley: I, I actually read an article yesterday

699
00:27:09.550 --> 00:27:12.110
which said, uh, oh, super Earth found

700
00:27:12.110 --> 00:27:14.030
potential life. Da, da, da, da, da. And I

701
00:27:14.030 --> 00:27:15.910
thought, yeah, here we go again. And I read

702
00:27:15.910 --> 00:27:17.590
it and of course when you get down to the

703
00:27:17.590 --> 00:27:19.190
second last paragraph, it says, of course

704
00:27:19.190 --> 00:27:21.150
there's no confirmation that this is even a

705
00:27:21.150 --> 00:27:21.870
rocky planet.

706
00:27:21.870 --> 00:27:24.830
Jonti Horner: But yeah, and to me it's like

707
00:27:24.830 --> 00:27:26.510
imagining that you're an alien visiting the

708
00:27:26.510 --> 00:27:27.990
Earth. Ah, and you're flying over the oceans

709
00:27:27.990 --> 00:27:29.670
and you say, we found the most human like

710
00:27:29.670 --> 00:27:31.750
animal yet. It's about two metres long, it's

711
00:27:31.750 --> 00:27:33.670
a couple of hundred kilos, 100 kilos. I mean,

712
00:27:33.670 --> 00:27:36.190
it's a dolphin, it's nothing like humans, but

713
00:27:36.190 --> 00:27:38.550
it, you know, it's that kind of thing. And I

714
00:27:38.550 --> 00:27:41.150
think I understand the urge, uh,

715
00:27:41.350 --> 00:27:44.270
for scientists to talk about things in the

716
00:27:44.270 --> 00:27:45.750
context of the habitable zone, in the

717
00:27:45.750 --> 00:27:47.590
purpose, because that's interesting. Is it

718
00:27:47.590 --> 00:27:50.350
too warm? Is it too cold? I understand the

719
00:27:50.350 --> 00:27:52.630
thing of saying this planet has similarities

720
00:27:52.630 --> 00:27:54.410
to the Earth. It's about the same size, size,

721
00:27:54.410 --> 00:27:56.130
or it would be about the same temperature.

722
00:27:56.450 --> 00:27:58.290
What tends to happen though then is that the

723
00:27:58.290 --> 00:28:00.130
pressure release from the universities gets a

724
00:28:00.130 --> 00:28:01.770
little bit more hyperbolic in it because they

725
00:28:01.770 --> 00:28:04.290
want to get the reads and the clicks, want to

726
00:28:04.290 --> 00:28:06.970
get the word out there. It then gets into the

727
00:28:06.970 --> 00:28:09.610
media, who again are being more hyperbolic,

728
00:28:09.610 --> 00:28:11.130
and we're seeing it at, ah, the minute, with

729
00:28:11.130 --> 00:28:13.170
the articles about the meteor shower that's

730
00:28:13.170 --> 00:28:14.810
active at the minute, where people are

731
00:28:14.810 --> 00:28:16.570
building it up and blowing it up to a level

732
00:28:16.570 --> 00:28:19.370
that is not practical and not observable and

733
00:28:19.370 --> 00:28:22.160
leads to this point. It's not helped by the

734
00:28:22.160 --> 00:28:23.720
fact that there are people who are making

735
00:28:23.720 --> 00:28:25.320
careers out of

736
00:28:26.440 --> 00:28:28.720
discussing how Earth like planets are that

737
00:28:28.720 --> 00:28:30.040
they didn't discover, that they weren't

738
00:28:30.040 --> 00:28:32.040
involved with to get themselves clicked and

739
00:28:32.040 --> 00:28:33.720
to get money. And a lot of the beautiful

740
00:28:33.720 --> 00:28:36.240
visuals you get cropping up online about

741
00:28:36.240 --> 00:28:38.280
Earth like planets come from one resource,

742
00:28:38.280 --> 00:28:40.520
which is called the Planetary Habitability

743
00:28:40.760 --> 00:28:43.760
Laboratory in Puerto Rico, which has been

744
00:28:43.760 --> 00:28:45.920
an ongoing source of frustration for me and

745
00:28:45.920 --> 00:28:48.240
colleagues because there's been storeys that

746
00:28:48.240 --> 00:28:49.960
people I know have published about planets.

747
00:28:49.960 --> 00:28:52.200
And then this entity

748
00:28:52.600 --> 00:28:54.440
puts out their own press release saying,

749
00:28:54.520 --> 00:28:56.400
we've calculated this magic number and this

750
00:28:56.400 --> 00:28:57.960
is the most Earth like planet found and it's

751
00:28:57.960 --> 00:28:59.360
probably got life. And the scientists who

752
00:28:59.360 --> 00:29:01.000
discovered it have said none of those things.

753
00:29:01.560 --> 00:29:04.480
Yeah. Um, and all the coverage is, look

754
00:29:04.480 --> 00:29:06.640
at this beautiful AI generated artwork. Isn't

755
00:29:06.640 --> 00:29:09.600
this amazing? So I do, and I

756
00:29:09.600 --> 00:29:11.560
had a fun storey about this a few months ago.

757
00:29:11.560 --> 00:29:13.200
I had a. An author get in touch with me,

758
00:29:13.200 --> 00:29:14.720
asking me to proofread a chapter of the book.

759
00:29:14.790 --> 00:29:16.750
A book, A book that they're doing. And they'd

760
00:29:16.750 --> 00:29:18.190
got a little bit in there about all the

761
00:29:18.190 --> 00:29:20.030
potentially Earth like habitable planets that

762
00:29:20.030 --> 00:29:21.470
have been found out there. And they use that

763
00:29:21.470 --> 00:29:24.310
as a resource. And I had to back them off on

764
00:29:24.310 --> 00:29:25.550
it and say, look, it's brilliant to talk

765
00:29:25.550 --> 00:29:27.790
about this. Please don't use this as a

766
00:29:27.790 --> 00:29:30.390
resource. If you use their equations,

767
00:29:30.629 --> 00:29:32.670
Venus would be the most habitable planet

768
00:29:32.670 --> 00:29:34.150
we've discovered other than the Earth.

769
00:29:35.430 --> 00:29:37.110
And I certainly wouldn't want to have a

770
00:29:37.110 --> 00:29:37.750
holiday there.

771
00:29:38.390 --> 00:29:41.090
Andrew Dunkley: No, no. Um, you'd need. Need 20

772
00:29:41.090 --> 00:29:44.050
gazillion plus sunscreen

773
00:29:44.050 --> 00:29:46.970
for starters or something like

774
00:29:46.970 --> 00:29:49.250
that. Now that'd be Mercury. But, um, it's.

775
00:29:49.250 --> 00:29:49.930
Yeah, it's.

776
00:29:49.930 --> 00:29:52.210
Jonti Horner: It's impossible unless it's impossible, you

777
00:29:52.210 --> 00:29:54.370
know, and we could live among the clouds.

778
00:29:54.370 --> 00:29:56.649
That'd be a bit different. But yeah, there's

779
00:29:56.649 --> 00:29:59.370
a lot of stuff around it. And it. We've

780
00:29:59.370 --> 00:30:01.170
talked before about other things. We talked

781
00:30:01.170 --> 00:30:03.530
about interstellar comets and the obfuscation

782
00:30:03.530 --> 00:30:04.970
of science when it comes to those. And

783
00:30:04.970 --> 00:30:06.490
they're definitely not aliens. And I'll say

784
00:30:06.490 --> 00:30:09.290
again, they definitely are not aliens. In

785
00:30:09.290 --> 00:30:12.130
this case, the exo Earth

786
00:30:12.610 --> 00:30:15.570
fatigue is real. People in the general public

787
00:30:15.570 --> 00:30:17.330
are convinced that we found planets like the

788
00:30:17.330 --> 00:30:19.770
Earth already. And I mean, it's great, it

789
00:30:19.770 --> 00:30:21.250
keeps people interested, but it also

790
00:30:21.250 --> 00:30:23.490
diminishes the impact when we finally do,

791
00:30:24.050 --> 00:30:25.890
you know, astronomers will finally find a

792
00:30:25.890 --> 00:30:27.930
planet that could genuinely be truly Earth.

793
00:30:27.930 --> 00:30:29.370
Like. We'll then need to do a lot of work to

794
00:30:29.370 --> 00:30:31.970
characterise it, but you can imagine in 10

795
00:30:31.970 --> 00:30:34.810
years time, we get data back from a planet

796
00:30:34.810 --> 00:30:37.030
that shows not only that it could be Earth

797
00:30:37.030 --> 00:30:38.590
like, but the surface temperature is right,

798
00:30:38.590 --> 00:30:39.870
and that there is liquid water in the

799
00:30:39.870 --> 00:30:42.310
atmosphere. And the scientific community will

800
00:30:42.310 --> 00:30:44.350
be, wow, this is our best discovery ever.

