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00:00:00 --> 00:00:02 Anna: Hello and welcome to Astronomy daily.
00:00:02 --> 00:00:05 It's Wednesday the 9th of September
00:00:05 --> 00:00:08 2026. This is series five,
00:00:08 --> 00:00:10 episode 189. And I'm
00:00:10 --> 00:00:11 Anna.
00:00:11 --> 00:00:14 Avery: And I'm Avery. Anna, uh, what's
00:00:14 --> 00:00:17 the smallest thing anyone has ever seen out
00:00:17 --> 00:00:18 beyond Neptune?
00:00:19 --> 00:00:21 Anna: As of yesterday, about five kilometres
00:00:21 --> 00:00:24 across, roughly the size of a decent suburb
00:00:24 --> 00:00:27 four and a half billion kilometres away in
00:00:27 --> 00:00:28 permanent twilight.
00:00:28 --> 00:00:29 Avery: And we can see that.
00:00:30 --> 00:00:33 Anna: Hubble and Webb can see that working the same
00:00:33 --> 00:00:35 patch of sky at the same moment. One
00:00:35 --> 00:00:37 invisible light, one in the infrared.
00:00:38 --> 00:00:41 27 brand new objects, the
00:00:41 --> 00:00:43 faintest ever directly detected out there.
00:00:43 --> 00:00:45 And the thing that makes it a lead storey
00:00:45 --> 00:00:48 isn't that we found them, it's what they're
00:00:48 --> 00:00:48 wearing.
00:00:49 --> 00:00:49 Avery: Meaning what?
00:00:50 --> 00:00:52 Anna: Meaning the smallest objects in the Kuiper
00:00:52 --> 00:00:55 Belt have the same colours as the big ones,
00:00:55 --> 00:00:58 which, if you know how those little ones are
00:00:58 --> 00:01:00 supposed to have been made, is not what you'd
00:01:00 --> 00:01:02 expect at all. They're remembering something
00:01:02 --> 00:01:04 they shouldn't be able to remember.
00:01:04 --> 00:01:07 Avery: That's our lead. After that, a
00:01:07 --> 00:01:09 volcano that grounded nearly 3
00:01:10 --> 00:01:12 flights. And the satellites that watched it
00:01:12 --> 00:01:12 happen.
00:01:13 --> 00:01:16 Anna: Two European spacecraft deliberately
00:01:16 --> 00:01:18 flown into the atmosphere over the South
00:01:18 --> 00:01:21 Pacific so that a team in a chartered jet
00:01:21 --> 00:01:23 could film them burning up and find out what
00:01:23 --> 00:01:25 a satellite turns into on the way down.
00:01:26 --> 00:01:28 Avery: And a galaxy that doubled in size in less
00:01:28 --> 00:01:31 than a billion years, caught by a 1
00:01:31 --> 00:01:33 metre telescope plus the
00:01:33 --> 00:01:36 Anna: sky for both hemispheres. New moon on
00:01:36 --> 00:01:38 Friday, which means the next few nights are
00:01:38 --> 00:01:40 as dark as September gets. Let's start out
00:01:40 --> 00:01:41 past Neptune.
00:01:42 --> 00:01:45 Avery: Alright? Before the new result set
00:01:45 --> 00:01:48 the scene, what actually is the Kuiper
00:01:48 --> 00:01:50 Belt and why do we care so much about it?
00:01:51 --> 00:01:54 Anna: Start with what it isn't. It isn't a belt in
00:01:54 --> 00:01:56 the sense of a neat ring, and it isn't
00:01:56 --> 00:01:58 crowded. It. If you were standing on one
00:01:58 --> 00:02:00 object, you would almost certainly not be
00:02:00 --> 00:02:03 able to see another one. What it is,
00:02:03 --> 00:02:06 is the leftovers. Beyond Neptune,
00:02:06 --> 00:02:09 out past, uh, 30 astronomical units, there's
00:02:09 --> 00:02:11 a population of icy bodies that never got
00:02:11 --> 00:02:12 assembled into a planet.
00:02:13 --> 00:02:14 Avery: Never got the chance.
00:02:15 --> 00:02:17 Anna: Never got the chance. And that's exactly why
00:02:17 --> 00:02:20 they matter. Everywhere else in the solar
00:02:20 --> 00:02:23 system, the raw material got processed. Earth
00:02:23 --> 00:02:25 melted, Mars melted. The asteroid
00:02:25 --> 00:02:28 belt has been ground down and cooked by four
00:02:28 --> 00:02:30 and a half billion years of collisions and
00:02:30 --> 00:02:33 sunlight. Out past Neptune, it is
00:02:33 --> 00:02:35 dark, it is cold. We're talking
00:02:35 --> 00:02:38 40, 50 degrees above absolute zero.
00:02:38 --> 00:02:40 And it is empty enough that things mostly
00:02:40 --> 00:02:43 leave each other alone. Those objects are the
00:02:43 --> 00:02:45 closest thing we have to the original
00:02:45 --> 00:02:47 building blocks still sitting where they were
00:02:47 --> 00:02:47 made.
00:02:48 --> 00:02:51 Avery: A fossil record A fossil record that's
00:02:51 --> 00:02:54 Anna: still in the ground. And there's a structure
00:02:54 --> 00:02:56 to it that's worth having because the whole
00:02:56 --> 00:02:59 result turns on it. There are two
00:02:59 --> 00:03:02 broad populations out there. The first
00:03:02 --> 00:03:04 are called the dynamically cold objects.
00:03:05 --> 00:03:08 Cold meaning their orbits are calm, nearly
00:03:08 --> 00:03:11 circular, barely tilted. Those
00:03:11 --> 00:03:13 ones almost certainly formed roughly where
00:03:13 --> 00:03:16 they are now and have never been disturbed.
00:03:17 --> 00:03:18 Avery: And they're distinctive.
