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Astrobiology Part 2: The Search for Life Beyond Earth In this captivating continuation of our exploration of astrobiology, hosts Andrew Dunkley and Professor Jonti Horner delve deeper into the complexities of life in the universe. Following up on their previous discussion, they tackle the intriguing factors that influence the potential for life on other planets, as well as the implications of our own technological advancements.
Episode Highlights:
- Review of Astrobiology: The episode kicks off with a quick recap of the previous discussion on the history of astrobiology, including the ongoing search for life within our solar system and beyond.
- The Exoplanet Era: Jonty shares insights on our current capabilities to identify exoplanets that may harbour life, discussing the significance of size, distance from stars, and other critical factors in determining habitability.
- Search for Extraterrestrial Intelligence: The hosts explore the challenges of detecting intelligent life and the fascinating concept of alien megastructures, as well as the importance of understanding what to look for in the cosmos.
- Planetary Systems and Habitability: The conversation shifts to the dynamics of planetary systems and how factors like Milankovitch cycles, orbital stability, and the presence of water influence a planet's ability to support life.
- Ethics of Seeding Life: A listener question prompts a discussion on the ethical implications of potentially seeding other planets with life, exploring the concept of panspermia and the responsibilities of humanity in the cosmos.
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Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
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- Recap of Astrobiology Part 1
- The Exoplanet Landscape
- Searching for Intelligent Life
- Factors Influencing Habitability
- Ethical Considerations in Seeding Life
00:00:00 --> 00:00:01 Andrew Dunkley: Hi there. Thanks for joining us again. This
00:00:01 --> 00:00:04 is Space Nuts where we talk astronomy and
00:00:04 --> 00:00:07 space science and all sorts of other things.
00:00:07 --> 00:00:09 And over the last, uh, few
00:00:10 --> 00:00:13 episodes we've been doing some specials
00:00:13 --> 00:00:15 because Fred Watson's away gallivanting
00:00:15 --> 00:00:18 around Scotland playing a lot of golf. Not.
00:00:18 --> 00:00:21 Uh, so we're doing some specials with Jonty
00:00:21 --> 00:00:24 Horner. Uh, and we're doing part
00:00:24 --> 00:00:25 two today of
00:00:25 --> 00:00:28 Astrobiology, a fascinating
00:00:28 --> 00:00:31 part of astronomy and space science. Uh,
00:00:31 --> 00:00:34 one area we get so many questions about. So
00:00:34 --> 00:00:37 stand by as we get into that on this
00:00:37 --> 00:00:39 episode of space nuts. 15
00:00:40 --> 00:00:40 seconds.
00:00:40 --> 00:00:43 Jonti Horner: Guidance is internal. 10,
00:00:43 --> 00:00:45 9, ignition sequence start.
00:00:46 --> 00:00:49 Space nuts. 5, 4, 3, 2. 1. 2,
00:00:49 --> 00:00:51 3, 4, 5, 5, 4, 3, 2, 1.
00:00:51 --> 00:00:53 Space nuts.
00:00:53 --> 00:00:55 Andrew Dunkley: Astronauts report it feels good.
00:00:56 --> 00:00:58 And back with us again is Johnty Horner,
00:00:58 --> 00:01:00 professor of astrophysics at the University
00:01:00 --> 00:01:02 of Southern Queensland. Jonty, hello.
00:01:02 --> 00:01:03 Jonti Horner: Noon. How are you?
00:01:03 --> 00:01:05 Andrew Dunkley: I'm m all right. Can you imagine Fred Watson
00:01:05 --> 00:01:06 playing golf?
00:01:06 --> 00:01:08 Jonti Horner: No, uh, not sure. I mean, growing up in
00:01:08 --> 00:01:10 Yorkshire, the weather wasn't always suited
00:01:10 --> 00:01:13 to it and we were too busy in gravel anyway,
00:01:13 --> 00:01:13 so.
00:01:14 --> 00:01:17 Andrew Dunkley: Yeah, took
00:01:17 --> 00:01:20 a moment. I got that. Yes, yes.
00:01:20 --> 00:01:22 Uh, used to look clean with the tongues.
00:01:22 --> 00:01:24 Jonti Horner: Used to have to get up in the morning at 10
00:01:24 --> 00:01:25 o' clock at night, half an hour before I went
00:01:25 --> 00:01:26 to bed.
00:01:27 --> 00:01:30 Andrew Dunkley: It's just one of the best pieces of comedy
00:01:30 --> 00:01:30 ever.
00:01:30 --> 00:01:31 Jonti Horner: And it's funny because it's true.
00:01:33 --> 00:01:34 Yes.
00:01:34 --> 00:01:36 Andrew Dunkley: Tell the young people that.
00:01:36 --> 00:01:37 Jonti Horner: They won't believe you.
00:01:39 --> 00:01:42 Andrew Dunkley: Oh gosh, it's all flooding back. Uh, we've
00:01:42 --> 00:01:44 got a lot to talk about so we better get
00:01:44 --> 00:01:44 started.
00:01:44 --> 00:01:47 Astrobiology Part two. Um,
00:01:47 --> 00:01:49 a couple of episodes ago we talked
00:01:49 --> 00:01:52 Astrobiology Part one, surprisingly. Um,
00:01:52 --> 00:01:54 let's just do a quick review.
00:01:54 --> 00:01:56 Jonti Horner: Yeah, this is a bit like the bit that really
00:01:56 --> 00:01:59 annoys you at the start of those multi
00:01:59 --> 00:02:01 episode shows where they're previously on
00:02:01 --> 00:02:03 Astrobiology. Um, but
00:02:05 --> 00:02:07 this is basically a case of Jonty talks too
00:02:07 --> 00:02:09 much and so therefore we run out of time. I
00:02:09 --> 00:02:11 mean, we don't need to sugarcoat that. And
00:02:11 --> 00:02:13 it's always a problem when you're talking
00:02:13 --> 00:02:14 about something you love and you're
00:02:14 --> 00:02:16 passionate about that. The time just flies by
00:02:16 --> 00:02:18 and hopefully it's flying by for the
00:02:18 --> 00:02:20 listeners as well, rather than boring them to
00:02:20 --> 00:02:22 tears. But you know, I can't really control
00:02:22 --> 00:02:24 that. In the first episode
00:02:25 --> 00:02:27 we talked a fair bit about the fact that
00:02:27 --> 00:02:29 we've always wondered whether there's life
00:02:29 --> 00:02:31 elsewhere. We talked a bit about the history
00:02:31 --> 00:02:33 in particular things like the ideas of
00:02:33 --> 00:02:35 potentially there being life on Mars that led
00:02:35 --> 00:02:37 to the panic over the War of the Worlds
00:02:37 --> 00:02:39 broadcast and the Fact that In the late
00:02:39 --> 00:02:41 1800s, people were that convinced there
00:02:41 --> 00:02:43 already was known to be life on Mars, that
00:02:43 --> 00:02:45 when a major prize was offered for the
00:02:45 --> 00:02:47 detection of life elsewhere, Mars was
00:02:47 --> 00:02:49 explicitly excluded because that's too easy,
00:02:49 --> 00:02:51 you know. So we've had these ideas for a very
00:02:51 --> 00:02:54 long time, but finding evidence of life
00:02:54 --> 00:02:56 out there is really, really difficult.
00:02:57 --> 00:02:59 We've talked a fair bit about the search for
00:02:59 --> 00:03:02 life within the solar system. You know,
00:03:02 --> 00:03:04 places like looking at Mars, looking at
00:03:04 --> 00:03:06 Europa, all the icy moons. And we talk about
00:03:06 --> 00:03:08 that a lot in the questions that we week by
00:03:08 --> 00:03:09 week as well on the show.
00:03:09 --> 00:03:12 And one thing I've always been really
00:03:12 --> 00:03:13 interested in and passionate about is the
00:03:13 --> 00:03:15 search for life outside the solar system.
00:03:16 --> 00:03:18 Given that we've moved into the exoplanet
00:03:18 --> 00:03:20 era, and we talked a lot about this in the
00:03:20 --> 00:03:22 previous episode as well, we're now in a
00:03:22 --> 00:03:24 position where 30 years ago would have seemed
00:03:24 --> 00:03:26 impossible. Thirty years ago, we'd only just
00:03:26 --> 00:03:28 found the first planet for under the Stars,
00:03:28 --> 00:03:30 and only just answered that question of
00:03:30 --> 00:03:32 whether there are planets at all beyond the
00:03:32 --> 00:03:35 solar system. Now we're at a position where
00:03:35 --> 00:03:37 we are finding places that theoretically, in
00:03:37 --> 00:03:40 the future, we could search to see whether
00:03:40 --> 00:03:42 there's any evidence of life in those
00:03:42 --> 00:03:44 planetary systems. And in all honesty,
00:03:44 --> 00:03:46 despite some of the hyperbolic media
00:03:47 --> 00:03:49 articles that you sometimes see, we haven't
00:03:49 --> 00:03:52 yet found a planet that would really look
00:03:52 --> 00:03:53 like another Earth. But we're getting there,
00:03:53 --> 00:03:55 we're getting closer, we're getting to
00:03:55 --> 00:03:57 planets that are more similar to ours in
00:03:57 --> 00:03:59 size, at more similar distance from their
00:03:59 --> 00:04:01 stars, and we're learning more about them.
00:04:01 --> 00:04:03 And it's very feasible then in the next
00:04:03 --> 00:04:05 decade or so, that we can actually start
00:04:05 --> 00:04:07 looking to see whether there's any evidence
00:04:07 --> 00:04:09 of life on those planets. Now, that's a
00:04:09 --> 00:04:12 little bit separate to looking for signs of
00:04:12 --> 00:04:15 communicative alien technological
00:04:15 --> 00:04:17 life, which is a search for extraterrestrial
00:04:17 --> 00:04:19 intelligence or the search for
00:04:19 --> 00:04:20 extraterrestrial artefacts. There two areas
00:04:20 --> 00:04:23 of science that are fascinating, but they're
00:04:23 --> 00:04:25 more like a search for a needle in a hair
00:04:25 --> 00:04:28 sack, where we don't even know if there is
00:04:28 --> 00:04:30 life elsewhere, never mind intelligent life.
00:04:30 --> 00:04:32 I mean, some people argue whether there's
00:04:32 --> 00:04:34 intelligent life on Earth looking at the news
00:04:34 --> 00:04:36 at the minute, but looking for intelligent
00:04:36 --> 00:04:38 life that has reached certain technological
00:04:38 --> 00:04:41 level to communicate with us is challenging.
00:04:41 --> 00:04:42 It's one of those things if we don't know
00:04:42 --> 00:04:44 what we're looking for, but if we don't look,
00:04:44 --> 00:04:47 we'll never find it. But it still led to some
00:04:47 --> 00:04:49 really fascinating research, and there's a
00:04:49 --> 00:04:51 guy who works with us as part of our Planet
00:04:51 --> 00:04:53 Search Consortium, a guy called Jason Reutt
00:04:53 --> 00:04:56 in the US who spent some of his time actually
00:04:56 --> 00:04:59 thinking about alien megastructures, the
00:04:59 --> 00:05:01 kind of things that feature so heavily in
00:05:01 --> 00:05:03 some advanced science fiction, like Larry
00:05:03 --> 00:05:06 Niven's Ringworld or Dyson Spheres, these
00:05:06 --> 00:05:08 enormous structures that you can imagine a
00:05:09 --> 00:05:11 civilization building. If their technologies
00:05:11 --> 00:05:14 are far above ours, as ours is from the Stone
00:05:14 --> 00:05:16 Age, the idea that you could build something
00:05:16 --> 00:05:18 to harness all the material in your planetary
00:05:18 --> 00:05:20 system m harness all the energy from your
00:05:20 --> 00:05:22 star. Now, many people argue that while
00:05:22 --> 00:05:23 that's theoretically possible, it just
00:05:23 --> 00:05:26 wouldn't be worth the effort. But what
00:05:26 --> 00:05:28 Jason's been looking into is
00:05:29 --> 00:05:31 effectively not could people do
00:05:31 --> 00:05:34 this? But rather if they did, what would it
00:05:34 --> 00:05:36 look like? So it's not really putting any
00:05:36 --> 00:05:39 weight on the probability of
00:05:39 --> 00:05:41 these things existing, but rather saying,
00:05:41 --> 00:05:44 here are things we could imagine that are
00:05:44 --> 00:05:46 within the bounds of physical possibility to
00:05:46 --> 00:05:47 build. Even if they'd be on this
00:05:47 --> 00:05:50 technologically, what would they look like to
00:05:50 --> 00:05:52 our different kinds of telescopes? What would
00:05:52 --> 00:05:54 the signatures be? And, um, that work's
00:05:54 --> 00:05:57 really important because if you don't have an
00:05:57 --> 00:05:59 idea what these peculiar objects would look
00:05:59 --> 00:06:02 like, when you find something unusual, you
00:06:02 --> 00:06:04 won't have that thing to reference again to
00:06:04 --> 00:06:06 cheque it out. So both the search for
00:06:06 --> 00:06:08 extraterrestrial intelligence and the search
00:06:08 --> 00:06:11 for alien artefacts, a kind of
00:06:11 --> 00:06:13 a separate splinter of astrobiology that are
00:06:14 --> 00:06:16 ongoing, that are very precious to us here in
00:06:16 --> 00:06:17 Australia. Of course, we would have lost the
00:06:17 --> 00:06:20 Parks Radio telescope under the Liberal
00:06:20 --> 00:06:22 government in the 2010s in the previous
00:06:22 --> 00:06:25 decade because they wanted to shut it down
00:06:25 --> 00:06:27 and demolish it to save money. And it only
00:06:27 --> 00:06:30 kept going by a large investment
00:06:30 --> 00:06:33 as part of a project to listen
00:06:33 --> 00:06:36 for aliens. So, like 40. I remember
00:06:36 --> 00:06:38 that telescope has been used to search for
00:06:38 --> 00:06:40 extraterrestrial intelligence in the form of
00:06:40 --> 00:06:42 radio signals. And that has kept one of our,
00:06:43 --> 00:06:44 uh, incredible pieces of astronomical
00:06:44 --> 00:06:46 heritage in Australia. And something
00:06:46 --> 00:06:48 incredibly precious and beloved has kept it
00:06:48 --> 00:06:50 going and kept it standing despite the worst
00:06:50 --> 00:06:53 vagaries of politicians and
00:06:53 --> 00:06:54 all those challenges.
