Anna: Welcome to Astronomy Daily. I'm Anna.
Avery: And I'm avery. It's Monday, the 27th
of July, 2026, and tonight,
the smallest headliner we've had in a while
gets top billing.
Anna: That's right. Our lead is a world you
cannot see without a decent telescope,
one that half of the astronomy community will
tell you isn't even a planet. And today is
its brightest night of the year. Pluto
reaches opposition. We're going to spend some
proper time there. The discovery, the
demotion that people are still arguing about,
and the frozen world New Horizons actually
found waiting for us.
Avery: Then, um, three quick stops. A crew comes
home after 241 days in orbit.
New modeling suggests the most common planet
in the galaxy may be hiding oceans of molten
rock. And astronomers have taken the famous
first ever black hole image and pulled a
whole new layer of physics out of it.
Anna: And we'll close where we always do, under the
sky north and south, with a M meteor
shower that's putting on its best show for
our Southern Hemisphere listeners. Let's get
into it.
So, Avery set the scene for me. If someone
walks out tonight and looks up, are they
going to see Pluto?
Avery: Honestly, no. Not with their eyes and not
with a pair of binoculars. Tonight, Pluto
sits directly opposite the sun in our sky,
over in the constellation Capricornus. That's
what opposition means. Earth is passing
between Pluto and the Sun. So Pluto rises
at sunset, sits highest around midnight,
and it's fully lit and as close to us as it
gets all year. A, uh, touch under 35
astronomical units. So roughly 35
times the Earth's sun
Anna: distance, and that's as good as it gets.
Avery: And it's still faint, painfully
faint. We're talking about magnitude 15,
to put that in human terms. It's millions of
times dimmer than the faintest star you can
pick out on a dark night. You realistically
need an 8 inch telescope and a good star
chart. And even then, Pluto looks like
a star, a dot that only gives itself away
because it shifts position over a
Anna: couple of nights, which is exactly how it was
found in the first place. Let's rewind.
Because the Pluto story is one of the great
underdog tales in astronomy.
1894, Percival Lowell, the same
wealthy Bostonian who convinced himself
Mars was covered in canals, sets up an
observatory in Flagstaff, Arizona, and
becomes obsessed, um, with a planet X he
was sure was tugging on the orbits of Uranus
and Neptune.
Avery: And, um, he never found it. He died in 1916,
still hunting.
Anna: He did the search, went cold, then
restarting. And in 1929 the
job landed on a 23 year old Kansas farm
boy with no colonies college degree named
Clyde Tombaugh. His method was brutal,
painstaking work. Photograph the same patch
of sky on different nights. Then flick
between the two plates in a machine called a
blink comparator, looking for the one dot
out of hundreds of thousands that moved.
Avery: That is the definition of patience.
Anna: On the 18th of February 1930 he
found it. And here's a detail I love. The
name didn't come from an astronomer. It came
from an 11 year old English schoolgirl,
Venetia Burney. Over breakfast she
suggested Pluto, the Roman God of the
underworld, fitting for a cold, dark,
distant world. And the first two letters, P
and L also happen to honor Percival
Lowell. It stuck.
Avery: So for 76 years, Pluto is the ninth
planet. It's on every classroom wall, um,
every lunchbox, every mobile over a
cottage. Then 2006 happens.
Anna: Then 2006 happens. And this is
the part people still get heated about. So
let me try to be fair to both sides because
there genuinely are two good sides.
The trouble started in the years before when
astronomers began finding other icy
bodies out past Neptune in a region called
the Kuiper belt. And in 2005
a team found Eris, which at the time
looked to be bigger than Pluto.
Avery: And that's the crunch. If Pluto's a planet,
is eris planet number 10? What about the
next 20 objects we
Anna: find out there exactly the corner they were
backed into. So in August
2006, the International Astronomical
Union voted on a formal definition of planet
for the first time. Three rules. It has to
orbit the Sun. It has to be roundish under
its own gravity and the killer it, it
has to, uh, have cleared its neighborhood of
other debris. Pluto passes the first two
easily, but it shares its zone with all that
Kuiper Belt material. So it fails the third
reclassified as a dwarf planet. It
even got a minor planet catalog
Avery: number 134340,
a demotion with a filing number.
