The Smallest Things Remember

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Anna: Hello and welcome to Astronomy daily.

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It's Wednesday the 9th of September

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2026. This is series five,

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episode 189. And I'm

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Anna.

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Avery: And I'm Avery. Anna, uh, what's

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the smallest thing anyone has ever seen out

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beyond Neptune?

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Anna: As of yesterday, about five kilometres

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across, roughly the size of a decent suburb

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four and a half billion kilometres away in

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permanent twilight.

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Avery: And we can see that.

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Anna: Hubble and Webb can see that working the same

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patch of sky at the same moment. One

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invisible light, one in the infrared.

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27 brand new objects, the

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faintest ever directly detected out there.

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And the thing that makes it a lead storey

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isn't that we found them, it's what they're

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wearing.

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Avery: Meaning what?

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Anna: Meaning the smallest objects in the Kuiper

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Belt have the same colours as the big ones,

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which, if you know how those little ones are

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supposed to have been made, is not what you'd

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expect at all. They're remembering something

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they shouldn't be able to remember.

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Avery: That's our lead. After that, a

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volcano that grounded nearly 3,000

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flights. And the satellites that watched it

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happen.

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Anna: Two European spacecraft deliberately

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flown into the atmosphere over the South

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Pacific so that a team in a chartered jet

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could film them burning up and find out what

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a satellite turns into on the way down.

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Avery: And a galaxy that doubled in size in less

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than a billion years, caught by a 1

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metre telescope plus the

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Anna: sky for both hemispheres. New moon on

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Friday, which means the next few nights are

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as dark as September gets. Let's start out

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past Neptune.

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Avery: Alright? Before the new result set

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the scene, what actually is the Kuiper

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Belt and why do we care so much about it?

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Anna: Start with what it isn't. It isn't a belt in

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the sense of a neat ring, and it isn't

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crowded. It. If you were standing on one

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object, you would almost certainly not be

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able to see another one. What it is,

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is the leftovers. Beyond Neptune,

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out past, uh, 30 astronomical units, there's

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a population of icy bodies that never got

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assembled into a planet.

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Avery: Never got the chance.

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Anna: Never got the chance. And that's exactly why

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they matter. Everywhere else in the solar

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system, the raw material got processed. Earth

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melted, Mars melted. The asteroid

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belt has been ground down and cooked by four

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and a half billion years of collisions and

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sunlight. Out past Neptune, it is

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dark, it is cold. We're talking

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40, 50 degrees above absolute zero.

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And it is empty enough that things mostly

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leave each other alone. Those objects are the

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closest thing we have to the original

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building blocks still sitting where they were

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made.

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Avery: A fossil record A fossil record that's

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Anna: still in the ground. And there's a structure

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to it that's worth having because the whole

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result turns on it. There are two

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broad populations out there. The first

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are called the dynamically cold objects.

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Cold meaning their orbits are calm, nearly

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circular, barely tilted. Those

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ones almost certainly formed roughly where

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they are now and have never been disturbed.

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Avery: And they're distinctive.

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Anna: Very. They're red, deeply,

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uniformly red. That's irradiated

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organic material on the surface, built up

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over billions of years. The second

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population is the dynamically hot

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objectselliptical orbits, tilted,

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scattered. Those didn't form where we find

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them. They formed closer in and were flung

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outward when the giant planets migrated early

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on. And they're a mixed bag of colours

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because they came from a range of starting

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distances.

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Avery: So colour is a birth certificate.

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Anna: Colour is roughly a birth

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certificate. That's the premise. Now

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here's the problem we've had for 30 years.

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Everything I've just described, we learned

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from the big ones. Objects a hundred

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kilometres across and up. Ground based

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telescopes bottom out at about 25 kilometres.

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And below that, it's guesswork.

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Avery: So what did they do?

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Anna: They pointed Hubble and Webb at the same

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patch of sky simultaneously. Same

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field, same time. One working in

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visible light and one in the infrared. And

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the simultaneity is not a detail, it's the

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whole trick. These are faint objects moving

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against the background stars. And if you want

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a colour, you need the two measurements taken

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at the same moment, otherwise you're

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comparing an object to a slightly different

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version of itself.

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Avery: And, um, how faint are we talking?

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Anna: NASA's own description is the best one I've

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read. One of these objects is the equivalent

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of standing on the Earth and picking out a

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small swarm of fireflies on the moon.

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Avery: That's absurd.

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Anna: It's absurd. And they found 27 of them.

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27 previously unknown trans

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Neptunian objects, the faintest ever

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directly detected and the smallest is about

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five kilometres across. That's five times

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smaller than anything a ground based

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telescope can reach.

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Avery: And, um, two papers came out of it.

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Anna: Two papers, both published yesterday, 8th

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September in the Astronomical Journal.

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One on colour, led by Anastasia Morgan, a

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PhD candidate at Northern Arizona University.

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One on the size distribution, led by

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Marielle Eduardo, a PhD candidate at the

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University of Victoria in Canada, with the

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National Research Council of Canada and NASA

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Goddard involved, Across both.

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Avery: Start with the colours. What was the

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expectation?

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Anna: The expectation was that the small ones would

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look different. And there's a good reason for

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that expectation. Nobody thinks a five

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kilometre Object out there is a pristine

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original. The standard assumption is that

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objects that small are fragments,

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shrapnel, the debris left over when bigger

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things hit each other.