00:06:55 --> 00:06:58 Andrew Dunkley: Could you argue that we, uh, have
00:06:58 --> 00:07:00 already created a
00:07:00 --> 00:07:03 megastructure around Earth with the number of
00:07:03 --> 00:07:05 satellites that are currently in orbit and
00:07:05 --> 00:07:08 the so many thousands more that are going to
00:07:08 --> 00:07:09 be put up there in the near future?
00:07:09 --> 00:07:11 Jonti Horner: Certainly feels like that from the inside.
00:07:11 --> 00:07:13 Looking out. I mean, I'm enjoying all the
00:07:13 --> 00:07:16 photos. People are, uh, of Comet 2025
00:07:16 --> 00:07:19 R3 Pan stars at the minute, which behind
00:07:19 --> 00:07:20 both of us are our attempts. We're showing
00:07:20 --> 00:07:22 them off. Andrew's ever so proud from his
00:07:22 --> 00:07:23 attempt last night.
00:07:24 --> 00:07:25 Andrew Dunkley: My first ever comet.
00:07:25 --> 00:07:27 Jonti Horner: Fabulous photos that people are getting, but
00:07:27 --> 00:07:29 I've seen a lot of them getting photobombed
00:07:29 --> 00:07:32 by Starlink satellites. And I've got. I'm
00:07:32 --> 00:07:34 currently, thanks to learning something new
00:07:34 --> 00:07:35 about astrophotography over the last two
00:07:35 --> 00:07:37 days. I'm going back to images I took of
00:07:37 --> 00:07:39 Comet Atlas and Comet um, Church in Chan
00:07:39 --> 00:07:41 Atlas, which were the great comets of 2024
00:07:41 --> 00:07:44 and 2025 to reprocess those
00:07:44 --> 00:07:47 images. But one of my abiding Comet Atlas
00:07:47 --> 00:07:49 was I had this incredible view of it on the
00:07:49 --> 00:07:51 horizon. Took this long series of photos and
00:07:51 --> 00:07:54 every single blooming photo was ruined by a
00:07:54 --> 00:07:55 Starlink satellite because I got a Starlink
00:07:55 --> 00:07:57 train passing overhead that had recently been
00:07:57 --> 00:07:59 launched. All of which went straight through
00:07:59 --> 00:08:01 the middle of the comet and rendered all the
00:08:01 --> 00:08:03 photos unusable on my only really good clear
00:08:03 --> 00:08:06 night. Now, I may be able to solve it, but
00:08:06 --> 00:08:08 that isn't quite at the megastructure stage
00:08:08 --> 00:08:11 yet for me in that I suspect with the
00:08:11 --> 00:08:13 level of technology we've got now or in the
00:08:13 --> 00:08:16 near future, that network of
00:08:16 --> 00:08:17 satellites around the Earth, uh, wouldn't be
00:08:17 --> 00:08:20 something we could detect orbiting a planet
00:08:20 --> 00:08:22 around another star. Right. They're not there
00:08:22 --> 00:08:24 yet, but they're the forebears of something
00:08:24 --> 00:08:27 that could be. Now, being that
00:08:27 --> 00:08:29 they're around a planet rather than a star,
00:08:29 --> 00:08:31 their signature will be different. And given
00:08:31 --> 00:08:34 that we are very skilled now at
00:08:34 --> 00:08:36 broadcasting in one direction rather than
00:08:36 --> 00:08:38 many, and that broadcasting directionally
00:08:38 --> 00:08:40 rather than broadcasting the boy band one
00:08:40 --> 00:08:43 direction should be said, um, broadcasting
00:08:44 --> 00:08:46 in a directional sense. We are moving towards
00:08:46 --> 00:08:48 the point where we're going to stop shrieking
00:08:48 --> 00:08:50 like a screaming infant into the cosmos
00:08:50 --> 00:08:52 anyway. So it may be that we're going to go
00:08:52 --> 00:08:54 radio silent fairly soon, and satellites like
00:08:54 --> 00:08:56 that are going to be part of that journey.
00:08:57 --> 00:08:59 But I think they are an indication of how
00:08:59 --> 00:09:01 quickly these things can happen. You know, if
00:09:01 --> 00:09:03 we were talking a decade ago, we'd have been
00:09:03 --> 00:09:05 talking about a couple of thousand satellites
00:09:05 --> 00:09:07 orbiting Earth. We're now talking about
00:09:07 --> 00:09:09 roughly 50. With plants have more than a
00:09:09 --> 00:09:12 million within the next decade, it's getting
00:09:13 --> 00:09:16 quite terrifying, actually. As much from the
00:09:16 --> 00:09:18 atmosphere and climate side of things as
00:09:18 --> 00:09:20 anything else. You know, if we have a million
00:09:20 --> 00:09:23 Starlink satellites in orbit in five years or
00:09:23 --> 00:09:26 10 years time, they have an average lifetime
00:09:26 --> 00:09:27 of five years, which means we'd have more
00:09:27 --> 00:09:29 than 500 per day burning up in the
00:09:29 --> 00:09:31 atmosphere. And that's
00:09:32 --> 00:09:35 a factor of 100, if not more times
00:09:35 --> 00:09:37 material entering the atmosphere on a daily
00:09:37 --> 00:09:39 basis than we get from the background of
00:09:39 --> 00:09:42 space stuff falling in. We'll be running an
00:09:42 --> 00:09:44 experiment in atmospheric science that we've
00:09:44 --> 00:09:47 never run, dumping hundreds of
00:09:47 --> 00:09:49 tonnes of aluminium into the upper atmosphere
00:09:49 --> 00:09:49 every day.
00:09:50 --> 00:09:52 Andrew Dunkley: Yeah, what's the effect going to be? And
00:09:52 --> 00:09:55 that's the $64 question, I suppose.
00:09:55 --> 00:09:57 Jonti Horner: But now the interesting thing there, coming
00:09:57 --> 00:10:00 back to the astrobiology, is that might
00:10:00 --> 00:10:02 well create a signature in the Earth's
00:10:02 --> 00:10:04 atmosphere that would be detectable
00:10:05 --> 00:10:07 from observers from around another star.
00:10:08 --> 00:10:10 Because one of the ways that we would look
00:10:10 --> 00:10:13 for biosignatures, at least early
00:10:13 --> 00:10:16 on, will be to look at the light
00:10:16 --> 00:10:19 from a star reaching us whilst a given
00:10:19 --> 00:10:21 planet is transiting between us and the star,
00:10:21 --> 00:10:24 so blocking a bit of that star's light. We
00:10:24 --> 00:10:25 can currently do this with giant planets,
00:10:25 --> 00:10:28 Jupiter sized, and a fraction of the light
00:10:28 --> 00:10:30 from the star passes through the planet's
00:10:30 --> 00:10:33 atmosphere. And you get imprinted on the
00:10:33 --> 00:10:35 stars like the chemical fingerprint of the
00:10:35 --> 00:10:37 constituents of the outer layers of the
00:10:37 --> 00:10:39 atmosphere where the lights pass through in
00:10:39 --> 00:10:41 the form of absorption lines. And um, by
00:10:41 --> 00:10:43 studying them, we can work out some of the
00:10:43 --> 00:10:45 chemical species that are prevalent there and
00:10:45 --> 00:10:46 even learn a bit about the structure of the
00:10:46 --> 00:10:48 atmosphere, the presence of clouds, things
00:10:48 --> 00:10:51 like that. Now when we get to the point where
00:10:51 --> 00:10:53 we've got all those satellites burning up in
00:10:53 --> 00:10:56 our atmosphere, imagining with the kind of
00:10:56 --> 00:10:57 technology that we're looking at developing
00:10:57 --> 00:11:00 within the next decade or so, or maybe a
00:11:00 --> 00:11:02 little bit longer, imagining being on a
00:11:02 --> 00:11:04 nearby star looking at the sun while the
00:11:04 --> 00:11:06 Earth is transiting, you're suddenly
00:11:06 --> 00:11:09 introducing a huge spike of aluminium and
00:11:09 --> 00:11:11 into the absorption in an Earth like planet's
00:11:11 --> 00:11:14 atmosphere. And there is no natural way that
00:11:14 --> 00:11:16 I'm aware of that you could get that.
00:11:17 --> 00:11:19 So that would not only be a sign of something
00:11:19 --> 00:11:21 way going on, it would be a bio signature of
00:11:21 --> 00:11:24 technologically developed life that is not
00:11:24 --> 00:11:26 quite so developed as to have learned that
00:11:26 --> 00:11:26 pollution is bad.
00:11:28 --> 00:11:30 Andrew Dunkley: Maybe that's how we find an
00:11:30 --> 00:11:33 intelligent species, uh, beyond Earth.
00:11:33 --> 00:11:36 They find us first and send us a, you
00:11:36 --> 00:11:37 know, welcome pack.
00:11:37 --> 00:11:40 Jonti Horner: Yes. 10 helpful things you can do to fix your
00:11:40 --> 00:11:42 problems. Stop burning things up in the
00:11:42 --> 00:11:43 atmosphere.
00:11:44 --> 00:11:47 Andrew Dunkley: Um, yes, yeah, they may have already
00:11:47 --> 00:11:50 learned that lesson, but um, yeah, okay,
00:11:50 --> 00:11:52 so that's where we're at so far. Where do we
00:11:52 --> 00:11:55 go from here on the astrobiology
00:11:55 --> 00:11:55 train?
00:11:55 --> 00:11:58 Jonti Horner: Well, where we moved to in the latter part of
00:11:58 --> 00:12:00 the last astrobiology episode
00:12:00 --> 00:12:03 was my argument that
00:12:03 --> 00:12:05 you can't just look at a planet and say it's
00:12:05 --> 00:12:07 at the right temperature in the habitable
00:12:07 --> 00:12:10 zone. Um, we can look There. Whee.
00:12:10 --> 00:12:12 It kind of feels a bit like that when you
00:12:12 --> 00:12:15 read a lot of storeys, that the only
00:12:15 --> 00:12:16 consideration that comes into play is how far
00:12:16 --> 00:12:19 the planet is from its star. And I think
00:12:19 --> 00:12:21 instead, it's fairer to say that there are a
00:12:21 --> 00:12:24 huge variety of factors that can make
00:12:24 --> 00:12:27 one planet more or less suitable for the
00:12:27 --> 00:12:28 development of life and therefore for the
00:12:28 --> 00:12:31 observability of life on planets around other
00:12:31 --> 00:12:33 stars. And therefore, given that the
00:12:33 --> 00:12:35 observations to find life are going to be
00:12:35 --> 00:12:37 overwhelmingly the hardest we've ever had to
00:12:37 --> 00:12:40 carry out, we'll have hundreds, if not
00:12:40 --> 00:12:41 thousands of targets to choose from, but
00:12:41 --> 00:12:43 we'll only be able to look at a tiny handful
00:12:43 --> 00:12:46 of them in detail at first. So we need to be
00:12:46 --> 00:12:48 very careful about where we look. The
00:12:48 --> 00:12:50 proximity of the planet and its host star to
00:12:50 --> 00:12:53 the sun will be important because the closer
00:12:53 --> 00:12:55 the star is to a zombie we get for a given
00:12:55 --> 00:12:58 brightness of star, and also the more widely
00:12:58 --> 00:13:00 separated on the sky a star and planet will
00:13:00 --> 00:13:02 be for a given orbital distance between them.
00:13:02 --> 00:13:04 Closer they are, the more widely separated
00:13:04 --> 00:13:06 they are. And while people listening can't
00:13:06 --> 00:13:08 see this, I'm at the minute pointing fingers
00:13:08 --> 00:13:10 up at the side of my eyes to Andrew and then
00:13:10 --> 00:13:12 moving them towards the camera. Fingers are
00:13:12 --> 00:13:14 the same distance apart, but they get wider
00:13:14 --> 00:13:15 and wider apart on the screen as they get
00:13:15 --> 00:13:18 closer. Yeah. So there are clear reasons that
00:13:18 --> 00:13:21 we will look at stars that are nearer to
00:13:21 --> 00:13:23 us rather than further away. But beyond
00:13:23 --> 00:13:25 that, I think it's really important to
00:13:25 --> 00:13:28 consider all the different things that could
00:13:28 --> 00:13:30 factor in to make a given planet more
00:13:30 --> 00:13:33 suitable or less suitable for the
00:13:33 --> 00:13:35 development of life, and view them as like
00:13:36 --> 00:13:38 sliders on a mixing board in a sound studio,
00:13:39 --> 00:13:41 where you can fine tune things to see which
00:13:41 --> 00:13:43 gets the best sound, which gets the best
00:13:43 --> 00:13:46 score. You can rank your targets and
00:13:46 --> 00:13:48 you can start with the most promising ones,
00:13:48 --> 00:13:50 because with limited resources, you don't
00:13:50 --> 00:13:52 just want to do an unbiased survey, you want
00:13:52 --> 00:13:54 to instead maximise your chances of a
00:13:54 --> 00:13:56 positive result. Now, we're heavily biassed.
