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Stellar Q&A: Rusty Moons, Space Stations & What If Earth Disappeared? · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: Hi there. Thanks for joining us. This is a Q
• 0:02
  and A edition of Space Nuts. Not only do
• 0:05
  we talk astronomy and space science, we
• 0:07
  pretend to answer questions from our
• 0:09
  wonderful, uh, audience. We've got a bunch
• 0:11
  today. Bill, uh, is asking about small
• 0:14
  bodies in solar systems.
• 0:17
  I don't think that's got anything to do with
• 0:19
  weight loss, but we'll see. Uh, Peter is
• 0:21
  asking about, uh, leaving something behind
• 0:23
  that could survive the destruction of Earth.
• 0:26
  Wow, that's a what if question. Tiny moons
• 0:29
  and giant planets and issues with a
• 0:32
  giant space station. Those are, uh,
• 0:34
  questions we will endeavour to answer today
• 0:36
  on this edition of Space Nuts.
• 0:39
  Professor Fred Watson: 15 seconds. Guidance is internal.
• 0:42
  10, 9. Ignition
• 0:44
  sequence start. Space Nuts. 5, 4,
• 0:47
  3, 2. 1. 2, 3, 4, 5, 5,
• 0:50
  4, 3, 2, 1. Space Nuts
• 0:52
  astronauts report it feels good.
• 0:56
  Andrew Dunkley: And with us again is Professor Fred Watson
• 0:58
  Watson, um, astronomer at large. Hello,
• 1:00
  Fred Watson.
• 1:00
  Professor Fred Watson: Hello, Andrew. Uh, fancy seeing you here.
• 1:03
  Andrew Dunkley: Yes, unusual. Both wearing black.
• 1:05
  Professor Fred Watson: Is it black? Uh,
• 1:08
  it is, yeah.
• 1:11
  It's the, um, this is the, the shirt
• 1:14
  that if I have Jordy sitting on my lap, you,
• 1:17
  you can't see him at all because it's exactly
• 1:20
  the same colour as he is. Jet black.
• 1:23
  Andrew Dunkley: Uh, that'll make a good Instagram photo.
• 1:25
  Professor Fred Watson: Well, it might do. Just two eyes poking
• 1:28
  out.
• 1:29
  Andrew Dunkley: Now, um, we've got a lot to get through, so
• 1:32
  we'll start straight away with, uh, a
• 1:34
  question that comes from Bill
• 1:37
  and he asks if small bodies in the solar
• 1:40
  system formed by accretion of fine dust
• 1:43
  and gas, why are they not all
• 1:46
  fluffy, low gravity powder
• 1:48
  puffs? Um, we're
• 1:51
  all dense stony. Uh, or, uh, were
• 1:54
  all dense stony or metallic objects
• 1:56
  originally part of a larger body that could,
• 1:59
  could differentiate under, uh, decent
• 2:01
  gravity levels, then were smashed to small
• 2:04
  pieces in collisions. Uh, thanks for the
• 2:07
  great podcasts. Uh, that comes from Bill.
• 2:10
  Um, so, yeah, why isn't everything
• 2:12
  puffy?
• 2:14
  Professor Fred Watson: Um, I think it was to start with. Well, there
• 2:17
  you go. Yeah. So,
• 2:20
  um, people often say,
• 2:23
  people who should know better often say that
• 2:26
  if you want to know how planet formation
• 2:28
  starts, look under your bed because
• 2:32
  the bits of fluff that you tend to find under
• 2:34
  your bed are, uh, made of dust
• 2:37
  sticking together, uh, usually by
• 2:39
  electrostatic forces, which we think played a
• 2:42
  part in the early, uh, evolution of planets.
• 2:45
  Uh, these things stick together. You build
• 2:48
  up bigger and bigger fluff balls. Um,
• 2:51
  and eventually the
• 2:54
  fluff balls, because. Exactly,
• 2:57
  um, as Bill says, they do tend to collide
• 3:00
  with one another. We're now talking about a
• 3:02
  very, a very, very
• 3:05
  dense, dusty environment. We're talking about
• 3:07
  the protoplanetary disc that Surrounded the
• 3:10
  sun. Uh, very dusty place
• 3:13
  with lots of, um, basically
• 3:16
  lots of capacity for uh, dust
• 3:19
  fluff balls to build up to have bigger and
• 3:22
  bigger sizes. Eventually
• 3:25
  these various forces uh, will
• 3:27
  cause the dust balls to sort of
• 3:30
  collapse. Probably collisions will contribute
• 3:33
  to, um, by that I mean that they
• 3:36
  tend to lose their porosity. In other words,
• 3:39
  they become more solid.
• 3:41
  Um, now having said that, there are objects
• 3:44
  in space that we know are very
• 3:47
  porous.