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Avery: And if you smash something open, you're

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seeing the inside.

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Anna: Exactly. That red surface is a rind.

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It's a few metres of irradiated material

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built up over billions of years, and

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underneath it the ice is fresh and much less

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red. So if the small objects are collision

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fragments, a good fraction of them should be

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showing us their interiors. And the

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population as a whole should look bluer and

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messier than the big ones.

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Avery: And, um, they don't.

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Anna: They don't. The small ones match the big

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ones. Within each population, the little

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objects carry the same colour relationship as

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their large counterparts. Morgan's line

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is that the smallest objects are somehow

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remembering and preserving the history of how

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they were made.

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Avery: And that holds for both populations, the calm

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ones and the scattered ones.

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Anna: That's the part that got my attention. It

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holds for the hot population too, the ones

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that were thrown outward from somewhere else.

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David Trilling at Northern Arizona puts it

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this these dynamically hot objects

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retain a signature of where they were born,

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even though they've been orbitally scrambled

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since. So you've got a five kilometre lump of

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ice on a wild tilted orbit which has been

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kicked halfway across the solar system by

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Neptune, and. And it is still visibly wearing

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the colour of the neighbourhood it grew up

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in.

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Avery: Now, the second paper sizes.

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Anna: The size distribution is the other half of

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the argument, and honestly, it might be the

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stronger half. If you count objects by size,

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you get a curve. How many small ones for

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every big one. And the shape of that curve is

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a fingerprint of how the population was made.

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Gradual accretion, pebbles sticking to

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pebbles, grinding and colliding gives you one

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shape, direct rapid formation gives you

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another.

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Avery: And what did they find?

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Anna: The same shape in both populations.

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Eduardo's finding is that planetesimal M

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formation ends up producing the same

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distribution of sizes for the cold objects

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and the hot objects, despite the fact that

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they formed in different regions of the disc.

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Different neighbourhoods, same recipe.

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Avery: So the process doesn't care where you are.

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Anna: The process appears not to care where you

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are. And put the two papers together and you

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get something quite specific. These small

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objects are not primarily collisional rubble.

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They look like they were made small and have

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stayed that way. Which lines up with a model

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that's been gaining ground for about 15

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years. The idea that planetesimals don't

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grind their way up from dust grain to boulder

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to mountain, but form quickly at large

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sizes when a cloud of pebbles collapses under

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its own gravity.

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Avery: And we've actually seen one of these up, uh,

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close. We have.

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Anna: And it's the best supporting evidence there

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is. New Horizons flew past

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Arakoth on New Year's Day 2019.

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A cold classical object. Two

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lobes resting against each other like a

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snowman. Nothing about it looked violent.

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The two halves came together at walking pace.

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That is what gentle in place formation

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looks like. And this new work, says

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Arakoth, probably isn't a curiosity.

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It's the type specimen.

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Avery: What are the caveats? There are always

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caveats.

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Anna: Three, and they're the honest kind.

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27 Objects is a real detection, but it

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is a small sample. And everything here

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is a statement about populations, not

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a measurement of any individual rock.

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Second, these are broad colours from a

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handful of filters, not spectra.

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And third, all of this is one

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patch of sky. A very deep patch,

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but one line of sight.

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Avery: So what fixes that?

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Anna: Volume. And that's the part that lands

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closest to home for a lot of our listeners,

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because the machine built to deliver volume

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is in the southern hemisphere. The Vera Rubin

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Observatory sits on Cerro Pachon in Chile

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and its whole design premise is repeatedly

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imaging the entire southern sky. It is

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expected to find trans neptunian objects in

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numbers that make our current catalogue look

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like a pilot study. Tens of thousands

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of them.

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Avery: Different job to Webb, though,

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completely different job.

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Anna: And they need each other. Rubin finds

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them and gives you orbits. Hubble and Webb

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are what you point at, the interesting ones.

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And there's a third piece that Australia and

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New Zealand happen to be very good

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stellar occultations. You work

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out when a tiny object will pass in front of

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a background star. You put telescopes along

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the shadow path and you time the blink.

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That's how you get a real size and shape for

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something you can't resolve. A lot of those

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shadow paths cross the southern oceans and a

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lot of that work gets done by people with

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portable gear standing in a paddock at three

267
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in the morning.

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Avery: Which is a nice place to leave it.

269
00:10:59.220 --> 00:11:02.100
Anna: It's a nice place to leave it. 27 new

270
00:11:02.100 --> 00:11:04.780
objects, the smallest ones the size of a

271
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suburb. And they're still wearing the colours

272
00:11:07.060 --> 00:11:09.340
of a solar system that hasn't existed for

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four and a half billion years.

274
00:11:11.860 --> 00:11:14.220
Avery: Storey2 and it's a change of

275
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altitude. A knock.

276
00:11:15.860 --> 00:11:18.720
Krakatow, the volcano in the Sunda

277
00:11:18.720 --> 00:11:21.560
Strait between Java and Sumatra, has

278
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spent the last five days doing serious damage

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to the aviation map of Southeast Asia.

280
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And the reason it's on this show is that the

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entire response ran through satellites.

282
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Anna: Give me the event first.

