Looks Are Deceiving!
Ganymede is larger in size than Pluto and Mercury; however, its mass is less than 50% of Mercury's. More than half the mass of this moon is made up of water ice.
Known as the biggest satellite to ever orbit a planet, Jupiter III, now known as Ganymede, is very interesting to study. Although it was discovered in the 1600s, it is billions of years old; 4.5 billion to be precise, which is the same age as Jupiter. It was discovered by Galileo Galilei on the 7th of January, 1610, when studying celestial bodies. At first, he was not entirely positive about its identity; but a few days and some research later, he came to the conclusion that there are four large moons orbiting Jupiter, Ganymede being the biggest. This revelation brought out the truth that the Earth, in fact, revolved around the sun; as planets other than the Earth had moons revolving around them as well, the solar system could not possibly be centered around the earth. There is evidence of a large moon orbiting Jupiter, in ancient Chinese astronomical records that date back to 365 BC. The records state that this moon was visible directly, without a telescope; this is believed to be Ganymede. The following are some more amazing and interesting facts about this moon.
Ganymede is seventh in line from Jupiter, and is the largest moon in the solar system.
Titan, Saturn's satellite, was the largest moon before Ganymede's discovery. The latter is only 2% greater in diameter than the former!
It was named by Galileo as Jupiter III. It was later renamed after the handsome Trojan prince Ganymede, who was taken by Zeus to Olympus, to become a cupbearer of the Olympian Gods.
The other three Galilean moons apart from Ganymede are Io, Europa, and Callisto. They can all be seen through a small telescope.
If Ganymede revolved around the sun instead of around Jupiter, it would have been classified as a planet.
There are color variations on the surface of this moon. It is mostly brownish in color, but some icy parts are bright and shiny.
The surface of Ganymede is made up of two different types. The dark region is about 4 billion years old, and completely filled with craters. It covers about 40% of the moon. The remaining 60% lighter area is less older, and is covered with a wide network of ridges and grooves.
Many of these grooves are quite tall and very long. There are some that are more than 1,500 feet tall, and thousands of miles long.
The darker areas are proof that there was volcanic activity on the moon!
Polar caps are present on Ganymede.
Ganymede is 3,267 miles in diameter, that is 5262 kilometers!
It is 665,000 miles (1,070,400 kilometers) away from Jupiter.
It takes 7 earth days and 3 earth hours for Ganymede to complete one rotation around Jupiter, and also one revolution. It orbits Jupiter at a speed of 24,321 miles/hour (39,165 kilometers/hour).
The average temperature of this moon during the day is between -171°F to -297°F (-113°C to -183°C), and drops to about -315°F (-193°C) at night.
Ganymede's circumference is 40% of the earth's. It is 16,532 kilometers, while that of the earth is 40,075 kilometers.
The surface gravity of the moon is 1.428 m/s2.
The distance between Ganymede and the Sun ranges between 459,571,997 and 507,705,130 miles, depending on Jupiter's position in the orbit.
This moon is made up of three parts, an iron core, followed by a mantle of silicate rock, and a crust of very thick ice.
It is believed that there may be a saltwater ocean about 124 miles under the icy surface!
The crust of ice is thought to be about 500 miles (800 kilometers) thick.
Ganymede's atmosphere is a very thin layer, not enough to sustain life on the moon. It contains O, O2, O3 (ozone), and hydrogen in small quantities.
This is the only moon that has a magnetosphere. A magnetosphere is a region which contains charged particles. However, the magnetic field of the moon is trapped in the much stronger magnetic field of Jupiter.
Io, Europa, and Ganymede follow an orbital resonance of 1:2:4. This means that for every 4 rotations of Io around Jupiter, Europa makes 2 and Ganymede makes 1.
Ganymede and Jupiter are in a tidal lock, which means that the same side of the moon and the planet always face each other. This is why Ganymede takes the same amount of time for one complete rotation and revolution.
This moon has been photographed by six spacecrafts; they were Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, the Galileo spacecraft, and New Horizons.
These were some fascinating facts about Ganymede. It is an astounding phenomenon that remains a topic of interest among astronomers; there is another space shuttle scheduled to pay a visit to Ganymede in 2022. It remains to be seen what new things it can find out.