Ganymede, the largest moon orbiting Jupiter, is the biggest satellite in the entire solar system. Its sheer scale often prompts the question of how it compares to our own world. An examination of the raw measurements of both bodies clarifies the significant differences in their dimensions and physical composition. This comparison provides a full planetary context for Jupiter’s massive moon.
The Physical Dimensions of Ganymede
Ganymede is an immense celestial body with a mean diameter of approximately 5,270 kilometers, establishing it as the largest moon in the solar system. Its massive size is paired with a low average density of about 1.93 grams per cubic centimeter. This low density suggests Ganymede is composed of roughly equal parts silicate rock and water ice. The total mass of the satellite is estimated at 1.48 x 10^23 kilograms.
Earth’s Size for Planetary Context
Earth is a terrestrial planet with a fundamentally different structure and considerably greater mass than Ganymede. Our planet has an average equatorial diameter of about 12,756 kilometers, making it the largest of the inner solar system’s rocky worlds. Earth’s mean density is significantly higher than Ganymede’s, measuring about 5.51 grams per cubic centimeter. This density results from Earth having a large, dense iron-nickel core surrounded by a rocky mantle. The total mass of Earth is 5.97 x 10^24 kilograms.
Direct Size Comparison and Ratios
The most direct comparison of Ganymede to Earth reveals that the Jovian moon is slightly over 41% of Earth’s diameter. This means that Earth is more than twice as wide as Ganymede. Although Ganymede is large, its volume is only about 7% of Earth’s total volume. This volume discrepancy means that more than 14 objects the size of Ganymede could fit inside Earth. The mass difference is even more pronounced due to Ganymede’s icy composition; its total mass is only about 2.5% of Earth’s mass.
Size Relative to Planets
Despite being a moon, Ganymede’s scale places it among the solar system’s major bodies, surpassing the size of other planets. Its diameter of 5,270 kilometers makes it larger than the planet Mercury (4,880 kilometers across) and substantially bigger than the dwarf planet Pluto. The crucial difference remains the density and mass, where the rocky, metal-rich Earth vastly outweighs the icy Ganymede.
Ganymede’s Unique Planetary Attributes
Ganymede’s immense size contributes to two unique features that set it apart from every other moon in the solar system. Scientific data indicates the presence of a vast, deep subsurface saltwater ocean buried beneath its icy crust, potentially containing more water than all of Earth’s surface water combined. Ganymede is also the only moon known to generate its own intrinsic magnetic field. This field is generated by convection within its liquid, iron-rich core, similar to the process that creates Earth’s magnetic field. The existence of this ocean and magnetic field elevate Ganymede to a body of intense scientific interest, making it a prime target for missions exploring the potential for habitability.