The Moon in Five Hours

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Anna: Hello and welcome to Astronomy daily.

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It's Tuesday, September 8,

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2026. I'm Anna and this is series

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five, episode 188.

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Avery: And I'm Avery. Anna, uh, how long did

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it take to build the moon?

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Anna: Depending on which model you read, anywhere

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from a month to a few hundred years.

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Avery: And the paper we're leading with today says

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five hours.

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Anna: Five hours. Not the debris settling, not

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the first draught. An intact moon in

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orbit five hours after the collision that

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made it. And the reason nobody found that

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before is almost comically mundane.

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Everyone had been modelling rock as if it

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were water.

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Avery: That's our lead, and it comes from Southwest

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research institute.

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Anna: Then three more eight quasars whose

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black holes are 10 times too big for the

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galaxies they live in and are still eating.

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A pair of massive stars that didn't form

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together at all, but fell past each other and

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got caught. And Dragonfly, NASA's

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nuclear powered helicopter for Titan, which

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just got its wiring and a name for the place

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it's going

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Avery: to land, plus the sky for both

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hemispheres. And if you're in North America,

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put the show on and then go outside because

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the moon is going to hide Jupiter this

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afternoon in broad daylight.

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Anna: In daylight. We'll tell you how to do that

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safely later on.

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Let's start with the Moon and the five hours.

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Avery: Alright? Before the new result. Give

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me the version we've all been taught, because

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I want to know exactly what's being

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challenged.

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Anna: The giant impact hypothesis. The standard

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model. Since the mid-70s, roughly four and

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a half billion years ago, a body about the

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size of Mars hit the young Earth. We call it

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Theia. Not head on. A glancing

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blow.

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Avery: And that produces the Moon. How?

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Anna: In the classical picture, it doesn't produce

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the Moon, it produces a mess. Theia

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is destroyed. A chunk of Earth's mantle goes

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with it and all of that ends up as a disc of

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vaporised and molten rock circling the Earth.

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A ring system made of magma. Then

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over anywhere from about a month to a couple

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of hundred years, depending on whose

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simulation you read. That disc cools and

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clumps and builds a moon.

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Avery: So the moon is assembled out of debris

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slowly after the fact.

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Anna: Assembled out of debris after the fact.

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That's the model in every textbook. And it

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works beautifully, except for one thing that

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has bothered people for about 25 years, which

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is the Moon looks too much like Earth.

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If you take a lunar sample and measure its

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oxygen isotopes, the ratio of

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oxygen 17 to oxygen 16, say

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you get a number that is indistinguishable

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from Earth's. Same for titanium, same

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for chromium. Now everybody in the solar

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system has its own isotopic fingerprint.

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Mars is measurably different. The meteorites

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we have from the asteroid belt are different.

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Everything has its own signature because

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everything formed in a slightly different

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part of the disc.

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Avery: But the Moon doesn't.

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Anna: And that's a problem, because in the

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classical model, the disc and therefore the

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moon is mostly theia, something

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like 60 to 80% theia.

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So the Moon should carry Theia's fingerprint,

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not Earth's. And it doesn't. People call it

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the isotopic crisis. And the fixes on

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offer all work, but none of them is clean.

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Make the impact violent enough to mix

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everything into one vapour cloud or, or make

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Thea, uh, a chemical twin of Earth. Which is

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possible, but is a coincidence you have to

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buy.

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Avery: Okay, so what's new?

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Anna: What's new is that a team led by a Dean

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Denton at Southwest Research Institute with

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Robin Canop, who is one of the architects of

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the modern giant impact model, and Eric

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Asfalg at the University of Arizona

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went back and changed one assumption. Not

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the speed, not the angle, not the size,

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the strength.

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Avery: The strength of what?

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Anna: Of rock. In essentially every giant

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impact simulation ever run, the two

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colliding bodies are treated as strengthless

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fluids. Which sounds mad, but there's a good

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reason. At those energies, rock genuinely

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does behave more like a liquid than a solid.

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The pressures are so far beyond anything it

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can resist that its own material strength,

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the thing that makes a boulder a boulder

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rather than a puddle, is negligible.

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So you ignore it and you save an enormous

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amount of computing time.

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Avery: And the assumption turns out to be wrong.

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Anna: The assumption turns out to be incomplete.

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Which is more interesting, because strength

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isn't a fixed property. It depends on

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temperature. Hot rock is weak,

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cold rock is strong. And these bodies were

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not all at the same temperature. A young

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protoplanet, still hot from its own formation

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and full of short lived radioactive isotopes,

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is a soft object. An older one that's had a

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hundred million years to cool is a much

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tougher one.

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Avery: So they put temperature dependent strength

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into the model.

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Anna: They put temperature dependent strength into

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the model, ran the canonical impact,

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the same parameters as the original

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modelling, nothing exotic. And out of one of

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those runs came an intact moon. Not a

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disc, a satellite. In about five hours,

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five hours from impact to moon,

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five hours from impact to a self gravitating

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body in orbit around the Earth. Deton's own

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description is that she used the same

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parameters as the Original impact modelling

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and within around five hours, an intact moon

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emerged. And I want to be careful here,

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because this is the bit the headlines

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flatten. The point is not that we now know

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the moon formed in five hours. The point is

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that a variable everybody had reasonably

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ignored turns out to swing the outcome from

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one formation pathway to a completely

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different one.