Ouch. Not everyone accepted it,
not at all.
Anna: And this is the bit I want listeners to sit
with because it's not settled science. It's a
definition. And definitions are choices.
The loudest objection comes from planetary
scientists and Alan Stern, who leads the New
Horizons mission, is the most prominent.
Their argument is roughly clearing the
neighborhood is a strange test because it
depends on where an object is, not what it
is. Put Earth out at Pluto's distance and
Earth wouldn't clear that huge orbit either.
They prefer a geophysical definition if
it's big enough for gravity to pull it round.
And it's not a star, it's a planet, full
stop. By that logic, Pluto is a planet, and
so are, uh, a dozen other round worlds.
Avery: And the counterargument, the dynamical
camp.
Anna: The folks who wrote the IAU rule say a
definition has to be useful. And anything
round gives you potentially hundreds of
planets, which tells you nothing about how
the solar system is actually organized.
Clearing your orbit captures something real.
The eight major planets are gravitationally
dominant and the Kuiper bell objects simply
aren't. So it's genuinely a values question.
Do you classify by the object itself or by
the role it plays in the system? Reasonable
people land differently.
Avery: And then, as if the universe wanted to make
everyone regret the timing, New
Anna: horizon shows up the best twist in the
whole saga. The probe launched in January
2006, seven months before the vote.
So it left Earth as a mission to the ninth
planet and arrived in July 2015
at a dwarf planet. And what it sent back
demolished the idea that small and far means
dull and dead.
Avery: This is my favorite part. Because we expected
a cratered frozen billiard
Anna: ball, we got a stunningly complex
active world. There's a vast bright plain of
frozen nitrogen sputnik plantina that
sits inside a uh, giant heart shaped feature
the whole Internet fell for. And that heart
isn't static. The nitrogen ice is slowly
churning, convecting like a lava lamp in
ultra slow motion. Which is why it has almost
no crater. The surface is being
resurfaced. There's mountains of water ice
as tall as the rockies. Because at Pluto's
temperatures, water ice is hard as rock. A
thin blue tinged nitrogen atmosphere with
layers of haze and a real possibility of a
liquid water ocean sloshing beneath the
crust.
Avery: A subsurface ocean on um, a world people were
arguing wasn't important enough to be a
planet.
Anna: Which is the poetry of it, isn't it? The
label we hang on Pluto changed nothing about
Pluto. It's exactly as fascinating as the day
before the vote. And it's not alone out
there. It has five moons of its own. The big
one, Charon, so large that the two of them
orbit a point in empty space between them
Like a slow cosmic waltz.
Avery: So tonight, when it's at its brightest and
best place for the year, that faint 15th
magnitude.in Capricornus is a churning, hazy,
possibly ocean bearing world with a heart on
its face.
Anna: That's the one and whatever you want to call
it, planet, dwarf planet, Kuiper belt object.
Tonight is Pluto's night. We'll tell you
exactly where to point a scope in the sky.
Watch. Clyde Tombaugh, by the way, passed
away in 1997. And new horizons
carried a small portion of his ashes on that
flyby. He got to visit the world he found.
Avery: Okay, I'm not crying. You're crying.
Lets bring it back to Earth literally.
Speaking of coming home, three people did
exactly that yesterday on, um, Sunday, a
Soyuz MS.28 capsule parachuted down
onto the steppe of Kazakhstan, bringing NASA
astronaut Chris Williams and Roscosmos
cosmonauts Sergey Kut Sverchkov and Sergey
Mikhayev back after 241 days
aboard the International Space Station.
Anna: 241 days put a number on what
that actually is.
Avery: Nearly eight months, around
3,885 laps of the
Earth and more than 102 million miles
traveled, all while effectively standing
still in orbit. They launched back on the
27th of November, American Thanksgiving. So
they've missed an entire summer and winter
depending on your hemisphere.
Anna: And it was a first flight for two of them.
Avery: It was first mission for Williams and for
Mikhayv. Gutsverchkov's the veteran. He's
now passed 425 days in space
across two flights. And I want to flag the
quiet significance here. A, uh, NASA
astronaut and two Russian cosmonauts riding
home together in a Russian capsule. Whatever
the politics on the ground, the crude side of
this partnership just keeps functioning, seat
swaps and all.