283
00:11:34.840 --> 00:11:37.840
Avery: It escalated on 4 September and went

284
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into its major explosive phase on the

285
00:11:40.600 --> 00:11:43.360
5th, which ran for more than 24

286
00:11:43.360 --> 00:11:45.600
hours before settling back into the

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Strombolian pattern it's been in for.

288
00:11:49.330 --> 00:11:52.010
At the peak, Indonesia's Meteorological

289
00:11:52.010 --> 00:11:54.370
Agency had ash going up to about

290
00:11:54.450 --> 00:11:56.970
6,000 metres to the east of the

291
00:11:56.970 --> 00:11:59.930
volcano and 15,000 metres

292
00:11:59.930 --> 00:12:01.770
to the west. That's

293
00:12:01.770 --> 00:12:04.609
50,000ft. That is well above

294
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the cruising altitude of everything flying

295
00:12:06.930 --> 00:12:07.570
that day.

296
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Anna: And the disruption.

297
00:12:09.890 --> 00:12:12.570
Avery: Eight airports closed across Java and

298
00:12:12.570 --> 00:12:15.490
Sumatra. Ash fall across five

299
00:12:15.490 --> 00:12:18.010
provinces, into Jakarta and West

300
00:12:18.010 --> 00:12:18.690
Java.

301
00:12:19.370 --> 00:12:22.330
2,961 flights

302
00:12:22.330 --> 00:12:24.850
grounded and something like a hundred and

303
00:12:24.850 --> 00:12:27.730
seventy thousand travellers stranded, a

304
00:12:27.730 --> 00:12:30.050
decent number of them Australians, because

305
00:12:30.050 --> 00:12:32.930
that corridor is on the way to and from a lot

306
00:12:32.930 --> 00:12:35.890
of places we fly. Operations were

307
00:12:35.890 --> 00:12:37.770
essentially back by yesterday.

308
00:12:38.410 --> 00:12:40.330
Anna: So m. Where does the space part come in?

309
00:12:40.890 --> 00:12:43.090
Avery: It's the whole nervous system of the

310
00:12:43.090 --> 00:12:45.940
response. There is a global arrangement

311
00:12:45.940 --> 00:12:48.580
for this. 9 volcanic ash

312
00:12:48.580 --> 00:12:51.380
advisory centres, each responsible for a

313
00:12:51.380 --> 00:12:54.180
slice of the planet. The one that covers

314
00:12:54.180 --> 00:12:57.060
Indonesia is the Darwin Centre, run

315
00:12:57.060 --> 00:12:59.460
by Australia's Bureau of Meteorology

316
00:13:00.259 --> 00:13:02.460
and the advisories they were issuing through

317
00:13:02.460 --> 00:13:04.900
the week. Plume height, direction,

318
00:13:05.060 --> 00:13:07.980
forecast, drift are built primarily on

319
00:13:07.980 --> 00:13:10.950
geostationary satellite imagery which. Which

320
00:13:10.950 --> 00:13:13.070
for that part of the world means Japan's

321
00:13:13.070 --> 00:13:15.990
Himawari nine sitting over the equator

322
00:13:15.990 --> 00:13:18.550
and imaging the full disc of the earth

323
00:13:18.710 --> 00:13:19.910
every 10 minutes.

324
00:13:20.630 --> 00:13:21.990
Anna: 10 minutes is fast.

325
00:13:22.790 --> 00:13:25.710
Avery: It has to be. An ash cloud at

326
00:13:25.710 --> 00:13:28.590
50,000ft moves and it doesn't

327
00:13:28.590 --> 00:13:31.510
show up on aircraft weather radar. Radar

328
00:13:31.510 --> 00:13:34.190
is built to see water droplets and dry

329
00:13:34.190 --> 00:13:36.390
ash is close to invisible to it.

330
00:13:37.100 --> 00:13:39.740
So the only warning a crew gets is the one

331
00:13:39.740 --> 00:13:42.220
that comes up from the ground and the ground

332
00:13:42.300 --> 00:13:43.580
gets it from orbit.

333
00:13:43.980 --> 00:13:46.260
Anna: And there's a reason everyone treats this so

334
00:13:46.260 --> 00:13:46.940
seriously.

335
00:13:47.660 --> 00:13:50.540
Avery: There is, and it's a British airways flight

336
00:13:50.540 --> 00:13:53.420
in 1982 over Java. As it

337
00:13:53.420 --> 00:13:56.300
happens, a, uh, 747 flew

338
00:13:56.300 --> 00:13:58.780
through an ash cloud nobody knew was there

339
00:13:58.780 --> 00:14:01.020
and lost all four engines.

340
00:14:01.580 --> 00:14:04.540
Ash melts in the hot section of a jet engine,

341
00:14:04.860 --> 00:14:07.420
then resolidifies as glass on the

342
00:14:07.420 --> 00:14:10.080
turbine blades and chokes it. That

343
00:14:10.080 --> 00:14:12.880
aircraft glided for 16 minutes before

344
00:14:12.880 --> 00:14:15.760
they got the engines restarted. Nobody

345
00:14:15.760 --> 00:14:18.720
was killed. And the entire modern advisory

346
00:14:18.720 --> 00:14:21.400
system exists because of flights like that

347
00:14:21.400 --> 00:14:21.720
one.

348
00:14:22.600 --> 00:14:24.679
Anna: And NASA published imagery

349
00:14:25.400 --> 00:14:27.080
this morning our time.

