Cosmic Life Hunt: Delving into Astrobiology Part 2 & the Quest for Extraterrestrial Existence

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Andrew Dunkley: Hi there. Thanks for joining us again. This

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is Space Nuts where we talk astronomy and

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space science and all sorts of other things.

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And over the last, uh, few

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episodes we've been doing some specials

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because Fred Watson's away gallivanting

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around Scotland playing a lot of golf. Not.

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Uh, so we're doing some specials with Jonty

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Horner. Uh, and we're doing part

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two today of

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Astrobiology, a fascinating

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part of astronomy and space science. Uh,

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one area we get so many questions about. So

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stand by as we get into that on this

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episode of space nuts. 15

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seconds.

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Jonti Horner: Guidance is internal. 10,

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9, ignition sequence start.

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Space nuts. 5, 4, 3, 2. 1. 2,

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

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Space nuts.

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Andrew Dunkley: Astronauts report it feels good.

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And back with us again is Johnty Horner,

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professor of astrophysics at the University

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of Southern Queensland. Jonty, hello.

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Jonti Horner: Noon. How are you?

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Andrew Dunkley: I'm m all right. Can you imagine Fred Watson

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playing golf?

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Jonti Horner: No, uh, not sure. I mean, growing up in

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Yorkshire, the weather wasn't always suited

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to it and we were too busy in gravel anyway,

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so.

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Andrew Dunkley: Yeah, took

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a moment. I got that. Yes, yes.

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Uh, used to look clean with the tongues.

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Jonti Horner: Used to have to get up in the morning at 10

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o' clock at night, half an hour before I went

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to bed.

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Andrew Dunkley: It's just one of the best pieces of comedy

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ever.

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Jonti Horner: And it's funny because it's true.

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Yes.

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Andrew Dunkley: Tell the young people that.

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Jonti Horner: They won't believe you.

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Andrew Dunkley: Oh gosh, it's all flooding back. Uh, we've

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got a lot to talk about so we better get

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started.

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Astrobiology Part two. Um,

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a couple of episodes ago we talked

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Astrobiology Part one, surprisingly. Um,

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let's just do a quick review.

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Jonti Horner: Yeah, this is a bit like the bit that really

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annoys you at the start of those multi

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episode shows where they're previously on

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Astrobiology. Um, but

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this is basically a case of Jonty talks too

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much and so therefore we run out of time. I

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mean, we don't need to sugarcoat that. And

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it's always a problem when you're talking

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about something you love and you're

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passionate about that. The time just flies by

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and hopefully it's flying by for the

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listeners as well, rather than boring them to

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tears. But you know, I can't really control

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that. In the first episode

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we talked a fair bit about the fact that

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we've always wondered whether there's life

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elsewhere. We talked a bit about the history

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in particular things like the ideas of

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potentially there being life on Mars that led

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to the panic over the War of the Worlds

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broadcast and the Fact that In the late

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1800s, people were that convinced there

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already was known to be life on Mars, that

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when a major prize was offered for the

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detection of life elsewhere, Mars was

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explicitly excluded because that's too easy,

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you know. So we've had these ideas for a very

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long time, but finding evidence of life

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out there is really, really difficult.

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We've talked a fair bit about the search for

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life within the solar system. You know,

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places like looking at Mars, looking at

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Europa, all the icy moons. And we talk about

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that a lot in the questions that we week by

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week as well on the show.

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And one thing I've always been really

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interested in and passionate about is the

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search for life outside the solar system.

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Given that we've moved into the exoplanet

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era, and we talked a lot about this in the

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previous episode as well, we're now in a

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position where 30 years ago would have seemed

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impossible. Thirty years ago, we'd only just

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found the first planet for under the Stars,

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and only just answered that question of

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whether there are planets at all beyond the

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solar system. Now we're at a position where

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we are finding places that theoretically, in

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the future, we could search to see whether

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there's any evidence of life in those

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planetary systems. And in all honesty,

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despite some of the hyperbolic media

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articles that you sometimes see, we haven't

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yet found a planet that would really look

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like another Earth. But we're getting there,

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we're getting closer, we're getting to

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planets that are more similar to ours in

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size, at more similar distance from their

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stars, and we're learning more about them.

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And it's very feasible then in the next

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decade or so, that we can actually start

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looking to see whether there's any evidence

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of life on those planets. Now, that's a

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little bit separate to looking for signs of

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communicative alien technological

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life, which is a search for extraterrestrial

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intelligence or the search for

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extraterrestrial artefacts. There two areas

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of science that are fascinating, but they're

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more like a search for a needle in a hair

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sack, where we don't even know if there is

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life elsewhere, never mind intelligent life.

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I mean, some people argue whether there's

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intelligent life on Earth looking at the news

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at the minute, but looking for intelligent

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life that has reached certain technological

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level to communicate with us is challenging.

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It's one of those things if we don't know

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what we're looking for, but if we don't look,

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we'll never find it. But it still led to some

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really fascinating research, and there's a

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guy who works with us as part of our Planet

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Search Consortium, a guy called Jason Reutt

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in the US who spent some of his time actually

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thinking about alien megastructures, the

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kind of things that feature so heavily in

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some advanced science fiction, like Larry

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Niven's Ringworld or Dyson Spheres, these

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enormous structures that you can imagine a

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civilization building. If their technologies

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are far above ours, as ours is from the Stone

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Age, the idea that you could build something

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to harness all the material in your planetary

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system m harness all the energy from your

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star. Now, many people argue that while

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that's theoretically possible, it just

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wouldn't be worth the effort. But what

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Jason's been looking into is

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effectively not could people do

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this? But rather if they did, what would it

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look like? So it's not really putting any

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weight on the probability of

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these things existing, but rather saying,

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here are things we could imagine that are

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within the bounds of physical possibility to

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build. Even if they'd be on this

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technologically, what would they look like to

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our different kinds of telescopes? What would

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the signatures be? And, um, that work's

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really important because if you don't have an

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idea what these peculiar objects would look

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like, when you find something unusual, you

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won't have that thing to reference again to

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cheque it out. So both the search for

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extraterrestrial intelligence and the search

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for alien artefacts, a kind of

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a separate splinter of astrobiology that are

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ongoing, that are very precious to us here in

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Australia. Of course, we would have lost the

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Parks Radio telescope under the Liberal

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government in the 2010s in the previous

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decade because they wanted to shut it down

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and demolish it to save money. And it only

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kept going by a large investment

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as part of a project to listen

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for aliens. So, like 40. I remember

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that telescope has been used to search for

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extraterrestrial intelligence in the form of

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radio signals. And that has kept one of our,

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uh, incredible pieces of astronomical

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heritage in Australia. And something

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incredibly precious and beloved has kept it

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going and kept it standing despite the worst

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vagaries of politicians and

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all those challenges.

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Andrew Dunkley: Could you argue that we, uh, have

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already created a

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megastructure around Earth with the number of

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satellites that are currently in orbit and

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the so many thousands more that are going to

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be put up there in the near future?

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Jonti Horner: Certainly feels like that from the inside.

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Looking out. I mean, I'm enjoying all the

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photos. People are, uh, of Comet 2025

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R3 Pan stars at the minute, which behind

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both of us are our attempts. We're showing

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them off. Andrew's ever so proud from his

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attempt last night.

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Andrew Dunkley: My first ever comet.

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Jonti Horner: Fabulous photos that people are getting, but

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I've seen a lot of them getting photobombed

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by Starlink satellites. And I've got. I'm

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currently, thanks to learning something new

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about astrophotography over the last two

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days. I'm going back to images I took of

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Comet Atlas and Comet um, Church in Chan

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Atlas, which were the great comets of 2024

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and 2025 to reprocess those

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images. But one of my abiding Comet Atlas

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was I had this incredible view of it on the

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horizon. Took this long series of photos and

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every single blooming photo was ruined by a

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Starlink satellite because I got a Starlink

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train passing overhead that had recently been

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launched. All of which went straight through

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the middle of the comet and rendered all the

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photos unusable on my only really good clear

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night. Now, I may be able to solve it, but

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that isn't quite at the megastructure stage

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yet for me in that I suspect with the

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level of technology we've got now or in the

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near future, that network of

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satellites around the Earth, uh, wouldn't be

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something we could detect orbiting a planet

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around another star. Right. They're not there

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yet, but they're the forebears of something

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that could be. Now, being that

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they're around a planet rather than a star,

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their signature will be different. And given

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that we are very skilled now at

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broadcasting in one direction rather than

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many, and that broadcasting directionally

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rather than broadcasting the boy band one

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direction should be said, um, broadcasting

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in a directional sense. We are moving towards

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the point where we're going to stop shrieking

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like a screaming infant into the cosmos

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anyway. So it may be that we're going to go

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radio silent fairly soon, and satellites like

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that are going to be part of that journey.

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But I think they are an indication of how

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quickly these things can happen. You know, if

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we were talking a decade ago, we'd have been

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talking about a couple of thousand satellites

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orbiting Earth. We're now talking about

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roughly 50,000. With plants have more than a

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million within the next decade, it's getting

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quite terrifying, actually. As much from the

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atmosphere and climate side of things as

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anything else. You know, if we have a million

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Starlink satellites in orbit in five years or

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10 years time, they have an average lifetime

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of five years, which means we'd have more

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than 500 per day burning up in the

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atmosphere. And that's

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a factor of 100, if not more times

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material entering the atmosphere on a daily

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basis than we get from the background of

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space stuff falling in. We'll be running an

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experiment in atmospheric science that we've

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never run, dumping hundreds of

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tonnes of aluminium into the upper atmosphere

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every day.

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Andrew Dunkley: Yeah, what's the effect going to be? And

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that's the $64,000 question, I suppose.

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Jonti Horner: But now the interesting thing there, coming

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back to the astrobiology, is that might

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well create a signature in the Earth's

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atmosphere that would be detectable

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from observers from around another star.

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Because one of the ways that we would look

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for biosignatures, at least early

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on, will be to look at the light

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from a star reaching us whilst a given

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planet is transiting between us and the star,

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so blocking a bit of that star's light. We

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can currently do this with giant planets,

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Jupiter sized, and a fraction of the light

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from the star passes through the planet's

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atmosphere. And you get imprinted on the

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stars like the chemical fingerprint of the

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constituents of the outer layers of the

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atmosphere where the lights pass through in

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the form of absorption lines. And um, by

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studying them, we can work out some of the

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chemical species that are prevalent there and

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even learn a bit about the structure of the

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atmosphere, the presence of clouds, things

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like that. Now when we get to the point where

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we've got all those satellites burning up in

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our atmosphere, imagining with the kind of

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technology that we're looking at developing

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within the next decade or so, or maybe a

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little bit longer, imagining being on a

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nearby star looking at the sun while the

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Earth is transiting, you're suddenly

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introducing a huge spike of aluminium and

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into the absorption in an Earth like planet's

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atmosphere. And there is no natural way that

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I'm aware of that you could get that.

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So that would not only be a sign of something

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way going on, it would be a bio signature of

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technologically developed life that is not

304
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quite so developed as to have learned that

305
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pollution is bad.

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Andrew Dunkley: Maybe that's how we find an

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intelligent species, uh, beyond Earth.

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They find us first and send us a, you

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know, welcome pack.

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Jonti Horner: Yes. 10 helpful things you can do to fix your

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problems. Stop burning things up in the

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atmosphere.

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Andrew Dunkley: Um, yes, yeah, they may have already

314
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learned that lesson, but um, yeah, okay,

315
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so that's where we're at so far. Where do we

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go from here on the astrobiology

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train?

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Jonti Horner: Well, where we moved to in the latter part of

319
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the last astrobiology episode

320
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was my argument that

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you can't just look at a planet and say it's

322
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at the right temperature in the habitable

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zone. Um, we can look There. Whee.

324
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It kind of feels a bit like that when you

325
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read a lot of storeys, that the only

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consideration that comes into play is how far

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the planet is from its star. And I think

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instead, it's fairer to say that there are a

329
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huge variety of factors that can make

330
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one planet more or less suitable for the

331
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development of life and therefore for the

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observability of life on planets around other

333
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stars. And therefore, given that the

334
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observations to find life are going to be

335
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overwhelmingly the hardest we've ever had to

336
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carry out, we'll have hundreds, if not

337
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thousands of targets to choose from, but

338
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we'll only be able to look at a tiny handful

339
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of them in detail at first. So we need to be

340
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very careful about where we look. The

341
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proximity of the planet and its host star to

342
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the sun will be important because the closer

343
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the star is to a zombie we get for a given

344
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brightness of star, and also the more widely

345
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separated on the sky a star and planet will

346
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be for a given orbital distance between them.

347
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Closer they are, the more widely separated

348
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they are. And while people listening can't

349
00:13:06.620 --> 00:13:08.860
see this, I'm at the minute pointing fingers

350
00:13:08.860 --> 00:13:10.540
up at the side of my eyes to Andrew and then

351
00:13:10.540 --> 00:13:12.340
moving them towards the camera. Fingers are

352
00:13:12.340 --> 00:13:14.180
the same distance apart, but they get wider

353
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and wider apart on the screen as they get

354
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closer. Yeah. So there are clear reasons that

355
00:13:18.340 --> 00:13:21.099
we will look at stars that are nearer to

356
00:13:21.099 --> 00:13:23.740
us rather than further away. But beyond

357
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that, I think it's really important to

358
00:13:25.740 --> 00:13:28.740
consider all the different things that could

359
00:13:28.820 --> 00:13:30.900
factor in to make a given planet more

360
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suitable or less suitable for the

361
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development of life, and view them as like

362
00:13:36.290 --> 00:13:38.850
sliders on a mixing board in a sound studio,

363
00:13:39.170 --> 00:13:41.810
where you can fine tune things to see which

364
00:13:41.810 --> 00:13:43.610
gets the best sound, which gets the best

365
00:13:43.610 --> 00:13:46.490
score. You can rank your targets and

366
00:13:46.490 --> 00:13:48.450
you can start with the most promising ones,

367
00:13:48.450 --> 00:13:50.930
because with limited resources, you don't

368
00:13:50.930 --> 00:13:52.650
just want to do an unbiased survey, you want

369
00:13:52.650 --> 00:13:54.530
to instead maximise your chances of a

370
00:13:54.530 --> 00:13:56.930
positive result. Now, we're heavily biassed.

