Latest / Space News Today / ”Jupiter’s not quite as big as we thought.” | Space Nuts: Astronomy Insights & Cosmic Discoveries

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”Jupiter’s not quite as big as we thought.” | Space Nuts: Astronomy Insights & Cosmic Discoveries · Space News Today

• 0:00
  Hello there. Thanks for joining us yet
• 0:02
  again. This is Space Nuts. My name is
• 0:04
  Andrew Dunley. Uh we're here to talk
• 0:06
  astronomy and space science. And on
• 0:08
  today's program, we're going to look at
• 0:10
  a tiny weeny itsybitsy Jupiter. Yes,
• 0:13
  it's not nearly as big as they thought
• 0:15
  it was. In fact, it could lose status as
• 0:19
  a consequence of this. Maybe not, but
• 0:21
  we'll talk about that. We're also going
• 0:23
  to look at a flipping interesting comet
• 0:26
  and uh solar gravitational lens focal
• 0:29
  points. Could we visit them and what
• 0:31
  will that mean? We'll find out on this
• 0:34
  episode of Space Nuts.
• 0:36
  >> 15 seconds. Guidance is internal. 10 9
• 0:40
  Ignition sequence start.
• 0:42
  >> Space Nuts.
• 0:43
  >> 5 4 3 2 1 2 3 4 5 2 1
• 0:48
  >> Space nuts.
• 0:49
  >> Astronauts report. It feels good.
• 0:52
  >> And joining us again to talk about all
• 0:54
  of that stuff and probably a lot more is
• 0:56
  Professor Fred Watson, astronomer at
• 0:58
  large. Hello, Fred.
• 0:59
  >> Hello, Andrew. Good to see you again.
• 1:03
  >> Yep. As always,
• 1:04
  >> love the hoopy shirt.
• 1:06
  >> Oh, yeah. Sorry. It's a very tatty old
• 1:09
  one. This shirt should be buttoning it
• 1:11
  up. This one's tatty.
• 1:12
  >> Tatty, but it's white and it's got more
• 1:14
  food on it than I've ever put in his
• 1:16
  stomach. So,
• 1:16
  >> has it got the Has it got the Space
• 1:18
  Notes logo on it?
• 1:19
  >> Uh, hang on. I'm I've got one here
• 1:22
  somewhere. A Space Nuts logo.
• 1:24
  >> Oh, yeah.
• 1:25
  >> No, I have It's not on It's not not on
• 1:27
  this shirt. It's on the other wide
• 1:28
  shirt.
• 1:30
  >> But um Where did that logo go?
• 1:33
  >> I've lost me logo. Anyway, we'll we'll
• 1:36
  find out better than losing your mojo.
• 1:38
  >> That's true, too. Yes, indeed. Uh let's
• 1:42
  begin because we got a lot to talk
• 1:44
  about. This uh first story uh looks at
• 1:47
  Jupiter, the biggest planet in our solar
• 1:49
  system until we find planet 9. And this
• 1:54
  is a story that's suggesting that
• 1:56
  Jupiter's not quite as big as we thought
• 1:58
  it was.
• 2:00
  >> Yeah. It's it shrunk by well 8
• 2:04
  kilometers.
• 2:05
  >> Yeah.
• 2:06
  >> At the equator and 24 kilometers at the
• 2:09
  poles. So what this is all about and and
• 2:11
  I should just give you the numbers. Uh
• 2:15
  so the revised radius of Jupiter at its
• 2:19
  equator is 71,488
• 2:22
  kilometers
• 2:23
  >> which is actually um I think 4
• 2:27
  kilometers less than we thought before.
• 2:30
  Uh which doubles up to up to uh 8
• 2:33
  kilometers when you're talking about
• 2:34
  diameter. uh but its polar radius uh
• 2:37
  which is
• 2:39
  um 66,842
• 2:43
  and those two numbers are quite
• 2:44
  different which is why Jupiter's
• 2:46
  flattened but at its poles just as
• 2:48
  Saturn is uh but that's actually 24
• 2:51
  kilometers less than the previous
• 2:54
  estimations so for the diameter. So, um,
• 2:58
  it's not a huge amount, but it's
• 3:02
  >> not not when you not when you're talking
• 3:03
  about the size of the planet. That's
• 3:05
  >> exactly that's what I mean. Yeah.
• 3:06
  71,0004. So, it's what 140,000
• 3:11
  kilometers or thereabouts in diameter,
• 3:13
  which is um Yep. 11 Earth diameters,
• 3:17
  which is what we always say.
• 3:18
  >> Um, so uh why well, first of all, how
• 3:22
  have these measurements been made? Uh
• 3:24
  and the answer is that the old
• 3:25
  measurements actually go back a long
• 3:27
  way. They come from the Voyager and
• 3:30
  Pioneer era of the exploration of the
• 3:34
  outer planets and that goes back to the
• 3:36
  70s and 80s. Oh, it does.
