About 588 million kilometers away from the earth, sits a gas giant about two and a half times the mass of all the other planets in the Solar System combined. What we are talking about is Jupiter. Due to its large mass and rapid formation, the planet played a significant role in shaping the Solar System. And just as interesting as the planet is, so are its massive collection of moons. Jupiter is home to over 63 moons, out of which the largest ones are Ganymede, Europa, Io, and Callisto. They have been named as Galilean satellites or moons after Italian astronomer Galileo Galilei observed them in 1610. At that time, the four luminous objects were mistaken for stars. However, ongoing observation showed that they were orbiting Jupiter in a way that could only be explained by the existence of satellites. The German astronomer Simon Marius claimed to have seen the moons around the same time but did not publish his observations, which is why Galileo had been credited with the discovery.
The most fascinating of the Galilean moons is the Europa – the smallest of the Galilean moons and the second closest to Jupiter. Mostly made up of water and ice, the moon is thought to have twice as much as water as Earth does. Europa draws the attention of astrobiologists due to its potential of possessing a habitable zone. The probability of the presence of water in the planet suggests that Europa could conceivably serve as an abode for extraterrestrial life.
The largest moon of Jupiter and in the solar system, Ganymede is the only moon known to have its own internal magnetic field. Possessing a metallic core, the moon has a thin oxygen atmosphere including O, O2, and possibly O3 (ozone), and some atomic hydrogen.
The second largest of the four largest moons of Jupiter and the third largest moon in the Solar System, Callisto comprises equal amounts of rocks and ice, making it the least dense of the Galilean satellites. Its surface is very heavily cratered, and one of its major features is a basin called Valhalla which is about 3000 km wide.
The most volcanically active body in the solar system, Io is the innermost of the four Galilean moons and the fourth largest moon in the Solar System. With over 400 active volcanoes, its surface is made up of sulfur and dotted with over 100 mountains. Io has n extremely thin atmosphere comprising mainly of Sulphur dioxide.
Recently, a study suggests that Saturn, the planet next to Jupiter may have played a role in the creation of the four Galilean moons. Previous studies say that the moons developed from the disk of matter that surrounded Jupiter during the planet’s final stages of formation. However, it’s unclear where the materials of this disk came from and how they may have surrounded the gas giant.
Jupiter created a gap in the protoplanetary disk, which could have isolated the young planet from the rest of the disk. Now questions arise that how Jupiter managed to collect enough solid materials that formed the Galilean moons. Thomas Ronnet, an astrophysicist from Aix Marseille University and his colleagues decided to investigate this matter using computer models of the gap that formed in the disk to learn what exactly may have happened. The models revealed that at the outer edge of the gap, a reservoir of planetesimals (the building blocks of a planet) collected over time. The models also suggest that Saturn’s core may have been formed within the planetesimal reservoir or migrated through it. Saturn’s gravitational pull then dispersed the planetesimals toward Jupiter and the inner solar system, thus offering the explanation for the origin of the solid materials that formed Jupiter’s moons. “The formation of Saturn’s core within this reservoir, or its prompt inward migration, allows planetesimals to be redistributed from this reservoir towards Jupiter and the inner Solar System, thereby providing sufficient amount of material to form the Galilean satellites,” the researchers wrote in their study, which was submitted to The Astrophysical Journal on April 9, 2018.