• 3:48
  Andrew Dunkley: Um, well we've found powder puff planets,
• 3:51
  haven't we?
• 3:52
  Professor Fred Watson: Yes, that's right. Uh, yes, almost exactly
• 3:55
  a good description of them. I'm just thinking
• 3:57
  more nearer to home though. Um, uh,
• 4:00
  uh, Phobos, the larger moon of Mars,
• 4:03
  is thought to have a composition a bit like
• 4:07
  um. God, the word's gone.
• 4:09
  Uh, stuff that forms when
• 4:12
  eruptions, um, take place
• 4:14
  underwater.
• 4:15
  Andrew Dunkley: Like a honeycomb.
• 4:16
  Professor Fred Watson: Yes, um, but it's got a word. Oh, that's
• 4:19
  ridiculous. When you get to a certain age,
• 4:21
  words just disappear. It'll come to me
• 4:24
  in a minute. I know. Uh, but yeah,
• 4:27
  the stuff that floats on the water
• 4:29
  underground eruption. Pumice. The very word.
• 4:32
  That's what I was looking for. Thank you.
• 4:34
  Thank you, Andrew. So pumice is, you know,
• 4:36
  it's porous, it's a stony
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  structure, uh, that's got a lot of gaps in it
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  and I guess that might well be an
• 4:44
  intermediate structure of many of these
• 4:46
  objects. Ah, as I said, Phobos is like
• 4:49
  that, um, one of Saturn's moons and I
• 4:52
  can't remember which one it is, it's the one
• 4:54
  shaped like a potato. That'll probably come
• 4:56
  to me in a minute as well. Uh, it's also
• 4:59
  got that sort of structure. Um, so
• 5:01
  maybe, you know, when you get things like
• 5:03
  that colour colliding, uh, then
• 5:06
  and building up in size, then you're
• 5:09
  eventually going to get to this situation
• 5:12
  where gravity takes over, uh, and it
• 5:14
  pulls um, these low
• 5:18
  density materials into something
• 5:20
  more solid.
• 5:22
  Andrew Dunkley: Um, is it a malthea, A mouth?
• 5:25
  Professor Fred Watson: No, uh, it's one with a better known name.
• 5:28
  Ah. It's very highly cratered and
• 5:31
  potato shaped.
• 5:33
  Andrew Dunkley: Ah, okay.
• 5:34
  Professor Fred Watson: It's uh, yeah, it's one of the most cratered
• 5:36
  objects in the, in the solar system. I'm
• 5:38
  annoyed. I can't remember it. It's
• 5:40
  ridiculous. I was getting too
• 5:43
  old for this, Andrew.
• 5:44
  Andrew Dunkley: Oh no you're not.
• 5:45
  Professor Fred Watson: No, no, maybe I'm not.
• 5:46
  Andrew Dunkley: No, it keeps your brain active.
• 5:48
  Professor Fred Watson: Well, except it's demonstrating quite
• 5:51
  clearly, uh, that the memory banks are
• 5:53
  disappearing. Anyway, um, it'll come to me,
• 5:56
  as I said, in a minute. It's not Enceladus,
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  but it's something like that. Uh, so, uh,
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  if you've got, you know, gravity taking over,
• 6:04
  then you' to get basically solid rock
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  emerging from that. Uh, uh,
• 6:10
  as Bill says, dense, stony or metallic
• 6:12
  objects, that's basically what they turn
• 6:14
  into. And then they collide. Uh,
• 6:18
  um, the larger objects are differentiated.
• 6:20
  That means the heavy stuff sinks to the
• 6:22
  middle. Uh, exactly as Bill says, but they
• 6:24
  collide. And that's how you can get stony
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  meteorites or metallic
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  meteorites because the metal tends to sink
• 6:31
  mostly, uh, to the middle. So I
• 6:34
  think, um, it is a natural process, but it's
• 6:37
  one in a way it's counterintuitive to us. You
• 6:40
  know, how do you get from a dust, a fluff
• 6:42
  ball under your bed. How do you get from that
• 6:45
  to a stone to a rock?
• 6:47
  Andrew Dunkley: Gravity.
• 6:48
  Professor Fred Watson: Yes, that's right, gravity. But over a long
• 6:50
  period of time. Uh, and probably heat as
• 6:53
  well. You know, you've got heat processes
• 6:55
  coming into this too. So, um,
• 6:57
  uh, I, uh,
• 7:00
  think uh, what um,
• 7:03
  Bill's saying is right. If the small bodies
• 7:06
  in the solar system formed by accretion of
• 7:08
  fine dust and gas, why are they not all
• 7:10
  fluffy, low gravity powder puffs? Well, some
• 7:13
  of them are and that's. Perhaps you could
• 7:15
  describe them like um,
• 7:18
  Phobos. Uh, perhaps he could describe them as
• 7:21
  unevolved. They haven't evolved much.
