After the Sun, the Moon is the second brightest object in our sky. However, our moon is not the only moon in the solar system, nor is it the largest by a long shot! Following the order of the moons by size, you would begin with Jupiter’s Ganymede. It has a diameter of 5279 km, and is so large that it has its own magnetic field and its bigger then Mercury and Pluto.
Titan, one of the moons orbiting planet Saturn, is the second largest moon, measuring 5149 km wide. Callisto, which orbits Jupiter, is the next largest moon, measuring 4821 km across. Jupiter has some of the largest moons in the solar system in its orbit – Io and Europa are 3643 km and 3122 km across, respectively. Earth’s own moon is 3475 km in radius while Neptune’s Triton is 2707 km across.
The order of moons by size under 2000 km radius is as follows: Saturn’s Rhea and Iapetus (1530 km and 1470 km), Charon of Pluto (1205 km), Dione and Tethys, both of Saturn, 1120 km and 1070 km in radius, respectively.
Moons whose radius is below 1000 km in radius include Titania, which goes around Uranus (788.9 km), Enceladus of Saturn (500 km), Proteus of Neptune (420 km), Mimas of Saturn (400 km) and Nereid of Neptune (338 km).
Jupiter has some of the largest moons in the solar system in its orbit, but it also has some of the smallest – the four small moons in the inner groups are all less than 200 km in diameter. There are a number of moons orbiting planets under 200 km in diameter: Larissa and Galatea of Neptune are 194 km and 176 km, respectively. The dwarf planet Haumea has a moon, Hi’iaka, measuring 155 km across. Despina of Neptune is slightly smaller at 150 km across. Eris is a dwarf planet with one known moon, Dysnomia. Dysnomia’s exact radius is unknown, but is thought to be about 100 km.
Moons can range from the enormous to the relatively smaller, such as Nix of Pluto (88 km) and Namaka of Haumea (85 km). Thalassa of Neptune is slightly smaller at 82 km in diameter. Hydra of Pluto is much smaller at 72 km in diameter, but it’s bigger than Naiad, Halimede, Neso Sao, Laomedeia, and Psamathe of Neptune, which are 66 km, 62 km, 60 km, 44 km, 42 km and 38 km in radius, respectively. The smallest moons in the solar system are Saturn’s Pan (19 km wide), and Phobos and Deimos of Mars, which are 11.1 km and 11 km in diameter respectively.