Moons of the Solar System

Ganymede, which orbits Jupiter, is the largest moon in the Solar System. Its diameter is about 5,262 kilometres.

Titan, which orbits Saturn, is the second largest moon, with a diameter of about 5,150 kilometres.

Mercury, the smallest planet, has a diameter of about 4,879 kilometres, so both Ganymede and Titan are wider than it.

Callisto, the third of the giants, measures about 4,821 kilometres across, just short of Mercury.

Neptune's moon Triton is about as big as Pluto.

Earth's Moon has a diameter of about 3,475 kilometres.

Io, the innermost of Jupiter's four large moons, is about 3,640 kilometres across, not much larger than the Moon.

Europa is about 3,122 kilometres across, slightly smaller than Earth's Moon, and is the fourth largest of Jupiter's moons.

Galileo Galilei first observed Jupiter's four largest moons, Io, Europa, Ganymede and Callisto, in 1610 with an early telescope.

Callisto is Jupiter's second-biggest moon and ranks among the three largest moons in the Solar System.

Europa is the sixth-closest moon to Jupiter.

Ganymede is one of three Jovian moons thought to hold oceans of liquid water beneath their icy crusts.

Titan is the only moon in the Solar System known to have a substantial atmosphere. Its surface pressure is about 60% higher than Earth's.

Titan has clouds, rain, rivers, lakes and seas of liquid hydrocarbons such as methane and ethane.

Scientists believe Europa has a saltwater ocean under its icy shell that holds about twice as much water as Earth's oceans.

Saturn's small moon Enceladus has a global ocean beneath a thick icy shell.

As of August 2026, Saturn had 293 confirmed moons, far more than any other planet.

As of October 2026, there were 461 officially recognized moons orbiting planets, including the dwarf planet Pluto.

Mars has two moons, Phobos and Deimos, which are lumpy and dark rather than round.

Pluto has five moons. The largest, Charon, is about half Pluto's size.

The European Space Agency's Juice spacecraft launched on 14 April 2023 and is due to reach Jupiter in July 2031. It will then make an orbital tour of Ganymede.

NASA's Europa Clipper launched on 14 October 2024.

NASA's Dragonfly rotorcraft is planned to launch to Titan in 2028 and spend three years making multiple landings.