Reading Io’s Hidden Heat: Juno’s First Subsurface Reading | Today’s Space News

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Anna: On the most volcanic world on the solar

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system, hundreds of erupting mountains have

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been hurling light and heat into space

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as long as we've been able to watch.

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Avery: But that's the surface underneath. In the

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first few meters of crust, there was a

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temperature nobody had ever actually

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measured.

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Anna: Until a spacecraft built to study

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Jupiter's clouds pointed its instrument

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down at a moon and read the heat

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beneath the ground.

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Avery: Welcome to Astronomy Daily.

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Anna: Hello and welcome to Astronomy daily

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for Tuesday, the 28th of July,

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2026. I'm Anna.

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Avery: And I'm Avery. Whether you're under southern

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skies here in Australia and New Zealand, or

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across North America and the rest of the

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Northern Hemisphere, good day and good

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evening wherever this finds you.

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Anna: Big show. Today, our lead takes us to

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IO, Jupiter's fiery moon, and a

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genuine first, the temperature below its

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surface surface. Then two cosmic puzzles

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that might turn out to be the same puzzle. A

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fresh way to hunt for alien signals and

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a burst of space weather arriving at Earth

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just about now.

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Avery: Plus a, uh, skywatch with meteor showers

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peaking all week. Though the moon has other

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ideas. Let's get into it.

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Anna: So let's start with the star of the show, and

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it's a moon, IO, Jupiter's

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innermost large moon and the most

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volcanically active body in the entire

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solar system. If you've seen the pictures,

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it's that slightly unsettling pizza

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colored world. Yellows, oranges,

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sulfur reds, blotched with hundreds of

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volcanoes, some of them throwing plumes

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hundreds of kilometers into space.

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Avery: It's genuinely hard to overstay how active

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IO is. More than 400 active

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volcanoes, lava lakes, the works.

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Per square meter, it pumps out many times

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more heat than Earth does.

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Anna: And that's the puzzle at the heart of today's

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story. All that volcanism is powered by

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something called tidal heating. IO

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orbits Jupiter on a slightly stretched

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elliptical path. And Jupiter's enormous

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gravity is constantly squeezing and

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flexing the moon, like bending a paperclip

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back and forth until it warms up, except on

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a planetary scale. And forever.

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Avery: Flex a paperclip fast enough, it gets hot in

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your fingers. IO is that paperclip. And

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Jupiter never stops bending it.

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Anna: Exactly. But here's the thing. For

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all the decades we've studied IO, almost

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everything we knew about that heat came from

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looking at the surface infrared cameras,

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which read the temperature of the very top

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layer. What we'd never done, what

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nobody had ever done for a rocky world other

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than Earth, it is measure the temperature

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below the surface under the ground.

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Avery: And that's exactly what NASA's Juno

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spacecraft just did.

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Anna: It is. Juno has been orbiting

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Jupiter since 2016, and it made

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two very close passes of IO in

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late December 2023 and early

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February 2024, sweeping within

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about 1500 kilometers, roughly

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930 miles of the surface.

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And on both passes, it used an instrument

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called the Microwave Radiometer.

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MWR for short.

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Avery: And this is the part I love, because that

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instrument was never designed to do this. The

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MWR was built to look down through Jupiter's

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thick clouds and read the giant planet's

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atmosphere at different depths. It has six

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antennas, each tuned to a different

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wavelength.

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Anna: And that multi wavelength design turns

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out to be the whole trick. Different

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wavelengths of microwave energy escape from

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different depths. So if you point that

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instrument at solid ground instead of cloud,

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each channel is effectively reading the

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temperature at a slightly different depth

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below the surface, all at once, all

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from orbit, using nothing but the natural

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heat the crust is already giving off.

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Avery: So it's like a thermometer that reads several

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depths at the same time without ever touching

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the ground.

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Anna: That's a lovely way to put it. And what did

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it find? Within just the first few meters of

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crust, the temperature climbs by more than 20

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degrees Celsius over 40 Fahrenheit.

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That might not sound dramatic, but for a

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world whose surface sits at around minus

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143 Celsius, a rise

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that steep, that shallow, tells you there's

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serious heat welling up from below.

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Avery: Put a number on it. How much heat are we

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talking?

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Anna: The team estimates a heat flow of roughly 1

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to 3 watts per square meter, up to about

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30 times Earth's global average, seeping

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up through the top 10 meters or so of crust,

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most likely from a mix of that tidal heating

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and lava still cooling underground.