801
00:30:44.350 --> 00:30:46.910
This is so cool. And nobody'll care because,

802
00:30:46.910 --> 00:30:48.510
well, you've done it 10 times already. The

803
00:30:48.510 --> 00:30:49.110
media told me.

804
00:30:49.110 --> 00:30:51.870
Andrew Dunkley: So, yeah, I think I've found

805
00:30:51.870 --> 00:30:54.870
it. Um, a potentially habitable

806
00:30:54.870 --> 00:30:57.430
new planet has been discovered 146 light

807
00:30:57.430 --> 00:31:00.230
years away. Um, but then it goes.

808
00:31:00.230 --> 00:31:02.350
It goes on to say, but it might be minus 70

809
00:31:02.350 --> 00:31:05.110
degrees Celsius, um, but there's a storey

810
00:31:05.110 --> 00:31:06.910
like that coming out every other week.

811
00:31:07.320 --> 00:31:09.660
Jonti Horner: Um, and if you want to play that game, our

812
00:31:09.660 --> 00:31:11.780
definitions of habitability, based very much

813
00:31:11.780 --> 00:31:13.820
as we talked about in the previous episode,

814
00:31:13.820 --> 00:31:16.620
on our understanding of where

815
00:31:16.620 --> 00:31:18.900
Earth life could thrive and in the solar

816
00:31:18.900 --> 00:31:20.380
system. We've got potentially habitable

817
00:31:20.380 --> 00:31:22.020
worlds all over the place. Mars is

818
00:31:22.020 --> 00:31:23.820
potentially habitable on the borderline.

819
00:31:24.300 --> 00:31:26.060
Depending on what you think about bacteria in

820
00:31:26.060 --> 00:31:27.780
the atmosphere, Venus could be habitable for

821
00:31:27.780 --> 00:31:30.060
that type of life. We've got all the icy

822
00:31:30.060 --> 00:31:32.980
objects with buried subsurface oceans that

823
00:31:32.980 --> 00:31:34.980
are habitable, but not detectably habitable

824
00:31:34.980 --> 00:31:37.510
because there's ice in the way. I don't think

825
00:31:37.510 --> 00:31:40.310
it. It benefits people to overplay

826
00:31:40.310 --> 00:31:41.870
these discoveries, even though I fully

827
00:31:41.870 --> 00:31:44.470
understand the reason why people do,

828
00:31:45.430 --> 00:31:47.750
and I don't think it does anybody a service

829
00:31:47.830 --> 00:31:50.590
long term. Um, it is the unfortunate

830
00:31:50.590 --> 00:31:53.550
reality of what it is. But, hey,

831
00:31:53.550 --> 00:31:55.270
people are interested. Of course, you'll play

832
00:31:55.270 --> 00:31:57.550
to that in the kind of modern media cycle.

833
00:31:57.550 --> 00:31:59.630
Nobody remembers the retraction. They all

834
00:31:59.630 --> 00:32:01.270
remember the discovery. You know, everybody

835
00:32:01.270 --> 00:32:03.880
remembers cold fusion back from when I was a

836
00:32:03.880 --> 00:32:06.080
kid and a teenager. Um, that was, of course,

837
00:32:06.080 --> 00:32:07.880
published in the Journal of Irreproducible

838
00:32:07.880 --> 00:32:10.130
Results, otherwise known as Nature. Um,

839
00:32:10.680 --> 00:32:11.560
these things happen.

840
00:32:13.080 --> 00:32:14.040
Andrew Dunkley: Yeah, they do.

841
00:32:14.180 --> 00:32:16.840
Um, so, all right, where to next? With

842
00:32:17.320 --> 00:32:20.000
exoplanets, with, uh, so many

843
00:32:20.000 --> 00:32:22.960
discovered, um, that that's provided a

844
00:32:22.960 --> 00:32:25.680
baseline for the probability that every star

845
00:32:25.680 --> 00:32:28.640
has at least 10 planets around us.

846
00:32:29.680 --> 00:32:31.950
Jonti Horner: Um, we're finding them in a growing variety

847
00:32:31.950 --> 00:32:33.870
of ways. It's instructive a little bit to

848
00:32:33.870 --> 00:32:35.470
look back at history. You know, if I took you

849
00:32:35.470 --> 00:32:38.470
back to the early 1800s, our telescopes

850
00:32:38.470 --> 00:32:41.070
had finally got good enough to measure the

851
00:32:41.070 --> 00:32:43.030
motion of nearby stars against the background

852
00:32:43.030 --> 00:32:45.710
stars. Um, that allowed us to start measuring

853
00:32:45.710 --> 00:32:47.230
the distance to nearby stars using

854
00:32:47.230 --> 00:32:49.070
trigonometric parallax, where you look at a

855
00:32:49.070 --> 00:32:50.670
star from one side of the Earth's orbit, then

856
00:32:50.670 --> 00:32:52.390
the other and see it move against the

857
00:32:52.390 --> 00:32:54.070
background just like your finger moves if you

858
00:32:54.070 --> 00:32:56.430
look from one eye or the other. That same

859
00:32:56.430 --> 00:32:59.350
trick at ah, that time people start measuring

860
00:32:59.350 --> 00:33:01.470
it and they realise that nearby stars also

861
00:33:01.550 --> 00:33:04.350
moved through space. They were

862
00:33:04.350 --> 00:33:06.670
undergoing what we now know as proper motion,

863
00:33:06.670 --> 00:33:08.910
moving against the background stars in a

864
00:33:08.910 --> 00:33:10.670
straight line, which is their true space

865
00:33:10.670 --> 00:33:13.110
movement through the galaxy as seen by people

866
00:33:13.110 --> 00:33:15.870
on Earth. A guy called Friedrich

867
00:33:15.870 --> 00:33:18.310
Wilhelm Bessel, who was a fabulous astronomer

868
00:33:18.310 --> 00:33:20.950
in the early 1800s was doing

869
00:33:20.950 --> 00:33:23.650
observations of Sirius, which is our, uh, one

870
00:33:23.650 --> 00:33:25.650
of our class's star systems. It's a brightest

871
00:33:25.650 --> 00:33:28.090
star in the night sky and he found that once

872
00:33:28.090 --> 00:33:30.170
he took away the parallax Martian, the wobble

873
00:33:30.170 --> 00:33:31.410
left and right because of the Earth going

874
00:33:31.410 --> 00:33:34.290
around the sun, that Sirius was wobbling

875
00:33:34.290 --> 00:33:35.970
as it moved across the night sky. And it

876
00:33:35.970 --> 00:33:37.170
looked as though it was being pulled around

877
00:33:37.170 --> 00:33:39.810
by something as massive as the sun, but you

878
00:33:39.810 --> 00:33:42.570
could see nothing there. There obviously was

879
00:33:42.570 --> 00:33:44.210
something there pulling it around. It turns

880
00:33:44.210 --> 00:33:46.770
out that was the indirect discovery of what

881
00:33:46.770 --> 00:33:48.770
we now know as Sirius B, the white dwarf

882
00:33:48.770 --> 00:33:50.490
star. It wasn't the first white dwarf to be

883
00:33:50.490 --> 00:33:53.110
found, but in this case it was discovered

884
00:33:53.110 --> 00:33:55.230
indirectly. We saw Sirius doing something

885
00:33:55.230 --> 00:33:58.030
unexpected. We saw it wobbling and we used

886
00:33:58.030 --> 00:34:00.950
that to infer the presence of the white dwarf

887
00:34:00.950 --> 00:34:03.830
star around it. And of course we got another

888
00:34:03.830 --> 00:34:05.910
example of this a little bit later in the

889
00:34:05.910 --> 00:34:08.710
1800s with the discovery of Neptune, not

890
00:34:08.710 --> 00:34:10.670
through direct observation, but initially

891
00:34:10.670 --> 00:34:13.290
through mathematics, through John, um,

892
00:34:13.470 --> 00:34:15.990
Couch, Adams and Urban, uh, Le

893
00:34:15.990 --> 00:34:18.950
Verrier, doing calculations of how Uranus

894
00:34:18.950 --> 00:34:21.460
was moving across the sky, seeing that it was

895
00:34:21.460 --> 00:34:24.260
moving as though something we couldn't see

896
00:34:24.260 --> 00:34:26.220
was pulling on it. Predicting where that

897
00:34:26.220 --> 00:34:27.980
thing will be in Neptune was duly found. So

898
00:34:27.980 --> 00:34:30.900
they set this heritage of inferring

899
00:34:30.900 --> 00:34:32.860
the presence of something we cannot see

900
00:34:32.860 --> 00:34:35.700
because of its effect on something else. And

901
00:34:35.700 --> 00:34:38.700
that has been foundational to how we find

902
00:34:38.700 --> 00:34:40.100
planets around other stars. That's

903
00:34:40.100 --> 00:34:42.980
fundamentally how for more than 99% of

904
00:34:42.980 --> 00:34:45.540
them we've discovered them. There have been

905
00:34:45.700 --> 00:34:48.280
slip ups on the way in the 1940s,

906
00:34:48.420 --> 00:34:50.690
1950s, Edwin Vanderkamp, who's director of

907
00:34:50.690 --> 00:34:52.450
Spruill Observatory, thought he'd found

908
00:34:52.450 --> 00:34:54.850
planets around Barnard's Star, which is a

909
00:34:54.850 --> 00:34:56.410
star with the biggest proper motion in the

910
00:34:56.410 --> 00:34:58.850
sky. Turned out that he'd actually discovered

911
00:34:58.850 --> 00:35:00.970
the cleaner because what was happening was

912
00:35:00.970 --> 00:35:03.210
that his telescope was getting dirty. He used

913
00:35:03.210 --> 00:35:05.610
a lens telescope, a refracting telescope

914
00:35:06.090 --> 00:35:08.690
as the front Objective lens got

915
00:35:08.690 --> 00:35:11.610
Grottier the way in which it meant red light

916
00:35:11.610 --> 00:35:13.290
compared to blue light changed, causing

917
00:35:13.290 --> 00:35:15.130
Barnard's star position to shift against the

918
00:35:15.130 --> 00:35:16.570
background sounds. And when it got cleaned,

919
00:35:16.570 --> 00:35:19.510
it all went back to normal. He went very sad.