• 3:37
  >> Um they uh so what what led to the
• 3:42
  diameter or the size of Jupiter that
• 3:44
  we've been using since then uh is a is
• 3:47
  what's called a radio occultation. So
• 3:49
  the spacecraft is behind as it passes
• 3:53
  behind Jupiter uh its signals get
• 3:56
  refracted actually by uh the atmosphere
• 3:59
  of the planet probably scattered as
• 4:01
  well. Uh but you can time it very
• 4:03
  accurately. Uh you time when the the
• 4:06
  spacecraft disappears behind the planet
• 4:07
  and you know its trajectory. uh you can
• 4:10
  then time when it reappears and from
• 4:12
  that you can calculate the and knowing
• 4:14
  about Jupiter's motion and the
• 4:16
  spacecraft's motion you can calculate
• 4:17
  what the diameter is. Uh so those are
• 4:20
  the values that we've been using ever
• 4:22
  since.
• 4:22
  >> Ah you know I think I know where all of
• 4:24
  this went wrong. They didn't allow for
• 4:26
  it stopping for gas.
• 4:29
  >> Um the the planet or the spacecraft?
• 4:31
  >> The spacecraft.
• 4:32
  >> Well, it's a gas giant. That's right.
• 4:34
  The planet's a gas giant. So yes, that's
• 4:37
  a good point. Yeah.
• 4:38
  >> Um anyway, I let that one pass. Um so,
• 4:41
  moving on. Wasn't very good. It was It
• 4:45
  was all right for the start of the show.
• 4:46
  They usually get better as we go along.
• 4:49
  Um it's uh the new measurements come of
• 4:52
  course from the spacecraft that is
• 4:54
  currently in orbit and working away very
• 4:56
  hard uh at at Jupiter in orbit around
• 4:59
  the planet and that is Juno. NASA's Juno
• 5:02
  mission which has been orbiting Jupiter
• 5:05
  since 2016 uh and doing pretty well.
• 5:08
  It's Yes. It's a decade since we've had
• 5:10
  Juno which gosh it time flies doesn't
• 5:12
  it? Sure does.
• 5:13
  >> Anyway, um so that's allowed much more
• 5:16
  accurate measurements because the space
• 5:18
  that Juno spacecraft its orbit is very
• 5:20
  well understood. It's fairly close to
• 5:23
  Jupiter. Um, but you might think, you
• 5:26
  know, well, why are we so keen to know
• 5:30
  the diameter of the planet to such a
• 5:33
  high degree of accuracy? Uh, and the the
• 5:36
  answer is um to do with our model
• 5:41
  because it is. Yeah, that's right. It's
• 5:44
  to do with our modeling of the planet's
• 5:46
  interior. Um because a small difference
• 5:49
  like that can make a big difference to
• 5:52
  what we imagine the in interior of the
• 5:55
  planet is like and remember of course
• 5:57
  everybody that Jupiter all we see is its
• 6:00
  cloud belts when we look at the planet
• 6:02
  we don't see any surface or any hint of
• 6:05
  a surface so the internal structure of
• 6:07
  Jupiter is something we have to deduce
• 6:09
  from other measurements and the the an
• 6:12
  accurate measurement of the diameter of
• 6:14
  the planet comes into that um so That's
• 6:17
  that's the reason it also uh you know
• 6:20
  one of the other things that's of
• 6:21
  interest in Jupiter is the the behavior
• 6:24
  of the atmosphere itself and the winds
• 6:25
  that blow in Jupiter's atmosphere and
• 6:28
  that also needs an accurate
• 6:30
  understanding of the diameter of the
• 6:33
  planet. Yeah, I actually I was just
• 6:36
  looking at that diagram uh that shows
• 6:38
  the different potential diameter
• 6:42
  situations based on the behavior of the
• 6:45
  planet. And yeah, without wind it loses
• 6:47
  another what 14 kilometers in.
• 6:50
  >> Yes, that's right. It does. Um if you if
• 6:53
  you uh if you imagine the winds aren't
• 6:55
  there, it does. It shrinks. So So the
• 6:57
  And by 14 kilometers exactly, that's the
• 7:00
  radius, not the not the diameter. Um so
• 7:03
  um we we have um you know a tiny figure
• 7:10
  that looks minuscule compared with the
• 7:12
  diameter of the planet itself but it is
• 7:14
  important in understanding the upper
• 7:16
  atmosphere. It's uh if there were no
• 7:19
  winds uh then what we will be seeing
• 7:22
  will be 14 kilometers smaller. I I'm
• 7:25
  surprised that it's taken us a decade to
• 7:27
  figure it out. And Juno is there been
• 7:30
  there nearly 10 years.
• 7:32
  >> Yeah. Um but maybe um you know the the
• 7:36
  accuracy that we're getting with this
• 7:38
  relies on many uh passages of Juno
• 7:42
  around Jupiter. um there will and
• 7:46
  because you're always you know that the
• 7:48
  chord that um of the Jupiter's disc that
• 7:52
  the planet that the spacecraft flies
• 7:54
  behind is different every time. And so
• 7:57
  we you probably need to um build up a
• 8:01
  statistically significant sample of
• 8:04
  entry and egress times when you're
• 8:06
  looking at you know the object
• 8:08
  disappearing by behind the planet.