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Avery: 30 times Earth's average welling up through

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the ground. That's the engine of all those

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volcanoes caught in the act.

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Anna: And there was a second surprise in the same

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data. The MWR also showed that most of

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IO's surface is remarkably smooth and made

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of very low density material, which fits a

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world that's constantly repaving itself with

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fresh volcanic deposits, burying its own

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craters almost as fast as they form.

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Avery: Now the study is in the Journal of

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Geophysical Research Planets, led by Shannon

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Brown at JPL. And NASA put it out on the

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22nd. But, Anna, uh, I think the really big

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deal here might not even be IO itself. It's

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the method.

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Anna: I completely agree. This is the first time

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anyone has read a subsurface temperature

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profile of a rocky body from orbit. And

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that technique doesn't care whether the World

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is fiery or frozen. Point it at an icy

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moon, Europa Enceladus, and in principle,

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you could sense the warmth of an ocean

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beneath the ice or work out how thick that

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ice actually is.

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Avery: Which is precisely the question those

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missions are built to answer. Europa Clipper

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is already on its way

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Anna: and it gets better and closer to home. Juno's

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principal investigator, Scott Bolton, pointed

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out that you could fly an MWR type instrument

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over a volcano here on Earth and read the

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same kind of subsurface temperature gradient.

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A whole new way to study our own volcanoes

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from the air.

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Avery: So an instrument built for Jupiter's clouds

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ends up potentially rewriting how we study

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volcanoes on Earth. That's the kind of

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accidental genius that makes me love this

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stuff.

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Anna: It's the story of exploration in miniature,

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isn't it? You build a tool for one job, you

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point it somewhere new and it hands you a

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capability nobody planned for. IO got its

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first ever subsurface reading and we got a

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new way to take the temperature of worlds.

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Avery: Ours included a fitting lead. And keep

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IO in your back of your mind, because Jupiter

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itself is going to come back around in our

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skywatch in a slightly surprising way.

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Anna: Ooh, a, uh, tease. Alright. From a moon

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on fire to something at the very edge of what

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we can see.

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Avery: Now onto story two.

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JWST's little red

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dots. So, Anna, set us up nicely to the

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deep early universe. One of the strangest

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things the James Webb's telescope has turned

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up since it started sending back data in 2022

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is a whole population of objects

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nicknamed little red dots.

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Anna: I love that they just called them what they

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look like.

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Avery: Astronomers are refreshingly literal.

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Sometimes they're exactly that. Tiny,

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intensely red, compact points of light.

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And they're ancient. They show up around 600

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million years after the Big Bang. And then

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here's the weird part. They seem to vanish by

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the time the universe is about a billion and

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a half years old. Nobody's been sure what

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they even are. Supermassive black holes

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wrapped in gas bursts of furious star

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formation. Something else entirely.

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Anna: And there's a new answer this week.

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Avery: A new idea, and it's a clever one. A team led

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by John Chisum at the University of Texas at

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Austin, published in the Astrophysical

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Journal Letters, suggests the little red dots

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might be globular clusters caught in the act

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of being born.

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Anna: Globular clusters, those dense, ancient

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balls of hundreds of thousands of stars that

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hang around the outskirts of galaxies like

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ours.

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Avery: Those exact things, around 150 of them,

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orbit the Milky Way. And their origin has

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been its own long standing mystery. So this

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paper does something elegant. It takes two

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puzzles. What are little red dots? And where

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do globular clusters come from? Ann proposes

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they're the same puzzle that the little red

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dots are simply what globular clusters look

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like while they were forming.

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Anna: Two birds, one stone.

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Avery: That's exactly the phrase the researchers

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reach for in the model. A, uh, young cluster

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of stars supplies the blue ultraviolet light.

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And a single short lived, absolutely

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colossal star at the center, a

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supermassive star tens of thousands of

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times the Sun's mass, supplies the red.

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And crucially, it predicts specific chemical

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fingerprints, unusual amounts of helium and

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nitrogen, the very oddities we already see in

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the stars of today's globular clusters.

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Anna: So the test is in the chemistry.

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Avery: The test is in the chemistry and the team is

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careful about it. Co author Mike Boylan

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Kolchin put it. Well, there's no single

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smoking gun yet. But this would explain a lot

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of surprising observations at once. They're

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calling it plausible and laying out ways to

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stress test it.

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Anna: There's a lovely framing. I saw that these

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might be, uh, cosmic dinosaurs that never

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actually went extinct.

