The Galilean Moons

The Moons Of Jupiter

By Madison Nef

Jupiter is the largest known planet in our Solar System as of right now. It also holds the record for the most moons in stable orbit around any planet IN THE ENTIRE SOLAR SYSTEM at the astonishing number of 67.

In this paper, I obviously am not going to be covering ALL 67 of these moons in this one paper; that would be far too many! Instead, I’d like to focus on the 4 largest of these moons, or the Galilean moons. These moons were first discovered in the early 1600’s when an astronomer named Galileo Galilei studied the sky for the first time using one of the earliest telescopes. At this time, he could only see 4 moons… they were the first to be discovered; but many more were discovered in the years that followed.

These four moons are the only ones large enough to be seen through a normal, small telescope like the one Galileo used. Since he was the first to discover them, they are so named the Galilean moons.

Okay, let’s get right into things now! Four moons; roughly 3 paragraphs about each if I can muster it. Here we go.

The Four Galilean Moons (And their stories)

Io

Io is the third largest moon of Jupiter. It was named after a maiden who Jupiter fell in love with in Greek mythology. A summarized version of this story is essentially that Io was a maiden living on Argos, and she was extremely kind-hearted and beautiful and everyone loved her. Jupiter observed her from above and grew to love her- in fact, he loved her to the point where he would make lengthy visits to Argos to see her.

This was all well and good, but Juno, who was the equivalent of Jupiter’s wife, did not like Io at all. When she figured out where Jupiter was disappearing to, she got extremely jealous and highly angered with him… and with Io, who didn’t even know who Jupiter was. She was under the belief that he was a prince from a far-off land.

Juno came down to Argos, and in an effort to protect Io, Jupiter turned her into a white dairy cow, thinking that he could easily change her back to normal later. However, Juno realized his trick and took the cow for herself. She made the transformation permanent, and Io was forced to live the rest of her life as a cow.

Back on track. The moon Io is an extremely violent place where any human being wouldn’t survive long enough to enjoy the gorgeous colors and surroundings this moon is thought to have. It has been guaranteed that it has higher mountains than anywhere on earth, and it also has many volcanoes.

However, we may never be able to visit it as it lies within a very dangerous part of Jupiter’s magnetic field. The radiation level in this area is SO HIGH that it has been estimated to be more than 1000 times stronger than the level of radiation needed to kill a human. And even if you DID survive the radiation for long enough to reach its surface… you still wouldn’t be safe.

Io has gigantic volcanoes that erupt with extreme frequency and spurt sulfuric acid everywhere. These spurts then land on the moon’s surface, which causes the gorgeous red, yellow and oranges that make Io look the way it does.

Europa

Europa is a cold, smooth, ice covered world. A long time ago in space there was a period of time when it was very common for asteroids and comets to hit other worlds… this was called the Heavy Bombardment Period. During this time most worlds, including Earth, were scarred with bowl shaped impressions; or craters. Most of these worlds remain scarred today. However, some, like the Earth, have since recovered their surfaces with new rock lava or ice, hiding these scars.

Because Europa is smooth, we know it too has recovered its surface since the Heavy Bombardment Period. This, along with a few other clues, has led scientists to believe that beneath its icy outer shell lays a liquid water ocean that is likely heated by Europa's hot core. This makes Europa one of the most likely places for life to exist outside of the Earth.

Ganymede

Not much is known about Ganymede. It, like Europa, has a smooth icy surface but it was recently discovered that it also has liquid ocean water beneath that exterior. Ganymede is the largest of Jupiter’s moon, being large in diameter than the planets of Mercury and Pluto. Ganymede was named after an extremely attractive Trojan boy from Greek mythology who Zeus took from Earth to be a cup-bearer for the gods.

Since this section seems rather short, I’ll include the story of Ganymede from mythology.

The Myth of Ganymede
A singularly beautiful boy called Ganymede was playing one day on the hills near Troy, when a great black cloud suddenly overspread the sun and a sudden wind sent the dust and the leaves flying. There was a roll of thunder, with a few flashes of lightning, and then an enormous black eagle suddenly swooped down from the cloud, caught up Ganymede in its talons, and sailed away.

Tros, Ganymede's father, who was in a neighboring field, saw all that happened; but although he shouted and ran and threw sticks and stones toward the fast rising bird, the eagle was far beyond the reach of such missiles long before Tros arrived at the hill where Ganymede had been playing.

So the poor father, overcome with grief, went home and told his wife what had happened. When the neighbors heard the story, they all gathered together at the house of Tros and mourned with the grief-stricken father and mother. It was of no use to search for Ganymede, for the eagle had taken him far beyond the mountains of that country.

A few days later a strange visitor came to the house of Tros. He carried a curious rod with snakes twined round it, and two shadowy wings fluttered from his cap. "Do not mourn for Ganymede," said he, "the boy has met with great good fortune. His beauty has caused him to be loved by Jupiter, who has taken him for his cup-bearer; he pours ruby nectar into a golden cup for the king of the gods; he will never die nor grow old."

When Tros heard these words, he was comforted.

Callisto

Callisto is the eighth moon from the surface of Jupiter, and the second largest.  This moon was named after a nymph, loved by Zeus but hated by Hera. Hera changed her into a bear, Zeus then placed her in the sky as the constellation Ursa Major. 

Not much is known about this moon besides the fact that it is almost the same size as the planet Mercury.  

And there you have it! A little something about each of the 4 Galilean moons. I hope you learned as much from this as I did.

Maddie