When astronomers first found Pluto in 1930, they thought it was alone — just one tiny world at the edge of the solar system. They were wrong. Pluto has not one, not two, but five moons. All five were discovered between 1978 and 2012, mostly thanks to the Hubble Space Telescope, and all five are named after figures from the dark land of Greek mythology to match Pluto, the god of the underworld.
Pluto has five moons: Charon, Styx, Nix, Kerberos and Hydra. Charon is by far the largest — about half the size of Pluto itself. The other four are much smaller. All five were discovered between 1978 and 2012.
Meet the Five Moons
Here are Pluto's five moons in order, from biggest to smallest:
1. Charon — The Twin Moon (1,212 km)
Charon is huge for a moon. At 1,212 km across, it is half the width of Pluto itself. That makes Charon the biggest moon in the solar system compared to the world it orbits. Pluto and Charon are tidally locked, which means they always show each other the same face — and Charon is so big that the two of them share a centre point in space between them. Many scientists call Pluto and Charon a "double dwarf planet." Meet Charon in detail.
2. Hydra — The Outer Spinner (~51 km)
Hydra is Pluto's furthest moon. About 51 km across and shaped like a slightly squashed potato, Hydra is named after the many-headed serpent from Greek mythology that lived in the underworld swamps. Hercules famously had to fight one of these monsters as part of his twelve labours.
Hydra spins very fast — one full rotation every 10 hours. It was discovered by the Hubble Space Telescope in 2005.
3. Nix — The Night Moon (~50 km)
Nix is similar in size to Hydra — about 50 km across, also shaped like an irregular lumpy potato. It is named after Nyx, the Greek goddess of the night.
Nix has one slightly weird feature: a giant red patch on one side, which scientists think might be the remains of an old impact crater. It was discovered alongside Hydra in 2005.
4. Kerberos — The Black Moon (~12 km)
Kerberos is one of Pluto's smallest moons, only about 12 km across. It is named after Kerberos (or Cerberus), the three-headed dog from Greek mythology who guarded the gates of the underworld so nobody could escape.
When New Horizons photographed Kerberos in 2015, scientists got a surprise: it was much smaller and darker than expected. Some moons reflect light brightly, but Kerberos is jet-black — one of the darkest objects in the Pluto system. It was discovered in 2011.
5. Styx — The Tiniest (~10 km)
Styx is the smallest moon of Pluto — only about 10 km across. It is named after the river Styx in Greek mythology, which marked the boundary between the world of the living and the world of the dead.
Styx is the most recently discovered Pluto moon, only spotted in 2012 by the Hubble Space Telescope.
Imagine a small dark river. A ferryman waiting to carry you across. A three-headed dog at the gate. A goddess of night watching above. A many-headed serpent in the swamps beyond. That's every Pluto moon, all together. The whole system is the underworld of Greek myth, in miniature, orbiting Pluto.
How the Small Moons Spin
Earth's Moon spins exactly once for every orbit it makes — that's why we always see the same face. Pluto and Charon do the same thing to each other. But the four small moons (Styx, Nix, Kerberos and Hydra) do something completely different.
They tumble. They spin chaotically, wobbling and somersaulting as they orbit, like a stone you've thrown end-over-end through the air. Pluto and Charon are so close to each other and so big that their combined gravity yanks the small moons around in unpredictable ways. If you stood on Nix or Hydra, the Sun would rise from one direction one day and a completely different direction the next.
Where the Moons Came From
Scientists think Pluto's five moons all formed in a single big event a long time ago. Billions of years back, when the outer solar system was still young, another large object slammed into Pluto. The crash shattered both worlds and scattered material into a ring around what was left of Pluto. The biggest piece pulled itself together into Charon. The leftover smaller bits became Styx, Nix, Kerberos and Hydra.
That's the leading theory, anyway. We will know more for certain when (or if) another spacecraft visits Pluto. More on the New Horizons mission.
Does Pluto Have Rings?
Scientists have looked. New Horizons checked the Pluto system carefully for rings during the 2015 flyby and didn't find any. But it's possible Pluto has very faint dust rings that are too thin for current telescopes to see — created by tiny impacts on the four small moons that throw dust into space.
One big partner.
Four small tumblers.
All five named after the dark.
Read about Charon, Pluto's twin, the underworld mythology behind the moon names, or jump back to the main Pluto facts page.
Frequently Asked Questions
How many moons does Pluto have?
Pluto has five moons: Charon, Styx, Nix, Kerberos and Hydra. Charon is by far the largest, about half the size of Pluto itself. The four smaller moons were discovered by the Hubble Space Telescope between 2005 and 2012.
What are the names of Pluto's moons?
Pluto's five moons are Charon, Styx, Nix, Kerberos and Hydra. All five are named after figures from Greek and Roman mythology connected to the underworld — to match Pluto, who is the Roman god of the underworld.
What is Pluto's biggest moon?
Pluto's biggest moon is Charon. It is 1,212 km across — about half the diameter of Pluto itself. That makes Charon the largest moon in the solar system compared to the world it orbits.
Does Pluto have rings?
As far as we know, no. NASA's New Horizons spacecraft searched carefully for rings during its 2015 flyby and didn't find any. But faint dust rings created by tiny impacts on the small moons are still possible — they may just be too thin to see.
Why are Pluto's moons named after the underworld?
Pluto is the Roman god of the dark underworld where souls go after death. Astronomers chose names from the same mythology for all of Pluto's moons to match. Charon is the ferryman, Styx is the river, Kerberos is the three-headed guard dog, Nix is the night goddess, and Hydra is a many-headed serpent.