Jupiter’s Largest Moons: Io, Europa, Ganymede, and Callisto


In this article, we will introduce you the largest moons of Jupiter. Jupiter is considered the planet with the largest number of moons in our Solar System. There are 69 known moons of Jupiter, but the most massive or, better to say, the major moons of Jupiter are the Galilean four moons. These objects were discovered in 1610 by Galileo Galilei and Simon Marius, which were the first objects found to orbit a body that was neither Earth nor the Sun.

The Galilean moons are the four largest moons of Jupiter; they are Io, Europa, Ganymede, and Callisto. As previously stated, they were found in January 1610 by Galileo Galilei and are the first objects discovered to circle another planet. Except for the Sun and the eight planets, they are the biggest objects in the Solar System, having a radius greater than any dwarf planet.

The Galilean moons are Io, Europa, Ganymede, and Callisto
  1. Ganymede is the largest moon of Jupiter and most massive in the Solar System. Also, it is the largest moon without a substantial atmosphere. Ganymede has a diameter of 5,268 km and is 8% larger than Mercury. It is the only moon known to have a magnetic field. Ganymede is composed of approximately equal amounts of silicate rock and water ice. It is a fully differentiated body with an iron-rich, liquid core and an internal ocean that may contain more water than all of Earth’s oceans combined. The satellite’s name was soon suggested by astronomer Simon Marius, after the mythological Ganymede, cupbearer of the Greek gods and Zeus’s lover.
Ganymede has a diameter of 5,268 km

2. Callisto is Jupiter’s second-biggest moon, after Ganymede, although it is the Solar System’s third-largest moon, after Ganymede and Saturn’s largest moon Titan. With 4821 kilometers in diameter, Callisto is nearly 99 % the diameter of Mercury but only about a third the mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km. Callisto is made up of about rock and ice and has the lowest density and surface gravity among Jupiter’s main moons. The Galileo spacecraft’s analysis found that Callisto may contain a tiny silicate core and a subsurface ocean of liquid water at depths exceeding 100 kilometers. Its surface is completely covered with impact craters. It is surrounded by a thin atmosphere made of carbon dioxide, molecular oxygen, and a very powerful ionosphere. 

Callisto has 4,821 km in diameter

3. Io is considered one of the largest moons of Jupiter. It is the densest moon in the Solar System and has the least quantity of water of any known celestial object. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus’ lovers. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. Io is a rocky, volcanically active moon of Jupiter which has a diameter of 3,636 km.

Io is rocky, volcanically active moon of Jupiter which has a diameter of 3,636 km

4. Europa is the smallest of the four Galilean moons orbiting Jupiter and the sixth-closest to the planet. Europa was named after the legendary mother of King Minos of Crete and lover of Zeus. Slightly smaller than Earth’s Moon, Europa has a diameter of 3,100 km. Europa is primarily made of silicate rock and has a water-ice crust and probably an iron-nickel core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, whereas craters are relatively rare. Europa has the smoothest surface of any known solid object in the Solar System.

Europa has a diameter of 3,100 km

To conclude our post, we would like to mention that Galileo’s discovery demonstrated the telescope’s usefulness as a tool for astronomers by proving that things in space could not be seen with the naked eye.

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