Jupiter's Moon Ganymede
Written by Fraser Cain
Ganymede is Jupiter's largest moon. In fact, it's the largest moon in the entire Solar System, measuring 5,268 km across – it's even bigger than Mercury. It's the 7th closest moon of Jupiter, and the 3rd Galilean satellite.
Since Ganymede is further away from Jupiter than Io and Europa, it doesn't experience the same kinds of tidal flexing as those other moons. But astronomers do think there's a salt water ocean 200 km below Ganymede's surface, in between layers of ice.
There are two kinds of terrain on Ganymede's surface: dark regions with craters that are at least 4 billion years old, and then lighter regions with grooves and ridges.
Ganymede is the only moon in the Solar System with its own magnetosphere. The magnetic field is probably generated by convection within the moon's liquid iron core.
It orbits in a 4:2:1 resonance with Europa and Io. In other words, for every orbit of Ganymede, Europa completes 2 orbits, and Io completes 4; but the moons are never lined up on the same side of Jupiter.
As with all the Galilean moons, Ganymede was first discovered by Galileo Galilei in 1610. It was named after the Greek mythology's Ganymede, cupbearer of the gods and a lover of Zeus.
Here's an article from Universe Today about Ganymede's lumpy interior.
Here's more information on Ganymede from the Nine Planets, and JPL's Fact Sheet.
We've also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter's Moons.
Filed under: Astronomy
