Ganymede Facts

Ganymede Facts

Ganymede is the largest satellite in the solar system, and is a moon of Jupiter. It is larger than Mercury and Pluto, and only slightly smaller than Mars.

If it were orbiting the sun rather than Jupiter it could definitely be considered a planet. Let’s explore some Ganymede facts.

Ganymede structure

(Click to enlarge image)

Ganymede Overview

  • Age: Ganymede is about 4.5 billion years old, roughly the same age as Jupiter.
  • Distance from Jupiter: Ganymede is the seventh moon and third Galilean satellite outward from Jupiter, orbiting at about 665,000 miles (1.070 million km). It takes Ganymede about seven Earth days to orbit Jupiter.
  • Size: Ganymede’s mean radius is 1,635 miles (2,631 km). Due to its size, Ganymede can be viewed with the naked eye. Early Chinese astronomical records show the discovery of a moon of Jupiter, which was more than likely the first sighting of Ganymede. Although Ganymede is larger than Mercury it only has half its mass, which makes it low density.
  • Temperature: Daytime temperatures on the surface average -171°F to -297°F (-77°C to -147°C), and night temperatures drop to -379°F (-193°C). With these temperatures, scientists believe that it’s unlikely there are any living organisms on Ganymede. 

How was Ganymede Discovered?

  • Ganymede was discovered by Galileo Galilei on January 7, 1610.
  • This discovery was the first time a moon was seen orbiting a planet other than Earth.
  • Galileo’s discovery revealed that planets orbit the sun, instead of our solar system revolving around Earth.

How did Ganymede get its Name?

  • Galileo called this moon Jupiter III.
  • When this naming system was abandoned in the mid-1800s, the moon was named after Ganymede, a Trojan prince in Greek mythology. Zeus, a counterpart of Jupiter in Roman mythology, carried Ganymede, who had taken the form of an eagle, to Olympus, where he became a cupbearer to the Olympian gods and one of Zeus’ lovers.


The Exploration of Ganymede

  • There have been several spacecraft that have flown by Jupiter and its moons.
  • Pioneer 10 arrived first, in 1973.
  • This was followed by Pioneer 11 in 1974.
  • Voyager 1 and Voyager 2 came back with amazing photos during their flybys.
  • The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images which has led us to understand the moon a bit more. 

Features of Ganymede

  • Ganymede has a core of metallic iron, which is followed by a layer of rock, which is topped by a crust of mostly ice that is very thick.
  • There are a number of bumps on Ganymede’s surface, which may be rock formations.
  • In February 2014, NASA and the United States Geological Survey unveiled the first detailed map of Ganymede in images and a video animation created using observations from NASA’s Voyager 1 and Voyager 2 spacecraft, as well as the dedicated Jupiter-orbiting Galileo spacecraft.

Ganymede map

  • Ganymede’s surface is made up of two types of terrain—about 40% is dark with a number of craters and 60% is lighter in colour and has grooves that form elaborate patterns to give the satellite its unique appearance.
  • The grooves, which were likely formed as a result of tectonic activity or water being released from beneath the surface, are as high as 2,000 feet (610m) and stretch for thousands of miles.
  • Scientists believe that this moon has a saltwater ocean 124 miles (200km) below its surface.

Ganymede’s Atmosphere

  • If people ever thought that it was possible for life on Ganymede, then it’s just not possible due to its thin oxygen atmosphere.
  • It is the only satellite in the solar system to have a magnetosphere. Typically found in planets, including Earth and Jupiter, a magnetosphere is a comet-shaped area in which charged particles are trapped or ricocheted. Ganymede’s magnetosphere is entirely entrenched within the magnetosphere of Jupiter.

Ganymede is an interesting moon, and has some cool features. Do you know any other facts about Ganymede?

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