371
00:13:56.930 --> 00:13:58.890
We only know of one kind of life and that's

372
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Earth life. So we are very biassed towards

373
00:14:01.410 --> 00:14:03.410
looking for places that could support life

374
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like Earth life, because that's the only kind

375
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of life we do know exists that'll factor into

376
00:14:08.310 --> 00:14:10.510
it as well. But in the previous episode,

377
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towards the end, we talked about the way in

378
00:14:12.430 --> 00:14:13.990
which the location in the galaxy could

379
00:14:13.990 --> 00:14:16.510
potentially influence this, with the caveat,

380
00:14:16.510 --> 00:14:17.670
of course, that, uh, we're going to be

381
00:14:17.670 --> 00:14:19.190
looking at everything nearby. So whilst

382
00:14:19.190 --> 00:14:20.870
that's interesting scientifically, it's not

383
00:14:20.870 --> 00:14:23.190
that relevant. And then we also talked about

384
00:14:23.190 --> 00:14:25.430
the way that the nature of the stars that the

385
00:14:25.430 --> 00:14:28.380
planet orbits can influence things. And uh,

386
00:14:28.430 --> 00:14:30.020
not just from the point of view of is a star,

387
00:14:30.020 --> 00:14:32.910
ah, stable or single, but down to more subtle

388
00:14:32.910 --> 00:14:35.070
things like the fact that stars brighten over

389
00:14:35.070 --> 00:14:37.330
time. So just because a planet is in the

390
00:14:37.330 --> 00:14:39.570
habitable zone now doesn't mean it's been in

391
00:14:39.570 --> 00:14:42.090
that zone for long enough for life to become

392
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well established.

393
00:14:42.770 --> 00:14:45.170
So we talked about all that, where we

394
00:14:45.170 --> 00:14:47.610
finished up though we didn't get to my own

395
00:14:48.170 --> 00:14:50.050
personal favourite parts of the science and

396
00:14:50.050 --> 00:14:52.170
the stuff I'm more directly involved with,

397
00:14:52.890 --> 00:14:54.850
which are the more local influences on the

398
00:14:54.850 --> 00:14:57.090
planet, that is the influence of the

399
00:14:57.090 --> 00:14:59.050
planetary system in which that planet moves,

400
00:14:59.050 --> 00:15:00.770
all the other planets and all the debris

401
00:15:00.770 --> 00:15:03.690
therein, but also the impact of the planet

402
00:15:03.690 --> 00:15:06.050
itself, what it's made of, how it behaves.

403
00:15:06.050 --> 00:15:07.830
And there's a lot of subtlety in that that.

404
00:15:08.070 --> 00:15:10.430
When I prepared with my old mentor, Professor

405
00:15:10.430 --> 00:15:12.870
Barry Jones this review article on this 16

406
00:15:12.870 --> 00:15:15.670
years ago now, we dug into and it

407
00:15:15.670 --> 00:15:18.390
highlighted to me how none of these questions

408
00:15:18.390 --> 00:15:20.230
can be answered from people within a single

409
00:15:20.230 --> 00:15:23.030
research silo at all. You need researchers

410
00:15:23.030 --> 00:15:24.670
from all different disciplines of human

411
00:15:24.670 --> 00:15:27.510
experience, from the sciences, the biological

412
00:15:27.510 --> 00:15:29.830
sciences, physical sciences, geosciences,

413
00:15:29.830 --> 00:15:31.830
chemistry and astronomers all to come

414
00:15:31.830 --> 00:15:34.830
together. You probably also need philosophers

415
00:15:34.830 --> 00:15:36.430
and archaeologists to come into the

416
00:15:36.430 --> 00:15:38.280
discussion to talk about, about how we look

417
00:15:38.280 --> 00:15:40.400
and why we look and what we look for. And

418
00:15:40.400 --> 00:15:43.120
that's particularly true when we start moving

419
00:15:43.120 --> 00:15:46.080
from simple life to life that could talk

420
00:15:46.080 --> 00:15:48.560
back to us. And a very dear friend of mine in

421
00:15:48.560 --> 00:15:50.480
Australia who Fred Watson probably knows very

422
00:15:50.480 --> 00:15:52.680
well as well is Professor Alice Gorman down

423
00:15:52.680 --> 00:15:55.280
at Adelaide, who's a space archaeologist and

424
00:15:55.280 --> 00:15:57.680
has given some of the most astonishing and

425
00:15:57.680 --> 00:15:59.480
mind blowing talks I've ever seen from the

426
00:15:59.480 --> 00:16:01.680
point of view of someone who is trained in

427
00:16:01.680 --> 00:16:04.480
archaeology looking at the record of human

428
00:16:04.480 --> 00:16:06.440
space flight and what we should do to

429
00:16:06.440 --> 00:16:08.440
preserve artefacts like the Apollo landing

430
00:16:08.440 --> 00:16:09.980
site for future generations. Generations how

431
00:16:09.980 --> 00:16:11.060
we should consider that

432
00:16:13.300 --> 00:16:14.900
Andrew Dunkley: I absolutely agree because

433
00:16:16.180 --> 00:16:19.100
it was probably one of the

434
00:16:19.100 --> 00:16:21.860
greatest achievements in human history, if

435
00:16:21.860 --> 00:16:23.780
not the greatest achievement in human

436
00:16:23.780 --> 00:16:25.940
history. I mean inventing the wheel probably

437
00:16:25.940 --> 00:16:27.740
would have been a pretty cool thing too, but

438
00:16:27.740 --> 00:16:29.340
I don't know where that happened or when and

439
00:16:29.340 --> 00:16:31.980
they never would have thought to commemorate

440
00:16:31.980 --> 00:16:34.820
it. But um, it is something that

441
00:16:34.820 --> 00:16:37.000
should, should, you know, when we eventually

442
00:16:37.000 --> 00:16:39.480
have permanent residents on the moon,

443
00:16:39.960 --> 00:16:42.200
at least need to put a cyclone fence around

444
00:16:42.200 --> 00:16:44.520
it just for the time being until we can build

445
00:16:45.080 --> 00:16:48.080
a proper structure to protect

446
00:16:48.080 --> 00:16:48.320
it.

447
00:16:48.320 --> 00:16:49.880
Jonti Horner: Probably a good place to have rabbit proof

448
00:16:49.880 --> 00:16:51.960
fence because that will, that'll do the job.

449
00:16:52.400 --> 00:16:55.000
Andrew Dunkley: Um, yeah, well, you know that rabbits will

450
00:16:55.000 --> 00:16:57.600
ultimately be on the moon. They tend to be

451
00:16:57.600 --> 00:16:58.100
everywhere else.

452
00:16:58.100 --> 00:17:00.480
Jonti Horner: Um, now one of the greatest conference talks

453
00:17:00.480 --> 00:17:02.400
ever witnessed actually was a talk by a list

454
00:17:02.400 --> 00:17:03.920
talking about archaeology. And it was from

455
00:17:03.920 --> 00:17:06.730
the education and biases

456
00:17:06.730 --> 00:17:08.290
point of view. And I know this is already a

457
00:17:08.290 --> 00:17:10.290
bit off topic, but it's a storey I think

458
00:17:10.290 --> 00:17:12.370
really well worth repeating. Alice is an

459
00:17:12.370 --> 00:17:14.210
archaeologist and so she teaches archaeology

460
00:17:14.210 --> 00:17:16.850
students and she gave this talk about how she

461
00:17:16.850 --> 00:17:18.770
took a group of her uh, final year students

462
00:17:19.250 --> 00:17:21.410
to this site in Fairlie Regional New South

463
00:17:21.410 --> 00:17:24.250
Wales for a two day dig. Basically go out

464
00:17:24.250 --> 00:17:25.770
there, dig and come back to me with what you

465
00:17:25.770 --> 00:17:27.290
find and tell me about the storey of the

466
00:17:27.290 --> 00:17:29.890
site. And after two days all these

467
00:17:30.130 --> 00:17:31.730
young students came back and said, look, we

468
00:17:31.730 --> 00:17:33.250
didn't really find much, we found a few

469
00:17:33.930 --> 00:17:35.610
Aboriginal artefacts and that's kind of

470
00:17:35.610 --> 00:17:37.210
interesting, but all we found was a load of

471
00:17:37.210 --> 00:17:38.930
rubbish. We found all these blooming cable

472
00:17:38.930 --> 00:17:40.850
ties and bits of plastic that are polluting

473
00:17:40.850 --> 00:17:43.810
the site. What she then went on to do

474
00:17:43.810 --> 00:17:46.210
was the whole point was that the cable ties

475
00:17:46.210 --> 00:17:48.170
were actually the archaeology that she was

476
00:17:48.170 --> 00:17:50.420
interested in. So she went um, on and um,

477
00:17:50.810 --> 00:17:52.490
said in the talk that this was an old

478
00:17:52.490 --> 00:17:54.730
decommissioned listening station that had

479
00:17:54.730 --> 00:17:56.730
been built I think in like the late 1940s,

480
00:17:56.730 --> 00:17:58.610
post World War II, and operated into maybe

481
00:17:58.610 --> 00:18:00.930
the late 60s, early 70s before being

482
00:18:00.930 --> 00:18:03.530
demolished and removed. But by looking at the

483
00:18:03.530 --> 00:18:05.430
cable ties where they'd been identified had

484
00:18:05.900 --> 00:18:08.060
knowing a little bit about how cable ties and

485
00:18:08.060 --> 00:18:10.060
cable tie technology changed over the years,

486
00:18:10.620 --> 00:18:12.820
you could not only map out exactly where all

487
00:18:12.820 --> 00:18:14.380
the buildings had been and where the wire

488
00:18:14.380 --> 00:18:16.300
runs have been and get the structure of this

489
00:18:16.700 --> 00:18:19.620
long vanished building, you could also

490
00:18:19.620 --> 00:18:21.970
work out which bits were built when. And um,

491
00:18:22.220 --> 00:18:24.260
the whole importance here was partly that

492
00:18:24.260 --> 00:18:25.660
whole thing of one man's trash is another

493
00:18:25.660 --> 00:18:28.060
man's treasure, but it's also how

494
00:18:28.620 --> 00:18:30.870
as a scientist and a researcher, uh,

495
00:18:31.520 --> 00:18:34.000
you will miss things and you'll make mistakes

496
00:18:34.000 --> 00:18:36.760
because of your own personal biases that are

497
00:18:36.760 --> 00:18:39.720
quite often unconscious. And in this case for

498
00:18:39.720 --> 00:18:40.920
these students who've been studying

499
00:18:40.920 --> 00:18:43.560
archaeology, their unconscious bias was that

500
00:18:43.560 --> 00:18:46.080
anything modern is not archaeology. That's

501
00:18:46.080 --> 00:18:48.440
rubbish in the way of good archaeology. And

502
00:18:48.440 --> 00:18:50.240
so they totally miss the point. And it's a

503
00:18:50.240 --> 00:18:52.480
fabulous learning thing. It's why as

504
00:18:52.480 --> 00:18:54.680
scientists we use statistics so much. I know

505
00:18:54.680 --> 00:18:56.440
there's all this stuff about you can show

506
00:18:56.440 --> 00:18:58.200
anything with statistics, damn lies and

507
00:18:58.200 --> 00:19:00.160
statistics, all the rest of it. But

508
00:19:00.160 --> 00:19:01.920
fundamentally the reason that we use

509
00:19:01.920 --> 00:19:04.580
statistics as a tool school is because we as

510
00:19:04.580 --> 00:19:06.460
humans are biassed we've got this incredible

511
00:19:06.460 --> 00:19:09.380
evolutionary ability to see patterns when

512
00:19:09.380 --> 00:19:11.780
they're barely there, but we also have a very

513
00:19:11.780 --> 00:19:13.740
strong ability to see patterns that we expect

514
00:19:13.740 --> 00:19:15.580
to see when those patterns aren't actually

515
00:19:15.580 --> 00:19:18.340
there. And, um, that's certainly true of the

516
00:19:18.340 --> 00:19:20.260
canals on Mars. You know, Giovanni

517
00:19:20.260 --> 00:19:23.060
Schiaparelli saw these canals, these

518
00:19:23.060 --> 00:19:25.740
channels on, um, Mars, which I think the best

519
00:19:25.740 --> 00:19:27.660
explanation is that Mars was really bright.

520
00:19:27.660 --> 00:19:29.100
He had a big telescope and he was actually

521
00:19:29.100 --> 00:19:30.740
seeing the projection of his own capillaries

522
00:19:30.740 --> 00:19:33.100
in his eye, like I'm gonna see tomorrow when

523
00:19:33.100 --> 00:19:34.740
I get my eye test at the opticians and they

524
00:19:34.740 --> 00:19:37.060
do the bright light thing. But all these

525
00:19:37.060 --> 00:19:38.900
other observers with less good eyes and less

526
00:19:38.900 --> 00:19:40.860
good telescopes suddenly started seeing the

527
00:19:40.860 --> 00:19:43.660
canals. And it's this

528
00:19:43.660 --> 00:19:45.620
whole thing of when you're really straining

529
00:19:45.620 --> 00:19:47.140
at the limits of your vision, you see what

530
00:19:47.140 --> 00:19:48.820
you think you're going to see, not what there

531
00:19:48.820 --> 00:19:51.540
actually is. And that's true with our data.

532
00:19:51.540 --> 00:19:54.420
Uh, therefore, you use statistics

533
00:19:54.420 --> 00:19:55.900
to give you a feel for whether what you're

534
00:19:55.900 --> 00:19:57.980
seeing is significant or not, or whether it

535
00:19:57.980 --> 00:20:00.260
exists in the first place. And that's a way

536
00:20:00.260 --> 00:20:03.260
of us combating those biases. Now, that wasn'

537
00:20:03.720 --> 00:20:05.440
in that way to the archaeology students who

538
00:20:05.440 --> 00:20:07.160
thought that cable ties were rubbish, but it

539
00:20:07.160 --> 00:20:10.080
was a fabulous reminder of how we really

540
00:20:10.080 --> 00:20:12.320
need to be aware not only of the explicit

541
00:20:12.320 --> 00:20:14.520
biases, which are the things we choose to do.

542
00:20:15.560 --> 00:20:18.320
If they're doing a survey of people on hair

543
00:20:18.320 --> 00:20:20.040
loss and they say we interviewed men between

544
00:20:20.040 --> 00:20:23.040
18 and 30, that's clearly biassed to

545
00:20:23.040 --> 00:20:25.280
be for men between 18 and 30, not for men of

546
00:20:25.280 --> 00:20:27.680
our age, for example. That's an explicit

547
00:20:27.680 --> 00:20:29.400
bias, it's one that's a conscious choice.