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Avery: That's the one we used to think the

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dinosaurs simply vanished. Then we

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realized they became birds. The suggestion

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here is that the little red dots didn't

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disappear either. They grew up into the

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globular clusters. You can still point a

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backyard telescope at tonight. The strange

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early universe. And the familiar one might be

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far more connected than we thought.

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Anna: From the oldest starlight to possibly

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no starlight at all.

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Because the next one is all about listening.

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For more than 60 years, the Search for

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Extraterrestrial Intelligence, SETI has

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mostly listened in one narrow stretch of the

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radio dial, a band between about

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1.4 and 1.7 gigahertz

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that astronomers call the water hole.

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Avery: Why there?

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Anna: Two reasons. It's a naturally quiet part of

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the spectrum and it sits right between the

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frequencies given off by hydrogen and by

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hydroxyl, the two pieces that together make

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water. The romantic idea is that any water

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based civilization might recognize it as

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an obvious meeting place. A, ah, cosmic

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watering hole.

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Avery: Poetic, but maybe a touch assumption

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heavy.

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Anna: That's exactly the point a young researcher

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has just made. Louisa Mason, a PhD

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student at the University of Manchester,

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presented work at the Royal Astronomical

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Society's National Astronomy meeting, arguing

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we might be listening on the wrong channel

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entirely. And rather than ask for expensive

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new telescope time, she did something smart.

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She went digging in the archives.

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Avery: Old data.

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Anna: Old data from Alma, that enormous array of

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dishes up on the chajenant plateau In Chile,

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which observes at much higher millimeter and

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submillimeter frequencies that SETI has

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barely touched. She ran the first ever

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SETI search through archived ALMA

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observations, hunting for narrow artificial

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looking signals.

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Avery: Um, and did she find E.T.

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Anna: she did not. No technosignatures, which is

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the honest and entirely expected result from

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just four archived observations. But here's

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the finding that made me sit up when she

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properly modeled how many stars were sitting

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in the background of those observations.

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Stars caught in the frame. While ALMA was

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pointed at something else. The count jumped

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from a previous estimate of around

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288,000 stars

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to more than six million.

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Avery: Six million. Just from recounting what was

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already there.

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Anna: More than six million. She calls it

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stellar bycatch. All the stars you

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survey by accident every single time you

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point a big telescope anywhere. It

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means archives around the world may already

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hold a vastly larger SETI survey

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than anyone realized, hiding inside data

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gathered for complet completely different

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reasons.

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Avery: I love that you don't always need a bigger

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net. Sometimes you just need to count what

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you've already caught.

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Anna: Beautifully put. New frequencies and

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millions of free stars. Not a bad

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afternoon's work.

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And speaking of signals arriving, there's one

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headed for Earth right now.

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Avery: And this one's live unfolding as we record

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our own star has been rustless. There's an

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active region on the sun cataloged as region

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4494. And on the 26th

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it let off a moderate flare. An M M class

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flare. An M M3.2 to be exact.

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Anna: M class being middle of the road as

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flares go.

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Avery: Moderate, yes, below the big X class

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monsters, but nothing to sneeze at. And

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separately, a cloud of solar material. A, uh,

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coronal mass ejection launched back on the

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24th is due to give Earth a glancing

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blow right about now.

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Anna: A glancing blow. So not a direct

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hit.

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Avery: Not a direct hit, which is the good news. But

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even a side wipe can rattle our magnetic

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field. Forecasters are calling for G1,

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possibly nudging up to G2

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geomagnetic storm levels across the

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27th and 28th. And the fun part for

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us is what that does to the sky. Aurorae.

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Anna: Uh, aurorae.

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Avery: When that solar material meets the magnetic

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field, it funnels particles down over the

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poles and lights up the atmosphere. The

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southern lights, the Aurora Australis for our

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listeners down here. And the northern lights

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up top at, uh, G1 to G2, we're

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mostly talking higher latitudes. So

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Tasmania and the deep south of New Zealand

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have the better odds. Here up north, think

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Scotland, Scandinavia and the northern tier

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of the US and Canada.

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Anna: And I should say space weather moves fast.

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By the time you're hearing this, the numbers

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may well have shifted.

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Avery: Good caveat. So if you're keen, check the

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live alerts, the Space Weather Prediction

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center or the Bureau of Meteorology's Space

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Weather Service here in Australia for the

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current picture. But it's worth a glance at

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the southern horizon tonight because the sun

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may just have laid on a show.