• 8:10
  Occultation is what we call it. um uh an
• 8:13
  occultation is when one object hides
• 8:15
  another and that's how you're measuring
• 8:17
  uh these diameters. So yeah, it's
• 8:19
  probably it's probably taken 10 years
• 8:22
  partly to amass the data to give us this
• 8:24
  kind of level of accuracy.
• 8:26
  >> So okay, how accurate do you think it is
• 8:29
  now compared to those early um flybys
• 8:32
  with Voyager and Pioneer?
• 8:35
  >> That's a really good question actually.
• 8:37
  I haven't seen any error estimates on
• 8:41
  and um as you know in physics and
• 8:44
  certainly in astronomy too you always
• 8:46
  need a plus or minus an error estimate
• 8:48
  as to you know what the likelihood of
• 8:51
  your measurement um being that number is
• 8:56
  uh and I haven't seen it for these so I
• 8:58
  don't know the answer to that but my
• 8:59
  guess is that we're talking about in the
• 9:02
  region of a kilometer which is um pretty
• 9:05
  impressive for something that diameter
• 9:08
  uh and something that's that far away,
• 9:10
  half a billion kilometers away.
• 9:12
  >> Yeah.
• 9:12
  >> So, does this mean that our estimations
• 9:15
  of other planets in the solar system are
• 9:17
  probably a bit off as well? Uh when you
• 9:19
  consider that uh like Neptune, for
• 9:22
  example, I think we've only visited
• 9:23
  once. Would that be right?
• 9:25
  >> Yeah. Yeah, that's right. Uh so, yes, I
• 9:29
  I I think you're right. you know, you
• 9:31
  certainly the the um estimates of
• 9:34
  planets beyond Jupiter and Saturn in
• 9:37
  terms of their diameter and physical
• 9:39
  characteristics will have much bigger
• 9:42
  error limits on them just because we
• 9:44
  can't make the measurements as
• 9:45
  accurately as you can when you've got a
• 9:47
  spacecraft in orbit around one of them.
• 9:50
  >> Okay. So, um that's that's a work in
• 9:53
  progress. Whenever we go back, we might
• 9:55
  be able to
• 9:56
  >> fix that. But, uh I don't know. Have
• 9:58
  they got any missions planned for
• 10:00
  Neptune and Uranus or anything?
• 10:02
  >> There's there's always calls for them
• 10:04
  because they're such interesting worlds.
• 10:06
  >> Yeah.
• 10:06
  >> Um but I don't think I mean I think
• 10:08
  there are uh there are lots of proposals
• 10:12
  but I don't think there's anything
• 10:13
  funded. Might be wrong about that.
• 10:14
  >> Maybe our listeners can tell me if I'm
• 10:16
  wrong about that. They they may well cuz
• 10:18
  a lot of the actually we've got one
• 10:20
  fellow on Facebook who regularly uh
• 10:23
  researches some of the things we talk
• 10:24
  about and he publishes his findings on
• 10:26
  on the Facebook podcast group.
• 10:28
  >> Good on
• 10:29
  >> um yeah and I I think it's great. I've
• 10:32
  read a few of his um explanations and
• 10:34
  they're they're very good. Um so we're
• 10:36
  probably going to get sacked but uh it's
• 10:38
  um
• 10:40
  surprised them sacked us all.
• 10:44
  >> Well they they can afford us. that's why
• 10:46
  we're still here. Um,
• 10:47
  >> well, that's true. Yes, true. Very true.
• 10:50
  >> No, it's it's it's a really good
• 10:51
  discussion point. So, it sort of keeps
• 10:53
  the momentum going when when we discuss
• 10:55
  these things. So, I'm sure it'll work on
• 10:57
  our uh our tiny Jupiter story. Uh, which
• 11:00
  um
• 11:00
  >> Good.
• 11:01
  >> Yes. Which you can read about at the
• 11:03
  daily galaxy.com website or you can read
• 11:05
  the paper at Nature Astronomy. This is
• 11:09
  Space Nuts with Andrew Dunley and
• 11:11
  Professor Fred Watson.
• 11:17
  That's agre that's agreement. He's at
• 11:20
  for goodness sake. I'm really sorry.
• 11:25
  >> Okay.
• 11:26
  >> He gets very enthusiastic. Hang on. Hang
• 11:28
  on.
• 11:31
  >> Space nuts.
• 11:33
  >> I I couldn't help but turn that into a
• 11:35
  link.
• 11:36
  >> It's It's Yeah. Brilliant. I'll tell
• 11:38
  him.
• 11:39
  >> Oh gosh. It's just too good. It's just
• 11:41
  too good. But he was going off his nut
• 11:42
  that day, wasn't he?
• 11:44
  >> He was.
• 11:46
  He was. He does. Yes. He's very highly
• 11:48
  strung nut, though.
