Pluto

Far out at the edge of our solar system, almost six billion kilometres from the Sun, spins a small frozen world with a giant heart of ice. That world is Pluto. It used to be called the ninth planet, but in 2006 astronomers gave it a new name: a dwarf planet. Pluto is smaller than Earth’s Moon, a year there lasts 248 Earth years, and it was named by an 11-year-old girl. Ready to explore one of the strangest places in space?

Here is everything you need to know about Pluto — from its five moons and ice volcanoes to the spacecraft that flew past it carrying the ashes of the man who discovered it.

Quick Facts About Pluto

Pluto at a Glance
Classification	Dwarf planet (since 2006)
Diameter	2,377 km (1,477 mi)
Distance from the Sun	5.9 billion km (39.5 AU avg)
Day length	6.4 Earth days (153 hours)
Year length	248 Earth years
Surface temperature	−229 °C (−380 °F) avg
Gravity	6.3% of Earth’s
Moons	5 (Charon, Styx, Nix, Kerberos, Hydra)
Discovered by	Clyde Tombaugh, 18 Feb 1930
Named by	Venetia Burney, age 11
Spacecraft visited	New Horizons (14 July 2015)

Is Pluto a Planet? The Big Question, Answered

For 76 years Pluto was called the ninth planet. Then on 24 August 2006, a group of astronomers from all over the world met in Prague and voted to change the rules. Under the new rules, Pluto became the first dwarf planet.

This wasn’t a punishment. It was a tidy-up. Astronomers had been finding more and more icy worlds out beyond Neptune — some almost as big as Pluto. They needed a clearer way to sort them all out. So they wrote down exactly what it takes to be a planet — and Pluto didn’t quite make the list.

The Three Rules to Be a Planet

To be called a planet, a space object must do three things:

• 1. Orbit the Sun. Pluto does. ✅
• 2. Be round, because its own gravity has squashed it into a ball. Pluto does. ✅
• 3. Be the boss of its lane around the Sun. Pluto isn’t. ❌

That third rule is the one Pluto fails. Pluto shares its lane with millions of icy rocks in the Kuiper Belt — a giant doughnut-shaped traffic jam beyond Neptune — and its gravity isn’t strong enough to push them out of the way. Read the full story on why Pluto isn’t a planet anymore.

What Is a Dwarf Planet?

A dwarf planet is like a planet’s smaller cousin. It orbits the Sun and it’s round, but it hasn’t cleared its orbit. Pluto isn’t lonely in this club. There are five officially recognised dwarf planets: Pluto, Eris, Haumea, Makemake and Ceres. Ceres lives in the asteroid belt between Mars and Jupiter; the other four are far out past Neptune. Astronomers think there could be hundreds more dwarf planets hiding in the dark, just waiting to be found. Meet the other dwarf planets.

How Pluto Was Discovered (and Named by an 11-Year-Old)

Pluto is so far away and so small that it took humans a very long time to spot it. The story has two heroes: a young astronomer from Kansas who found it, and a schoolgirl from Oxford who named it.

The Search for “Planet X”

In the early 1900s, an American astronomer called Percival Lowell believed there was a mystery planet pulling on the orbits of Uranus and Neptune. He called it “Planet X” (X for “unknown,” not the number ten) and spent years hunting for it. He died in 1916 without ever finding it.

His observatory in Arizona kept searching. In 1929 they hired a 24-year-old farm boy called Clyde Tombaugh, who had built his own telescopes out of car parts. His job? Take thousands of photographs of the night sky and look for anything that moved. On 18 February 1930, Tombaugh sat at a machine called a blink comparator — it flickered two photos of the same patch of sky on and off, like an early flip-book. One tiny dot was in a different spot in the two pictures. That moving dot was Pluto. Full story on the Pluto discovery.

Venetia Burney, Aged 11, Names a Planet

When the news of the new “ninth planet” reached England, an 11-year-old girl in Oxford called Venetia Burney was eating breakfast and reading the paper with her grandfather. He asked her what she would call it. She thought for a moment and said: “Pluto.” She had been learning about Roman myths at school, and Pluto was the god of the dark, cold underworld — a perfect match for a faraway, freezing world.

Her grandfather knew an astronomer at Oxford and passed the suggestion along. The Lowell Observatory loved it. The first two letters, P and L, even matched Percival Lowell’s initials. Venetia lived to be 90 and got to see Pluto get its own spacecraft visit before she died. More about Pluto’s mythology and name.

Pluto by the Numbers — Size, Distance, Day & Year

To really understand Pluto you have to picture how small, how far away, and how slow it is. The numbers are wonderfully strange.

Pluto Is Smaller Than Our Moon

Pluto is 2,377 km (1,477 mi) across. That’s tiny. It’s only about half the width of the United States — if you laid Pluto on a map of America, it would stretch from Los Angeles to Kansas City. Pluto is smaller than seven moons in our solar system, including Jupiter’s giant moon Ganymede, Saturn’s hazy Titan — and our own Moon. See the full Pluto vs Earth comparison.