920
00:35:19.510 --> 00:35:21.950
But he went to his grave in the 70s convinced

921
00:35:22.030 --> 00:35:23.790
he was a victim of an injustice and he'd

922
00:35:23.790 --> 00:35:26.510
found planets around Barnassar. We now have

923
00:35:26.510 --> 00:35:27.990
found planets around Barnard, sir, but

924
00:35:27.990 --> 00:35:29.230
they're very different to the ones he

925
00:35:29.230 --> 00:35:32.230
proposed. We also had the fabulous

926
00:35:32.230 --> 00:35:34.430
Storey just prior to the pulsar planets

927
00:35:34.430 --> 00:35:36.590
actually being found, the same researchers

928
00:35:37.390 --> 00:35:38.830
thought they'd found a planet around a

929
00:35:38.830 --> 00:35:40.750
different pulsar and announced it at a

930
00:35:40.750 --> 00:35:42.630
conference. And someone went away and said a

931
00:35:42.630 --> 00:35:44.280
little bit, bit. Something a bit odd about

932
00:35:44.280 --> 00:35:46.840
this. What had been done was they were

933
00:35:46.840 --> 00:35:49.080
measuring the timing of the pulsars. So

934
00:35:49.080 --> 00:35:51.520
pulsars are super, ah, condensed

935
00:35:51.520 --> 00:35:54.440
neutron stars, leftovers from the explosion

936
00:35:54.440 --> 00:35:56.840
of star as a supernova, which have a couple

937
00:35:56.840 --> 00:35:58.640
of magnetic hotspots on their surface. And as

938
00:35:58.640 --> 00:36:00.680
they spin, they beam radio waves into space

939
00:36:00.680 --> 00:36:02.800
like lighthouse beams. And when the beam

940
00:36:02.800 --> 00:36:05.240
sweeps across as we get pulses of radio waves

941
00:36:05.560 --> 00:36:06.920
like the ticking of a clock.

942
00:36:07.320 --> 00:36:09.680
Andrew Dunkley: Yep. With this pulse, they're very, they're

943
00:36:09.680 --> 00:36:10.760
very precise, aren't they?

944
00:36:10.760 --> 00:36:11.920
Jonti Horner: Yeah, they're viewed as being the most

945
00:36:11.920 --> 00:36:13.640
accurate clocks in the universe, aside from

946
00:36:13.640 --> 00:36:15.540
when they have the old glitch or. And I've

947
00:36:15.540 --> 00:36:18.020
had plenty of watchers that do that in this

948
00:36:18.020 --> 00:36:20.260
case, uh, he was observing this pulsar and

949
00:36:20.260 --> 00:36:22.060
sometimes the pulses arrived a little early,

950
00:36:22.060 --> 00:36:23.540
sometimes they arrived a little there. And

951
00:36:23.540 --> 00:36:26.020
this was happening periodically, so

952
00:36:26.100 --> 00:36:28.220
ruled everything else out. There must be

953
00:36:28.220 --> 00:36:29.740
something causing the distance between the

954
00:36:29.740 --> 00:36:31.460
pulsar and the solar system to vary

955
00:36:31.460 --> 00:36:33.780
periodically though, uh, it must be a planet.

956
00:36:34.340 --> 00:36:36.300
Turned out that after the conference someone

957
00:36:36.300 --> 00:36:38.100
said, there's something a little bit odd

958
00:36:38.100 --> 00:36:39.220
here, maybe you should just do a double

959
00:36:39.220 --> 00:36:41.340
cheque before you publish it. Went away and

960
00:36:41.340 --> 00:36:43.970
found a single typo in their code that meant

961
00:36:43.970 --> 00:36:45.450
they didn't properly account for the motion

962
00:36:45.450 --> 00:36:47.410
of the Earth around the sun. So they had

963
00:36:47.410 --> 00:36:49.210
discovered a planet, but they discovered that

964
00:36:49.210 --> 00:36:50.610
the one that they were set on, they

965
00:36:50.610 --> 00:36:53.570
discovered the Earth. I mean it's a

966
00:36:53.570 --> 00:36:56.290
fabulous discovery. Now we laugh about this,

967
00:36:56.290 --> 00:36:58.750
but it shows how hard these observations are.

968
00:36:58.750 --> 00:37:00.690
Uh, finding planets around other stars is

969
00:37:01.170 --> 00:37:02.810
incredibly difficult. We've had the

970
00:37:02.810 --> 00:37:05.690
wherewithal to understand the methods

971
00:37:05.690 --> 00:37:07.850
that we would use for a couple of hundred

972
00:37:07.850 --> 00:37:10.380
years, but it was only in the

973
00:37:10.540 --> 00:37:13.380
90s it really became feasible to do them. And

974
00:37:13.380 --> 00:37:15.220
in those early days in particular, there were

975
00:37:15.220 --> 00:37:17.620
two methods that hugely

976
00:37:17.620 --> 00:37:20.540
dominated. For the first, probably 10

977
00:37:20.540 --> 00:37:23.540
years, 12 years of the exoplanet area era,

978
00:37:23.540 --> 00:37:25.580
the main way we found planets was what you

979
00:37:25.580 --> 00:37:27.220
call the radial velocity technique, the

980
00:37:27.220 --> 00:37:29.740
wobble technique, which is using the Doppler

981
00:37:29.740 --> 00:37:32.200
effect. And you see a distance star. And, um,

982
00:37:32.200 --> 00:37:33.700
we can measure its light and we can break

983
00:37:33.700 --> 00:37:35.460
that light to its component colours, seeing

984
00:37:35.460 --> 00:37:37.540
what we call the Fraunhofel lines littered

985
00:37:37.540 --> 00:37:39.780
across it, which are dark lines that are the

986
00:37:39.780 --> 00:37:41.660
chemical fingerprint of what the star's made

987
00:37:41.660 --> 00:37:43.620
of. And, um, we can measure their positions

988
00:37:43.620 --> 00:37:45.380
in the lab incredibly precisely. And if the

989
00:37:45.380 --> 00:37:47.820
star's moving towards us, its light gets a

990
00:37:47.820 --> 00:37:49.620
bit blue shifted and all those lines move a

991
00:37:49.620 --> 00:37:51.460
little bit to the blue. And if it's moving

992
00:37:51.460 --> 00:37:52.980
away from us, they move a little bit to the

993
00:37:52.980 --> 00:37:54.420
red. And if you can monitor it for long

994
00:37:54.420 --> 00:37:56.580
enough, you can see the star coming backward

995
00:37:56.580 --> 00:37:59.540
and forward, it's wobbling. You can infer the

996
00:37:59.540 --> 00:38:01.140
presence of something massive pulling it

997
00:38:01.140 --> 00:38:03.920
round. You can figure out the, the orbital

998
00:38:03.920 --> 00:38:06.880
distance of that object by how

999
00:38:06.880 --> 00:38:08.800
long it takes for the wobble. So it comes

1000
00:38:08.800 --> 00:38:10.680
towards us, goes away, comes towards us again

1001
00:38:10.680 --> 00:38:13.200
as it does one full lap. That gives you the

1002
00:38:13.200 --> 00:38:16.160
orbital period. You can infer the mass based

1003
00:38:16.160 --> 00:38:18.160
on the size of the wobble. But we're only

1004
00:38:18.160 --> 00:38:19.920
measuring that component along our line of

1005
00:38:19.920 --> 00:38:21.520
sight. So you get a minimum mass that it

1006
00:38:21.520 --> 00:38:23.040
could be, and it could be higher than that.

