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Comet Updates, Meteor Showers & the Secrets of Uranus' Moon Ariel · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: Hello again. Thanks for joining us on another
• 0:02
  episode of Space Nuts. Where we talk
• 0:04
  astronomy and space science. My name is
• 0:06
  Andrew Dunkley, your host, and it's good to
• 0:08
  have your company. Coming up on this
• 0:11
  episode, we will be doing an update on
• 0:14
  3i Atlas. Yes, I did pronounce it correctly.
• 0:16
  This week we'll also take, uh, a look at a
• 0:19
  few other comets. That are skimming around
• 0:21
  our, uh, region at the moment. Um,
• 0:24
  from comets to meteor showers that are making
• 0:27
  the news. And including the Draconids media
• 0:30
  shower. And the, uh, the
• 0:33
  moon of Uranus called Ariel, or
• 0:36
  Ariel is making the news. This is a really
• 0:38
  interesting story. And we'll be talking about
• 0:40
  asteroids being thrown at us by Venus
• 0:43
  in the next few thousand years. That's all
• 0:45
  coming up on this episode of space
• 0:48
  nuts.
• 0:49
  Jonti Horner: 15 seconds. Guidance is internal.
• 0:51
  10, 9. Ignition
• 0:54
  sequence start. Space nuts. 5, 4,
• 0:57
  3, 2, 1, 2, 3.
• 1:01
  Space nuts.
• 1:02
  Andrew Dunkley: Astronauts report at Neil's. Good.
• 1:06
  And as you would be aware, Professor Fred
• 1:08
  Watson is on the road or on a plane or
• 1:11
  on a bus or something. Uh, but he'll be away
• 1:14
  for several weeks. And in his
• 1:17
  stead is Professor Jonti Horner. Professor of
• 1:19
  astrophysics at the University of Southern
• 1:22
  Queensland, joining us again. Hello, Jonti.
• 1:24
  Jonti Horner: Good morning. How are you getting on?
• 1:25
  Andrew Dunkley: I'm getting on quite well. What about you?
• 1:28
  Jonti Horner: Um, oh, not too bad. I've never been a great
• 1:30
  fan of mornings, but I'm. I'm powering
• 1:33
  through and mainlining coffee and doing all
• 1:35
  those kind of healthy things to try and be
• 1:36
  coherent today.
• 1:38
  Andrew Dunkley: Mainlining m Coffee. I love that I should try
• 1:40
  it. But, uh, yeah, it's good to have you
• 1:42
  back. We've had a few people asking, you
• 1:43
  know, is he. Is he coming back? When.
• 1:45
  Jonti Horner: When will we.
• 1:45
  Andrew Dunkley: When will we see him again? Well, today. So
• 1:48
  great to have you back, Jonti. And, uh, and.
• 1:50
  And we're going to get straight into it
• 1:52
  because we got a lot to talk about.
• 1:54
  Jonti Horner: And.
• 1:55
  Andrew Dunkley: And we'll start off with a, um, an update on
• 1:58
  the comet. Uh, the Exo
• 2:00
  Comet, I suppose you'd call it. I don't know,
• 2:02
  3I Atlas. What's happening there?
• 2:05
  Jonti Horner: Well, it keeps getting lots and lots of
• 2:07
  media. And unfortunately, it keeps getting
• 2:09
  lots and lots of bad media as well. Thanks to
• 2:10
  a certain, uh, astronomer in the US who
• 2:13
  should probably remain nameless. And I wish
• 2:15
  he would remain nameless. It is the
• 2:18
  object, of course, that was found a few
• 2:20
  months ago. Speeding through the solar
• 2:22
  system. Much, much faster than a speeding
• 2:24
  bullet. Everybody uses a speeding bullet
• 2:26
  analogy. And in kind of solar system terms,
• 2:28
  bullets are really slow. So pretty much
• 2:30
  everything's faster than speeding bullet. But
• 2:32
  anyway, this thing's tearing through our
• 2:34
  solar system at such a speed that even when
• 2:37
  it gets so far away from the sun that it
• 2:39
  doesn't notice the sun anymore, it will still
• 2:41
  be going at more than 58 kilometers a second.
• 2:43
  Wow. Which is pretty remarkable all
• 2:46
  told. And it's been coming through the solar
• 2:48
  system on this slightly curved path
• 2:51
  because the sun will deflect it, it's going
• 2:53
  to change its direction coming through. And
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  um, we've been getting a good view of it and
• 2:57
  it's the third ever interstellar object that
• 3:00
  we've got to see after Ummao MAU and Borisov.
• 3:03
  And it's a relatively small, fairly run of
• 3:05
  the mill comet, except for the fact that it's
• 3:08
  a comet that formed around a star that isn't
• 3:09
  the sun.
• 3:10
  Andrew Dunkley: Yeah.
• 3:11
  Jonti Horner: And that is pretty awesome and really
• 3:14
  fantastic. And because we found it so early,
• 3:17
  people have had a lot of time to study it.
• 3:19
  Get some really good data now, unfortunately
• 3:21
  from the Earth, it's now ducked out of view.
• 3:23
  It's passing closest to the sun on the 29th
• 3:26
  of this month. It's just come very close to
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  Mars, which I'll come to in a minute, but
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  it's swinging in towards its closest approach
• 3:32
  to the sun, getting more active, all looking
• 3:34
  good, but it's passing through on the far
• 3:36
  side of the sun. So it's now from the Earth's
• 3:38
  point of view, effectively lost to view for a
• 3:40
  couple of months. It's ducked out of sight
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  and we can't really see it.
• 3:45
  Fortunately we're still going to get
• 3:47
  something of a view of it though, because as
• 3:49
  I just mentioned, it's just passed close to
• 3:51
  Mars. Came within about 30 million
• 3:54
  kilometers of Mars, very roughly speaking.
• 3:56
  Mhm. Which means if you were on Mars
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  and you weren't worried about getting home,
• 4:01
  you still wouldn't be able to see it with the
• 4:03
  naked eye. It's genuinely quite a dim,
• 4:06
  faint comet from that point of view. So from
• 4:08
  Mars at the minute will probably be about
• 4:10
  factor of 100 times 2. Fancy with the naked
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  eye, but we have all these spacecraft both
• 4:14
  orbiting Mars and on Mars surface that can
• 4:17
  look up and hopefully gather some data. So
• 4:20
  I saw actually a Reddit thread this morning
• 4:22
  claiming to show the first images from the
• 4:24
  Perseverance rover of the comet. Now
• 4:27
  I'm a little bit skeptical about this because
• 4:29
  I saw it on a Reddit thread that someone had
• 4:31
  posted a random image rather than on the NASA
• 4:33
  website. But at this close approach,
• 4:37
  there's been a concerted effort for both the
• 4:39
  European Space Agency's missions and the
• 4:41
  NASA spacecraft around and, uh, on Mars
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  to actually try and get some data and try and
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  get some images of this object. Now, we've
• 4:48
  not got any of that back yet, notwithstanding
• 4:51
  the claimed first image from perseverance.
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  But this is going to be really, really useful
• 4:55
  because it allows us to peer at this object
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  as it's getting closest to the sun, when it
• 5:00
  should technically be most active and
• 5:01
  therefore there'd be the most to learn about
• 5:03
  it. It's giving off the most gas, so there's
• 5:06
  the most to observe while it's hidden out of
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  view. From our point of view, that's going to
• 5:11
  be really, really interesting. It's
• 5:13
  unfortunate that the shutdown in the US is
• 5:16
  happening at the minute. I mean, it's
• 5:17
  unfortunate for many, many reasons, but one
• 5:19
  of them is that a lot of staff working with
• 5:21
  NASA are currently furloughed and not able to
• 5:24
  work. And that will probably delay the
• 5:26
  results coming out. But it doesn't stop the
• 5:28
  spacecraft working. They just get on with it.
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  So we will get to see the results at some
• 5:32
  point, but sadly not quite yet.
• 5:35
  And however we're going to get them. It's
• 5:38
  not the end of the story in terms of
• 5:39
  spacecraft looking at this thing though,
• 5:41
  because there's a couple of other spacecraft
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  that will probably be able to snag some good
• 5:44
  photos as it moves further through the solar
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  system. We've got the wonderful name Juice,
• 5:50
  which is a Jupiter Icy Moons explorer, which
• 5:52
  is currently winging its way out towards
• 5:54
  Jupiter. That will get a really good view of
• 5:57
  Three Eye Atlas over the next month or so
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  as it goes one way and ATLAS goes the other
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  way. Effectively not as close as Mars is to
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  it. But the advantage is Juice will be
• 6:06
  inside, closer to the sun than the comet. So
• 6:09
  it will be looking away from the sun, get a
• 6:11
  decent view now, but it'll get an even better
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  view in about a month's time when it's a bit
• 6:15
  further from the sun and can therefore
• 6:17
  observe for longer without overheating the
• 6:18
  spacecraft effectively. Yeah, so we're going
• 6:21
  to get that data, uh, and it's going to be
• 6:22
  really interesting to see what comes of this.