• 7:23
  I think it might be Hyperion, the one I'm
• 7:26
  thinking of.
• 7:26
  Andrew Dunkley: Okay.
• 7:28
  Professor Fred Watson: I think it might be Hyperion. I'll have a
• 7:29
  look, Have a look, See if it's um, shaped
• 7:32
  like a potato and got lots of graters on it.
• 7:35
  Andrew Dunkley: Yeah. Well, there's got to be a photo of it
• 7:36
  somewhere. Yes, it is.
• 7:38
  Professor Fred Watson: Yeah.
• 7:38
  Andrew Dunkley: Yeah.
• 7:38
  Professor Fred Watson: Okay, good.
• 7:39
  Andrew Dunkley: It's got, it's got that big, um.
• 7:42
  It's got a massive crater in it actually.
• 7:43
  Professor Fred Watson: Yeah. Yes, yes. Yeah, yeah.
• 7:46
  So, um, so these are you got
• 7:47
  Andrew Dunkley: there in the end, Fred Watson.
• 7:48
  Professor Fred Watson: In the end? Yeah, it's. Yes. It's just the
• 7:51
  processing speeds down a bit. I must be
• 7:53
  offline or something like that. Probably need
• 7:56
  a reboot. God, don't say that. Might
• 7:59
  never come back.
• 8:01
  Andrew Dunkley: Well, that's happened. My car did that while
• 8:02
  we were away. Uh, came home
• 8:05
  and to, uh, to, to stop falling asleep. We
• 8:08
  decided we'd go and do the groceries straight
• 8:09
  after getting off a long haul flight.
• 8:11
  Professor Fred Watson: Oh, yes. Yeah.
• 8:12
  Andrew Dunkley: And the car wouldn't start.
• 8:15
  Yeah, the battery died, so.
• 8:17
  Professor Fred Watson: Oh, the battery died.
• 8:18
  Andrew Dunkley: Yeah. That's another 315 bucks. Thank you
• 8:21
  very much.
• 8:22
  Professor Fred Watson: Yes.
• 8:22
  Andrew Dunkley: Anyway, it happens. It was four years. It
• 8:25
  lasted four years.
• 8:26
  Professor Fred Watson: Oh, that's all right. That's about as long as
• 8:27
  you get from a battery.
• 8:28
  Andrew Dunkley: Yes, it is indeed. But thanks, Bill, for the
• 8:31
  question. Uh, I think you answered it
• 8:33
  yourself, but, um, y, uh, although
• 8:35
  if you're, um, someone like me,
• 8:38
  um, and you don't clean under the bed, uh,
• 8:41
  you can watch planets evolve.
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  That's what's happening.
• 8:46
  Professor Fred Watson: Yep, you can.
• 8:47
  Andrew Dunkley: All right, uh, thanks, Bill.
• 8:48
  Our next question, uh, is
• 8:51
  coming from Peter.
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  Speaker C: Hello, this is Peter in Lamington
• 8:56
  Spa. And I want to know
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  what would it take for
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  humans to
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  make something that will survive
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  the destruction of Earth
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  and then potentially be incorporated
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  into a new planet when all the bits of Earth
• 9:18
  become a different planet and sometime in the
• 9:20
  future, Is it possible?
• 9:24
  Andrew Dunkley: Have a good evening. Thank you, Peter. That's
• 9:27
  a what if question. Uh, yeah, I wonder.
• 9:30
  That's a very. It's a long haul science
• 9:33
  fiction situation. You build something
• 9:36
  that will survive the destruction of Earth
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  and then somehow the planet reconstitutes
• 9:40
  itself and billions of years later there's an
• 9:43
  intelligent race living on the planet and
• 9:45
  they go, oh, hello. What's all this then?
• 9:48
  Professor Fred Watson: This is some leftover of humankind? Yeah,
• 9:51
  whatever they were.
• 9:53
  Andrew Dunkley: There was a TV series that I watched many
• 9:55
  years ago called Childhood's End, and
• 9:59
  it was about the destruction of Earth. And
• 10:02
  before it, before it was destroyed,
• 10:05
  um, the humans asked the aliens
• 10:08
  that rescued the children, basically, um,
• 10:11
  can we just leave something behind so they
• 10:13
  know we were here? So they left. Music.
• 10:17
  Professor Fred Watson: Lovely. I like that. Yes, I like that very
• 10:20
  much.
• 10:20
  Andrew Dunkley: I just spoiled the whole thing too, by the
• 10:22
  way.
