What temperature changes did Juno detect beneath Io's surface?

Juno detected a temperature rise of over 20°C within a few meters of the surface, with heat flow reaching approximately 30 times Earth's average heat flow.

What space weather events occurred around the episode date?

An M3.2 solar flare from region AR4494 occurred on July 26, followed by a glancing CME on July 24, with G1–G2 geomagnetic storms and possible auroras expected on July 27–28.

What astronomical events were visible during the skywatch period?

The full Buck Moon occurred on July 29, with the Southern Delta Aquariids and Alpha Capricornids meteor showers peaking around July 30–31, plus evening Venus and pre-dawn Saturn, Mars, and Mercury visible.

What did the ALMA SETI survey find?

The first SETI survey of archived ALMA data opened the millimeter band for SETI searches and identified 6.1 million background stars as incidental detections.

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

Anna: On the most volcanic world on the solar

system, hundreds of erupting mountains have

been hurling light and heat into space

as long as we've been able to watch.

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

first few meters of crust, there was a

temperature nobody had ever actually

measured.

Anna: Until a spacecraft built to study

Jupiter's clouds pointed its instrument

down at a moon and read the heat

beneath the ground.

Avery: Welcome to Astronomy Daily.

Anna: Hello and welcome to Astronomy daily

for Tuesday, the 28th of July,

2026. I'm Anna.

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

skies here in Australia and New Zealand, or

across North America and the rest of the

Northern Hemisphere, good day and good

evening wherever this finds you.

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

IO, Jupiter's fiery moon, and a

genuine first, the temperature below its

surface surface. Then two cosmic puzzles

that might turn out to be the same puzzle. A

fresh way to hunt for alien signals and

a burst of space weather arriving at Earth

just about now.

Avery: Plus a, uh, skywatch with meteor showers

peaking all week. Though the moon has other

ideas. Let's get into it.

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

it's a moon, IO, Jupiter's

innermost large moon and the most

volcanically active body in the entire

solar system. If you've seen the pictures,

it's that slightly unsettling pizza

colored world. Yellows, oranges,

sulfur reds, blotched with hundreds of

volcanoes, some of them throwing plumes

hundreds of kilometers into space.

Avery: It's genuinely hard to overstay how active

IO is. More than 400 active

volcanoes, lava lakes, the works.

Per square meter, it pumps out many times

more heat than Earth does.

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

story. All that volcanism is powered by

something called tidal heating. IO

orbits Jupiter on a slightly stretched

elliptical path. And Jupiter's enormous

gravity is constantly squeezing and

flexing the moon, like bending a paperclip

back and forth until it warms up, except on

a planetary scale. And forever.

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

your fingers. IO is that paperclip. And

Jupiter never stops bending it.

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

all the decades we've studied IO, almost

everything we knew about that heat came from

looking at the surface infrared cameras,

which read the temperature of the very top

layer. What we'd never done, what

nobody had ever done for a rocky world other

than Earth, it is measure the temperature

below the surface under the ground.

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

spacecraft just did.

Anna: It is. Juno has been orbiting

Jupiter since 2016, and it made

two very close passes of IO in

late December 2023 and early

February 2024, sweeping within

about 1500 kilometers, roughly

930 miles of the surface.

And on both passes, it used an instrument

called the Microwave Radiometer.

MWR for short.

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

instrument was never designed to do this. The

MWR was built to look down through Jupiter's

thick clouds and read the giant planet's

atmosphere at different depths. It has six

antennas, each tuned to a different

wavelength.

Anna: And that multi wavelength design turns

out to be the whole trick. Different

wavelengths of microwave energy escape from

different depths. So if you point that

instrument at solid ground instead of cloud,

each channel is effectively reading the

temperature at a slightly different depth

below the surface, all at once, all

from orbit, using nothing but the natural

heat the crust is already giving off.

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

depths at the same time without ever touching

the ground.

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

it find? Within just the first few meters of

crust, the temperature climbs by more than 20

degrees Celsius over 40 Fahrenheit.

That might not sound dramatic, but for a

world whose surface sits at around minus

143 Celsius, a rise

that steep, that shallow, tells you there's

serious heat welling up from below.

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

talking?

Anna: The team estimates a heat flow of roughly 1

to 3 watts per square meter, up to about

30 times Earth's global average, seeping

up through the top 10 meters or so of crust,

most likely from a mix of that tidal heating

and lava still cooling underground.

Avery: 30 times Earth's average welling up through

the ground. That's the engine of all those

volcanoes caught in the act.

Anna: And there was a second surprise in the same

data. The MWR also showed that most of

IO's surface is remarkably smooth and made

of very low density material, which fits a

world that's constantly repaving itself with

fresh volcanic deposits, burying its own

craters almost as fast as they form.

Avery: Now the study is in the Journal of

Geophysical Research Planets, led by Shannon

Brown at JPL. And NASA put it out on the

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

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

the method.