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  I think it's going to be one of these cases
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  where the data we get
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  now from Mars, from Juice and all the data we
• 6:31
  gather from Earth will be yielding results
• 6:35
  that have been discussed for years to come.
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  You know, we'll talk a little bit later about
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  results about Jupiter's moon, about, sorry,
• 6:42
  about Uranus's. Moon aerial, which are, uh,
• 6:45
  based in part on observations that were taken
• 6:47
  40 years ago. So these things have a really
• 6:49
  long lifetime and it takes a long time for
• 6:52
  everybody to pick through them to get all of
• 6:54
  the wonderful juicy bits of gossip out,
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  essentially all the wonderful information we
• 6:58
  can learn. So I think all this data is going
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  to give us stuff that will be yielding
• 7:02
  awesome scientific results, new stories,
• 7:05
  new discussions on space nuts for 5, 10 years
• 7:08
  to come at least.
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  Andrew Dunkley: Yeah, we're starting to see a lot of, um,
• 7:12
  that happen these days with new technology
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  that you'd be able to reanalyze old data and
• 7:17
  come up with new concepts and sometimes new
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  answers. Uh, another factor that you just
• 7:22
  mentioned was, uh, the photo on Reddit. Uh,
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  we are now reaching a point where
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  it's difficult to trust
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  what's happening because of AI. And that's a
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  discussion for another day. But I suppose the
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  way around that is to go to reputable
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  sources, which you mentioned NASA. So that's,
• 7:41
  yeah, it's, it's, it's getting, uh, like I
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  spend a lot of time on social media and
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  sometimes I look at an image and, or a video
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  and go, hang on a minute. That,
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  that's not. Yeah, but it looks so convincing.
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  And that's, that's the problem. Uh, so that's
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  three I atlas and we'll have more to talk
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  about, uh, in the not too distant future. Few
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  other comments that we might, uh, skim over.
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  Jonti Horner: Boom, boom.
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  Andrew Dunkley: Uh, with, um, within our,
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  um, perimeters, I suppose, or our, um, uh,
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  close to Earth.
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  And the first One is, uh, C 2025
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  R2.
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  Jonti Horner: Swan. Yes.
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  Andrew Dunkley: Uh, what's happening with that one?
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  Jonti Horner: Quickly, this one was a big
• 8:19
  surprise. You know, people like me who are
• 8:21
  dead keen on going out and looking at comets,
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  it's um, they're not really my kind of main
• 8:25
  professional focus. But there's something
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  I've always loved since I was a little kid as
• 8:29
  an amateur astronomer. So I get really
• 8:30
  excited and hyped up when we get a good
• 8:32
  comet. So I've always got this kind of
• 8:34
  background awareness of what bright comets
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  are coming up. I check a couple of really
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  good websites I keep an eye on and I go to
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  those every couple of weeks and just see if
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  anything new's cropped up. And I'm also in a
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  Facebook comic group, um, purely as an
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  observer, I've got to say I don't really post
• 8:49
  in there because I'm not an expert and I see
• 8:51
  people posting in there when new discoveries
• 8:53
  are made. And normally when we get A comet
• 8:56
  that gets bright enough to be visible with
• 8:58
  the naked eye, we get at least a few months
• 8:59
  notice. We're getting better and better at
• 9:02
  finding these things further and further out.
• 9:04
  And that of course is going to get even more
• 9:06
  the case in the years to come with the
• 9:08
  incredible Vera Rubin Observatory. But if you
• 9:11
  go back to uh, kind of our, ah, parents or
• 9:13
  grandparents, generations, there was this
• 9:16
  real possibility for bright comet to just
• 9:18
  suddenly pop up out of nowhere and
• 9:20
  totally unexpected. A really good example of
• 9:23
  this is back in 1910 when everybody was
• 9:26
  hyped up, looking forward to an apparition of
• 9:28
  Comet Hallie, which appeared in May that
• 9:29
  year. And, um, was really good that time. It
• 9:32
  wasn't like 1986 when it was, to be honest,
• 9:34
  pretty ropey. It was pretty awful.
• 9:36
  Andrew Dunkley: I remember that.
• 9:37
  Jonti Horner: Yeah, that was the worst apparition of Comet
• 9:39
  Hallie for 2000 years. It will be better next
• 9:42
  time around. And just to make you and I feel
• 9:43
  old, it's now closer to the next apparition
• 9:45
  of Comet Hallie than the last. So it is
• 9:47
  nearer to 2061 than 1986. But
• 9:50
  back in 1910 everybody was hyped up and
• 9:53
  looking forward to Comet Hallie, which was
• 9:55
  going to put on a really good show. And then
• 9:57
  in January 1910, suddenly this comet was
• 10:00
  discovered by miners in the Transvaal when
• 10:02
  they were leaving the mine first thing in the
• 10:04
  morning in South Africa. Visible with a
• 10:06
  naked eye as bright as the brightest stars
• 10:09
  in the dawn sky before sunrise. Um, that
• 10:12
  was the Great Comet of 1910 and it was
• 10:15
  first visible when it was at perihelion
• 10:18
  because it sneaked up on us from the far side
• 10:20
  of the sun, effectively. Um, and now that was
• 10:23
  really quite close to the sun. It was visible
• 10:25
  in broad daylight for four days continuously.
• 10:28
  That's how it was one of the brightest comets
• 10:30
  of the 20th century.
• 10:32
  Which brings us to this one, 2025 R
• 10:35
  AH2 Swan. It is not as bright as
• 10:38
  a Great Comet of 1910. If it was, everybody
• 10:40
  would know about it. Yes, but back
• 10:42
  bizarrely about three weeks ago now,
• 10:45
  it went from being unknown to being the
• 10:48
  brightest comet in the night sky at the time
• 10:50
  it was discovered, which is unheard of. And
• 10:53
  it was almost naked eye visibility when it
• 10:55
  was discovered. Um, it was about magnitude 7
• 10:57
  and a half, so a factor of two to three times
• 11:00
  too faint to see with the naked eye. If
• 11:02
  you've got good eyesight and a really dark
• 11:04
  sky, it is still on the cusp
• 11:07
  of naked eye visibility. Some of the
• 11:09
  observations people are sending in of it
• 11:11
  report it being just Bright enough to see
• 11:12
  with the naked eye, others just a little bit
• 11:15
  too faint. This one is still
• 11:17
  better seen for people in the Southern
• 11:19
  hemisphere than the Northern hemisphere,
• 11:21
  which, it's seems to be a recurring theme for
• 11:23
  comets, but it's not always the case. And um,
• 11:26
  there's been some absolutely glorious photos
• 11:28
  coming of it, particularly in the first few
• 11:30
  days after it was discovered actually because
• 11:32
  it was discovered very near to the bright
• 11:34
  star Spiker in the constellation Virgo,
• 11:37
  near Mars, which was close to Spiker at
• 11:40
  the time. So you've got these glorious photos
• 11:42
  taken by some of the world's best comet
• 11:44
  photographers that show this beautiful comet
• 11:47
  with a lovely long iron tail next to the
• 11:49
  bright red star Mars, the bright blue, bright
• 11:52
  red planet Mars, sorry, bright blue star
• 11:54
  Spiker in Virgo. And uh, just putting on an
• 11:56
  incredible shot. And it stayed. It's not
• 11:59
  brightened much more because we discovered it
• 12:01
  when it was about as bright as it was going
• 12:03
  to get. But it's hovering on the edge of
• 12:05
  naked eye. Visibility will remain so for
• 12:07
  another few weeks because it's been moving
• 12:10
  away from the sun but towards the uh, Earth.
• 12:12
  And that's been balancing out effectively.
• 12:14
  Yeah, so that's been putting on a fabulous
• 12:16
  show particularly for astrophotographers down
• 12:19
  here in the Southern hemisphere. Seems that
• 12:21
  it's a comet that comes around about every
• 12:22
  thousand years or so. There were even
• 12:24
  suggestions that uh, the Earth could get a
• 12:26
  minor meteor shower from this comet
• 12:29
  around today or yesterday as we cross where
• 12:31
  the comet is going to be in a few weeks time.
• 12:34
  We cross its orbit today. That seems
• 12:36
  unlikely. Although, um, totally in passing, I
• 12:39
  have seen notifications that uh, there has
• 12:41
  been a brand new meteor shower observed for
• 12:43
  the very first time just over the last couple
• 12:45
  of weeks deep in our southern sky by
• 12:48
  these old sky camera networks. Now, probably
• 12:50
  not related at all, but it's interesting how
• 12:53
  all these things happen at once. So that's
• 12:54
  been a really interesting comment and it's a
• 12:56
  real reminder that we might not
• 12:59
  necessarily get really good warning the next
• 13:01
  time we get a really good comment. We
• 13:03
  probably will, especially with Vera Rubin.