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Avery: So it's a sensitivity result.

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Anna: It's a sensitivity result and it's a

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genuinely uncomfortable one, because it means

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a lot of previous work may have been

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exploring only half the possibility space.

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Avery: You said one of the runs. What did the others

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do?

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Anna: This is the part I find lovely. They got

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two distinct outcomes, and which

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one you land in depends on how hot Theia was,

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which is really a question about when the

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impact happened, if Theia was young and

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hot. The paper puts that at an impact less

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than about 60 million years after the solar

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system started forming. It's a weak body,

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it comes apart completely. You get the

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immediate moon made overwhelmingly of Thea's

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mantle.

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Avery: And if it was older, if the

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Anna: impact came later, 100 to 150

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million years in Theia has cooled,

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it's stronger and it holds together better.

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More of it survives the encounter and ends up

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merging into the Earth. And what's left? Over

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goes the classical route a disc and

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a moon that assembles gradually.

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Avery: So the moon's own history is a clock.

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Anna: The moon's initial state becomes a clock. And

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that's the real prize here, because the date

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of the giant impact is one of the genuinely

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open numbers in planetary science. The

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estimates span something like a hundred

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million years. If the state the moon started

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in depends on when it was hit, then in

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principle you can run that backwards. You

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look at what the moon is actually made of and

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you read off the timing.

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Avery: Can we do that yet?

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Anna: Not from where we're standing. To separate

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these two scenarios properly, you want deep

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material, mantle or close to it.

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And that is an argument for the sample return

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Artemis is building towards and for the

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Chinese South Pole missions. This paper has

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just made that argument considerably sharper.

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Avery: What's the caveat? There's always a

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caveat.

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Anna: 2 and the authors are upfront about both.

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This is a simulation, not an observation.

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A better simulation, because it includes

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physics that was missing. But the strength

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model for rock at those pressures is itself

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an approximation. And they ran the canonical

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case, one region of parameter space.

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The full survey, every angle, every speed,

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every temperature is somebody's next several

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years.

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Avery: Does it fix the isotope problem?

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Anna: It nudges it in a helpful direction. The

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paper argues that Earth and theia most likely

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formed from similar regions of the

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protoplanetary disc, near neighbours,

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chemically speaking, which is what you'd want

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to explain the match. And it distinguishes

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both of them from Mars, which formed

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somewhere different. So it's not a solution

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to the isotopic crisis, so much as a

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reframing of what a solution has to look

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like.

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Avery: Alright, Southern hemisphere angle.

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Anna: You've got one, I've got one. And it's about

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400 kilometres inland from Geraldton.

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Because if the timing of the giant impact is

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the number in play, then the hard floor under

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that number is sitting in Western Australia,

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the Jack Hills in the Narrier. Nice terrain.

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That's where the oldest known pieces of the

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Earth are zircon crystals. Tiny,

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a fraction of a millimetre, dated to about

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4.4 billion years.

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Avery: And zircons survive things.

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Anna: Zircons survive almost everything. You can

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lose the rock that contained them and the

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crystal keeps its date. And what those Jack

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Hills grains tell you is that by 4.4

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billion years ago, the Earth had a solid

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crust. And on the isotopic evidence,

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probably liquid water. Which means the

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moon forming impact, an event that turns the

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entire surface into a magma ocean, has to be

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older than that.

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Avery: So the late branch of this new model is up

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against a hard deadline.

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Anna: And the deadline is a handful of grains of

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sand from the Western Australian outback.

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I love that the constraint on how the Moon

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was born is sitting in a creek bed in the

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Murchison.

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Avery: That's a good line to move on from Storey

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2, published yesterday in Astronomy and

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Astrophysics. And it's about black holes that

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are the wrong size. Anna, uh, what's the rule

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they're breaking?

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Anna: The rule is co evolution. Every

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big galaxy has a supermassive black hole at

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its centre. And the mass of the black hole

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tracks the mass of the galaxy's stars

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remarkably tightly. Typically, the black

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hole is a few tenths of a percent of the

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stellar mass. Not 1%, a

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few tenths of one.

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Avery: And that ratio holds across enormous

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ranges

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Anna: across a factor of a thousand in galaxy mass,

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which is why people take it seriously. The

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interpretation has always been that the two

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grow together and regulate each other. The

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black hole feeds, it blazes as a quasar,

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it blows gas out of the galaxy that shuts

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down both its own supply and the galaxy's

266
00:10:46.830 --> 00:10:48.890
star formation. A thermostat.

267
00:10:49.370 --> 00:10:52.370
Avery: So here's the result. Johannes Buchner at the

268
00:10:52.370 --> 00:10:55.050
Max Planck Institute for Extraterrestrial

269
00:10:55.050 --> 00:10:57.290
Physics, with colleagues at Penn State,

270
00:10:57.450 --> 00:11:00.210
Illinois, Cal Poly, the Centre for

271
00:11:00.210 --> 00:11:02.890
Astrophysics and the Space Telescope Science

272
00:11:02.890 --> 00:11:05.890
institute went through 140 square

273
00:11:05.890 --> 00:11:08.730
degrees of the E Rosita X ray survey.