350
00:14:27.720 --> 00:14:30.440
Avery: NASA's Earth Observatory ran it as their

351
00:14:30.440 --> 00:14:33.320
image of the day. The operational land

352
00:14:33.320 --> 00:14:36.140
imager on Landsat 8 and veers

353
00:14:36.140 --> 00:14:38.900
on Suomi NPP showing the

354
00:14:38.900 --> 00:14:41.660
plume and the ashfall. Different

355
00:14:41.660 --> 00:14:44.660
job from Himawari. The geostationary

356
00:14:44.660 --> 00:14:47.260
satellites give you speed, the polar

357
00:14:47.260 --> 00:14:50.060
orbiters give you Resolution and

358
00:14:50.060 --> 00:14:50.500
Anak

359
00:14:50.500 --> 00:14:52.220
Anna: Krakatau itself has history.

360
00:14:52.380 --> 00:14:54.940
Avery: The name means child of Krakatau.

361
00:14:55.180 --> 00:14:57.940
The parent volcano is the one that destroyed

362
00:14:57.940 --> 00:15:00.580
itself in 1883 in the

363
00:15:00.580 --> 00:15:03.270
loudest event in recorded history. The

364
00:15:03.270 --> 00:15:06.230
child grew out of the Caldera and in December

365
00:15:06.230 --> 00:15:09.030
2018, one flank of it collapsed

366
00:15:09.030 --> 00:15:11.990
into the sea and generated a tsunami that

367
00:15:11.990 --> 00:15:14.510
killed more than 400 people with

368
00:15:14.510 --> 00:15:17.470
essentially no warning. So this is a well

369
00:15:17.470 --> 00:15:20.270
instrumented, closely watched mountain. And

370
00:15:20.270 --> 00:15:23.030
even so, the useful early data this

371
00:15:23.030 --> 00:15:25.910
week came from 360,000

372
00:15:25.990 --> 00:15:28.590
kilometres of sight line, not from the

373
00:15:28.590 --> 00:15:30.470
summit storey 3.

374
00:15:30.950 --> 00:15:33.830
Anna: On 31 August and 1 September,

375
00:15:34.070 --> 00:15:36.790
the European Space Agency deliberately flew

376
00:15:36.790 --> 00:15:39.270
two of its own satellites into the atmosphere

377
00:15:39.270 --> 00:15:41.950
over the South Pacific and then chartered a

378
00:15:41.950 --> 00:15:44.150
jet and flew a team underneath them to watch

379
00:15:44.150 --> 00:15:46.310
it happen. On purpose,

380
00:15:46.870 --> 00:15:49.510
entirely on purpose. And it's one of the more

381
00:15:49.510 --> 00:15:52.350
quietly impressive things ESA has done. The

382
00:15:52.350 --> 00:15:54.910
satellites were Samba and Tango, two of the

383
00:15:54.910 --> 00:15:57.780
four Cluster spacecraft. Cluster launched in

384
00:15:57.780 --> 00:16:00.620
2004. Identical satellites flying

385
00:16:00.620 --> 00:16:02.380
in formation so that they could measure

386
00:16:02.380 --> 00:16:04.580
Earth's magnetosphere in three dimensions

387
00:16:05.140 --> 00:16:07.940
rather than one line at a time. 26

388
00:16:07.940 --> 00:16:10.660
years of operations. It is one of the great

389
00:16:10.740 --> 00:16:12.180
unglamorous missions.

390
00:16:12.820 --> 00:16:14.780
Avery: And rather than just letting them come

391
00:16:14.780 --> 00:16:17.220
Anna: down, rather than letting them come down

392
00:16:17.220 --> 00:16:20.140
whenever and wherever, ESA has been doing

393
00:16:20.140 --> 00:16:22.860
targeted reentries, steering each one

394
00:16:22.860 --> 00:16:25.380
into a specific window over open ocean.

395
00:16:26.010 --> 00:16:28.810
Salsa went first in September 2024.

396
00:16:29.210 --> 00:16:32.170
Samba came down on 31 August this year,

397
00:16:32.250 --> 00:16:35.050
and tango, the last one at

398
00:16:35.050 --> 00:16:37.650
23, 30 and 31 seconds, Central

399
00:16:37.650 --> 00:16:40.570
European Summer Time on 1 September

400
00:16:40.970 --> 00:16:42.930
over the South Pacific, a few hundred

401
00:16:42.930 --> 00:16:44.330
kilometres from Tonga.

402
00:16:44.730 --> 00:16:46.810
Avery: And that precision buys you something.

403
00:16:47.370 --> 00:16:49.530
Anna: It buys you the ability to put an aeroplane

404
00:16:49.530 --> 00:16:52.020
in the right place. The campaign is called

405
00:16:52.020 --> 00:16:54.700
Rosie, led by an international team under

406
00:16:54.700 --> 00:16:57.260
Jirzi Shilha, who runs a Slovak company

407
00:16:57.260 --> 00:17:00.060
called Astro Solutions. They flew a business

408
00:17:00.060 --> 00:17:02.900
jet fitted with 30 instruments, cameras and

409
00:17:02.900 --> 00:17:04.900
spectrometers with filters chosen for

410
00:17:04.900 --> 00:17:07.620
specific elements. 29 of the 30

411
00:17:07.620 --> 00:17:10.380
worked. They got about 50 seconds on each

412
00:17:10.380 --> 00:17:13.060
satellite from something like 120 kilometres

413
00:17:13.060 --> 00:17:15.740
away. And the description from onboard was

414
00:17:15.740 --> 00:17:18.250
that there was a sudden explosion as the

415
00:17:18.250 --> 00:17:19.490
satellites came apart.