1007
00:38:23.600 --> 00:38:25.200
So we can learn about the orbit. That's the

1008
00:38:25.200 --> 00:38:27.120
radial velocity technique. And that is an

1009
00:38:27.120 --> 00:38:29.610
indirect method. You see the station wobbling

1010
00:38:29.610 --> 00:38:31.650
and infer the presence of a planet or planets

1011
00:38:31.650 --> 00:38:33.970
around it. The technique that's taken over

1012
00:38:33.970 --> 00:38:36.570
from it is the transit technique. That's

1013
00:38:36.570 --> 00:38:38.250
where a planet's going around its star and

1014
00:38:38.250 --> 00:38:39.930
its orbits just lined up right, that every

1015
00:38:39.930 --> 00:38:41.450
time it goes around, it blocks a bit of the

1016
00:38:41.450 --> 00:38:43.530
star's light. The star dims and then

1017
00:38:43.530 --> 00:38:45.810
brightens again periodically. And, um, by

1018
00:38:45.810 --> 00:38:47.730
measuring the periodic dimming, you can infer

1019
00:38:47.730 --> 00:38:49.730
the presence of something blocking the star's

1020
00:38:49.730 --> 00:38:51.570
light. Again, that gives you the orbital

1021
00:38:51.570 --> 00:38:54.330
period, because you get one dip per orbit and

1022
00:38:54.330 --> 00:38:56.130
it gives you the size, the diameter of the

1023
00:38:56.130 --> 00:38:57.450
planet, because a bigger planet will block,

1024
00:38:57.520 --> 00:38:59.600
block more light. But fundamentally, again,

1025
00:38:59.600 --> 00:39:02.000
it's an indirect method. You see a star doing

1026
00:39:02.000 --> 00:39:04.720
something odd and infer the presence of a

1027
00:39:04.720 --> 00:39:07.120
planet. Now, both these methods

1028
00:39:08.000 --> 00:39:10.120
were known and were used for hundreds of

1029
00:39:10.120 --> 00:39:12.800
years. We saw binary

1030
00:39:12.800 --> 00:39:15.520
stars being observed because of the

1031
00:39:15.520 --> 00:39:18.040
dimming during the eclipses. Um, John

1032
00:39:18.040 --> 00:39:20.280
Goodrick, um, a British astronomer who died

1033
00:39:20.280 --> 00:39:22.880
at a very young age, explained Algol. The

1034
00:39:22.880 --> 00:39:24.980
Wink of Kingdom star has been a binary star

1035
00:39:24.980 --> 00:39:27.860
back in the early 1700s. That is effectively

1036
00:39:27.860 --> 00:39:29.500
the same as A transit technique, it's just

1037
00:39:29.500 --> 00:39:32.100
you've got a bigger, uh, blocker. Problem is

1038
00:39:32.180 --> 00:39:34.420
our eyes are only sensitive to variations in

1039
00:39:34.420 --> 00:39:37.020
light at about the 20% level. Smaller

1040
00:39:37.020 --> 00:39:38.660
variations than that, we just don't pick up.

1041
00:39:38.660 --> 00:39:40.860
Your lights can be flickering by 20% and

1042
00:39:40.860 --> 00:39:43.620
you'll barely notice it. For a binary star,

1043
00:39:43.700 --> 00:39:45.500
the brightness can change by a factor of two

1044
00:39:45.500 --> 00:39:48.180
or more. For an exoplanet, Jupiter,

1045
00:39:48.180 --> 00:39:51.000
uh, blocks about 1% of the light from the sun

1046
00:39:51.150 --> 00:39:53.750
on that is just something you cannot see with

1047
00:39:53.750 --> 00:39:56.230
a naked eye. So to be able to use the transit

1048
00:39:56.230 --> 00:39:58.710
technique, we had to wait for detectors that

1049
00:39:58.710 --> 00:40:00.590
were sensitive enough to measure incredibly

1050
00:40:00.590 --> 00:40:02.510
fine variations in brightness to come along,

1051
00:40:02.910 --> 00:40:04.670
which is why we've only been able to use a

1052
00:40:04.670 --> 00:40:07.630
transit technique this millennium. It wasn't

1053
00:40:07.630 --> 00:40:09.590
really possible before that. Similarly, with

1054
00:40:09.590 --> 00:40:12.230
the radial velocity technique, we could

1055
00:40:12.230 --> 00:40:14.750
measure the wobble of stars from binary

1056
00:40:14.750 --> 00:40:17.230
stars for decades. Because the movement of

1057
00:40:17.230 --> 00:40:18.930
the lines were sufficiently big, you could

1058
00:40:18.930 --> 00:40:20.490
measure it on a photographic plate and you

1059
00:40:20.490 --> 00:40:21.970
could measure speeds of kilometres per

1060
00:40:21.970 --> 00:40:23.050
second. Fairly easy.

1061
00:40:23.690 --> 00:40:25.530
Planets like Jupiter going around the sun

1062
00:40:25.610 --> 00:40:28.170
cause wobbles measured in metres per second,

1063
00:40:28.570 --> 00:40:31.330
maybe 10 metres per second. That is, again,

1064
00:40:31.330 --> 00:40:33.850
this such a small wobble that taking photos

1065
00:40:33.850 --> 00:40:36.650
on photographic plates of the spectral lines,

1066
00:40:36.650 --> 00:40:38.490
the resolution isn't good enough. Our

1067
00:40:38.730 --> 00:40:41.170
spectrograph we've got up at Matt Kent in our

1068
00:40:41.170 --> 00:40:43.890
facility, Merv Ross Rallis. Typically, the

1069
00:40:43.890 --> 00:40:45.720
measurements we're making are measurements of

1070
00:40:45.870 --> 00:40:48.350
a thousandth of a pixel shift

1071
00:40:48.830 --> 00:40:50.950
in a given line. And the only way we can do

1072
00:40:50.950 --> 00:40:52.390
that is because you're seeing thousands of

1073
00:40:52.390 --> 00:40:54.750
lines at once and you can work out

1074
00:40:54.750 --> 00:40:56.710
statistically what they're doing. So even

1075
00:40:56.710 --> 00:40:58.470
with the most modern cameras and most modern

1076
00:40:58.470 --> 00:41:00.910
technology, it's still hard. And that's why,

1077
00:41:00.910 --> 00:41:03.190
even though we had the wherewithal to

1078
00:41:03.190 --> 00:41:05.350
understand the physics and, um, to know how

1079
00:41:05.350 --> 00:41:07.790
to do the techniques, 200 years ago,

1080
00:41:08.430 --> 00:41:10.750
we were stuck in a technology gap. We just

1081
00:41:10.750 --> 00:41:12.630
had to wait for the technology to reach the

1082
00:41:12.630 --> 00:41:14.870
right place. And that's why finding the first

1083
00:41:14.870 --> 00:41:16.710
was hard. But once you found one, you'll find

1084
00:41:16.710 --> 00:41:18.700
tech 10, you'll find 100, you'll find a

1085
00:41:18.700 --> 00:41:20.460
thousand. I'd m point people, incidentally,

1086
00:41:20.460 --> 00:41:23.140
to the astonishingly beautiful videos by

1087
00:41:23.140 --> 00:41:25.700
System Sounds, in partnership with NASA, that

1088
00:41:25.700 --> 00:41:28.460
were put out to celebrate the 4 and 5000th

1089
00:41:28.460 --> 00:41:31.060
discovered exoplanets, where they run the

1090
00:41:31.060 --> 00:41:33.380
discoveries over time on a, on a map of the

1091
00:41:33.380 --> 00:41:35.580
sky where the discoveries are marked with a

1092
00:41:35.580 --> 00:41:38.220
little ring. And every planet gets its own

1093
00:41:38.220 --> 00:41:40.860
musical note, where the musical note tells

1094
00:41:40.860 --> 00:41:42.460
you the orbital period of that planet around

1095
00:41:42.460 --> 00:41:44.400
the star. So a high Pitched note like a ding

1096
00:41:45.030 --> 00:41:46.630
will be a planet really close and going

1097
00:41:46.630 --> 00:41:48.990
around really quick and low pitch note like a

1098
00:41:48.990 --> 00:41:51.070
ding that'll be a planet a long, long way

1099
00:41:51.070 --> 00:41:53.950
away going around really slowly. And um, it

1100
00:41:53.950 --> 00:41:56.870
shows you the diversity we found but it also

1101
00:41:56.870 --> 00:41:59.590
shows you this incredibly accelerating

1102
00:41:59.590 --> 00:42:01.230
rate at which we're getting better at doing

1103
00:42:01.230 --> 00:42:03.590
it because now we've crossed that threshold

1104
00:42:03.590 --> 00:42:06.030
where the technology wasn't good enough. And

1105
00:42:06.030 --> 00:42:08.390
now the technology keeps getting better, we

1106
00:42:08.390 --> 00:42:09.870
get better at doing it and the numbers

1107
00:42:09.870 --> 00:42:11.630
continue m to rise. And depending who you

1108
00:42:11.630 --> 00:42:13.950
talk to, there are people who suggest we may

1109
00:42:13.950 --> 00:42:15.470
well actually we'll certainly cross the

1110
00:42:15.470 --> 00:42:17.830
10,000 count by 2030.