274
00:11:09.050 --> 00:11:11.210
They picked out 200 quasars

275
00:11:11.530 --> 00:11:14.490
selected on hard X rays, which is the honest

276
00:11:14.490 --> 00:11:16.880
way to do it because. Because dust can hide a

277
00:11:16.880 --> 00:11:19.520
growing black hole at optical wavelengths,

278
00:11:19.520 --> 00:11:21.400
but not in hard X rays.

279
00:11:21.880 --> 00:11:23.880
Anna: And eight of the 200 are wrong.

280
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Avery: Eight are badly wrong. Black hole to

281
00:11:27.240 --> 00:11:29.600
host galaxy mass ratios above

282
00:11:29.600 --> 00:11:32.400
5%. That's roughly 10 times

283
00:11:32.400 --> 00:11:35.000
what the relation says they should be. The

284
00:11:35.000 --> 00:11:37.280
black holes themselves run from about a

285
00:11:37.280 --> 00:11:39.600
hundred million to three billion solar

286
00:11:39.600 --> 00:11:41.960
masses. They're, uh, at redshifts between

287
00:11:42.040 --> 00:11:44.680
0.3 and 0.8.

288
00:11:45.200 --> 00:11:47.080
So we're looking at them as they were between

289
00:11:47.080 --> 00:11:49.520
about three and a half and seven billion

290
00:11:49.600 --> 00:11:52.560
years ago. And they are all still actively

291
00:11:52.560 --> 00:11:55.040
feeding some of them at close to the

292
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theoretical maximum rate.

293
00:11:57.200 --> 00:11:59.800
Anna: So they're not fossils. They're not objects

294
00:11:59.800 --> 00:12:01.560
that finished growing early and then had

295
00:12:01.560 --> 00:12:02.800
their galaxy stripped away.

296
00:12:03.200 --> 00:12:05.760
Avery: That's the key point. They're still eating.

297
00:12:06.000 --> 00:12:08.880
And they're not rare freaks, either. The

298
00:12:08.880 --> 00:12:11.480
team put a floor on their space density of at

299
00:12:11.480 --> 00:12:13.840
least 4 per cubic gigaparsec.

300
00:12:14.490 --> 00:12:17.210
Which sounds tiny, but for objects this

301
00:12:17.210 --> 00:12:19.930
extreme, it's a population, not an

302
00:12:19.930 --> 00:12:20.490
accident.

303
00:12:21.290 --> 00:12:22.330
Anna: So what does it mean?

304
00:12:22.890 --> 00:12:25.810
Avery: The author's phrase is an accretion channel

305
00:12:25.810 --> 00:12:28.010
disconnected from the stellar population.

306
00:12:28.570 --> 00:12:31.170
Some way of feeding a black hole that doesn't

307
00:12:31.170 --> 00:12:33.930
involve and doesn't disturb the

308
00:12:33.930 --> 00:12:36.770
galaxy's ability to make stars. And

309
00:12:36.770 --> 00:12:39.170
there's a bonus. You'll remember that

310
00:12:39.170 --> 00:12:42.010
JWST has been finding black holes

311
00:12:42.010 --> 00:12:44.130
that look far, far too massive for their

312
00:12:44.130 --> 00:12:46.610
galaxies in the very early universe.

313
00:12:46.930 --> 00:12:49.610
And the explanation people reached for was

314
00:12:49.610 --> 00:12:52.370
exotic seeds. Direct collapse of

315
00:12:52.370 --> 00:12:55.250
enormous gas clouds. Special conditions

316
00:12:55.250 --> 00:12:57.810
that only existed at cosmic dawn.

317
00:12:58.530 --> 00:13:01.450
Anna: And if you find the same thing halfway to the

318
00:13:01.450 --> 00:13:03.370
present day, then maybe

319
00:13:03.370 --> 00:13:06.290
Avery: you don't need the special conditions. Maybe

320
00:13:06.290 --> 00:13:08.410
it's a channel that operates whenever the

321
00:13:08.410 --> 00:13:10.930
circumstances allow. Including now.

322
00:13:11.650 --> 00:13:14.450
That's a much less dramatic explanation, and

323
00:13:14.450 --> 00:13:16.370
it's the kind that tends to be right.

324
00:13:17.090 --> 00:13:17.730
Anna: Caveats.

325
00:13:18.450 --> 00:13:21.130
Avery: Eight objects. And measuring a black

326
00:13:21.130 --> 00:13:24.090
hole's mass from a single spectrum carries

327
00:13:24.090 --> 00:13:27.050
real systematic uncertainty. You're

328
00:13:27.050 --> 00:13:29.290
using the width of an emission line as a

329
00:13:29.290 --> 00:13:32.130
proxy for orbital speed and calibrating

330
00:13:32.130 --> 00:13:33.890
that is an entire field.

331
00:13:34.770 --> 00:13:37.130
Separating a galaxy's starlight from the

332
00:13:37.130 --> 00:13:39.330
quasar's glare is also hard.

333
00:13:39.990 --> 00:13:42.550
The team knows all of this. That's why the

334
00:13:42.550 --> 00:13:45.230
headline number is a floor rather than a

335
00:13:45.230 --> 00:13:45.510
count.

