Ganymede

Ganymede is a moon of Jupiter, is the largest and most massive moon in the Solar System, the ninth largest person in the system, and the largest person without an atmosphere, he is 8% larger than Mercury, he has the lowest moment of inertia factor of any solid body in the solar system.

he is made out silicate rock and water ice, has an iron-rich liquid core, and a huge ocean that has more water than Earth, a third of his surface is covered with dark areas, who are impact craters that date back to 4 billion years ago

he is born with his left arm having a bionic part on it, which he didn't want, and Jupiter is still trying to remove his bionic part so that it's easier to fix his left arm's joint.

he likes to play video games, some of his favorite games include Minecraft and Fortnite, he owns an Xbox One, a PlayStation 4, and a Nintendo Switch

he also is the only moon in the system with a magnetic field, his magnetic field is generated by convection within his liquid iron core.

Orbit and rotation
Ganymede completes a full orbit around Jupiter every 7 days and 3 hours, like most of his fellow friends, he is tidally locked, so his day is also 7 days and 3 hours

he participates with orbital resonances with Io and Europa

Size
he is the largest moon in the system, he is smaller than Mars, Venus, and Earth, but bigger than Mercury, Titan, Callisto, Io, and the Moon

Surface
Ganymede's skin is a mix of two types of terrain, very old dark regions and slightly younger lighter regions

cyrovolcanism once played a minor role on him

hot water plumes may have risen from his core to his surface before, leading to the deformation of his lithosphere

a feature on Ganymede is a huge dark plain called Galileo Regio, a region that contains a series of concentric grooves, or maybe furrows

like Earth and Mars, Ganymede has polar ice caps, these ice caps are made out of frost water

Internal Structure
Ganymede has an iron and iron-sulfide core, a silicate mantle, and outer layers of water ice

above the rocky mantle is tetragonal ice (that is, Ice 6), an extensive saltwater ocean that has more water then Earth, and has hexagonal ice

water in his saltwater ocean may have been an important factor of life developing in the ocean

Atmosphere
Ganymede has an exosphere similar to the one found on his sister Europa

History
he was born from an accretion in Jupiter's subnebula, his birth took about 10,000 years to do so, much shorter than the 100,000 years for Callisto's birth

In fiction
he appeared in many works of fiction, examples include
 * in Tidal Moon most of Ganymede's surface is flooded every 3 months due to Jupiter's tides
 * in Power Rangers, he is the hiding place chosen by Zordon
 * he is the location on a mining colony is the series Return to Jupiter
 * in One Must Fall: 2097, the prize is on his surface

Trivia

 * he is the only moon with a magnetic field