• 10:22
  Professor Fred Watson: Um, I don't think you did really, uh,
• 10:25
  because. Yes, that's a kind of concept, isn't
• 10:28
  it, that you're leaving behind? Uh, and
• 10:32
  my mind, when I read Peter's question or
• 10:35
  heard Peter's question, went to
• 10:38
  more concrete things, not necessarily made of
• 10:41
  concrete.
• 10:43
  Andrew Dunkley: I was about to say that.
• 10:46
  Professor Fred Watson: But in a sense we've already done it, Andrew,
• 10:48
  because there are five
• 10:52
  little spacecraft which are,
• 10:55
  ah, absolute, um,
• 10:59
  uh, monuments to humanity leaving the
• 11:01
  solar system, um, way, way beyond
• 11:04
  the orbit of Earth. Voyager 1 is
• 11:07
  probably beyond. Actually,
• 11:10
  that's not quite true. I, uh, was going to
• 11:13
  say beyond the limits of the sun. When it
• 11:15
  turns into a red giant star, um,
• 11:19
  Voyager 1 will probably survive,
• 11:22
  um, the red giant phase of
• 11:25
  our sun, uh, which will take place in
• 11:28
  a few billion years, three or four
• 11:30
  billion years. Um, it'll survive that,
• 11:33
  but might not survive the formation of
• 11:36
  a planetary nebula when you've got hot gas
• 11:39
  coming off the, uh, being puffed off the
• 11:42
  surface of the red Giant. It might actually
• 11:44
  melt in that because it's because planetary
• 11:47
  nebulae get to be light years in diameter.
• 11:49
  Uh, our Voyager, uh, is only, well, it's
• 11:52
  nearly a light day away. Um, on the other
• 11:54
  hand, we've got 3 or 4 billion years to play
• 11:57
  with because the sun's not going to do
• 11:59
  anything really nasty, um, within that
• 12:01
  time. So yes, Voyager 1 will be well out of
• 12:04
  the way, probably will survive the
• 12:06
  eventual evolution, um, and
• 12:11
  uh, final evolutionary stages of the sun when
• 12:13
  it actually turns into a white dwarf star. So
• 12:16
  yes, uh, those spacecraft, Voyager
• 12:19
  1, Voyager 2, Pioneer 10, Pioneer 11,
• 12:22
  is that right? And New Horizons,
• 12:25
  they're the five that are leaving the solar
• 12:27
  system which will probably outlive humanity.
• 12:30
  Andrew Dunkley: They probably won't. They probably won't be
• 12:32
  the last.
• 12:33
  Professor Fred Watson: They won't be the last. No, I think that's
• 12:35
  right. Uh, but,
• 12:37
  um, I mean
• 12:40
  the idea of, um, the Earth, uh,
• 12:43
  being destroyed, the
• 12:46
  kinds of things that might destroy the Earth,
• 12:48
  ah, are first of all, that eventual
• 12:50
  evolution of the sun to a red giant star that
• 12:53
  will almost certainly melt the Earth because
• 12:57
  the Sun's, um, surface, put
• 13:00
  it that way, will be, um, a quarter of a
• 13:03
  mile from the Earth. And we might be on the
• 13:04
  inside of, uh, could even,
• 13:07
  uh, overtake the planet Mars. Uh,
• 13:10
  so it's hard to imagine how you'd rebuild
• 13:13
  the Earth, uh, from the debris that is really
• 13:15
  just molecules, uh, because it'll have been
• 13:17
  vaporised. Um, so I think, uh,
• 13:21
  in addressing this question, you've really
• 13:23
  got to think about things that uh, have
• 13:26
  left the Earth. And that really basically
• 13:28
  pushes your mind to spacecraft. There are
• 13:31
  some spacecraft which are, uh, in orbit
• 13:34
  around the sun, uh, which
• 13:36
  are spacecraft that have been sent
• 13:39
  exploring the inner solar system. Mostly
• 13:42
  these days we try and get rid of them. We
• 13:44
  plunge them, uh, into either, uh, Jupiter or
• 13:47
  Saturn. Jupiter in the case of Galileo,
• 13:49
  Saturn in the case of Cassini. Uh, those
• 13:52
  spacecraft were destroyed purposely so that
• 13:55
  they didn't accidentally land on one of the
• 13:58
  moons of Jupiter or Saturn and leave microbes
• 14:00
  behind. Um, so you're really talking about
• 14:03
  something that's left the solar system. And
• 14:05
  that leaves those five spacecraft
• 14:07
  I've mentioned. And they definitely will
• 14:09
  outlast humankind.
• 14:11
  Andrew Dunkley: Okay, there you have it, Peter. Um, so we've
• 14:14
  already done it kind of, uh, I don't think
• 14:17
  you could probably build some kind
• 14:19
  of monolith or something that would survive
• 14:22
  the red giant phase of
• 14:25
  the sun and, and overwhelm Earth. That would
• 14:28
  all get destroyed, um, unless you did
• 14:31
  it deep down inside. But I don't even Know,
• 14:33
  if you could do that, I think a
• 14:36
  red giant phase would be pretty cataclysmic,
• 14:38
  wouldn't it?