416
00:17:19.970 --> 00:17:22.570
Avery: What are they actually measuring? Because it

417
00:17:22.570 --> 00:17:25.010
isn't the light show, it isn't

418
00:17:25.490 --> 00:17:26.130
two things.

419
00:17:26.370 --> 00:17:29.090
Anna: The first is engineering what breaks up when

420
00:17:29.170 --> 00:17:31.970
at, uh, what altitude and what survives. That

421
00:17:31.970 --> 00:17:34.250
feeds directly into the models used to decide

422
00:17:34.250 --> 00:17:36.090
whether a spacecraft can be allowed to re

423
00:17:36.090 --> 00:17:38.730
enter uncontrolled at all. The second is the

424
00:17:38.730 --> 00:17:41.010
one that's becoming urgent chemistry.

425
00:17:41.490 --> 00:17:43.650
A satellite doesn't disappear when it burns,

426
00:17:43.650 --> 00:17:46.040
it's. It becomes vapour. And that vapour

427
00:17:46.040 --> 00:17:48.520
stays in the upper atmosphere. Their filters

428
00:17:48.520 --> 00:17:51.520
were tuned for titanium, sodium, potassium

429
00:17:51.520 --> 00:17:54.000
and aluminium. And the compound they care

430
00:17:54.000 --> 00:17:56.920
most about is aluminium oxide. Because there

431
00:17:56.920 --> 00:17:59.640
is a real open question about what it does to

432
00:17:59.640 --> 00:18:01.560
ozone chemistry at those altitudes.

433
00:18:01.640 --> 00:18:04.440
Avery: And the reason that's urgent is arithmetic.

434
00:18:04.920 --> 00:18:07.520
Anna: It's pure arithmetic. We are

435
00:18:07.520 --> 00:18:10.240
launching constellations of tens of

436
00:18:10.240 --> 00:18:13.090
thousands of satellites with design lives

437
00:18:13.090 --> 00:18:16.050
of about five years. Which means that from

438
00:18:16.050 --> 00:18:18.930
here on satellites re entering the atmosphere

439
00:18:19.090 --> 00:18:21.930
is not an occasional event, it's a

440
00:18:21.930 --> 00:18:24.810
continuous process. And we are running

441
00:18:24.810 --> 00:18:27.250
that experiment without knowing the answer.

442
00:18:27.970 --> 00:18:30.890
Stane Lemons, ESA's acting head of Space

443
00:18:30.890 --> 00:18:33.490
debris, framed this week's data as being

444
00:18:33.490 --> 00:18:36.290
about improving re entry models and building

445
00:18:36.290 --> 00:18:38.780
better satellites. Which is the polite

446
00:18:38.780 --> 00:18:41.260
version of saying we have been guessing and,

447
00:18:41.260 --> 00:18:41.700
uh, there's

448
00:18:41.700 --> 00:18:42.820
Avery: a follow up mission.

449
00:18:43.140 --> 00:18:45.300
Anna: There is, and it's a lovely idea.

450
00:18:45.700 --> 00:18:48.100
Draco launching in 2027

451
00:18:48.500 --> 00:18:51.140
is a spacecraft built for the sole purpose of

452
00:18:51.140 --> 00:18:53.980
destroying itself while taking notes. Over

453
00:18:53.980 --> 00:18:56.860
200 sensors, four cameras and

454
00:18:56.860 --> 00:18:59.420
a capsule designed to survive the breakup and

455
00:18:59.420 --> 00:19:02.300
transmit the recording afterwards. So instead

456
00:19:02.300 --> 00:19:04.660
of watching From a jet 100 kilometres away,

457
00:19:05.330 --> 00:19:06.610
we get the view from inside.

458
00:19:07.090 --> 00:19:09.010
Avery: How did isa mark the end of it?

459
00:19:09.410 --> 00:19:11.970
Anna: Philippe Escoube, who has managed Cluster,

460
00:19:12.290 --> 00:19:14.130
said that once you build something like this,

461
00:19:14.130 --> 00:19:16.810
you imbue it with a soul. 26

462
00:19:16.810 --> 00:19:19.690
years, four spacecraft, and the last thing

463
00:19:19.690 --> 00:19:22.090
they did was come home in a controlled way

464
00:19:22.090 --> 00:19:25.090
over the emptiest ocean on Earth and teach

465
00:19:25.090 --> 00:19:26.370
us something on the way down.

466
00:19:27.010 --> 00:19:27.970
Avery: Storey four.

467
00:19:28.370 --> 00:19:30.530
And, um, this one is about a galaxy you have

468
00:19:30.530 --> 00:19:32.290
almost certainly seen A picture of

469
00:19:33.300 --> 00:19:35.740
Messier 74, the Phantom

470
00:19:35.740 --> 00:19:38.660
Galaxy, about 32 million light

471
00:19:38.660 --> 00:19:41.620
years away in Pisces, perfectly face on

472
00:19:41.860 --> 00:19:44.260
two beautifully clean spiral arms.