• 13:05
  But there's always a possibility that
• 13:07
  something like this will come along where
• 13:09
  effectively due to the quirks of
• 13:12
  celestial mechanics, it approaches the sun
• 13:16
  swinging in on a curved orbit whilst
• 13:19
  hiding behind the sun from our point of view,
• 13:21
  staying within about 30 or 40 degrees of the
• 13:24
  sun in the sky, which means it's lost in the
• 13:25
  twilight glare and it only pops up, it swings
• 13:28
  around the sun to our side of the Sun. That's
• 13:31
  what's happened here that's what happened
• 13:32
  with the Great Comet in 1910 as well. It just
• 13:35
  happened to come in. In such a direction that
• 13:37
  as it moved, it stayed hidden. You know,
• 13:40
  bit like a small child playing peekaboo, I
• 13:42
  guess, kind of trying to stay hidden behind
• 13:43
  the thing as you move around.
• 13:44
  Andrew Dunkley: Yep. Okay, so that's Swan,
• 13:47
  and, uh, it's a. It's around for a little
• 13:50
  while longer. Uh, the other two that are in
• 13:52
  the news at the moment are a six lemon and
• 13:54
  R3 pan stars. What's happening there?
• 13:58
  Jonti Horner: A three lemon is one that was discovered back
• 14:00
  in January. So with these comet names,
• 14:03
  they're a little bit like a calendar that can
• 14:04
  tell you exactly when comets are found. So if
• 14:06
  you hear a Comet described as
• 14:08
  C2025A6, which is what
• 14:11
  we've got with Comet Lemon, the C tells you
• 14:14
  that it's a comet that is not a short period
• 14:17
  comet. It's not been seen at multiple
• 14:18
  apparitions. In this case, it's a comet with
• 14:21
  a period of more than a thousand years, but
• 14:22
  less than 10,000 years, probably about 1400.
• 14:25
  Andrew Dunkley: Mhm.
• 14:26
  Jonti Horner: The 2025 tells you it was discovered in the
• 14:28
  year 2025. And, um, the letter tells you
• 14:31
  which fortnight of the year it was discovered
• 14:33
  in. So the letter A here tells you the first
• 14:35
  two weeks of January. Right. So this comet
• 14:37
  was found right at the start of this year.
• 14:39
  And, um, it looked like it was going to be
• 14:41
  promising, but it wasn't heralded as
• 14:44
  being the equivalent of kind of Comet Atlas
• 14:46
  we had at the start of the year, or Comet
• 14:47
  Church in Shan Atlas last year, which were
• 14:49
  great comets. I'd classify them as they were
• 14:51
  really bright, easily visible from even
• 14:54
  brightly light polluted areas. They were
• 14:56
  really spectacular. This comet is currently
• 14:59
  best visible from the northern hemisphere. We
• 15:01
  don't really get to see it down south just
• 15:03
  yet, but it's swinging into perihelion. It's
• 15:05
  currently about the same brightness as the
• 15:08
  comet I just discussed, Comet R2, Swan.
• 15:11
  But this one is still brightening, and at its
• 15:13
  brightest it will, unless it does something
• 15:15
  unexpected. You know, comets famous saying
• 15:18
  says comets are like cats. They have tails
• 15:20
  and they do whatever they want. There's
• 15:22
  always a chance that this thing could undergo
• 15:24
  a fragmentation event and brighten by a
• 15:26
  factor of 100. That kind of thing does
• 15:28
  happen. Not necessarily all that likely,
• 15:31
  but if it continues brightening as it
• 15:33
  currently is, and it's behaving really well
• 15:35
  at the minute, it will probably at its
• 15:37
  brightest, be comparably bright to the
• 15:39
  Andromeda Galaxy. So Visible, uh, with the
• 15:41
  naked eye from dark sky sites, if you know
• 15:44
  where to look, but not visible from the
• 15:46
  middle of like polluted Sydney or Brisbane or
• 15:49
  somewhere like that, unless you've got
• 15:51
  binoculars. But it's going to be the
• 15:53
  brightest comet in our sky since Comet Atlas
• 15:56
  back in January. It's going to be a fairly
• 15:58
  good site. Again, there are some absolutely
• 16:00
  astonishingly good photographs coming in from
• 16:02
  the northern hemisphere of this. It's really
• 16:03
  photogenic and it's going to be above the
• 16:06
  threshold for naked eye visibility for about
• 16:08
  two months, building up to that peak and then
• 16:11
  fading away again. So it's going to be a
• 16:13
  really good site. Currently, it is best
• 16:15
  visible from the Northern hemisphere, I
• 16:18
  believe it's currently quite high in the
• 16:20
  northern sky, edging towards the,
• 16:23
  the southern outskirts of Ursa Major, that
• 16:25
  kind of part of the sky. But it's then going
• 16:27
  to start ducking southwards and by the
• 16:30
  time it's at its brightest, which is going to
• 16:32
  be the start of November, it will be visible
• 16:34
  from both hemispheres, albeit I think,
• 16:37
  easier to see from the Northern hemisphere
• 16:39
  still. But this is going to be a naked eye
• 16:41
  comet. Naked eye caveat,
• 16:44
  not that spectacular, but visible if you know
• 16:46
  where to look. Um, for those who go out and
• 16:49
  look at comets and that therefore it's
• 16:51
  probably a little bit brighter than Pons
• 16:53
  Brooks was last year. Pons Brooks was, you
• 16:56
  know, captors of Devil's Comet and all those
• 16:58
  kind of weird names that these things seem to
• 17:00
  get in the media. If you saw that one with
• 17:02
  the naked eye, this comet should be a bit
• 17:05
  brighter than that and a bit easier to spot.
• 17:07
  But it's probably a really good opportunity
• 17:08
  for people to dust off their camera gear, do
• 17:11
  a little bit of planning and go take some
• 17:13
  photos. So it's going to be pretty good. And
• 17:16
  nobody complains about a naked eye comet.
• 17:18
  Andrew Dunkley: No, they don't.
• 17:18
  And R3 pan starrs, I'm guessing from its
• 17:21
  name, is a very recent discovery.
• 17:23
  Jonti Horner: It is. This was discovered very, very
• 17:25
  recently and we still know surprisingly
• 17:27
  little about it, actually. I mean, if I go to
• 17:30
  the place I normally look at the light curves
• 17:32
  for these comets from where it aggregates all
• 17:34
  the observations and tries to predict forward
• 17:36
  how bright it's going to be. That has a
• 17:38
  really nice light curve for this object, but
• 17:41
  it has no observations on the light curve at
• 17:44
  the minute. So this is very new. It is still
• 17:46
  very faint. I mean, with this one we're
• 17:48
  talking about something that's probably a
• 17:50
  factor of 50,000 times too fancy with the
• 17:53
  naked eye at uh, the minute, very recent
• 17:56
  discovery by that wonderful automated
• 17:58
  search facility on the top of Hawaii Pan
• 18:00
  starts. The reason this has got my attention
• 18:03
  is that it is going to pass
• 18:05
  incredibly close to the line between the sun
• 18:08
  and the Earth, uh, which we've seen with
• 18:11
  those two great comets we had in the last 12
• 18:13
  months. And when you get an object that
• 18:15
  passes directly between the sun and the
• 18:17
  Earth, if it happens to be a particularly
• 18:19
  dusty comet and shedding a lot of dust,
• 18:21
  there's a phenomenon called forward
• 18:23
  scattering which we in Australia are fairly
• 18:25
  familiar with on, um, dusty days because near
• 18:27
  sunset the sky is unbearably bright and it's
• 18:29
  awful driving west at sunset, which is
• 18:32
  something people in Toowoomba, um, are very
• 18:33
  familiar with because our roads are kind of
• 18:35
  east, west, north, south. And so around the
• 18:37
  equinoxes you drive towards the sunset and
• 18:40
  get snow blind effects. Skiers are familiar
• 18:43
  with it for the same reason. You know, on a
• 18:45
  kind of day where there's a lot of small ice
• 18:47
  crystals in the air, the sky can be very
• 18:49
  bright in the direction of the Sun. This
• 18:52
  phenomenon of forward scattering can make
• 18:54
  comets brighten by more than a
• 18:57
  factor of 100, depending on the orientation
• 19:00
  when they're close to the sun in the sky, um,
• 19:03
  or when they're close to that line between
• 19:04
  the Earth and Sun. Now this object Pan stars,
• 19:07
  it looks like it's a fairly small comet, but
• 19:09
  we've not got much information about it yet.
• 19:11
  But its orbit's fairly well constrained and
• 19:14
  it is going to come very close to the sun in
• 19:16
  the sky from our point of view. For a time,
• 19:18
  people were even suggesting it could transit
• 19:19
  the disk of the sun, um, even though we
• 19:21
  wouldn't see anything because it'd be too
• 19:22
  small to be visible, it could pass so
• 19:25
  perfectly between us, it will cross across
• 19:26
  the disc of the sun from our point of view.
• 19:29
  What that all means is that if this
• 19:32
  comet becomes fairly active,
• 19:35
  there's a chance that it could become quite
• 19:37
  bright in April next year. Now,
• 19:40
  how bright is utterly unknown at the
• 19:43
  minute, but it's worth flagging up because
• 19:44
  it's an interesting one. The light curve I'm
• 19:46
  looking at as I talk about this is, in
• 19:49
  all honesty, with the lack of observations,
• 19:51
  we've got something of a fiction. It could
• 19:53
  get a lot brighter than this or fainter than
• 19:54
  this. But it suggests that without this
• 19:57
  forward scattering process, this comet will
• 19:59
  be too small to be visible with a naked eye.