• 14:39
  Professor Fred Watson: Yeah. Uh, yes. If your planet's being
• 14:42
  vaporised. Your planet's being vaporised. It
• 14:44
  is, yeah.
• 14:47
  Andrew Dunkley: Indeed. Thank you, Peter. Great to hear from
• 14:49
  you. I love what if questions. So, um, thanks
• 14:52
  for serving it up. This is Space Nuts with
• 14:55
  Andrew Dunkley and Professor Fred Watson
• 14:57
  Watson.
• 15:00
  Professor Fred Watson: Swiften Tranquilly Base here.
• 15:03
  The eagle has landed. Space Nuts.
• 15:06
  Andrew Dunkley: Our next question, Fred Watson, comes from
• 15:08
  Martin in Heswall. Heswall, is that right?
• 15:11
  Professor Fred Watson: Yes, Heswall. Yeah.
• 15:13
  Andrew Dunkley: Where's that? I'm going to guess it's the UK
• 15:15
  somewhere.
• 15:16
  Professor Fred Watson: It is indeed. It's, um, uh, on the Wirral
• 15:19
  Peninsula. So if you think of Liverpool,
• 15:21
  you've been to Liverpool? I have. And done
• 15:23
  the Beatles experience.
• 15:24
  Andrew Dunkley: Yes.
• 15:25
  Professor Fred Watson: Is that right? Yes. Yeah. Well, across the
• 15:27
  River Mersey from Liverpool is the Wirral
• 15:29
  Peninsula and Heswall is
• 15:33
  one of the towns on that, um, I've said
• 15:35
  before, and in fact we've had listener
• 15:38
  comments about this, I had a girlfriend once
• 15:40
  who lived on the Wirral Peninsula and so I
• 15:43
  used to be a very regular visitor there to a
• 15:45
  village called Barnston, which was not that
• 15:46
  far from Heswall. There you are. All right.
• 15:49
  It's very pretty too. It's a pretty village.
• 15:51
  Hmm.
• 15:52
  Andrew Dunkley: Okay. Just wanted to know where you
• 15:55
  were, Martin. So thank you for that. Uh, I
• 15:57
  hope, uh, you'll answer this question.
• 15:58
  According to Wikipedia, there are, uh, now
• 16:02
  known to be 292 satellites,
• 16:05
  uh, with confirmed orbits around Saturn.
• 16:07
  Presumably, many of these moons are very
• 16:10
  small. So is there a minimum size for
• 16:13
  an object to be called a moon? And is
• 16:16
  there a minimum size for an object to
• 16:18
  maintain a stable orbit around a planet?
• 16:21
  Uh, as all the giant plan have ring
• 16:24
  systems, would the smaller particles just
• 16:27
  be absorbed into the rings? Conversely, I
• 16:30
  suppose that many objects could be knocked
• 16:32
  out of the rings to form independent
• 16:34
  satellites that may become permanently
• 16:36
  separated from the rings. Will Saturn get,
• 16:39
  uh, to 1,000 moons or more?
• 16:42
  Also, uh, can you recommend a website
• 16:45
  which has the latest data about, uh, the
• 16:47
  solar system, as the numbers vary from one
• 16:50
  site to the next, no doubt due to how recent
• 16:53
  the information is. Keep up the work. Thanks,
• 16:56
  Martin. Um, that's a good question because,
• 16:58
  yeah, we know that the ring systems,
• 17:02
  um, are full of dust and ice, but they've
• 17:04
  also got larger objects that are referred to
• 17:07
  regularly as moons.
• 17:10
  Professor Fred Watson: Um, it's interesting, this was one of the
• 17:12
  exact questions that came up in the Q and
• 17:14
  A night, the science in the pub night that we
• 17:17
  had on Lord Howe island at the Dark Sky
• 17:20
  Festival.
• 17:21
  Andrew Dunkley: That was Martin. He was, he was there.
• 17:24
  No he probably wasn't.
• 17:26
  Professor Fred Watson: Carry on. There was a Martin
• 17:28
  there.
• 17:30
  Andrew Dunkley: Did he have a British accent?
