Moons Of Jupiter





Source: NASA/JPL

If you have been reading this blog, you’d notice that we’ve pretty much covered all the planets of the Solar System, discovering their diversity, each and every one of them a fascinating world with its own unique characteristics and idiosyncrasies. They differ vastly in size, mass, density, orbit, state of aggregation and so on and so forth. Just like the planets they orbit, the moons are also a great source for useful information which can help us understand the universe a little bit better. We’re going to take a closer look into the moons of the largest planet in our Solar System: Jupiter.

With 67 moons in total, among which are the four large moons known as the Galilean satellites, Jupiter could almost be viewed as a separate solar system. The total number of moons changes constantly, and most of the moons are quite small, with about 50 of them with a diameter of 6.2 miles or less. Most of them were discovered by spacecrafts launched in seventies, like NASA’s Voyager in 1979, but also in the nineties, when Galileo spacecraft also made some discoveries. Because of its massive size, which is around 300 times the size of Earth, Jupiter has a huge area of gravitational stability around it in order to support a high number of moons. Jupiter also has the strongest magnetic field of all the planets in the Solar System, which allows it to trap any object passing near it into its orbit. The orbital period of Jupiter’s moons ranges from seven hours to almost three years. While some orbits are circular, which is characteristic for moons that are closer to the planet, the ones that are the farthest from Jupiter have irregularly shaped orbits. One unique fact about the outer 33 moons is that they orbit in the opposite direction to Jupiter’s rotation, indicating that the moons were once asteroids that got caught into Jupiter’s orbit after the entire system was already formed.

The four Galilean moons, discovered by the Italian astronomer Galileo Galilei in 1610, are now called Io, Europa, Ganymede and Callisto, whereas Galilei referred to them as I, II, III and IV, before the numerical system for naming the moons was deemed impractical due to the increasing number of new moons being discovered. Galileo’s discovery was revolutionary as it revealed that not all objects in space revolved around Earth, as was the common belief at that time. The four smaller moons, along with the four large Galilean moons are closer to the planet and they provide the dust that makes up Jupiter’s rings.

The closest moon Jupiter, Io, is the only celestial body in the solar system besides Earth to have volcanic activity. The second Galilean moon, Europa, has a high degree of reflectivity, making it one of the brightest moons in the Solar System. Ganymede is the only moon to have its own magnetic field. It is about the size of Mercury, but it has half the mass. Callisto’s defining characteristic is that it is the most heavily cratered object in the entire Solar System.


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