Facts About Ganymede - The Largest Moon In The Solar System

Ganymede - Facts about Ganymede

Ganymede is the largest and most massive among the moons of Jupiter. It was discovered on 7th January 1610 by Galileo Galilei. He used to call it "Jupiter III". After the numerical naming system was abandoned, it was named after a Trojan prince in Greek mythology. Ganymede is also the biggest moon in the solar system, even larger than the planet Mercury and dwarf planet Pluto. NASA and the United States Geological Survey published the first-ever map of Ganymede in February 2015 based on Voyager and Galileo spacecraft observations.

Facts about Ganymede

Ganymede Profile

Name Ganymede
Satellite of Jupiter
Distance from Jupiter (avg) 1,070,400 km
Radius 2,634.1 km
Volume 7.66 × 1010 km3
Mass 1.48 × 1023 kg
Surface area 8.72 million km2
Gravity 1.42 m/s2
Max Temperature -121 ℃ or -186 °F
Min Temperature -203 ℃ or -333 °F
Length of day 7.15 Earth days
Length of year 7.15 Earth days
Discovered By Galileo Galilei
Discovered On January 7, 1610

Quick facts about Ganymede

  1. If Ganymede is revolving around the Sun rather than Jupiter, it would be classified as a planet. 
  2. It is the only known moon in the solar system which possess its own magnetic field.
  3. The magnetic field is probably generated due to its molten core, just like earth.
  4. Ganymede also has an atmosphere, but it is very thin and is made up of oxygen.
  5. Till now, seven spacecraft have photographed Ganymede.
  6. Pioneer 10 in 1973 and Pioneer 11 in 1974 were the first to visit and returned images of Ganymede.
  7. Until Voyager 1 and Voyager 2 measured the actual size of Jovian satellite, Titan (the largest moon of Saturn) was thought to be larger than Ganymede.
  8. It also has polar ice caps made up of thin layers of water ice sheets.
  9. The polar caps were first detected by Voyager spacecraft.
  10. ESA has planned to send a spacecraft in 2022, named JUICE (Jupiter Icy Moon Explorer), to visit the three icy Galilean moons and to orbit and study Ganymede.

Detailed Facts About Ganymede

  • Ganymede was discovered in 1610

Galileo Galilei - discoverer of the four largest moons of Jupiter
Galileo Galilei - the discoverer of the four largest moons of Jupiter

When Galileo Galilei was observing Jupiter on January 7, 1610, he stumbled across the four largest moons of Jupiter. However, he recognised them as three stars. They were Ganymede, Callisto and a combined light from Io and Europa. Again he turned his telescope towards Jupiter on January 13 and saw the four moons separately for the first time. Thereafter, by observing the movements of the moons, he theorised that the stars were actually bodies revolving around Jupiter.

It was the first time that a body was observed as revolving around another object than earth. From this observation, it was understood that not all the things revolve around the Earth, as previously believed that Earth is the centre of the universe.
  • Ganymede can be seen by naked eyes

Technically, Ganymede along with the other three Galilean moons are visible through the naked eye. However, Jupiter is so bright that its glare hides them. If the giant planet's glare is obstructed by a branch of a high tree which is perpendicular to the orbital planes of the moons, one or more Galilean moon might be visible in some favourable conditions.
  • Chinese had seen Ganymede before the West

Before the Galileo had spotted Ganymede, Gan De - A Chinese astronomer and astrologer, reported a "small reddish star" next to Jupiter, in the summer of 364 BC. Later, Xi Zeezong, a Chinese astronomer and historian, has claimed that the small reddish star was nothing but Jupiter's largest moon Ganymede. However, astronomers are perplexed that the how Gan De was able to recognise its colour as the Jovian moons are too faint.
  • Ganymede is the largest of all the moons in the solar system

Ganymede compared to other moons of the solar system
Ganymede compared to other moons of the solar system

With an immense diameter of about 5,2682 km or 3,273.5 miles, Ganymede is the most massive and largest moon in the solar system. By comparison to the other Galilean moons, it is 9% bigger than Callisto, 40% bigger than Io and 68% larger than Europa. In the solar system, it is bigger than planet Mercury by 8% and not much smaller than Mars. Furthermore, its mass is 10 per cent larger than the next largest moon Titan and twice that of our moon.
  • The internal structure of Ganymede is fully differentiated

Internal structure of Ganymede
The internal structure of Ganymede

A differentiated planetary body is that whose constituents are separated into layers; that is its denser materials sink down to the centre, and less dense materials come up to the surface. This is what happened with the internal structure of Ganymede. Like our earth, Ganymede has a core of liquid iron-nickel, a Silicate mantle and the outer layer is possibly water ice and liquid water.
  • The Ganymedian surface is separated into two parts

Lighter and Darker regions on Ganymede
Lighter and Darker regions on Ganymede

The surface of Ganymede is composed of two types of lands - dark regions and lighter regions. Dark areas are highly cratered, ancient and cover almost one-third of the surface. In comparison, the lighter part is relatively younger and has fewer craters than dark regions. However, it contains an extensive array of grooves and ridges. How were the grooves formed is still an unsolved problem in planetary science.

The researchers believe that the grooves are the result of the past tidal heating. This heating mechanism may have heated the interior part and developed cracks. These cracks also wiped out the 70 per cent of the old dark regions.
  • The age of the dark regions is the same as the highlands of the moon

Crater Gula(top) and Achelous(botton) on the grooved terrain, captured by Galileo spacecraft
Crater Gula (top) and Achelous (bottom) on the grooved terrain, captured by Galileo spacecraft 

The surface of Ganymede is full of craters, but it is more intense on the dark terrain. By measuring the density of the craters, scientists estimated that the dark regions are old as the highlands of the Moon that is 4 billion years old. However, how young the lighter terrain is uncertain.

Some of the craters are overlayed by the grooves while some are crosscut, indicating that the formation of the grooves started in the early stage of its surface. Like mercury, there are also "ghost" craters (known as a palimpsest). These are the craters whose relief has been disappeared and left behind a circular albedo feature.
  • Ganymede has an ocean underneath its surface

Aurora on Ganymede
Aurora on Ganymede

In the 1970s, scientists first theorised that Ganymede has an ocean, beneath the surface between two layers of ice. Again in 2002, the measurement of the magnetic field taken by the Galileo spacecraft gave some indication of the ocean. This theory was confirmed in March 2015 when scientists were observing the auroras of Ganymede.

Since Ganymede is enclosed in Jupiter's magnetic field, changes in the giant planet's magnetic field also influence the auroras of the Ganymede. By observing the movement of the auroras, they concluded that a large saltwater ocean is lurking beneath the icy crust. The depth of the ocean is 100 kilometres (60 miles ) that is ten times deeper than our planet's ocean. According to the evidence found, researchers think that it might be the largest water ocean in the solar system.
  • Ganymede was formed around Jupiter.

It is believed that Ganymede is made from the dust and gas cloud, which is left after the formation of Jupiter. Ganymede probably took almost 10,000 years to take its shape from the dust cloud. The accretion process possibly happened near Jupiter, where the cloud is much dense, which prevented the accretional heat from escaping its interior. This heat further helped it to be differentiated into molten core, silicate mantle and a thick icy crust, giving a multilayered interior and melting of ice into an enormous ocean.

More Ganymede Facts

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