• 11:48
  >> Yes. He is. Well, that that's how he
• 11:50
  that's how he greeted us when we visited
• 11:52
  you late last year. He came tearing down
• 11:54
  the stairs.
• 11:56
  >> Yeah. Doing his rooster impersonation.
• 11:58
  >> No one could ever rob you, Fred. No one.
• 12:00
  >> That's the one good thing about it. Yes,
• 12:03
  that is the one good thing.
• 12:04
  >> They don't have to be big aggressive
• 12:06
  dogs. They they just have to be loud.
• 12:09
  >> Or or even, you know, a brush turkey
• 12:11
  going past the window in the middle of
• 12:12
  the night. That's enough as well.
• 12:15
  >> Yes, that's uh that's all it takes
• 12:17
  sometimes. Now, let's move on to our
• 12:20
  next story. And this this is a story
• 12:22
  that's got scientists uh really well,
• 12:25
  the headline says scientists stunned.
• 12:27
  We're talking about uh a comet that has
• 12:30
  done something really really unusual.
• 12:34
  Unusual. We're talking about comet 41P.
• 12:37
  What's it done this time?
• 12:40
  >> Cuz it keeps making the news this one.
• 12:42
  >> Yes, it does. Tuttle Jacobini Cresac is
• 12:46
  its full name. Uh comet better known as
• 12:49
  41P. Uh it's an object uh probably a
• 12:53
  kilometer across. A flying iceberg like
• 12:56
  basically like comets are. Um and it
• 12:59
  orbits the sun I think about every 5 and
• 13:01
  a half years. So it's in a what we will
• 13:03
  call a short period comet orbit. Um and
• 13:07
  it's uh when it passes near the sun, of
• 13:10
  course it does what comets do. It uh out
• 13:12
  gases uh produces um u basically plumes
• 13:17
  of of gas leaving its surface. Um it's
• 13:20
  usually water ice being converted
• 13:23
  directly to water vapor by the process
• 13:26
  known as sublimation. Um uh but what has
• 13:30
  been recorded uh in uh uh in fact in
• 13:36
  quite a while ago actually I think this
• 13:38
  is eight years ago by a NASA spacecraft
• 13:40
  observations made by NASA Swift
• 13:42
  spacecraft um measuring its rotation and
• 13:47
  basically over 60 days what's that sort
• 13:51
  of nine weeks or something like that
• 13:54
  >> um it slowed down from rotating once
• 13:58
  every 20 hours to once every 53 hours.
• 14:03
  Uh so that is a you know it's almost a
• 14:05
  three factor of three uh in this the um
• 14:09
  level of spin that this comet has got.
• 14:12
  >> Yeah.
• 14:12
  >> Uh and it's there's suggestion
• 14:16
  that maybe it's now rotating in the
• 14:20
  other direction uh from what it was
• 14:24
  before that there's been some sort of
• 14:26
  reverse. It hasn't slowed down to about
• 14:28
  1/3. It's It's reversed. So, it's it's
• 14:31
  slowed down five times
• 14:34
  >> cuz it's going back the other way.
• 14:36
  >> It could be I mean, part of it could be
• 14:39
  due to how you measure the rotation
• 14:41
  because it could be tumbling as well.
• 14:43
  So, you might be seeing it going the
• 14:45
  other way around. But, it does seem to
• 14:46
  be I think you're right. It's I think
• 14:48
  what you've just said is correct that
• 14:49
  it's a it's a reversal, a genuine
• 14:52
  reversal of its rotation direction. Um,
• 14:55
  so yes, it's it's got much more than a
• 14:58
  factor of three. That's right.
• 14:59
  >> That kills my theory because my first
• 15:01
  thought was, well, this must just be an
• 15:03
  observational error. But an
• 15:06
  observational error wouldn't get it the
• 15:07
  wrong way round, unless of course you
• 15:10
  you're talking about the color of the
• 15:11
  universe, but we won't go there. But um,
• 15:15
  >> wasn't my fault.
• 15:18
  >> Um, so yeah. Uh, what else could be
• 15:21
  causing this change of behavior? it. I
• 15:24
  think if if it was anything other than a
• 15:26
  comet, you know, if it was an asteroid
• 15:29
  doing this or a planetisimal or or a a
• 15:33
  distant one of the distant Kyper belt
• 15:35
  objects or something like that, it was
• 15:37
  if it was any of those, we would be
• 15:40
  utterly gobsmacked. Uh because there's
• 15:42
  no physical mechanism to do that other
• 15:44
  than an interaction with another body.
• 15:47
  You know, if you had two bodies
• 15:49
  gravitating close together, it could
• 15:52
  have an effect on the rotation.