• 17:32
  Professor Fred Watson: Uh no, he's quite Australian but
• 17:35
  he's not from Haswell. But yeah, uh,
• 17:38
  but interesting coincidence to get the two
• 17:41
  and I don't think at the moment there is
• 17:45
  a uh limiting size
• 17:48
  to differentiate between a ring particle
• 17:52
  and a moon. Um
• 17:55
  so uh, it
• 17:58
  is a great question um how
• 18:01
  do you define a moon around a planet which is
• 18:03
  festooned with objects orbiting around it
• 18:07
  in the form of rings. So we think the rings
• 18:09
  of Saturn are uh the debris
• 18:12
  of uh probably a satellite
• 18:15
  that came within the Roche limit
• 18:18
  of the the planet. The Roche limit
• 18:21
  being the point at which uh a solid
• 18:24
  object can't actually survive within
• 18:27
  that distance. In other words that close to
• 18:30
  the planet. Um and so
• 18:32
  it broke up into lots of small particles.
• 18:36
  Probably the biggest ring sized
• 18:40
  sorry the biggest ring particles
• 18:43
  uh, uh in the region of 10 metres
• 18:47
  because the rings themselves are only about
• 18:49
  100 metres thick. Yeah it's quite
• 18:52
  staggering.
• 18:54
  Um and 250,000 kilometres
• 18:57
  in diameter. So yes it's quite a contrast.
• 19:00
  Um a sort of blade of material in space is
• 19:03
  the way I've always described it. Uh
• 19:07
  but some of the smaller satellites of
• 19:09
  Saturn and some of them are actually embedded
• 19:12
  in the ring system. Uh some of them
• 19:15
  are measured in
• 19:18
  single digit kilometres so they're not that
• 19:21
  much more than
• 19:24
  the biggest ring particles and I'm not sure
• 19:27
  that there is a definition between the two.
• 19:30
  Uh and in a sense you could say that every
• 19:33
  solid object within Saturn's rings is a
• 19:36
  satellite and so you're then talking about
• 19:38
  millions or maybe even billions of
• 19:41
  moons of Saturn. Uh it's a great
• 19:44
  question and one that I don't have an answer
• 19:46
  for and I perhaps ough who have checked it
• 19:49
  out in the wake of the question that came uh
• 19:52
  at the science in the pub science in the bolo
• 19:55
  on Lord Howe island the week before last when
• 19:58
  we did the Dark Sky Festival there.
• 19:59
  Andrew Dunkley: Yeah, yeah he also
• 20:02
  asked about uh website. Yeah ah
• 20:05
  well I just did a quick cheque and top uh of
• 20:08
  the tree is NASA for up
• 20:11
  to date solar system information.
• 20:15
  Uh yeah, uh but the other ones that you could
• 20:17
  try uh the sky
• 20:19
  mylive.com apparently is
• 20:22
  very highly rated um says
• 20:25
  it offers comprehensive information about the
• 20:27
  most interesting celestial objects and sets
• 20:29
  tools designed to support the exploration et
• 20:32
  cetera. Uh the planets today
• 20:35
  uh is also there and there's a specific uh
• 20:38
  NASA page that you can look up
• 20:41
  called Eyes on the Solar System. Um,
• 20:44
  and it provides a 3D solar
• 20:47
  scape if you like. So there's a few
• 20:50
  ideas if you uh, want to um, chase them
• 20:53
  up, Martin. But um, there'd be plenty more
• 20:56
  out there. There's um, just to name a few
• 20:58
  more, Global Solar Atlas,
• 21:00
  um, the NOAA homepage,
• 21:03
  the Space Weather Prediction homepage, um,
• 21:06
  and Planet Labs just to name a few. So
• 21:10
  um, and they're constantly being updated as
• 21:13
  far as I'm aware, as things change or as
• 21:15
  new things come to light. So might be worth
• 21:18
  chasing all of those up because they do seem
• 21:21
  to be, um, highly credentialed. Fred Watson?
• 21:24
  Professor Fred Watson: Yeah, I was going to say I usually go
• 21:27
  to NASA when I want the latest figures on
• 21:30
  this sort of thing. M. So,
• 21:33
  uh, you've confirmed that and also given a
• 21:35
  few other options as well, which is good.
• 21:37
  Andrew Dunkley: Yep, plenty to look at. There's lots of great
• 21:38
  sites out there. Just don't go to the ones
• 21:41
  that start with um, words
• 21:43
  starting with F and e.
• 21:51
  Professor Fred Watson: I was thought you were going to say don't go
• 21:53
  to ones that start with space and have knots
• 21:55
  in the.
• 21:57
  Andrew Dunkley: That's, that's good advice too.
• 21:59
  Professor Fred Watson: Yeah.
• 22:00
  Andrew Dunkley: Okay, thank you, Martin.
• 22:02
  Our final question today comes from
• 22:05
  Finn.
