World Facts

Biggest Moons In Our Solar System

At 5,262 kilometers in diameter, Jupiter's Ganymede is the largest moon in our solar system.

The moon is a solid natural object that orbits around a planet. It is a planet’s natural satellite. No definite scientific explanation has satisfactorily answered the question of how moons came into existence, although there are several theories. The Earth’s Moon was thought to be the only moon but after the invention of the telescope, other moons on other planets were discovered. Each planet has one or more moons except Mercury and Venus. Jupiter has 67 moons the highest number in the solar system. Technological advancements have made it possible for man to discover and even go on expeditions to the moon. The biggest moons in our solar systems are:


Ganymede is by far the largest moon and orbits around planet Jupiter with a diameter of 5,262 kilometers. It is bigger in size than some of the planets like Mercury and Pluto and would have easily been classified as a planet if it was orbiting the sun. It has its own magnetic field. Its discovery was made by Galileo Galilei the Italian astronomer on January 7, 1610. The satellite orbits around Jupiter at a distance of 1,0700,400 km and takes 7.1 days to complete one orbit. The surface of Ganymede has two types of terrains. It consists of lighter, younger areas and a darker cratered region. The planet’s atmosphere is thin and has oxygen contained in dispersed molecules. Water ice and rocky material make up the planet, and it thought to have underground oceans. The name is derived from a prince in Greek mythology.


Titan Moon orbits Saturn and is the second largest moon with a diameter of 5,150 km. Christiaan Huygens a Dutch astronomer discovered this moon in 1655. It has a dense atmosphere that is similar to that of Earth. 90% of the atmosphere is mostly nitrogen, and the rest is methane and small amounts of ammonia, argon, and ethane. It orbits around Saturn in 16 days. The moon has seas and lakes on its surface that are filled with liquid hydrocarbons. It is the only body other than the earth that has water bodies in our solar system. The name Titan is derived from Greek mythology about ancient gods called Titans. Ice and rocky materials make up most of Titan’s mass.


Callisto Moon is the second largest moon that orbit planet Jupiter and the third largest moon among all. It has a diameter of 4,821 km and estimated to be 4.5 billion years old; its surface is mostly cratered. It has not had any geological activities for most of its existence. It was discovered by Galileo Galilei on January 7, 1610. Its name is derived from Greek mythology of a nymph called Callisto. It orbits Jupiter at an estimated distance of 1,882,700 km. Callisto takes 16.7 days to rotate on its axis and also orbit Jupiter. It is the farthest moon from Jupiter, meaning it has not been largely affected by Jupiter’s magnetosphere. Water ice constitutes most of its mass and other materials such as magnesium and hydrated silicates. Callisto has a dark surface, and a salty sea is thought to lie underneath the surface.


IO moon also orbits around planet Jupiter and has a diameter of 3,643 km. It is the fourth largest moon and was discovered by 1610 by Galileo Galilei. It is the most active body after Earth with volcanic activity. The surface of IO is mostly made of floodplains of liquid rock and lava lakes. It orbits at an estimated 422,000 km from Jupiter in 1.77 Earth-days and is the fifth moon of the planet Jupiter. The moon has a splotchy appearance of white, red, yellow, black, and orange. The atmosphere of IO mostly consists of Sulphur dioxide. It was named after a nymph called IO who was seduced by the gods Zeus in Greek mythology. Under the smooth surface of IO is a layer made of the iron core and an outer layer made of brown silicate.

Other big moons and the planets they orbit in include, The Earth’s Moon (3,475km), Europa, Jupiter (3,122km), Triton, Neptune (2,707km), Titania, Uranus (1,578km), Rhea, Saturn (1,529km) and Oberon, Saturn (1,523km). Most of the observations on these moons are done from the ground. Improved technology has helped scientists send man-made satellites to revolve around the solar system and enable the discovery of more information on these moons.

Biggest Moons In Our Solar System

RankMoon, PlanetAverage Diameter
1Ganymede, Jupiter5,262 kilometers
2Titan, Saturn5,150 kilometers
3Callisto, Jupiter4,821 kilometers
4Io, Jupiter3,643 kilometers
5The Earth's Moon3,475 kilometers
6Europa, Jupiter3,122 kilometers
7Triton, Neptune2,707 kilometers
8Titania, Uranus1,578 kilometers
9Rhea, Saturn1,529 kilometers
10Oberon, Uranus1,523 kilometers

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