• 15:54
  >> But, uh, in fact, more especially a
• 15:56
  collision, that would do it as well. Um,
• 15:58
  but with a comet, you've got this
• 16:00
  process that it outgasses. what I was
• 16:02
  saying earlier as it gets near the sun
• 16:05
  um the there basically the ices start to
• 16:09
  vaporize and you get a thrust from the
• 16:12
  from the outgassing material uh which is
• 16:16
  what we call a non-gravitational
• 16:17
  perturbation. It's when uh when you know
• 16:21
  the the outgassing material is acting
• 16:23
  like a rocket engine and it's changing
• 16:26
  the dynamics of the object as it's
• 16:29
  orbiting the sun. Um, and you can
• 16:31
  imagine that if there was um a formation
• 16:35
  of ice on the on the surface of the
• 16:38
  comet that essentially tilted the blast
• 16:41
  of the of the um escaping material uh as
• 16:46
  it as it sublimated as the as the um the
• 16:49
  material the water mostly went straight
• 16:52
  from a solid to a gas. Um it's like
• 16:55
  having a you know a sort of verier
• 16:57
  thruster. It's like where you've got a a
• 16:59
  thrust that is changing the rotation of
• 17:01
  a spacecraft because it's not going um
• 17:04
  the line of of the of the thrust is not
• 17:07
  going through the center of gravity of
• 17:09
  the comet. If it's off the center of
• 17:11
  gravity, then it's going to impart a
• 17:12
  rotation on it. And if it's strong
• 17:14
  enough, then it might be enough to slow
• 17:16
  it down and perhaps even reverse its uh
• 17:18
  reverse its rotation. So that's what the
• 17:21
  thinking is, but it's never been seen
• 17:22
  before.
• 17:23
  >> No. Well, like retro rockets.
• 17:26
  >> Yeah, that's right. is a retro rocket,
• 17:29
  but one that that's not slowing it down
• 17:32
  in its orbit. It's changing its rotation
• 17:34
  because of the angle that the the
• 17:35
  rocket, if you want to call it that, the
• 17:38
  rocket exhaust is coming out.
• 17:40
  >> Yeah. At the moment, it's 774 million
• 17:43
  kilometers from Earth, 5.18 astronomical
• 17:47
  units. And uh as you mentioned, this
• 17:51
  unusual behavior was checked back in
• 17:54
  2017 and they've only just sort of put a
• 17:59
  paper together to try and explain it. Um
• 18:01
  it's got a 5.4 year orbit, so it comes
• 18:04
  back quite often.
• 18:05
  >> Yeah, that's right. It's um it it's it's
• 18:08
  capt basically captured by Jupiter.
• 18:11
  >> So its orbit is dictated. It would have
• 18:13
  been in its early history, it would have
• 18:15
  been a comet coming into the inner solar
• 18:18
  system from the or cloud, this spherical
• 18:20
  sort of reservoir of comets. Um, but
• 18:22
  would have had its orbit modified maybe
• 18:25
  several times by the influence of
• 18:26
  Jupiter, which is why it's now in this
• 18:29
  really short um short period orbit, 5.4
• 18:33
  years. Yeah.
• 18:34
  >> Um there has been a suggestion that if
• 18:38
  you've got these sort of oblique
• 18:39
  outgassing that we've just been talking
• 18:41
  about that would change the rotation of
• 18:43
  the object that that might also signal
• 18:47
  that there might be weaknesses in the
• 18:48
  comet structure and it may even be a
• 18:51
  precursor to it breaking up which is
• 18:53
  something that I think will be observed
• 18:55
  with great interest as to how it uh how
• 18:58
  it progresses uh since since this change
• 19:01
  of spin.
• 19:01
  >> Yeah, maybe. And we we'll find we could
• 19:03
  find out as late as or as soon as late
• 19:06
  2028
• 19:08
  I think is its next appearance near the
• 19:11
  sun or near us or whatever you like. So
• 19:14
  um
• 19:15
  >> yeah we'll keep an eye on 41p I guess
• 19:19
  >> 41p that's right. Um there was a
• 19:21
  proposal long long ago uh to send a
• 19:26
  spacecraft to it because it's a short
• 19:28
  period comet. So it's always in the
• 19:30
  inner solar system and that was what was
• 19:32
  then called Ezro European Space Research
• 19:35
  Organization the the precursor of the
• 19:38
  European Space Agency. Uh this is in the
• 19:40
  1960s. They looked at sending a probe to
• 19:43
  that comet but they changed their mind
• 19:45
  so it never went.
• 19:47
  >> A yes. I'm sure that happens a lot in in
• 19:51
  astronomy. I mean, it's not an easy not
• 19:54
  an easy thing to um to do to to, you
• 19:58
  know, set up a mission and actually
• 20:00
  execute it. You got to come up with the
• 20:01
  dollars and Yeah. You know, it's only
• 20:05
  only so many 10-centent pieces can fit
• 20:07
  on a jar on the mantle piece. So,
• 20:10
  >> yeah. Yeah, that's right.
• 20:12
  >> Yeah. All right. Um, you can read all
• 20:15
  about uh comet 41P
• 20:19
  uh at um it's at the daily galaxy.com
• 20:22
  website, but you can also read the
• 20:23
  paper. I think it's just uh been
• 20:26
  pre-published or pre there's a pre-print
• 20:29
  available uh on the archive. Uh this is
• 20:32
  Space Nuts. Andrew Dunley here with
• 20:34
  Professor Fred. What's that?