• 20:01
  But with forward scattering, it could get as
• 20:03
  bright or brighter than Comet Lemon. So it
• 20:06
  could get brighter than the andromeda Galaxy,
• 20:08
  albeit when it's quite close to the sun in
• 20:09
  the sky and therefore it could be visible to
• 20:12
  the naked eye for a week or two. Now if it
• 20:14
  turns out to be a larger, more substantial
• 20:16
  comet than those first observations suggests,
• 20:19
  that all ramps up and it could be even
• 20:21
  better. There's a small chance I'd say that
• 20:24
  this thing could be visible with the naked
• 20:25
  eye in April, but it's just again one, once
• 20:28
  again a reminder of as we get better at uh,
• 20:31
  these kind of all sky surveys, we're going to
• 20:33
  find interesting comets earlier. We're
• 20:36
  eventually going to get to the point where an
• 20:38
  object like Comet R2 Swan that we've got at
• 20:40
  the minute can't surprise us because we'll
• 20:43
  get our telescopes good enough that we'd find
• 20:44
  it a really long way away before it hides
• 20:46
  behind the sun. And so uh,
• 20:49
  you know, it wouldn't surprise me if the next
• 20:51
  great comet was found months ahead of time
• 20:53
  rather than weeks ahead of time. And we get
• 20:55
  prior artists, um, and because it's
• 20:58
  observed that early, we might have this level
• 21:01
  of uncertainty in an object that's a bit
• 21:03
  brighter than this and people will either
• 21:06
  be calm and cautious or hyperbolic
• 21:09
  and excited. And then we get to see that's
• 21:11
  part of the fun of it.
• 21:13
  Andrew Dunkley: M. Yeah, indeed.
• 21:14
  Okay, so plenty, uh, or potentially plenty
• 21:16
  for skywatchers to look forward to and a lot
• 21:19
  going on at the moment. And while you've been
• 21:21
  talking about those comments, I've been
• 21:22
  looking up some of the media pictures and
• 21:24
  it's interesting to see that um, the quality
• 21:26
  of the outlet dictates the
• 21:30
  genuineness uh, of the photo. Let me just say
• 21:32
  that this, this is Space
• 21:35
  Nuts with Andrew Dunkley and John de Horner.
• 21:38
  Jonti Horner: 3, 2, 1.
• 21:40
  Andrew Dunkley: Space nuts from comets to
• 21:43
  meteor showers. And there's uh, there's a
• 21:46
  few making the news at the moment.
• 21:47
  Jonti Horner: Jonti, there are. It's a good time of the
• 21:50
  year for meteor observers, um, particularly
• 21:53
  in the Northern hemisphere. Whilst comets
• 21:55
  seem to get a slightly better deal in the
• 21:57
  Southern hemisphere over long periods of
• 21:59
  time. The Northern hemisphere gets the better
• 22:01
  of the meteor showers. We're getting a fair
• 22:03
  bit of coverage already about the Orionid
• 22:05
  meteor shower which is already
• 22:08
  active but is building to a peak around the
• 22:10
  20th, 21st of October. Now the
• 22:13
  Orionids are uh, a meteor shower that's
• 22:16
  caused by Comet Hallie which has been
• 22:18
  whizzing around the sun on its current
• 22:20
  roughly 76 year orbit for thousands, if not
• 22:22
  tens of thousands of years. It's a very big
• 22:25
  cometary nucleus Laying down lots of dust.
• 22:27
  And that dust has spread out to such an
• 22:30
  extent that every year the Earth, uh, crosses
• 22:32
  through that tube of dust left behind by the
• 22:34
  comet on two separate occasions. Yeah, we get
• 22:36
  the Etraquarian meteor shower in May, which
• 22:39
  is one of the year's best meteor showers. But
• 22:42
  it's really hard to see. Um, you need to be
• 22:44
  up in a couple of hours before dawn to see
• 22:46
  anything. And that favors Southern Hemisphere
• 22:47
  observers. So it's not as well known, not as
• 22:49
  well observed. Then you have the Orionids
• 22:52
  in October. And, um, the Orionids are not as
• 22:55
  good as the Aquarids. They're probably in the
• 22:58
  second kind of tier of meteor showers. So
• 23:00
  you've got the big three in the form of the
• 23:02
  Quadrantids in January, the Perseids in
• 23:05
  August, and, um, the Geminids, which are the
• 23:07
  best meteor shower in a typical year in
• 23:09
  December. And they're reliable every
• 23:11
  year, uh, really good rates. And they're the
• 23:13
  ones that, uh, you tell your friends who are
• 23:15
  not into astronomy to go out and look at
• 23:17
  because they're good enough that someone
• 23:18
  who's not that excited already will still see
• 23:20
  a good show. The Orion into the, like, the
• 23:23
  next tier down, they are. If you're someone
• 23:25
  who's really keen on astronomy and you're
• 23:27
  happy to spend an hour or two sitting out in
• 23:29
  the middle of the night, you'll see a
• 23:31
  reasonable number and they're lovely to see,
• 23:33
  but they're probably not active enough that
• 23:35
  someone who's not that keen on astronomy will
• 23:37
  get a real buzz out of it, if that makes
• 23:40
  sense. So if you're somewhere in
• 23:42
  Northern Europe and North America, where
• 23:44
  you've got long dark nights at the minute and
• 23:47
  you were out all night, you might see 15 or
• 23:49
  20 of these per hour in the early morning
• 23:52
  hours in late October, you know,
• 23:54
  the kind of 19th, 20th, 21st, 22nd
• 23:58
  from Australia, the rates are a bit lower
• 24:00
  because a point in the sky these meters come
• 24:02
  from the radiant is lower in the sky at its
• 24:04
  highest. And geometry means, therefore, the
• 24:07
  same number of meteors are spread over a
• 24:09
  larger volume of atmosphere. So you'll see a
• 24:11
  smaller number of them from wherever you're
• 24:13
  sat. But you can still see if you're in kind
• 24:15
  of the top end of Australia, I'd say 10 or 15
• 24:18
  per hour. If you're down at the southern end,
• 24:20
  a little bit less than that. The further
• 24:21
  south you go, the worse it'll get. This year,
• 24:23
  though, is particularly good because it's New
• 24:25
  Moon. And so what that means is you've Got
• 24:28
  ideal viewing conditions. You don't have
• 24:31
  the glowing orb of doom scattering light in
• 24:34
  the sky and basically blocking the view of
• 24:36
  all the interesting stuff. I've always been,
• 24:38
  as an amateur astronomer that side of my
• 24:40
  life. Frustrated by the Moon because it stops
• 24:42
  us seeing all the good stuff. But, um, that's
• 24:44
  particularly true of meteor showers. That's
• 24:47
  iron. It's. They're getting a lot of
• 24:49
  coverage. Um, what I would say with it is
• 24:51
  unless you're a really avid meteor observer
• 24:54
  or unless you're going out anyway, don't buy
• 24:56
  into the hype. There'll be a lot of overblown
• 24:59
  articles. And I'm seeing them already from
• 25:00
  some of the less reputable media outlets
• 25:02
  online. Talking about the skies falling. And
• 25:05
  this will be the best thing you'll ever see.
• 25:06
  And that just sets people up for
• 25:08
  disappointment. So it was a little bit sad.
• 25:10
  But if you do want to go out and see the
• 25:12
  Orionids. Around the 20th of October
• 25:15
  is the best time. Unlike
• 25:18
  most meteor showers, the Orionids and the
• 25:21
  Aquarids in May, both these Comet Hallie
• 25:23
  meteor showers have quite a broad maximum. So
• 25:26
  if it's cloudy on the night of the peak.
• 25:28
  You'll still get a decent show for two or
• 25:30
  three nights either side. It's a much flatter
• 25:32
  plateau, effectively. And they do sometimes
• 25:34
  throw a bit of a surprise our way. They are
• 25:37
  fast meteors, um, have a tendency to produce
• 25:39
  quite a few bright ones as well. And you see
• 25:41
  them best if you're out in the early hours of
• 25:43
  the morning, after midnight. That's kind of
• 25:45
  the best time. With the best rates being just
• 25:46
  before dawn. But they are visible from about
• 25:49
  10:30 at night.
• 25:51
  Andrew Dunkley: Okay.
• 25:51
  Now, um, the other meteor shower
• 25:54
  that you wanted to talk about, uh, that could
• 25:56
  be worth a look is the Draconids. I don't
• 25:58
  know much about this one.
• 26:00
  Jonti Horner: This is a really fun little shower. Because
• 26:02
  it's illustrative of how meteor showers are
• 26:05
  really changeable over time. The
• 26:08
  way a meteor shower forms is you've got a
• 26:11
  comet going around the sun. And a comet is a
• 26:13
  dirty snowball, a snowy dirt ball. So when
• 26:15
  it's far from the sun, it just looks like an
• 26:17
  asteroid. Nothing's happening. It's a tiny
• 26:19
  speck of light, few kilometers across.