00:13:56 --> 00:13:58 We only know of one kind of life and that's
00:13:58 --> 00:14:01 Earth life. So we are very biassed towards
00:14:01 --> 00:14:03 looking for places that could support life
00:14:03 --> 00:14:05 like Earth life, because that's the only kind
00:14:05 --> 00:14:08 of life we do know exists that'll factor into
00:14:08 --> 00:14:10 it as well. But in the previous episode,
00:14:10 --> 00:14:12 towards the end, we talked about the way in
00:14:12 --> 00:14:13 which the location in the galaxy could
00:14:13 --> 00:14:16 potentially influence this, with the caveat,
00:14:16 --> 00:14:17 of course, that, uh, we're going to be
00:14:17 --> 00:14:19 looking at everything nearby. So whilst
00:14:19 --> 00:14:20 that's interesting scientifically, it's not
00:14:20 --> 00:14:23 that relevant. And then we also talked about
00:14:23 --> 00:14:25 the way that the nature of the stars that the
00:14:25 --> 00:14:28 planet orbits can influence things. And uh,
00:14:28 --> 00:14:30 not just from the point of view of is a star,
00:14:30 --> 00:14:32 ah, stable or single, but down to more subtle
00:14:32 --> 00:14:35 things like the fact that stars brighten over
00:14:35 --> 00:14:37 time. So just because a planet is in the
00:14:37 --> 00:14:39 habitable zone now doesn't mean it's been in
00:14:39 --> 00:14:42 that zone for long enough for life to become
00:14:42 --> 00:14:42 well established.
00:14:42 --> 00:14:45 So we talked about all that, where we
00:14:45 --> 00:14:47 finished up though we didn't get to my own
00:14:48 --> 00:14:50 personal favourite parts of the science and
00:14:50 --> 00:14:52 the stuff I'm more directly involved with,
00:14:52 --> 00:14:54 which are the more local influences on the
00:14:54 --> 00:14:57 planet, that is the influence of the
00:14:57 --> 00:14:59 planetary system in which that planet moves,
00:14:59 --> 00:15:00 all the other planets and all the debris
00:15:00 --> 00:15:03 therein, but also the impact of the planet
00:15:03 --> 00:15:06 itself, what it's made of, how it behaves.
00:15:06 --> 00:15:07 And there's a lot of subtlety in that that.
00:15:08 --> 00:15:10 When I prepared with my old mentor, Professor
00:15:10 --> 00:15:12 Barry Jones this review article on this 16
00:15:12 --> 00:15:15 years ago now, we dug into and it
00:15:15 --> 00:15:18 highlighted to me how none of these questions
00:15:18 --> 00:15:20 can be answered from people within a single
00:15:20 --> 00:15:23 research silo at all. You need researchers
00:15:23 --> 00:15:24 from all different disciplines of human
00:15:24 --> 00:15:27 experience, from the sciences, the biological
00:15:27 --> 00:15:29 sciences, physical sciences, geosciences,
00:15:29 --> 00:15:31 chemistry and astronomers all to come
00:15:31 --> 00:15:34 together. You probably also need philosophers
00:15:34 --> 00:15:36 and archaeologists to come into the
00:15:36 --> 00:15:38 discussion to talk about, about how we look
00:15:38 --> 00:15:40 and why we look and what we look for. And
00:15:40 --> 00:15:43 that's particularly true when we start moving
00:15:43 --> 00:15:46 from simple life to life that could talk
00:15:46 --> 00:15:48 back to us. And a very dear friend of mine in
00:15:48 --> 00:15:50 Australia who Fred Watson probably knows very
00:15:50 --> 00:15:52 well as well is Professor Alice Gorman down
00:15:52 --> 00:15:55 at Adelaide, who's a space archaeologist and
00:15:55 --> 00:15:57 has given some of the most astonishing and
00:15:57 --> 00:15:59 mind blowing talks I've ever seen from the
00:15:59 --> 00:16:01 point of view of someone who is trained in
00:16:01 --> 00:16:04 archaeology looking at the record of human
00:16:04 --> 00:16:06 space flight and what we should do to
00:16:06 --> 00:16:08 preserve artefacts like the Apollo landing
00:16:08 --> 00:16:09 site for future generations. Generations how
00:16:09 --> 00:16:11 we should consider that
00:16:13 --> 00:16:14 Andrew Dunkley: I absolutely agree because
00:16:16 --> 00:16:19 it was probably one of the
00:16:19 --> 00:16:21 greatest achievements in human history, if
00:16:21 --> 00:16:23 not the greatest achievement in human
00:16:23 --> 00:16:25 history. I mean inventing the wheel probably
00:16:25 --> 00:16:27 would have been a pretty cool thing too, but
00:16:27 --> 00:16:29 I don't know where that happened or when and
00:16:29 --> 00:16:31 they never would have thought to commemorate
00:16:31 --> 00:16:34 it. But um, it is something that
00:16:34 --> 00:16:37 should, should, you know, when we eventually
00:16:37 --> 00:16:39 have permanent residents on the moon,
00:16:39 --> 00:16:42 at least need to put a cyclone fence around
00:16:42 --> 00:16:44 it just for the time being until we can build
00:16:45 --> 00:16:48 a proper structure to protect
00:16:48 --> 00:16:48 it.
00:16:48 --> 00:16:49 Jonti Horner: Probably a good place to have rabbit proof
00:16:49 --> 00:16:51 fence because that will, that'll do the job.
00:16:52 --> 00:16:55 Andrew Dunkley: Um, yeah, well, you know that rabbits will
00:16:55 --> 00:16:57 ultimately be on the moon. They tend to be
00:16:57 --> 00:16:58 everywhere else.
00:16:58 --> 00:17:00 Jonti Horner: Um, now one of the greatest conference talks
00:17:00 --> 00:17:02 ever witnessed actually was a talk by a list
00:17:02 --> 00:17:03 talking about archaeology. And it was from
00:17:03 --> 00:17:06 the education and biases
00:17:06 --> 00:17:08 point of view. And I know this is already a
00:17:08 --> 00:17:10 bit off topic, but it's a storey I think
00:17:10 --> 00:17:12 really well worth repeating. Alice is an
00:17:12 --> 00:17:14 archaeologist and so she teaches archaeology
00:17:14 --> 00:17:16 students and she gave this talk about how she
00:17:16 --> 00:17:18 took a group of her uh, final year students
00:17:19 --> 00:17:21 to this site in Fairlie Regional New South
00:17:21 --> 00:17:24 Wales for a two day dig. Basically go out
00:17:24 --> 00:17:25 there, dig and come back to me with what you
00:17:25 --> 00:17:27 find and tell me about the storey of the
00:17:27 --> 00:17:29 site. And after two days all these
00:17:30 --> 00:17:31 young students came back and said, look, we
00:17:31 --> 00:17:33 didn't really find much, we found a few
00:17:33 --> 00:17:35 Aboriginal artefacts and that's kind of
00:17:35 --> 00:17:37 interesting, but all we found was a load of
00:17:37 --> 00:17:38 rubbish. We found all these blooming cable
00:17:38 --> 00:17:40 ties and bits of plastic that are polluting
00:17:40 --> 00:17:43 the site. What she then went on to do
00:17:43 --> 00:17:46 was the whole point was that the cable ties
00:17:46 --> 00:17:48 were actually the archaeology that she was
00:17:48 --> 00:17:50 interested in. So she went um, on and um,
00:17:50 --> 00:17:52 said in the talk that this was an old
00:17:52 --> 00:17:54 decommissioned listening station that had
00:17:54 --> 00:17:56 been built I think in like the late 1940s,
00:17:56 --> 00:17:58 post World War II, and operated into maybe
00:17:58 --> 00:18:00 the late 60s, early 70s before being
00:18:00 --> 00:18:03 demolished and removed. But by looking at the
00:18:03 --> 00:18:05 cable ties where they'd been identified had
00:18:05 --> 00:18:08 knowing a little bit about how cable ties and
00:18:08 --> 00:18:10 cable tie technology changed over the years,
00:18:10 --> 00:18:12 you could not only map out exactly where all
00:18:12 --> 00:18:14 the buildings had been and where the wire
00:18:14 --> 00:18:16 runs have been and get the structure of this
00:18:16 --> 00:18:19 long vanished building, you could also
00:18:19 --> 00:18:21 work out which bits were built when. And um,
00:18:22 --> 00:18:24 the whole importance here was partly that
00:18:24 --> 00:18:25 whole thing of one man's trash is another
00:18:25 --> 00:18:28 man's treasure, but it's also how
00:18:28 --> 00:18:30 as a scientist and a researcher, uh,
00:18:31 --> 00:18:34 you will miss things and you'll make mistakes
00:18:34 --> 00:18:36 because of your own personal biases that are
00:18:36 --> 00:18:39 quite often unconscious. And in this case for
00:18:39 --> 00:18:40 these students who've been studying
00:18:40 --> 00:18:43 archaeology, their unconscious bias was that
00:18:43 --> 00:18:46 anything modern is not archaeology. That's
00:18:46 --> 00:18:48 rubbish in the way of good archaeology. And
00:18:48 --> 00:18:50 so they totally miss the point. And it's a
00:18:50 --> 00:18:52 fabulous learning thing. It's why as
00:18:52 --> 00:18:54 scientists we use statistics so much. I know
00:18:54 --> 00:18:56 there's all this stuff about you can show
00:18:56 --> 00:18:58 anything with statistics, damn lies and
00:18:58 --> 00:19:00 statistics, all the rest of it. But
00:19:00 --> 00:19:01 fundamentally the reason that we use
00:19:01 --> 00:19:04 statistics as a tool school is because we as
00:19:04 --> 00:19:06 humans are biassed we've got this incredible
00:19:06 --> 00:19:09 evolutionary ability to see patterns when
00:19:09 --> 00:19:11 they're barely there, but we also have a very
00:19:11 --> 00:19:13 strong ability to see patterns that we expect
00:19:13 --> 00:19:15 to see when those patterns aren't actually
00:19:15 --> 00:19:18 there. And, um, that's certainly true of the
00:19:18 --> 00:19:20 canals on Mars. You know, Giovanni
00:19:20 --> 00:19:23 Schiaparelli saw these canals, these
00:19:23 --> 00:19:25 channels on, um, Mars, which I think the best
00:19:25 --> 00:19:27 explanation is that Mars was really bright.
00:19:27 --> 00:19:29 He had a big telescope and he was actually
00:19:29 --> 00:19:30 seeing the projection of his own capillaries
00:19:30 --> 00:19:33 in his eye, like I'm gonna see tomorrow when
00:19:33 --> 00:19:34 I get my eye test at the opticians and they
00:19:34 --> 00:19:37 do the bright light thing. But all these
00:19:37 --> 00:19:38 other observers with less good eyes and less
00:19:38 --> 00:19:40 good telescopes suddenly started seeing the
00:19:40 --> 00:19:43 canals. And it's this
00:19:43 --> 00:19:45 whole thing of when you're really straining
00:19:45 --> 00:19:47 at the limits of your vision, you see what
00:19:47 --> 00:19:48 you think you're going to see, not what there
00:19:48 --> 00:19:51 actually is. And that's true with our data.
00:19:51 --> 00:19:54 Uh, therefore, you use statistics
00:19:54 --> 00:19:55 to give you a feel for whether what you're
00:19:55 --> 00:19:57 seeing is significant or not, or whether it
00:19:57 --> 00:20:00 exists in the first place. And that's a way
00:20:00 --> 00:20:03 of us combating those biases. Now, that wasn'
00:20:03 --> 00:20:05 in that way to the archaeology students who
00:20:05 --> 00:20:07 thought that cable ties were rubbish, but it
00:20:07 --> 00:20:10 was a fabulous reminder of how we really
00:20:10 --> 00:20:12 need to be aware not only of the explicit
00:20:12 --> 00:20:14 biases, which are the things we choose to do.
00:20:15 --> 00:20:18 If they're doing a survey of people on hair
00:20:18 --> 00:20:20 loss and they say we interviewed men between
00:20:20 --> 00:20:23 18 and 30, that's clearly biassed to
00:20:23 --> 00:20:25 be for men between 18 and 30, not for men of
00:20:25 --> 00:20:27 our age, for example. That's an explicit
00:20:27 --> 00:20:29 bias, it's one that's a conscious choice.
00:20:29 --> 00:20:31 Implicit biases are the sneaky ones, where
00:20:31 --> 00:20:33 you don't realise you're making them. And
00:20:33 --> 00:20:35 that's why I've made it so clear up front
00:20:35 --> 00:20:37 here that we can imagine
00:20:38 --> 00:20:40 all kinds of life. Science fiction does it
00:20:40 --> 00:20:43 wonderfully, but our implicit bias is that,
00:20:43 --> 00:20:44 uh, when we talk about the search for life,
00:20:44 --> 00:20:46 at least in the very short term, we're
00:20:46 --> 00:20:49 actually looking for life like us, not you
00:20:49 --> 00:20:51 and I, but lifelike Earth, uh, life based on
00:20:51 --> 00:20:54 a planet with oceans, living on the surface,
00:20:54 --> 00:20:56 modifying the atmosphere, because that's the
00:20:56 --> 00:20:58 one kind of life we know exists, but also
00:20:58 --> 00:21:00 because that's the one kind of life we could
00:21:00 --> 00:21:02 probably identify with our observations. Life
00:21:02 --> 00:21:05 beneath the ice on Europa is fascinating, but
00:21:05 --> 00:21:07 we can't see it in the solar system. We
00:21:07 --> 00:21:09 wouldn't have a prayer if Europa was found
00:21:09 --> 00:21:11 orbiting another star, because the ice is in
00:21:11 --> 00:21:14 the way life on a surface that modifies an
00:21:14 --> 00:21:16 atmosphere is at least something we
00:21:16 --> 00:21:18 theoretically could detect. So that's making
00:21:18 --> 00:21:20 the implicit explicit.
