Largest Moons of Jupiter

Data

Source: Wikipedia — Moons of Jupiter.

Note: What You Should Know About the Moons of Jupiter

The Big Four: The Galilean Moons

Jupiter doesn't just have a lot of moons — it has a lot of interesting moons. The four largest, ranked in the table above, are called the Galilean moons because the astronomer Galileo Galilei first spotted them through his telescope back in 1610. That single discovery was a huge deal: it proved that not everything in the sky orbits the Earth, and it helped reshape how we understood the solar system. Ganymede, Callisto, Io, and Europa are each a world of its own — several of them are big enough to be "planets" if they orbited the Sun instead.

Ganymede — The Moon That Outshines a Planet

At 5,268 km across, Ganymede is the largest moon in the entire solar system and the biggest in this chart at number one. It's actually bigger than the planet Mercury (which is only about 4,879 km) and even larger than Pluto. Ganymede is unique among moons because it's the only one known to generate its own magnetic field. It also appears to hide a salty subsurface ocean beneath its icy crust, which makes it a fascinating target in the search for habitable worlds.

Callisto — The Cratered Grandfather

Callisto (4,821 km) is almost as big as Ganymede, but it's a very different kind of world. Its surface is one of the most heavily cratered in the solar system — a record of impacts stretching back billions of years. Because it sits a little farther from Jupiter than the other Galilean moons, it feels much less of Jupiter's intense radiation, which makes Callisto a prime real-estate candidate for a future human base on Jupiter's system.

Io — The Volcanic Fire World

Io (3,643 km) is the most volcanically active body in the solar system. Jupiter's enormous gravity, combined with the tugging of the other moons, constantly stretches and squeezes Io — an effect called tidal heating. That internal friction keeps its interior molten and powers hundreds of active volcanoes that spew sulfur across its colorful surface. It's the closest thing we have to a real-life pressure cooker in the sky.

Europa — The Ocean Moon

Europa (3,122 km) may be small compared to its siblings, but it packs the biggest question in planetary science: could there be life in its ocean? Beneath a smooth, cracked shell of ice, scientists believe Europa holds a global ocean of liquid water — more water, possibly, than all of Earth's oceans combined. Its surface is covered in striking reddish-brown streaks, likely minerals from the ocean below. That's why Europa is a top priority for NASA and ESA missions searching for habitable environments beyond Earth.

The Small Guys Still Matter

The rest of the moons in this chart — Amalthea, Himalia, Thebe, and Elara — are tiny by comparison. At 167 km, Amalthea is the largest of Jupiter's inner moons and gives Jupiter one of its faint thin rings. These smaller moons are a mix of captured asteroids and irregular satellites that likely fell into Jupiter's orbit early in the solar system's history. Understanding them helps scientists untangle how the whole Jovian system formed.

How Many Moons Does Jupiter Actually Have?

Jupiter is a moon factory. As of recent counts, astronomers have confirmed more than 90 moons orbiting the planet, and the number keeps climbing as telescopes get better. The vast majority are small irregular moons far from the planet, but their sheer number highlights just how much of a gravitational heavyweight Jupiter is — it dominates its corner of the solar system.

Why These Moons Matter for Habitability

• Ganymede, Europa, and Callisto all show strong evidence of subsurface liquid-water oceans beneath their icy shells.
• Where there is liquid water, energy, and the right chemistry, there is the possibility of life as we know it — which is why Europa tops the list for future exploration.
• Europa Clipper and JUICE are real missions either en route to or planned for Jupiter's system, chasing answers to that exact question.

Fun Facts

• If you could shrink the solar system, the Galilean moons would each be impressive planets in their own right.
• Jupiter is so massive that its gravity stretches Io enough to keep it constantly erupting.
• The cracks on Europa's surface are driven by the same tidal stretching that melts Io from the inside.
• Ganymede's magnetic field is something no other moon in the solar system has managed to match.
• Many of Jupiter's outer moons orbit backwards — they're captured bodies that circle the planet in the opposite direction of its rotation.
• Seen clearly through binoculars or a small telescope, just four tiny points of light by Jupiter can reveal the bodies that changed science forever.
• Jupiter's moons travel an incredible variety of paths, from near-perfect circles to wildly tilted, stretched-out orbits.
• The Galilean moons are named after people Galileo himself discovered or honored — and one, Europa, also lends its name to a moon of a whole other planet's story.
• Each Galilean moon is a different kind of world: one icy, one cratered, one volcanic, and one shrouded in a hidden ocean.