On this date in 1996 Galileo, NASA’s Jupiter probe, passed within 524 miles of its moon Ganymede. 10 things you might not know about Ganymede.
It was named after a beautiful boy in Greek mythology who was carried off by Zeus disguised as an eagle. He became the cup bearer to the gods. Zeus, of course, is the Greek equivalent of the Roman god Jupiter.
Ganymede was discovered by Italian astronomer Galileo Galilei on Jan. 7, 1610, along with three other large moons. This was the first time any planet other than Earth was found to have a moon.
The diameter of Ganymede is 3,270 miles (5,260 kilometres), which means it is the biggest moon in the solar system and is actually bigger than Mercury and Pluto.
It is 665,000 miles (1,070,000 kilometres) from Jupiter and takes about a week to orbit the planet. It’s tidally locked with Jupiter, so the same side always faces the planet; and it’s in what’s called an orbital resonance with Io and Europa. Every time Ganymede orbits Jupiter once, Europa orbits twice, and Io orbits four times. It’s this which has caused these moons to maintain eccentric orbits.
Ganymede is the only moon known to have its own magnetic field.
There may be more water on Ganymede than on Earth. NASA’s Hubble Space Telescope has found evidence that there could be a massive underground saltwater ocean on Ganymede which is ten times deeper than the oceans on Earth. This ocean is covered by a 95-mile (150-kilometer) crust of ice. Since scientists believe it was the interaction of salt water and rock which first caused the appearance of life, and there’s also a small amount of Oxygen in the atmosphere.
Daytime surface temperatures on Ganymede range from -297 to -171 degrees Fahrenheit (90 to 160 Kelvin). It takes sunlight 43 minutes to reach it.
Surface features on Ganymede are named after Near Eastern, Middle Eastern and Egyptian deities.
It has inspired a number of science fiction writers and has appeared in books and TV shows including The Expanse and Red Dwarf. Arthur C Clarke was inspired by images from Voyager 2 of grooved ridges cutting across parts of Ganymede, and created Ganymede City for his novel 3001: The Final Odyssey. Robert A Heinlein used Ganymede as a setting, too, in Farmer in the Sky.
There is a spacecraft from Earth on its way to Ganymede as I write. It’s called The Jupiter Icy Moons Explorer (JUICE), and it was launched on 14 April 2023. It’s expected to enter orbit around Ganymede in 2032, and crash land on the moon in 2034.
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