• 26:22
  When it gets close to the sun, the surface
• 26:24
  gets hot. And all the ices on the surface
• 26:26
  sublime. They turn to gas, erupt from the
• 26:29
  surface in jets. Because they only sublime if
• 26:32
  they're exposed to enough heat to get off.
• 26:34
  And a lot of the surface is caked up and
• 26:36
  blocked up. So you get these little active
• 26:38
  areas casting jets of material into space
• 26:41
  and carrying with them a lot of dust.
• 26:44
  So comets, when they're closer to the sun,
• 26:46
  shed gas and dust. And that's why they get
• 26:47
  the coma and the tails that make them
• 26:49
  brighter and easier to see and so
• 26:51
  spectacular. The dust that they shed
• 26:54
  is ejected from them at, uh, speeds of
• 26:56
  meters or tens of meters or maybe hundreds of
• 26:59
  meters per second. But typically 1 or
• 27:02
  10 meters a second while the comet's going
• 27:04
  around the sun at a speed measured in tens of
• 27:06
  kilometers per second. So that means that the
• 27:09
  dust will end up moving on essentially the
• 27:10
  same orbit as the comet. It won't move on to
• 27:13
  a drastically different orbit. The
• 27:16
  smallest grains of dust are blown away by the
• 27:18
  sun and the solar wind and radiation
• 27:20
  pressure. But the bigger bits of dust kind of
• 27:22
  stay moving around the sun on an orbit
• 27:24
  similar to that of the comet. But because of
• 27:26
  that ejection speed, some of the dust grains
• 27:29
  move on orbits that have a shorter period
• 27:31
  than the comet. Some move on periods slightly
• 27:33
  longer than the comet. So over time, they
• 27:35
  spread out ahead and behind the comet in its
• 27:37
  orbit until eventually the orbit is clogged
• 27:40
  with dust all the way around. So if you go
• 27:42
  across the orbit when the comet isn't there,
• 27:44
  you'll still run into dust because there'll
• 27:45
  always be something there. Then when you
• 27:48
  get the Earth, uh, running across one of
• 27:50
  these orbits, if they intersect in space
• 27:52
  every year, we'll go through that dust and
• 27:54
  we'll get a meteor shower. Now, comets,
• 27:56
  orbits are constantly changing. And that's
• 27:59
  particularly true of a family of comets we
• 28:01
  call the Jupiter family comets, or the short
• 28:03
  period comets. These are comets captured by
• 28:05
  Jupiter, flung into the inner solar system,
• 28:07
  moving on orbits that are kind of five, six,
• 28:09
  seven years long. So you'll get a comet
• 28:12
  will be nudged, dropped onto a new orbit, and
• 28:14
  it will start laying down dust on that orbit.
• 28:17
  But it might not be there particularly long
• 28:18
  until it's flung onto a different orbit. The
• 28:20
  orbit's constantly being tweaked and changed.
• 28:23
  That means that you get these dust trails
• 28:25
  that build up over time, but you can even
• 28:27
  orphan them. You can take the comet away and
• 28:29
  the dust trail remains, which is the case of
• 28:30
  some of our meteor showers. It also means,
• 28:33
  uh, that when a comet is relatively newly
• 28:36
  placed onto a given orbit, that
• 28:39
  orbit won't have fully clogged up with dust
• 28:41
  yet. So most years when we cross where that
• 28:43
  orbit will be, we'll get very few meteors
• 28:45
  because the dust just hasn't had time to
• 28:47
  spread out yet. But if you catch it on a year
• 28:50
  when the comet is relatively nearby, you
• 28:52
  might run into dust. The final little
• 28:55
  piece of all this puzzle that I'm talking
• 28:57
  through is that dust, uh, that was emitted,
• 28:59
  uh, at the last few apparitions of the comet
• 29:02
  will not have had time to spread out a huge
• 29:04
  amount laterally. So you get these almost
• 29:06
  like javelins. Very thin, very long
• 29:09
  filaments of dust that are much
• 29:12
  denser. And if the Earth goes through one of
• 29:15
  those, suddenly, you can get a really big
• 29:16
  meteor outburst. And, um, instead of getting
• 29:18
  one or two meters an hour, you might get
• 29:20
  hundreds or thousands. Wow. So that's a
• 29:23
  lengthy bit of background exposition to kind
• 29:24
  of explain what's happening in the background
• 29:26
  here. The Draconig meteor shower is one that
• 29:29
  kind of shot to fame in the year, uh, 1933,
• 29:32
  when there was an incredible meteor storm,
• 29:34
  um, where people saw literally
• 29:37
  thousands of meteors per hour. That's more
• 29:40
  than one a second raining down,
• 29:42
  Absolutely incredibly spectacular.
• 29:45
  All radiating out from this point in the
• 29:47
  night sky. Near the Northern hemisphere
• 29:48
  constellation of Draco. There was a slightly
• 29:51
  less spectacular but still very intense
• 29:53
  meteor storm from this shower in
• 29:55
  1946. And since then,
• 29:58
  most years you get two or three meters an
• 30:01
  hour from this meteor shower. They're very
• 30:02
  slow meteors. They're typically fairly faint
• 30:05
  as well. But there's always a little bit
• 30:07
  going on. But every six years or so,
• 30:11
  the comet comes back to perihelion, and
• 30:13
  there's a chance of us getting an outburst.
• 30:15
  Now, whether we get one or not depends on the
• 30:17
  gravity of all the other planets pulling the
• 30:19
  comet's orbit. And these debris streams
• 30:20
  around, Sometimes they'll miss us underneath
• 30:23
  or they'll miss us above. And we don't run
• 30:24
  through them. But it's become an active thing
• 30:27
  of trying to figure out what's going to
• 30:29
  happen next. Could we ever get another
• 30:32
  meteor storm from this shower? Now, we've
• 30:34
  had a few outbursts that are not storms, but
• 30:37
  are good. A few years ago, there was an
• 30:38
  outburst where there were a hundred meters an
• 30:40
  hour visible for a couple of hours, which is
• 30:41
  a pretty good meteor shower. Yeah. That's
• 30:44
  led to, uh, people using this meteor shower
• 30:47
  as a really good test bed for how we model
• 30:49
  how these things work. Trying to improve our
• 30:52
  computer models of how all the dust moves,
• 30:54
  where it's all going to be so that we can
• 30:56
  predict forward and say what's going to
• 30:58
  happen at the next operation. And a paper
• 31:00
  came out literally just a couple of days ago
• 31:04
  that explored this in some depth it's from
• 31:07
  some of the leading meteor astronomers in the
• 31:09
  world. Doing modeling of the Draconids. And
• 31:12
  what it suggested is that this week,
• 31:14
  literally the week that we're recording this.
• 31:17
  There is a potential for the Draconis to have
• 31:19
  a fairly good outburst. On Wednesday
• 31:22
  night. Into Thursday morning Australian time.
• 31:24
  So that's around the 8th of November, the
• 31:27
  evening of the 8th of November, universal
• 31:29
  time, early hours of the morning. 9th, sorry,
• 31:32
  October 8th of October, universal time,
• 31:35
  early hours of the morning of the 9th of
• 31:37
  October, for us here in Australia.
• 31:39
  That there'll be a bit of an outburst. Now,
• 31:41
  this is probably not going to be an outburst.
• 31:44
  That's particularly spectacular visually.
• 31:47
  Reason for that is its full Moon. So it
• 31:49
  brings us back to the Moon. Getting in our
• 31:51
  way and spoiling all of our fun. If the full
• 31:53
  Moon wasn't the full Moon. It's likely that
• 31:56
  this outburst. Could be somewhere between 30
• 31:58
  meters per hour and 100, maybe even 200 per
• 32:01
  hour. But the Draconids tend to come in
• 32:03
  fairly slow. And they tend to be small, faint
• 32:05
  meteors. So almost all of them will be lost
• 32:07
  to the naked eye in the moonlight.
• 32:10
  Unless they're not, because this is just a
• 32:12
  prediction. So something could happen that is
• 32:14
  better than we expect. What's most likely to
• 32:17
  happen, though, is that, uh, people will see
• 32:18
  a few meteors through the moonlight. And that
• 32:21
  will tell you there's a lot more going on
• 32:23
  than you can see. But the
• 32:25
  astronomers doing observations with radar
• 32:29
  will see an outburst. And it will probably be
• 32:32
  the strongest radar meteor shower of the
• 32:34
  year. So these are people almost doing
• 32:37
  kind of, uh. Beyond the horizon. Radio
• 32:40
  listening. One of the most common ways you
• 32:41
  can listen to meteors in radio
• 32:44
  wavelengths.
• 32:45
  Is to look at an angle low to the
• 32:48
  horizon. When you're in a country where there
• 32:50
  are, uh, other countries far enough away.
• 32:52
  That their radio broadcasts can bounce off
• 32:55
  the ionized trails left behind by the meteors
• 32:57
  80 kilometers up. And bounce back down to
• 32:59
  you. So, obviously, for a lot of places, this
• 33:01
  just doesn't work. Because you're looking out
• 33:03
  over the ocean. But people in Europe or
• 33:05
  people in North America. Quite often there's
• 33:08
  a city at about the right distance. It's
• 33:10
  quite a big bit of wiggle room. That if
• 33:12
  you're pointing your detector roughly in that
• 33:14
  direction. Every time there's a meteor.