548
00:20:29.800 --> 00:20:31.680
Implicit biases are the sneaky ones, where

549
00:20:31.680 --> 00:20:33.770
you don't realise you're making them. And

550
00:20:33.770 --> 00:20:35.650
that's why I've made it so clear up front

551
00:20:35.650 --> 00:20:37.890
here that we can imagine

552
00:20:38.370 --> 00:20:40.690
all kinds of life. Science fiction does it

553
00:20:40.690 --> 00:20:43.460
wonderfully, but our implicit bias is that,

554
00:20:43.460 --> 00:20:44.890
uh, when we talk about the search for life,

555
00:20:44.890 --> 00:20:46.690
at least in the very short term, we're

556
00:20:46.690 --> 00:20:49.049
actually looking for life like us, not you

557
00:20:49.049 --> 00:20:51.890
and I, but lifelike Earth, uh, life based on

558
00:20:51.890 --> 00:20:54.090
a planet with oceans, living on the surface,

559
00:20:54.090 --> 00:20:56.330
modifying the atmosphere, because that's the

560
00:20:56.330 --> 00:20:58.130
one kind of life we know exists, but also

561
00:20:58.690 --> 00:21:00.440
because that's the one kind of life we could

562
00:21:00.440 --> 00:21:02.600
probably identify with our observations. Life

563
00:21:02.600 --> 00:21:05.440
beneath the ice on Europa is fascinating, but

564
00:21:05.440 --> 00:21:07.600
we can't see it in the solar system. We

565
00:21:07.600 --> 00:21:09.880
wouldn't have a prayer if Europa was found

566
00:21:09.880 --> 00:21:11.640
orbiting another star, because the ice is in

567
00:21:11.640 --> 00:21:14.400
the way life on a surface that modifies an

568
00:21:14.400 --> 00:21:16.319
atmosphere is at least something we

569
00:21:16.319 --> 00:21:18.680
theoretically could detect. So that's making

570
00:21:18.680 --> 00:21:20.680
the implicit explicit.

571
00:21:21.800 --> 00:21:23.960
Andrew Dunkley: Gotcha. All right, we're gonna take a breath,

572
00:21:24.300 --> 00:21:27.160
uh, and get back to Astrobiology Part 2

573
00:21:27.560 --> 00:21:29.000
on Space Nuts.

574
00:21:30.520 --> 00:21:32.780
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Jonti Horner: 3, 2, 1

628
00:23:50.360 --> 00:23:51.640
space nuts.

629
00:23:51.960 --> 00:23:54.520
Andrew Dunkley: And you're with Andrew Dunkley and Professor

630
00:23:54.520 --> 00:23:57.080
Jonty Horner okay, what next,

631
00:23:57.080 --> 00:23:59.480
Jonty, in this search for

632
00:23:59.560 --> 00:24:01.000
extraterrestrial life?

633
00:24:01.000 --> 00:24:03.600
Jonti Horner: Well, I think we come back to moving away

634
00:24:03.600 --> 00:24:05.640
from the diversions of archaeology and stuff

635
00:24:05.640 --> 00:24:08.360
to the factors that could make a planet more

636
00:24:08.360 --> 00:24:11.000
or less suitable as a target. And like I

637
00:24:11.000 --> 00:24:12.440
said, we talked about the galaxy, we talked

638
00:24:12.440 --> 00:24:15.320
about the stars. To me, as a person who

639
00:24:15.320 --> 00:24:16.640
comes originally from a solar system

640
00:24:16.640 --> 00:24:18.380
background, particularly fascinated with

641
00:24:18.380 --> 00:24:20.260
comets and asteroids and stuff like that,

642
00:24:21.300 --> 00:24:23.660
there are a lot of factors that have been

643
00:24:23.660 --> 00:24:26.340
proposed that relate to

644
00:24:26.580 --> 00:24:28.460
the interaction of planets and the

645
00:24:28.460 --> 00:24:30.180
interaction with the debris that's around

646
00:24:30.580 --> 00:24:32.420
that could render planets more or less

647
00:24:32.420 --> 00:24:35.300
suitable as targets. Now one

648
00:24:35.300 --> 00:24:37.620
example of this is the stability of orbits.

649
00:24:37.620 --> 00:24:40.020
You know, there are a variety of different

650
00:24:40.340 --> 00:24:42.500
models of the solar system's youth, some of

651
00:24:42.500 --> 00:24:44.100
which suggest that there were periods of

652
00:24:44.340 --> 00:24:46.740
chaotic instability where the planets orbits

653
00:24:46.740 --> 00:24:49.130
got stirred up, planets maybe even swapped

654
00:24:49.440 --> 00:24:51.880
orbits. Now this is the kind of thing we can

655
00:24:51.880 --> 00:24:53.600
model. And when we discover planetary

656
00:24:53.600 --> 00:24:56.480
systems, we can take the planets that we

657
00:24:56.480 --> 00:24:58.840
think are there and put them into computer

658
00:24:58.840 --> 00:25:00.760
software to run their orbits forward and back

659
00:25:00.760 --> 00:25:03.160
in time to see how they behave. And that's

660
00:25:03.160 --> 00:25:05.280
actually part of my day to day work. That's

661
00:25:05.760 --> 00:25:08.400
the technology I use and lots of tools I've

662
00:25:08.400 --> 00:25:10.280
used in the past to kill planetary systems

663
00:25:10.280 --> 00:25:12.400
that people thought were there because I run

664
00:25:12.400 --> 00:25:14.120
simulations and showed they're simply not

665
00:25:14.120 --> 00:25:15.620
stable on very short timescales.

666
00:25:17.130 --> 00:25:18.930
But on longer time scales, these kind of

667
00:25:18.930 --> 00:25:21.930
perturbations can have a significant impact

668
00:25:22.170 --> 00:25:24.730
on the orbits of planets. You can get

669
00:25:24.730 --> 00:25:27.370
significant shifts over time. You can get

670
00:25:27.370 --> 00:25:29.890
encounters and stirring up, which means

671
00:25:29.890 --> 00:25:32.050
sometimes that a planet will be on an orbit

672
00:25:32.050 --> 00:25:34.690
now that is not the orbit it's occupied in

673
00:25:34.690 --> 00:25:37.010
the past. And uh, those are things that we

674
00:25:37.010 --> 00:25:38.650
could probably pull out, tease out from the

675
00:25:38.650 --> 00:25:40.850
simulation kind of work that I do. And

676
00:25:40.850 --> 00:25:42.710
obviously a planet that is now in the

677
00:25:43.340 --> 00:25:45.140
habitable zone, um, but that was previously

678
00:25:45.140 --> 00:25:47.860
well outside it would not be a good place to

679
00:25:47.860 --> 00:25:50.660
look. Even though it looks good now, it's not

680
00:25:50.660 --> 00:25:52.900
great. It's like, I guess, you know, you've

681
00:25:52.900 --> 00:25:54.820
got two petri dishes in front of you that you

682
00:25:54.820 --> 00:25:56.300
could look at for life, but you can tell that

683
00:25:56.300 --> 00:25:58.020
one of them's been absolutely melted in a

684
00:25:58.020 --> 00:26:00.420
fire. It's at room temperature now, but that

685
00:26:00.420 --> 00:26:02.620
doesn't mean it always has been that same

686
00:26:02.620 --> 00:26:04.820
kind of idea. So that on a coarse scale has

687
00:26:04.820 --> 00:26:06.660
an effect. But there's a subtler version of

688
00:26:06.660 --> 00:26:08.660
that that I've done a little bit of work on

689
00:26:08.660 --> 00:26:10.940
in the past. And I've got a PhD student

690
00:26:10.940 --> 00:26:12.560
working with me at the moment minute, who's

691
00:26:12.560 --> 00:26:13.720
going to look into this a lot more. A

692
00:26:13.720 --> 00:26:16.280
wonderful student called Amber Tilly. It's

693
00:26:16.280 --> 00:26:18.040
the idea of the Milankovitch cycles.

694
00:26:19.080 --> 00:26:22.040
Now, on Earth, we

695
00:26:22.120 --> 00:26:24.280
look at climate change in the short term as

696
00:26:24.280 --> 00:26:26.960
being a big problem because it's a very rapid

697
00:26:26.960 --> 00:26:29.000
change that is being caused by human action.

698
00:26:29.480 --> 00:26:32.160
But on much longer timescales, the climate of

699
00:26:32.160 --> 00:26:34.840
Earth is periodically variable. We've had ice

700
00:26:34.840 --> 00:26:37.160
ages and interglacial periods for the last 2

701
00:26:37.160 --> 00:26:39.850
or 3 million years, which are the direct

702
00:26:39.850 --> 00:26:42.290
result of the subtle nudges and tweaks on

703
00:26:42.290 --> 00:26:44.410
the, uh, Earth from all the other objects in

704
00:26:44.410 --> 00:26:46.370
the solar system, primarily the other

705
00:26:46.370 --> 00:26:48.770
planets, and not mainly Jupiter to be honest.

706
00:26:48.770 --> 00:26:51.570
But most of the planets contribute. These are

707
00:26:51.570 --> 00:26:54.170
called the Milankovitch cycles. They have a

708
00:26:54.170 --> 00:26:56.610
number of effects. Firstly, the Earth on its

709
00:26:56.610 --> 00:26:59.490
axis precesses. It wobbles with a period of

710
00:26:59.490 --> 00:27:02.450
about 23,000 years. So our polar

711
00:27:02.450 --> 00:27:04.890
axis, which is tilted by currently 23 and a

712
00:27:04.890 --> 00:27:07.280
half degrees to the plane of our orbit,

713
00:27:07.520 --> 00:27:09.880
wobbles around like a kid's wobbly spinning

714
00:27:09.880 --> 00:27:12.360
toy coming to a stop. It precesses, wobbles

715
00:27:12.360 --> 00:27:13.880
around a bit like the thing in Inception

716
00:27:13.880 --> 00:27:16.000
about to fall over. You see this procession?

717
00:27:16.720 --> 00:27:18.720
That's a procession of the equinoxes. That's

718
00:27:18.720 --> 00:27:20.400
why your horoscopes are wrong. While it's one

719
00:27:20.400 --> 00:27:22.080
of the many reasons that your horoscopes are

720
00:27:22.080 --> 00:27:23.560
wrong, but it's particularly why your

721
00:27:23.560 --> 00:27:26.520
horoscopes are out by one particular one

722
00:27:26.520 --> 00:27:29.440
full calendar month. Because the

723
00:27:29.440 --> 00:27:31.850
horoscopes are based on where the sun is, was

724
00:27:31.850 --> 00:27:34.730
in the sky at that date 2,000 years ago.

725
00:27:35.050 --> 00:27:37.130
And, um, the axis of the Earth has wobbled

726
00:27:37.130 --> 00:27:38.890
round, so it's now one constellation round.

727
00:27:39.610 --> 00:27:42.130
So when the sun is in Aries, according to

728
00:27:42.130 --> 00:27:44.090
your horoscope, it's actually now in Pisces,

729
00:27:45.290 --> 00:27:47.529
all because of the wobble. That wobble takes

730
00:27:47.529 --> 00:27:50.410
23,000 years to complete. That means that

731
00:27:50.410 --> 00:27:52.610
the direction that the Earth is pointing

732
00:27:52.610 --> 00:27:55.570
changes over time. Essentially. Added

733
00:27:55.570 --> 00:27:57.730
to that, you've got a very slight wobble up

734
00:27:57.730 --> 00:27:59.650
and down where the tilt fire axis, which is

735
00:27:59.650 --> 00:28:02.290
currently 23 and a half degrees, changes from

736
00:28:02.290 --> 00:28:04.830
about 22 to, to 24 degrees, rocking back and

737
00:28:04.830 --> 00:28:07.070
forward. So that causes the size of the

738
00:28:07.070 --> 00:28:09.150
Arctic and Antarctic circles to grow and

739
00:28:09.150 --> 00:28:12.150
shrink very slightly. On um, top of all that,

740
00:28:12.150 --> 00:28:13.710
you've then got the Earth's orbit around the

741
00:28:13.710 --> 00:28:16.390
sun flexing and tilting. Its shape

742
00:28:16.390 --> 00:28:18.710
becomes more circular and more elongated,

743
00:28:19.189 --> 00:28:21.670
more eccentric. With a longer period period,

744
00:28:21.670 --> 00:28:23.910
I think about 100,000 years, something like

745
00:28:23.910 --> 00:28:26.310
that, our orbit, compared to the orbits of

746
00:28:26.310 --> 00:28:28.830
Jupiter and Saturn, tilts a little bit up and

747
00:28:28.830 --> 00:28:31.270
down the inclination changes, which adds to

748
00:28:31.270 --> 00:28:33.590
the change of the tilt in our spin axis a

749
00:28:33.590 --> 00:28:36.290
little bit. We also have the Earth's orbit

750
00:28:36.290 --> 00:28:37.930
precessing around in just the same way our

751
00:28:37.930 --> 00:28:39.690
poles do, and that's a little bit harder to

752
00:28:39.690 --> 00:28:42.370
visualise. But what that means is that the

753
00:28:42.530 --> 00:28:45.490
direction, if you drew a line from the sun

754
00:28:45.570 --> 00:28:47.240
through the Earth and out into space at, ah,

755
00:28:47.290 --> 00:28:49.770
the point the Earth was at perihelion closest

756
00:28:49.770 --> 00:28:52.490
to the sun, that direction will

757
00:28:52.490 --> 00:28:54.410
gradually move round over time, doing a full

758
00:28:54.410 --> 00:28:56.490
lap with a period of several tens of

759
00:28:56.490 --> 00:28:58.650
thousands of years. So our perihelion

760
00:28:58.650 --> 00:29:01.360
possession processes as well, all of the,

761
00:29:01.590 --> 00:29:04.390
that combined means that, uh,

762
00:29:04.390 --> 00:29:06.830
on average the amount of energy reaching the

763
00:29:06.830 --> 00:29:08.870
Earth's polar regions, averaged over a given

764
00:29:08.870 --> 00:29:11.870
year, varies with type. Sometimes the

765
00:29:11.870 --> 00:29:13.910
poles get a bit more energy and the ice

766
00:29:14.070 --> 00:29:16.590
sheets retreat. Sometimes they get a bit less

767
00:29:16.590 --> 00:29:18.190
energy and the ice sheets come back towards

768
00:29:18.190 --> 00:29:20.390
the equator again. Now, there's a lot of

769
00:29:20.390 --> 00:29:22.110
complex feedback from the Earth because ice

770
00:29:22.110 --> 00:29:24.830
is more reflective than water or land. So

771
00:29:24.830 --> 00:29:26.750
when ice is growing, it has a tendency to

772
00:29:26.750 --> 00:29:29.320
keep growing, and when it's shrinking, that

773
00:29:29.320 --> 00:29:31.320
has a tendency to run away as well. So you've

774
00:29:31.320 --> 00:29:33.800
got all these different feedbacks. But what

775
00:29:33.800 --> 00:29:35.520
that means is that on the Earth we've got

776
00:29:35.520 --> 00:29:38.480
these periodic variations in the

777
00:29:38.480 --> 00:29:40.160
amount of energy at the poles which lead to

778
00:29:40.160 --> 00:29:42.200
periodic glaciations and interglacial

779
00:29:42.200 --> 00:29:44.680
periods. That's the Milankovitch cycles.

