Ganymede Moon Facts

Discovered by Galileo Galilei in 1610 with three other Jupiter moons, Europa, Io, and Callisto, Ganymede is the 7th moon Jupiter’s 67 moons.

Ganymede Moon Profile

Discovered By:Galileo Galilei January 7, 1610
Diameter:5,262.4 km
Mass:1.48 x 10^23 kg (2.0 Moons)
Orbit Distance:1,070,400 km
Orbit Period:7.16 days
Surface Temperature:-163 °C

These four moons are called Galilean moons and Ganymede is so larger that if it was orbiting a Sun instead of Jupiter, it would be considered a planet.

Just a bit smaller than Mars, Galileo originally called Ganymede Jupiter III, but later renamed by German astronomer Johannes Kepler after a mythological Greek Trojan prince who was a cupbearer for the gods.

With twice the mass of our Earth, Ganymede is the largest moon in our Solar System.

Scientists have long thought that if Jupiter had a larger mass it would be a gas giant that experienced nuclear fusion, turning it into a sun.

Magnetic Field

It has many moons in its orbit that could have been planets. Ganymede is the only moon within our solar system that has its own magnetic field.

Although very light, it’s believed that the field was created due to the liquid iron core at Ganymede’s center. But the magnetic field isn’t the only thing that makes Ganymede notable.

Layers of water

It is made up of layers of water ice and silicate rock in almost equal amounts, and scientists believe that there just might be liquid saltwater under its thick crust of ice.

Researchers think that this water may be as close to the surface as 124 miles and that it is next to the moon’s rocky mantle.


This theory would make Ganymede an excellent candidate for finding potential life. There is a thin atmosphere of oxygen on Ganymede but it isn’t great enough to be life supporting.

Another interesting thing about Ganymede is that it is thought to have tectonic activity that builds up heat and friction, causing the surface to have activity that covers the impacts from comets and asteroids.

Dark areas cover 40% of the surface and may be impacts from around 4 billion years ago.

There are lighter areas that are not that old, with grooves that scientists believe are due to the tectonic activity.

Ganymede is tidally-locked to Jupiter. This means that it has one side that faces the planet and one side that faces away from the planet.

How long dose it take to orbit Jupiter

The moon is orbiting Jupiter at 24,321 mph/39,165 kmh, and it takes Ganymede 7.16 Earth days to complete one Jupiter orbit.

Surface temperatures on Ganymede average -171 F to -207 F during daytime areas and at night it can reach -193 C.

Scientists are very interested in Ganymede and there have been quite a few spacecraft flybys that have gathered data on this moon.

The early missions in the 1970’s offered only blurred images, however, the later 2007 New Horizon mission sent back incredible detail on the topography and make up of Ganymede.

So far, there have been six space missions that have flown by Ganymede.

Facts about Ganymede Moon

  • Until the Voyager 1 and 2 space missions that flew by Ganymede, scientists thought the largest moon in the solar system was Saturn’s moon, Titan.
  • The core of Ganymede is made up of metallic iron and then a layer of rock with a surface crust that is mostly thick ice.
  • Ganymede has many “bumps” on its surface that scientists think are rock formations.
  • The Hubble Space Telescope viewed the auroras on Ganymede to determine the magnetic field changes between Jupiter and Ganymede.
  • Ganymede’s auroras seem to “rock,” which is a strong indication that there is salt water under the surface.
  • Scientists don’t believe that there are any hot water vents on Ganymede to bring water to the surface due to the high internal pressure.
  • We already know that Ganymede has polar ice caps that are made up of water ice.


    • What position does Ganymede have as one of Jupiter’s moons?
    • Before information was discovered about Ganymede, which moon was considered to be the largest in the solar system?
    • Who discovered Ganymede?
      Galileo Galilei
    • What planet in the solar system is just a little bit larger than Ganymede?
    • What name was originally given to Ganymede?
      Jupiter III
    • What is Ganymede’s core believed to be made of?
      metallic iron
    • Back to : Astronomy for Kids