• 33:16
  You'll suddenly get this reflective ionized
• 33:18
  trail 80 km up. Radio waves that would
• 33:21
  have normally escaped the atmosphere. And
• 33:23
  gone on into space. Will bounce off that and
• 33:25
  bounce down to you. And you'll get a little
• 33:26
  burst of radio noise. And so that means
• 33:29
  people can count meteors. And it's likely
• 33:31
  that this draconian outburst will be
• 33:33
  confirmed not by people looking with the
• 33:35
  naked ey, but by people listening with radio
• 33:38
  antennas. And they're saying in terms of
• 33:40
  radio signals, you could get more than a
• 33:42
  thousand per hour. So it could be a fairly
• 33:44
  intense outburst, just not one that is really
• 33:47
  visible with a naked eye. It's worth flagging
• 33:50
  up though, is it's a good insight into how we
• 33:52
  do the science of this, that kind of
• 33:54
  beautiful interplay of theory and experiment
• 33:56
  and observation where we predict something,
• 33:59
  we test that prediction, and that allows us
• 34:00
  to improve our models to make the next
• 34:02
  prediction, prediction even better. But it's
• 34:04
  also worth flagging up because the one
• 34:06
  prediction you can make is that all
• 34:08
  predictions will be wrong. And so while we're
• 34:10
  saying that it'll probably be only 40 or 50
• 34:12
  per hour or 20 per hour with the naked eye,
• 34:15
  and the Moon will hide most of them, you
• 34:17
  can't rule out that it'll be better than
• 34:18
  that. So if you're up in the early hours of
• 34:20
  the morning on Wednesday night into
• 34:23
  Thursday morning, it's worth having a bit of
• 34:25
  a look. The forecast peak is forecast to be
• 34:27
  at 3pm Universal Time, between 3 and 4pm
• 34:30
  Universal Time, which is Greenwich Mean Time.
• 34:33
  So you can work out from that what time it'll
• 34:35
  be for you. For many people it'll be in the
• 34:37
  daytime. So sorry, but this time kind of
• 34:39
  favors people in East Asia and Australia,
• 34:41
  that kind of area. So we might see something,
• 34:44
  we might not. But it's worth a look.
• 34:46
  Andrew Dunkley: Okie doke. Yeah. Uh, if you want to read
• 34:48
  about that, uh, you can do so at the Harvard
• 34:51
  Edu website or go to the Arxiv
• 34:54
  website where the paper was published. And
• 34:57
  I'd read out, I'd read out the whole thing,
• 34:59
  but you'll never remember it.
• 35:02
  Jonti Horner: I was going to say one thing I should mention
• 35:04
  with that is the draconids are best seen from
• 35:07
  the northern hemisphere. So if you're in the
• 35:08
  southern hemisphere and you want to see this
• 35:10
  nearer to the equator, you are the better.
• 35:12
  And in reality, I'd say that people south
• 35:15
  of the line about at, uh, Brisbane's
• 35:17
  latitude, it's not even worth bothering
• 35:19
  because the radiant will be so low in the sky
• 35:21
  that you will see nothing at all really is
• 35:23
  more of a Northern Hemisphere thing. So I
• 35:24
  want, you know, want to make sure that we
• 35:26
  don't get somebody down in New Zealand going
• 35:28
  out looking for it and saying, I saw nothing.
• 35:30
  But, well, you saw nothing because you can't
• 35:32
  see anything from there. I'm really sorry.
• 35:34
  Andrew Dunkley: Yes, that's the way it goes though. That's
• 35:36
  the way it goes. Yeah.
• 35:37
  Jonti Horner: Yes.
• 35:37
  Andrew Dunkley: All right, uh, this is Space Nuts with Andrew
• 35:40
  Dunkley and Professor Jonti Horner.
• 35:42
  Jonti Horner: Space Nuts.
• 35:44
  Andrew Dunkley: All right, let's move on to Uranus and
• 35:46
  the Moon. Ariel. This is a really
• 35:49
  fascinating story about, uh, what might have
• 35:51
  been, uh, in its past. A
• 35:54
  hidden ocean on, on a rather small object.
• 35:57
  Jonti Horner: It is, and it's part of this ongoing
• 36:00
  journey, discovery that we're getting where
• 36:02
  fundamentally the kind of world that I grew
• 36:05
  up in as a kid excited by astronomy in the
• 36:08
  80s and 90s just isn't the same anymore.
• 36:10
  I was growing up and the kind of accepted
• 36:13
  wisdom was that water was incredibly rare and
• 36:15
  liquid water particularly rare, and therefore
• 36:18
  life would be uncommon in the cosmos. And
• 36:20
  this was one of the kind of centerpieces of
• 36:21
  the rare Earth hypothesis, which basically
• 36:24
  said don't even bother looking for life
• 36:25
  elsewhere because where all there is. And
• 36:27
  I've never particularly put much stock in
• 36:30
  that idea. But what we've seen in the last 30
• 36:32
  years or so is that, uh, water is actually
• 36:35
  incredibly more common than people would
• 36:38
  have thought. And that's not a surprise. You
• 36:40
  know, if you look at, uh, the universe as a
• 36:43
  whole, Hydrogen is by far the most common
• 36:45
  atom. Oxygen is the third most common atom.
• 36:47
  And if you put them together, you get water.
• 36:50
  And we see in the after solar system, we see
• 36:52
  in the form of these comets we talked about
• 36:53
  earlier on. Water ice is incredibly abundant
• 36:56
  and in fact of the solid material in the
• 36:59
  solar system, water ice is by far the
• 37:02
  largest amount of mass of everything.
• 37:05
  Once you're out at Jupiter's orbit and
• 37:07
  further out, all the icy moons, all the
• 37:09
  comets, all the trans neptunian objects are
• 37:12
  uh, basically lots of water ice with a bit of
• 37:13
  other stuff going on. So solid water is
• 37:16
  really common. Liquid water though, people
• 37:19
  said, well, we've got a lot of it on Earth,
• 37:21
  but elsewhere it's not that common. And then
• 37:22
  we found liquid water in Mars as polar caps.
• 37:25
  And we've found all these deeply buried
• 37:27
  subsurface oceans, the kind of poster child
• 37:30
  of which is Europa. And you know, even in the
• 37:33
  kind of wonderful films, you know, all these
• 37:34
  worlds are yours except Europa. Attempt no
• 37:36
  landing there, that whole kind of thing.
• 37:39
  So we found all these subsurface oceans and
• 37:41
  the more we look, the more we find them.
• 37:43
  There was a story earlier this year that the
• 37:45
  dwarf planet series in the Ashram asteroid
• 37:47
  belt had a subsurface ocean in the past.
• 37:49
  Yeah.
• 37:50
  And now we come to Ariel. Ariel is one
• 37:53
  of Uranus's moons. And Uranus's moons we got
• 37:55
  some lovely images of, from the Voyager 2
• 37:58
  spacecraft back when, back when I was a wee
• 38:00
  band back in kind of 1985,
• 38:03
  1986 time. Voyager 2
• 38:05
  flew past Uranus as part of its grand tour of
• 38:08
  the outer solar system. And
• 38:10
  as we always say, it flew past faster than a
• 38:13
  speeding bullet. So it didn't have very long
• 38:15
  to hang around and take images. And because
• 38:18
  Uranus is tipped over on its side and
• 38:21
  its moon's orbit above Uranus's equator,
• 38:24
  they're all tipped over on their side. So you
• 38:26
  had basically mid summer at Uranus there.
• 38:28
  And all of these moons had one hemisphere
• 38:30
  illuminated and one hemisphere dark, which
• 38:33
  meant that as Voyager 2 flew through,
• 38:36
  we got all these beautiful pictures of
• 38:38
  Uranus's moons. But for all those moons, we
• 38:40
  only saw one side of them. We saw the
• 38:42
  southern hemisphere illuminated by daylight,
• 38:45
  but we didn't get to see the other side. Uh,
• 38:47
  and we saw these really unusual objects.
• 38:49
  Miranda is kind of the most famous for this,
• 38:51
  which almost looks like somebody's taken a
• 38:53
  moon and smashed it apart with a hammer and
• 38:55
  then rebuilt it haphazardly. You've got all
• 38:58
  these very different features next to each
• 38:59
  other. It looks really odd. Ariel
• 39:02
  is a bit bigger than Miranda and also, um,
• 39:05
  looks really odd. It's got areas on its
• 39:07
  surface that are clearly very, very old.
• 39:09
  They're fairly relatively low albedo, they're
• 39:12
  not that reflective, and they're incredibly
• 39:14
  heavily cratered. But it also has these
• 39:17
  areas that are much more reflective,
• 39:20
  much smoother. They have far fewer craters.