473
00:19:44.740 --> 00:19:47.580
Webb's infrared image of it went everywhere

474
00:19:47.580 --> 00:19:48.500
a few years back.

475
00:19:49.220 --> 00:19:51.620
Anna: So what's changed its size?

476
00:19:52.180 --> 00:19:54.300
Avery: A study out of the Instituto de

477
00:19:54.300 --> 00:19:57.020
Astrophica de Canarias, published in

478
00:19:57.020 --> 00:19:59.660
Astronomy and Astrophysics and released on

479
00:19:59.660 --> 00:20:01.950
4th September, finds that M

480
00:20:01.950 --> 00:20:04.900
M74 is more than twice as big as

481
00:20:04.900 --> 00:20:07.620
the catalogues say. The galaxy we've been

482
00:20:07.620 --> 00:20:10.340
looking at is about 45,000 light

483
00:20:10.340 --> 00:20:13.220
years across. They're tracing stars out

484
00:20:13.220 --> 00:20:14.700
to roughly a hundred thousand.

485
00:20:15.260 --> 00:20:17.339
Anna: How did everyone miss half a galaxy?

486
00:20:17.740 --> 00:20:20.220
Avery: Because it's faint? This is the low

487
00:20:20.220 --> 00:20:22.620
surface brightness problem and it's one of

488
00:20:22.620 --> 00:20:25.550
the great quiet biases in astronomy. A,

489
00:20:25.550 --> 00:20:28.180
uh, galaxy doesn't have an edge, it has a

490
00:20:28.180 --> 00:20:30.260
point where the light drops below whatever

491
00:20:30.260 --> 00:20:32.490
your survey can detect. And, and we have

492
00:20:32.490 --> 00:20:34.970
spent a century calling that point the edge.

493
00:20:35.610 --> 00:20:38.170
Ignacio Ruiz with Ignacio

494
00:20:38.170 --> 00:20:40.570
Trujillo and Michele Sarah riccart

495
00:20:40.890 --> 00:20:43.450
went about 10 times deeper than the Sloan

496
00:20:43.450 --> 00:20:46.410
survey. And here's the part I like. They

497
00:20:46.410 --> 00:20:48.570
did it with a one metre telescope.

498
00:20:49.050 --> 00:20:49.850
Anna: One metre.

499
00:20:50.330 --> 00:20:53.290
Avery: The Transient Survey telescope. A, uh, one

500
00:20:53.290 --> 00:20:55.610
metre aperture and enough patience.

501
00:20:56.330 --> 00:20:59.130
Deep imaging isn't only about how big your

502
00:20:59.130 --> 00:21:01.770
mirror is. It's about how carefully you

503
00:21:01.770 --> 00:21:03.950
handle the sky background and, and the

504
00:21:03.950 --> 00:21:06.830
scattered light. This is a result that a very

505
00:21:06.830 --> 00:21:09.670
large telescope chasing very distant

506
00:21:09.670 --> 00:21:12.230
things was never going to go looking for.

507
00:21:12.710 --> 00:21:13.990
Anna: And what's actually out there?

508
00:21:14.070 --> 00:21:16.790
Avery: A, uh, disc of young stars. The average age

509
00:21:16.790 --> 00:21:19.670
in that outer region is 640 million

510
00:21:19.830 --> 00:21:22.430
years, which for a galaxy that's been around

511
00:21:22.430 --> 00:21:24.950
for billions is essentially yesterday.

512
00:21:25.510 --> 00:21:28.110
So M, M74 didn't slowly ooze

513
00:21:28.110 --> 00:21:31.030
outward. It grew a new outer disc, fast

514
00:21:31.890 --> 00:21:33.970
Anna: triggered by what a neighbour.

515
00:21:34.290 --> 00:21:37.170
Avery: UGC 1176, about

516
00:21:37.170 --> 00:21:40.170
400,000 light years away, appears

517
00:21:40.170 --> 00:21:42.210
to have passed close about a billion years

518
00:21:42.210 --> 00:21:45.210
ago. Gravitationally, that's a stir, not a

519
00:21:45.210 --> 00:21:48.130
collision. It doesn't wreck the spiral. It

520
00:21:48.130 --> 00:21:50.570
drags gas outward and lights up star

521
00:21:50.570 --> 00:21:52.370
formation where there wasn't any.

522
00:21:52.930 --> 00:21:55.450
Anna: And the broader claim that this is

523
00:21:55.450 --> 00:21:57.810
Avery: probably common and we simply haven't been

524
00:21:57.810 --> 00:22:00.660
able to see it. If galaxies routinely

525
00:22:00.660 --> 00:22:03.060
double in size in under a billion years

526
00:22:03.140 --> 00:22:05.980
through encounters like this one, then galaxy

527
00:22:05.980 --> 00:22:08.780
growth is a lot lumpier and a lot faster

528
00:22:08.780 --> 00:22:11.260
than the smooth picture we teach. And the

529
00:22:11.260 --> 00:22:13.220
evidence has been sitting in the outskirts

530
00:22:13.220 --> 00:22:16.020
the whole time, just below where anyone was

531
00:22:16.020 --> 00:22:16.340
looking.

532
00:22:17.140 --> 00:22:19.740
Anna: Okay, moving on to Skywatch. And the headline

533
00:22:19.740 --> 00:22:22.580
is Darkness. New Moon

534
00:22:22.580 --> 00:22:25.230
falls on Friday the 11th of September at

535
00:22:25.230 --> 00:22:27.710
4:27 in the morning, Universal Time.

