Why is Pluto still so faint despite being at its brightest?

Pluto reaches only magnitude ~15 at opposition, making it invisible to the naked eye and requiring telescopes to observe.

What did New Horizons discover about Pluto in 2015?

New Horizons found the nitrogen-ice plain of Sputnik Planitia, a famous heart-shaped feature, water-ice mountains, a hazy atmosphere, and evidence of a possible subsurface ocean.

Who discovered Pluto and when?

Clyde Tombaugh discovered Pluto in 1930 using a blink comparator, following Percival Lowell's prediction of 'Planet X.' The name was suggested by 11-year-old Venetia Burney.

How long was the Soyuz MS-28 crew in space?

The crew spent 241 days in space, completing approximately 3,856 orbits and traveling over 102 million miles.

Pluto's Big Night & a Sharper Look at M87's Black Hole | Today's Space News

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 [email protected]

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.

Pluto's Big Night & a Sharper Look at M87's Black Hole | Today's Space News

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