Our solar system exists approximately 26,000 light-years away from the center of the Milky Way Galaxy, and was formed about 4.6 billion years ago. More than 200 billion stars like the Sun are believed to exist in our galaxy. The Sun is the center of our solar system. Eight planets (e.g., Earth, Mars), moons (e.g., Earth’s Moon, Phobos), dwarf planets (e.g., Pluto, Ceres), small bodies (e.g., asteroids, such as Itokawa and Ryugu), comets (e.g., Churyumov-Gerasimenko) have been orbiting about the Sun like a disk.
The Sun, a star, produces enormous amounts of energy and can glow by itself, while planets have much less energy and cannot glow on their own.
Differences between a star and a planet: A star is a bright, glowing ball of gases such as the Sun. A planet is not as bright as the Sun or non-glowing objects that orbit a star such as Mars, Venus, and Saturn.
The formational history of our solar system
The Solar System formed from the gravitational collapse of a giant interstellar molecular cloud of gas composed mainly of molecular hydrogen and helium. The dense part of the molecular clouds, called molecular cloud cores, are contracted by gravity, which is the beginning of the solar system. The gas in the center formed the primordial Sun, and the gas that contracts later became a rotating gas disk called the primordial solar nebula. The primordial solar nebula contains a mixture of solid particles from molecular clouds called dust, whose nature depends on the distance from the Sun. A lot of hard-to-vaporize materials like rocks exist closer to the Sun, while many easy-to-vaporize ones like ice exist far away from the Sun. For this reason, there are two types of planets in the solar system; rocky planets made of rocks and metals, such as Mercury, Venus, Earth, and Mars, and outer planets made of gas and ice, such as Jupiter, Saturn, Uranus, and Neptune.
About 4.6 billion years ago, planetesimals with a diameter of about 10 km were formed by the coalescence and growth of dust in the primordial solar nebula, and these planetesimals grew to larger sizes by gathering in large numbers to form atomic planets. The proto-planets then collided and merged repeatedly, eventually forming terrestrial planets. During this period, an enormous amount of heat will be provided. The planet is believed to be melted at that time, resulting in separations of heavy metals, which formed the iron- and nickel-rich core at the center.