Anna: I completely agree. This is the first time

anyone has read a subsurface temperature

profile of a rocky body from orbit. And

that technique doesn't care whether the World

is fiery or frozen. Point it at an icy

moon, Europa Enceladus, and in principle,

you could sense the warmth of an ocean

beneath the ice or work out how thick that

ice actually is.

Avery: Which is precisely the question those

missions are built to answer. Europa Clipper

is already on its way

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

principal investigator, Scott Bolton, pointed

out that you could fly an MWR type instrument

over a volcano here on Earth and read the

same kind of subsurface temperature gradient.

A whole new way to study our own volcanoes

from the air.

Avery: So an instrument built for Jupiter's clouds

ends up potentially rewriting how we study

volcanoes on Earth. That's the kind of

accidental genius that makes me love this

stuff.

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

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

point it somewhere new and it hands you a

capability nobody planned for. IO got its

first ever subsurface reading and we got a

new way to take the temperature of worlds.

Avery: Ours included a fitting lead. And keep

IO in your back of your mind, because Jupiter

itself is going to come back around in our

skywatch in a slightly surprising way.

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

on fire to something at the very edge of what

we can see.

Avery: Now onto story two.

JWST's little red

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

deep early universe. One of the strangest

things the James Webb's telescope has turned

up since it started sending back data in 2022

is a whole population of objects

nicknamed little red dots.

Anna: I love that they just called them what they

look like.

Avery: Astronomers are refreshingly literal.

Sometimes they're exactly that. Tiny,

intensely red, compact points of light.

And they're ancient. They show up around 600

million years after the Big Bang. And then

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

the time the universe is about a billion and

a half years old. Nobody's been sure what

they even are. Supermassive black holes

wrapped in gas bursts of furious star

formation. Something else entirely.

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

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

by John Chisum at the University of Texas at

Austin, published in the Astrophysical

Journal Letters, suggests the little red dots

might be globular clusters caught in the act

of being born.

Anna: Globular clusters, those dense, ancient

balls of hundreds of thousands of stars that

hang around the outskirts of galaxies like

ours.

Avery: Those exact things, around 150 of them,

orbit the Milky Way. And their origin has

been its own long standing mystery. So this

paper does something elegant. It takes two

puzzles. What are little red dots? And where

do globular clusters come from? Ann proposes

they're the same puzzle that the little red

dots are simply what globular clusters look

like while they were forming.

Anna: Two birds, one stone.

Avery: That's exactly the phrase the researchers

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

of stars supplies the blue ultraviolet light.

And a single short lived, absolutely

colossal star at the center, a

supermassive star tens of thousands of

times the Sun's mass, supplies the red.

And crucially, it predicts specific chemical

fingerprints, unusual amounts of helium and

nitrogen, the very oddities we already see in

the stars of today's globular clusters.

Anna: So the test is in the chemistry.

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

careful about it. Co author Mike Boylan

Kolchin put it. Well, there's no single

smoking gun yet. But this would explain a lot

of surprising observations at once. They're

calling it plausible and laying out ways to

stress test it.

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

might be, uh, cosmic dinosaurs that never

actually went extinct.

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

dinosaurs simply vanished. Then we

realized they became birds. The suggestion

here is that the little red dots didn't

disappear either. They grew up into the

globular clusters. You can still point a

backyard telescope at tonight. The strange

early universe. And the familiar one might be

far more connected than we thought.

Anna: From the oldest starlight to possibly

no starlight at all.

Because the next one is all about listening.

For more than 60 years, the Search for

Extraterrestrial Intelligence, SETI has

mostly listened in one narrow stretch of the

radio dial, a band between about

1.4 and 1.7 gigahertz

that astronomers call the water hole.

Avery: Why there?

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

the spectrum and it sits right between the

frequencies given off by hydrogen and by

hydroxyl, the two pieces that together make

water. The romantic idea is that any water

based civilization might recognize it as

an obvious meeting place. A, ah, cosmic

watering hole.

Avery: Poetic, but maybe a touch assumption

heavy.

Anna: That's exactly the point a young researcher

has just made. Louisa Mason, a PhD

student at the University of Manchester,

presented work at the Royal Astronomical

Society's National Astronomy meeting, arguing

we might be listening on the wrong channel

entirely. And rather than ask for expensive

new telescope time, she did something smart.

She went digging in the archives.

Avery: Old data.

Anna: Old data from Alma, that enormous array of

dishes up on the chajenant plateau In Chile,

which observes at much higher millimeter and

submillimeter frequencies that SETI has

barely touched. She ran the first ever

SETI search through archived ALMA

observations, hunting for narrow artificial

looking signals.

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

Anna: she did not. No technosignatures, which is

the honest and entirely expected result from

just four archived observations. But here's

the finding that made me sit up when she

properly modeled how many stars were sitting

in the background of those observations.

Stars caught in the frame. While ALMA was

pointed at something else. The count jumped

from a previous estimate of around

288,000 stars

to more than six million.

