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.