Largest Moons of the Solar System

Data

Note: The Solar System's Biggest Moons, from Ganymede to Miranda

A Ranking Led by Jupiter and Saturn

The nine largest moons in the solar system are all in orbit around the giant planets, and Jupiter alone hosts three of the top four. Ganymede tops the list at 5,268 km in diameter, followed by Saturn's Titan at 5,149 km, then Jupiter's Callisto at 4,821 km and Io at 3,643 km. Our own Moon ranks fifth at 3,476 km, and the list stretches through Europa, Triton, and a string of ice moons down to Miranda at just 472 km.

• Ganymede, at 5,268 km, is larger than the planet Mercury, which measures about 4,879 km across.
• Titan comes within about 119 km of Ganymede, making the top two effectively the same size class.
• Jupiter's four Galilean moons, Ganymede, Callisto, Io, and Europa, fill ranks 1, 3, 4, and 6.
• Saturn contributes four moons to the list: Titan, Rhea, Iapetus, and Dione, plus Tethys and Enceladus further down.
• Uranus places four moons here as well: Titania, Oberon, Umbriel, and Ariel, all above 1,000 km except Miranda.

Two Giants with Very Different Worlds

Ganymede is not just big; it is the only moon known to generate its own magnetic field, evidence of a molten metallic core beneath its icy crust. It also hides a salty ocean under roughly 100 km of ice, making it a prime target in the search for habitable environments. Titan is equally remarkable: a thick orange atmosphere of nitrogen and methane, rain and rivers of liquid methane, and a surface that may hide a subsurface water ocean. It is the only moon with a substantial atmosphere and the only place besides Earth with stable liquid on its surface.

Smaller Giants and Cold Outposts

Earth's Moon ranks fifth and is the largest relative to its planet of any major moon, a fact that helps drive our ocean tides. Triton, Neptune's largest moon at 2,707 km, orbits backwards relative to Neptune's rotation, a strong clue that it was captured from the Kuiper Belt. Charon, at 1,212 km, is so large compared to Pluto that the pair is often treated as a double dwarf planet system; Charon is about half of Pluto's own diameter.

Why Size Matters for Science

Size correlates strongly with geological activity and potential habitability. Large moons retain internal heat longer, and that heat can sustain subsurface oceans, volcanoes, or active surfaces. Io, at 3,643 km, is the most volcanically active body in the solar system, powered by tidal heating from Jupiter. Enceladus, a modest 504 km, shows that even small moons can matter: its south polar geysers spray water into space and have made it a leading candidate for finding life beyond Earth.

Fun Facts

• Ganymede's diameter of 5,268 km makes it bigger than Mercury, the smallest planet.
• Titan's atmosphere is about 50 percent denser than Earth's, even though gravity there is much weaker.
• Io is squeezed by Jupiter's gravity so hard that its surface rises and falls by about 100 meters, driving constant volcanic eruptions.
• Europa, at 3,122 km, is slightly smaller than Earth's Moon but is thought to hold twice as much water as all of Earth's oceans.
• Our Moon is the largest moon relative to its planet; no other planet has a moon so close to its own size.
• Miranda, at 472 km, has some of the strangest surface features known, including cliff faces up to 20 km tall.
• Dysnomia, at about 700 km, is the moon of dwarf planet Eris, and it takes its name from the Greek goddess of lawlessness.
• Tethys and Dione, both over 1,000 km, are made mostly of water ice, giving them densities close to that of pure ice.
• The Moon is drifting away from Earth at about 3.8 cm per year, slowly lengthening our days.