00:03:19 --> 00:03:21 Anna: Very. They're red, deeply,
00:03:21 --> 00:03:24 uniformly red. That's irradiated
00:03:24 --> 00:03:27 organic material on the surface, built up
00:03:27 --> 00:03:29 over billions of years. The second
00:03:29 --> 00:03:31 population is the dynamically hot
00:03:31 --> 00:03:34 objectselliptical orbits, tilted,
00:03:34 --> 00:03:36 scattered. Those didn't form where we find
00:03:36 --> 00:03:39 them. They formed closer in and were flung
00:03:39 --> 00:03:42 outward when the giant planets migrated early
00:03:42 --> 00:03:45 on. And they're a mixed bag of colours
00:03:45 --> 00:03:47 because they came from a range of starting
00:03:47 --> 00:03:47 distances.
00:03:48 --> 00:03:50 Avery: So colour is a birth certificate.
00:03:51 --> 00:03:53 Anna: Colour is roughly a birth
00:03:53 --> 00:03:56 certificate. That's the premise. Now
00:03:56 --> 00:03:58 here's the problem we've had for 30 years.
00:03:59 --> 00:04:01 Everything I've just described, we learned
00:04:01 --> 00:04:03 from the big ones. Objects a hundred
00:04:03 --> 00:04:06 kilometres across and up. Ground based
00:04:06 --> 00:04:09 telescopes bottom out at about 25 kilometres.
00:04:09 --> 00:04:11 And below that, it's guesswork.
00:04:12 --> 00:04:13 Avery: So what did they do?
00:04:13 --> 00:04:15 Anna: They pointed Hubble and Webb at the same
00:04:15 --> 00:04:18 patch of sky simultaneously. Same
00:04:18 --> 00:04:21 field, same time. One working in
00:04:21 --> 00:04:24 visible light and one in the infrared. And
00:04:24 --> 00:04:27 the simultaneity is not a detail, it's the
00:04:27 --> 00:04:29 whole trick. These are faint objects moving
00:04:29 --> 00:04:32 against the background stars. And if you want
00:04:32 --> 00:04:34 a colour, you need the two measurements taken
00:04:34 --> 00:04:37 at the same moment, otherwise you're
00:04:37 --> 00:04:39 comparing an object to a slightly different
00:04:39 --> 00:04:40 version of itself.
00:04:40 --> 00:04:42 Avery: And, um, how faint are we talking?
00:04:43 --> 00:04:46 Anna: NASA's own description is the best one I've
00:04:46 --> 00:04:48 read. One of these objects is the equivalent
00:04:48 --> 00:04:51 of standing on the Earth and picking out a
00:04:51 --> 00:04:53 small swarm of fireflies on the moon.
00:04:54 --> 00:04:55 Avery: That's absurd.
00:04:55 --> 00:04:58 Anna: It's absurd. And they found 27 of them.
00:04:59 --> 00:05:01 27 previously unknown trans
00:05:01 --> 00:05:04 Neptunian objects, the faintest ever
00:05:04 --> 00:05:07 directly detected and the smallest is about
00:05:07 --> 00:05:09 five kilometres across. That's five times
00:05:09 --> 00:05:11 smaller than anything a ground based
00:05:11 --> 00:05:12 telescope can reach.
00:05:13 --> 00:05:15 Avery: And, um, two papers came out of it.
00:05:15 --> 00:05:18 Anna: Two papers, both published yesterday, 8th
00:05:18 --> 00:05:20 September in the Astronomical Journal.
00:05:21 --> 00:05:24 One on colour, led by Anastasia Morgan, a
00:05:24 --> 00:05:26 PhD candidate at Northern Arizona University.
00:05:27 --> 00:05:29 One on the size distribution, led by
00:05:29 --> 00:05:32 Marielle Eduardo, a PhD candidate at the
00:05:32 --> 00:05:35 University of Victoria in Canada, with the
00:05:35 --> 00:05:38 National Research Council of Canada and NASA
00:05:38 --> 00:05:39 Goddard involved, Across both.
00:05:40 --> 00:05:42 Avery: Start with the colours. What was the
00:05:42 --> 00:05:43 expectation?
00:05:43 --> 00:05:45 Anna: The expectation was that the small ones would
00:05:45 --> 00:05:48 look different. And there's a good reason for
00:05:48 --> 00:05:50 that expectation. Nobody thinks a five
00:05:50 --> 00:05:52 kilometre Object out there is a pristine
00:05:52 --> 00:05:55 original. The standard assumption is that
00:05:55 --> 00:05:57 objects that small are fragments,
00:05:57 --> 00:06:00 shrapnel, the debris left over when bigger
00:06:00 --> 00:06:01 things hit each other.
00:06:01 --> 00:06:03 Avery: And if you smash something open, you're
00:06:03 --> 00:06:04 seeing the inside.
00:06:05 --> 00:06:08 Anna: Exactly. That red surface is a rind.
00:06:08 --> 00:06:10 It's a few metres of irradiated material
00:06:10 --> 00:06:13 built up over billions of years, and
00:06:13 --> 00:06:16 underneath it the ice is fresh and much less
00:06:16 --> 00:06:19 red. So if the small objects are collision
00:06:19 --> 00:06:21 fragments, a good fraction of them should be
00:06:21 --> 00:06:24 showing us their interiors. And the
00:06:24 --> 00:06:26 population as a whole should look bluer and
00:06:26 --> 00:06:27 messier than the big ones.
00:06:28 --> 00:06:29 Avery: And, um, they don't.
00:06:30 --> 00:06:32 Anna: They don't. The small ones match the big
00:06:32 --> 00:06:35 ones. Within each population, the little
00:06:35 --> 00:06:37 objects carry the same colour relationship as
00:06:37 --> 00:06:40 their large counterparts. Morgan's line
00:06:40 --> 00:06:42 is that the smallest objects are somehow
00:06:42 --> 00:06:45 remembering and preserving the history of how
00:06:45 --> 00:06:46 they were made.