Anna: What was Williams actually doing up there?
It's easy to forget these are working science
missions, not just endurance feats.
Avery: Right. And his work is genuinely down to
Earth in its aims. He supported research into
novel cancer therapies which benefit from the
way proteins and cells behave in microgravity
and into manufacturing high performance
materials, the kind used in advanced
electronics and computing that you can make
more plainly without gravity pulling
everything around. The pair of cosmonauts
also did a spacewalk back in May to install a
solar radiation instrument on the station's
exterior.
Anna: And the handover keeps the station rolling
seamlessly.
Avery: Command passed to NASA's Jessica Meyer as
Expedition 74 became 75 and
a fresh crew. Anil, uh Menin and two
cosmonauts arrived earlier this month to keep
the lab staffed. The hard part now,
ironically, is gravity. After eight months,
just holding your own head up is exhausting.
The readjustment takes weeks.
Anna: Welcome home to the three of them now from
people orbiting one planet to the most common
kind of planet in the entire galaxy.
Avery: Moving on to story three, sub Neptune's
clouds of Rock, oceans of magma. What's this
all about?
Anna: Here's a fact that still catches me out. The
most common type of planet in the Milky Way
is a type we don't have. It's the sub
Neptune. Bigger than Earth, smaller than
Neptune. There's nothing like it in our solar
system, yet they turn up everywhere else. Out
of more than 6,000 confirmed exoplanets, well
over 2,000 are, uh, sub Neptunes.
Avery: And we barely understand what they're made
of.
Anna: That's the frustration. They could be small,
rocky cores wrapped in thick hydrogen
atmospheres, or they could be water worlds,
volatile, rich, drowning in water and carbon
molecules. And we can't easily tell because
even the James Webb telescope can only read
the very top of the atmosphere. And these
atmospheres are deep and hazy. New
modeling from a team at Arizona State,
recently published, offers a clever way
through. And it puts clouds at the center of
the story.
Avery: Clouds on a planet where weather must
mean something wild.
Anna: Wild is the word deep down, where the
pressure is crushing. The team modeled clouds
made of vaporized rock and salt. Think
aluminum oxide, iron silicates,
potassium chloride. Actual mineral
clouds. And here's the key finding those
clouds act like a blanket. They trap heat
trying to escape from the interior, which
pushes the boundary between the atmosphere
and the solid body to temperatures high
enough to melt rock.
Avery: So beneath the clouds, you might have an
ocean of magma, a global magma
Anna: ocean in the cloudy scenario. In the cloud
free version, that boundary is cooler and
might stay solid. Same planet from the
outside, two completely different interiors,
depending on the clouds. And that matters for
us for a very practical reason. It changes
how we interpret what Webb sees, and it feeds
directly into which of these worlds we bother
calling potentially habitable.
Avery: To be fair, this is modeling, not a direct
observation, completely fair.
Anna: This is simulation work, pointing observers
at what to look for. Not a photograph of
magma, but it reframes clouds from being just
an annoying smudge that ruins our data into
an active ingredient, shaping the whole
planet. For the galaxy's most common world,
that's
Avery: a meaningful shift from world we're modeling
to a monster we've actually photographed.
Let's go to M M87.
Anna: Next up, story four, a sharper look at M
M87's black hole.
Avery: Cast your mind back to 2019, that
first ever image of a black hole, the orange
donut. That was M M87,
the supermassive black hole at the heart of
a giant galaxy in Virgo, about
55 million light years away. Weighing
in at around six and a half billion
suns. That Single image was one of the
defining science pictures of the decade.
Anna: And now a team has gone back to the data and
done something new with it.
Avery: They have. Researchers led by the Shanghai
Astronomical Observatory with international
collaborators have produced the first
spatially resolved dual frequency spectral
map of M M87. And I know that's a mouthful,
so let me unpack it because it's clever.
Anna: Please. Dual frequency spectral map needs a
translation.
Avery: Think of it like this. The 2019 picture was
a single color photo of the ring. What this
team did was image the black hole at two
different radio wavelengths, 1.3
millimeters and 3.5 millimeters, using the
Event Horizon Telescope and a partner network
called the GMVA from observations back in
2018. Then they compared them point
by point to see how the color of the glow
changes as you move outward from the center.