• 39:23
  And they've also got these incredibly large
• 39:25
  canyons, fishering Valley type features on
• 39:28
  them. And, um, again, it looks a very
• 39:32
  odd world, a bit like Miranda. You've got
• 39:34
  very different surfaces relatively close to
• 39:36
  each other that look very different to one
• 39:38
  another geologically. They look like they've
• 39:40
  got very different histories. That's 40 years
• 39:43
  ago. And this is a really good example of
• 39:44
  what we talked about earlier, where data
• 39:47
  from the past continues to have value as our
• 39:50
  tools improve so we can better understand
• 39:52
  it. Because a new result that's come out in
• 39:55
  the last couple of weeks is a result of
• 39:58
  really impressive computer modeling trying to
• 40:01
  figure out what's going on with Arial. Why
• 40:03
  does it look so unusual?
• 40:06
  Typically, when we see smooth surfaces with
• 40:08
  far fewer craters, we consider
• 40:11
  them to be younger because impact craters are
• 40:14
  happening all the time. And so the longer you
• 40:16
  have to be exposed to space, the more craters
• 40:18
  you'll get. Which leads to this kind of
• 40:21
  science of crater counting, where you can
• 40:23
  estimate the edge of a surface by seeing how
• 40:25
  many craters it's got per square kilometer or
• 40:27
  whatever. Yeah. So the fact that
• 40:30
  aerial surface is in places smoother
• 40:33
  and brighter suggests that that surface is
• 40:35
  younger, um, and that there's been
• 40:37
  significant resurfacing there. And the idea
• 40:39
  is that there was probably cryovolcanism,
• 40:41
  where molten water was erupting over the
• 40:44
  surface and then freezing in just the same
• 40:46
  way that molten rock on Earth erupts and then
• 40:48
  sets in volcanic eruptions.
• 40:51
  But that was a bit speculative. What
• 40:54
  this new modeling has done is it's looked at
• 40:56
  the history of the orbit of Ariel and
• 40:59
  suggested that in the past, Ariel's orbit was
• 41:01
  probably a little bit more eccentric than it
• 41:03
  is now. Probably an eccentricity up to about
• 41:05
  0.04, which is a bit more eccentric
• 41:08
  than the orbit of the Earth, but less
• 41:10
  eccentric than the orbit of Mars. On an
• 41:12
  orbit that is just slightly eccentric like
• 41:15
  that. Ariel, which is sandwiched in between
• 41:17
  all these other moons and, um, is near a
• 41:19
  pretty massive planet in the form of Uranus,
• 41:21
  would have been subject to fairly intense
• 41:23
  tidal forces that would have squashed and
• 41:26
  squeezed it. And that's very much
• 41:29
  equivalent to what's happening in the Jupiter
• 41:30
  system with IO and Europa, these
• 41:33
  moons that are squashed and squeezed by
• 41:35
  Jupiter's gravity in the nearby moons, which
• 41:37
  dumps a lot of heat into the interior of
• 41:39
  these moons, keeping them hot, driving
• 41:42
  volcanism, allowing that deeply buried
• 41:45
  ocean in Europa. Uh, well said, deeply
• 41:47
  buried, probably under about 10km of ice to
• 41:49
  stay liquid because it's an internal heat
• 41:51
  source driven by this tidal heating. Yeah.
• 41:54
  What this work has said is that Ariel, too,
• 41:56
  probably had a lot of internal heat from
• 41:59
  tidal heating. It's a big object that's
• 42:01
  primarily made of water ice. And when you
• 42:03
  heat water ice, what happens is it melts. And
• 42:05
  so the idea is that, uh, for a very long
• 42:07
  period of time, probably hundreds of millions
• 42:09
  of years, if not billions of years, buried
• 42:12
  under the surface of Ariel, and possibly even
• 42:13
  relatively shallow at some times, was this
• 42:16
  ocean of liquid water that, again,
• 42:19
  just like Europa, probably contained more
• 42:21
  liquid water than there is on the entirety of
• 42:24
  the planet Earth.
• 42:25
  Andrew Dunkley: Wow.
• 42:26
  Jonti Horner: That water would have behaved like the mantle
• 42:28
  of the Earth, with volcanic eruptions of
• 42:31
  water breaking through cracks in the surface,
• 42:35
  resurfacing these areas of Ariel, giving us
• 42:37
  the clues that we see now, probably
• 42:40
  more than a billion years after this ocean
• 42:42
  for a solid, Ariel's orbit settled down.
• 42:44
  Tidal forces Lessened on, uh, it. It cooled
• 42:47
  down, Everything froze solid. But we're left
• 42:50
  with these fossilized clues that are
• 42:52
  evidence of this much more interesting past,
• 42:55
  potentially when you have this moon with a
• 42:57
  soft central liquid center. Yeah, and it's,
• 43:00
  it's interesting in itself. It's interesting
• 43:02
  because of this interplay between observation
• 43:04
  and theory and, um, how it shows you that
• 43:07
  observations may not bear fruit for
• 43:09
  decades. It might be that the observations we
• 43:12
  make now are not fully understood for 10, 20,
• 43:15
  30 years as our technology and m. Our
• 43:17
  modeling and our theories develop in that
• 43:19
  time. But it's also interesting from the
• 43:22
  whole question of, are we alone in the
• 43:24
  universe? Is there life elsewhere? Because
• 43:27
  it's reminding us that liquid water is much
• 43:29
  more commonplace in the cosmos than we think
• 43:31
  it is now. Finding life on
• 43:34
  buried oceans is challenging
• 43:37
  in the solar system. It's not really
• 43:39
  something that's feasible going forward,
• 43:41
  looking at planets around other stars. But it
• 43:43
  is a reminder that there might be an
• 43:45
  incredible diversity of potential habitats
• 43:47
  for life to become, develop and thrive
• 43:51
  all, all through the solar system, all out
• 43:53
  there in the cosmos, and certainly in the
• 43:55
  solar system. These are the kind of locations
• 43:57
  that we can visit. There's a really growing
• 43:59
  push among, um, planetary scientists that
• 44:02
  Uranus should be the next place to get a
• 44:04
  probe. We've seen incredible
• 44:07
  science done by orbiters like Galileo and
• 44:10
  Juno that went to Jupiter, like cne that went
• 44:12
  Saturn. But for Uranus, we've only seen one
• 44:15
  face of the planet, one face of all its moons
• 44:18
  as we flew through on a drive by,
• 44:20
  essentially. And the argument is,
• 44:23
  if we could send a spacecraft there, that did
• 44:25
  for Uranus what Cassini did for Saturn, what
• 44:29
  Galileo and Juno did for Jupiter. There is
• 44:32
  so much we'd learn. And Uranus is such an
• 44:34
  oddity among the planets with its satellite
• 44:35
  system, with everything all tipped over. It's
• 44:38
  got a very different history to the other
• 44:40
  planets. There's some violent event in
• 44:43
  the past, quite possibly something more
• 44:45
  massive than the Earth, uh, hitting Uranus,
• 44:47
  knocking it over, disrupting the satellite
• 44:49
  system, giving us the moons we see as a
• 44:52
  secondary satellite system. The original
• 44:53
  moons were destroyed, formed a disk of
• 44:56
  material, and new moons formed from them.
• 44:58
  It's a very wonderful narrative
• 45:01
  that is our best explanation for what we see.
• 45:03
  But it may not be the right one. And, um, the
• 45:05
  only way we'll find out, the only way we'll
• 45:06
  learn more about this is to go there, send
• 45:09
  a spacecraft there. So this is
• 45:12
  so exciting for people that it's actually the
• 45:15
  top priority of the planetary science decadal
• 45:18
  plan. In the US Trying to argue for
• 45:21
  funding to build a mission. Now, if that
• 45:23
  mission was approved, it will probably be
• 45:26
  another 20 years before it gets there, uh, if
• 45:28
  not more. And um, that's one of the
• 45:30
  challenges that people face because you are
• 45:32
  dealing with governments that change on
• 45:34
  timescales of three or four years, who
• 45:37
  often seem to have the policy that whatever
• 45:39
  the previous government decided was wrong. So
• 45:41
  therefore we need to cancel it. And you've
• 45:43
  got to navigate those waters to try and get a
• 45:45
  mission to happen where the development alone
• 45:48
  can be 10 or 20 years. So it's really
• 45:50
  challenging, especially in the current
• 45:51
  climate. But the hopes of planetary
• 45:54
  scientists across the world are that at some
• 45:57
  point a mission like this will get approved
• 45:59
  and we'll get to go back there and find out
• 46:00
  what's actually going on.
• 46:02
  Andrew Dunkley: Yes, indeed. But, um, what I'm finding
• 46:04
  fascinating is that, um, the more we look and
• 46:06
  the more information we gather and
• 46:09
  analyze, uh, these ice
• 46:11
  moons, these subsurface ocean moons in
• 46:14
  the outer solar system are starting to become
• 46:17
  the norm really.
• 46:21
  They're identifying more and more of them, or
• 46:23
  at least they're suspicious that some of them
• 46:25
  are there that we weren't thinking about
• 46:28
  before that are starting to show those kinds
• 46:30
  of tendencies. And his is yet another
• 46:33
  one. So, uh, yeah, there's plenty to, to look
• 46:36
  for out, uh, out around that, uh, that
• 46:39
  where the gas giants are and beyond. Really
• 46:41
  fascinating stuff.