336
00:13:46.230 --> 00:13:48.910
Anna: And it's erosita again. Two episodes

337
00:13:48.910 --> 00:13:51.430
running, it's erosita again.

338
00:13:51.910 --> 00:13:54.790
Avery: The same all sky X ray survey that gave us

339
00:13:54.790 --> 00:13:57.670
that six minute white dwarf binary yesterday.

340
00:13:58.150 --> 00:14:00.830
It has been extraordinarily productive for a

341
00:14:00.830 --> 00:14:03.350
telescope that has been sitting silent since

342
00:14:03.430 --> 00:14:04.550
2022.

343
00:14:04.799 --> 00:14:07.760
Anna: Storey3 also published yesterday,

344
00:14:08.000 --> 00:14:10.800
this time in Nature Astronomy. And

345
00:14:10.800 --> 00:14:13.680
it's a birth storey. Avery. About

346
00:14:13.680 --> 00:14:16.560
90% of massive stars are not alone.

347
00:14:16.960 --> 00:14:19.720
They come in pairs or triples or

348
00:14:19.720 --> 00:14:20.080
more.

349
00:14:20.800 --> 00:14:23.800
Avery: 90%. So the single massive

350
00:14:23.800 --> 00:14:25.280
star is the exception.

351
00:14:25.840 --> 00:14:28.600
Anna: The single massive star is the oddity. And

352
00:14:28.600 --> 00:14:31.080
that matters enormously because massive stars

353
00:14:31.080 --> 00:14:33.010
in pairs are, uh, are what eventually become

354
00:14:33.010 --> 00:14:35.610
the neutron star and black hole binaries that

355
00:14:35.610 --> 00:14:38.570
LIGO and Virgo hear merging. The question

356
00:14:38.570 --> 00:14:40.690
has always been how the pairs form in the

357
00:14:40.690 --> 00:14:43.130
first place. And there have been two answers.

358
00:14:43.770 --> 00:14:44.650
Avery: Give me both.

359
00:14:45.370 --> 00:14:48.249
Anna: One, disc fragmentation. A

360
00:14:48.249 --> 00:14:50.930
single star forms. It has a big accretion

361
00:14:50.930 --> 00:14:53.250
disc around it. The disc is heavy enough to

362
00:14:53.250 --> 00:14:56.090
become unstable and it breaks up and a piece

363
00:14:56.090 --> 00:14:58.890
of it collapses into a second star. That

364
00:14:58.890 --> 00:15:01.250
gives you a close pair orbiting more or less

365
00:15:01.250 --> 00:15:03.690
in the same plane with their discs neatly

366
00:15:03.690 --> 00:15:06.370
aligned because they came from the same disc.

367
00:15:06.930 --> 00:15:09.490
And two core fragmentation.

368
00:15:09.890 --> 00:15:12.450
The cloud core that's collapsing splits early

369
00:15:12.770 --> 00:15:15.290
before the stars really get going. And you

370
00:15:15.290 --> 00:15:18.010
get two protostars far apart. Both

371
00:15:18.010 --> 00:15:20.610
processes are in the models. Nobody had a

372
00:15:20.610 --> 00:15:23.370
clean example of a third possibility, which

373
00:15:23.370 --> 00:15:25.990
is two separate cores forming

374
00:15:25.990 --> 00:15:28.950
independently that happen to fall past each

375
00:15:28.950 --> 00:15:31.390
other and don't escape a

376
00:15:31.390 --> 00:15:33.670
capture. And that's what this team says

377
00:15:33.670 --> 00:15:36.310
they're watching. The object is IRAS

378
00:15:36.470 --> 00:15:38.090
07299

379
00:15:38.450 --> 00:15:40.950
1651, about

380
00:15:40.950 --> 00:15:43.510
1,680 parsecs away.

381
00:15:43.910 --> 00:15:46.070
Call it five and a half thousand light years.

382
00:15:46.550 --> 00:15:49.230
The work is led by Yi Chen Zhang at Shanghai

383
00:15:49.230 --> 00:15:52.180
Jiaotong University with Guido Garay at the

384
00:15:52.180 --> 00:15:54.660
Universidad uh de Chile. And it's built on

385
00:15:54.660 --> 00:15:57.460
eight years of observations from 2016 to

386
00:15:57.460 --> 00:15:58.300
2024.

387
00:15:58.780 --> 00:16:01.340
Avery: Eight years. What's in the data set?

388
00:16:01.660 --> 00:16:04.460
Anna: ALMA, the Jansky Very Large Array

389
00:16:04.460 --> 00:16:07.420
and JWST. And the picture they

390
00:16:07.420 --> 00:16:10.420
build is two massive protostars about

391
00:16:10.420 --> 00:16:13.340
200 astronomical units apart. So

392
00:16:13.340 --> 00:16:16.340
five times the sun to Pluto distance on a

393
00:16:16.340 --> 00:16:17.980
violently eccentric orbit.

394
00:16:18.510 --> 00:16:20.670
Avery: And the eccentricity is the evidence.

395
00:16:21.230 --> 00:16:23.710
Anna: The eccentricity is half the evidence.

