The Formation of Asteroids
Asteroids are formed from small pieces of rocks like the rest of the solar system. The small particles run into each other, and if they don't collide, they will stay together because their gravity pulls them.
Asteroids are made out of rocks, metals and other substances. And astronomers say that some of them even contain water.
Asteroids also differ from size and shape. Some of the asteroids are small, while others are big as football stadiums. And even some of the asteroids are large as planets, and astronomers often think and decide, whether they are actual planets or not. The asteroids can be breakable or they can be very hard. If the asteroid is a stone, it is most likely to turn into a pile of rubble. But if the asteroid is an iron, it is going to be tough and solid.
Asteroids are also called "dwarf planets" or "minot planets", not actual "planets", and the reason for it is that even though they are small to be a planet, they orbit the sun. The asteroids are placed near Jupiter in the Asteroid Belt. The Asteroid Belt contains billions and trillions of asteroids. Once, the Main Belt had so many materials that it could've built a planet. But Jupiter's gravity stopped the formation and swept all the materials too far apart so that they won't be able to make a planet again. And if the entire mass of the Main Belt could make a planet again, it would be half the mass of the Moon.
One of the examples would be Pluto. Once when it was first found, Pluto was known as the smallest planet and the ninth of the solar system. But today, Pluto is known as a "dwarf planet." And Pluto is in a place called Kuiper Belt, which is a place where population of small bodies that orbit the sun beyond Neptune.
The reason Pluto is not a planet anymore is that in 2003, and astronomer thought that he had found a planet. The planet was larger than Pluto and he named the object Eris. After finding Eris, it made many astronomers to discuss about what makes a planet a "planet." Then one group of astronomers decided that Pluto isn't a planet because of its size and location. So Pluto and other objects similar to it are called "dwarf or minor planets."