00:06:46 --> 00:06:49 Avery: And that holds for both populations, the calm
00:06:49 --> 00:06:51 ones and the scattered ones.
00:06:51 --> 00:06:53 Anna: That's the part that got my attention. It
00:06:53 --> 00:06:56 holds for the hot population too, the ones
00:06:56 --> 00:06:58 that were thrown outward from somewhere else.
00:06:59 --> 00:07:01 David Trilling at Northern Arizona puts it
00:07:01 --> 00:07:04 this these dynamically hot objects
00:07:04 --> 00:07:06 retain a signature of where they were born,
00:07:06 --> 00:07:08 even though they've been orbitally scrambled
00:07:08 --> 00:07:11 since. So you've got a five kilometre lump of
00:07:11 --> 00:07:14 ice on a wild tilted orbit which has been
00:07:14 --> 00:07:16 kicked halfway across the solar system by
00:07:16 --> 00:07:19 Neptune, and. And it is still visibly wearing
00:07:19 --> 00:07:21 the colour of the neighbourhood it grew up
00:07:21 --> 00:07:21 in.
00:07:21 --> 00:07:24 Avery: Now, the second paper sizes.
00:07:24 --> 00:07:26 Anna: The size distribution is the other half of
00:07:26 --> 00:07:29 the argument, and honestly, it might be the
00:07:29 --> 00:07:32 stronger half. If you count objects by size,
00:07:32 --> 00:07:35 you get a curve. How many small ones for
00:07:35 --> 00:07:37 every big one. And the shape of that curve is
00:07:37 --> 00:07:40 a fingerprint of how the population was made.
00:07:40 --> 00:07:43 Gradual accretion, pebbles sticking to
00:07:43 --> 00:07:46 pebbles, grinding and colliding gives you one
00:07:46 --> 00:07:48 shape, direct rapid formation gives you
00:07:48 --> 00:07:49 another.
00:07:49 --> 00:07:50 Avery: And what did they find?
00:07:51 --> 00:07:53 Anna: The same shape in both populations.
00:07:54 --> 00:07:56 Eduardo's finding is that planetesimal M
00:07:56 --> 00:07:58 formation ends up producing the same
00:07:58 --> 00:08:00 distribution of sizes for the cold objects
00:08:00 --> 00:08:03 and the hot objects, despite the fact that
00:08:03 --> 00:08:05 they formed in different regions of the disc.
00:08:05 --> 00:08:08 Different neighbourhoods, same recipe.
00:08:08 --> 00:08:10 Avery: So the process doesn't care where you are.
00:08:11 --> 00:08:13 Anna: The process appears not to care where you
00:08:13 --> 00:08:16 are. And put the two papers together and you
00:08:16 --> 00:08:18 get something quite specific. These small
00:08:18 --> 00:08:20 objects are not primarily collisional rubble.
00:08:21 --> 00:08:23 They look like they were made small and have
00:08:23 --> 00:08:25 stayed that way. Which lines up with a model
00:08:25 --> 00:08:27 that's been gaining ground for about 15
00:08:27 --> 00:08:30 years. The idea that planetesimals don't
00:08:30 --> 00:08:33 grind their way up from dust grain to boulder
00:08:33 --> 00:08:36 to mountain, but form quickly at large
00:08:36 --> 00:08:39 sizes when a cloud of pebbles collapses under
00:08:39 --> 00:08:40 its own gravity.
00:08:40 --> 00:08:42 Avery: And we've actually seen one of these up, uh,
00:08:42 --> 00:08:43 close. We have.
00:08:43 --> 00:08:46 Anna: And it's the best supporting evidence there
00:08:46 --> 00:08:48 is. New Horizons flew past
00:08:48 --> 00:08:51 Arakoth on New Year's Day 2019.
00:08:52 --> 00:08:54 A cold classical object. Two
00:08:54 --> 00:08:57 lobes resting against each other like a
00:08:57 --> 00:09:00 snowman. Nothing about it looked violent.
00:09:00 --> 00:09:03 The two halves came together at walking pace.
00:09:04 --> 00:09:07 That is what gentle in place formation
00:09:07 --> 00:09:09 looks like. And this new work, says
00:09:09 --> 00:09:12 Arakoth, probably isn't a curiosity.
00:09:12 --> 00:09:14 It's the type specimen.
00:09:14 --> 00:09:17 Avery: What are the caveats? There are always
00:09:17 --> 00:09:18 caveats.
00:09:18 --> 00:09:20 Anna: Three, and they're the honest kind.
00:09:21 --> 00:09:24 27 Objects is a real detection, but it
00:09:24 --> 00:09:27 is a small sample. And everything here
00:09:27 --> 00:09:30 is a statement about populations, not
00:09:30 --> 00:09:32 a measurement of any individual rock.
00:09:33 --> 00:09:35 Second, these are broad colours from a
00:09:35 --> 00:09:37 handful of filters, not spectra.
00:09:38 --> 00:09:40 And third, all of this is one
00:09:40 --> 00:09:43 patch of sky. A very deep patch,
00:09:43 --> 00:09:45 but one line of sight.
00:09:45 --> 00:09:47 Avery: So what fixes that?
00:09:47 --> 00:09:50 Anna: Volume. And that's the part that lands
00:09:50 --> 00:09:52 closest to home for a lot of our listeners,
00:09:53 --> 00:09:55 because the machine built to deliver volume
00:09:55 --> 00:09:58 is in the southern hemisphere. The Vera Rubin
00:09:58 --> 00:10:01 Observatory sits on Cerro Pachon in Chile
00:10:01 --> 00:10:04 and its whole design premise is repeatedly
00:10:04 --> 00:10:07 imaging the entire southern sky. It is
00:10:07 --> 00:10:09 expected to find trans neptunian objects in
00:10:09 --> 00:10:12 numbers that make our current catalogue look
00:10:12 --> 00:10:14 like a pilot study. Tens of thousands
00:10:14 --> 00:10:15 of them.