1111
00:42:18.470 --> 00:42:20.110
Might not be long after that before we cross

1112
00:42:20.110 --> 00:42:22.510
100,000 mark. That will all depend on Gaia,

1113
00:42:22.510 --> 00:42:24.710
but also the Nancy Grace Roman telescope

1114
00:42:24.710 --> 00:42:26.950
that's due to launch in a few years time.

1115
00:42:27.590 --> 00:42:30.310
Andrew Dunkley: Yeah, it's going to be amazing. Uh,

1116
00:42:30.310 --> 00:42:32.950
and uh, who knows what we will find.

1117
00:42:33.270 --> 00:42:35.510
And we'll talk about uh, a bit more in a

1118
00:42:35.510 --> 00:42:37.590
moment here on Space Nuts.

1119
00:42:40.540 --> 00:42:42.700
Three, two, one.

1120
00:42:43.260 --> 00:42:44.460
Jonti Horner: Space Nuts.

1121
00:42:44.620 --> 00:42:46.660
Andrew Dunkley: And you're with Andrew Dunkley and Professor

1122
00:42:46.660 --> 00:42:49.540
Jonty Horner. We're talking exoplanets on

1123
00:42:49.540 --> 00:42:52.420
this special episode. Uh, it's

1124
00:42:52.420 --> 00:42:55.220
our last segment. So, um, over to you

1125
00:42:55.220 --> 00:42:57.020
Jonty. Where do you, where do you want to go

1126
00:42:57.020 --> 00:42:59.380
to finish off this particularly interesting

1127
00:42:59.380 --> 00:42:59.900
topic?

1128
00:42:59.900 --> 00:43:02.540
Jonti Horner: Well, I think it's also worth flagging out

1129
00:43:02.540 --> 00:43:04.380
the diversity places that are doing this work

1130
00:43:04.380 --> 00:43:05.940
as well. I mean amateur astronomers are

1131
00:43:05.940 --> 00:43:07.500
contributing a huge amount. We're now at the

1132
00:43:07.500 --> 00:43:09.680
point where, where the technology's moved on

1133
00:43:09.680 --> 00:43:12.360
enough that you can observe and measure

1134
00:43:12.360 --> 00:43:15.200
exoplanet transits using a fairly cheap off

1135
00:43:15.200 --> 00:43:17.200
the shelf telescope. Many amateur astronomers

1136
00:43:17.200 --> 00:43:19.480
will occasionally observe the transit of one

1137
00:43:19.480 --> 00:43:21.160
of our bright planets. There was an article

1138
00:43:21.640 --> 00:43:23.919
on Australia's ABC News recently about some

1139
00:43:23.919 --> 00:43:25.680
amateur astronomers who banded together to be

1140
00:43:25.680 --> 00:43:28.200
involved in planet discovery. I'm

1141
00:43:29.640 --> 00:43:32.000
increasingly proud of the facility we've got

1142
00:43:32.000 --> 00:43:34.480
at Uni sq, which is as far as we know, the

1143
00:43:34.480 --> 00:43:37.000
only dedicated Southern Hemisphere exoplanet

1144
00:43:37.000 --> 00:43:38.560
observatory in the Southern Hemisphere.

1145
00:43:38.640 --> 00:43:40.560
There's a lot of facilities looking for them,

1146
00:43:40.960 --> 00:43:43.640
but we've got our own facility at Matt Kent

1147
00:43:43.640 --> 00:43:46.200
Observatory just outside Toowoomba that all

1148
00:43:46.200 --> 00:43:47.840
it does is look for planets and learn more

1149
00:43:47.840 --> 00:43:49.760
about them. It doesn't split its time with

1150
00:43:49.760 --> 00:43:52.160
other tasks. Its job is planet search.

1151
00:43:52.640 --> 00:43:54.480
And it's really important to stress that

1152
00:43:54.720 --> 00:43:56.280
particularly for the younger listeners from

1153
00:43:56.280 --> 00:43:58.800
Australia, there's this perception

1154
00:43:59.120 --> 00:44:01.400
that the only place you can go to do real

1155
00:44:01.400 --> 00:44:03.520
science and to become a scientist is to go to

1156
00:44:03.520 --> 00:44:05.440
the big cities, the big capital cities, to

1157
00:44:05.440 --> 00:44:08.320
the group Fake Universities and for people in

1158
00:44:08.320 --> 00:44:09.960
regional Australia, and particularly people

1159
00:44:09.960 --> 00:44:12.760
from less prestigious

1160
00:44:12.760 --> 00:44:14.640
backgrounds, lower socioeconomic backgrounds,

1161
00:44:14.640 --> 00:44:16.120
all the rest of it, there's this very much

1162
00:44:16.120 --> 00:44:18.200
feeling that it's a big city thing and you've

1163
00:44:18.200 --> 00:44:19.840
got to go to the right schools. But we're at

1164
00:44:19.840 --> 00:44:22.080
a small regional university in regional

1165
00:44:22.080 --> 00:44:24.080
Australia and we're leading the world in

1166
00:44:24.080 --> 00:44:27.080
this. You know, we have two of my colleagues,

1167
00:44:27.090 --> 00:44:29.360
um, Professor George Zhao and Associate

1168
00:44:29.360 --> 00:44:31.960
Professor Chelsea Huang are, uh, between them

1169
00:44:31.960 --> 00:44:34.600
responsible for 30% of all time Australia

1170
00:44:34.760 --> 00:44:36.880
has ever had allocated on the James Webb

1171
00:44:36.880 --> 00:44:39.340
Space Telescope. And, uh, they've sat to

1172
00:44:39.340 --> 00:44:41.020
study planets around other stars. So I do

1173
00:44:41.020 --> 00:44:43.420
want to stress to people listening that this

1174
00:44:43.420 --> 00:44:45.820
is not just something that's done in the US

1175
00:44:45.820 --> 00:44:47.420
or it's not just something that's done at the

1176
00:44:47.420 --> 00:44:49.940
world's top 10 universities. It's something

1177
00:44:49.940 --> 00:44:51.820
that you can participate in yourself. There's

1178
00:44:51.820 --> 00:44:53.900
some fabulous citizen science programmes out

1179
00:44:53.900 --> 00:44:55.740
there and uh, there is going to be an

1180
00:44:55.740 --> 00:44:58.740
increasing extreme wealth

1181
00:44:58.740 --> 00:45:00.570
of data coming out in the coming years that

1182
00:45:00.570 --> 00:45:02.860
uh, astronomers simply won't have enough

1183
00:45:02.860 --> 00:45:04.630
hands to go through. So I'm sure that, that

1184
00:45:04.630 --> 00:45:06.590
if people keep their eyes out, there will be

1185
00:45:06.590 --> 00:45:08.870
other citizen science programmes pop up in

1186
00:45:08.870 --> 00:45:10.350
the coming years. You know, we've got,

1187
00:45:10.670 --> 00:45:12.350
currently I'm looking at the wonderful NASA

1188
00:45:12.350 --> 00:45:15.030
Rexoplanet archive here, looking at the

1189
00:45:15.030 --> 00:45:16.550
different methods planets have been

1190
00:45:16.550 --> 00:45:18.910
discovered by, and we've now got, I think

1191
00:45:18.910 --> 00:45:20.990
it's 11 different methods that have been

1192
00:45:20.990 --> 00:45:22.910
used. Of our

1193
00:45:22.990 --> 00:45:25.230
6283 planets,

1194
00:45:25.470 --> 00:45:28.070
4640 have been found by the

1195
00:45:28.070 --> 00:45:30.110
transit method. That's overwhelmingly the

1196
00:45:30.110 --> 00:45:32.120
most successful now. And that's because you

1197
00:45:32.120 --> 00:45:33.680
can play a numbers game. You can look at

1198
00:45:33.680 --> 00:45:36.440
thousands of stars at once, looking to see if

1199
00:45:36.440 --> 00:45:38.120
any of them wink. And that's what the Kepler

1200
00:45:38.120 --> 00:45:40.360
spacecraft and more recently NASA's test

1201
00:45:40.360 --> 00:45:43.000
spacecraft did. We've got nearly

1202
00:45:43.000 --> 00:45:44.960
1200 planets found with the radial velocity

1203
00:45:44.960 --> 00:45:47.359
method, the wobbled method. Now should be

1204
00:45:47.359 --> 00:45:49.320
said this is a discovery method and a lot of

1205
00:45:49.320 --> 00:45:51.320
these planets have then been studied using

1206
00:45:51.320 --> 00:45:52.840
other methods. But this is how they were

1207
00:45:52.840 --> 00:45:55.640
found. So between those two were, uh, what,

1208
00:45:55.640 --> 00:45:58.170
5800 of the known

1209
00:45:58.170 --> 00:46:00.770
planets, 6200 were found by those.