00:21:21 --> 00:21:23 Andrew Dunkley: Gotcha. All right, we're gonna take a breath,
00:21:24 --> 00:21:27 uh, and get back to Astrobiology Part 2
00:21:27 --> 00:21:29 on Space Nuts.
00:21:30 --> 00:21:32 Let's take a little break from the to tell
00:21:32 --> 00:21:35 you about online, uh, security with our
00:21:35 --> 00:21:38 sponsor NordVPN. Now, ah, you
00:21:38 --> 00:21:40 probably heard us talk about NORDVPN before.
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00:21:53 --> 00:21:55 and I were overseas, we ran into a situation
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00:23:47 --> 00:23:49 Jonti Horner: 3, 2, 1
00:23:50 --> 00:23:51 space nuts.
00:23:51 --> 00:23:54 Andrew Dunkley: And you're with Andrew Dunkley and Professor
00:23:54 --> 00:23:57 Jonty Horner okay, what next,
00:23:57 --> 00:23:59 Jonty, in this search for
00:23:59 --> 00:24:01 extraterrestrial life?
00:24:01 --> 00:24:03 Jonti Horner: Well, I think we come back to moving away
00:24:03 --> 00:24:05 from the diversions of archaeology and stuff
00:24:05 --> 00:24:08 to the factors that could make a planet more
00:24:08 --> 00:24:11 or less suitable as a target. And like I
00:24:11 --> 00:24:12 said, we talked about the galaxy, we talked
00:24:12 --> 00:24:15 about the stars. To me, as a person who
00:24:15 --> 00:24:16 comes originally from a solar system
00:24:16 --> 00:24:18 background, particularly fascinated with
00:24:18 --> 00:24:20 comets and asteroids and stuff like that,
00:24:21 --> 00:24:23 there are a lot of factors that have been
00:24:23 --> 00:24:26 proposed that relate to
00:24:26 --> 00:24:28 the interaction of planets and the
00:24:28 --> 00:24:30 interaction with the debris that's around
00:24:30 --> 00:24:32 that could render planets more or less
00:24:32 --> 00:24:35 suitable as targets. Now one
00:24:35 --> 00:24:37 example of this is the stability of orbits.
00:24:37 --> 00:24:40 You know, there are a variety of different
00:24:40 --> 00:24:42 models of the solar system's youth, some of
00:24:42 --> 00:24:44 which suggest that there were periods of
00:24:44 --> 00:24:46 chaotic instability where the planets orbits
00:24:46 --> 00:24:49 got stirred up, planets maybe even swapped
00:24:49 --> 00:24:51 orbits. Now this is the kind of thing we can
00:24:51 --> 00:24:53 model. And when we discover planetary
00:24:53 --> 00:24:56 systems, we can take the planets that we
00:24:56 --> 00:24:58 think are there and put them into computer
00:24:58 --> 00:25:00 software to run their orbits forward and back
00:25:00 --> 00:25:03 in time to see how they behave. And that's
00:25:03 --> 00:25:05 actually part of my day to day work. That's
00:25:05 --> 00:25:08 the technology I use and lots of tools I've
00:25:08 --> 00:25:10 used in the past to kill planetary systems
00:25:10 --> 00:25:12 that people thought were there because I run
00:25:12 --> 00:25:14 simulations and showed they're simply not
00:25:14 --> 00:25:15 stable on very short timescales.
00:25:17 --> 00:25:18 But on longer time scales, these kind of
00:25:18 --> 00:25:21 perturbations can have a significant impact
00:25:22 --> 00:25:24 on the orbits of planets. You can get
00:25:24 --> 00:25:27 significant shifts over time. You can get
00:25:27 --> 00:25:29 encounters and stirring up, which means
00:25:29 --> 00:25:32 sometimes that a planet will be on an orbit
00:25:32 --> 00:25:34 now that is not the orbit it's occupied in
00:25:34 --> 00:25:37 the past. And uh, those are things that we
00:25:37 --> 00:25:38 could probably pull out, tease out from the
00:25:38 --> 00:25:40 simulation kind of work that I do. And
00:25:40 --> 00:25:42 obviously a planet that is now in the
00:25:43 --> 00:25:45 habitable zone, um, but that was previously
00:25:45 --> 00:25:47 well outside it would not be a good place to
00:25:47 --> 00:25:50 look. Even though it looks good now, it's not
00:25:50 --> 00:25:52 great. It's like, I guess, you know, you've
00:25:52 --> 00:25:54 got two petri dishes in front of you that you
00:25:54 --> 00:25:56 could look at for life, but you can tell that
00:25:56 --> 00:25:58 one of them's been absolutely melted in a
00:25:58 --> 00:26:00 fire. It's at room temperature now, but that
00:26:00 --> 00:26:02 doesn't mean it always has been that same
00:26:02 --> 00:26:04 kind of idea. So that on a coarse scale has
00:26:04 --> 00:26:06 an effect. But there's a subtler version of
00:26:06 --> 00:26:08 that that I've done a little bit of work on
00:26:08 --> 00:26:10 in the past. And I've got a PhD student
00:26:10 --> 00:26:12 working with me at the moment minute, who's
00:26:12 --> 00:26:13 going to look into this a lot more. A
00:26:13 --> 00:26:16 wonderful student called Amber Tilly. It's
00:26:16 --> 00:26:18 the idea of the Milankovitch cycles.
00:26:19 --> 00:26:22 Now, on Earth, we
00:26:22 --> 00:26:24 look at climate change in the short term as
00:26:24 --> 00:26:26 being a big problem because it's a very rapid
00:26:26 --> 00:26:29 change that is being caused by human action.
00:26:29 --> 00:26:32 But on much longer timescales, the climate of
00:26:32 --> 00:26:34 Earth is periodically variable. We've had ice
00:26:34 --> 00:26:37 ages and interglacial periods for the last 2
00:26:37 --> 00:26:39 or 3 million years, which are the direct
00:26:39 --> 00:26:42 result of the subtle nudges and tweaks on
00:26:42 --> 00:26:44 the, uh, Earth from all the other objects in
00:26:44 --> 00:26:46 the solar system, primarily the other
00:26:46 --> 00:26:48 planets, and not mainly Jupiter to be honest.
00:26:48 --> 00:26:51 But most of the planets contribute. These are
00:26:51 --> 00:26:54 called the Milankovitch cycles. They have a
00:26:54 --> 00:26:56 number of effects. Firstly, the Earth on its
00:26:56 --> 00:26:59 axis precesses. It wobbles with a period of
00:26:59 --> 00:27:02 about 23 years. So our polar
00:27:02 --> 00:27:04 axis, which is tilted by currently 23 and a
00:27:04 --> 00:27:07 half degrees to the plane of our orbit,
00:27:07 --> 00:27:09 wobbles around like a kid's wobbly spinning
00:27:09 --> 00:27:12 toy coming to a stop. It precesses, wobbles
00:27:12 --> 00:27:13 around a bit like the thing in Inception
00:27:13 --> 00:27:16 about to fall over. You see this procession?
00:27:16 --> 00:27:18 That's a procession of the equinoxes. That's
00:27:18 --> 00:27:20 why your horoscopes are wrong. While it's one
00:27:20 --> 00:27:22 of the many reasons that your horoscopes are
00:27:22 --> 00:27:23 wrong, but it's particularly why your
00:27:23 --> 00:27:26 horoscopes are out by one particular one
00:27:26 --> 00:27:29 full calendar month. Because the
00:27:29 --> 00:27:31 horoscopes are based on where the sun is, was
00:27:31 --> 00:27:34 in the sky at that date 2 years ago.
00:27:35 --> 00:27:37 And, um, the axis of the Earth has wobbled
00:27:37 --> 00:27:38 round, so it's now one constellation round.
00:27:39 --> 00:27:42 So when the sun is in Aries, according to
00:27:42 --> 00:27:44 your horoscope, it's actually now in Pisces,
00:27:45 --> 00:27:47 all because of the wobble. That wobble takes
00:27:47 --> 00:27:50 23 years to complete. That means that
00:27:50 --> 00:27:52 the direction that the Earth is pointing
00:27:52 --> 00:27:55 changes over time. Essentially. Added
00:27:55 --> 00:27:57 to that, you've got a very slight wobble up
00:27:57 --> 00:27:59 and down where the tilt fire axis, which is
00:27:59 --> 00:28:02 currently 23 and a half degrees, changes from
00:28:02 --> 00:28:04 about 22 to, to 24 degrees, rocking back and
00:28:04 --> 00:28:07 forward. So that causes the size of the
00:28:07 --> 00:28:09 Arctic and Antarctic circles to grow and
00:28:09 --> 00:28:12 shrink very slightly. On um, top of all that,
00:28:12 --> 00:28:13 you've then got the Earth's orbit around the
00:28:13 --> 00:28:16 sun flexing and tilting. Its shape
00:28:16 --> 00:28:18 becomes more circular and more elongated,
00:28:19 --> 00:28:21 more eccentric. With a longer period period,
00:28:21 --> 00:28:23 I think about 100 years, something like
00:28:23 --> 00:28:26 that, our orbit, compared to the orbits of
00:28:26 --> 00:28:28 Jupiter and Saturn, tilts a little bit up and
00:28:28 --> 00:28:31 down the inclination changes, which adds to
00:28:31 --> 00:28:33 the change of the tilt in our spin axis a
00:28:33 --> 00:28:36 little bit. We also have the Earth's orbit
00:28:36 --> 00:28:37 precessing around in just the same way our
00:28:37 --> 00:28:39 poles do, and that's a little bit harder to
00:28:39 --> 00:28:42 visualise. But what that means is that the
00:28:42 --> 00:28:45 direction, if you drew a line from the sun
00:28:45 --> 00:28:47 through the Earth and out into space at, ah,
00:28:47 --> 00:28:49 the point the Earth was at perihelion closest
00:28:49 --> 00:28:52 to the sun, that direction will
00:28:52 --> 00:28:54 gradually move round over time, doing a full
00:28:54 --> 00:28:56 lap with a period of several tens of
00:28:56 --> 00:28:58 thousands of years. So our perihelion
00:28:58 --> 00:29:01 possession processes as well, all of the,
00:29:01 --> 00:29:04 that combined means that, uh,
00:29:04 --> 00:29:06 on average the amount of energy reaching the
00:29:06 --> 00:29:08 Earth's polar regions, averaged over a given
00:29:08 --> 00:29:11 year, varies with type. Sometimes the
00:29:11 --> 00:29:13 poles get a bit more energy and the ice
00:29:14 --> 00:29:16 sheets retreat. Sometimes they get a bit less
00:29:16 --> 00:29:18 energy and the ice sheets come back towards
00:29:18 --> 00:29:20 the equator again. Now, there's a lot of
00:29:20 --> 00:29:22 complex feedback from the Earth because ice
00:29:22 --> 00:29:24 is more reflective than water or land. So
00:29:24 --> 00:29:26 when ice is growing, it has a tendency to
00:29:26 --> 00:29:29 keep growing, and when it's shrinking, that
00:29:29 --> 00:29:31 has a tendency to run away as well. So you've
00:29:31 --> 00:29:33 got all these different feedbacks. But what
00:29:33 --> 00:29:35 that means is that on the Earth we've got
00:29:35 --> 00:29:38 these periodic variations in the
00:29:38 --> 00:29:40 amount of energy at the poles which lead to
00:29:40 --> 00:29:42 periodic glaciations and interglacial
00:29:42 --> 00:29:44 periods. That's the Milankovitch cycles.
00:29:45 --> 00:29:47 It means that on timescales of tens of
00:29:47 --> 00:29:49 thousands of years, our climate is relatively
00:29:49 --> 00:29:52 changeable. What would
00:29:52 --> 00:29:54 happen if the planets were on different
00:29:54 --> 00:29:57 orbits or if you were in a
00:29:57 --> 00:29:59 planetary system with a totally different
00:29:59 --> 00:30:01 architecture? The result would be very
00:30:01 --> 00:30:04 different Milankovitch cycles. You'd have
00:30:04 --> 00:30:06 different periods and you'd also have
00:30:06 --> 00:30:08 different amplitudes. You could imagine
00:30:08 --> 00:30:10 scenarios where instead of our Earth rocking
00:30:10 --> 00:30:13 a little bit from 22 to 24 degrees and back
00:30:13 --> 00:30:16 with its polar axis, it could be like Mars,
00:30:16 --> 00:30:18 whose spin axis varies chaotically, can even
00:30:18 --> 00:30:21 tip over on its side. You could have systems
00:30:21 --> 00:30:23 where there's barely any change whatsoever.
00:30:23 --> 00:30:25 You've got this full gap. Now the beauty is,
00:30:25 --> 00:30:28 again, we've got the tools to test this.