00:10:16 --> 00:10:17 Avery: Different job to Webb, though,
00:10:18 --> 00:10:19 completely different job.
00:10:19 --> 00:10:22 Anna: And they need each other. Rubin finds
00:10:22 --> 00:10:25 them and gives you orbits. Hubble and Webb
00:10:25 --> 00:10:27 are what you point at, the interesting ones.
00:10:27 --> 00:10:29 And there's a third piece that Australia and
00:10:29 --> 00:10:31 New Zealand happen to be very good
00:10:32 --> 00:10:35 stellar occultations. You work
00:10:35 --> 00:10:37 out when a tiny object will pass in front of
00:10:37 --> 00:10:40 a background star. You put telescopes along
00:10:40 --> 00:10:42 the shadow path and you time the blink.
00:10:43 --> 00:10:45 That's how you get a real size and shape for
00:10:45 --> 00:10:48 something you can't resolve. A lot of those
00:10:48 --> 00:10:51 shadow paths cross the southern oceans and a
00:10:51 --> 00:10:52 lot of that work gets done by people with
00:10:52 --> 00:10:55 portable gear standing in a paddock at three
00:10:55 --> 00:10:56 in the morning.
00:10:56 --> 00:10:58 Avery: Which is a nice place to leave it.
00:10:59 --> 00:11:02 Anna: It's a nice place to leave it. 27 new
00:11:02 --> 00:11:04 objects, the smallest ones the size of a
00:11:04 --> 00:11:07 suburb. And they're still wearing the colours
00:11:07 --> 00:11:09 of a solar system that hasn't existed for
00:11:09 --> 00:11:10 four and a half billion years.
00:11:11 --> 00:11:14 Avery: Storey2 and it's a change of
00:11:14 --> 00:11:15 altitude. A knock.
00:11:15 --> 00:11:18 Krakatow, the volcano in the Sunda
00:11:18 --> 00:11:21 Strait between Java and Sumatra, has
00:11:21 --> 00:11:24 spent the last five days doing serious damage
00:11:24 --> 00:11:27 to the aviation map of Southeast Asia.
00:11:27 --> 00:11:30 And the reason it's on this show is that the
00:11:30 --> 00:11:32 entire response ran through satellites.
00:11:33 --> 00:11:34 Anna: Give me the event first.
00:11:34 --> 00:11:37 Avery: It escalated on 4 September and went
00:11:37 --> 00:11:40 into its major explosive phase on the
00:11:40 --> 00:11:43 5th, which ran for more than 24
00:11:43 --> 00:11:45 hours before settling back into the
00:11:45 --> 00:11:47 Strombolian pattern it's been in for.
00:11:49 --> 00:11:52 At the peak, Indonesia's Meteorological
00:11:52 --> 00:11:54 Agency had ash going up to about
00:11:54 --> 00:11:56 6 metres to the east of the
00:11:56 --> 00:11:59 volcano and 15 metres
00:11:59 --> 00:12:01 to the west. That's
00:12:01 --> 00:12:04 50ft. That is well above
00:12:04 --> 00:12:06 the cruising altitude of everything flying
00:12:06 --> 00:12:07 that day.
00:12:08 --> 00:12:09 Anna: And the disruption.
00:12:09 --> 00:12:12 Avery: Eight airports closed across Java and
00:12:12 --> 00:12:15 Sumatra. Ash fall across five
00:12:15 --> 00:12:18 provinces, into Jakarta and West
00:12:18 --> 00:12:18 Java.
00:12:19 --> 00:12:22 2 flights
00:12:22 --> 00:12:24 grounded and something like a hundred and
00:12:24 --> 00:12:27 seventy thousand travellers stranded, a
00:12:27 --> 00:12:30 decent number of them Australians, because
00:12:30 --> 00:12:32 that corridor is on the way to and from a lot
00:12:32 --> 00:12:35 of places we fly. Operations were
00:12:35 --> 00:12:37 essentially back by yesterday.
00:12:38 --> 00:12:40 Anna: So m. Where does the space part come in?
00:12:40 --> 00:12:43 Avery: It's the whole nervous system of the
00:12:43 --> 00:12:45 response. There is a global arrangement
00:12:45 --> 00:12:48 for this. 9 volcanic ash
00:12:48 --> 00:12:51 advisory centres, each responsible for a
00:12:51 --> 00:12:54 slice of the planet. The one that covers
00:12:54 --> 00:12:57 Indonesia is the Darwin Centre, run
00:12:57 --> 00:12:59 by Australia's Bureau of Meteorology
00:13:00 --> 00:13:02 and the advisories they were issuing through
00:13:02 --> 00:13:04 the week. Plume height, direction,
00:13:05 --> 00:13:07 forecast, drift are built primarily on
00:13:07 --> 00:13:10 geostationary satellite imagery which. Which
00:13:10 --> 00:13:13 for that part of the world means Japan's
00:13:13 --> 00:13:15 Himawari nine sitting over the equator
00:13:15 --> 00:13:18 and imaging the full disc of the earth
00:13:18 --> 00:13:19 every 10 minutes.
00:13:20 --> 00:13:21 Anna: 10 minutes is fast.
00:13:22 --> 00:13:25 Avery: It has to be. An ash cloud at
00:13:25 --> 00:13:28 50ft moves and it doesn't
00:13:28 --> 00:13:31 show up on aircraft weather radar. Radar
00:13:31 --> 00:13:34 is built to see water droplets and dry
00:13:34 --> 00:13:36 ash is close to invisible to it.