780
00:29:45.240 --> 00:29:47.200
It means that on timescales of tens of

781
00:29:47.200 --> 00:29:49.240
thousands of years, our climate is relatively

782
00:29:49.240 --> 00:29:52.040
changeable. What would

783
00:29:52.040 --> 00:29:54.720
happen if the planets were on different

784
00:29:54.720 --> 00:29:57.630
orbits or if you were in a

785
00:29:57.630 --> 00:29:59.310
planetary system with a totally different

786
00:29:59.310 --> 00:30:01.830
architecture? The result would be very

787
00:30:01.830 --> 00:30:04.590
different Milankovitch cycles. You'd have

788
00:30:04.590 --> 00:30:06.430
different periods and you'd also have

789
00:30:06.430 --> 00:30:08.710
different amplitudes. You could imagine

790
00:30:08.710 --> 00:30:10.710
scenarios where instead of our Earth rocking

791
00:30:10.710 --> 00:30:13.510
a little bit from 22 to 24 degrees and back

792
00:30:13.510 --> 00:30:16.030
with its polar axis, it could be like Mars,

793
00:30:16.030 --> 00:30:18.630
whose spin axis varies chaotically, can even

794
00:30:18.630 --> 00:30:21.470
tip over on its side. You could have systems

795
00:30:21.470 --> 00:30:23.150
where there's barely any change whatsoever.

796
00:30:23.150 --> 00:30:25.840
You've got this full gap. Now the beauty is,

797
00:30:25.840 --> 00:30:28.480
again, we've got the tools to test this.

798
00:30:28.800 --> 00:30:30.640
We can run the kind of computational

799
00:30:30.640 --> 00:30:32.880
simulations that I've spent my career doing

800
00:30:33.120 --> 00:30:35.120
and, uh, model the orbits of a planet over

801
00:30:35.120 --> 00:30:36.640
time under the influence of all the other

802
00:30:36.640 --> 00:30:39.560
planets. And I did a lot of simulations of

803
00:30:39.560 --> 00:30:42.360
this between 2012 and 2020. I

804
00:30:42.360 --> 00:30:44.000
kept coming back to the idea, but never got

805
00:30:44.000 --> 00:30:46.400
around to publishing it until we got to 2020,

806
00:30:46.800 --> 00:30:49.160
where I published it with, um, Stephen Cain

807
00:30:49.160 --> 00:30:51.120
from University of California, Riverside. Pam

808
00:30:51.120 --> 00:30:53.280
Vervoort, who was his PhD student at the

809
00:30:53.280 --> 00:30:55.810
time, a couple of other people, people where

810
00:30:55.810 --> 00:30:58.490
we said, what is the influence of Jupiter on

811
00:30:58.490 --> 00:31:00.210
our Milankovitch cycles? What would happen if

812
00:31:00.210 --> 00:31:02.250
you move Jupiter closer to the sun or further

813
00:31:02.250 --> 00:31:04.970
away? If you made Jupiter's

814
00:31:04.970 --> 00:31:07.530
orbit more eccentric or less eccentric, how

815
00:31:07.530 --> 00:31:09.350
would that change the period and, um,

816
00:31:09.350 --> 00:31:11.210
amplitude of the Earth's? Milankovic cycles

817
00:31:12.170 --> 00:31:14.090
did the test. And in many cases, moving

818
00:31:14.090 --> 00:31:16.090
Jupiter destroyed the solar system, which

819
00:31:16.090 --> 00:31:18.250
meant the Earth wouldn't be here, which was

820
00:31:18.250 --> 00:31:21.010
kind of fun, but not very helpful. But for

821
00:31:21.010 --> 00:31:22.870
the versions of the solar system where the,

822
00:31:23.100 --> 00:31:26.060
the Earth was not removed, we got to see

823
00:31:26.060 --> 00:31:28.580
the range, the variety of Milankovitch cycles

824
00:31:28.580 --> 00:31:31.300
we would have from moving Jupiter in a bit

825
00:31:31.300 --> 00:31:33.060
closer or moving it a bit further away. And

826
00:31:33.060 --> 00:31:34.940
for those really interested, we moved Jupiter

827
00:31:34.940 --> 00:31:37.740
in as far as 3 Au from the sun, out as far as

828
00:31:37.740 --> 00:31:40.020
7 Au from the sun, where 5 Au is about where

829
00:31:40.020 --> 00:31:42.780
it is at the minute, 5.2. What we

830
00:31:42.780 --> 00:31:44.900
found, which is quite surprising, is that the

831
00:31:44.900 --> 00:31:46.860
Earth's, uh, Milankovitch cycles are neither

832
00:31:47.180 --> 00:31:49.020
unusually big or unusually small. They're

833
00:31:49.020 --> 00:31:50.810
somewhere in the middle. Middle. Which is a

834
00:31:50.810 --> 00:31:52.610
bit of an argument against a hypothesis

835
00:31:52.610 --> 00:31:55.090
called the Rare Earth hypothesis.

836
00:31:55.570 --> 00:31:58.376
This idea has been around for about 20, 25,

837
00:31:58.470 --> 00:32:01.330
30 years, and I've never really liked it.

838
00:32:01.330 --> 00:32:04.330
It's the idea that life on Earth is such a

839
00:32:04.330 --> 00:32:07.090
remarkable, incredible fluke

840
00:32:07.650 --> 00:32:09.730
that we will never find life elsewhere. And

841
00:32:09.730 --> 00:32:11.650
the authors put forward all these

842
00:32:11.650 --> 00:32:13.810
peculiarities about the Earth, uh, and argue

843
00:32:13.810 --> 00:32:15.970
that without them we would not be here.

844
00:32:16.900 --> 00:32:18.980
And it's a bit of a philosophical thing, but

845
00:32:19.300 --> 00:32:21.180
I think it's very dangerous to look at

846
00:32:21.180 --> 00:32:23.620
somewhere that has life and say, this place

847
00:32:23.620 --> 00:32:25.420
has all these unusual things and they are

848
00:32:25.420 --> 00:32:27.100
therefore required for life because we've

849
00:32:27.100 --> 00:32:29.820
never found life elsewhere. A good example is

850
00:32:29.820 --> 00:32:31.260
the presence of a large moon. And we'll talk

851
00:32:31.260 --> 00:32:33.580
about this a bit more later on. We have life

852
00:32:33.580 --> 00:32:35.380
on Earth and we have a big moon, so it's

853
00:32:35.380 --> 00:32:37.220
natural to think you need a big moon to have

854
00:32:37.220 --> 00:32:39.780
life. But we won't know that until we find

855
00:32:39.780 --> 00:32:42.380
life elsewhere. But that led to this argument

856
00:32:42.380 --> 00:32:44.500
of rare Earth life will be uncommon in the

857
00:32:44.500 --> 00:32:47.060
universe. If rare Earth were true,

858
00:32:47.460 --> 00:32:48.940
then when you look at something like the

859
00:32:48.940 --> 00:32:50.900
Milankovitch cycles, you would expect our

860
00:32:50.900 --> 00:32:52.820
Earth to be unusual in some way,

861
00:32:54.020 --> 00:32:56.660
to have conditions that favour life over your

862
00:32:56.660 --> 00:32:59.380
typical system. And we simply don't find that

863
00:32:59.380 --> 00:33:01.419
our Milankovitch cycles are fairly run of the

864
00:33:01.419 --> 00:33:03.220
mill. They're not big, they're not small,

865
00:33:03.220 --> 00:33:06.140
they're not fast. They're not slow, they're

866
00:33:06.140 --> 00:33:08.020
somewhere in the middle. Now,

867
00:33:08.810 --> 00:33:11.420
um, sorry, Pam went with that. Pam lava vault

868
00:33:11.420 --> 00:33:11.580
was.

869
00:33:11.580 --> 00:33:13.460
She then took the output of that and run it

870
00:33:13.460 --> 00:33:15.780
into climate modelling software, which was

871
00:33:15.780 --> 00:33:17.480
fabulous. And she published that work, work

872
00:33:17.480 --> 00:33:20.360
with us in 2022, where

873
00:33:20.360 --> 00:33:22.400
she was able to link the Milankovitch cycles.

874
00:33:22.400 --> 00:33:24.400
We predicted if you moved Jupiter around

875
00:33:25.360 --> 00:33:28.200
with the amplitude and frequency of the

876
00:33:28.200 --> 00:33:29.960
ice ages, we'd get. And it was really

877
00:33:29.960 --> 00:33:31.240
interesting because it turned out that when

878
00:33:31.240 --> 00:33:33.680
you factor in some of the feedback mechanisms

879
00:33:33.680 --> 00:33:35.840
that are in climate modelling, you actually

880
00:33:35.840 --> 00:33:37.840
could change the Earth's Milkovitch cycles a

881
00:33:37.840 --> 00:33:39.880
little bit and get very drastically different

882
00:33:39.880 --> 00:33:42.560
ice ages, much more frequent and shallower,

883
00:33:42.560 --> 00:33:45.280
or much less frequent and deeper just by

884
00:33:45.280 --> 00:33:47.800
small changes. Now, now, it's all

885
00:33:47.800 --> 00:33:49.560
fascinating just from the solar system point

886
00:33:49.560 --> 00:33:51.880
of view, but what we're really doing is we're

887
00:33:51.880 --> 00:33:54.520
putting down tools that when we find

888
00:33:54.520 --> 00:33:56.840
planets that could be suitable, we can do

889
00:33:56.840 --> 00:33:58.920
these same tests. We can look at them and

890
00:33:58.920 --> 00:34:00.480
say, we're thinking that you might be a

891
00:34:00.480 --> 00:34:02.600
target for life. Let's see what your

892
00:34:02.600 --> 00:34:04.360
Melankovic cycles are like. Let's see how

893
00:34:04.360 --> 00:34:06.920
stable your climate is. And if we find

894
00:34:06.920 --> 00:34:09.120
somewhere that flops between snowball Earth

895
00:34:09.120 --> 00:34:12.080
and a hothouse every 10 years, or that has

896
00:34:12.080 --> 00:34:13.960
incredibly long snowball Earth periods

897
00:34:13.960 --> 00:34:15.960
followed by short periods of temperate

898
00:34:15.960 --> 00:34:18.039
climate climate, even though everything else

899
00:34:18.039 --> 00:34:19.610
looks good, that's probably not as, uh,

900
00:34:19.679 --> 00:34:21.959
suitable for life as somewhere that is

901
00:34:21.959 --> 00:34:24.239
temperate all the time. So we can use that as

902
00:34:24.239 --> 00:34:26.519
a bit of a filter. And that's where the new

903
00:34:26.519 --> 00:34:28.519
PhD student we've got, Amber Tilly, comes in.

904
00:34:28.519 --> 00:34:30.039
Amber's, um, going to be doing the same kind

905
00:34:30.039 --> 00:34:32.399
of work, moving it forward, where she's going

906
00:34:32.399 --> 00:34:33.999
to be looking at a whole slew of different

907
00:34:33.999 --> 00:34:36.799
parameters to see how the

908
00:34:36.799 --> 00:34:39.279
Milankovitch cycles change as you vary

909
00:34:39.279 --> 00:34:41.479
things. She's both going to look at what

910
00:34:41.479 --> 00:34:42.919
would happen if the Earth was a bit more

911
00:34:42.919 --> 00:34:44.599
massive or less massive. How would that

912
00:34:44.599 --> 00:34:46.799
change things? Because of the feedback, you

913
00:34:46.799 --> 00:34:48.149
make Earth more massive, it interacts,

914
00:34:48.219 --> 00:34:49.859
interacts more with other things, stirs them

915
00:34:49.859 --> 00:34:52.739
up, you get a feedback there. She's also

916
00:34:52.739 --> 00:34:54.339
going to look, working with colleagues of

917
00:34:54.339 --> 00:34:57.139
ours overseas, at, uh, models of planet

918
00:34:57.139 --> 00:34:59.739
formation that form planetary systems similar

919
00:34:59.739 --> 00:35:02.539
to the solar system as theoretical

920
00:35:02.539 --> 00:35:04.739
data, and say, what would the Milankovitch

921
00:35:04.739 --> 00:35:07.019
cycles be like in this hypothetical system?

922
00:35:07.499 --> 00:35:09.419
So it's not just a purely hypothetical

923
00:35:09.419 --> 00:35:10.859
question, it's something we can actually dig

924
00:35:10.859 --> 00:35:13.659
into and, um, we can test. And I think

925
00:35:13.659 --> 00:35:15.379
that's fundamental to science. It's no good

926
00:35:15.379 --> 00:35:16.779
just arguing something you want to be able to

927
00:35:16.779 --> 00:35:17.520
Test. Test it.

928
00:35:18.480 --> 00:35:21.120
Andrew Dunkley: Yeah. I suppose what you're suggesting is

929
00:35:21.360 --> 00:35:24.000
that by mucking around with

930
00:35:24.960 --> 00:35:27.640
what we know and making slight alterations,

931
00:35:27.640 --> 00:35:30.600
it gives you an idea of what to look

932
00:35:30.600 --> 00:35:33.560
for going forward in identifying

933
00:35:33.560 --> 00:35:34.640
potential targets.

934
00:35:34.880 --> 00:35:37.520
Jonti Horner: Absolutely. And it's good because one of the

935
00:35:37.520 --> 00:35:39.080
reasons that you'd want to use the Earth is

936
00:35:39.080 --> 00:35:41.600
because we've got a ground truth. You can run

937
00:35:41.600 --> 00:35:43.080
the Earth with the current solar system

938
00:35:43.080 --> 00:35:45.080
parameters and put them into a climate model.

