Ganymede is the largest moon, and one of the four Galilean moons of planet Jupiter. Ganymede is larger than Mercury and Pluto, and 2/3 the size of Mars. It would be considered a planet if it were orbiting the Sun instead of Jupiter.

Ganymede is the only mooon in the solar system to possess a magnetic field, has a tenuous oxygen atmosphere, and is believed to have six times the water on Earth in the form of several subsurface saltwater oceans sandwiched between layers of ice.

Ganymede, along with Callisto, Europa, and Io, were discovered by the Italian astronomer Galileo Galilei in 1610.

Ganymede 4K pan-zoom image

Pan, zoom, or go full-screen with this megapixel image of Ganymede.

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  Source image: NASA (Galileo)

Ganymede facts

Designation: Jupiter III
Magnitude: 4.6
Mass: 1.48 x 1023 kg
Radius: 2,631 km
Density: 1.94 gm/cm3
Distance from planet: 1.07 million km
Rotational period: 7.15 days
Orbital period: 7.15 days
Orbital velocity: 10.88 km/sec
Eccentricity of orbit: 0.002
Inclination of orbit: 0.195 °
Albedo: 0.42
Atmosphere: trace O2
Temperature (mean): -121°C / -203°C

Ganymede surface features

A few notable surface features on Ganymede:

Achelous crater
Barnard Regio large area
Galileo Regio large area
Gula crater
Hershef crater
Marius Regio large area
Memphis Facula bright spot
Nicholson Regio large area
Perrine Regio large area
Tashmetum crater

Ganymede, which had been a million kilometers away across the system a few seconds before, zoomed toward them, flicked past, and was lost to sight behind them.

- Dan Simmons, Illium