Out of the eight planets that make up our solar system, quite a few of them have more than 16 moons. For example, Saturn has 53 named moons. It also has 29 more moons that are awaiting to be confirmed and named. Uranus has 27 named moons, but the planet with the highest number of known moons is Jupiter.
The number of known moons on Jupiter is 79. These moons include the four Galilean moons known for their larger size. Galileo Galilei discovered them in 1610. The largest of these moons is Ganymede, and its diameter is larger than that of Mercury. Yes, one of the moons of Jupiter is larger than an entire planet.
The Galilean Moons Of Jupiter
Out of the 79 known moons of Jupiter, the four Galilean moons are the most well-known ones. They were the first discovered objects orbiting a body in space that wasn’t the Earth or the Sun. In the 19th century, more and more moons were getting discovered; however, these were much smaller.
People named these moons after the lovers or the daughters of the gods Jupiter from the Roman mythology and Zeus from Greek mythology. When comparing the rest of the moons orbiting Jupiter to the Galilean moons, their mass comprises only 0.003% of the total mass of the moons orbiting the planet. This goes to show just how enormous the Galilean moons are.
When we look at the other moons that orbit around Jupiter, eight are regular satellites. These moons orbit the planet in almost perfectly circular orbits. The four Galilean moons have a spherical shape because of their large mass. If these moons were orbiting around the Sun, they would be considered dwarf planets. The other satellites are smaller than these four and are the source of the dust that is the main ingredient of the rings around Jupiter.
All of the other moons orbiting around Jupiter are irregular satellites. Their orbits are farther away from the planets and are considerably more irregular than the ones of the eight satellites. Scientists presume that Jupiter itself captured these other moons from various solar orbits. All of the moons of Jupiter have wildly different physical characteristics. Their orbital characteristics are somewhat similar when it comes to the eight satellites, but also vary when we start talking about the other smaller moons.
The four Galilean moons are all over 1,900 miles in diameter. Ganymede is the ninth biggest object in the Solar System. The only things larger than Ganymede, is the Sun and seven planets, excluding Mercury. The rest of the moons are all less than 160 miles in diameter. However, the large majority of them are no more than 3.1 miles in diameter.
We previously mentioned how all of the moons of Jupiter except for the Galilean moons make up only 0.003% of the total mass of everything orbiting the planet. Now that you are more familiar with their actual size, it is easier to picture how this is possible. Interestingly, many of the moons revolve in the direction that is opposite to the way Jupiter is spinning. This is called retrograde motion.