939
00:35:45.080 --> 00:35:47.530
And you should get what we see so we can

940
00:35:47.530 --> 00:35:49.130
ground truth it, which is really, really

941
00:35:49.130 --> 00:35:51.850
important. And, um, that is, I think, one of

942
00:35:51.850 --> 00:35:54.130
the main, most obvious ways where even in a

943
00:35:54.130 --> 00:35:56.010
dynamically stable system, a system that

944
00:35:56.010 --> 00:35:58.890
isn't tearing itself apart, interaction

945
00:35:58.890 --> 00:36:00.530
between planets could have a significant

946
00:36:00.610 --> 00:36:03.130
impact on habitability. And we want to look

947
00:36:03.130 --> 00:36:05.010
into it. It's really, really fascinating.

948
00:36:06.050 --> 00:36:08.930
Andrew Dunkley: Indeed it is. All right, um, we

949
00:36:08.930 --> 00:36:11.810
are talking astrobiology on this

950
00:36:11.970 --> 00:36:14.770
special episode of Space Nuts with Professor

951
00:36:14.770 --> 00:36:15.890
Jonty Horner.

952
00:36:15.890 --> 00:36:16.370
Back in.

953
00:36:19.310 --> 00:36:21.270
Okay, we checked all four systems and

954
00:36:21.270 --> 00:36:23.070
Jonti Horner: being with a go, space nets.

955
00:36:23.310 --> 00:36:25.950
Andrew Dunkley: Jody, I thought we might just start off

956
00:36:25.950 --> 00:36:28.670
this, uh, final segment with a

957
00:36:28.750 --> 00:36:30.910
question from the audience. Uh, it's funny

958
00:36:30.910 --> 00:36:33.590
because this question's come in before any of

959
00:36:33.590 --> 00:36:36.590
these astrobiology episodes have

960
00:36:36.590 --> 00:36:39.310
been released. And yet it's

961
00:36:39.310 --> 00:36:41.510
exactly what we've been talking about. This

962
00:36:41.510 --> 00:36:42.750
comes from Chris.

963
00:36:42.910 --> 00:36:45.630
Jonti Horner: Hi, um, I'm Chris from Axmouth in the uk.

964
00:36:46.270 --> 00:36:48.110
I'd, uh, just like to ask, um, given that

965
00:36:48.110 --> 00:36:50.690
interstellar travel to distance solar systems

966
00:36:50.690 --> 00:36:52.970
is likely to remain impractical for humans,

967
00:36:53.540 --> 00:36:55.770
um, do you think a more realistic long term

968
00:36:55.770 --> 00:36:56.970
strategy would be to

969
00:36:57.050 --> 00:36:58.970
Andrew Dunkley: seed the galaxy with the basic building

970
00:36:58.970 --> 00:37:01.690
blocks of life? Uh, for example,

971
00:37:01.860 --> 00:37:04.050
uh, sending autonomous probes carrying

972
00:37:04.050 --> 00:37:06.530
microbes or prebiotic material that could

973
00:37:06.530 --> 00:37:08.490
Jonti Horner: eventually take hold on suitable planets,

974
00:37:08.890 --> 00:37:09.210
even

975
00:37:09.210 --> 00:37:11.450
Andrew Dunkley: if that process takes thousands or millions

976
00:37:11.450 --> 00:37:11.930
of years.

977
00:37:12.490 --> 00:37:12.970
Jonti Horner: Thanks.

978
00:37:14.330 --> 00:37:16.380
Andrew Dunkley: There's a, uh, thought from Chris. So

979
00:37:17.420 --> 00:37:19.420
he's probably suggesting, you know, could we

980
00:37:19.420 --> 00:37:22.260
seed other planets? Uh, would that be

981
00:37:22.260 --> 00:37:24.780
the way to go? Uh, and autonomous,

982
00:37:25.060 --> 00:37:27.980
uh, vehicles. I think last

983
00:37:27.980 --> 00:37:29.580
time we talked about this a couple of

984
00:37:29.580 --> 00:37:32.300
episodes ago, you, you suggested it's,

985
00:37:32.300 --> 00:37:34.860
it's beyond us to actually

986
00:37:34.940 --> 00:37:37.860
send a human mission to another world

987
00:37:37.860 --> 00:37:40.860
to investigate life. But we could

988
00:37:41.340 --> 00:37:43.580
go the way of autonomous vehicles.

989
00:37:44.200 --> 00:37:46.720
Uh, but for the major

990
00:37:47.760 --> 00:37:50.730
distances, like the impossible distances, uh,

991
00:37:50.730 --> 00:37:53.240
we would have to come up with equipment in

992
00:37:53.240 --> 00:37:56.200
the future that could do it from a

993
00:37:56.200 --> 00:37:58.750
stable environment nearby. Um,

994
00:37:59.120 --> 00:38:00.440
I don't know how you want to tackle that

995
00:38:00.440 --> 00:38:00.720
question.

996
00:38:01.200 --> 00:38:02.600
Jonti Horner: There's a fair bit to it, and I mean, it

997
00:38:02.600 --> 00:38:05.200
reminds me of the wonderful Bobbyverse books

998
00:38:05.200 --> 00:38:07.160
that I've quite enjoyed. You know, um, the

999
00:38:07.160 --> 00:38:09.400
Storey of the Self Intelligent Von Neumann

1000
00:38:09.400 --> 00:38:11.800
probes, which are, uh, easy listening and

1001
00:38:11.800 --> 00:38:13.360
work very well as audiobooks.

1002
00:38:14.560 --> 00:38:17.440
It's a challenging one. So we could

1003
00:38:17.520 --> 00:38:20.400
do this. It would be feasible.

1004
00:38:20.560 --> 00:38:22.440
The question would become whether it's

1005
00:38:22.440 --> 00:38:25.440
ethical and right. Yes, and that's a really

1006
00:38:25.440 --> 00:38:27.520
challenging one. Now, there is something that

1007
00:38:27.520 --> 00:38:30.400
costs research missions

1008
00:38:30.480 --> 00:38:32.920
a vast amount of money called planetary

1009
00:38:32.920 --> 00:38:35.640
protection. And it's the idea that if we're

1010
00:38:35.640 --> 00:38:37.880
sending a spacecraft that has a possibility

1011
00:38:37.880 --> 00:38:40.870
of touching down on a place where we are

1012
00:38:40.870 --> 00:38:42.870
currently interested in looking for life,

1013
00:38:42.870 --> 00:38:45.550
where there could be life, such as Mars, such

1014
00:38:45.550 --> 00:38:48.030
as Europa, uh, Ganymede, Titan, around

1015
00:38:48.030 --> 00:38:50.910
Saturn. We don't want to take life with

1016
00:38:50.910 --> 00:38:52.630
us because you don't want to find life on

1017
00:38:52.630 --> 00:38:54.630
Mars only to discover it's what you took with

1018
00:38:54.630 --> 00:38:56.550
you. And also we don't want to pollute or

1019
00:38:56.550 --> 00:38:59.190
contaminate those environments. So there's a

1020
00:38:59.190 --> 00:39:01.750
huge amount of effort and expense, goes into

1021
00:39:02.070 --> 00:39:04.590
extreme sterilisation of spacecraft to kind

1022
00:39:04.590 --> 00:39:06.950
of prevent exactly the hypothesis being

1023
00:39:06.950 --> 00:39:08.870
discussed here. At the same time,

1024
00:39:09.870 --> 00:39:12.750
that idea of populating the galaxy with

1025
00:39:12.750 --> 00:39:15.430
simple life that could one day grow

1026
00:39:15.430 --> 00:39:18.110
to resemblers or something else has

1027
00:39:18.110 --> 00:39:20.270
cropped a few times in science fiction. I

1028
00:39:20.270 --> 00:39:23.110
believe that was how Star Trek got

1029
00:39:23.110 --> 00:39:25.910
around the fact that all of their humanoid

1030
00:39:25.910 --> 00:39:27.870
species looked like people with makeup on.

1031
00:39:28.390 --> 00:39:30.790
Um, which of course is a budgetary issue and

1032
00:39:30.790 --> 00:39:32.790
a special effects issue. But they had an

1033
00:39:32.790 --> 00:39:34.390
episode where people found the founders,

1034
00:39:34.390 --> 00:39:37.090
which were an alien, ancient alien humanoid

1035
00:39:37.090 --> 00:39:39.570
race at seed of the galaxy. And billions of

1036
00:39:39.570 --> 00:39:41.290
years later all these different planets had

1037
00:39:41.290 --> 00:39:43.530
grown humanoids that looked like them and.

1038
00:39:43.530 --> 00:39:46.050
Oh, well, convenient job done. Stop asking us

1039
00:39:46.050 --> 00:39:48.970
that question now, please. Effectively it

1040
00:39:48.970 --> 00:39:51.410
is something we could do and the timescales

1041
00:39:51.410 --> 00:39:53.250
would be immense. It's also something that,

1042
00:39:53.650 --> 00:39:55.930
in all honesty, has already happened. There's

1043
00:39:55.930 --> 00:39:58.610
this idea called panspermia, which is the

1044
00:39:58.610 --> 00:40:00.450
idea that life could be transferred through

1045
00:40:00.450 --> 00:40:02.570
space from planet to planet, carried by

1046
00:40:02.570 --> 00:40:05.450
debris from impacts and talking. Thirty or

1047
00:40:05.450 --> 00:40:07.310
40 years ago, it was viewed as very much

1048
00:40:07.310 --> 00:40:09.750
crank science, not feasible. But every

1049
00:40:09.750 --> 00:40:11.390
experiment that people have ever done

1050
00:40:11.470 --> 00:40:13.430
suggests that it could work. And I've even

1051
00:40:13.430 --> 00:40:15.630
had a PhD student just submit his thesis,

1052
00:40:16.030 --> 00:40:18.430
Greg Davis, who has been looking at this

1053
00:40:19.150 --> 00:40:20.950
from the point of view of the viability of

1054
00:40:20.950 --> 00:40:23.790
bacteria transferred from Earth to Mars or

1055
00:40:23.790 --> 00:40:26.510
Mars to Earth in the radiation environment in

1056
00:40:26.510 --> 00:40:27.950
the solar system. And it seems to work.

1057
00:40:29.470 --> 00:40:31.650
Now, to me, the fact that biological, uh,

1058
00:40:32.310 --> 00:40:34.270
material from Earth will have rained down on

1059
00:40:34.270 --> 00:40:36.230
Mars and Europa and Ganymede and everywhere

1060
00:40:36.230 --> 00:40:38.270
else for the last 4 billion years

1061
00:40:39.030 --> 00:40:40.990
probably means that we're being a bit over

1062
00:40:40.990 --> 00:40:43.190
cautious with our planet protection efforts

1063
00:40:43.190 --> 00:40:45.230
because we're trying not to take something

1064
00:40:45.230 --> 00:40:47.310
there when it's already there, it's already

1065
00:40:47.310 --> 00:40:49.310
been delivered. The other thing is that

1066
00:40:49.310 --> 00:40:51.150
anything we take with us to a place that has

1067
00:40:51.150 --> 00:40:52.790
an incredibly, incredibly different

1068
00:40:52.790 --> 00:40:55.230
environment, if there is life there already,

1069
00:40:55.230 --> 00:40:57.470
that life should hugely outcompete anything

1070
00:40:57.470 --> 00:40:59.150
we take with us because it's better adapted

1071
00:40:59.150 --> 00:41:01.590
for that environment. And that would be one

1072
00:41:01.590 --> 00:41:03.310
of the challenges with this, is sending stuff

1073
00:41:03.310 --> 00:41:05.270
out. It'd have to be lucky to get exactly the

1074
00:41:05.270 --> 00:41:06.630
right environment to grow. But with the

1075
00:41:06.630 --> 00:41:09.270
amount of real estate we've got out there it

1076
00:41:09.270 --> 00:41:12.190
could happen. People have even in some more

1077
00:41:12.190 --> 00:41:15.070
extreme sci fi suggested kind of

1078
00:41:15.310 --> 00:41:18.230
this type approach as a way to

1079
00:41:18.230 --> 00:41:20.350
begin terraforming planets ahead of human

1080
00:41:20.350 --> 00:41:21.990
arrival. This idea that you could send

1081
00:41:21.990 --> 00:41:24.670
generation ships which have to go

1082
00:41:24.830 --> 00:41:26.510
slowly because they're really big and carry a

1083
00:41:26.510 --> 00:41:28.190
lot of people. But you could send faster

1084
00:41:28.190 --> 00:41:31.030
moving, smaller things first to start

1085
00:41:31.030 --> 00:41:33.030
working on the biosphere of a planet to make

1086
00:41:33.030 --> 00:41:35.670
it so that when we get there that planet is a

1087
00:41:35.670 --> 00:41:37.230
suitable home. So there's a lot of ways it

1088
00:41:37.230 --> 00:41:40.170
could be taken. Taken. I think to do it

1089
00:41:40.170 --> 00:41:42.930
in the near future in an official organised

1090
00:41:42.930 --> 00:41:44.970
way would require a significant shift in

1091
00:41:44.970 --> 00:41:46.890
global morality in the way we think about

1092
00:41:47.130 --> 00:41:49.770
other habitats. If we found that

1093
00:41:49.770 --> 00:41:52.610
Mars absolutely has no life and

1094
00:41:52.610 --> 00:41:54.570
possibly that it never had life, which I

1095
00:41:54.570 --> 00:41:56.850
think is probably unlikely, then I could see

1096
00:41:56.850 --> 00:41:58.890
people arguing then for terraforming.

1097
00:41:58.890 --> 00:42:00.690
Similarly people have argued about, I think

1098
00:42:00.690 --> 00:42:03.290
Carl Sagan suggested this, creating

1099
00:42:03.530 --> 00:42:06.190
engineering bacteria that could float in the

1100
00:42:06.190 --> 00:42:08.750
clouds of Venus and um, precipitate out the

1101
00:42:08.750 --> 00:42:10.910
carbon to eventually make Venus a more

1102
00:42:11.150 --> 00:42:13.270
habitable planet on long timescales. The idea

1103
00:42:13.270 --> 00:42:15.790
of terraforming these worlds is real. But I

1104
00:42:15.790 --> 00:42:18.790
think it would require either a state

1105
00:42:18.790 --> 00:42:21.070
to go its own way because as we know, once

1106
00:42:21.070 --> 00:42:22.830
things are up in space, ain't nobody going to

1107
00:42:22.830 --> 00:42:24.950
stop you. Uh, as was the case with the

1108
00:42:24.950 --> 00:42:27.390
Israeli spacecraft that spattered tamigards,

1109
00:42:27.820 --> 00:42:29.750
um, water bears over the moon to show that

1110
00:42:29.750 --> 00:42:32.590
they could, which was so dumb it's untrue.