A Day on Pluto Lasts 6.4 Earth Days

One day on Pluto — the time it takes to spin once around — is 6.4 Earth days, or 153 hours. So if you lived on Pluto, sunrise-to-sunrise would feel endless. Pluto also spins almost on its side, tipped over at 122 degrees. The only other places in the solar system that spin like that are Venus and Uranus.

A Year on Pluto = 248 Earth Years

And here is the most mind-bending number of all: a year on Pluto lasts 248 Earth years. That’s how long Pluto takes to make one trip around the Sun. Pluto has only travelled about a third of the way around since Clyde Tombaugh first spotted it in 1930. It won’t complete a full Pluto-year-since-discovery until the year 2178.

Pluto’s Strange Orbit — When It Beats Neptune to the Sun

Most planets loop the Sun in neat circles. Pluto is the rebel. Its orbit is a long, stretched-out oval — and it’s tilted sideways, like a Frisbee thrown off-kilter. That tilt creates something amazing: for about 20 years out of every 248, Pluto sneaks inside Neptune’s orbit and becomes closer to the Sun than Neptune is. The last time was 1979 to 1999. If you were a kid in the 1990s, you lived through it.

Don’t worry — Pluto and Neptune will never crash. They take turns, locked in a careful rhythm. Neptune does three laps for every two Pluto makes. The next time Pluto sneaks in front? Around the year 2227. Pluto’s orbit explained.

Pluto’s Surface — A Heart of Ice, Mountains and Volcanoes

Until 2015, no one knew what Pluto really looked like. It was just a blurry blob in even the most powerful telescopes. Then NASA’s New Horizons spacecraft flew past, and what it saw took everyone’s breath away.

The Heart of Pluto

Pluto has a heart. A huge one. A bright, pale, heart-shaped region about 1,600 km wide stretches across its surface — bigger than the entire country of France. Scientists named it Tombaugh Regio in honour of the man who discovered Pluto. The left half of the heart is a flat plain of frozen nitrogen so smooth it looks like a frozen lake. It’s called Sputnik Planitia, and scientists think a slushy ocean of liquid water may be hiding underneath. Pluto’s surface for kids.

Ice Volcanoes (Yes, Really)

Two huge mountains on Pluto, called Wright Mons and Piccard Mons, look like volcanoes — but not the kind that erupt hot lava. Imagine a volcano that spits out slushy water and ammonia instead of molten rock. Scientists call these cryovolcanoes, or “ice volcanoes.” As far as we know, Pluto is the only place in the outer solar system where you can see them up close.

Why Pluto Is Reddish-Brown

Some parts of Pluto are bright white — that’s the nitrogen ice. But other patches are a rusty reddish-brown. The colour comes from a sticky chemical called tholin, which forms when sunlight hits the methane in Pluto’s air. The tholins drift down like coloured snow and pile up over billions of years — painting Pluto in slow motion. The darkest patch even has its own creepy name: Cthulhu Macula, after a monster from a famous horror story.

Does Pluto Have Air? (Yes — Blue Air That Freezes)

Pluto has a very thin atmosphere, made mostly of nitrogen — the same gas you breathe in every day. It is so thin you would never be able to breathe it, but when New Horizons looked back at Pluto with the Sun behind it, the photo showed something beautiful: Pluto’s air glows blue. The reason is the same reason Earth’s sky is blue — tiny haze particles scatter blue light better than other colours.

Here’s the weirdest part. When Pluto moves far away from the Sun, it gets so cold that its atmosphere freezes solid and falls to the ground as nitrogen snow. Then, when Pluto swings back nearer the Sun, the snow turns back into gas. Pluto’s air is constantly disappearing and coming back. Pluto’s atmosphere for kids.

How Cold Is Pluto?

Pluto is one of the coldest places we know about. The average surface temperature is −229 °C (−380 °F) — far colder than the coldest spot on Earth, which is around −89 °C in Antarctica. It’s so cold on Pluto that nitrogen falls from the sky as snow, water is harder than rock, and standing on the surface at noon would feel about as bright as twilight on Earth, just after the sun goes down. If you tried to drive a car from Earth to Pluto at highway speeds, it would take you over 6,700 years to get there.

Pluto’s 5 Moons — Charon, Styx, Nix, Kerberos and Hydra

For a small world, Pluto has a surprising family of five moons. All of their names come from the Greek myths about the underworld, to match Pluto’s own name.

Charon — Pluto’s Twin Moon

Charon is huge compared to Pluto. It is 1,212 km wide — about half the size of Pluto itself. That makes Charon the biggest moon in the solar system compared to the world it orbits.

In fact, Charon is so big that Pluto and Charon don’t really orbit each other in a normal way. They both swing around a point in empty space between them. Because of this, many scientists call Pluto and Charon a “double dwarf planet.” And they are both tidally locked, which means they always show each other the same face — like two dancers staring into each other’s eyes while they spin. Meet Charon, Pluto’s twin moon.

