How many moons does pluto have?

1. How many moons orbit Pluto?

Pluto has five moons: Charon, Styx, Nix, Kerberos, and Hydra. Pluto is not a planet, but it has enough gravity to hold moons (see the table below to see how Pluto compares with other planets in the solar system).

Have you noticed that Pluto has more moons than Mercury, Venus, Earth, and Mars combined? Well, that number alone does not capture what makes this system so fascinating. When NASA's New Horizons spacecraft flew through the Pluto system in July 2015, scientists already knew something unusual: some of Pluto’s small moons don’t spin smoothly. Because Pluto and Charon orbit each other, their gravity keeps tugging the moons in changing directions, so the moons can wobble and tumble. Mission scientist Mark Showalter described it as "not just chaos, but pandemonium."

2. Charon: the moon that is almost a planet

Charon has a diameter of about 1,200 kilometers, and it measures roughly half the size of Pluto itself. This ratio is not common for a moon. For comparison, the Earth's Moon is only about one-quarter the diameter of the Earth.

This unusual size creates a gravitational relationship that sets Pluto and Charon apart from every other planet-moon pair we know. The two bodies do not orbit the way you might expect; Pluto does not sit still while Charon circles around it. Instead, both worlds orbit a shared center of mass called the barycenter, and this point lies in empty space between them, roughly 900–1,000 kilometers above Pluto's surface.

Because neither body contains the barycenter within itself, some astronomers argue that Pluto and Charon should be classified as a binary dwarf planet system rather than a planet with a moon.

2.1 The "kiss and capture" origin

For decades, scientists believed Charon formed much like the Earth’s Moon: through a violent collision that blasted debris into orbit, which then coalesced into a satellite. But research published in January 2025 by scientists at the University of Arizona proposed a different origin.

Using impact simulations, the research team suggested that Pluto and proto-Charon did not behave like the hot, fluid bodies involved in Earth’s Moon-forming impact. Because Pluto and Charon are smaller, colder, and made mainly of rock and ice, they may have kept their shape during the collision. Instead of stretching and merging, the two bodies could have temporarily stuck together, rotating as a single snowman-shaped object before separating while remaining gravitationally bound.

The researchers call this a "kiss and capture" scenario. Lead researcher Adeene Denton noted that most planetary collision scenarios fall into two categories: "hit and run" (where an impactor strikes and keeps going) or "graze and merge" (where objects collide and combine). In their model, Pluto and Charon fit neither pattern.

This idea has implications beyond explaining how Charon formed. The collision and the tidal pull between Pluto and Charon could have added extra heat inside them. That extra heat may have helped Pluto form or keep a subsurface ocean.

3. The four outer moons: chaos in motion

Beyond Charon lie four much smaller moons: Styx, Nix, Kerberos, and Hydra. These irregularly shaped chunks of ice and rock are small—mostly tens of kilometers across, with Hydra being the largest. They orbit in nearly circular paths in the same plane as Charon, suggesting they formed from the same ancient collision.

But their behavior is anything but orderly. Unlike most moons in our solar system, which are tidally locked (always showing the same face to their parent body), Pluto's small moons can spin wildly on their axes.

3.1 Hydra: the whirling dervish

Hydra rotates once every 10 hours while taking 38 Earth days to complete one orbit around Pluto. That means Hydra spins 89 times for every single trip around the dwarf planet. According to Showalter, if Hydra were spinning much faster, material would fly off its surface due to centrifugal force.

3.2 Nix: where the sun rises in the east and sets in the north

Nix is tilted on its axis by 132 degrees and rotates backward relative to its orbit. Showalter has speculated that Nix can flip its entire pole orientation. This means that if you stood on its surface, the sun might rise in the east one day and set in the north. The rotation can be hard to predict over time.

Only one other moon in our solar system, Saturn's Hyperion, is known to tumble chaotically like this. The cause in Pluto's system is the gravitational tug-of-war created by Pluto and Charon whirling around each other. This constantly shifting gravitational field applies unpredictable torques to the small moons, preventing them from settling into stable rotation states.

3.3 The resonance that almost works

Despite the chaos, there is an underlying order. Styx, Nix, and Hydra are locked in a three-body orbital resonance reminiscent of the famous Laplace resonance linking Jupiter's moons Io, Europa, and Ganymede. If you were sitting on Nix, you would see Styx complete two orbits around Pluto for every three orbits Hydra completes.

However, perturbations from the other bodies inject chaos into this otherwise stable configuration. The moons' orbital periods fall into a neat 3:4:5:6 ratio with Charon's orbital period, but they are not perfectly locked. Hydra is very close to its resonance, while Styx drifts more noticeably. Scientists believe these near-resonances are relics from the early solar system, when Charon's orbit was still evolving and dragging the smaller moons along with it.

4. Unanswered mysteries

New Horizons answered many questions about Pluto's moons, but it also raised new ones that scientists are still working to explain.

4.1 Why are the small moons so bright?

Nix, Hydra, and Styx have surfaces as bright as fresh snow. This is puzzling because over billions of years, the constant rain of dark, reddish dust from the Kuiper Belt should have coated them, turning them dingy. Their bright, icy surfaces suggest something is refreshing them, perhaps small impacts that excavate cleaner ice from beneath the surface. But nobody knows for certain.

4.2 Why is Kerberos so dark?

While the other small moons gleam white, Kerberos can look darker in some images. That contrast is still puzzling, and scientists are still working to understand why the small moons do not all look the same.

4.3 Where is the missing debris?

Giant impact models predict that the collision which formed Pluto's moon system should have produced more debris. Scientists expected to find additional tiny moons or at least a faint ring system. Yet New Horizons found the Pluto system remarkably clean. Did the debris coalesce entirely into the moons we see, get ejected from the system, or rain down onto Pluto and Charon? The answer could tell us more about how planetary systems evolve after catastrophic collisions.

5. Why are all of Pluto's moons named after underworld figures?

Every moon in the Pluto system takes its name from Greek and Roman mythology associated with the realm of the dead. This tradition began in 1930 when 11-year-old Venetia Burney suggested naming the newly discovered world after the Roman god of the underworld. The name stuck, and subsequent discoveries have followed the theme.

Charon was the ferryman who carried souls of the dead across the River Styx to the underworld. The moon's discoverer, James Christy, chose the name partly for its mythological connection and partly because it resembled his wife Charlene's name. This personal touch explains why "Charon" has two accepted pronunciations: one with a hard "K" sound (the Greek way) and one with a soft "Sh" sound (the Charlene way).

Nix is named after the Greek goddess of darkness and night, who in mythology was the mother of Charon. The spelling was changed from "Nyx" because an asteroid already carried that name. Similarly, Kerberos uses the Greek spelling of Cerberus, the three-headed dog that guarded the underworld's entrance, because an asteroid had already claimed the Latin spelling.

Hydra was the nine-headed serpent that Hercules battled. And Styx, of course, is the river that souls crossed to reach Hades. The International Astronomical Union maintains these naming conventions to honor the mythological tradition established when Pluto was first discovered.

6. How many more surprises could Pluto still reveal?

New Horizons gave us our first close look at Pluto's moons, but the flyby lasted only hours. The spacecraft is now billions of kilometers away, exploring other Kuiper Belt objects.

No follow-up mission has been approved yet, but the discoveries from New Horizons have made Pluto a priority for future exploration. The possibility of a subsurface ocean, the chaotic motion of the small moons, and the unanswered questions about Kerberos all make compelling cases for sending another spacecraft.