00:30:28 --> 00:30:30 We can run the kind of computational
00:30:30 --> 00:30:32 simulations that I've spent my career doing
00:30:33 --> 00:30:35 and, uh, model the orbits of a planet over
00:30:35 --> 00:30:36 time under the influence of all the other
00:30:36 --> 00:30:39 planets. And I did a lot of simulations of
00:30:39 --> 00:30:42 this between 2012 and 2020. I
00:30:42 --> 00:30:44 kept coming back to the idea, but never got
00:30:44 --> 00:30:46 around to publishing it until we got to 2020,
00:30:46 --> 00:30:49 where I published it with, um, Stephen Cain
00:30:49 --> 00:30:51 from University of California, Riverside. Pam
00:30:51 --> 00:30:53 Vervoort, who was his PhD student at the
00:30:53 --> 00:30:55 time, a couple of other people, people where
00:30:55 --> 00:30:58 we said, what is the influence of Jupiter on
00:30:58 --> 00:31:00 our Milankovitch cycles? What would happen if
00:31:00 --> 00:31:02 you move Jupiter closer to the sun or further
00:31:02 --> 00:31:04 away? If you made Jupiter's
00:31:04 --> 00:31:07 orbit more eccentric or less eccentric, how
00:31:07 --> 00:31:09 would that change the period and, um,
00:31:09 --> 00:31:11 amplitude of the Earth's? Milankovic cycles
00:31:12 --> 00:31:14 did the test. And in many cases, moving
00:31:14 --> 00:31:16 Jupiter destroyed the solar system, which
00:31:16 --> 00:31:18 meant the Earth wouldn't be here, which was
00:31:18 --> 00:31:21 kind of fun, but not very helpful. But for
00:31:21 --> 00:31:22 the versions of the solar system where the,
00:31:23 --> 00:31:26 the Earth was not removed, we got to see
00:31:26 --> 00:31:28 the range, the variety of Milankovitch cycles
00:31:28 --> 00:31:31 we would have from moving Jupiter in a bit
00:31:31 --> 00:31:33 closer or moving it a bit further away. And
00:31:33 --> 00:31:34 for those really interested, we moved Jupiter
00:31:34 --> 00:31:37 in as far as 3 Au from the sun, out as far as
00:31:37 --> 00:31:40 7 Au from the sun, where 5 Au is about where
00:31:40 --> 00:31:42 it is at the minute, 5.2. What we
00:31:42 --> 00:31:44 found, which is quite surprising, is that the
00:31:44 --> 00:31:46 Earth's, uh, Milankovitch cycles are neither
00:31:47 --> 00:31:49 unusually big or unusually small. They're
00:31:49 --> 00:31:50 somewhere in the middle. Middle. Which is a
00:31:50 --> 00:31:52 bit of an argument against a hypothesis
00:31:52 --> 00:31:55 called the Rare Earth hypothesis.
00:31:55 --> 00:31:58 This idea has been around for about 20, 25,
00:31:58 --> 00:32:01 30 years, and I've never really liked it.
00:32:01 --> 00:32:04 It's the idea that life on Earth is such a
00:32:04 --> 00:32:07 remarkable, incredible fluke
00:32:07 --> 00:32:09 that we will never find life elsewhere. And
00:32:09 --> 00:32:11 the authors put forward all these
00:32:11 --> 00:32:13 peculiarities about the Earth, uh, and argue
00:32:13 --> 00:32:15 that without them we would not be here.
00:32:16 --> 00:32:18 And it's a bit of a philosophical thing, but
00:32:19 --> 00:32:21 I think it's very dangerous to look at
00:32:21 --> 00:32:23 somewhere that has life and say, this place
00:32:23 --> 00:32:25 has all these unusual things and they are
00:32:25 --> 00:32:27 therefore required for life because we've
00:32:27 --> 00:32:29 never found life elsewhere. A good example is
00:32:29 --> 00:32:31 the presence of a large moon. And we'll talk
00:32:31 --> 00:32:33 about this a bit more later on. We have life
00:32:33 --> 00:32:35 on Earth and we have a big moon, so it's
00:32:35 --> 00:32:37 natural to think you need a big moon to have
00:32:37 --> 00:32:39 life. But we won't know that until we find
00:32:39 --> 00:32:42 life elsewhere. But that led to this argument
00:32:42 --> 00:32:44 of rare Earth life will be uncommon in the
00:32:44 --> 00:32:47 universe. If rare Earth were true,
00:32:47 --> 00:32:48 then when you look at something like the
00:32:48 --> 00:32:50 Milankovitch cycles, you would expect our
00:32:50 --> 00:32:52 Earth to be unusual in some way,
00:32:54 --> 00:32:56 to have conditions that favour life over your
00:32:56 --> 00:32:59 typical system. And we simply don't find that
00:32:59 --> 00:33:01 our Milankovitch cycles are fairly run of the
00:33:01 --> 00:33:03 mill. They're not big, they're not small,
00:33:03 --> 00:33:06 they're not fast. They're not slow, they're
00:33:06 --> 00:33:08 somewhere in the middle. Now,
00:33:08 --> 00:33:11 um, sorry, Pam went with that. Pam lava vault
00:33:11 --> 00:33:11 was.
00:33:11 --> 00:33:13 She then took the output of that and run it
00:33:13 --> 00:33:15 into climate modelling software, which was
00:33:15 --> 00:33:17 fabulous. And she published that work, work
00:33:17 --> 00:33:20 with us in 2022, where
00:33:20 --> 00:33:22 she was able to link the Milankovitch cycles.
00:33:22 --> 00:33:24 We predicted if you moved Jupiter around
00:33:25 --> 00:33:28 with the amplitude and frequency of the
00:33:28 --> 00:33:29 ice ages, we'd get. And it was really
00:33:29 --> 00:33:31 interesting because it turned out that when
00:33:31 --> 00:33:33 you factor in some of the feedback mechanisms
00:33:33 --> 00:33:35 that are in climate modelling, you actually
00:33:35 --> 00:33:37 could change the Earth's Milkovitch cycles a
00:33:37 --> 00:33:39 little bit and get very drastically different
00:33:39 --> 00:33:42 ice ages, much more frequent and shallower,
00:33:42 --> 00:33:45 or much less frequent and deeper just by
00:33:45 --> 00:33:47 small changes. Now, now, it's all
00:33:47 --> 00:33:49 fascinating just from the solar system point
00:33:49 --> 00:33:51 of view, but what we're really doing is we're
00:33:51 --> 00:33:54 putting down tools that when we find
00:33:54 --> 00:33:56 planets that could be suitable, we can do
00:33:56 --> 00:33:58 these same tests. We can look at them and
00:33:58 --> 00:34:00 say, we're thinking that you might be a
00:34:00 --> 00:34:02 target for life. Let's see what your
00:34:02 --> 00:34:04 Melankovic cycles are like. Let's see how
00:34:04 --> 00:34:06 stable your climate is. And if we find
00:34:06 --> 00:34:09 somewhere that flops between snowball Earth
00:34:09 --> 00:34:12 and a hothouse every 10 years, or that has
00:34:12 --> 00:34:13 incredibly long snowball Earth periods
00:34:13 --> 00:34:15 followed by short periods of temperate
00:34:15 --> 00:34:18 climate climate, even though everything else
00:34:18 --> 00:34:19 looks good, that's probably not as, uh,
00:34:19 --> 00:34:21 suitable for life as somewhere that is
00:34:21 --> 00:34:24 temperate all the time. So we can use that as
00:34:24 --> 00:34:26 a bit of a filter. And that's where the new
00:34:26 --> 00:34:28 PhD student we've got, Amber Tilly, comes in.
00:34:28 --> 00:34:30 Amber's, um, going to be doing the same kind
00:34:30 --> 00:34:32 of work, moving it forward, where she's going
00:34:32 --> 00:34:33 to be looking at a whole slew of different
00:34:33 --> 00:34:36 parameters to see how the
00:34:36 --> 00:34:39 Milankovitch cycles change as you vary
00:34:39 --> 00:34:41 things. She's both going to look at what
00:34:41 --> 00:34:42 would happen if the Earth was a bit more
00:34:42 --> 00:34:44 massive or less massive. How would that
00:34:44 --> 00:34:46 change things? Because of the feedback, you
00:34:46 --> 00:34:48 make Earth more massive, it interacts,
00:34:48 --> 00:34:49 interacts more with other things, stirs them
00:34:49 --> 00:34:52 up, you get a feedback there. She's also
00:34:52 --> 00:34:54 going to look, working with colleagues of
00:34:54 --> 00:34:57 ours overseas, at, uh, models of planet
00:34:57 --> 00:34:59 formation that form planetary systems similar
00:34:59 --> 00:35:02 to the solar system as theoretical
00:35:02 --> 00:35:04 data, and say, what would the Milankovitch
00:35:04 --> 00:35:07 cycles be like in this hypothetical system?
00:35:07 --> 00:35:09 So it's not just a purely hypothetical
00:35:09 --> 00:35:10 question, it's something we can actually dig
00:35:10 --> 00:35:13 into and, um, we can test. And I think
00:35:13 --> 00:35:15 that's fundamental to science. It's no good
00:35:15 --> 00:35:16 just arguing something you want to be able to
00:35:16 --> 00:35:17 Test. Test it.
00:35:18 --> 00:35:21 Andrew Dunkley: Yeah. I suppose what you're suggesting is
00:35:21 --> 00:35:24 that by mucking around with
00:35:24 --> 00:35:27 what we know and making slight alterations,
00:35:27 --> 00:35:30 it gives you an idea of what to look
00:35:30 --> 00:35:33 for going forward in identifying
00:35:33 --> 00:35:34 potential targets.
00:35:34 --> 00:35:37 Jonti Horner: Absolutely. And it's good because one of the
00:35:37 --> 00:35:39 reasons that you'd want to use the Earth is
00:35:39 --> 00:35:41 because we've got a ground truth. You can run
00:35:41 --> 00:35:43 the Earth with the current solar system
00:35:43 --> 00:35:45 parameters and put them into a climate model.
00:35:45 --> 00:35:47 And you should get what we see so we can
00:35:47 --> 00:35:49 ground truth it, which is really, really
00:35:49 --> 00:35:51 important. And, um, that is, I think, one of
00:35:51 --> 00:35:54 the main, most obvious ways where even in a
00:35:54 --> 00:35:56 dynamically stable system, a system that
00:35:56 --> 00:35:58 isn't tearing itself apart, interaction
00:35:58 --> 00:36:00 between planets could have a significant
00:36:00 --> 00:36:03 impact on habitability. And we want to look
00:36:03 --> 00:36:05 into it. It's really, really fascinating.
00:36:06 --> 00:36:08 Andrew Dunkley: Indeed it is. All right, um, we
00:36:08 --> 00:36:11 are talking astrobiology on this
00:36:11 --> 00:36:14 special episode of Space Nuts with Professor
00:36:14 --> 00:36:15 Jonty Horner.
00:36:15 --> 00:36:16 Back in.
00:36:19 --> 00:36:21 Okay, we checked all four systems and
00:36:21 --> 00:36:23 Jonti Horner: being with a go, space nets.
00:36:23 --> 00:36:25 Andrew Dunkley: Jody, I thought we might just start off
00:36:25 --> 00:36:28 this, uh, final segment with a
00:36:28 --> 00:36:30 question from the audience. Uh, it's funny
00:36:30 --> 00:36:33 because this question's come in before any of
00:36:33 --> 00:36:36 these astrobiology episodes have
00:36:36 --> 00:36:39 been released. And yet it's
00:36:39 --> 00:36:41 exactly what we've been talking about. This
00:36:41 --> 00:36:42 comes from Chris.
00:36:42 --> 00:36:45 Jonti Horner: Hi, um, I'm Chris from Axmouth in the uk.
00:36:46 --> 00:36:48 I'd, uh, just like to ask, um, given that
00:36:48 --> 00:36:50 interstellar travel to distance solar systems
00:36:50 --> 00:36:52 is likely to remain impractical for humans,
00:36:53 --> 00:36:55 um, do you think a more realistic long term
00:36:55 --> 00:36:56 strategy would be to
00:36:57 --> 00:36:58 Andrew Dunkley: seed the galaxy with the basic building
00:36:58 --> 00:37:01 blocks of life? Uh, for example,
00:37:01 --> 00:37:04 uh, sending autonomous probes carrying
00:37:04 --> 00:37:06 microbes or prebiotic material that could
00:37:06 --> 00:37:08 Jonti Horner: eventually take hold on suitable planets,
00:37:08 --> 00:37:09 even
00:37:09 --> 00:37:11 Andrew Dunkley: if that process takes thousands or millions
00:37:11 --> 00:37:11 of years.
00:37:12 --> 00:37:12 Jonti Horner: Thanks.
00:37:14 --> 00:37:16 Andrew Dunkley: There's a, uh, thought from Chris. So
00:37:17 --> 00:37:19 he's probably suggesting, you know, could we
00:37:19 --> 00:37:22 seed other planets? Uh, would that be
00:37:22 --> 00:37:24 the way to go? Uh, and autonomous,
00:37:25 --> 00:37:27 uh, vehicles. I think last
00:37:27 --> 00:37:29 time we talked about this a couple of
00:37:29 --> 00:37:32 episodes ago, you, you suggested it's,
00:37:32 --> 00:37:34 it's beyond us to actually
00:37:34 --> 00:37:37 send a human mission to another world
00:37:37 --> 00:37:40 to investigate life. But we could
00:37:41 --> 00:37:43 go the way of autonomous vehicles.
00:37:44 --> 00:37:46 Uh, but for the major
00:37:47 --> 00:37:50 distances, like the impossible distances, uh,
00:37:50 --> 00:37:53 we would have to come up with equipment in
00:37:53 --> 00:37:56 the future that could do it from a
00:37:56 --> 00:37:58 stable environment nearby. Um,
00:37:59 --> 00:38:00 I don't know how you want to tackle that
00:38:00 --> 00:38:00 question.
00:38:01 --> 00:38:02 Jonti Horner: There's a fair bit to it, and I mean, it
00:38:02 --> 00:38:05 reminds me of the wonderful Bobbyverse books
00:38:05 --> 00:38:07 that I've quite enjoyed. You know, um, the
00:38:07 --> 00:38:09 Storey of the Self Intelligent Von Neumann
00:38:09 --> 00:38:11 probes, which are, uh, easy listening and
00:38:11 --> 00:38:13 work very well as audiobooks.
00:38:14 --> 00:38:17 It's a challenging one. So we could
00:38:17 --> 00:38:20 do this. It would be feasible.