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Anna: A perfect handover because it's time to look

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up.

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Skywatch. Though this is meteor week

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in theory, we've got a run of showers

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peaking over the next few nights. The July

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Gamma Draconids tonight, the Pisces

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Austrianids around the 28th and 29th. And

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then the big one for us, the Southern Delta

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Aquarids, building to their peak around the

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30th, alongside the alpha capricornids

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on the 30th and 31st.

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Avery: And in theory being the operative phrase,

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because there's a giant obstacle rising in

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the east.

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Anna: The Moon. The Full Buck Moon lands on the

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29th, and a nearly full moon all week

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is going to flood the sky with light and wash

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out most of these meteors, which tend to be

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on the faint side to begin with.

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Avery: So is it a write off?

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Anna: Not at all. You just have to be smart about

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it first. The Southern Delta Aquariids

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genuinely favor us. In the south, the

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radiant over near the star Skat in

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Aquarius climbs high overhead from southern

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latitudes. Which is exactly why this is so

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often the Southern hemisphere's best shower

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of the year. Though for our listeners in

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Australia and New Zealand, look after

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midnight into the pre dawn hours when that

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radiant is highest.

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Avery: And um, for the Northern hemisphere, for

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Anna: North America and other northern listeners,

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the radiant sits lower in the southern sky.

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But the southern United States, Mexico and

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Southern Europe still get a decent view. Same

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advice. The hours after midnight local time

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into the couple of hours before dawn are your

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best window. And face south.

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Avery: And here's the pro tip that beats the Moon.

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The Alpha Capricornids. They're not

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numerous, only a handful an hour. But they're

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famous for slow, bright, colorful

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fireballs. And a fireball doesn't care about

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moonlight. So even in a bright week, one

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brilliant, lazy Alpha Capricornid drifting

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across the sky is worth the wait. North or

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south?

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Anna: Lovely. And if the meteors do get washed out,

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there are planets to fall back on in the

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evening. Low in the west after sunset, Venus

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is blazing away, unmistakable. And climbing

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a little higher each night as it heads for

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00:16:40.820 --> 00:16:42.620
its best evening showing in August.

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Avery: And, um, the morning sky.

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Anna: The morning belongs to Saturn. Golden well up

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in the pre dawn sky. And it actually paused

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in its motion against the background stars

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this week. Mars is climbing higher before

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dawn too. And if you've got a clear flat

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horizon, elusive Mercury is making a

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low pre dawn appearance in the last days of

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the month.

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Avery: And one that ties us right back to where we

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started. Jupiter.

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Anna: Yes, here's the lovely irony. We

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opened the show at IO, a moon of Jupiter. But

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Jupiter itself as just slipped behind the

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sun. It reaches solar conjunction on the

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29th, essentially lined up on the far side

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of our star. So the very planet whose moon

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we spent our whole lead story on is the one

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planet you can't actually see in the sky

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right now.

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Avery: The moon. We can study up close. The planet

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we've temporarily lost space has a sense of

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humor.

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Anna: It'll be back in the morning sky in late

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August. And one last one for our northern

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00:17:36.530 --> 00:17:38.690
friends before we go. Look straight up after

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dark and you'll find the summer triangle.

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00:17:40.930 --> 00:17:43.490
Vega, uh, Deneb, uh, and Altair riding high

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00:17:43.490 --> 00:17:46.090
overhead, a reliable anchor on a moonlit

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night.

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Avery: North or south, there's always something up

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there.

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Anna: And that's our show for Tuesday, A first look

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00:17:51.410 --> 00:17:53.530
beneath the skin of the solar system's most

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volcanic moon. Two cosmic mysteries that

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00:17:56.210 --> 00:17:58.770
might be one. A fresh way to listen for

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00:17:58.770 --> 00:18:01.050
company, and a burst of weather from our own

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00:18:01.050 --> 00:18:01.410
star.

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00:18:01.410 --> 00:18:03.300
Avery: If you enjoyed it, find. Follow Astronomy

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00:18:03.300 --> 00:18:05.580
Daily wherever you get your podcasts and find

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00:18:05.580 --> 00:18:08.300
our new website@astronomydaily,IO

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00:18:08.300 --> 00:18:10.900
and on the socials strodaily

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00:18:10.900 --> 00:18:12.340
pod. We're back tomorrow.

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Anna: Until then, from Avery and me, keep looking

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up.

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Avery: Clear skies.

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Sam. Hmm.