Ganymede

Moon· orbits Jupiter

Ganymede is the largest moon in the Solar System — bigger than the planet Mercury — and the only moon known to generate its own magnetic field, evidence of a subsurface ocean.

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Key facts

Mass

1.48 × 10²³ kg

0.0248 M⊕

Radius

2,631 km

1.51× wider than our Moon

Surface gravity

1.43 m/s²

15% of Earth's gravity

Day length

7.2 days

Orbit around Jupiter

7.16 Earth days

Science

Physical

Mass: 1.48 × 10²³ kg · 0.0248 M⊕; JPL / IAU mean radii; spacecraft-tracked GM where measured
Radius: 2,631 km · 1.51× wider than our Moon; JPL SSD Planetary Satellite Physical Parameters (mean radius)
Density: 1,942 kg/m³ · 1.9× water; Computed from mass and radius
Surface gravity: 1.43 m/s² · 15% of Earth's gravity; Computed from mass and radius
Escape velocity: 2.74 km/s · 25% of Earth's escape velocity; Computed from mass and radius

Orbit around Jupiter

Distance from Jupiter: 1,070,400 km; From JPL orbital elements
Orbital period: 7.2 days; From JPL orbital elements
Eccentricity: 0.001; From JPL orbital elements
Inclination to Jupiter's Laplace plane: 0.20 °; From JPL orbital elements · The Laplace plane is the one a moon's orbit precesses about: close in it is the planet's equatorial plane, the plane of the rings, and further out it tilts toward the planet's own orbit.

Rotation

Rotation period: 7.2 days
Tidal locking: Tidally locked to its parent

Temperature

Minimum: 70 K (-203 °C)
Mean: 110 K (-163 °C)
Maximum: 152 K (-121 °C)

Composition

Bulk composition: Roughly equal parts rock and water ice, differentiated into an iron core, a rock mantle and a thick ice shell over a probable salty ocean.

Radiation & temperature

Insolation: 0.0355 S⊕ · 4% of the sunlight Earth receives; Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
Bond albedo: 0.35 · reflects 35% of incoming sunlight
Equilibrium temperature: 108 K (-165 °C); Computed from albedo + distance from the Sun (airless black body)
Measured mean temperature: 110 K (-163 °C)
Surface magnetic field: 719 nT · 1% of Earth's magnetic field

Discovery & history

Discovered: January 7, 1610
By: Galileo Galilei
Method: Visual discovery (telescopic)
Name: Ganymede, a Trojan youth carried to Olympus by Zeus.

A Galilean moon found in 1610 and the largest moon in the Solar System — bigger than the planet Mercury, and the only moon with its own magnetic field.