Ganymede g1 true 2
Adjective(s) Unknown
Orbital properties
Aphelion/apoapsis 1071600 km
Perihelion/periapsis 1069200 km
Semi-major axis 1,070,400 km
Orbital eccentricity 0.0013
Orbital period 7.15455296 d
Average orbital speed 10.880 km/s
Physical properties
Radius 2634.1±0.3 km (0.413 Earths)
Mass 1.4819×1023 kg (0.025 Earths)
Mean density 1.936 g/cm3
Escape velocity 2.741 km/s
Rotation period synchronous
Average surface temperature min mean max

70 110 152

Apparent magnitude 4.61 (opposition)

4.38 (in 1951)

Moons 0

Ganymede is the largest moon in the Solar System.


It was discovered by Galileo on January 7th, 1610. Ganymede, along with the other three Galilean satellites, were the first moons to be discovered orbiting another planet.


  • Ganymede is a moon of Jupiter.
  • It is one of the four Galilean Moons. The other three are Io, Callisto, and Europa.
  • It takes about one week for Ganymede to circle Jupiter.
  • Ganymede is larger than the planet Mercury, and would be considered a planet if it didn't orbit Jupiter.
  • Although Ganymede is larger in diameter, Mercury is more massive due to its high density.
  • Ganymede's diameter is 5262 km.
  • Ganymede's density is 1.94.
  • It is the only moon with it's own magnetic field, likely caused by convection currents.
  • Ganymede is about twice as massive as Earth's Moon.
  • Ganymede has a thin oxygen atmosphere, and possibly has an ozone layer. 
  • Saturns moon Titan was thought to be bigger until the Voyager spacecrafts proved otherwise.
  • It may have an underground ocean of water. That may contain life.
  • The Jupiter Icy Moon Explorer (JIMO) that is expected to launch in 2022 is planned to orbit Ganymede.