536
00:22:27.950 --> 00:22:30.670
That's 2:27 on Friday afternoon in Sydney.

537
00:22:31.070 --> 00:22:33.270
So tonight, tomorrow night and right through

538
00:22:33.270 --> 00:22:36.110
the weekend, you have about as dark a sky

539
00:22:36.110 --> 00:22:38.350
as September gives you wherever you are.

540
00:22:39.070 --> 00:22:41.950
Southern hemisphere first from Sydney

541
00:22:41.950 --> 00:22:44.550
and anywhere at similar latitudes. This is

542
00:22:44.550 --> 00:22:46.590
the last really good month for the centre of

543
00:22:46.590 --> 00:22:49.590
the galaxy as darkness falls. Scorpius

544
00:22:49.590 --> 00:22:52.450
and Sagittarius are high close to overhead

545
00:22:52.450 --> 00:22:54.890
and the core of the Milky Way runs right

546
00:22:54.890 --> 00:22:57.890
through them under a dark sky away from town.

547
00:22:58.210 --> 00:23:00.690
That band is not subtle. It has

548
00:23:00.690 --> 00:23:03.570
texture. It has dark lanes and the dark

549
00:23:03.570 --> 00:23:05.850
lanes are dust clouds between us and the

550
00:23:05.850 --> 00:23:08.650
centre. You do not need a telescope. You

551
00:23:08.650 --> 00:23:10.690
need 40 minutes with no phone screen.

552
00:23:11.250 --> 00:23:13.570
Avery: And after that it starts sliding west,

553
00:23:14.210 --> 00:23:16.770
Anna: it starts sliding west through October. So

554
00:23:16.770 --> 00:23:19.730
this is the window. Venus

555
00:23:19.730 --> 00:23:22.330
is low in the west just after sunset and it's

556
00:23:22.330 --> 00:23:24.690
building. Greatest Brilliancy comes on the

557
00:23:24.690 --> 00:23:26.690
18th of September at magnitude

558
00:23:26.690 --> 00:23:29.450
-4.8. You may see the 22nd

559
00:23:29.450 --> 00:23:31.290
quoted elsewhere. That's a different

560
00:23:31.290 --> 00:23:33.410
definition and we're going with the 18th.

561
00:23:33.810 --> 00:23:35.970
Saturn is up in the east through the evening,

562
00:23:36.050 --> 00:23:38.170
climbing towards opposition on the 4th of

563
00:23:38.170 --> 00:23:41.010
October with the rings about 7 degrees open.

564
00:23:41.970 --> 00:23:44.700
Avery: North America, same dark window.

565
00:23:44.700 --> 00:23:46.900
Anna: And it's the better half of the year for you

566
00:23:46.900 --> 00:23:49.580
in one specific way. The teapot

567
00:23:49.980 --> 00:23:52.780
Sagittarius sits low in the south after dusk

568
00:23:52.780 --> 00:23:55.660
and the teapot asterism is genuinely easy

569
00:23:55.660 --> 00:23:58.420
once you've seen it. NASA's own guidance for

570
00:23:58.420 --> 00:24:01.380
next week, the 14th to the 20th, is to

571
00:24:01.380 --> 00:24:03.100
use the returning crescent Moon to find

572
00:24:03.100 --> 00:24:05.980
Antares in Scorpius first, then step

573
00:24:05.980 --> 00:24:08.740
across to the teapot, follow the steam from

574
00:24:08.740 --> 00:24:10.940
the spout to the thickest part and. And you

575
00:24:10.940 --> 00:24:12.820
are looking at the centre of the Milky Way

576
00:24:13.300 --> 00:24:15.980
lower for you than it is for us. So you want

577
00:24:15.980 --> 00:24:17.380
a clear southern horizon,

578
00:24:17.540 --> 00:24:19.900
Avery: but that's the direction both

579
00:24:19.900 --> 00:24:21.220
hemispheres morning

580
00:24:21.220 --> 00:24:23.700
Anna: sky, Jupiter and Mars before dawn

581
00:24:23.940 --> 00:24:26.900
both. Jupiter is unmistakable

582
00:24:26.980 --> 00:24:29.300
and closing on Regulus through the month.

583
00:24:29.940 --> 00:24:32.780
Mars is fainter and lower and takes a bit

584
00:24:32.780 --> 00:24:35.740
more work and a date for the calendar

585
00:24:35.740 --> 00:24:38.540
in both hemispheres. The 19th

586
00:24:38.540 --> 00:24:41.020
is international. Observe the Moon night,

587
00:24:41.420 --> 00:24:44.060
which is a good excuse to point anything you

588
00:24:44.060 --> 00:24:46.780
own at the terminator, the line between

589
00:24:46.780 --> 00:24:49.340
lunar day and night, where the shadows are

590
00:24:49.340 --> 00:24:51.740
long and the craters look three dimensional.

591
00:24:52.220 --> 00:24:54.780
Avery: And um, the equinox the 22nd.

