Hugo's Solar System
Dwarf planet
Pluto
The icy dwarf planet with a heart, far out in the Kuiper Belt
Tiny and chilly, with mountains of ice,
Pluto's a loner but terribly nice.From Hugo's Journey Through Space
Key facts
- Diameter
- About 1,480 miles / 2,377 km, roughly one-fifth the width of Earth
- Distance from the Sun
- About 39 AU on average (3.7 billion miles / 5.9 billion km); ranges from 30 AU to 49.3 AU
- One orbit
- About 248 Earth years
- One day (rotation)
- About 153 hours (6.4 Earth days)
- Average temperature
- About -232 °C
- Known moons
- 5 (as of September 2026)
- Named after
- The Roman god of the underworld, suggested by 11-year-old Venetia Burney in 1930
- Discovered
- 18 February 1930 by Clyde Tombaugh at Lowell Observatory, Arizona
- Visited by
- New Horizons, flyby on 14 July 2015
- Sunlight travel time
- About 5.5 hours from the Sun
- Surface gravity
- About 6% of Earth's
About Pluto
Pluto is a small, icy world. It lives very far from the Sun. The Sun looks like a bright star there. Pluto is a dwarf planet. It is smaller than our Moon. It is very, very cold. The ice on Pluto is hard as rock. Pluto has a big heart shape on it. The heart is made of frozen gas. Pluto has five moons. The biggest moon is called Charon. A spaceship called New Horizons flew past Pluto. It took the first close-up photos. Pluto is a long way from home.
Pluto is a dwarf planet in the Kuiper Belt, far beyond Neptune. It is about 2,377 kilometres across, smaller than Earth's Moon. Pluto was found in 1930 by Clyde Tombaugh at Lowell Observatory. An eleven-year-old girl called Venetia Burney suggested its name.
For 76 years people called it the ninth planet. In 2006 astronomers decided it was a dwarf planet instead. Pluto is an icy sphere with a heart-shaped plain of frozen nitrogen. Its surface temperature is about minus 232 degrees Celsius, cold enough to freeze air.
Pluto takes 248 years to complete one orbit of the Sun. Its orbit is a stretched oval, so sometimes it comes closer than Neptune. Pluto rotates slowly, so one day there lasts about 153 hours. Its axis is tilted a lot, so it spins almost on its side.
Pluto has a thin atmosphere of nitrogen, methane and carbon monoxide. Its gravity is weak, only about six per cent of Earth's gravity. Pluto has five moons, as of August 2026. The largest, Charon, is about half the size of Pluto itself.
In 2015 the New Horizons spacecraft flew past and photographed Pluto. It found mountains of water ice about 2 to 3 kilometres high.
Pluto is the best-known dwarf planet and the largest known object in the Kuiper Belt. Clyde Tombaugh discovered it at Lowell Observatory in Arizona on 18 February 1930, and the name, suggested by eleven-year-old Venetia Burney, was announced that May. Pluto was counted as the ninth planet until 2006, when the International Astronomical Union defined the word planet and placed Pluto in the new category of dwarf planet, because it has not cleared the neighbourhood of its orbit.
NASA gives Pluto an equatorial diameter of about 2,377 km, roughly one-fifth the width of Earth and smaller than our Moon. Its mass is about one-sixth that of the Moon, and surface gravity is about 6 per cent of Earth's. Pluto orbits the Sun once every 248 years on a markedly elliptical, tilted path that ranges from about 30 AU to 49.3 AU; on average it is about 39 AU, or 5.9 billion km, away, and sunlight takes about 5.5 hours to reach it. A day on Pluto lasts about 153 hours, and its axis is tilted 57 degrees. Pluto and Charon are tidally locked to each other. The average temperature is about -232 °C.
The surface is mostly nitrogen ice with methane and carbon monoxide ices, and the thin nitrogen atmosphere had a surface pressure of about 1 pascal in 2015. Its most famous feature is the heart-shaped Tombaugh Regio; the western lobe, Sputnik Planitia, is a basin about 1,000 km wide filled with slowly flowing nitrogen ice. Mountains of water ice rise 2 to 3 km, and craters reach about 260 km across.
Pluto has five known moons as of August 2026: Charon, Styx, Nix, Kerberos and Hydra. Charon is about 1,212 km across, roughly half Pluto's diameter.
Only one spacecraft has visited. NASA's New Horizons, launched on 19 January 2006, passed about 7,800 km above Pluto's surface on 14 July 2015, then flew past the Kuiper Belt object Arrokoth on 1 January 2019. Two points often misstated: Pluto is not the most massive dwarf planet (Eris is about 27 per cent more massive, though slightly smaller in diameter, 2,326 km against 2,377 km), and Pluto was never removed from the solar system in 2006; it was simply reclassified.
Did you know?
- Pluto's name was suggested by an eleven-year-old girl from Oxford, Venetia Burney, in March 1930.
- From 1979 to 1999 Pluto was closer to the Sun than Neptune, because its stretched orbit crosses inside Neptune's.
- Pluto's heart-shaped plain, Sputnik Planitia, is about 1,000 km wide and filled with slowly flowing nitrogen ice.
Moons of Pluto
Pluto has 5 known moons as of September 2026. The largest are listed here. How many moons does Pluto have?
- Charon
- Hydra
- Nix
- Kerberos
- Styx
Questions children ask
Why isn't Pluto a planet any more?
In 2006 astronomers agreed a planet must orbit the Sun, be round, and have cleared other objects from its path. Pluto shares the Kuiper Belt with many icy bodies, so it became a dwarf planet. It is still there, just in a new category.
How cold is Pluto?
Very cold indeed. NASA gives an average of about -232 °C, and it can drop to around -240 °C. At those temperatures nitrogen, which is a gas on Earth, freezes solid and makes up most of Pluto's surface.
Has anyone sent a spacecraft to Pluto?
Yes, one. NASA's New Horizons launched in January 2006 and flew about 7,800 km above Pluto on 14 July 2015, taking the first close-up pictures. It is now deep in the Kuiper Belt and still working.
How many moons does Pluto have?
Five, as of August 2026: Charon, Styx, Nix, Kerberos and Hydra. Charon is about half the size of Pluto, which makes it the largest moon compared with its parent body anywhere in the solar system.
Quick quiz
Three questions for space cadets. Nothing is recorded.
- In which year was Pluto discovered?
- What is the name of Pluto's largest moon?
- Which spacecraft flew past Pluto in 2015?
Eris
Charon
The Moon