1111
00:42:33.160 --> 00:42:36.070
Um, yep, there are water bears on the moon,

1112
00:42:36.390 --> 00:42:38.310
probably desiccated and dried up, but they

1113
00:42:38.310 --> 00:42:40.390
can come back from that, we know that. Um, so

1114
00:42:40.390 --> 00:42:42.110
you could have a nation just decide to do it

1115
00:42:42.110 --> 00:42:44.630
anyway. At the end of the day, if a

1116
00:42:44.630 --> 00:42:46.670
random government decided to send a

1117
00:42:46.670 --> 00:42:49.430
spacecraft to Mars within a capsule inside

1118
00:42:49.590 --> 00:42:52.150
laden with biological bacterial life

1119
00:42:52.390 --> 00:42:55.230
to spurt out on the surface, no way we could

1120
00:42:55.230 --> 00:42:57.860
stop them. And once it's done, it's done. Um,

1121
00:42:57.990 --> 00:43:00.510
but I think the block to the question is not

1122
00:43:00.510 --> 00:43:02.070
actually a scientific one, it's an ethical

1123
00:43:02.070 --> 00:43:04.460
one and it's about how we, we choose to

1124
00:43:04.460 --> 00:43:06.300
interact with the galaxy going forward and

1125
00:43:06.300 --> 00:43:08.300
particularly our local environment. That'll

1126
00:43:08.300 --> 00:43:10.020
determine at what stage we do that, if we

1127
00:43:10.020 --> 00:43:11.380
ever do so. It's a really good question.

1128
00:43:12.100 --> 00:43:14.700
Andrew Dunkley: It is. Uh, thanks for the uh, question,

1129
00:43:14.700 --> 00:43:16.660
Chris. Uh, Chris, you might be interested to

1130
00:43:16.660 --> 00:43:19.299
look up the BBC radio science

1131
00:43:19.299 --> 00:43:22.060
fiction comedy called Paradise Lost in Space.

1132
00:43:22.060 --> 00:43:24.900
Have you heard of this one? It's so funny.

1133
00:43:24.900 --> 00:43:27.860
It's about two blokes who um, get ejected

1134
00:43:28.180 --> 00:43:30.620
from a spaceship by an exploding toilet or

1135
00:43:30.620 --> 00:43:32.940
something and they end up on a world that's

1136
00:43:32.940 --> 00:43:35.570
occupied by uh, an insect, intelligent but

1137
00:43:35.570 --> 00:43:38.210
very naive species. So

1138
00:43:38.690 --> 00:43:41.170
basically what they do is they try to

1139
00:43:41.650 --> 00:43:44.210
pass on their Earth knowledge and

1140
00:43:44.210 --> 00:43:46.130
intelligence to these, these people

1141
00:43:46.930 --> 00:43:48.930
and ultimately destroy the planet.

1142
00:43:50.850 --> 00:43:51.730
Jonti Horner: It's a perfect reflection.

1143
00:43:51.970 --> 00:43:52.330
Andrew Dunkley: Brilliant.

1144
00:43:52.330 --> 00:43:53.890
Jonti Horner: It's very funny. Yes.

1145
00:43:55.330 --> 00:43:58.290
Andrew Dunkley: Yeah, it's funny stuff. So yeah, it's called

1146
00:43:58.470 --> 00:44:01.450
um, Paradise Lost in Space. I

1147
00:44:01.450 --> 00:44:03.290
only remember it because we ran it as a

1148
00:44:03.290 --> 00:44:05.850
series on the ABC some years ago and, and got

1149
00:44:05.850 --> 00:44:08.530
a uh, fabulous response. And I always,

1150
00:44:08.610 --> 00:44:10.410
I sat there in the studio while we were

1151
00:44:10.410 --> 00:44:12.930
running it and I just cackled as to. Because

1152
00:44:13.490 --> 00:44:16.210
I could imagine that's what we might do.

1153
00:44:16.770 --> 00:44:19.450
Not on purpose, but um. Yeah. And it's what

1154
00:44:19.450 --> 00:44:21.650
you say, it's the ethics of sending

1155
00:44:23.090 --> 00:44:26.090
our ah, junk to other places that are already

1156
00:44:26.090 --> 00:44:28.490
occupied. Yeah. Um,

1157
00:44:29.010 --> 00:44:31.040
we're running out of time I suppose. But um,

1158
00:44:32.100 --> 00:44:33.700
how do you want to wind this up? Uh, how do

1159
00:44:33.700 --> 00:44:33.940
you.

1160
00:44:34.180 --> 00:44:36.100
There's so much to talk about, it could go on

1161
00:44:36.100 --> 00:44:36.420
for hours.

1162
00:44:36.420 --> 00:44:38.540
Jonti Horner: I know more to talk about. I think I'll carry

1163
00:44:38.540 --> 00:44:41.020
on until you kind of get the hook and pull me

1164
00:44:41.020 --> 00:44:43.660
off about the different things that influence

1165
00:44:43.660 --> 00:44:45.260
planet's habitability. Because we've talked

1166
00:44:45.260 --> 00:44:48.260
about Milankovitch cycles. We also have as

1167
00:44:48.260 --> 00:44:50.180
the influence of the planetary system impact

1168
00:44:50.180 --> 00:44:53.100
us just as the dinosaurs, they had a very bad

1169
00:44:53.100 --> 00:44:55.540
day. And there has historically been this

1170
00:44:55.540 --> 00:44:57.940
idea that ties into the rare Earth thing that

1171
00:44:57.940 --> 00:45:00.700
Jupiter is our friend and saviour and without

1172
00:45:00.700 --> 00:45:02.660
Jupiter we'd be hit by asteroids more often

1173
00:45:02.660 --> 00:45:04.760
and we wouldn't be here. And therefore life

1174
00:45:04.760 --> 00:45:07.280
is rare in the universe. Um, idea

1175
00:45:07.680 --> 00:45:09.640
basically that Jupiter is our bestest friend

1176
00:45:09.640 --> 00:45:12.400
and it's honestly a lot of cobs wallop and

1177
00:45:12.720 --> 00:45:15.160
it's both one of my favourite bits of

1178
00:45:15.160 --> 00:45:16.680
research I ever did. And probably one of the

1179
00:45:16.680 --> 00:45:19.360
biggest bugbears of my career is uh, I

1180
00:45:19.600 --> 00:45:22.560
did work again with Barry Jones starting 20

1181
00:45:22.560 --> 00:45:24.880
years ago for a few years that resulted in a

1182
00:45:24.880 --> 00:45:27.120
series of pep called Jupiter Friend or Foe.

1183
00:45:27.440 --> 00:45:29.880
And we did simulations to test the role of

1184
00:45:29.880 --> 00:45:32.400
Jupiter in protecting us from impacts or not.

1185
00:45:32.800 --> 00:45:34.790
And it turns out that Jupiter is not shielded

1186
00:45:35.020 --> 00:45:37.820
all if you took Jupiter away, Earth would be

1187
00:45:37.820 --> 00:45:40.820
hit less often. If however you

1188
00:45:40.820 --> 00:45:42.580
replace Jupiter with a planet, the mass of

1189
00:45:42.580 --> 00:45:45.380
Saturn, Earth would be hit more often than we

1190
00:45:45.380 --> 00:45:47.540
are today. And with Jupiter, the mass it

1191
00:45:47.540 --> 00:45:49.060
currently is, we'd be hit more than if it

1192
00:45:49.060 --> 00:45:50.899
wasn't there, but less than if we put Saturn

1193
00:45:50.899 --> 00:45:53.260
there. All down to the subtleties of how

1194
00:45:53.260 --> 00:45:55.980
gravity all works. And so basically if you

1195
00:45:55.980 --> 00:45:57.620
replace Jupiter with Saturn, it's like the

1196
00:45:57.620 --> 00:45:59.500
anti Goldilocks case where you've lesser

1197
00:45:59.500 --> 00:46:01.980
porridge with strychnine. But the reality is

1198
00:46:01.980 --> 00:46:04.540
that Jupiter's role is complicated,

1199
00:46:05.500 --> 00:46:07.740
best illustrated by Comet Lexell in

1200
00:46:07.740 --> 00:46:10.620
1770, which I always love. Comet Lexell was

1201
00:46:11.020 --> 00:46:13.260
a great comet. It was very bright in our sky.

1202
00:46:13.260 --> 00:46:15.380
Discovered by Charles Messier I think 1st of

1203
00:46:15.380 --> 00:46:18.180
June 1770. Quickly got as

1204
00:46:18.180 --> 00:46:19.940
bright as the brightest stars in the sky, but

1205
00:46:19.940 --> 00:46:22.260
looked unusual. It was very big and fuzzy and

1206
00:46:22.260 --> 00:46:24.340
it moved unusually rapidly across the sky at

1207
00:46:24.340 --> 00:46:26.660
its quickest, covering 42 degrees in a single

1208
00:46:26.660 --> 00:46:29.580
hour. When they worked out the orbit of this

1209
00:46:29.580 --> 00:46:31.380
thing, they found a that it had come very

1210
00:46:31.380 --> 00:46:32.900
close to the Earth. It passed within 2

1211
00:46:32.900 --> 00:46:34.770
million kilometres, which is the close

1212
00:46:34.920 --> 00:46:36.760
closest approach of a large comet in

1213
00:46:37.000 --> 00:46:40.000
historical times. It also was moving

1214
00:46:40.000 --> 00:46:41.920
on an orbit that was just less than six years

1215
00:46:41.920 --> 00:46:44.360
in period. Big bright comet going around

1216
00:46:44.360 --> 00:46:46.080
every six years. Why on Earth have we not

1217
00:46:46.080 --> 00:46:47.680
seen it before? Why have we not seen it in

1218
00:46:47.680 --> 00:46:50.520
1764 or 1758? Well,

1219
00:46:50.520 --> 00:46:52.240
when they worked out the orbit and run it

1220
00:46:52.240 --> 00:46:54.160
back in time and this was hard at the time

1221
00:46:54.160 --> 00:46:56.000
because they didn't have mechanical

1222
00:46:56.000 --> 00:46:58.280
computers, they had human computers who sat

1223
00:46:58.280 --> 00:47:00.320
there and did calculations with abakai and

1224
00:47:00.320 --> 00:47:02.650
slide rules and all the rest of it. They

1225
00:47:02.650 --> 00:47:04.490
found that three years before it nearly hit

1226
00:47:04.490 --> 00:47:07.170
the Earth it was very close to Jupiter. In

1227
00:47:07.170 --> 00:47:08.810
fact, prior to that it had been moving on an

1228
00:47:08.810 --> 00:47:11.130
orbit that came nowhere near the Earth, that

1229
00:47:11.130 --> 00:47:12.930
was probably hundreds or thousands of years

1230
00:47:12.930 --> 00:47:15.330
in period and it was flying in to come

1231
00:47:15.330 --> 00:47:16.890
nowhere near the inner solar system. When it

1232
00:47:16.890 --> 00:47:18.490
had this close encounter with Jupiter that

1233
00:47:18.490 --> 00:47:20.570
trapped it and threw it at the Earth and

1234
00:47:20.570 --> 00:47:22.690
captured it onto the six year long Jupiter

1235
00:47:22.690 --> 00:47:25.090
family comet orbit. So Jupiter took something

1236
00:47:25.090 --> 00:47:27.265
that was coming nowhere near us and threw it

1237
00:47:27.265 --> 00:47:30.110
out at us. We don't see the comet

1238
00:47:30.110 --> 00:47:33.030
anymore because 2 times 6 years is

1239
00:47:33.030 --> 00:47:34.990
12 years and Jupiter takes 12 years to go

1240
00:47:34.990 --> 00:47:37.470
around the sun. So the comet did two laps in

1241
00:47:37.470 --> 00:47:39.950
the time Jupiter took to take one. And when

1242
00:47:39.950 --> 00:47:41.990
the comet got back out there again 12 years

1243
00:47:42.230 --> 00:47:44.150
after the first encounter, Jupiter was there,

1244
00:47:44.150 --> 00:47:45.670
grabbed hold of it and threw it away again,

1245
00:47:45.830 --> 00:47:48.790
never to return. So in just this 12 year

1246
00:47:48.790 --> 00:47:51.030
period, Jupiter threw something at us and

1247
00:47:51.030 --> 00:47:53.350
then cleaned up after itself. And whether

1248
00:47:53.350 --> 00:47:55.030
Jupiter's more of a shield or more of a

1249
00:47:55.030 --> 00:47:56.670
threat is down to the balance of those two

1250
00:47:56.670 --> 00:47:59.350
effects. Um, and what we found in our

1251
00:47:59.350 --> 00:48:02.190
simulations is, to be honest with Jupiter, we

1252
00:48:02.190 --> 00:48:03.990
get hit more than we would do if it wasn't

1253
00:48:03.990 --> 00:48:06.910
there. That takes away the idea

1254
00:48:06.910 --> 00:48:09.430
that it's our protector. It takes away the

1255
00:48:09.430 --> 00:48:11.590
idea that you need a shield to shield a

1256
00:48:11.590 --> 00:48:14.470
planet to prevent life from being wiped out.

1257
00:48:14.950 --> 00:48:17.430
Another nail in the coffin of rare Earth. And

1258
00:48:17.430 --> 00:48:19.990
it bugs me a bit that so many documentaries

1259
00:48:19.990 --> 00:48:22.190
still trot out this trite idea that Jupiter

1260
00:48:22.190 --> 00:48:24.150
shields us from impacts. And it's wonderful

1261
00:48:24.550 --> 00:48:27.070
because I disprove that 20 years ago. It's

1262
00:48:27.070 --> 00:48:29.820
much more complicated. But even that idea

1263
00:48:29.820 --> 00:48:31.580
gets complicated because obviously we don't

1264
00:48:31.580 --> 00:48:32.550
want to have the Earth punishingly, uh,

1265
00:48:33.180 --> 00:48:36.180
pummelling because we'd be wiped out. But

1266
00:48:36.180 --> 00:48:37.660
where the Earth formed in the solar system,

1267
00:48:37.660 --> 00:48:40.620
it probably formed dry. We formed interior to

1268
00:48:40.620 --> 00:48:42.580
the location of the ice line. So there wasn't

1269
00:48:42.580 --> 00:48:45.220
any available solid water, the water was all

1270
00:48:45.220 --> 00:48:47.940
gas. So how the Earth got its water was a

1271
00:48:47.940 --> 00:48:50.740
long, outstanding problem, exacerbated by the

1272
00:48:50.740 --> 00:48:52.100
fact that towards the end of our planet's

1273
00:48:52.100 --> 00:48:53.980
formation, we got smashed into by an object

1274
00:48:53.980 --> 00:48:56.340
the size of Mars, which stripped off a lot of

1275
00:48:56.340 --> 00:48:57.740
the Earth's core and mantle and would have

1276
00:48:57.740 --> 00:48:59.820
desiccated our planet because m water would

1277
00:48:59.820 --> 00:49:01.680
have been in the. Or a mantle, in the crust

1278
00:49:01.680 --> 00:49:04.320
and mantle. Sorry, up near the surface. Yeah.