592
00:24:55.180 --> 00:24:58.020
Anna: Spring here, autumn there and day

593
00:24:58.020 --> 00:25:00.940
and night close to equal everywhere. Looking

594
00:25:01.100 --> 00:25:03.980
further ahead, 6 October brings a

595
00:25:03.980 --> 00:25:06.380
pre dawn lunar occultation of Jupiter

596
00:25:07.020 --> 00:25:09.220
and Sky and Telescope have been billing that

597
00:25:09.220 --> 00:25:11.740
one as the spectacular event of the year.

598
00:25:12.300 --> 00:25:14.180
We'll build to it properly closer to

599
00:25:14.180 --> 00:25:16.780
Avery: the time safety line before we go.

600
00:25:17.180 --> 00:25:19.580
Anna: It matters this fortnight because Venus is

601
00:25:19.580 --> 00:25:22.300
brilliant and low in the west and every year

602
00:25:22.300 --> 00:25:24.340
around now people get the idea of trying to

603
00:25:24.340 --> 00:25:27.260
find it in daylight. It is genuinely possible

604
00:25:27.660 --> 00:25:29.860
and it is one of the easiest ways to hurt

605
00:25:29.860 --> 00:25:32.620
yourself in this hobby. Never sweep the sky

606
00:25:32.620 --> 00:25:34.780
near the sun with binoculars or a telescope.

607
00:25:35.310 --> 00:25:37.110
You can be on the sun before you know you're

608
00:25:37.110 --> 00:25:40.030
near it and unfiltered, that is permanent

609
00:25:40.030 --> 00:25:42.630
damage in less than a second if you're going

610
00:25:42.630 --> 00:25:44.950
to look anywhere near the sun. The standard

611
00:25:44.950 --> 00:25:45.790
is ISO

612
00:25:45.790 --> 00:25:48.030
123122.

613
00:25:48.510 --> 00:25:50.830
That's the specification for certified solar

614
00:25:50.830 --> 00:25:53.750
viewers and eclipse glasses. Sunglasses

615
00:25:53.750 --> 00:25:56.110
are not that stacked. Sunglasses are not that

616
00:25:56.350 --> 00:25:58.830
exposed film and smoked glass are not that

617
00:25:59.150 --> 00:26:01.420
cheque the certification cheque, the filter

618
00:26:01.420 --> 00:26:03.580
for scratches and pinholes. And if it's a

619
00:26:03.580 --> 00:26:05.860
telescope filter, it goes on the front of the

620
00:26:05.860 --> 00:26:08.060
instrument, never the eyepiece end.

621
00:26:08.780 --> 00:26:11.340
Avery: Wait for it to get properly dark and let

622
00:26:11.340 --> 00:26:12.620
Venus come to you.

623
00:26:13.180 --> 00:26:15.780
Anna: Wait for it to get properly dark. It'll be

624
00:26:15.780 --> 00:26:17.900
the brightest thing in the western sky. And

625
00:26:17.900 --> 00:26:19.020
it will not be hard.

626
00:26:19.500 --> 00:26:21.900
Avery: And that's Astronomy daily for Wednesday

627
00:26:21.980 --> 00:26:23.601
9th September.

628
00:26:23.772 --> 00:26:26.660
Anna: 27 of the faintest objects ever seen

629
00:26:26.660 --> 00:26:29.180
beyond Neptune, still wearing the colours

630
00:26:29.180 --> 00:26:32.060
they were born with. A volcano tracked from

631
00:26:32.060 --> 00:26:34.540
orbit while 3,000 flights waited.

632
00:26:35.100 --> 00:26:38.020
Two European spacecraft flown home over the

633
00:26:38.020 --> 00:26:40.300
Pacific and filmed on the way down.

634
00:26:40.780 --> 00:26:42.980
And a galaxy that turns out to be twice the

635
00:26:42.980 --> 00:26:43.740
size we thought.

636
00:26:44.380 --> 00:26:46.620
Avery: Every paper and release we've mentioned is

637
00:26:46.620 --> 00:26:49.220
linked in the show notes, along with the full

638
00:26:49.220 --> 00:26:50.540
episode transcript.

639
00:26:50.860 --> 00:26:53.820
Anna: That's astronomydaily IO, the whole back

640
00:26:53.820 --> 00:26:56.140
catalogue is there, the newsletter, if you'd

641
00:26:56.140 --> 00:26:58.340
rather read than listen, and the contact

642
00:26:58.420 --> 00:27:00.420
form, which is where a lot of our best

643
00:27:00.420 --> 00:27:01.460
questions come from.

644
00:27:01.780 --> 00:27:03.860
Avery: You'll find us on X, Facebook,

645
00:27:04.340 --> 00:27:07.140
Tumblr, Instagram, TikTok and

646
00:27:07.140 --> 00:27:10.060
YouTube @astrodaily pod, and of

647
00:27:10.060 --> 00:27:12.850
course, wherever you get your podcasts, A,

648
00:27:12.850 --> 00:27:15.620
uh, rating genuinely helps other people find

649
00:27:15.620 --> 00:27:15.940
us.

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00:27:16.340 --> 00:27:19.260
Anna: We're back tomorrow. Until then, keep looking

651
00:27:19.260 --> 00:27:21.700
up. And if you're anywhere dark this week,

652
00:27:22.180 --> 00:27:24.340
go and look at the middle of the galaxy while

653
00:27:24.340 --> 00:27:25.300
it's still overhead.

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00:27:25.780 --> 00:27:26.900
Avery: Clear skies, everyone.