• 20:38
  >> I'm going to step off the limb now.
• 20:42
  That's one small step for man,
• 20:47
  one leap for mankind.
• 20:50
  >> Space nuts.
• 20:52
  >> Now, Fred, to our final story on this
• 20:54
  episode, we've talked many times about
• 20:57
  gravitational lensing and some of the
• 20:59
  strange things that it does. You can
• 21:01
  watch something happen two, three, four
• 21:03
  times over the course of many years
• 21:06
  because of gravitational lensing because
• 21:07
  the light is redirected and takes longer
• 21:11
  to get here. And so you can see
• 21:12
  something and go, "Oh, what was that?
• 21:14
  Hang on. I'll I'll know again in a
• 21:16
  couple of years." Because
• 21:18
  yeah, not quite. But um what we're
• 21:21
  talking about in
• 21:22
  >> Yeah.
• 21:23
  >> What we're talking about in this
• 21:24
  particular case though is actually going
• 21:27
  out to a solar gravitational lens focal
• 21:31
  point. Is that the crux of the story?
• 21:33
  >> It it is. That's right. It's a this is a
• 21:36
  really interesting kind of essay really
• 21:38
  on the universe today website by Andy
• 21:42
  Thomas Wick uh about um about the solar
• 21:45
  gravitational lens and about how you'd
• 21:47
  get there. Um but the solar
• 21:49
  gravitational lens itself is really
• 21:51
  interesting. So the idea is exactly as
• 21:54
  you've said if you've got a an object of
• 21:57
  any mass and it happens with planets as
• 21:59
  well as stars uh it's going to bend the
• 22:03
  light passing around it because it's
• 22:05
  distorting space uh under the uh under
• 22:08
  the protocols introduced by um not in
• 22:12
  sorry as we understand it by the
• 22:14
  protocols introduced by Einstein's
• 22:16
  general theory of relativity that's what
• 22:18
  lets us calc do all the calculations
• 22:20
  about this sort of So, you've got an
• 22:22
  object in space. It's bending the light
• 22:24
  around it, which means it acts kind of
• 22:26
  like a lens. It's a very odd sort of
• 22:28
  lens, though. Um, I've seen a glass kind
• 22:32
  of interpretation of a gravitational
• 22:34
  lens. Um, there's a specialist who uh
• 22:38
  who works on this stuff in Melbourne who
• 22:40
  showed me her glass version of a
• 22:42
  gravitational lens. And it it resembles,
• 22:45
  you know, the the bottom of a wine glass
• 22:47
  where the the stalk comes up out of the
• 22:49
  middle of that. I I know them very well,
• 22:51
  Fred.
• 22:52
  >> Yeah. Yeah. Um well, if you break the
• 22:54
  wine glass off and you're left with that
• 22:57
  sort of flared part at the bottom,
• 22:59
  that's more or less the same as a
• 23:01
  gravitational lens in the way it would
• 23:02
  act on the light going around it.
• 23:04
  >> So, it's not it's not like a magnifying
• 23:06
  glass, which is what you'd like it to
• 23:08
  be. It's this very peculiar cuspshaped
• 23:11
  lens. And so it gives you um a focus
• 23:16
  that is blurred, but it's because you
• 23:19
  know the properties of the of the object
• 23:21
  that's doing the lensing. And in this
• 23:23
  case, we're talking about the sun. Uh
• 23:25
  because you know the properties of the
• 23:27
  sun, you can calculate what that
• 23:29
  blurring does to the image and you can
• 23:32
  essentially compensate it. So you could
• 23:34
  recreate
• 23:36
  uh the light coming from a very distant
• 23:38
  object um and recreate the image that
• 23:42
  the sun is forming as though it was a
• 23:44
  proper lens rather than a peculiar
• 23:46
  cusped lens. And that's what's sort of
• 23:49
  being proposed. Could we send a
• 23:51
  spacecraft to uh the solar gravitational
• 23:55
  lens focus where you could look directly
• 24:00
  back at a planet on the other side of
• 24:03
  the sun around a distant star? So you're
• 24:08
  looking into another solar system a long
• 24:10
  way away, but you're using the sun's
• 24:12
  gravity to bend that light by relativity
• 24:15
  and focus it to a point. Uh, and if you
• 24:18
  put a spacecraft there with a camera and
• 24:21
  a fancy computer, you might be able to
• 24:23
  reveal continents on an exoplanet, for
• 24:26
  example.
• 24:28
  >> Um, or even cities. That's the sort of
• 24:30
  thing that people are thinking of. So,
• 24:33
  here's the snag, though. That's a great
• 24:35
  idea, but snag.
• 24:36
  >> I think I just read that exact paragraph
• 24:40
  as you were about to say it, so I might
• 24:41
  blow the whistle.
• 24:43
  >> Yeah. Well, you can.
