Ganymede is the largest satellite in the solar system with a diameter of 5,268 km (3270 miles). It is larger than Mercury and Pluto, and three-quarters the size of Mars. If Ganymede orbited the Sun instead of orbiting Jupiter, it would easily be classified as a planet.

Composition
Like Callisto, Ganymede is most likely composed of a rocky core with a water/ice mantle and a crust of rock and ice. Its low density of 1.94 gm/cm3,indicates that the core takes up about 50% of the satellite's diameter. Ganymede's mantle is most likely composed of ice and silicates, and its crust is probably a thick layer of water ice.

Science Findings

• Possible Internal Structures of the Galilean Satellites (November 18, 1997).
• Galileo Finds a Magnetic Field on Ganymede (December 12, 1996).
• Hubble Finds Thin Oxygen Atmosphere on Ganymede (October 23, 1996).
• Galileo Spacecraft Makes New Discoveries at Ganymede (July 10, 1996)

More about Ganymede

Diameter (km):
5,268

Mass (kg):
1.48e23

Mass (Earth = 1)
0.0247

Surface Gravity
  (Earth = 1):
0.145

Mean Distance from
  Jupiter (km):
1,070,000

Mean Distance From
  Jupiter (Rj):
15.1

Mean Distance from
  Sun (AU):
5.203

Orbital period (days):
7.154553

Rotational period (days):
7.154553

Density (gm/cm³)
1.94

Orbit Eccentricity:
0.002

Orbit Inclination
  (degrees):
0.183

Orbit Speed (km/sec):
10.9

Escape Velocity (km/sec):
2.74

Visual Albedo:
0.43

Subsolar Temperature (K):
156

Equatorial Subsurface
  Temperature (K):
117

Surface Composition:
Dirty Ice