00:38:20 --> 00:38:22 The question would become whether it's
00:38:22 --> 00:38:25 ethical and right. Yes, and that's a really
00:38:25 --> 00:38:27 challenging one. Now, there is something that
00:38:27 --> 00:38:30 costs research missions
00:38:30 --> 00:38:32 a vast amount of money called planetary
00:38:32 --> 00:38:35 protection. And it's the idea that if we're
00:38:35 --> 00:38:37 sending a spacecraft that has a possibility
00:38:37 --> 00:38:40 of touching down on a place where we are
00:38:40 --> 00:38:42 currently interested in looking for life,
00:38:42 --> 00:38:45 where there could be life, such as Mars, such
00:38:45 --> 00:38:48 as Europa, uh, Ganymede, Titan, around
00:38:48 --> 00:38:50 Saturn. We don't want to take life with
00:38:50 --> 00:38:52 us because you don't want to find life on
00:38:52 --> 00:38:54 Mars only to discover it's what you took with
00:38:54 --> 00:38:56 you. And also we don't want to pollute or
00:38:56 --> 00:38:59 contaminate those environments. So there's a
00:38:59 --> 00:39:01 huge amount of effort and expense, goes into
00:39:02 --> 00:39:04 extreme sterilisation of spacecraft to kind
00:39:04 --> 00:39:06 of prevent exactly the hypothesis being
00:39:06 --> 00:39:08 discussed here. At the same time,
00:39:09 --> 00:39:12 that idea of populating the galaxy with
00:39:12 --> 00:39:15 simple life that could one day grow
00:39:15 --> 00:39:18 to resemblers or something else has
00:39:18 --> 00:39:20 cropped a few times in science fiction. I
00:39:20 --> 00:39:23 believe that was how Star Trek got
00:39:23 --> 00:39:25 around the fact that all of their humanoid
00:39:25 --> 00:39:27 species looked like people with makeup on.
00:39:28 --> 00:39:30 Um, which of course is a budgetary issue and
00:39:30 --> 00:39:32 a special effects issue. But they had an
00:39:32 --> 00:39:34 episode where people found the founders,
00:39:34 --> 00:39:37 which were an alien, ancient alien humanoid
00:39:37 --> 00:39:39 race at seed of the galaxy. And billions of
00:39:39 --> 00:39:41 years later all these different planets had
00:39:41 --> 00:39:43 grown humanoids that looked like them and.
00:39:43 --> 00:39:46 Oh, well, convenient job done. Stop asking us
00:39:46 --> 00:39:48 that question now, please. Effectively it
00:39:48 --> 00:39:51 is something we could do and the timescales
00:39:51 --> 00:39:53 would be immense. It's also something that,
00:39:53 --> 00:39:55 in all honesty, has already happened. There's
00:39:55 --> 00:39:58 this idea called panspermia, which is the
00:39:58 --> 00:40:00 idea that life could be transferred through
00:40:00 --> 00:40:02 space from planet to planet, carried by
00:40:02 --> 00:40:05 debris from impacts and talking. Thirty or
00:40:05 --> 00:40:07 40 years ago, it was viewed as very much
00:40:07 --> 00:40:09 crank science, not feasible. But every
00:40:09 --> 00:40:11 experiment that people have ever done
00:40:11 --> 00:40:13 suggests that it could work. And I've even
00:40:13 --> 00:40:15 had a PhD student just submit his thesis,
00:40:16 --> 00:40:18 Greg Davis, who has been looking at this
00:40:19 --> 00:40:20 from the point of view of the viability of
00:40:20 --> 00:40:23 bacteria transferred from Earth to Mars or
00:40:23 --> 00:40:26 Mars to Earth in the radiation environment in
00:40:26 --> 00:40:27 the solar system. And it seems to work.
00:40:29 --> 00:40:31 Now, to me, the fact that biological, uh,
00:40:32 --> 00:40:34 material from Earth will have rained down on
00:40:34 --> 00:40:36 Mars and Europa and Ganymede and everywhere
00:40:36 --> 00:40:38 else for the last 4 billion years
00:40:39 --> 00:40:40 probably means that we're being a bit over
00:40:40 --> 00:40:43 cautious with our planet protection efforts
00:40:43 --> 00:40:45 because we're trying not to take something
00:40:45 --> 00:40:47 there when it's already there, it's already
00:40:47 --> 00:40:49 been delivered. The other thing is that
00:40:49 --> 00:40:51 anything we take with us to a place that has
00:40:51 --> 00:40:52 an incredibly, incredibly different
00:40:52 --> 00:40:55 environment, if there is life there already,
00:40:55 --> 00:40:57 that life should hugely outcompete anything
00:40:57 --> 00:40:59 we take with us because it's better adapted
00:40:59 --> 00:41:01 for that environment. And that would be one
00:41:01 --> 00:41:03 of the challenges with this, is sending stuff
00:41:03 --> 00:41:05 out. It'd have to be lucky to get exactly the
00:41:05 --> 00:41:06 right environment to grow. But with the
00:41:06 --> 00:41:09 amount of real estate we've got out there it
00:41:09 --> 00:41:12 could happen. People have even in some more
00:41:12 --> 00:41:15 extreme sci fi suggested kind of
00:41:15 --> 00:41:18 this type approach as a way to
00:41:18 --> 00:41:20 begin terraforming planets ahead of human
00:41:20 --> 00:41:21 arrival. This idea that you could send
00:41:21 --> 00:41:24 generation ships which have to go
00:41:24 --> 00:41:26 slowly because they're really big and carry a
00:41:26 --> 00:41:28 lot of people. But you could send faster
00:41:28 --> 00:41:31 moving, smaller things first to start
00:41:31 --> 00:41:33 working on the biosphere of a planet to make
00:41:33 --> 00:41:35 it so that when we get there that planet is a
00:41:35 --> 00:41:37 suitable home. So there's a lot of ways it
00:41:37 --> 00:41:40 could be taken. Taken. I think to do it
00:41:40 --> 00:41:42 in the near future in an official organised
00:41:42 --> 00:41:44 way would require a significant shift in
00:41:44 --> 00:41:46 global morality in the way we think about
00:41:47 --> 00:41:49 other habitats. If we found that
00:41:49 --> 00:41:52 Mars absolutely has no life and
00:41:52 --> 00:41:54 possibly that it never had life, which I
00:41:54 --> 00:41:56 think is probably unlikely, then I could see
00:41:56 --> 00:41:58 people arguing then for terraforming.
00:41:58 --> 00:42:00 Similarly people have argued about, I think
00:42:00 --> 00:42:03 Carl Sagan suggested this, creating
00:42:03 --> 00:42:06 engineering bacteria that could float in the
00:42:06 --> 00:42:08 clouds of Venus and um, precipitate out the
00:42:08 --> 00:42:10 carbon to eventually make Venus a more
00:42:11 --> 00:42:13 habitable planet on long timescales. The idea
00:42:13 --> 00:42:15 of terraforming these worlds is real. But I
00:42:15 --> 00:42:18 think it would require either a state
00:42:18 --> 00:42:21 to go its own way because as we know, once
00:42:21 --> 00:42:22 things are up in space, ain't nobody going to
00:42:22 --> 00:42:24 stop you. Uh, as was the case with the
00:42:24 --> 00:42:27 Israeli spacecraft that spattered tamigards,
00:42:27 --> 00:42:29 um, water bears over the moon to show that
00:42:29 --> 00:42:32 they could, which was so dumb it's untrue.
00:42:33 --> 00:42:36 Um, yep, there are water bears on the moon,
00:42:36 --> 00:42:38 probably desiccated and dried up, but they
00:42:38 --> 00:42:40 can come back from that, we know that. Um, so
00:42:40 --> 00:42:42 you could have a nation just decide to do it
00:42:42 --> 00:42:44 anyway. At the end of the day, if a
00:42:44 --> 00:42:46 random government decided to send a
00:42:46 --> 00:42:49 spacecraft to Mars within a capsule inside
00:42:49 --> 00:42:52 laden with biological bacterial life
00:42:52 --> 00:42:55 to spurt out on the surface, no way we could
00:42:55 --> 00:42:57 stop them. And once it's done, it's done. Um,
00:42:57 --> 00:43:00 but I think the block to the question is not
00:43:00 --> 00:43:02 actually a scientific one, it's an ethical
00:43:02 --> 00:43:04 one and it's about how we, we choose to
00:43:04 --> 00:43:06 interact with the galaxy going forward and
00:43:06 --> 00:43:08 particularly our local environment. That'll
00:43:08 --> 00:43:10 determine at what stage we do that, if we
00:43:10 --> 00:43:11 ever do so. It's a really good question.
00:43:12 --> 00:43:14 Andrew Dunkley: It is. Uh, thanks for the uh, question,
00:43:14 --> 00:43:16 Chris. Uh, Chris, you might be interested to
00:43:16 --> 00:43:19 look up the BBC radio science
00:43:19 --> 00:43:22 fiction comedy called Paradise Lost in Space.
00:43:22 --> 00:43:24 Have you heard of this one? It's so funny.
00:43:24 --> 00:43:27 It's about two blokes who um, get ejected
00:43:28 --> 00:43:30 from a spaceship by an exploding toilet or
00:43:30 --> 00:43:32 something and they end up on a world that's
00:43:32 --> 00:43:35 occupied by uh, an insect, intelligent but
00:43:35 --> 00:43:38 very naive species. So
00:43:38 --> 00:43:41 basically what they do is they try to
00:43:41 --> 00:43:44 pass on their Earth knowledge and
00:43:44 --> 00:43:46 intelligence to these, these people
00:43:46 --> 00:43:48 and ultimately destroy the planet.
00:43:50 --> 00:43:51 Jonti Horner: It's a perfect reflection.
00:43:51 --> 00:43:52 Andrew Dunkley: Brilliant.
00:43:52 --> 00:43:53 Jonti Horner: It's very funny. Yes.
00:43:55 --> 00:43:58 Andrew Dunkley: Yeah, it's funny stuff. So yeah, it's called
00:43:58 --> 00:44:01 um, Paradise Lost in Space. I
00:44:01 --> 00:44:03 only remember it because we ran it as a
00:44:03 --> 00:44:05 series on the ABC some years ago and, and got
00:44:05 --> 00:44:08 a uh, fabulous response. And I always,
00:44:08 --> 00:44:10 I sat there in the studio while we were
00:44:10 --> 00:44:12 running it and I just cackled as to. Because
00:44:13 --> 00:44:16 I could imagine that's what we might do.
00:44:16 --> 00:44:19 Not on purpose, but um. Yeah. And it's what
00:44:19 --> 00:44:21 you say, it's the ethics of sending
00:44:23 --> 00:44:26 our ah, junk to other places that are already
00:44:26 --> 00:44:28 occupied. Yeah. Um,
00:44:29 --> 00:44:31 we're running out of time I suppose. But um,
00:44:32 --> 00:44:33 how do you want to wind this up? Uh, how do
00:44:33 --> 00:44:33 you.
00:44:34 --> 00:44:36 There's so much to talk about, it could go on
00:44:36 --> 00:44:36 for hours.
00:44:36 --> 00:44:38 Jonti Horner: I know more to talk about. I think I'll carry
00:44:38 --> 00:44:41 on until you kind of get the hook and pull me
00:44:41 --> 00:44:43 off about the different things that influence
00:44:43 --> 00:44:45 planet's habitability. Because we've talked
00:44:45 --> 00:44:48 about Milankovitch cycles. We also have as
00:44:48 --> 00:44:50 the influence of the planetary system impact
00:44:50 --> 00:44:53 us just as the dinosaurs, they had a very bad
00:44:53 --> 00:44:55 day. And there has historically been this
00:44:55 --> 00:44:57 idea that ties into the rare Earth thing that
00:44:57 --> 00:45:00 Jupiter is our friend and saviour and without
00:45:00 --> 00:45:02 Jupiter we'd be hit by asteroids more often
00:45:02 --> 00:45:04 and we wouldn't be here. And therefore life
00:45:04 --> 00:45:07 is rare in the universe. Um, idea
00:45:07 --> 00:45:09 basically that Jupiter is our bestest friend
00:45:09 --> 00:45:12 and it's honestly a lot of cobs wallop and
00:45:12 --> 00:45:15 it's both one of my favourite bits of
00:45:15 --> 00:45:16 research I ever did. And probably one of the
00:45:16 --> 00:45:19 biggest bugbears of my career is uh, I
00:45:19 --> 00:45:22 did work again with Barry Jones starting 20
00:45:22 --> 00:45:24 years ago for a few years that resulted in a
00:45:24 --> 00:45:27 series of pep called Jupiter Friend or Foe.
00:45:27 --> 00:45:29 And we did simulations to test the role of
00:45:29 --> 00:45:32 Jupiter in protecting us from impacts or not.
00:45:32 --> 00:45:34 And it turns out that Jupiter is not shielded
00:45:35 --> 00:45:37 all if you took Jupiter away, Earth would be
00:45:37 --> 00:45:40 hit less often. If however you
00:45:40 --> 00:45:42 replace Jupiter with a planet, the mass of
00:45:42 --> 00:45:45 Saturn, Earth would be hit more often than we
00:45:45 --> 00:45:47 are today. And with Jupiter, the mass it
00:45:47 --> 00:45:49 currently is, we'd be hit more than if it
00:45:49 --> 00:45:50 wasn't there, but less than if we put Saturn
00:45:50 --> 00:45:53 there. All down to the subtleties of how
00:45:53 --> 00:45:55 gravity all works. And so basically if you
00:45:55 --> 00:45:57 replace Jupiter with Saturn, it's like the
00:45:57 --> 00:45:59 anti Goldilocks case where you've lesser
00:45:59 --> 00:46:01 porridge with strychnine. But the reality is
00:46:01 --> 00:46:04 that Jupiter's role is complicated,
00:46:05 --> 00:46:07 best illustrated by Comet Lexell in
00:46:07 --> 00:46:10 1770, which I always love. Comet Lexell was
00:46:11 --> 00:46:13 a great comet. It was very bright in our sky.