00:13:37 --> 00:13:39 So the only warning a crew gets is the one
00:13:39 --> 00:13:42 that comes up from the ground and the ground
00:13:42 --> 00:13:43 gets it from orbit.
00:13:43 --> 00:13:46 Anna: And there's a reason everyone treats this so
00:13:46 --> 00:13:46 seriously.
00:13:47 --> 00:13:50 Avery: There is, and it's a British airways flight
00:13:50 --> 00:13:53 in 1982 over Java. As it
00:13:53 --> 00:13:56 happens, a, uh, 747 flew
00:13:56 --> 00:13:58 through an ash cloud nobody knew was there
00:13:58 --> 00:14:01 and lost all four engines.
00:14:01 --> 00:14:04 Ash melts in the hot section of a jet engine,
00:14:04 --> 00:14:07 then resolidifies as glass on the
00:14:07 --> 00:14:10 turbine blades and chokes it. That
00:14:10 --> 00:14:12 aircraft glided for 16 minutes before
00:14:12 --> 00:14:15 they got the engines restarted. Nobody
00:14:15 --> 00:14:18 was killed. And the entire modern advisory
00:14:18 --> 00:14:21 system exists because of flights like that
00:14:21 --> 00:14:21 one.
00:14:22 --> 00:14:24 Anna: And NASA published imagery
00:14:25 --> 00:14:27 this morning our time.
00:14:27 --> 00:14:30 Avery: NASA's Earth Observatory ran it as their
00:14:30 --> 00:14:33 image of the day. The operational land
00:14:33 --> 00:14:36 imager on Landsat 8 and veers
00:14:36 --> 00:14:38 on Suomi NPP showing the
00:14:38 --> 00:14:41 plume and the ashfall. Different
00:14:41 --> 00:14:44 job from Himawari. The geostationary
00:14:44 --> 00:14:47 satellites give you speed, the polar
00:14:47 --> 00:14:50 orbiters give you Resolution and
00:14:50 --> 00:14:50 Anak
00:14:50 --> 00:14:52 Anna: Krakatau itself has history.
00:14:52 --> 00:14:54 Avery: The name means child of Krakatau.
00:14:55 --> 00:14:57 The parent volcano is the one that destroyed
00:14:57 --> 00:15:00 itself in 1883 in the
00:15:00 --> 00:15:03 loudest event in recorded history. The
00:15:03 --> 00:15:06 child grew out of the Caldera and in December
00:15:06 --> 00:15:09 2018, one flank of it collapsed
00:15:09 --> 00:15:11 into the sea and generated a tsunami that
00:15:11 --> 00:15:14 killed more than 400 people with
00:15:14 --> 00:15:17 essentially no warning. So this is a well
00:15:17 --> 00:15:20 instrumented, closely watched mountain. And
00:15:20 --> 00:15:23 even so, the useful early data this
00:15:23 --> 00:15:25 week came from 360
00:15:25 --> 00:15:28 kilometres of sight line, not from the
00:15:28 --> 00:15:30 summit storey 3.
00:15:30 --> 00:15:33 Anna: On 31 August and 1 September,
00:15:34 --> 00:15:36 the European Space Agency deliberately flew
00:15:36 --> 00:15:39 two of its own satellites into the atmosphere
00:15:39 --> 00:15:41 over the South Pacific and then chartered a
00:15:41 --> 00:15:44 jet and flew a team underneath them to watch
00:15:44 --> 00:15:46 it happen. On purpose,
00:15:46 --> 00:15:49 entirely on purpose. And it's one of the more
00:15:49 --> 00:15:52 quietly impressive things ESA has done. The
00:15:52 --> 00:15:54 satellites were Samba and Tango, two of the
00:15:54 --> 00:15:57 four Cluster spacecraft. Cluster launched in
00:15:57 --> 00:16:00 2004. Identical satellites flying
00:16:00 --> 00:16:02 in formation so that they could measure
00:16:02 --> 00:16:04 Earth's magnetosphere in three dimensions
00:16:05 --> 00:16:07 rather than one line at a time. 26
00:16:07 --> 00:16:10 years of operations. It is one of the great
00:16:10 --> 00:16:12 unglamorous missions.
00:16:12 --> 00:16:14 Avery: And rather than just letting them come
00:16:14 --> 00:16:17 Anna: down, rather than letting them come down
00:16:17 --> 00:16:20 whenever and wherever, ESA has been doing
00:16:20 --> 00:16:22 targeted reentries, steering each one
00:16:22 --> 00:16:25 into a specific window over open ocean.
00:16:26 --> 00:16:28 Salsa went first in September 2024.
00:16:29 --> 00:16:32 Samba came down on 31 August this year,
00:16:32 --> 00:16:35 and tango, the last one at
00:16:35 --> 00:16:37 23, 30 and 31 seconds, Central
00:16:37 --> 00:16:40 European Summer Time on 1 September
00:16:40 --> 00:16:42 over the South Pacific, a few hundred
00:16:42 --> 00:16:44 kilometres from Tonga.
00:16:44 --> 00:16:46 Avery: And that precision buys you something.
00:16:47 --> 00:16:49 Anna: It buys you the ability to put an aeroplane
00:16:49 --> 00:16:52 in the right place. The campaign is called
00:16:52 --> 00:16:54 Rosie, led by an international team under
00:16:54 --> 00:16:57 Jirzi Shilha, who runs a Slovak company
00:16:57 --> 00:17:00 called Astro Solutions. They flew a business
00:17:00 --> 00:17:02 jet fitted with 30 instruments, cameras and
00:17:02 --> 00:17:04 spectrometers with filters chosen for
00:17:04 --> 00:17:07 specific elements. 29 of the 30
00:17:07 --> 00:17:10 worked. They got about 50 seconds on each
00:17:10 --> 00:17:13 satellite from something like 120 kilometres
00:17:13 --> 00:17:15 away. And the description from onboard was
00:17:15 --> 00:17:18 that there was a sudden explosion as the
00:17:18 --> 00:17:19 satellites came apart.