396
00:16:24.190 --> 00:16:26.550
The other half is the discs. Each

397
00:16:26.550 --> 00:16:29.270
protostar has its own and they're tilted with

398
00:16:29.270 --> 00:16:31.590
respect to each other. If these two had

399
00:16:31.590 --> 00:16:34.309
formed from a single fragmenting disc, they'd

400
00:16:34.309 --> 00:16:37.230
share its plane. They don't. They look

401
00:16:37.230 --> 00:16:39.310
like two objects that formed somewhere else

402
00:16:39.390 --> 00:16:42.310
on their own terms and then met on

403
00:16:42.310 --> 00:16:44.910
what the paper calls a parabolic encounter,

404
00:16:45.440 --> 00:16:47.640
which is the astronomer's phrase for a flyby

405
00:16:47.640 --> 00:16:49.680
that was just barely slow enough to end in

406
00:16:49.680 --> 00:16:51.520
capture rather than a miss.

407
00:16:52.000 --> 00:16:54.840
Avery: How do you get captured. Two body gravity

408
00:16:54.840 --> 00:16:56.000
doesn't let you do that.

409
00:16:56.480 --> 00:16:57.200
Anna: It doesn't.

410
00:16:57.520 --> 00:17:00.280
Two bodies on a parabolic path fall past each

411
00:17:00.280 --> 00:17:02.760
other and separate again. You need somewhere

412
00:17:02.760 --> 00:17:05.160
to dump the energy. In this case the

413
00:17:05.160 --> 00:17:07.880
candidates are gas. There's plenty of it in a

414
00:17:07.880 --> 00:17:09.840
star forming core. And drag is very

415
00:17:09.840 --> 00:17:12.450
effective. And the cores themselves which are

416
00:17:12.450 --> 00:17:14.930
not points, they're extended, they're

417
00:17:14.930 --> 00:17:17.810
squishy and they can absorb orbital energy by

418
00:17:17.810 --> 00:17:20.290
deforming. That's the merger part of the

419
00:17:20.290 --> 00:17:21.130
paper's title.

420
00:17:21.450 --> 00:17:23.050
Avery: Southern hemisphere angle.

421
00:17:23.290 --> 00:17:26.090
Anna: It's baked in. The bulk of this is Alma

422
00:17:26.250 --> 00:17:29.010
66 dishes on the Chagnantor Plateau in

423
00:17:29.010 --> 00:17:32.010
northern Chile. 5000 metres up in the

424
00:17:32.010 --> 00:17:34.130
driest desert on Earth. Looking at

425
00:17:34.130 --> 00:17:36.330
wavelengths that only work if there's almost

426
00:17:36.330 --> 00:17:38.880
no water vapour above you. And there's a

427
00:17:38.880 --> 00:17:41.320
Chilean co author on the paper. Which is

428
00:17:41.320 --> 00:17:43.160
exactly how that investment is supposed to

429
00:17:43.160 --> 00:17:45.960
pay off. This is a southern sky object

430
00:17:46.280 --> 00:17:48.640
studied from the southern hemisphere. And the

431
00:17:48.640 --> 00:17:50.760
result is a new way of making the binaries

432
00:17:50.760 --> 00:17:53.000
whose collisions we eventually detect as

433
00:17:53.000 --> 00:17:54.040
gravitational waves.

434
00:17:54.760 --> 00:17:57.600
Avery: Last storey today and it's a progress report

435
00:17:57.600 --> 00:18:00.000
on my favourite mission that nobody has

436
00:18:00.000 --> 00:18:02.840
launched yet. Anna Dragonfly

437
00:18:02.840 --> 00:18:04.040
in one sentence.

438
00:18:04.670 --> 00:18:07.070
Anna: A nuclear powered eight rotor helicopter

439
00:18:07.390 --> 00:18:10.070
about the size of a small car that will fly

440
00:18:10.070 --> 00:18:12.030
around on Saturn's moon Titan.

441
00:18:12.350 --> 00:18:14.630
Avery: Which sounds absurd until you look at the

442
00:18:14.630 --> 00:18:17.470
numbers. Titan's air at the surface is

443
00:18:17.470 --> 00:18:20.389
about four times as dense as ours and the

444
00:18:20.389 --> 00:18:23.030
gravity is about 1/7 thick

445
00:18:23.030 --> 00:18:26.030
air, weak gravity. It is the easiest

446
00:18:26.030 --> 00:18:28.910
place in the solar system to fly. A person

447
00:18:28.910 --> 00:18:31.430
in a decent set of strapped on wings could

448
00:18:31.430 --> 00:18:32.030
manage it.

449
00:18:32.590 --> 00:18:33.470
Anna: So what's the news?

450
00:18:33.790 --> 00:18:36.590
Avery: Two things both from NASA and Johns

451
00:18:36.590 --> 00:18:39.230
Hopkins APL on 2 September.

452
00:18:39.710 --> 00:18:42.550
The first is an assembly milestone. Back in

453
00:18:42.550 --> 00:18:44.790
July the team installed the harness on the

454
00:18:44.790 --> 00:18:47.670
flight fuselage. The harness is the

455
00:18:47.670 --> 00:18:50.350
wiring. Every cable that connects every

456
00:18:50.350 --> 00:18:53.150
instrument, every rotor, every computer.