00:46:13 --> 00:46:15 Discovered by Charles Messier I think 1st of
00:46:15 --> 00:46:18 June 1770. Quickly got as
00:46:18 --> 00:46:19 bright as the brightest stars in the sky, but
00:46:19 --> 00:46:22 looked unusual. It was very big and fuzzy and
00:46:22 --> 00:46:24 it moved unusually rapidly across the sky at
00:46:24 --> 00:46:26 its quickest, covering 42 degrees in a single
00:46:26 --> 00:46:29 hour. When they worked out the orbit of this
00:46:29 --> 00:46:31 thing, they found a that it had come very
00:46:31 --> 00:46:32 close to the Earth. It passed within 2
00:46:32 --> 00:46:34 million kilometres, which is the close
00:46:34 --> 00:46:36 closest approach of a large comet in
00:46:37 --> 00:46:40 historical times. It also was moving
00:46:40 --> 00:46:41 on an orbit that was just less than six years
00:46:41 --> 00:46:44 in period. Big bright comet going around
00:46:44 --> 00:46:46 every six years. Why on Earth have we not
00:46:46 --> 00:46:47 seen it before? Why have we not seen it in
00:46:47 --> 00:46:50 1764 or 1758? Well,
00:46:50 --> 00:46:52 when they worked out the orbit and run it
00:46:52 --> 00:46:54 back in time and this was hard at the time
00:46:54 --> 00:46:56 because they didn't have mechanical
00:46:56 --> 00:46:58 computers, they had human computers who sat
00:46:58 --> 00:47:00 there and did calculations with abakai and
00:47:00 --> 00:47:02 slide rules and all the rest of it. They
00:47:02 --> 00:47:04 found that three years before it nearly hit
00:47:04 --> 00:47:07 the Earth it was very close to Jupiter. In
00:47:07 --> 00:47:08 fact, prior to that it had been moving on an
00:47:08 --> 00:47:11 orbit that came nowhere near the Earth, that
00:47:11 --> 00:47:12 was probably hundreds or thousands of years
00:47:12 --> 00:47:15 in period and it was flying in to come
00:47:15 --> 00:47:16 nowhere near the inner solar system. When it
00:47:16 --> 00:47:18 had this close encounter with Jupiter that
00:47:18 --> 00:47:20 trapped it and threw it at the Earth and
00:47:20 --> 00:47:22 captured it onto the six year long Jupiter
00:47:22 --> 00:47:25 family comet orbit. So Jupiter took something
00:47:25 --> 00:47:27 that was coming nowhere near us and threw it
00:47:27 --> 00:47:30 out at us. We don't see the comet
00:47:30 --> 00:47:33 anymore because 2 times 6 years is
00:47:33 --> 00:47:34 12 years and Jupiter takes 12 years to go
00:47:34 --> 00:47:37 around the sun. So the comet did two laps in
00:47:37 --> 00:47:39 the time Jupiter took to take one. And when
00:47:39 --> 00:47:41 the comet got back out there again 12 years
00:47:42 --> 00:47:44 after the first encounter, Jupiter was there,
00:47:44 --> 00:47:45 grabbed hold of it and threw it away again,
00:47:45 --> 00:47:48 never to return. So in just this 12 year
00:47:48 --> 00:47:51 period, Jupiter threw something at us and
00:47:51 --> 00:47:53 then cleaned up after itself. And whether
00:47:53 --> 00:47:55 Jupiter's more of a shield or more of a
00:47:55 --> 00:47:56 threat is down to the balance of those two
00:47:56 --> 00:47:59 effects. Um, and what we found in our
00:47:59 --> 00:48:02 simulations is, to be honest with Jupiter, we
00:48:02 --> 00:48:03 get hit more than we would do if it wasn't
00:48:03 --> 00:48:06 there. That takes away the idea
00:48:06 --> 00:48:09 that it's our protector. It takes away the
00:48:09 --> 00:48:11 idea that you need a shield to shield a
00:48:11 --> 00:48:14 planet to prevent life from being wiped out.
00:48:14 --> 00:48:17 Another nail in the coffin of rare Earth. And
00:48:17 --> 00:48:19 it bugs me a bit that so many documentaries
00:48:19 --> 00:48:22 still trot out this trite idea that Jupiter
00:48:22 --> 00:48:24 shields us from impacts. And it's wonderful
00:48:24 --> 00:48:27 because I disprove that 20 years ago. It's
00:48:27 --> 00:48:29 much more complicated. But even that idea
00:48:29 --> 00:48:31 gets complicated because obviously we don't
00:48:31 --> 00:48:32 want to have the Earth punishingly, uh,
00:48:33 --> 00:48:36 pummelling because we'd be wiped out. But
00:48:36 --> 00:48:37 where the Earth formed in the solar system,
00:48:37 --> 00:48:40 it probably formed dry. We formed interior to
00:48:40 --> 00:48:42 the location of the ice line. So there wasn't
00:48:42 --> 00:48:45 any available solid water, the water was all
00:48:45 --> 00:48:47 gas. So how the Earth got its water was a
00:48:47 --> 00:48:50 long, outstanding problem, exacerbated by the
00:48:50 --> 00:48:52 fact that towards the end of our planet's
00:48:52 --> 00:48:53 formation, we got smashed into by an object
00:48:53 --> 00:48:56 the size of Mars, which stripped off a lot of
00:48:56 --> 00:48:57 the Earth's core and mantle and would have
00:48:57 --> 00:48:59 desiccated our planet because m water would
00:48:59 --> 00:49:01 have been in the. Or a mantle, in the crust
00:49:01 --> 00:49:04 and mantle. Sorry, up near the surface. Yeah.
00:49:04 --> 00:49:06 So where did the water come from? And Earth
00:49:06 --> 00:49:08 is actually a remarkably dry planet, um,
00:49:08 --> 00:49:10 particularly at the moment in Queensland. The
00:49:10 --> 00:49:13 idea is down here. Yeah, the idea is that our
00:49:13 --> 00:49:15 water, at least in significant part, was
00:49:15 --> 00:49:18 delivered from further out by impacts in what
00:49:18 --> 00:49:20 is often described as a late veneer.
00:49:21 --> 00:49:23 That's really interesting air because that's
00:49:23 --> 00:49:25 a stochastic process, it's random, it's
00:49:25 --> 00:49:27 driven by the orbits of the planets and the
00:49:27 --> 00:49:29 cleanup phase of solar system formation.
00:49:29 --> 00:49:31 So different planetary systems will give
00:49:31 --> 00:49:34 planets with different amounts of water. But
00:49:34 --> 00:49:36 it's also indicating that you actually don't
00:49:36 --> 00:49:38 want too much shielding, you need
00:49:38 --> 00:49:40 impacts. Because if the Earth had never had
00:49:40 --> 00:49:42 the impacts, we'd have never got enough water
00:49:42 --> 00:49:45 for life to develop and thrive. On top of
00:49:45 --> 00:49:46 that, if the Earth didn't have enough
00:49:46 --> 00:49:48 impacts, the dinosaurs would never have been
00:49:48 --> 00:49:50 wiped out. And maybe you and I will be
00:49:50 --> 00:49:52 reptiles or maybe we'll be here, you know,
00:49:53 --> 00:49:55 so there's a whole aspect of that. Now,
00:49:55 --> 00:49:58 again, those Simulations I did, we can
00:49:58 --> 00:50:00 rerun through the planetary systems, we can
00:50:00 --> 00:50:02 find the debris belts in those systems, we
00:50:02 --> 00:50:04 can find the planets so we can model their
00:50:04 --> 00:50:06 impact rates. And I'd argue that we want to
00:50:06 --> 00:50:08 look somewhere that doesn't have too many
00:50:08 --> 00:50:10 impacts, but also doesn't have too few,
00:50:11 --> 00:50:13 because each of those could pose problems.
00:50:14 --> 00:50:17 That is a really big part of the storey
00:50:17 --> 00:50:19 and it feeds into the last point, really,
00:50:21 --> 00:50:23 which is the planet itself and a little bit
00:50:23 --> 00:50:26 tied to the large moon. So our Earth, it has
00:50:26 --> 00:50:28 been suggested again by the rare Earth crowd,
00:50:28 --> 00:50:31 that the large moon we have stabilises our
00:50:31 --> 00:50:33 atmosphere axis and has kept the Earth
00:50:33 --> 00:50:35 habitable. So therefore you need a giant
00:50:35 --> 00:50:38 satellite. But simulations by Dave
00:50:38 --> 00:50:40 Waltham, who's a guy I know very well in the
00:50:40 --> 00:50:42 uk, looked into this and what he found was
00:50:42 --> 00:50:44 that you could take the Moon away and, uh,
00:50:44 --> 00:50:46 the Earth's axis would still be fairly
00:50:46 --> 00:50:48 stable. It still wobbled between about 22 and
00:50:48 --> 00:50:50 24 degrees, maybe a little bit more. But
00:50:50 --> 00:50:52 quirkily, if you made the moon just 12
00:50:52 --> 00:50:54 kilometres larger in diameter,
00:50:55 --> 00:50:57 it would make the Earth's axis unstable and
00:50:57 --> 00:51:00 chaotic. So if the moon was only slightly
00:51:00 --> 00:51:03 larger, we would not be here. The
00:51:03 --> 00:51:04 other reason that a large moon has been
00:51:04 --> 00:51:07 suggested is that it drives bigger tides. And
00:51:07 --> 00:51:09 one of the common arguments for how life
00:51:09 --> 00:51:12 first got going and, um, for how life moved
00:51:12 --> 00:51:14 out of the oceans in both cases is to do with
00:51:14 --> 00:51:16 the large tidal intertidal areas that we
00:51:16 --> 00:51:18 have, where at low tide it's dry and at high
00:51:18 --> 00:51:21 tide it's underwater. And the idea is that
00:51:21 --> 00:51:23 without the moon those areas would be smaller
00:51:23 --> 00:51:25 and life would have had less chance to get
00:51:25 --> 00:51:26 going. I don't really buy that, because if
00:51:26 --> 00:51:29 you took the moon away, the tides of sun
00:51:29 --> 00:51:31 raises would still be half the size, so you'd
00:51:31 --> 00:51:33 still have substantial tides. But these are
00:51:33 --> 00:51:36 all the kind of questions people ask before
00:51:36 --> 00:51:38 you get to the planet itself. And the planet
00:51:38 --> 00:51:40 itself is where my head really hurt. Now, I'm
00:51:40 --> 00:51:43 not a geophysicist at
00:51:43 --> 00:51:45 all, so a lot of this was new to me. Now, we
00:51:45 --> 00:51:47 talked a little bit about the hydration. You
00:51:47 --> 00:51:49 could imagine anything from desert worlds to
00:51:49 --> 00:51:51 worlds with hundreds of kilometres depth of
00:51:51 --> 00:51:53 ocean. Now, if the ocean's too deep,
00:51:54 --> 00:51:56 the planet is probably habitable, but not
00:51:56 --> 00:51:59 detectably habitable because the life will be
00:51:59 --> 00:52:00 at the bottom of the ocean where the
00:52:00 --> 00:52:02 nutrients have been introduced by volc. But
00:52:02 --> 00:52:04 an ocean deeper than a few tens of kilometres
00:52:04 --> 00:52:07 is thought to become stagnant. And so it
00:52:07 --> 00:52:09 doesn't mix things up to the surface, so you
00:52:09 --> 00:52:11 don't want to look at water worlds that are
00:52:11 --> 00:52:13 ocean for hundreds or thousands of kilometres
00:52:13 --> 00:52:16 depth, but equally you want to have some mix
00:52:16 --> 00:52:18 of ocean and continent to allow all the
00:52:18 --> 00:52:20 carbon cycles and weathering to happen, to
00:52:20 --> 00:52:23 allow life to engage with the atmosphere. So
00:52:23 --> 00:52:24 that's a bit of a sweet spot there. But what
00:52:24 --> 00:52:27 I didn't realise was how critical
00:52:27 --> 00:52:30 water has been been to the
00:52:30 --> 00:52:33 maintenance of our atmosphere and um, thereby
00:52:33 --> 00:52:35 our climate against the vagaries of the solar
00:52:35 --> 00:52:37 wind and against the vagaries of plate
00:52:37 --> 00:52:40 tectonics. Now compare the Earth and Mars
00:52:40 --> 00:52:42 and the Earth is warm and wet. We've got a
00:52:42 --> 00:52:44 lovely thick atmosphere and we've not really
00:52:44 --> 00:52:46 lost much of our atmosphere. We've got the
00:52:46 --> 00:52:49 ozone layer which protects us to some degree
00:52:49 --> 00:52:51 from UV radiation. We've got a temperature
00:52:51 --> 00:52:53 inversion about 10 kilometres up in the
00:52:53 --> 00:52:55 atmosphere that traps water below that level.
00:52:55 --> 00:52:57 If water gets above that level, it freezes
00:52:57 --> 00:52:59 and falls back down. So the water can't get
00:52:59 --> 00:53:01 high enough to be ionised and split hydrogen
00:53:01 --> 00:53:04 and helium and lost. Mars doesn't have that.
