Jongjin Park
The universe is made up of stars. A star is called a star in Chinese characters, and a group of hundreds of billions of such stars is called a galaxy. In particular, the galaxy to which our star, the sun, belongs is called the Milky Way.
A star is a celestial body that produces light and heat by nuclear fusion. The most familiar of the stars we know is the sun, but if you see the sun near the North Star, it will be nothing more than a twinkling little star like any other star in the night sky.
A celestial body that revolves around such a star is called a planet. In the case of the sun, a total of eight planets orbit: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto, which orbited the outermost was excluded as a dwarf planet in 2006.
A satellite is a celestial body that orbits around a planet. Therefore, satellites revolve around planets, and planets orbit stars. For example, the earth we live in, the moon orbits the earth, and the earth orbits the sun. Hundreds of billions of stars like the sun gather to become galaxies, and about 2 trillion of such galaxies gather to form the universe.
Mercury and Venus, which orbit closest to the sun, have no moons. Then orbiting Earth there is only one satellite named Moon. The moon is too big to be a satellite, so it can be seen as a pair of planets in a way, but the moon is a satellite of the earth.
Mars orbits outside the Earth and has two moons. Jupiter, the largest in the solar system, has a total of 95 satellites, and the first satellite found on another planet other than the Earth’s moon was discovered by Galileo, who improved telescope performance with four satellites orbiting Jupiter. They are called Galilean satellites.
There are as many as 145 satellites orbiting Saturn in its next orbit. At this point, it becomes difficult to name them individually. In 2019, 20 satellites of Saturn were discovered at once, in February 2023, 12 satellites of Jupiter were newly added, and in May 2023, 62 satellites of Saturn were discovered again.
Uranus, which orbits the outer edge of the solar system, has 27 moons, and Neptune, the last planet, has 14 moons. In addition, satellites orbiting dwarf planets and asteroids have also been identified, with the smallest being only 45 m in diameter.
In the early days of the solar system’s formation, the sun was located at the center, and protoplanets orbiting the sun were formed around it. And as the remaining material is pushed away by the solar wind, it is a satellite made by being caught by the gravity of a nearby planet. Therefore, in the case of a planet close to the sun, it misses a lot of dust passing by at high speed, so naturally the number of satellites is small, and the farther away the planet is from the sun, the faster the dust passing by it decreases, so it is easy to be captured by the planet’s gravity, so the number of satellites decreases. many.
For this reason, Mercury and Venus, which are closest to the sun, have no moons at all, while Jupiter and Saturn, which are farther from the sun, have many moons. Of course, Jupiter and Saturn’s strong gravitational pull from their large bodies was able to trap much of the material passing by them. (author)
Jongjin Park