• 22:06
  Speaker C: Hello, Andrew and Fred Watson. It's Finn from
• 22:08
  NAN in the Adelaide Hills in South
• 22:11
  Australia. And a happy May 4th to you as
• 22:14
  well. I was watching a 40 year old
• 22:16
  documentary the other day about a space
• 22:18
  station orbiting a planet. And this
• 22:21
  space station, um, if it was to orbit
• 22:24
  the Earth, I would like to know how that
• 22:26
  would affect the orbit of our
• 22:28
  moon and maybe the orbit of the Earth
• 22:31
  around the sun. This space station being 150
• 22:34
  kilometres diameter with a mass of about 10
• 22:36
  to the 15 tonne. Um, I'd
• 22:39
  like to know, and if for whatever reason this
• 22:42
  space station happened to destroy our planet,
• 22:46
  how would the rest of the planets in the
• 22:48
  solar system be affected by that
• 22:50
  destruction? One last question,
• 22:53
  um, to you both is, um, what was the first
• 22:56
  animal in space?
• 22:58
  Andrew Dunkley: It was a dog.
• 22:59
  Speaker C: Ah, ah, don't think it was that. It was
• 23:02
  actually the cow because it jumped over the
• 23:04
  moon. Thank you.
• 23:06
  Professor Fred Watson: Dear, oh dear.
• 23:07
  Andrew Dunkley: Finn. That was probably one of the worst dad
• 23:09
  jokes I've ever heard. So,
• 23:13
  but you know, most welcome on this show.
• 23:19
  Professor Fred Watson: Yeah, it was good. It wasn't, wasn't even
• 23:20
  adequate that one, was it?
• 23:21
  Andrew Dunkley: No, it wasn't.
• 23:22
  Professor Fred Watson: No, no.
• 23:23
  Andrew Dunkley: We strive for adequacy and we didn't even
• 23:26
  achieve that. Thank you, Finn.
• 23:28
  Uh, so the substance of his question was,
• 23:31
  uh, you got a space Station orbiting Earth
• 23:34
  at 150 kilometres in
• 23:37
  diameter or whatever. Uh what kind
• 23:40
  of effect could that have on the orbit of the
• 23:42
  Moon? And ye
• 23:46
  get to the next part of the question after
• 23:47
  that. Could it have, would that have any.
• 23:49
  That's pretty big.
• 23:52
  Professor Fred Watson: It's well the critical thing was the mass
• 23:54
  which um Fin actually
• 23:57
  mentioned as being 10 to
• 24:00
  the 15 tonnes I think is what he said
• 24:04
  uh which is 10 to the 18
• 24:07
  kilogrammes. Um and
• 24:10
  so the bottom line is that's not enough
• 24:14
  uh the Earth just. Yeah, nah, ah forget it.
• 24:17
  So the earth's uh six times 10 to the
• 24:20
  24 kilogrammes. So it's
• 24:23
  um, what is it? It's
• 24:26
  six uh orders of magnitude bigger in
• 24:29
  mass than uh this space station
• 24:33
  and so the other. So
• 24:37
  it's certainly not going to affect the orbit
• 24:39
  of the ah Earth. It might perturb
• 24:42
  the orbit of the Moon a bit.
• 24:45
  Uh one of the considerations will be how far
• 24:47
  away is it from the
• 24:50
  Earth? And uh, our last question
• 24:53
  actually pointed to an answer to that
• 24:56
  and that is that if it's 150
• 24:59
  kilometres in diameter it has to be a long
• 25:02
  way away or else it's within the Roche limit
• 25:06
  of the Earth uh and it would just break up
• 25:08
  straight away. So I'm not going to guess how
• 25:10
  far away it has to be but it'll be a long way
• 25:12
  the earth if it's 150 kilometres in diameter.
• 25:16
  Um so that again um, basically
• 25:18
  mitigates any effects it might have
• 25:21
  on the orbital dynamics of the Earth. It
• 25:23
  certainly wouldn't affect the Earth's orbit
• 25:25
  around the Sun. Might just tweak the
• 25:28
  Moon's orbit around the Earth a bit.
• 25:30
  Uh wouldn't cause the demolition of the
• 25:33
  Earth. The orbits of the other planets
• 25:36
  wouldn't even bother to, to take any
• 25:39
  notice of it. Uh they are too
• 25:42
  stable compared with uh, a
• 25:45
  thing of that mass and that far away from the
• 25:48
  Earth. So ah it's an interesting
• 25:50
  thought uh and one that I
• 25:53
  think um we can say yes you could have a
• 25:56
  space station 150 kilometres in diameter
• 25:58
  weighing 10 to the 15 tonnes uh and it
• 26:01
  probably would not affect the status quo
• 26:04
  terribly badly.
• 26:06
  Andrew Dunkley: Okay, there you go. Uh and I just did a quick
• 26:08
  cheque but um, there's not much information
• 26:11
  about how fast space stations have to be away
• 26:13
  to avoid the Roche limit. But a solid object
• 26:16
  such as a Rocky body
• 26:20
  with 150 kilometre diameter would have to be
• 26:22
  at least 141,000 kilometres
• 26:25
  away from Earth. Um probably better off being
• 26:28
  over 200,000 kilometres away.
