📖 About Ganymede

Ganymede is the largest moon in our solar system, with a diameter of 5,268 km—larger than the planet Mercury. Discovered by Galileo Galilei in 1610, it is the third of the four Galilean satellites orbiting Jupiter. If Ganymede orbited the Sun instead of Jupiter, it would be classified as a planet.

Ganymede is the only moon known to possess its own intrinsic magnetic field, generating a small magnetosphere embedded within Jupiter’s massive one. This creates spectacular aurora displays at its poles. The moon’s interior is differentiated into an iron core, a rocky mantle, and an outer shell of ice. Scientists believe a saltwater ocean exists between layers of ice, roughly 200 km below the surface.

ESA’s JUICE (Jupiter Icy Moons Explorer) mission launched in April 2023 and will arrive at Jupiter in 2031. After multiple flybys of Callisto, Europa, and Ganymede, JUICE will enter orbit around Ganymede in 2034—becoming the first spacecraft to orbit a moon other than our own. The mission will study Ganymede’s ocean, magnetosphere, and habitability.

🔭 Key Features

🔬 Science & Future

Ganymede provides a unique laboratory for studying planetary magnetospheres and the interaction between a moon’s magnetic field and its parent planet’s magnetosphere. The discovery of its magnetic field by the Galileo spacecraft in 1996 was a major surprise and opened new questions about how small bodies generate and maintain magnetic fields.

The JUICE mission will carry ten scientific instruments to characterize Ganymede’s surface, subsurface, atmosphere, and magnetic environment. Understanding Ganymede’s ocean—its depth, salinity, and connection to the rocky interior—will help assess its potential for harboring life and inform future exploration of ocean worlds throughout the solar system.

📜 Discovery & Exploration

Galileo Galilei discovered Ganymede on January 7, 1610. The moon is named after a beautiful Trojan prince in Greek mythology who became cupbearer to the gods on Mount Olympus. Chinese astronomer Xi Zezong later showed that Gan De may have observed Ganymede with the naked eye as early as 365 BCE.

NASA’s Galileo spacecraft made six close flybys of Ganymede between 1996 and 2000, discovering the magnetic field and mapping the surface in detail. The Juno spacecraft has also observed Ganymede, capturing the closest images in over two decades during a 2021 flyby at just 1,038 km altitude.