00:17:19 --> 00:17:22 Avery: What are they actually measuring? Because it
00:17:22 --> 00:17:25 isn't the light show, it isn't
00:17:25 --> 00:17:26 two things.
00:17:26 --> 00:17:29 Anna: The first is engineering what breaks up when
00:17:29 --> 00:17:31 at, uh, what altitude and what survives. That
00:17:31 --> 00:17:34 feeds directly into the models used to decide
00:17:34 --> 00:17:36 whether a spacecraft can be allowed to re
00:17:36 --> 00:17:38 enter uncontrolled at all. The second is the
00:17:38 --> 00:17:41 one that's becoming urgent chemistry.
00:17:41 --> 00:17:43 A satellite doesn't disappear when it burns,
00:17:43 --> 00:17:46 it's. It becomes vapour. And that vapour
00:17:46 --> 00:17:48 stays in the upper atmosphere. Their filters
00:17:48 --> 00:17:51 were tuned for titanium, sodium, potassium
00:17:51 --> 00:17:54 and aluminium. And the compound they care
00:17:54 --> 00:17:56 most about is aluminium oxide. Because there
00:17:56 --> 00:17:59 is a real open question about what it does to
00:17:59 --> 00:18:01 ozone chemistry at those altitudes.
00:18:01 --> 00:18:04 Avery: And the reason that's urgent is arithmetic.
00:18:04 --> 00:18:07 Anna: It's pure arithmetic. We are
00:18:07 --> 00:18:10 launching constellations of tens of
00:18:10 --> 00:18:13 thousands of satellites with design lives
00:18:13 --> 00:18:16 of about five years. Which means that from
00:18:16 --> 00:18:18 here on satellites re entering the atmosphere
00:18:19 --> 00:18:21 is not an occasional event, it's a
00:18:21 --> 00:18:24 continuous process. And we are running
00:18:24 --> 00:18:27 that experiment without knowing the answer.
00:18:27 --> 00:18:30 Stane Lemons, ESA's acting head of Space
00:18:30 --> 00:18:33 debris, framed this week's data as being
00:18:33 --> 00:18:36 about improving re entry models and building
00:18:36 --> 00:18:38 better satellites. Which is the polite
00:18:38 --> 00:18:41 version of saying we have been guessing and,
00:18:41 --> 00:18:41 uh, there's
00:18:41 --> 00:18:42 Avery: a follow up mission.
00:18:43 --> 00:18:45 Anna: There is, and it's a lovely idea.
00:18:45 --> 00:18:48 Draco launching in 2027
00:18:48 --> 00:18:51 is a spacecraft built for the sole purpose of
00:18:51 --> 00:18:53 destroying itself while taking notes. Over
00:18:53 --> 00:18:56 200 sensors, four cameras and
00:18:56 --> 00:18:59 a capsule designed to survive the breakup and
00:18:59 --> 00:19:02 transmit the recording afterwards. So instead
00:19:02 --> 00:19:04 of watching From a jet 100 kilometres away,
00:19:05 --> 00:19:06 we get the view from inside.
00:19:07 --> 00:19:09 Avery: How did isa mark the end of it?
00:19:09 --> 00:19:11 Anna: Philippe Escoube, who has managed Cluster,
00:19:12 --> 00:19:14 said that once you build something like this,
00:19:14 --> 00:19:16 you imbue it with a soul. 26
00:19:16 --> 00:19:19 years, four spacecraft, and the last thing
00:19:19 --> 00:19:22 they did was come home in a controlled way
00:19:22 --> 00:19:25 over the emptiest ocean on Earth and teach
00:19:25 --> 00:19:26 us something on the way down.
00:19:27 --> 00:19:27 Avery: Storey four.
00:19:28 --> 00:19:30 And, um, this one is about a galaxy you have
00:19:30 --> 00:19:32 almost certainly seen A picture of
00:19:33 --> 00:19:35 Messier 74, the Phantom
00:19:35 --> 00:19:38 Galaxy, about 32 million light
00:19:38 --> 00:19:41 years away in Pisces, perfectly face on
00:19:41 --> 00:19:44 two beautifully clean spiral arms.
00:19:44 --> 00:19:47 Webb's infrared image of it went everywhere
00:19:47 --> 00:19:48 a few years back.
00:19:49 --> 00:19:51 Anna: So what's changed its size?
00:19:52 --> 00:19:54 Avery: A study out of the Instituto de
00:19:54 --> 00:19:57 Astrophica de Canarias, published in
00:19:57 --> 00:19:59 Astronomy and Astrophysics and released on
00:19:59 --> 00:20:01 4th September, finds that M
00:20:01 --> 00:20:04 M74 is more than twice as big as
00:20:04 --> 00:20:07 the catalogues say. The galaxy we've been
00:20:07 --> 00:20:10 looking at is about 45 light
00:20:10 --> 00:20:13 years across. They're tracing stars out
00:20:13 --> 00:20:14 to roughly a hundred thousand.
00:20:15 --> 00:20:17 Anna: How did everyone miss half a galaxy?
00:20:17 --> 00:20:20 Avery: Because it's faint? This is the low
00:20:20 --> 00:20:22 surface brightness problem and it's one of
00:20:22 --> 00:20:25 the great quiet biases in astronomy. A,
00:20:25 --> 00:20:28 uh, galaxy doesn't have an edge, it has a
00:20:28 --> 00:20:30 point where the light drops below whatever
00:20:30 --> 00:20:32 your survey can detect. And, and we have
00:20:32 --> 00:20:34 spent a century calling that point the edge.