• 26:30
  Professor Fred Watson: Yes that's the sort of distance I had in
• 26:32
  mind. Something like that. Three times as
• 26:35
  far away as the, the geostationary
• 26:37
  satellites. Huh.
• 26:38
  Andrew Dunkley: Are. There you are now.
• 26:39
  He had a second question as to what would
• 26:42
  happen to the other planets if Earth was
• 26:44
  destroyed, no longer existed. I think we've
• 26:46
  been down this road before and I can't
• 26:48
  remember the answer.
• 26:50
  Professor Fred Watson: Yeah, so, um, the other planets
• 26:52
  would more or less stay in the present
• 26:55
  orbits. Those orbits would be
• 26:58
  perturbed, uh, differently from what they are
• 27:00
  now. So perturbations are the gravitational
• 27:03
  effects of other bodies in the solar system.
• 27:06
  Uh, when you look at the way
• 27:09
  things are in orbit, you start off with a two
• 27:11
  body problem with the sun and your object in
• 27:14
  orbit. But then you modify it by
• 27:17
  taking into account the gravitational
• 27:19
  attraction of other bodies and it becomes a
• 27:20
  three body problem and then four body problem
• 27:22
  and all the rest of it. Now,
• 27:25
  that three body problem would change if the
• 27:27
  Earth wasn't there. Um, or the N body
• 27:30
  problem, I suppose it would be a solar system
• 27:32
  with seven planets rather than eight. Uh,
• 27:35
  that would change the dynamics of the planets
• 27:37
  a little bit, but they would basically
• 27:40
  remain in their present orbits, uh, with
• 27:42
  just changes to the orbit rather than the
• 27:45
  orbits being destroyed.
• 27:46
  Andrew Dunkley: So, uh, in other words, if Earth disappeared,
• 27:48
  no great loss.
• 27:50
  Professor Fred Watson: No, not really. I mean, uh, you know, Douglas
• 27:53
  Adams had it in one. Mostly harmless. Mostly
• 27:55
  harmless, that's right.
• 27:57
  Andrew Dunkley: Thanks to the white mice.
• 27:59
  Professor Fred Watson: Yes, that's right.
• 28:01
  Andrew Dunkley: I wonder how all the other mice felt about
• 28:03
  that. You know, it was
• 28:06
  musculus. Racism. That's what it was.
• 28:08
  Professor Fred Watson: It is, yes. Mass racism. Exactly. So,
• 28:12
  yeah, thanks.
• 28:14
  Andrew Dunkley: Uh, Finn, great question. We always love
• 28:16
  these what ifs. So, um, if you'd like to keep
• 28:18
  sending in questions like that, or if you've
• 28:20
  got something deadly serious to discuss with
• 28:22
  us, like, uh, I don't know, exploding
• 28:25
  rockets and whatever else, uh, you can send
• 28:27
  them in to us. Uh, just go to spacenuts
• 28:30
  IO or spacenutspodcast.com,
• 28:33
  click on the Ask me anything button.
• 28:36
  You won't be asking me, you'll be asking him.
• 28:39
  But, uh, I'll read it out or you can send us
• 28:41
  audio question. As long as you've got a
• 28:43
  device with a microphone, you're all set. Uh,
• 28:45
  and while you're there, have a look around.
• 28:47
  Uh, that brings us to the end. Fred Watson,
• 28:48
  thank you very much.
• 28:50
  Professor Fred Watson: Great pleasure, Andrew. Always good to chew
• 28:52
  the fat. And, uh, I, uh, hope we'll do it
• 28:54
  again soon.
• 28:54
  Andrew Dunkley: We will.
• 28:55
  That's Professor Fred Watson Watson,
• 28:56
  astronomer at large, part of the team here at
• 28:58
  Space Nuts and thanks to Huw in the studio.
• 29:01
  Uh, who couldn't be with us today. He was
• 29:02
  seeing his dietitian after he reached 10 to
• 29:04
  the 15 tonnes.
• 29:08
  I'm surprised he survived. And from me,
• 29:10
  Andrew Dunkley. Thanks for your company.
• 29:12
  We'll be back again soon with another episode
• 29:14
  of Space Nuts. See you then.
• 29:16
  Professor Fred Watson: Bye. Bye.
• 29:18
  Andrew Dunkley: You've been listening to the Space Nuts
• 29:20
  podcast, available at
• 29:23
  Apple Podcasts, Spotify,
• 29:25
  iHeartRadio or your favourite podcast
• 29:28
  player. You can also stream on
• 29:30
  demand@bytes.com. this has been another
• 29:33
  quality podcast production from
• 29:35
  bytes.com.