457
00:18:53.470 --> 00:18:55.990
It's the vehicle's nervous system. And it's

458
00:18:55.990 --> 00:18:58.030
one of those steps that isn't glamorous but.

459
00:18:58.180 --> 00:19:00.340
But does mark the transition from building

460
00:19:00.340 --> 00:19:03.100
parts to building a spacecraft. And the

461
00:19:03.100 --> 00:19:05.700
second, the landing area has a name.

462
00:19:06.020 --> 00:19:08.700
The International Astronomical Union has

463
00:19:08.700 --> 00:19:11.460
approved Amaqeek Undae for the dune field

464
00:19:11.460 --> 00:19:13.380
where Dragonfly will touch down.

465
00:19:14.020 --> 00:19:16.820
Undae is just the IAU's Latin term

466
00:19:16.820 --> 00:19:19.820
for dunes. Amakique comes from Mayan

467
00:19:19.820 --> 00:19:22.140
tradition. It's a name for a protective

468
00:19:22.140 --> 00:19:24.220
deity. And the meaning given in the

469
00:19:24.220 --> 00:19:26.610
announcement is. Is one who locks up the wind

470
00:19:27.170 --> 00:19:28.530
Anna: for a mission that flies.

471
00:19:29.010 --> 00:19:31.570
Avery: For a mission whose entire existence depends

472
00:19:31.570 --> 00:19:34.490
on air moving over rotors. Titan's

473
00:19:34.490 --> 00:19:36.890
dune fields are named after wind gods by

474
00:19:36.890 --> 00:19:39.730
convention. So it's a legitimate naming, but

475
00:19:39.730 --> 00:19:42.290
you could not have scripted it better. The

476
00:19:42.290 --> 00:19:44.530
field is about 500 miles across,

477
00:19:45.010 --> 00:19:47.970
800 kilometres, and it sits just south

478
00:19:47.970 --> 00:19:49.090
of Selk crater.

479
00:19:49.490 --> 00:19:51.890
Anna: And Selk is the destination that actually

480
00:19:51.970 --> 00:19:53.250
matters scientifically.

481
00:19:53.950 --> 00:19:56.430
Avery: Selk is the prize. It's an impact

482
00:19:56.510 --> 00:19:59.110
crater. And an impact on Titan means

483
00:19:59.110 --> 00:20:01.830
heat enough to melt water ice into

484
00:20:01.830 --> 00:20:04.750
liquid water and hold it liquid for a while.

485
00:20:05.310 --> 00:20:07.870
Titan has liquid water underneath as an

486
00:20:07.870 --> 00:20:10.750
ocean and complex organic chemistry on

487
00:20:10.750 --> 00:20:13.390
the surface in the form of those dunes which

488
00:20:13.390 --> 00:20:16.030
are made of organic sand, not silicate

489
00:20:16.030 --> 00:20:18.830
sand. What Selk gives you is a place where

490
00:20:18.830 --> 00:20:21.630
those two things were mixed together. Liquid

491
00:20:21.630 --> 00:20:24.590
water and complex organics in the same place

492
00:20:24.590 --> 00:20:27.550
at the same time. That is the setup for

493
00:20:27.550 --> 00:20:30.470
prebiotic chemistry. And Dragonfly is

494
00:20:30.470 --> 00:20:32.710
designed to fly from the dunes to the crater

495
00:20:32.710 --> 00:20:35.150
and sample both. Timeline

496
00:20:35.550 --> 00:20:37.950
launch in the summer of 2028,

497
00:20:38.350 --> 00:20:40.990
arrival at Titan in late 2034,

498
00:20:41.390 --> 00:20:44.230
and a 3.3 year primary mission after

499
00:20:44.230 --> 00:20:46.670
that. So this is a long game.

500
00:20:47.160 --> 00:20:49.240
If you're listening to this and you're in

501
00:20:49.240 --> 00:20:51.720
high school, you'll be well into your career

502
00:20:51.720 --> 00:20:53.560
before Dragonfly lands.

503
00:20:53.960 --> 00:20:56.520
Anna: And there's an Australian footnote to Titan.

504
00:20:57.000 --> 00:20:59.640
Avery: There is. When Huygens descended through

505
00:20:59.640 --> 00:21:01.240
Titan's atmosphere in January

506
00:21:01.560 --> 00:21:04.200
2005, one of its two data

507
00:21:04.200 --> 00:21:06.640
channels failed. And a, uh, set of radio

508
00:21:06.640 --> 00:21:09.240
telescopes on Earth, including Parkes,

509
00:21:09.400 --> 00:21:11.560
listened directly for the probe's faint

510
00:21:11.560 --> 00:21:14.110
carrier tone to, to reconstruct its descent.

511
00:21:14.590 --> 00:21:17.510
Titan sits low in the northern sky from here

512
00:21:17.510 --> 00:21:20.270
now, but when Dragonfly starts sending,

513
00:21:20.430 --> 00:21:22.550
southern dishes will be part of how we hear

514
00:21:22.550 --> 00:21:22.830
it.

515
00:21:23.310 --> 00:21:26.110
Anna: And that brings us to the sky and North

516
00:21:26.110 --> 00:21:28.150
America. This one is yours. And it is

517
00:21:28.150 --> 00:21:29.550
happening this afternoon.