1210
00:46:01.250 --> 00:46:03.930
That's 90 odd percent of the

1211
00:46:03.930 --> 00:46:06.850
remainder. We, uh, know of 278 planets that

1212
00:46:06.850 --> 00:46:08.930
were found by microlensing. This is where you

1213
00:46:08.930 --> 00:46:11.250
look at very distant stars like the middle of

1214
00:46:11.250 --> 00:46:13.890
the galaxy and look for planets and stars

1215
00:46:13.890 --> 00:46:15.610
that we can't see passing along our line of

1216
00:46:15.610 --> 00:46:18.410
sight and their mass bending light to

1217
00:46:18.410 --> 00:46:20.370
cause that background star to brighten then

1218
00:46:20.370 --> 00:46:23.370
fade. Very small number found so far.

1219
00:46:23.370 --> 00:46:25.880
But the Nancy Grace Roman telescope will

1220
00:46:25.880 --> 00:46:28.400
likely discover thousands, if not tens of

1221
00:46:28.400 --> 00:46:30.160
thousands of microlensing planets in the

1222
00:46:30.160 --> 00:46:32.120
coming years. Because that telescope's going

1223
00:46:32.120 --> 00:46:33.920
to go and stare at the middle of the galaxy,

1224
00:46:33.920 --> 00:46:36.400
among other things, and should be very useful

1225
00:46:36.400 --> 00:46:39.120
at that. We've got nearly a hundred planets

1226
00:46:39.120 --> 00:46:41.560
now discovered by direct imaging,

1227
00:46:41.960 --> 00:46:43.240
and they're really interesting because

1228
00:46:43.240 --> 00:46:44.560
they're the ones where we actually see the

1229
00:46:44.560 --> 00:46:46.320
planet and we find it by seeing the light

1230
00:46:46.320 --> 00:46:48.760
from the planet. So it's amazing that we're

1231
00:46:48.760 --> 00:46:51.200
nearly at 100 there. And my favourite movie

1232
00:46:51.200 --> 00:46:53.850
of all time Time is really the

1233
00:46:54.490 --> 00:46:57.010
movie of the planets orbiting the star HR

1234
00:46:57.010 --> 00:46:59.930
8799, where observations spanning

1235
00:46:59.930 --> 00:47:01.970
more than decade now have been made, where

1236
00:47:01.970 --> 00:47:03.970
you can see four planets around that star and

1237
00:47:03.970 --> 00:47:06.290
watch them move in their orbits. And you

1238
00:47:06.290 --> 00:47:08.330
think from where we were when I was a kid,

1239
00:47:08.490 --> 00:47:10.210
where we didn't even know if there were any

1240
00:47:10.210 --> 00:47:12.850
planets out there, we can now watch some of

1241
00:47:12.850 --> 00:47:15.050
them go around their stars in real time.

1242
00:47:15.610 --> 00:47:16.970
That's just astonishing.

1243
00:47:17.370 --> 00:47:19.370
There's a lot of other really niche methods

1244
00:47:19.370 --> 00:47:20.910
that have been used news, but they're kind of

1245
00:47:20.910 --> 00:47:23.790
the big four, I'd say. And I think the one

1246
00:47:23.790 --> 00:47:25.910
that's going to grow over the coming decade

1247
00:47:25.910 --> 00:47:28.350
more than any other is astrometry. So at the

1248
00:47:28.350 --> 00:47:30.390
minute there is a grand total of six planets

1249
00:47:30.390 --> 00:47:32.630
that have been discovered by astrometry. This

1250
00:47:32.630 --> 00:47:34.350
is measuring the positions of stars in the

1251
00:47:34.350 --> 00:47:36.310
sky and seeing them wobble side to side. It's

1252
00:47:36.310 --> 00:47:39.310
what Bessel did with Sirius to find Sirius B.

1253
00:47:39.710 --> 00:47:41.740
We've only found six so far, but the Gaia,

1254
00:47:41.740 --> 00:47:44.030
uh, spacecraft observed for a long time,

1255
00:47:44.030 --> 00:47:45.550
finished observing, but we're still getting

1256
00:47:45.550 --> 00:47:47.980
new data releases from. From it. Gaia data

1257
00:47:47.980 --> 00:47:50.420
release number four is coming allegedly in

1258
00:47:50.420 --> 00:47:52.940
December this year. Maybe push back a little

1259
00:47:52.940 --> 00:47:55.740
bit, but that's where they will have enough

1260
00:47:55.820 --> 00:47:57.980
quality and analysis of the data and enough

1261
00:47:58.220 --> 00:48:00.900
time period the data covers to start finding

1262
00:48:00.900 --> 00:48:03.580
planets in the Gaia data doing astrometry

1263
00:48:04.060 --> 00:48:06.380
and people are still predicting that could

1264
00:48:06.380 --> 00:48:08.300
yield tens of thousands of planets. Even if

1265
00:48:08.300 --> 00:48:11.220
you're a pessimist, it's easy that Gaia

1266
00:48:11.220 --> 00:48:14.100
could take over from Kepler and TESS as a

1267
00:48:14.100 --> 00:48:16.180
tool that found the most planets. That's just

1268
00:48:16.180 --> 00:48:18.500
in the next year or two. And what we're doing

1269
00:48:18.500 --> 00:48:21.260
then we're finding more, but where we're

1270
00:48:21.260 --> 00:48:22.780
shifting to is not just finding them, but

1271
00:48:22.780 --> 00:48:25.220
learning more about them, characterising

1272
00:48:25.220 --> 00:48:27.460
them. And that's where the future of

1273
00:48:27.460 --> 00:48:29.540
exoplanet science is. It's not just enough

1274
00:48:29.540 --> 00:48:31.980
now to find a planet, we want to learn more

1275
00:48:31.980 --> 00:48:33.900
about it. What's its atmosphere made of?

1276
00:48:34.140 --> 00:48:36.340
What's its internal composition? What's it

1277
00:48:36.340 --> 00:48:39.120
like? That's where we're going. And

1278
00:48:39.120 --> 00:48:42.070
um, we're making great leaps in that we are

1279
00:48:42.070 --> 00:48:44.310
finding out what chemical species are in the

1280
00:48:44.310 --> 00:48:45.750
atmospheres of different planets. Currently

1281
00:48:45.750 --> 00:48:47.230
only really doing it for the very biggest

1282
00:48:47.230 --> 00:48:49.390
ones because of the easiest to observe. But

1283
00:48:49.390 --> 00:48:51.070
that's very much the future. And that's what

1284
00:48:51.070 --> 00:48:53.190
will lead to the search for life elsewhere,

1285
00:48:53.430 --> 00:48:55.150
which I think is what really hooks a lot of

1286
00:48:55.150 --> 00:48:56.150
people into the subject.

1287
00:48:57.510 --> 00:48:59.750
Andrew Dunkley: Yeah, it's fascinating. For the record, the

1288
00:48:59.750 --> 00:49:02.590
first actual photograph of an

1289
00:49:02.590 --> 00:49:03.870
Exoplanet was in

1290
00:49:03.870 --> 00:49:05.830
2004

1291
00:49:07.840 --> 00:49:08.000
Jonti Horner: and

1292
00:49:08.000 --> 00:49:10.400
Andrew Dunkley: it was 2m, um, 1207b.

1293
00:49:10.480 --> 00:49:10.960
Jonti Horner: Yes.

1294
00:49:11.200 --> 00:49:13.390
Andrew Dunkley: Which apparently is an exoplanet, uh,

1295
00:49:13.390 --> 00:49:15.600
orbiting a gas giant.

1296
00:49:16.080 --> 00:49:18.880
Yes. Which is a big, a big one,

1297
00:49:18.960 --> 00:49:21.540
about five times the mass of Jupiter. So, um,

1298
00:49:21.540 --> 00:49:23.080
yeah, so that was the first one ever

1299
00:49:23.080 --> 00:49:25.440
photographed that we actually got to see a

1300
00:49:25.440 --> 00:49:28.400
picture of rather than just identified

1301
00:49:28.480 --> 00:49:29.200
through some.

1302
00:49:29.280 --> 00:49:30.920
Jonti Horner: I mean we're still just seeing them as a

1303
00:49:30.920 --> 00:49:33.360
single pixel. We're not going to be at the

1304
00:49:33.360 --> 00:49:35.560
point of Star Trek type images of the surface

1305
00:49:35.560 --> 00:49:37.160
for a long, long, long time because the

1306
00:49:37.160 --> 00:49:39.600
resolutions are challenged there. But that

1307
00:49:39.760 --> 00:49:42.120
was a breathtaking thing. And it is worth

1308
00:49:42.120 --> 00:49:44.040
noting that the overwhelming majority of the

1309
00:49:44.040 --> 00:49:46.680
direct imaging planets that we've imaged are

1310
00:49:46.680 --> 00:49:49.240
um, massive and um, young. And the thing

1311
00:49:49.240 --> 00:49:50.600
about them being young is they're still

1312
00:49:50.600 --> 00:49:52.400
hotter, which means they glow brighter and

1313
00:49:52.400 --> 00:49:53.680
therefore are easier to see.