The Four Small Moons

The other four moons — Styx, Nix, Kerberos and Hydra — are tiny. They are all less than 50 km across, oddly shaped like potatoes, and they spin chaotically as they orbit. Astronomers spotted them with the Hubble Space Telescope between 2005 and 2012. Nobody knew Pluto had this many moons until then. Meet all five of Pluto’s moons.

How We Know — The New Horizons Mission

Everything we know in detail about Pluto came from one mission. NASA’s New Horizons spacecraft launched on 19 January 2006 — the same year Pluto became a dwarf planet. It is the fastest spacecraft ever launched from Earth, crossing the Moon’s orbit in just nine hours. (For comparison, the Apollo astronauts took about three days.)

Even at that speed, it took 9 years and 5 months to reach Pluto. On 14 July 2015, New Horizons swept past Pluto at 14 km per second, less than 13,000 km above its surface, and took the first close-up photographs ever — including the famous picture of Pluto’s heart. After Pluto, New Horizons kept flying. In 2019 it visited a smaller object called Arrokoth, deep in the Kuiper Belt — the most distant world ever explored up close by a spacecraft. The New Horizons mission story.

Pluto’s Neighbourhood — The Kuiper Belt

Pluto isn’t alone out there. It lives inside the Kuiper Belt (say it “KY-per”), a giant doughnut-shaped ring of icy worlds, comets and rocks beyond Neptune. The Kuiper Belt stretches from about 30 to 50 times Earth’s distance from the Sun. Astronomers have already found over 2,000 objects there, and they think millions more are waiting to be discovered.

Pluto is the biggest, brightest dwarf planet in the Kuiper Belt — sometimes called the “King of the Kuiper Belt.” A 2024 update from the New Horizons team even suggested the belt is 20 percent bigger than scientists had thought. We’re still discovering new things about Pluto’s neighbourhood every year. The Kuiper Belt for kids.

How Pluto Compares to Earth

Pluto and Earth are wildly different. Earth is rocky, warm, full of liquid water, and packed with life. Pluto is icy, freezing, with rock-hard water-ice mountains and no life that we know of.

Earth’s gravity holds you firmly on the ground. Pluto’s gravity is only 6.3% of Earth’s, so you could jump six times higher — high enough to clear a one-storey house without trying. A child who weighs 100 lb (45 kg) on Earth would weigh just 6 lb (3 kg) on Pluto.

Pluto in Stories — The Roman God and the Disney Dog

Two famous Plutos share the name.

The first is Pluto, the Roman god of the underworld, who lived in a dark, cold world beneath the earth. (In Greek myths he is called Hades.) That’s the Pluto that 11-year-old Venetia Burney was thinking of when she named the dwarf planet.

The second is Pluto, Mickey Mouse’s dog. Walt Disney introduced him in 1930 — the very same year the new planet was discovered — and most historians agree the cartoon dog was named after the planet, not the other way around. So if anyone tells you Pluto is named after the Disney dog, you can politely tell them: the planet got there first. Read the full Pluto mythology story.

Mind-Blowing Wow Facts About Pluto

1. Pluto is so cold that nitrogen falls from the sky as snow.
2. Sunlight that reaches Earth in 8 minutes takes up to 7 hours to reach Pluto.
3. If you lived on Pluto, you’d have to wait 248 Earth years to celebrate one Pluto birthday.
4. Pluto’s heart-shaped region is bigger than the entire country of France.
5. Pluto is smaller than seven moons in our solar system — including Earth’s Moon.
6. Pluto and Charon are the only known pair that may be a “double dwarf planet.”
7. From Pluto’s surface, the Sun would look like a very bright star.
8. Pluto might have a slushy ocean of liquid water hidden under its surface.
9. Pluto’s blue sky is caused by haze particles — just like Earth’s blue sky.
10. A radio message from Pluto takes 5 hours to reach Earth.

Read 10 more wow facts on the 20 Amazing Pluto Facts spoke.

Pluto Glossary — Big Words Made Simple

Word	What it means
Dwarf planet	A round object that orbits the Sun but hasn’t cleared other rocks out of its lane.
Kuiper Belt	A giant doughnut-shaped ring of icy worlds out beyond Neptune. Pluto’s neighbourhood.
Tombaugh Regio	The huge heart-shaped pale region on Pluto’s surface, named after Pluto’s discoverer.
Sputnik Planitia	The left half of the heart — a flat plain of frozen nitrogen.
Cryovolcano	An “ice volcano” that erupts slushy water or ammonia instead of hot lava.
Tholin	A sticky reddish chemical that forms in Pluto’s atmosphere and paints the surface red.
Tidally locked	When two worlds always show each other the same face. Pluto and Charon are.
Barycenter	The shared centre point that two objects orbit around. Pluto and Charon’s barycenter is in space between them.
Perihelion	The closest point a planet gets to the Sun on its orbit.
Aphelion	The farthest point a planet gets from the Sun on its orbit.

Explore Every Part of Pluto

Pick any thread and pull it. We have a full page on each of these subjects, written for kids who want to go deeper.

Frequently Asked Questions