518
00:21:29.950 --> 00:21:32.430
Avery: The moon occults, uh, Jupiter in

519
00:21:32.430 --> 00:21:33.150
daylight.

520
00:21:33.150 --> 00:21:36.110
Anna: In daylight, the Moon passes in front of

521
00:21:36.110 --> 00:21:38.680
Jupiter and blots it out. It, it's visible

522
00:21:38.680 --> 00:21:41.000
across most of the continental United States.

523
00:21:41.320 --> 00:21:43.040
The exception is California and the

524
00:21:43.040 --> 00:21:45.560
southwestern states, plus Canada, the

525
00:21:45.560 --> 00:21:48.240
Caribbean, Greenland, most of Alaska and

526
00:21:48.240 --> 00:21:51.120
eastern Siberia for most of the lower

527
00:21:51.120 --> 00:21:54.040
48. It happens in the early to mid afternoon.

528
00:21:54.600 --> 00:21:57.160
Avery: And the moon is a 7% crescent

529
00:21:57.320 --> 00:21:59.960
about 30 degrees from the sun, which

530
00:21:59.960 --> 00:22:02.320
Anna: is what makes it both wonderful and genuinely

531
00:22:02.320 --> 00:22:04.840
hazardous. So let's do the safety properly.

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00:22:05.330 --> 00:22:07.250
You are pointing binoculars into a bright

533
00:22:07.250 --> 00:22:09.490
blue sky within 30 degrees of the sun.

534
00:22:10.050 --> 00:22:12.490
Never sweep binoculars or a telescope near

535
00:22:12.490 --> 00:22:15.210
the sun. Put a solid object between you and

536
00:22:15.210 --> 00:22:17.970
it, the corner of a building, the eaves of a

537
00:22:17.970 --> 00:22:20.570
roof, so the sun is physically blocked before

538
00:22:20.570 --> 00:22:23.250
you raise the glass. Do not look for the Moon

539
00:22:23.250 --> 00:22:26.170
by scanning across. Find it first with the

540
00:22:26.170 --> 00:22:26.930
sun hidden,

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00:22:27.090 --> 00:22:29.770
Avery: then hold your position and the Eye

542
00:22:29.770 --> 00:22:30.770
safety standard.

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00:22:31.310 --> 00:22:33.110
Anna: The standard for looking anywhere near the

544
00:22:33.110 --> 00:22:34.750
sun is ISO

545
00:22:34.750 --> 00:22:37.790
123122.

546
00:22:38.270 --> 00:22:40.670
That's the specification for solar viewers

547
00:22:40.670 --> 00:22:43.550
and eclipse glasses. Sunglasses do not

548
00:22:43.550 --> 00:22:46.270
meet it, smoked glass does not meet it, and

549
00:22:46.270 --> 00:22:49.230
exposed film does not meet it. And a filter

550
00:22:49.230 --> 00:22:51.110
of any kind belongs on the front of a

551
00:22:51.110 --> 00:22:53.750
telescope or binoculars, never on the

552
00:22:53.750 --> 00:22:56.630
eyepiece end. This is a daytime event next to

553
00:22:56.630 --> 00:22:59.010
the sun and it deserves the same discipline

554
00:22:59.010 --> 00:22:59.890
as an eclipse.

555
00:23:00.450 --> 00:23:02.530
Avery: Once you're on it, what do you see?

556
00:23:02.930 --> 00:23:05.370
Anna: Jupiter takes somewhere between one and three

557
00:23:05.370 --> 00:23:07.330
minutes to slide behind the bright edge of

558
00:23:07.330 --> 00:23:09.730
the crescent and about the same to come back

559
00:23:09.730 --> 00:23:12.410
out. And it reappears from the dark limb,

560
00:23:12.410 --> 00:23:14.770
which is the better half of the show because

561
00:23:14.770 --> 00:23:17.450
the planet just materialises out of empty sky

562
00:23:17.450 --> 00:23:19.090
with nothing visible next to it.

563
00:23:19.490 --> 00:23:21.490
Avery: And, um, this is the warm up act.

564
00:23:21.970 --> 00:23:24.920
Anna: Indeed it is. Sky and Telescope are billing

565
00:23:24.920 --> 00:23:27.840
the 6 October occultation as the one

566
00:23:27.840 --> 00:23:30.760
to wait for. That one's before dawn in a dark

567
00:23:30.760 --> 00:23:33.520
sky. And it will be the more spectacular of

568
00:23:33.520 --> 00:23:36.120
the pair by a distance. Consider today the

569
00:23:36.120 --> 00:23:38.320
rehearsal southern hemisphere.

570
00:23:38.560 --> 00:23:41.240
Avery: You don't get this afternoon's event, what do

571
00:23:41.240 --> 00:23:41.680
you get?