• 24:45
  >> No, no, you do it. It it's the distance,
• 24:47
  isn't it? It's it's Yeah. Um about
• 24:50
  somewhere between 650 and 900
• 24:53
  astronomical units is what's quoted in
• 24:55
  this in this article. And an
• 24:57
  astronomical unit is 150 million
• 24:59
  kilometers. So it is a number with a lot
• 25:02
  of zeros after it in kilometers. Um and
• 25:07
  you know it's getting your spacecraft
• 25:09
  there that is the issue. Uh we're
• 25:11
  talking about well the estimate here is
• 25:14
  four times further than Voyager 1 has
• 25:15
  traveled and that as we know is 23 light
• 25:19
  hours away. Um they reckon that it would
• 25:23
  be um more than another 130 years to uh
• 25:28
  for Voyager 1 to get to the the sun's
• 25:31
  gravitational lens point. By my
• 25:34
  calculation, and and this is probably
• 25:36
  way wrong, 97,500
• 25:39
  million kilometers.
• 25:41
  >> Sounds about right. Sounds like a lot.
• 25:43
  >> Yep.
• 25:44
  >> I didn't think my calculator could fit
• 25:45
  that many numbers on it.
• 25:48
  >> Remember the old the old calculators
• 25:50
  when they first came out? If you gave it
• 25:51
  too big a problem, it would just give
• 25:53
  you a little E.
• 25:54
  >> Yeah.
• 25:55
  >> E for error. No, I can't do that. Sorry.
• 25:57
  >> Yep. Yeah. This computer says no,
• 25:59
  really, isn't it?
• 26:00
  >> That's right. Yeah, that's a long way
• 26:02
  away and very difficult to achieve, but
• 26:06
  I think one day maybe we could do that.
• 26:08
  >> Yes. So that that's really the thrust of
• 26:10
  this article. How about you know what's
• 26:12
  the way to do it? Can you can you get to
• 26:16
  that point and they um the author's done
• 26:19
  some nice calculations which I haven't
• 26:21
  checked so I hope these are correct. I
• 26:23
  should check them. Anyway, um if you
• 26:27
  were trying to get to that solar
• 26:29
  gravitational lens point, focal point in
• 26:32
  20 years, then you need your spacecraft
• 26:34
  to travel at about 150 kilometers/s.
• 26:38
  Um uh it's which is very hard uh when
• 26:43
  you're pointing away from the sun. The
• 26:45
  Parker Solar Probe, they point out, and
• 26:48
  we kind of know this because we've
• 26:49
  talked about it, has actually got to
• 26:51
  nearly 200 kilometers/s,
• 26:53
  but that's only when it's at what we
• 26:55
  call perihelion. It's at its closest
• 26:57
  point to the sun where it's going
• 26:59
  fastest. Um, and what we're talking
• 27:02
  about here is something going in the
• 27:03
  opposite direction, going away from the
• 27:05
  sun. For it to travel at that sort of
• 27:07
  speed, you need an extraordinary amount
• 27:09
  of thrust. Um, I don't think you're
• 27:12
  talking about chemical rockets to get up
• 27:14
  to 150 kilometers/s.
• 27:16
  >> Light sales.
• 27:17
  >> So, light sails. Yeah, that's uh one of
• 27:20
  the things that you and I have spoken
• 27:22
  about before. If you can
• 27:24
  >> beam out laser light to a solar sail, a
• 27:28
  gigantic um piece of, you know,
• 27:31
  something very thin like myar that's
• 27:33
  reflective. Uh then the light itself
• 27:35
  pushes it along and you just keep going
• 27:37
  so that it just keeps up building up
• 27:39
  speed.
• 27:40
  >> Um there are um
• 27:42
  >> the trouble with that is when you get
• 27:44
  there, how do you stop it?
• 27:46
  >> Yeah, you don't. You just keep going.
• 27:47
  That's right.
• 27:48
  >> Unless Unless it had something on board
• 27:50
  to like you turn off the light and
• 27:54
  >> reverse or something. I don't know.
• 27:57
  >> Yeah. You're never going to slow it down
• 27:58
  because even if you turn off the light,
• 28:01
  it stops it accelerating, but it's still
• 28:03
  going at that speed. That's right.
• 28:05
  >> Um there's a a possibility that um you
• 28:11
  know, could you could you do the solar
• 28:14
  sail trick um and and
• 28:19
  basically um make it successful? The
• 28:23
  problem with solar sales is you you can
• 28:26
  only carry objects that are very light
• 28:28
  in weight or have low mass. And you
• 28:30
  might remember we've looked at this uh
• 28:33
  with um what was it the Breakthrough
• 28:35
  Starshot program which I think has now
• 28:38
  ceased. Breakthrough Starshot looked at
• 28:40
  the feasibility of using a solar sail to
• 28:42
  send a a spacecraft to Proxima Centuri
• 28:45
  which is only four light years away. Um,
• 28:48
  and uh, it could be done, but your
• 28:51
  spacecraft would basically consist of
• 28:54
  uh, one um, what's it called? Printed
• 28:57
  circuit board and a detector. Uh,
• 29:00
  there's not really room for anything
• 29:01
  else. It will be so it'd have to be so
• 29:03
  light in weight. It would be measured in
• 29:05
  grams rather than kilograms or tons. Uh,
• 29:09
  so that would be the problem with your,
• 29:11
  you know, with sending a a spacecraft to
• 29:13
  the uh, solar gravitational lens using a
• 29:16
  solar sail. So, you're talking then
• 29:18
  about nuclear sources and uh things of
• 29:20
  that sort that this very nice article uh
• 29:24
  goes into some of the uh the nicities of
• 29:27
  nuclear thermal propulsion and things of
• 29:29
  that sort. Even so, it's still a very
• 29:33
  tough ask to send a spacecraft to that
• 29:37
  interesting part of the sun's
• 29:40
  environment where you've got the solar
• 29:43
  the solar um uh gravity forming a focus.