00:20:35 --> 00:20:38 Ignacio Ruiz with Ignacio
00:20:38 --> 00:20:40 Trujillo and Michele Sarah riccart
00:20:40 --> 00:20:43 went about 10 times deeper than the Sloan
00:20:43 --> 00:20:46 survey. And here's the part I like. They
00:20:46 --> 00:20:48 did it with a one metre telescope.
00:20:49 --> 00:20:49 Anna: One metre.
00:20:50 --> 00:20:53 Avery: The Transient Survey telescope. A, uh, one
00:20:53 --> 00:20:55 metre aperture and enough patience.
00:20:56 --> 00:20:59 Deep imaging isn't only about how big your
00:20:59 --> 00:21:01 mirror is. It's about how carefully you
00:21:01 --> 00:21:03 handle the sky background and, and the
00:21:03 --> 00:21:06 scattered light. This is a result that a very
00:21:06 --> 00:21:09 large telescope chasing very distant
00:21:09 --> 00:21:12 things was never going to go looking for.
00:21:12 --> 00:21:13 Anna: And what's actually out there?
00:21:14 --> 00:21:16 Avery: A, uh, disc of young stars. The average age
00:21:16 --> 00:21:19 in that outer region is 640 million
00:21:19 --> 00:21:22 years, which for a galaxy that's been around
00:21:22 --> 00:21:24 for billions is essentially yesterday.
00:21:25 --> 00:21:28 So M, M74 didn't slowly ooze
00:21:28 --> 00:21:31 outward. It grew a new outer disc, fast
00:21:31 --> 00:21:33 Anna: triggered by what a neighbour.
00:21:34 --> 00:21:37 Avery: UGC 1176, about
00:21:37 --> 00:21:40 400 light years away, appears
00:21:40 --> 00:21:42 to have passed close about a billion years
00:21:42 --> 00:21:45 ago. Gravitationally, that's a stir, not a
00:21:45 --> 00:21:48 collision. It doesn't wreck the spiral. It
00:21:48 --> 00:21:50 drags gas outward and lights up star
00:21:50 --> 00:21:52 formation where there wasn't any.
00:21:52 --> 00:21:55 Anna: And the broader claim that this is
00:21:55 --> 00:21:57 Avery: probably common and we simply haven't been
00:21:57 --> 00:22:00 able to see it. If galaxies routinely
00:22:00 --> 00:22:03 double in size in under a billion years
00:22:03 --> 00:22:05 through encounters like this one, then galaxy
00:22:05 --> 00:22:08 growth is a lot lumpier and a lot faster
00:22:08 --> 00:22:11 than the smooth picture we teach. And the
00:22:11 --> 00:22:13 evidence has been sitting in the outskirts
00:22:13 --> 00:22:16 the whole time, just below where anyone was
00:22:16 --> 00:22:16 looking.
00:22:17 --> 00:22:19 Anna: Okay, moving on to Skywatch. And the headline
00:22:19 --> 00:22:22 is Darkness. New Moon
00:22:22 --> 00:22:25 falls on Friday the 11th of September at
00:22:25 --> 00:22:27 4:27 in the morning, Universal Time.
00:22:27 --> 00:22:30 That's 2:27 on Friday afternoon in Sydney.
00:22:31 --> 00:22:33 So tonight, tomorrow night and right through
00:22:33 --> 00:22:36 the weekend, you have about as dark a sky
00:22:36 --> 00:22:38 as September gives you wherever you are.
00:22:39 --> 00:22:41 Southern hemisphere first from Sydney
00:22:41 --> 00:22:44 and anywhere at similar latitudes. This is
00:22:44 --> 00:22:46 the last really good month for the centre of
00:22:46 --> 00:22:49 the galaxy as darkness falls. Scorpius
00:22:49 --> 00:22:52 and Sagittarius are high close to overhead
00:22:52 --> 00:22:54 and the core of the Milky Way runs right
00:22:54 --> 00:22:57 through them under a dark sky away from town.
00:22:58 --> 00:23:00 That band is not subtle. It has
00:23:00 --> 00:23:03 texture. It has dark lanes and the dark
00:23:03 --> 00:23:05 lanes are dust clouds between us and the
00:23:05 --> 00:23:08 centre. You do not need a telescope. You
00:23:08 --> 00:23:10 need 40 minutes with no phone screen.
00:23:11 --> 00:23:13 Avery: And after that it starts sliding west,
00:23:14 --> 00:23:16 Anna: it starts sliding west through October. So
00:23:16 --> 00:23:19 this is the window. Venus
00:23:19 --> 00:23:22 is low in the west just after sunset and it's
00:23:22 --> 00:23:24 building. Greatest Brilliancy comes on the
00:23:24 --> 00:23:26 18th of September at magnitude
00:23:26 --> 00:23:29 -4.8. You may see the 22nd
00:23:29 --> 00:23:31 quoted elsewhere. That's a different
00:23:31 --> 00:23:33 definition and we're going with the 18th.
00:23:33 --> 00:23:35 Saturn is up in the east through the evening,
00:23:36 --> 00:23:38 climbing towards opposition on the 4th of
00:23:38 --> 00:23:41 October with the rings about 7 degrees open.
00:23:41 --> 00:23:44 Avery: North America, same dark window.
00:23:44 --> 00:23:46 Anna: And it's the better half of the year for you
00:23:46 --> 00:23:49 in one specific way. The teapot
00:23:49 --> 00:23:52 Sagittarius sits low in the south after dusk
00:23:52 --> 00:23:55 and the teapot asterism is genuinely easy
00:23:55 --> 00:23:58 once you've seen it. NASA's own guidance for
00:23:58 --> 00:24:01 next week, the 14th to the 20th, is to
00:24:01 --> 00:24:03 use the returning crescent Moon to find
00:24:03 --> 00:24:05 Antares in Scorpius first, then step
00:24:05 --> 00:24:08 across to the teapot, follow the steam from
00:24:08 --> 00:24:10 the spout to the thickest part and. And you
00:24:10 --> 00:24:12 are looking at the centre of the Milky Way
00:24:13 --> 00:24:15 lower for you than it is for us. So you want
00:24:15 --> 00:24:17 a clear southern horizon,
00:24:17 --> 00:24:19 Avery: but that's the direction both
00:24:19 --> 00:24:21 hemispheres morning
00:24:21 --> 00:24:23 Anna: sky, Jupiter and Mars before dawn
00:24:23 --> 00:24:26 both. Jupiter is unmistakable
00:24:26 --> 00:24:29 and closing on Regulus through the month.