1314
00:49:54.370 --> 00:49:57.250
Andrew Dunkley: M okay, um,

1315
00:49:57.250 --> 00:50:00.080
last chance to talk about exoplanets.

1316
00:50:00.080 --> 00:50:01.960
We're going to wrap it up in a sec. Any, any

1317
00:50:01.960 --> 00:50:02.560
final comments?

1318
00:50:02.800 --> 00:50:05.070
Jonti Horner: Well, I think, I think there is so much more

1319
00:50:05.070 --> 00:50:07.350
we could talk about. I mean like every topic

1320
00:50:07.350 --> 00:50:09.150
we get onto, I talk too much. But we could

1321
00:50:09.150 --> 00:50:10.830
fill several hours worth of excitement

1322
00:50:10.830 --> 00:50:13.150
digging into the nitty gritty. But I think

1323
00:50:13.150 --> 00:50:14.870
the thing that leaps out to me probably even

1324
00:50:14.870 --> 00:50:17.670
more than the ubiquity of planets, the fact

1325
00:50:17.670 --> 00:50:19.590
that they're everywhere, is the diversity.

1326
00:50:19.990 --> 00:50:22.590
You know, when I was growing up, we thought

1327
00:50:22.590 --> 00:50:24.150
that there would be other planetary systems,

1328
00:50:24.150 --> 00:50:25.670
but we weren't sure. But we assumed they'd be

1329
00:50:25.670 --> 00:50:26.990
like the solar system, you know, rocky

1330
00:50:26.990 --> 00:50:28.950
planets on the interior, giant planets on the

1331
00:50:28.950 --> 00:50:31.480
outside. Yeah. And the first planets

1332
00:50:31.480 --> 00:50:33.400
discovered shattered that you had planets

1333
00:50:33.400 --> 00:50:35.520
around a pulsar, which makes no sense.

1334
00:50:36.110 --> 00:50:37.920
Um, we think there are probably a second

1335
00:50:37.920 --> 00:50:39.640
generation of planets. The initial planets

1336
00:50:39.640 --> 00:50:41.320
there were destroyed and new ones formed

1337
00:50:41.320 --> 00:50:43.800
after the supernova, but we're not sure. You

1338
00:50:43.800 --> 00:50:45.640
then found a hot Jupiter, a planet the size

1339
00:50:45.640 --> 00:50:47.320
of Jupiter, going around a star like the sun

1340
00:50:47.320 --> 00:50:49.560
every few days and that was enough to

1341
00:50:49.560 --> 00:50:51.160
revolutionise our understanding of how

1342
00:50:51.160 --> 00:50:53.680
planetary systems form. And with every new

1343
00:50:53.680 --> 00:50:55.440
technique and with every new facility and

1344
00:50:55.440 --> 00:50:58.090
with every new way of finding planets, we

1345
00:50:58.090 --> 00:51:00.530
find planets that are more different to the

1346
00:51:00.530 --> 00:51:02.090
solar system than we could ever possibly

1347
00:51:02.090 --> 00:51:04.810
imagine. The lightest, well, not the

1348
00:51:04.810 --> 00:51:06.530
lightest, the fluffiest planets, the lowest

1349
00:51:06.530 --> 00:51:08.210
density planets are so fluffy that they're

1350
00:51:08.210 --> 00:51:10.250
being torn apart by their stars. We mentioned

1351
00:51:10.250 --> 00:51:13.130
them early on. The highest density

1352
00:51:13.130 --> 00:51:16.010
of any planet in the exoplanet catalogue is

1353
00:51:16.170 --> 00:51:18.530
denser than any metal or mineral or anything

1354
00:51:18.530 --> 00:51:21.190
known on Earth by such a large distance. Uh,

1355
00:51:21.190 --> 00:51:22.730
there is speculation that it could be a

1356
00:51:22.730 --> 00:51:24.450
fragment of a white dwarf or something. That

1357
00:51:24.450 --> 00:51:27.450
it could be actually not a lump

1358
00:51:27.450 --> 00:51:29.730
of iron but a lump of white dwarf material or

1359
00:51:29.730 --> 00:51:32.250
something. We just don't know. And everything

1360
00:51:32.250 --> 00:51:34.490
in between. We're finding that the planets in

1361
00:51:34.490 --> 00:51:37.090
our solar system are pretty

1362
00:51:37.090 --> 00:51:39.730
average. We still don't have a handle on

1363
00:51:40.530 --> 00:51:42.970
how common are planets like the Earth. How

1364
00:51:42.970 --> 00:51:44.810
common are planets on, like the Earth? On

1365
00:51:44.810 --> 00:51:47.090
Earth like orbits. We also don't really have

1366
00:51:47.090 --> 00:51:49.050
a handle yet on how common are ah, planets

1367
00:51:49.050 --> 00:51:50.690
like Jupiter and Saturn, in other words

1368
00:51:50.850 --> 00:51:53.610
called Jupiters planets that take a decade

1369
00:51:53.610 --> 00:51:55.170
um, or more to orbit their star because

1370
00:51:55.170 --> 00:51:56.850
finding them hard you need to watch for a

1371
00:51:56.850 --> 00:51:59.330
long time. So we know much more about planets

1372
00:51:59.330 --> 00:52:01.250
close in and planets very different to our

1373
00:52:01.250 --> 00:52:04.170
own than we do about planet planetary systems

1374
00:52:04.170 --> 00:52:05.730
similar to the solar system. So I think one

1375
00:52:05.730 --> 00:52:08.370
of the big questions now is not is the solar

1376
00:52:08.370 --> 00:52:11.010
system unique but rather how

1377
00:52:11.250 --> 00:52:13.730
unusual or usual is the solar system,

1378
00:52:14.610 --> 00:52:17.370
our planetary systems like our one common or

1379
00:52:17.370 --> 00:52:19.690
are we a bit of an exception? We're not

1380
00:52:19.690 --> 00:52:21.890
really in a position to answer um, that yet.

1381
00:52:21.890 --> 00:52:24.610
It seems that the frequency of

1382
00:52:24.610 --> 00:52:26.530
Jupiter like planets around other stars is

1383
00:52:26.530 --> 00:52:29.450
somewhere between 5 and 20%. And by Jupiter

1384
00:52:29.450 --> 00:52:32.130
like, I mean Jupiter mass on a Jupiter like

1385
00:52:32.130 --> 00:52:34.170
orbit around stars like the sun.

1386
00:52:34.970 --> 00:52:37.370
But that's a big variety of,

1387
00:52:37.770 --> 00:52:39.810
you know, possibilities we just don't know

1388
00:52:39.810 --> 00:52:42.770
yet. And so even though we now

1389
00:52:42.770 --> 00:52:44.090
know that planets are everywhere, we've

1390
00:52:44.090 --> 00:52:46.170
barely scratched the surface. And it's the

1391
00:52:46.170 --> 00:52:47.570
kind of thing where if we had this chat again

1392
00:52:47.570 --> 00:52:49.330
in five years time the numbers would be

1393
00:52:49.330 --> 00:52:51.850
different but there would be whole swathes of

1394
00:52:51.850 --> 00:52:54.250
new knowledge then that we can't even predict

1395
00:52:54.250 --> 00:52:56.130
now. There will be things that surprise us

1396
00:52:56.450 --> 00:52:58.130
just as much in the years to come as hot

1397
00:52:58.130 --> 00:53:00.250
Jupiter's and pulsar planets did at the dawn

1398
00:53:00.250 --> 00:53:02.210
of the era. And that's part of the fun.

1399
00:53:03.170 --> 00:53:05.770
Andrew Dunkley: Yeah, and there'll probably be planets we

1400
00:53:05.770 --> 00:53:08.770
can't even imagine that would

1401
00:53:08.850 --> 00:53:10.650
be discovered that we couldn't have even

1402
00:53:10.650 --> 00:53:13.600
contemplated, contemplated existing.

1403
00:53:14.190 --> 00:53:17.000
Um, and I can't even pretend to make one up

1404
00:53:17.000 --> 00:53:18.920
at the moment. But there will be. Of course

1405
00:53:18.920 --> 00:53:21.360
the search, as you mentioned, is for an Earth

1406
00:53:21.360 --> 00:53:24.130
like planet. A planet, a, uh,

1407
00:53:24.200 --> 00:53:26.840
rocky planet in the right place orbiting a

1408
00:53:26.840 --> 00:53:29.520
star like ours, um, that

1409
00:53:29.840 --> 00:53:31.880
basically duplicates Earth. We just haven't

1410
00:53:31.880 --> 00:53:33.200
found one of those yet, have we?

1411
00:53:33.520 --> 00:53:36.400
Jonti Horner: No, no. With a caveat we may

1412
00:53:36.400 --> 00:53:38.600
have done and it have not been picked up.