• 29:47
  Uh even to get there, it's really to get
• 29:50
  there in, you know, 20 years or so, uh
• 29:53
  you're talking about really new
• 29:54
  technologies that we simply don't have
• 29:56
  at the moment.
• 29:57
  >> Yeah. Well, one day it might be a long
• 29:59
  way off, but uh the time may come and uh
• 30:02
  but then again, we might have figured
• 30:03
  everything out by then. So, yeah.
• 30:07
  Yeah. I mean, you you know, the other
• 30:09
  thing is you'd want to choose So, you've
• 30:12
  got to choose the direction that you go
• 30:13
  in.
• 30:14
  >> Yeah.
• 30:14
  >> Uh to be in the opposite direction to
• 30:16
  the planet that you want to observe.
• 30:18
  >> Y the exoplanet. And if you get that
• 30:21
  wrong, if you choose a a planet that's
• 30:23
  completely boring and has no surface
• 30:25
  features whatsoever,
• 30:27
  uh then you uh you don't really
• 30:30
  contribute much to our knowledge,
• 30:31
  particularly our knowledge of whether
• 30:32
  we're alone or not, whether there's life
• 30:34
  anywhere else.
• 30:35
  >> It's sort of like leaving the lens cap
• 30:36
  on the camera when you land on a Venus.
• 30:39
  >> Yes, that's right.
• 30:40
  >> Actually, they didn't leave it on. It
• 30:42
  melted on. I think
• 30:43
  >> it it Yeah. Well, one of them fell off
• 30:46
  as well, didn't it? fall offs on top of
• 30:48
  the on top of the scale that was going
• 30:50
  to give the uh the you know there's a
• 30:52
  ruler that they jettisoned to give the
• 30:55
  camera something to look at so you could
• 30:57
  measure the size of things and the lens
• 30:59
  cap landed right on top of it. I think
• 31:00
  that's what happened. We've had quite a
• 31:02
  few venous disasters over the years, but
• 31:05
  yeah, you're right. This would be very
• 31:07
  very difficult to swallow if you're
• 31:10
  bugging it up cuz you couldn't go and
• 31:12
  fix it. Not like
• 31:13
  >> Yeah. Well, that's right. You can't move
• 31:15
  it in any direction. You You're stuck on
• 31:17
  one planet really.
• 31:18
  >> Indeed. But it's it's food for thought
• 31:21
  though. Um but one day we'll figure out
• 31:23
  a way. If you'd like to read about that
• 31:26
  story, it is at univertoday.com as Fred
• 31:29
  said. And we're done. Fred, thank you
• 31:31
  very much.
• 31:32
  >> Oh, uh, yeah, that was that was great to
• 31:35
  talk about all those things. I hope
• 31:36
  we'll do it again sometime.
• 31:37
  >> Fun topics. I'm sure we will. Uh, if you
• 31:39
  would like to, um, visit us in the
• 31:42
  meantime. Don't forget to visit our
• 31:44
  website, spacenutspodcast.com or
• 31:46
  spacenuts.io IO or visit our social
• 31:49
  media platforms, the official Space Nuts
• 31:51
  Facebook page or Instagram page or
• 31:54
  YouTube channel or whatever you like. Or
• 31:56
  if you want to talk to likeminded Space
• 31:59
  Nutters, you can do that on the Space
• 32:02
  Nuts podcast group on Facebook, which is
• 32:04
  always a lot of fun. Thanks, Red. We'll
• 32:06
  see you soon.
• 32:07
  >> Yes, I hope so.
• 32:09
  >> Well, he said that. And uh thanks to
• 32:11
  Hugh in the studio um who couldn't be
• 32:13
  with us today. He was invited by a
• 32:16
  friend to see a comet and he couldn't
• 32:18
  wait so he ran over there. It turned out
• 32:20
  to be a goldfish.
• 32:21
  Some people will get that. And from me,
• 32:24
  Andrew Dunley, thanks for your company.
• 32:27
  See you on the next episode of Space
• 32:28
  Nuts. Bye-bye.
• 32:29
  >> Space Nuts.
• 32:30
  >> You've been listening to the Space Nuts
• 32:33
  podcast.
• 32:35
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• 32:38
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• 32:40
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