00:53:05 --> 00:53:06 Mars doesn't have much of a magnetic field
00:53:06 --> 00:53:08 whereas the Earth does. And the magnetic
00:53:08 --> 00:53:10 field protects the atmosphere from being
00:53:10 --> 00:53:12 stripped away from the outside in. Mars
00:53:12 --> 00:53:15 doesn't have plate tectonics, but we do. And
00:53:15 --> 00:53:18 um, plate tectonics prevents the atmosphere
00:53:18 --> 00:53:21 from being precipitated out onto the surface
00:53:21 --> 00:53:23 through chemistry and trapped there because
00:53:23 --> 00:53:25 plate tectonics recycles the crust. So
00:53:25 --> 00:53:27 anything that chemically gets weathered onto
00:53:27 --> 00:53:29 Earth's surface gets put back into the
00:53:29 --> 00:53:32 atmosphere through volcanic volcanoes. So
00:53:32 --> 00:53:34 Mars and Earth probably started out looking
00:53:34 --> 00:53:36 very similar and are now very, very
00:53:36 --> 00:53:38 different. And so the nature of the planet
00:53:38 --> 00:53:40 itself is going to be a real important
00:53:40 --> 00:53:43 factor. And plate tectonics looks like it's
00:53:43 --> 00:53:46 going to be fairly key. Plate tectonics is a
00:53:46 --> 00:53:47 mechanism by which you stop the atmosphere
00:53:47 --> 00:53:49 getting precipitated out and frozen in onto
00:53:49 --> 00:53:51 the surface, which is a big part of what's
00:53:51 --> 00:53:53 happened m on Mars because of that recycling
00:53:53 --> 00:53:56 effect. But it also turns out that plate
00:53:56 --> 00:53:58 tectonics is key in ensuring the
00:53:58 --> 00:54:01 magnetic field is retained. And um, this is a
00:54:01 --> 00:54:03 bit that really hurt my head because I'm
00:54:03 --> 00:54:06 like, I'm not a geophysicist. Seems that on
00:54:06 --> 00:54:09 the Earth if the Earth didn't have plate
00:54:09 --> 00:54:11 tectonics, we'd probably have lost most of
00:54:11 --> 00:54:14 our magnetic field like Mars and like Venus.
00:54:15 --> 00:54:16 What's happening is that the magnetic field
00:54:16 --> 00:54:19 is driven by convection currents in the outer
00:54:19 --> 00:54:21 mantle. Like when you see water boiling in a
00:54:21 --> 00:54:24 kettle overturn, um, motion of mollie and
00:54:24 --> 00:54:26 metal Rising and falling. That
00:54:26 --> 00:54:28 convection can only happen if you've got a
00:54:28 --> 00:54:30 big temperature difference between the bottom
00:54:30 --> 00:54:32 and the top of the outer core. Sorry.
00:54:33 --> 00:54:35 In order to get that temperature difference,
00:54:35 --> 00:54:37 you need to be able to very effectively cool
00:54:37 --> 00:54:39 the top of the outer core because otherwise
00:54:39 --> 00:54:40 it would warm up so much convection would
00:54:40 --> 00:54:42 stop because you don't have enough
00:54:42 --> 00:54:44 temperature difference. The way the outer
00:54:44 --> 00:54:46 core is cooled is by convection in the
00:54:46 --> 00:54:48 mantle. That takes the heat away from the top
00:54:48 --> 00:54:49 of the outer core and brings it to the
00:54:49 --> 00:54:51 surface. We've got these huge convection
00:54:51 --> 00:54:53 cells in the mantle that transfer heat very
00:54:53 --> 00:54:56 quickly. Allowing cool the outer core's top
00:54:56 --> 00:54:59 to get this big temperature difference allows
00:54:59 --> 00:55:01 a motion that drives a magnetic field.
00:55:02 --> 00:55:04 That motion is also what drives plate
00:55:04 --> 00:55:06 tectonics. Now, the quirky thing that came
00:55:06 --> 00:55:07 out of all of this when I was reading about
00:55:07 --> 00:55:10 it is that, uh, if you run simulations of the
00:55:10 --> 00:55:12 motion of the Earth's mantle and the crust
00:55:12 --> 00:55:15 and the Earth is dry, the Earth is too small
00:55:15 --> 00:55:18 to sustain plate tectonics because the mantle
00:55:18 --> 00:55:21 is too stiff. If you have water
00:55:21 --> 00:55:23 and you mix water into the mantle, you
00:55:23 --> 00:55:25 lubricate, lubricate it. You allow convection
00:55:25 --> 00:55:28 in the mantle, which allows plate tectonics,
00:55:28 --> 00:55:31 which allows you to recycle the surface. But
00:55:31 --> 00:55:33 that plate tectonics also allows you to cool
00:55:33 --> 00:55:35 the outer core to maintain the magnetic
00:55:35 --> 00:55:37 field, allowing you to have that magnetic
00:55:37 --> 00:55:39 shield that protects your planet from the
00:55:39 --> 00:55:40 atmosphere being whittled away from the
00:55:40 --> 00:55:43 outside in by the solar wind. It
00:55:43 --> 00:55:46 seems that the storey of plate tectonics, the
00:55:46 --> 00:55:48 Earth's magnetic field and, um, the
00:55:48 --> 00:55:51 atmosphere being retained, is all tied
00:55:51 --> 00:55:53 together by water. Which brings us back to
00:55:53 --> 00:55:55 that delivery question. If the Earth had not
00:55:55 --> 00:55:57 got that veneer of water, would plate
00:55:57 --> 00:56:00 tectonics still happen? The infinite
00:56:00 --> 00:56:02 suggestion, and this was fabulous work by
00:56:02 --> 00:56:03 people working with the great Craig o',
00:56:03 --> 00:56:06 Neill, a great Australian scientist who does
00:56:06 --> 00:56:08 earthquakes and, um, plate tectonics
00:56:08 --> 00:56:11 modelling in an astrobiology sense that
00:56:11 --> 00:56:14 says the Earth's plate tectonics are
00:56:14 --> 00:56:15 really hard to get started. If you run models
00:56:15 --> 00:56:17 of the Earth without plate tectonics with the
00:56:17 --> 00:56:19 young Earth, with how hot it was, plate
00:56:19 --> 00:56:22 tectonics don't just happen. However, if
00:56:22 --> 00:56:25 you introduce impacts from big asteroids,
00:56:25 --> 00:56:27 like the things you got at the end of planet
00:56:27 --> 00:56:29 formation, those can dump enough energy
00:56:29 --> 00:56:32 in terms of a downward pulse to push magma
00:56:32 --> 00:56:35 up somewhere else to trigger a convection
00:56:35 --> 00:56:38 cell that then becomes self sustaining. So
00:56:38 --> 00:56:40 it's quite possible that the same impact
00:56:41 --> 00:56:43 regime that led to the delivery of water,
00:56:43 --> 00:56:45 that led in the extreme case to the formation
00:56:45 --> 00:56:48 of the moon, also triggered plate
00:56:48 --> 00:56:50 Tectonics. And by triggering plate tectonics
00:56:50 --> 00:56:53 and delivering water to the mantle allowed
00:56:53 --> 00:56:55 the Earth to become the planet it is today to
00:56:55 --> 00:56:58 allow life to thrive. Now there's far, far
00:56:58 --> 00:56:59 more that you could look into about the
00:56:59 --> 00:57:01 planets themselves. I'm not like, say, a
00:57:01 --> 00:57:04 geophysicist, but the interplay of these
00:57:04 --> 00:57:05 things is fascinating and it's a real
00:57:05 --> 00:57:08 reminder of that multidisciplinary thing. You
00:57:08 --> 00:57:10 can't do it all if you're just an astronomy.
00:57:10 --> 00:57:13 You need everybody from all different
00:57:13 --> 00:57:15 disciplines to come together so we can figure
00:57:15 --> 00:57:17 out what factors are and, um, aren't
00:57:17 --> 00:57:19 important. So that when we find another
00:57:20 --> 00:57:22 thousand, another ten thousand, another
00:57:22 --> 00:57:24 hundred thousand planets, we can pick the
00:57:24 --> 00:57:26 best targets to search for life upon them.
00:57:26 --> 00:57:28 And that was a motivation and it just blew my
00:57:28 --> 00:57:31 mind when I got to that final part. Just how
00:57:31 --> 00:57:34 much complexity there is in the
00:57:34 --> 00:57:35 interplay between the atmosphere, the
00:57:35 --> 00:57:37 climate, the plate tectonics, the oceans
00:57:38 --> 00:57:41 that are so, uh, variable and so chaotic.
00:57:42 --> 00:57:44 What does that mean? How can we learn from
00:57:44 --> 00:57:46 that? Well, that's what we learn when we look
00:57:46 --> 00:57:47 at planets around other stars. But at least
00:57:47 --> 00:57:48 this gives us a bit of a starting point
00:57:49 --> 00:57:49 point, I think.
00:57:50 --> 00:57:52 Andrew Dunkley: Yeah, yeah, I see what you're saying. So it's
00:57:53 --> 00:57:55 like the popular press saying, oh, we found a
00:57:55 --> 00:57:57 rocky planet in the Goldilocks zone and it
00:57:57 --> 00:57:59 probably has water, so, you know, it's got to
00:57:59 --> 00:58:02 have life. Uh, there's so much more than
00:58:02 --> 00:58:04 that. Like, yeah, it's um.
00:58:04 --> 00:58:06 Jonti Horner: Even they probably have water is a leap
00:58:06 --> 00:58:09 because like, yeah, if we'd not had
00:58:09 --> 00:58:11 water added after the moon forming impact,
00:58:11 --> 00:58:12 the Earth would be a desert
00:58:14 --> 00:58:17 Andrew Dunkley: and we wouldn't probably exist at all.
00:58:17 --> 00:58:18 Jonti Horner: Absolutely, yeah.
00:58:18 --> 00:58:21 Andrew Dunkley: Fascinating stuff, Jonty. We'll leave it
00:58:21 --> 00:58:23 there. But, um, it's just such a
00:58:24 --> 00:58:25 fascinating topic. But
00:58:26 --> 00:58:29 what goes into, uh, the future
00:58:29 --> 00:58:31 identification of potential targets is
00:58:32 --> 00:58:34 so much more than most people would have
00:58:34 --> 00:58:35 considered. So thank you very much, really
00:58:35 --> 00:58:36 appreciate it.
00:58:36 --> 00:58:37 Jonti Horner: It's an absolute pleasure and thanks for
00:58:37 --> 00:58:40 letting me rant on my topics of choice for a
00:58:40 --> 00:58:43 change. Like I said, it would be helpful. I'm
00:58:43 --> 00:58:44 sure your readers will.
00:58:44 --> 00:58:46 Readers, listeners will give feedback on
00:58:46 --> 00:58:48 this, but I know we've done something
00:58:48 --> 00:58:51 different. I really do. I am aware
00:58:51 --> 00:58:52 of the fact that these are not your typical
00:58:52 --> 00:58:55 episodes and that may be different for
00:58:55 --> 00:58:56 people. So I appreciate the opportunity to do
00:58:56 --> 00:58:58 this, but if people have enjoyed it or
00:58:58 --> 00:59:00 didn't, it'd probably be worth letting Andrew
00:59:00 --> 00:59:03 and Fred Watson know once I'm gone. Um, won't
00:59:03 --> 00:59:04 hurt my feelings. Don't worry about it
00:59:04 --> 00:59:06 because if it's Something you've enjoyed.
00:59:06 --> 00:59:08 There's possibilities to do things like this
00:59:08 --> 00:59:10 again in future if it isn't. We tried it and
00:59:10 --> 00:59:12 it didn't work and that's entirely fine. Fine
00:59:12 --> 00:59:14 too. So hopefully it was fun, hopefully it
00:59:14 --> 00:59:16 was educational and I won't be too hurt, uh,
00:59:16 --> 00:59:17 if nobody enjoyed it.
00:59:18 --> 00:59:20 Andrew Dunkley: I'm pretty sure they did. Jonty, and we
00:59:20 --> 00:59:23 really appreciate your time and uh, we've,
00:59:23 --> 00:59:24 we've got one more episode to do with you.
00:59:25 --> 00:59:27 Uh, it's a Q and A episode and we, we're
00:59:27 --> 00:59:29 talking about, we haven't nailed it down yet,
00:59:29 --> 00:59:31 but we're talking about doing a, an
00:59:31 --> 00:59:32 astrophotography special.
00:59:32 --> 00:59:33 Jonti Horner: Yeah.
00:59:33 --> 00:59:34 Andrew Dunkley: Because we do get a lot of questions about
00:59:34 --> 00:59:37 astrophotography so, uh, that, that'd be
00:59:37 --> 00:59:38 worth getting into as well.
00:59:38 --> 00:59:40 Jonti Horner: Yeah. I've got a couple of good friends who
00:59:40 --> 00:59:42 uh, are award winning astrophotographers who
00:59:42 --> 00:59:44 we're going to try and rope into that. So
00:59:44 --> 00:59:46 watch this space is what I'd say. Yes.
00:59:46 --> 00:59:48 Andrew Dunkley: Fingers crossed we can nail that one down.
00:59:49 --> 00:59:50 Jonty, thanks so much. We'll see you real
00:59:50 --> 00:59:51 soon.
00:59:51 --> 00:59:52 Jonti Horner: Pleasure. Thank you for having me.
00:59:52 --> 00:59:54 Andrew Dunkley: Johnty Horner, professor of Astrophysics at
00:59:54 --> 00:59:57 the University of Southern Queensland.
00:59:58 --> 01:00:00 And if you've got time, jump on our website
01:00:00 --> 01:00:02 and have a look around. Uh, maybe send your
01:00:02 --> 01:00:05 comments and thoughts, uh, to us via the
01:00:05 --> 01:00:07 Ask me anything button at the top. It's
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01:00:15 --> 01:00:17 news. Um, maybe you'd like to become a
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01:00:20 --> 01:00:22 shop. Lots of goodies in our shop and plenty
01:00:22 --> 01:00:25 more. So cheque it out and thanks to Huw
01:00:25 --> 01:00:27 in the studio as always, because
01:00:28 --> 01:00:31 he does something which we one day might
01:00:31 --> 01:00:33 find out about. And from me, Andrew Dunkley,
01:00:33 --> 01:00:35 thanks for your company. We'll see you on the
01:00:35 --> 01:00:37 next episode of Space Nuts. Bye Bye.
01:00:38 --> 01:00:39 Space Nuts.
01:00:39 --> 01:00:40 You've been listening to the Space Nuts
01:00:40 --> 01:00:43 Jonti Horner: Arts podcast, available
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01:00:54 --> 01:00:56 production from Bytes. Com.
01:00:56 --> 01:00:57 Jonti Horner: Um,