1413
00:53:38.600 --> 00:53:40.000
There's more to learn about these things.

1414
00:53:40.230 --> 00:53:43.150
Things I still think of the planets

1415
00:53:43.150 --> 00:53:45.950
we've found so far. Venus is more like the

1416
00:53:45.950 --> 00:53:48.950
Earth than anything we've found so far. I

1417
00:53:48.950 --> 00:53:51.350
also think though, that that's even a

1418
00:53:51.350 --> 00:53:52.990
difficult question because what do we mean by

1419
00:53:52.990 --> 00:53:54.990
it being like the Earth? If you went and

1420
00:53:54.990 --> 00:53:57.350
looked at the solar system 4 billion years

1421
00:53:57.350 --> 00:53:59.510
ago, I don't think you'd have considered the

1422
00:53:59.510 --> 00:54:01.470
Earth an Earth like planet. It would have had

1423
00:54:01.470 --> 00:54:03.190
this incredibly thick atmosphere, very

1424
00:54:03.190 --> 00:54:04.710
different to ours, with a very different

1425
00:54:04.710 --> 00:54:07.440
composition. It would have been outside

1426
00:54:07.440 --> 00:54:09.120
the edge of the habitable zone because the

1427
00:54:09.120 --> 00:54:11.160
sun was that much fainter. But it would

1428
00:54:11.160 --> 00:54:12.640
probably still have liquid water on the

1429
00:54:12.640 --> 00:54:14.080
surface because it had such an intense

1430
00:54:14.080 --> 00:54:17.000
greenhouse effect. So there could

1431
00:54:17.000 --> 00:54:18.920
almost be a philosophical question about how

1432
00:54:18.920 --> 00:54:20.400
long would you consider the Earth to have

1433
00:54:20.400 --> 00:54:21.600
been an Earth like planet?

1434
00:54:22.800 --> 00:54:25.120
Andrew Dunkley: That's a really good point. Yeah. And

1435
00:54:26.000 --> 00:54:28.160
the possibility that we have observed planets

1436
00:54:28.160 --> 00:54:30.200
that just, ah, aren't where we are yet

1437
00:54:30.200 --> 00:54:32.130
because of the time differences in,

1438
00:54:32.930 --> 00:54:35.610
in, in the travel, uh, time of our vision.

1439
00:54:35.610 --> 00:54:38.410
So again, it mightn't be there yet

1440
00:54:38.410 --> 00:54:40.570
and it could be billions of years before it

1441
00:54:40.570 --> 00:54:42.690
is and we won't be around to confirm it.

1442
00:54:42.930 --> 00:54:45.490
There's all sorts of weirdisms that go into

1443
00:54:45.490 --> 00:54:48.090
this. My, the bottom line for me is if they

1444
00:54:48.090 --> 00:54:49.730
find one, it's got to have kangaroos on it.

1445
00:54:49.730 --> 00:54:51.570
Otherwise there's just no Earth like planets.

1446
00:54:51.570 --> 00:54:53.410
Jonti Horner: Oh, absolutely. I mean, would be very

1447
00:54:53.410 --> 00:54:55.490
interesting to imagine kangaroos in space. I

1448
00:54:55.490 --> 00:54:57.970
talk a lot about, um, the Dragonfly mission

1449
00:54:58.040 --> 00:55:00.280
going to Titan, and the fact that Titan is

1450
00:55:00.280 --> 00:55:01.920
the only other body we know of with permanent

1451
00:55:01.920 --> 00:55:03.480
liquid water on the surface. Well, not

1452
00:55:03.480 --> 00:55:05.080
permanent liquid water, permanent liquid on

1453
00:55:05.080 --> 00:55:07.320
the surface. The water there is harder than

1454
00:55:07.320 --> 00:55:09.280
granite frozen solid, but it's got liquid

1455
00:55:09.280 --> 00:55:11.800
methane and Ethernet there. But on Titan,

1456
00:55:12.440 --> 00:55:14.640
unlike on Earth, you could fly under your own

1457
00:55:14.640 --> 00:55:16.440
power. If you strapped a pair of wings on.

1458
00:55:16.600 --> 00:55:18.800
The gravity is low enough in the atmosphere,

1459
00:55:18.800 --> 00:55:21.080
dense enough that you could flap around and

1460
00:55:21.080 --> 00:55:23.720
saw. I have never thought about how a

1461
00:55:23.720 --> 00:55:26.150
kangaroo would react if you took it to Titan.

1462
00:55:26.310 --> 00:55:28.790
It would just, uh, launch itself. Just launch

1463
00:55:28.790 --> 00:55:31.110
itself. Um, it Would, of course, need a very,

1464
00:55:31.110 --> 00:55:33.230
very good space suit because it's so cold

1465
00:55:33.230 --> 00:55:35.030
there and kangaroos are not fans of the cold.

1466
00:55:35.030 --> 00:55:37.070
But, yeah, that would be the shock. If

1467
00:55:37.070 --> 00:55:39.350
Dragonfly hops around, flying around on the

1468
00:55:39.350 --> 00:55:41.710
surface of Titan, and then gets attacked by a

1469
00:55:41.710 --> 00:55:43.310
kangaroo when it comes into land. Like, we

1470
00:55:43.310 --> 00:55:45.030
see some of the videos online of kangaroos

1471
00:55:45.030 --> 00:55:47.110
being territorial. That would be the most

1472
00:55:47.110 --> 00:55:48.950
bizarre discovery of life elsewhere that I

1473
00:55:48.950 --> 00:55:50.800
think I could imagine. Kangaroos on Titan.

1474
00:55:51.430 --> 00:55:53.710
Andrew Dunkley: I wait with bated breath. Although kangaroos,

1475
00:55:53.710 --> 00:55:56.230
uh, do have one particular problem in this

1476
00:55:56.230 --> 00:55:58.230
country. They do not know how to get out of

1477
00:55:58.230 --> 00:56:00.790
the way of a car. Even when they do, they go,

1478
00:56:00.790 --> 00:56:02.430
oh, no, no, hang on, I want to get back in

1479
00:56:02.430 --> 00:56:05.110
front of you. Bang. Okay, see ya. Uh,

1480
00:56:05.110 --> 00:56:07.670
anyway, um, that's our problem. I'm sure it's

1481
00:56:07.670 --> 00:56:09.190
the same in other countries without other

1482
00:56:09.190 --> 00:56:11.710
animals and other planets, probably that

1483
00:56:11.710 --> 00:56:14.630
we're unaware of as yet. Uh, Jonty, that's

1484
00:56:14.870 --> 00:56:17.030
been a lot of fun. It's a, it's a fascinating

1485
00:56:17.030 --> 00:56:19.350
topic and it's one that will keep evolving, I

1486
00:56:19.350 --> 00:56:20.830
think is probably, probably the best way to

1487
00:56:20.830 --> 00:56:22.510
describe it. Thank you so much and we'll

1488
00:56:22.510 --> 00:56:23.470
catch you again real soon.

1489
00:56:23.470 --> 00:56:24.990
Jonti Horner: It's a pleasure and I look forward to it.

1490
00:56:25.790 --> 00:56:28.230
Andrew Dunkley: Professor Jonty Horner from the University of

1491
00:56:28.230 --> 00:56:31.110
Southern Queensland. And thanks, uh, to Huw

1492
00:56:31.110 --> 00:56:32.670
in the studio. Couldn't be with us today.

1493
00:56:32.670 --> 00:56:35.030
Made a fatal error. He's back in hospital. He

1494
00:56:35.030 --> 00:56:37.870
ran into an ex. And, uh, he called

1495
00:56:37.870 --> 00:56:39.150
his ex a planet.

1496
00:56:40.590 --> 00:56:42.590
Think about that. It's terrible. And don't

1497
00:56:42.590 --> 00:56:44.470
forget to visit us online if you dare, at

1498
00:56:44.470 --> 00:56:47.140
spacenutspodcast.com or spacenuts

1499
00:56:47.540 --> 00:56:49.740
IO until next time, thanks for your company.

1500
00:56:49.740 --> 00:56:51.780
We'll see you on the very next episode of

1501
00:56:51.860 --> 00:56:53.020
Space Nuts. Bye.

1502
00:56:53.020 --> 00:56:55.900
Jonti Horner: Bye. You've been listening to

1503
00:56:55.900 --> 00:56:57.380
the Space Nuts podcast,

1504
00:56:58.980 --> 00:57:01.780
available at Apple Podcasts, Spotify,

1505
00:57:02.020 --> 00:57:04.700
iHeartRadio or your favourite podcast

1506
00:57:04.700 --> 00:57:06.420
player. You can also stream on

1507
00:57:06.420 --> 00:57:08.100
demand@bytes.com.

1508
00:57:08.420 --> 00:57:10.500
Andrew Dunkley: this has been another quality podcast

1509
00:57:10.500 --> 00:57:12.330
production from bytes.com.

1510
00:57:12.330 --> 00:57:12.400
Jonti Horner: um,