572
00:23:42.000 --> 00:23:44.800
Anna: You get the best part of the year. Still from

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00:23:44.800 --> 00:23:47.040
Sydney, the centre of the galaxy is close to

574
00:23:47.040 --> 00:23:49.880
overhead as darkness falls. Scorpius and

575
00:23:49.880 --> 00:23:52.600
Sagittarius up high. The Milky Way running

576
00:23:52.600 --> 00:23:55.160
the length of the sky. And it's drifting west

577
00:23:55.160 --> 00:23:57.800
a little more each night. So this is the run

578
00:23:57.800 --> 00:24:00.480
out of the season. And New Moon falls on the

579
00:24:00.480 --> 00:24:03.160
11th at 27 minutes past 3

580
00:24:03.160 --> 00:24:06.160
UTC, which means the week either side of it

581
00:24:06.160 --> 00:24:08.680
is properly dark. If you're going to get out

582
00:24:08.680 --> 00:24:10.960
of town for one night this month, make it

583
00:24:10.960 --> 00:24:11.480
that week.

584
00:24:11.880 --> 00:24:13.080
Avery: Planets for the south.

585
00:24:13.160 --> 00:24:15.720
Anna: Venus low in the west after sunset.

586
00:24:16.310 --> 00:24:19.150
And it builds to greatest Brilliancy on the

587
00:24:19.150 --> 00:24:21.310
18th at magnitude

588
00:24:21.310 --> 00:24:24.230
-4.8. You'll see

589
00:24:24.230 --> 00:24:27.030
the 22nd quoted elsewhere. That's a different

590
00:24:27.030 --> 00:24:29.630
definition of the same event. And we're using

591
00:24:29.630 --> 00:24:32.310
the 18th. Saturn is up in the

592
00:24:32.310 --> 00:24:34.990
northeast by about 9 o' clock and it's the

593
00:24:34.990 --> 00:24:37.898
storey of the next month opposition on 4

594
00:24:38.002 --> 00:24:40.870
October. And the rings have opened back up to

595
00:24:40.870 --> 00:24:43.850
around 7 degrees, which after the near edge

596
00:24:43.850 --> 00:24:45.850
on view of last year, is a genuine

597
00:24:45.850 --> 00:24:48.650
improvement in a small telescope. And the

598
00:24:48.650 --> 00:24:50.850
Harvest Moon rides past Saturn at the end of

599
00:24:50.850 --> 00:24:53.490
the month. The 26th in the Americas,

600
00:24:53.890 --> 00:24:55.170
the 27th here.

601
00:24:55.170 --> 00:24:56.130
Avery: Morning sky.

602
00:24:56.530 --> 00:24:58.890
Anna: Both hemispheres get Jupiter and Mars before

603
00:24:58.890 --> 00:25:01.490
dawn. Jupiter unmistakable,

604
00:25:01.730 --> 00:25:04.290
closing on Regulus by mid month. And Mars

605
00:25:04.290 --> 00:25:06.690
fainter up near Castor and Pollux.

606
00:25:07.090 --> 00:25:09.450
And the equinox lands on the 23rd of

607
00:25:09.450 --> 00:25:12.200
September at 6 minutes past 12am in M

608
00:25:12.330 --> 00:25:14.970
UTC. That's 10 past 10 on the Wednesday

609
00:25:14.970 --> 00:25:17.890
morning in Sydney and 6 minutes past 8 on the

610
00:25:17.890 --> 00:25:20.490
Tuesday evening in New York. Spring for us,

611
00:25:20.730 --> 00:25:21.770
autumn for the north.

612
00:25:21.850 --> 00:25:24.090
Avery: And that's Astronomy daily for Tuesday,

613
00:25:24.170 --> 00:25:24.970
8

614
00:25:24.970 --> 00:25:27.250
Anna: September a moon that may have been built in

615
00:25:27.250 --> 00:25:30.090
five hours instead of five centuries, eight

616
00:25:30.090 --> 00:25:32.130
black holes that outgrew their galaxies and

617
00:25:32.130 --> 00:25:34.690
haven't stopped eating, two massive stars

618
00:25:34.690 --> 00:25:37.330
that fell past each other and got caught, and

619
00:25:37.330 --> 00:25:39.960
a helicopter for Titan that now has both its

620
00:25:39.960 --> 00:25:41.320
wiring and an address.

621
00:25:41.640 --> 00:25:43.880
Avery: Every paper and release we've mentioned is

622
00:25:43.880 --> 00:25:46.280
linked in the show notes, along with the full

623
00:25:46.280 --> 00:25:47.560
episode transcript.

624
00:25:47.560 --> 00:25:50.200
Anna: That's astronomydaily IO the whole back

625
00:25:50.200 --> 00:25:52.040
catalogue is there, plus the newsletter if

626
00:25:52.040 --> 00:25:54.360
you'd rather read it, and the contact form if

627
00:25:54.360 --> 00:25:56.520
you want to ask us something. We do read

628
00:25:56.520 --> 00:25:58.240
them, and they've been shaping segments

629
00:25:58.240 --> 00:25:58.680
lately.

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00:25:59.000 --> 00:26:01.880
Avery: You'll find us on X, at astrodaily Pod

631
00:26:02.040 --> 00:26:04.810
and wherever you get your podcasts. A

632
00:26:04.810 --> 00:26:07.570
rating genuinely helps other people find us.

633
00:26:08.130 --> 00:26:10.730
Anna: We're back tomorrow. Until then, clear skies

634
00:26:10.730 --> 00:26:13.130
and North America. Be careful out there this

635
00:26:13.130 --> 00:26:13.730
afternoon.

636
00:26:14.050 --> 00:26:16.370
Avery: Clear skies, everyone. See you tomorrow.