1279
00:49:04.480 --> 00:49:06.280
So where did the water come from? And Earth

1280
00:49:06.280 --> 00:49:08.220
is actually a remarkably dry planet, um,

1281
00:49:08.560 --> 00:49:10.840
particularly at the moment in Queensland. The

1282
00:49:10.840 --> 00:49:13.240
idea is down here. Yeah, the idea is that our

1283
00:49:13.240 --> 00:49:15.520
water, at least in significant part, was

1284
00:49:15.520 --> 00:49:18.440
delivered from further out by impacts in what

1285
00:49:18.440 --> 00:49:20.320
is often described as a late veneer.

1286
00:49:21.120 --> 00:49:23.200
That's really interesting air because that's

1287
00:49:23.200 --> 00:49:25.080
a stochastic process, it's random, it's

1288
00:49:25.080 --> 00:49:27.120
driven by the orbits of the planets and the

1289
00:49:27.120 --> 00:49:29.440
cleanup phase of solar system formation.

1290
00:49:29.920 --> 00:49:31.640
So different planetary systems will give

1291
00:49:31.640 --> 00:49:34.100
planets with different amounts of water. But

1292
00:49:34.100 --> 00:49:36.140
it's also indicating that you actually don't

1293
00:49:36.140 --> 00:49:38.500
want too much shielding, you need

1294
00:49:38.500 --> 00:49:40.660
impacts. Because if the Earth had never had

1295
00:49:40.660 --> 00:49:42.460
the impacts, we'd have never got enough water

1296
00:49:42.540 --> 00:49:45.220
for life to develop and thrive. On top of

1297
00:49:45.220 --> 00:49:46.540
that, if the Earth didn't have enough

1298
00:49:46.540 --> 00:49:48.339
impacts, the dinosaurs would never have been

1299
00:49:48.339 --> 00:49:50.340
wiped out. And maybe you and I will be

1300
00:49:50.340 --> 00:49:52.780
reptiles or maybe we'll be here, you know,

1301
00:49:53.180 --> 00:49:55.340
so there's a whole aspect of that. Now,

1302
00:49:55.340 --> 00:49:58.180
again, those Simulations I did, we can

1303
00:49:58.180 --> 00:50:00.140
rerun through the planetary systems, we can

1304
00:50:00.140 --> 00:50:02.020
find the debris belts in those systems, we

1305
00:50:02.020 --> 00:50:04.560
can find the planets so we can model their

1306
00:50:04.560 --> 00:50:06.440
impact rates. And I'd argue that we want to

1307
00:50:06.440 --> 00:50:08.840
look somewhere that doesn't have too many

1308
00:50:08.840 --> 00:50:10.920
impacts, but also doesn't have too few,

1309
00:50:11.560 --> 00:50:13.640
because each of those could pose problems.

1310
00:50:14.360 --> 00:50:17.080
That is a really big part of the storey

1311
00:50:17.160 --> 00:50:19.880
and it feeds into the last point, really,

1312
00:50:21.000 --> 00:50:23.920
which is the planet itself and a little bit

1313
00:50:23.920 --> 00:50:26.800
tied to the large moon. So our Earth, it has

1314
00:50:26.800 --> 00:50:28.960
been suggested again by the rare Earth crowd,

1315
00:50:28.960 --> 00:50:31.800
that the large moon we have stabilises our

1316
00:50:31.800 --> 00:50:33.710
atmosphere axis and has kept the Earth

1317
00:50:33.710 --> 00:50:35.390
habitable. So therefore you need a giant

1318
00:50:35.390 --> 00:50:38.390
satellite. But simulations by Dave

1319
00:50:38.390 --> 00:50:40.230
Waltham, who's a guy I know very well in the

1320
00:50:40.230 --> 00:50:42.710
uk, looked into this and what he found was

1321
00:50:42.710 --> 00:50:44.700
that you could take the Moon away and, uh,

1322
00:50:44.710 --> 00:50:46.150
the Earth's axis would still be fairly

1323
00:50:46.150 --> 00:50:48.149
stable. It still wobbled between about 22 and

1324
00:50:48.149 --> 00:50:50.590
24 degrees, maybe a little bit more. But

1325
00:50:50.590 --> 00:50:52.550
quirkily, if you made the moon just 12

1326
00:50:52.550 --> 00:50:54.670
kilometres larger in diameter,

1327
00:50:55.310 --> 00:50:57.910
it would make the Earth's axis unstable and

1328
00:50:57.910 --> 00:51:00.480
chaotic. So if the moon was only slightly

1329
00:51:00.480 --> 00:51:03.400
larger, we would not be here. The

1330
00:51:03.400 --> 00:51:04.920
other reason that a large moon has been

1331
00:51:04.920 --> 00:51:07.640
suggested is that it drives bigger tides. And

1332
00:51:07.640 --> 00:51:09.960
one of the common arguments for how life

1333
00:51:09.960 --> 00:51:12.400
first got going and, um, for how life moved

1334
00:51:12.400 --> 00:51:14.320
out of the oceans in both cases is to do with

1335
00:51:14.320 --> 00:51:16.360
the large tidal intertidal areas that we

1336
00:51:16.360 --> 00:51:18.600
have, where at low tide it's dry and at high

1337
00:51:18.600 --> 00:51:21.080
tide it's underwater. And the idea is that

1338
00:51:21.080 --> 00:51:23.360
without the moon those areas would be smaller

1339
00:51:23.600 --> 00:51:25.160
and life would have had less chance to get

1340
00:51:25.160 --> 00:51:26.960
going. I don't really buy that, because if

1341
00:51:26.960 --> 00:51:29.120
you took the moon away, the tides of sun

1342
00:51:29.120 --> 00:51:31.260
raises would still be half the size, so you'd

1343
00:51:31.260 --> 00:51:33.620
still have substantial tides. But these are

1344
00:51:33.620 --> 00:51:36.020
all the kind of questions people ask before

1345
00:51:36.020 --> 00:51:38.140
you get to the planet itself. And the planet

1346
00:51:38.140 --> 00:51:40.300
itself is where my head really hurt. Now, I'm

1347
00:51:40.300 --> 00:51:43.220
not a geophysicist at

1348
00:51:43.220 --> 00:51:45.060
all, so a lot of this was new to me. Now, we

1349
00:51:45.060 --> 00:51:47.540
talked a little bit about the hydration. You

1350
00:51:47.540 --> 00:51:49.500
could imagine anything from desert worlds to

1351
00:51:49.500 --> 00:51:51.460
worlds with hundreds of kilometres depth of

1352
00:51:51.460 --> 00:51:53.980
ocean. Now, if the ocean's too deep,

1353
00:51:54.700 --> 00:51:56.940
the planet is probably habitable, but not

1354
00:51:56.940 --> 00:51:59.340
detectably habitable because the life will be

1355
00:51:59.340 --> 00:52:00.500
at the bottom of the ocean where the

1356
00:52:00.500 --> 00:52:02.960
nutrients have been introduced by volc. But

1357
00:52:02.960 --> 00:52:04.960
an ocean deeper than a few tens of kilometres

1358
00:52:04.960 --> 00:52:07.040
is thought to become stagnant. And so it

1359
00:52:07.040 --> 00:52:09.240
doesn't mix things up to the surface, so you

1360
00:52:09.240 --> 00:52:11.320
don't want to look at water worlds that are

1361
00:52:11.640 --> 00:52:13.720
ocean for hundreds or thousands of kilometres

1362
00:52:13.720 --> 00:52:16.160
depth, but equally you want to have some mix

1363
00:52:16.160 --> 00:52:18.000
of ocean and continent to allow all the

1364
00:52:18.000 --> 00:52:20.800
carbon cycles and weathering to happen, to

1365
00:52:20.800 --> 00:52:23.240
allow life to engage with the atmosphere. So

1366
00:52:23.240 --> 00:52:24.880
that's a bit of a sweet spot there. But what

1367
00:52:24.880 --> 00:52:27.640
I didn't realise was how critical

1368
00:52:27.640 --> 00:52:30.290
water has been been to the

1369
00:52:30.290 --> 00:52:33.130
maintenance of our atmosphere and um, thereby

1370
00:52:33.130 --> 00:52:35.890
our climate against the vagaries of the solar

1371
00:52:35.890 --> 00:52:37.650
wind and against the vagaries of plate

1372
00:52:37.650 --> 00:52:40.250
tectonics. Now compare the Earth and Mars

1373
00:52:40.490 --> 00:52:42.410
and the Earth is warm and wet. We've got a

1374
00:52:42.410 --> 00:52:44.690
lovely thick atmosphere and we've not really

1375
00:52:44.690 --> 00:52:46.570
lost much of our atmosphere. We've got the

1376
00:52:46.570 --> 00:52:49.010
ozone layer which protects us to some degree

1377
00:52:49.010 --> 00:52:51.530
from UV radiation. We've got a temperature

1378
00:52:51.530 --> 00:52:53.210
inversion about 10 kilometres up in the

1379
00:52:53.210 --> 00:52:55.530
atmosphere that traps water below that level.

1380
00:52:55.770 --> 00:52:57.650
If water gets above that level, it freezes

1381
00:52:57.650 --> 00:52:59.970
and falls back down. So the water can't get

1382
00:52:59.970 --> 00:53:01.990
high enough to be ionised and split hydrogen

1383
00:53:01.990 --> 00:53:04.710
and helium and lost. Mars doesn't have that.

1384
00:53:05.030 --> 00:53:06.950
Mars doesn't have much of a magnetic field

1385
00:53:06.950 --> 00:53:08.830
whereas the Earth does. And the magnetic

1386
00:53:08.830 --> 00:53:10.390
field protects the atmosphere from being

1387
00:53:10.390 --> 00:53:12.990
stripped away from the outside in. Mars

1388
00:53:12.990 --> 00:53:15.720
doesn't have plate tectonics, but we do. And

1389
00:53:15.720 --> 00:53:18.310
um, plate tectonics prevents the atmosphere

1390
00:53:18.310 --> 00:53:21.190
from being precipitated out onto the surface

1391
00:53:21.190 --> 00:53:23.190
through chemistry and trapped there because

1392
00:53:23.190 --> 00:53:25.910
plate tectonics recycles the crust. So

1393
00:53:25.910 --> 00:53:27.630
anything that chemically gets weathered onto

1394
00:53:27.630 --> 00:53:29.670
Earth's surface gets put back into the

1395
00:53:29.670 --> 00:53:32.190
atmosphere through volcanic volcanoes. So

1396
00:53:32.190 --> 00:53:34.110
Mars and Earth probably started out looking

1397
00:53:34.110 --> 00:53:36.230
very similar and are now very, very

1398
00:53:36.230 --> 00:53:38.830
different. And so the nature of the planet

1399
00:53:38.830 --> 00:53:40.390
itself is going to be a real important

1400
00:53:40.470 --> 00:53:43.110
factor. And plate tectonics looks like it's

1401
00:53:43.110 --> 00:53:46.070
going to be fairly key. Plate tectonics is a

1402
00:53:46.070 --> 00:53:47.790
mechanism by which you stop the atmosphere

1403
00:53:47.790 --> 00:53:49.870
getting precipitated out and frozen in onto

1404
00:53:49.870 --> 00:53:51.350
the surface, which is a big part of what's

1405
00:53:51.350 --> 00:53:53.710
happened m on Mars because of that recycling

1406
00:53:53.710 --> 00:53:56.190
effect. But it also turns out that plate

1407
00:53:56.190 --> 00:53:58.490
tectonics is key in ensuring the

1408
00:53:58.890 --> 00:54:01.690
magnetic field is retained. And um, this is a

1409
00:54:01.690 --> 00:54:03.490
bit that really hurt my head because I'm

1410
00:54:03.490 --> 00:54:06.370
like, I'm not a geophysicist. Seems that on

1411
00:54:06.370 --> 00:54:09.330
the Earth if the Earth didn't have plate

1412
00:54:09.330 --> 00:54:11.650
tectonics, we'd probably have lost most of

1413
00:54:11.650 --> 00:54:14.490
our magnetic field like Mars and like Venus.

1414
00:54:15.130 --> 00:54:16.970
What's happening is that the magnetic field

1415
00:54:16.970 --> 00:54:19.250
is driven by convection currents in the outer

1416
00:54:19.250 --> 00:54:21.730
mantle. Like when you see water boiling in a

1417
00:54:21.730 --> 00:54:24.110
kettle overturn, um, motion of mollie and

1418
00:54:24.110 --> 00:54:26.590
metal Rising and falling. That

1419
00:54:26.590 --> 00:54:28.510
convection can only happen if you've got a

1420
00:54:28.510 --> 00:54:30.430
big temperature difference between the bottom

1421
00:54:30.430 --> 00:54:32.710
and the top of the outer core. Sorry.

1422
00:54:33.430 --> 00:54:35.190
In order to get that temperature difference,

1423
00:54:35.190 --> 00:54:37.030
you need to be able to very effectively cool

1424
00:54:37.030 --> 00:54:39.310
the top of the outer core because otherwise

1425
00:54:39.310 --> 00:54:40.950
it would warm up so much convection would

1426
00:54:40.950 --> 00:54:42.470
stop because you don't have enough

1427
00:54:42.470 --> 00:54:44.790
temperature difference. The way the outer

1428
00:54:44.790 --> 00:54:46.470
core is cooled is by convection in the

1429
00:54:46.470 --> 00:54:48.110
mantle. That takes the heat away from the top

1430
00:54:48.110 --> 00:54:49.470
of the outer core and brings it to the

1431
00:54:49.470 --> 00:54:51.910
surface. We've got these huge convection

1432
00:54:51.910 --> 00:54:53.990
cells in the mantle that transfer heat very

1433
00:54:53.990 --> 00:54:56.970
quickly. Allowing cool the outer core's top

1434
00:54:56.970 --> 00:54:59.170
to get this big temperature difference allows

1435
00:54:59.170 --> 00:55:01.010
a motion that drives a magnetic field.