Avery: Six million. Just from recounting what was

already there.

Anna: More than six million. She calls it

stellar bycatch. All the stars you

survey by accident every single time you

point a big telescope anywhere. It

means archives around the world may already

hold a vastly larger SETI survey

than anyone realized, hiding inside data

gathered for complet completely different

reasons.

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

net. Sometimes you just need to count what

you've already caught.

Anna: Beautifully put. New frequencies and

millions of free stars. Not a bad

afternoon's work.

And speaking of signals arriving, there's one

headed for Earth right now.

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

our own star has been rustless. There's an

active region on the sun cataloged as region

4494. And on the 26th

it let off a moderate flare. An M M class

flare. An M M3.2 to be exact.

Anna: M class being middle of the road as

flares go.

Avery: Moderate, yes, below the big X class

monsters, but nothing to sneeze at. And

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

coronal mass ejection launched back on the

24th is due to give Earth a glancing

blow right about now.

Anna: A glancing blow. So not a direct

hit.

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

even a side wipe can rattle our magnetic

field. Forecasters are calling for G1,

possibly nudging up to G2

geomagnetic storm levels across the

27th and 28th. And the fun part for

us is what that does to the sky. Aurorae.

Anna: Uh, aurorae.

Avery: When that solar material meets the magnetic

field, it funnels particles down over the

poles and lights up the atmosphere. The

southern lights, the Aurora Australis for our

listeners down here. And the northern lights

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

mostly talking higher latitudes. So

Tasmania and the deep south of New Zealand

have the better odds. Here up north, think

Scotland, Scandinavia and the northern tier

of the US and Canada.

Anna: And I should say space weather moves fast.

By the time you're hearing this, the numbers

may well have shifted.

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

live alerts, the Space Weather Prediction

center or the Bureau of Meteorology's Space

Weather Service here in Australia for the

current picture. But it's worth a glance at

the southern horizon tonight because the sun

may just have laid on a show.

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

up.

Skywatch. Though this is meteor week

in theory, we've got a run of showers

peaking over the next few nights. The July

Gamma Draconids tonight, the Pisces

Austrianids around the 28th and 29th. And

then the big one for us, the Southern Delta

Aquarids, building to their peak around the

30th, alongside the alpha capricornids

on the 30th and 31st.

Avery: And in theory being the operative phrase,

because there's a giant obstacle rising in

the east.

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

29th, and a nearly full moon all week

is going to flood the sky with light and wash

out most of these meteors, which tend to be

on the faint side to begin with.

Avery: So is it a write off?

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

it first. The Southern Delta Aquariids

genuinely favor us. In the south, the

radiant over near the star Skat in

Aquarius climbs high overhead from southern

latitudes. Which is exactly why this is so

often the Southern hemisphere's best shower

of the year. Though for our listeners in

Australia and New Zealand, look after

midnight into the pre dawn hours when that

radiant is highest.

Avery: And um, for the Northern hemisphere, for

Anna: North America and other northern listeners,

the radiant sits lower in the southern sky.

But the southern United States, Mexico and

Southern Europe still get a decent view. Same

advice. The hours after midnight local time

into the couple of hours before dawn are your

best window. And face south.

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

The Alpha Capricornids. They're not

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

famous for slow, bright, colorful

fireballs. And a fireball doesn't care about

moonlight. So even in a bright week, one

brilliant, lazy Alpha Capricornid drifting

across the sky is worth the wait. North or

south?

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

there are planets to fall back on in the

evening. Low in the west after sunset, Venus

is blazing away, unmistakable. And climbing

a little higher each night as it heads for

its best evening showing in August.

Avery: And, um, the morning sky.

Anna: The morning belongs to Saturn. Golden well up

in the pre dawn sky. And it actually paused

in its motion against the background stars

this week. Mars is climbing higher before

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

horizon, elusive Mercury is making a

low pre dawn appearance in the last days of

the month.

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

started. Jupiter.

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

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

Jupiter itself as just slipped behind the

sun. It reaches solar conjunction on the

29th, essentially lined up on the far side

of our star. So the very planet whose moon

we spent our whole lead story on is the one

planet you can't actually see in the sky

right now.

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

we've temporarily lost space has a sense of

humor.

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

August. And one last one for our northern

friends before we go. Look straight up after

dark and you'll find the summer triangle.

Vega, uh, Deneb, uh, and Altair riding high

overhead, a reliable anchor on a moonlit

night.

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

there.

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

beneath the skin of the solar system's most

volcanic moon. Two cosmic mysteries that

might be one. A fresh way to listen for

company, and a burst of weather from our own

star.

Avery: If you enjoyed it, find. Follow Astronomy

Daily wherever you get your podcasts and find

our new website@astronomydaily,IO

and on the socials strodaily

pod. We're back tomorrow.

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

up.

Avery: Clear skies.

Sam. Hmm.

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

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