That comparison is the spectral index, and
mapping it across the ring had never been
done before.
Anna: And what did the map show?
Avery: A, uh, clear structure. The signal is one
character inside the bright ring, and it
steepens, changes flavor as you move outward,
with the transition landing right at the ring
itself, about 30 micro arcseconds out.
And that's the headline. It tells us the ring
we photographed in 2019 isn't just a trick of
where the light happens to glow. It's tied to
a real physical change in the plasma right
around the event horizon.
Anna: So why does that matter beyond. Nice. A, uh,
sharper map.
Avery: Because reading a black hole means untangling
two things that are mixed together. The pure
warping of space by gravity and the messy
physics of superheated plasma spiraling in.
The researchers say looking at multiple
wavelengths lets them start to separate those
two. That's the path to understanding how
these monsters feed, how they fire off those
enormous jets, and eventually to a cleaner
test of Einstein's general relativity. It's
the difference between having a portrait and
starting to read the biography.
Anna: A portrait to a biography. I'll take that.
And on that note, let's step outside,
because it's skywatch time. And as always,
wherever you are on the planet, we've got
you. Avery, you take the south, I'll take the
north, and we'll meet in the middle at Pluto.
Avery: Deal. Southern hemisphere first. And friends
down south. This is your week. The Southern
Delta Aquarids are peaking. This is a shower
that genuinely favors the south. The radiant
in Aquarius climbs high after midnight for
you. And under a dark sky, you could see
something like 20 to 25 meteors an hour.
No equipment, just a reclining chair, a wide
Open view and some patience while your eyes
adapt.
Anna: And there's a comet. For the early risers,
There is Comet
Avery: 10P Tempel 1 low in the pre
dawn sky. It's uh, a binocular or small
telescope object rather than a naked eye
showpiece. But here's a southern bonus. It's
diving southward through August, so our
Southern Hemisphere listeners get the better
and improving view. Northern folks, catch it
now before it
Anna: drops away from you Northern Hemisphere. Your
headline is a star with a wonderful name.
Look high toward the north for the
constellation Cepheus. It looks like a
child's drawing of a house. And near the
bottom of that house sits Mu Cepheii,
better known as Herschel's Garnet Star. It's
one of the reddest stars you can see with the
naked eye. A, uh, bloated red supergiant so
vast that if you dropped it where the sun is,
its surface would swallow Jupiter.
Binoculars really bring out that deep ember
color. And you northern observers get the
Delta Aquariids too, just lower down toward
your southern horizon.
Avery: And now the meeting point, the one we teased
at the top, Pluto.
Anna: Pluto's at opposition tonight over in
Capricornus, which is beautifully placed for
the Southern Hemisphere high overhead and
perfectly workable low to mid northern skies
too. Now the honest part. At
magnitude 15, this is a genuine
challenge. You'll want at least an 8 inch
telescope, a detailed finder chart, and the
trick is patience. Sketch or photograph
the star field two or three nights running
and watch for the one star that moves. That
mover is Pluto. It is the ultimate
bragging rights target.
Avery: And, um, there's a catch tonight for
everyone.
Anna: There is a big bright moon, about
95% full, washing out the sky
all week. That won't bother the Garnet star
or the brighter meteors much, but it makes
faint Pluto even harder. If chasing
Pluto is your goal, wait for it to clear the
worst of the moonlight or give it a week. Oh,
and Saturn is rising after midnight over in
Pisces for both hemispheres, rings and all.
A lovely consolation prize in any scope,
north or south.
Avery: There's something up there for you tonight.
Anna: And that's Astronomy daily for Monday
27th July. A faint little
world having its big night, A crew safely
home, magma oceans on the galaxy's
commonest planet, and a, uh, sharper look at
the first black hole we ever photographed.
Avery: You can find show notes, links, and every
past episode@astronomydaily.IO
and the observant amongst you will notice
that we have a brand new website today, so
make sure you check it out. And we're
AstroDaily Pod Across Social. If
tonight's Pluto story settled or restarted,
an argument in your house, we'd love to hear
it.
Anna: For Avery, I'm Anna. Whatever you decide to
call Pluto, clear skies.
The stories.
Mhm.
Avery: We told.