1436
00:55:02.530 --> 00:55:04.570
That motion is also what drives plate

1437
00:55:04.570 --> 00:55:06.410
tectonics. Now, the quirky thing that came

1438
00:55:06.410 --> 00:55:07.890
out of all of this when I was reading about

1439
00:55:07.890 --> 00:55:10.170
it is that, uh, if you run simulations of the

1440
00:55:10.170 --> 00:55:12.450
motion of the Earth's mantle and the crust

1441
00:55:12.690 --> 00:55:15.570
and the Earth is dry, the Earth is too small

1442
00:55:15.570 --> 00:55:18.410
to sustain plate tectonics because the mantle

1443
00:55:18.410 --> 00:55:21.090
is too stiff. If you have water

1444
00:55:21.330 --> 00:55:23.410
and you mix water into the mantle, you

1445
00:55:23.410 --> 00:55:25.880
lubricate, lubricate it. You allow convection

1446
00:55:25.880 --> 00:55:28.000
in the mantle, which allows plate tectonics,

1447
00:55:28.320 --> 00:55:31.000
which allows you to recycle the surface. But

1448
00:55:31.000 --> 00:55:33.080
that plate tectonics also allows you to cool

1449
00:55:33.080 --> 00:55:35.320
the outer core to maintain the magnetic

1450
00:55:35.320 --> 00:55:37.480
field, allowing you to have that magnetic

1451
00:55:37.480 --> 00:55:39.560
shield that protects your planet from the

1452
00:55:39.560 --> 00:55:40.960
atmosphere being whittled away from the

1453
00:55:40.960 --> 00:55:43.800
outside in by the solar wind. It

1454
00:55:43.800 --> 00:55:46.520
seems that the storey of plate tectonics, the

1455
00:55:46.520 --> 00:55:48.640
Earth's magnetic field and, um, the

1456
00:55:48.640 --> 00:55:51.290
atmosphere being retained, is all tied

1457
00:55:51.290 --> 00:55:53.290
together by water. Which brings us back to

1458
00:55:53.290 --> 00:55:55.410
that delivery question. If the Earth had not

1459
00:55:55.410 --> 00:55:57.650
got that veneer of water, would plate

1460
00:55:57.650 --> 00:56:00.210
tectonics still happen? The infinite

1461
00:56:00.210 --> 00:56:02.010
suggestion, and this was fabulous work by

1462
00:56:02.010 --> 00:56:03.930
people working with the great Craig o',

1463
00:56:03.930 --> 00:56:06.169
Neill, a great Australian scientist who does

1464
00:56:06.650 --> 00:56:08.410
earthquakes and, um, plate tectonics

1465
00:56:08.410 --> 00:56:11.090
modelling in an astrobiology sense that

1466
00:56:11.090 --> 00:56:14.010
says the Earth's plate tectonics are

1467
00:56:14.010 --> 00:56:15.890
really hard to get started. If you run models

1468
00:56:15.890 --> 00:56:17.810
of the Earth without plate tectonics with the

1469
00:56:17.810 --> 00:56:19.970
young Earth, with how hot it was, plate

1470
00:56:19.970 --> 00:56:22.950
tectonics don't just happen. However, if

1471
00:56:22.950 --> 00:56:25.270
you introduce impacts from big asteroids,

1472
00:56:25.270 --> 00:56:27.110
like the things you got at the end of planet

1473
00:56:27.110 --> 00:56:29.830
formation, those can dump enough energy

1474
00:56:29.990 --> 00:56:32.990
in terms of a downward pulse to push magma

1475
00:56:32.990 --> 00:56:35.670
up somewhere else to trigger a convection

1476
00:56:35.670 --> 00:56:38.230
cell that then becomes self sustaining. So

1477
00:56:38.230 --> 00:56:40.950
it's quite possible that the same impact

1478
00:56:41.110 --> 00:56:43.350
regime that led to the delivery of water,

1479
00:56:43.670 --> 00:56:45.710
that led in the extreme case to the formation

1480
00:56:45.710 --> 00:56:48.190
of the moon, also triggered plate

1481
00:56:48.190 --> 00:56:50.990
Tectonics. And by triggering plate tectonics

1482
00:56:50.990 --> 00:56:53.480
and delivering water to the mantle allowed

1483
00:56:53.480 --> 00:56:55.360
the Earth to become the planet it is today to

1484
00:56:55.360 --> 00:56:58.120
allow life to thrive. Now there's far, far

1485
00:56:58.120 --> 00:56:59.480
more that you could look into about the

1486
00:56:59.480 --> 00:57:01.360
planets themselves. I'm not like, say, a

1487
00:57:01.360 --> 00:57:04.360
geophysicist, but the interplay of these

1488
00:57:04.360 --> 00:57:05.960
things is fascinating and it's a real

1489
00:57:05.960 --> 00:57:08.720
reminder of that multidisciplinary thing. You

1490
00:57:08.720 --> 00:57:10.440
can't do it all if you're just an astronomy.

1491
00:57:10.440 --> 00:57:13.040
You need everybody from all different

1492
00:57:13.040 --> 00:57:15.600
disciplines to come together so we can figure

1493
00:57:15.600 --> 00:57:17.480
out what factors are and, um, aren't

1494
00:57:17.480 --> 00:57:19.880
important. So that when we find another

1495
00:57:20.130 --> 00:57:22.210
thousand, another ten thousand, another

1496
00:57:22.210 --> 00:57:24.610
hundred thousand planets, we can pick the

1497
00:57:24.610 --> 00:57:26.530
best targets to search for life upon them.

1498
00:57:26.930 --> 00:57:28.810
And that was a motivation and it just blew my

1499
00:57:28.810 --> 00:57:31.610
mind when I got to that final part. Just how

1500
00:57:31.610 --> 00:57:34.170
much complexity there is in the

1501
00:57:34.170 --> 00:57:35.690
interplay between the atmosphere, the

1502
00:57:35.690 --> 00:57:37.890
climate, the plate tectonics, the oceans

1503
00:57:38.850 --> 00:57:41.810
that are so, uh, variable and so chaotic.

1504
00:57:42.530 --> 00:57:44.410
What does that mean? How can we learn from

1505
00:57:44.410 --> 00:57:46.290
that? Well, that's what we learn when we look

1506
00:57:46.290 --> 00:57:47.770
at planets around other stars. But at least

1507
00:57:47.770 --> 00:57:48.970
this gives us a bit of a starting point

1508
00:57:49.040 --> 00:57:49.600
point, I think.

1509
00:57:50.320 --> 00:57:52.880
Andrew Dunkley: Yeah, yeah, I see what you're saying. So it's

1510
00:57:53.200 --> 00:57:55.200
like the popular press saying, oh, we found a

1511
00:57:55.200 --> 00:57:57.760
rocky planet in the Goldilocks zone and it

1512
00:57:57.760 --> 00:57:59.920
probably has water, so, you know, it's got to

1513
00:57:59.920 --> 00:58:02.360
have life. Uh, there's so much more than

1514
00:58:02.360 --> 00:58:04.410
that. Like, yeah, it's um.

1515
00:58:04.560 --> 00:58:06.800
Jonti Horner: Even they probably have water is a leap

1516
00:58:06.800 --> 00:58:09.680
because like, yeah, if we'd not had

1517
00:58:09.680 --> 00:58:11.600
water added after the moon forming impact,

1518
00:58:11.600 --> 00:58:12.800
the Earth would be a desert

1519
00:58:14.320 --> 00:58:17.160
Andrew Dunkley: and we wouldn't probably exist at all.

1520
00:58:17.160 --> 00:58:18.720
Jonti Horner: Absolutely, yeah.

1521
00:58:18.720 --> 00:58:21.320
Andrew Dunkley: Fascinating stuff, Jonty. We'll leave it

1522
00:58:21.320 --> 00:58:23.760
there. But, um, it's just such a

1523
00:58:24.080 --> 00:58:25.520
fascinating topic. But

1524
00:58:26.800 --> 00:58:29.120
what goes into, uh, the future

1525
00:58:29.120 --> 00:58:31.600
identification of potential targets is

1526
00:58:32.000 --> 00:58:34.040
so much more than most people would have

1527
00:58:34.040 --> 00:58:35.720
considered. So thank you very much, really

1528
00:58:35.720 --> 00:58:36.280
appreciate it.

1529
00:58:36.280 --> 00:58:37.400
Jonti Horner: It's an absolute pleasure and thanks for

1530
00:58:37.400 --> 00:58:40.280
letting me rant on my topics of choice for a

1531
00:58:40.280 --> 00:58:43.280
change. Like I said, it would be helpful. I'm

1532
00:58:43.280 --> 00:58:44.160
sure your readers will.

1533
00:58:44.160 --> 00:58:46.120
Readers, listeners will give feedback on

1534
00:58:46.120 --> 00:58:48.160
this, but I know we've done something

1535
00:58:48.160 --> 00:58:51.080
different. I really do. I am aware

1536
00:58:51.080 --> 00:58:52.680
of the fact that these are not your typical

1537
00:58:52.680 --> 00:58:55.040
episodes and that may be different for

1538
00:58:55.040 --> 00:58:56.720
people. So I appreciate the opportunity to do

1539
00:58:56.720 --> 00:58:58.680
this, but if people have enjoyed it or

1540
00:58:58.680 --> 00:59:00.880
didn't, it'd probably be worth letting Andrew

1541
00:59:00.880 --> 00:59:03.280
and Fred Watson know once I'm gone. Um, won't

1542
00:59:03.280 --> 00:59:04.640
hurt my feelings. Don't worry about it

1543
00:59:04.640 --> 00:59:06.120
because if it's Something you've enjoyed.

1544
00:59:06.280 --> 00:59:08.200
There's possibilities to do things like this

1545
00:59:08.200 --> 00:59:10.880
again in future if it isn't. We tried it and

1546
00:59:10.880 --> 00:59:12.690
it didn't work and that's entirely fine. Fine

1547
00:59:12.690 --> 00:59:14.490
too. So hopefully it was fun, hopefully it

1548
00:59:14.490 --> 00:59:16.380
was educational and I won't be too hurt, uh,

1549
00:59:16.410 --> 00:59:17.450
if nobody enjoyed it.

1550
00:59:18.570 --> 00:59:20.810
Andrew Dunkley: I'm pretty sure they did. Jonty, and we

1551
00:59:20.810 --> 00:59:23.130
really appreciate your time and uh, we've,

1552
00:59:23.130 --> 00:59:24.970
we've got one more episode to do with you.

1553
00:59:25.020 --> 00:59:27.330
Uh, it's a Q and A episode and we, we're

1554
00:59:27.330 --> 00:59:29.330
talking about, we haven't nailed it down yet,

1555
00:59:29.330 --> 00:59:31.210
but we're talking about doing a, an

1556
00:59:31.210 --> 00:59:32.650
astrophotography special.

1557
00:59:32.810 --> 00:59:33.290
Jonti Horner: Yeah.

1558
00:59:33.290 --> 00:59:34.970
Andrew Dunkley: Because we do get a lot of questions about

1559
00:59:34.970 --> 00:59:37.730
astrophotography so, uh, that, that'd be

1560
00:59:37.730 --> 00:59:38.890
worth getting into as well.

1561
00:59:38.890 --> 00:59:40.460
Jonti Horner: Yeah. I've got a couple of good friends who

1562
00:59:40.460 --> 00:59:42.640
uh, are award winning astrophotographers who

1563
00:59:42.640 --> 00:59:44.520
we're going to try and rope into that. So

1564
00:59:44.520 --> 00:59:46.840
watch this space is what I'd say. Yes.

1565
00:59:46.840 --> 00:59:48.840
Andrew Dunkley: Fingers crossed we can nail that one down.

1566
00:59:49.000 --> 00:59:50.720
Jonty, thanks so much. We'll see you real

1567
00:59:50.720 --> 00:59:51.000
soon.

1568
00:59:51.080 --> 00:59:52.360
Jonti Horner: Pleasure. Thank you for having me.

1569
00:59:52.760 --> 00:59:54.920
Andrew Dunkley: Johnty Horner, professor of Astrophysics at

1570
00:59:54.920 --> 00:59:57.720
the University of Southern Queensland.

1571
00:59:58.040 --> 01:00:00.560
And if you've got time, jump on our website

1572
01:00:00.560 --> 01:00:02.840
and have a look around. Uh, maybe send your

1573
01:00:02.840 --> 01:00:05.800
comments and thoughts, uh, to us via the

1574
01:00:05.800 --> 01:00:07.880
Ask me anything button at the top. It's

1575
01:00:07.880 --> 01:00:10.440
labelled ama. And while you're there, cheque

1576
01:00:10.440 --> 01:00:12.660
out the Astronomy AstroDailyPod feed. Maybe

1577
01:00:12.660 --> 01:00:15.180
sign up for your daily dose of astronomy

1578
01:00:15.180 --> 01:00:17.980
news. Um, maybe you'd like to become a

1579
01:00:17.980 --> 01:00:20.140
subscriber. You can do that. Visit, uh, the

1580
01:00:20.140 --> 01:00:22.660
shop. Lots of goodies in our shop and plenty

1581
01:00:22.660 --> 01:00:25.660
more. So cheque it out and thanks to Huw

1582
01:00:25.660 --> 01:00:27.300
in the studio as always, because

1583
01:00:28.580 --> 01:00:31.580
he does something which we one day might

1584
01:00:31.580 --> 01:00:33.900
find out about. And from me, Andrew Dunkley,

1585
01:00:33.900 --> 01:00:35.220
thanks for your company. We'll see you on the

1586
01:00:35.220 --> 01:00:37.860
next episode of Space Nuts. Bye Bye.

1587
01:00:38.020 --> 01:00:39.060
Space Nuts.

1588
01:00:39.060 --> 01:00:40.910
You've been listening to the Space Nuts

1589
01:00:40.980 --> 01:00:43.860
Jonti Horner: Arts podcast, available

1590
01:00:43.940 --> 01:00:46.180
at Apple Podcasts, Spotify,

1591
01:00:46.260 --> 01:00:49.180
iHeartRadio or your favourite podcast

1592
01:00:49.180 --> 01:00:51.460
player. You can also stream on demand at

1593
01:00:51.460 --> 01:00:52.240
bytes. Com.

1594
01:00:52.240 --> 01:00:54.940
Andrew Dunkley: Um, this has been another quality podcast

1595
01:00:54.940 --> 01:00:56.740
production from Bytes. Com.

1596
01:00:56.740 --> 01:00:57.520
Jonti Horner: Um,