00:24:29 --> 00:24:32 Mars is fainter and lower and takes a bit
00:24:32 --> 00:24:35 more work and a date for the calendar
00:24:35 --> 00:24:38 in both hemispheres. The 19th
00:24:38 --> 00:24:41 is international. Observe the Moon night,
00:24:41 --> 00:24:44 which is a good excuse to point anything you
00:24:44 --> 00:24:46 own at the terminator, the line between
00:24:46 --> 00:24:49 lunar day and night, where the shadows are
00:24:49 --> 00:24:51 long and the craters look three dimensional.
00:24:52 --> 00:24:54 Avery: And um, the equinox the 22nd.
00:24:55 --> 00:24:58 Anna: Spring here, autumn there and day
00:24:58 --> 00:25:00 and night close to equal everywhere. Looking
00:25:01 --> 00:25:03 further ahead, 6 October brings a
00:25:03 --> 00:25:06 pre dawn lunar occultation of Jupiter
00:25:07 --> 00:25:09 and Sky and Telescope have been billing that
00:25:09 --> 00:25:11 one as the spectacular event of the year.
00:25:12 --> 00:25:14 We'll build to it properly closer to
00:25:14 --> 00:25:16 Avery: the time safety line before we go.
00:25:17 --> 00:25:19 Anna: It matters this fortnight because Venus is
00:25:19 --> 00:25:22 brilliant and low in the west and every year
00:25:22 --> 00:25:24 around now people get the idea of trying to
00:25:24 --> 00:25:27 find it in daylight. It is genuinely possible
00:25:27 --> 00:25:29 and it is one of the easiest ways to hurt
00:25:29 --> 00:25:32 yourself in this hobby. Never sweep the sky
00:25:32 --> 00:25:34 near the sun with binoculars or a telescope.
00:25:35 --> 00:25:37 You can be on the sun before you know you're
00:25:37 --> 00:25:40 near it and unfiltered, that is permanent
00:25:40 --> 00:25:42 damage in less than a second if you're going
00:25:42 --> 00:25:44 to look anywhere near the sun. The standard
00:25:44 --> 00:25:45 is ISO
00:25:45 --> 00:25:48 123122.
00:25:48 --> 00:25:50 That's the specification for certified solar
00:25:50 --> 00:25:53 viewers and eclipse glasses. Sunglasses
00:25:53 --> 00:25:56 are not that stacked. Sunglasses are not that
00:25:56 --> 00:25:58 exposed film and smoked glass are not that
00:25:59 --> 00:26:01 cheque the certification cheque, the filter
00:26:01 --> 00:26:03 for scratches and pinholes. And if it's a
00:26:03 --> 00:26:05 telescope filter, it goes on the front of the
00:26:05 --> 00:26:08 instrument, never the eyepiece end.
00:26:08 --> 00:26:11 Avery: Wait for it to get properly dark and let
00:26:11 --> 00:26:12 Venus come to you.
00:26:13 --> 00:26:15 Anna: Wait for it to get properly dark. It'll be
00:26:15 --> 00:26:17 the brightest thing in the western sky. And
00:26:17 --> 00:26:19 it will not be hard.
00:26:19 --> 00:26:21 Avery: And that's Astronomy daily for Wednesday
00:26:21 --> 00:26:23 9th September.
00:26:23 --> 00:26:26 Anna: 27 of the faintest objects ever seen
00:26:26 --> 00:26:29 beyond Neptune, still wearing the colours
00:26:29 --> 00:26:32 they were born with. A volcano tracked from
00:26:32 --> 00:26:34 orbit while 3 flights waited.
00:26:35 --> 00:26:38 Two European spacecraft flown home over the
00:26:38 --> 00:26:40 Pacific and filmed on the way down.
00:26:40 --> 00:26:42 And a galaxy that turns out to be twice the
00:26:42 --> 00:26:43 size we thought.
00:26:44 --> 00:26:46 Avery: Every paper and release we've mentioned is
00:26:46 --> 00:26:49 linked in the show notes, along with the full
00:26:49 --> 00:26:50 episode transcript.
00:26:50 --> 00:26:53 Anna: That's astronomydaily IO, the whole back
00:26:53 --> 00:26:56 catalogue is there, the newsletter, if you'd
00:26:56 --> 00:26:58 rather read than listen, and the contact
00:26:58 --> 00:27:00 form, which is where a lot of our best
00:27:00 --> 00:27:01 questions come from.
00:27:01 --> 00:27:03 Avery: You'll find us on X, Facebook,
00:27:04 --> 00:27:07 Tumblr, Instagram, TikTok and
00:27:07 --> 00:27:10 YouTube @astrodaily pod, and of
00:27:10 --> 00:27:12 course, wherever you get your podcasts, A,
00:27:12 --> 00:27:15 uh, rating genuinely helps other people find
00:27:15 --> 00:27:15 us.
00:27:16 --> 00:27:19 Anna: We're back tomorrow. Until then, keep looking
00:27:19 --> 00:27:21 up. And if you're anywhere dark this week,
00:27:22 --> 00:27:24 go and look at the middle of the galaxy while
00:27:24 --> 00:27:25 it's still overhead.
00:27:25 --> 00:27:26 Avery: Clear skies, everyone.