• 46:43
  Uh, now finally, let's uh, do this one. Uh,
• 46:46
  asteroids controlled by Venus and what that
• 46:48
  means for Earth, our sister planet, might
• 46:50
  start throwing stuff at us in a few thousand
• 46:53
  years time.
• 46:54
  Jonti Horner: Oh, absolutely. This is a story that's all
• 46:57
  about few objects that have been discovered
• 47:00
  relatively recently that are very, very hard
• 47:02
  to spot that fall under the broad heading
• 47:05
  of near Earth asteroids. They're things
• 47:07
  moving in the inner solar system on unstable
• 47:09
  orbits. And obviously we've seen deep impact,
• 47:12
  we've seen Armageddon. We know that these
• 47:14
  things can pose as a threat. And there's a
• 47:16
  big growing push to find them and to peer
• 47:19
  through the growing numbers of starlink
• 47:21
  satellites that make it harder and harder for
• 47:23
  us to do that. And it's one of the things
• 47:25
  Vera Rubin is going to be great at. Vera
• 47:26
  Rubin is going to be great at everything, to
• 47:28
  be honest. But it'll be fabulous. NEAR EARTH
• 47:30
  ASTEROID FINDING MACHINE but these ones
• 47:33
  are going to be challenging even for Rubin.
• 47:36
  These are asteroids that spend their entire
• 47:38
  orbits closer to the sun than us. I've seen
• 47:41
  them described as apaheel asteroids as their
• 47:44
  family name. These are things where even when
• 47:46
  they're furthest from the sun, they're still
• 47:48
  closer to the sun than we are. And what that
• 47:50
  means is that they're always to some degree
• 47:52
  lost in the Sun's glare. They're hard to
• 47:55
  spot. Now there's a growing
• 47:58
  population of these that have been found that
• 48:00
  are moving, uh, on orbits with a similar
• 48:01
  orbital period to Venus, maybe even trapped
• 48:04
  in one to one resonance with Venus. So they
• 48:06
  complete one lap of the sun in the time it
• 48:08
  takes Venus to complete one lap. And we found
• 48:11
  a few of these. All of the ones we found are
• 48:14
  on relatively eccentric orbits,
• 48:16
  eccentricities of about 0.38 or greater,
• 48:19
  which means that the point at ah, which
• 48:21
  they're furthest from The sun is 38% bigger
• 48:23
  than their mean distance, their semi major
• 48:25
  axis and the point at which they're closest
• 48:27
  to the sun is 38% smaller,
• 48:30
  basically. So if you know the semi major
• 48:32
  axis, call that letter A, the
• 48:35
  distance between these objects and the sun at
• 48:37
  their aphelion, their furthest point is
• 48:39
  equal to 1 plus the eccentricity
• 48:42
  multiplied by semi major axis. So next entry
• 48:45
  of 0.38 gives you
• 48:47
  1.38 times the semi major axis. That's
• 48:49
  basically the way this works out. So what
• 48:52
  that means is if you're on an orbit that is
• 48:55
  a semi major axis, the same as Venus, which
• 48:57
  is a little bit more than 0.7 astronomical
• 48:59
  units, if you have an eccentricity of about
• 49:02
  0.38 or more, you'll get close to the
• 49:05
  Earth's orbit when you're furthest from the
• 49:06
  sun, uh, and that means that you're further
• 49:09
  from the sun in the sky and you're easier to
• 49:10
  find. So we've got an observation bias.
• 49:14
  If we find a lot of objects then in the one
• 49:16
  to one resonance with Venus that are on
• 49:18
  eccentric orbits, we can suggest that
• 49:20
  there are going to be far more of them that
• 49:22
  are not on eccentric orbits because they're
• 49:24
  harder to find. So we're finding the law
• 49:26
  hanging fruit. So the idea is that there is a
• 49:29
  population of hundreds of these objects,
• 49:31
  possibly even thousands of them, m ranging in
• 49:33
  size up to hundreds of meters, maybe even a
• 49:35
  few kilometers in size, that are uh, near
• 49:38
  Earth asteroids that have evolved quite a
• 49:40
  long time in their orbits, moved into the
• 49:42
  inner solar system and bounce down to Venus
• 49:44
  and they're kind of held in a freezer there.
• 49:46
  They're kind of held out of our way in a
• 49:48
  reservoir. Not to be worried about. The
• 49:51
  new work is that people have done some
• 49:53
  orbital simulations of the kind that I do in
• 49:55
  my day. To day life. And um, they've looked
• 49:58
  at what will happen to these things over
• 50:00
  time. Because moving on orbits in the inner
• 50:01
  solar system is an inherently unstable
• 50:04
  situation. You're vulnerable to the
• 50:06
  whims of the gravity of all the other
• 50:08
  planets. And that means your orbit gets
• 50:10
  bounced around, you have close encounters
• 50:11
  with the planets. Um, that means that things
• 50:14
  are not stable in that one to one resonance
• 50:17
  with Venus on really long timescales, they'll
• 50:18
  eventually escape and move around. And what
• 50:21
  this study has shown is that uh, for these
• 50:23
  objects that we currently cannot see, they're
• 50:25
  currently most of them hidden from view.
• 50:29
  They are on orbits that can evolve to become
• 50:31
  Earth crossing once again, maybe even within
• 50:34
  just a few thousand years. And so that this
• 50:36
  is a previously, um, unthought of
• 50:39
  reservoir of potentially hazardous asteroids
• 50:43
  that we can't easily detect with our normal
• 50:45
  methods. And um, that Vera Rubin, with all
• 50:47
  its brilliant abilities will be challenged to
• 50:50
  pick up. And so it's flagging up another
• 50:53
  area of objects that uh, they don't pose a
• 50:55
  threat to us right now. Probably
• 50:58
  there might be some of them on orbits that
• 50:59
  just reach the Earth, so they could do. But
• 51:01
  most of these don't pose an immediate threat,
• 51:03
  but they pose a longer term threat. And the
• 51:06
  kind of, I guess, punchline of all of this is
• 51:08
  that we need to become better, we need to be
• 51:10
  creative and think about how we can find
• 51:12
  asteroids like this are hidden in the sun's
• 51:14
  glare. What we can do in order to try
• 51:17
  and quantify the ones that are there and
• 51:19
  figure out if any of them pose a threat,
• 51:20
  that's kind of their punchline. And I think
• 51:23
  it is just a really great reminder of the
• 51:26
  fact that we always think we now know so
• 51:27
  much, we know so much more than we used to
• 51:30
  do. And you always have this niggling
• 51:32
  impression at the back of your mind that our
• 51:34
  knowledge is almost complete. There are no
• 51:35
  surprises still to come. And that's just not
• 51:37
  the case. Uh, part of the reason that I love
• 51:40
  science, part of the reason that most
• 51:41
  scientists still do their job is not because
• 51:44
  we know everything, but because we know
• 51:45
  nothing. We still got so much more to learn.
• 51:47
  And it's the surprises, it's the unknowns
• 51:49
  that really motivate people and get people
• 51:51
  excited. And this is just a really good
• 51:53
  example of that, that here's all these
• 51:55
  objects that uh, we weren't even talking
• 51:57
  about 10 years ago that are a potential
• 52:00
  threat to us and we need to learn more about
• 52:01
  them. How do we do that? And that will drive
• 52:03
  technology and exploration in the years to
• 52:05
  come.
• 52:05
  Andrew Dunkley: Yes, indeed. And, uh, if we've got a few
• 52:08
  thousand years of wiggle room before it
• 52:10
  starts throwing rocks at us, we may be able
• 52:12
  to put probes out there to monitor it
• 52:16
  and get those early warnings. So we may
• 52:18
  develop the technology to, uh, defend
• 52:21
  ourselves down the track. But if you want to
• 52:23
  read about that, uh, the paper is available
• 52:26
  through, uh, Astronomy and Astrophysics, the
• 52:28
  journal, or you can look at it on the
• 52:31
  space.com website. Fascinating
• 52:34
  stuff. And Jonti, thanks for joining us.
• 52:37
  Great to have you back for a few weeks and,
• 52:39
  uh, we'll catch you on the next episode.
• 52:41
  Jonti Horner: Look forward to it.
• 52:42
  Thanks for having me back, professor, uh.
• 52:44
  Andrew Dunkley: Jonti Horner, professor of Astrophysics at
• 52:46
  the University of Southern Queensland. Thanks
• 52:48
  to him. And I, uh, would have thanked Huw in
• 52:51
  the studio, but he forgot to set his clock
• 52:53
  forward for daylight saving in New South
• 52:54
  Wales yesterday and couldn't join us. And
• 52:56
  from me, Andrew Dunkley, thanks for your
• 52:58
  company. See you on the next episode of Space
• 53:00
  Nuts. Until then, bye bye. Uh,
• 53:03
  you'll be listening to the Space Nuts
• 53:05
  podcast, available
• 53:08
  at Apple Podcasts, Spotify,
• 53:10
  iHeartRadio or your favorite podcast
• 53:13
  player.
• 53:13
  Jonti Horner: You can also stream on demand@bytes.com.
• 53:17
  Andrew Dunkley: This has been another quality podcast
• 53:19
  production from sites.um com.