When we think of the solar system, we tend to think of the Sun and the nine planets that orbit it. But there’s a lot more orbiting the Sun than just planets (and dwarf planets — we see you, Pluto!)
Take asteroids, for example. Asteroids are the debris left over from the formation of the solar system. Four and a half billion years ago, our solar system was nothing more than a rotating cloud of gas and dust. When that cloud collapsed, possibly due to the shockwaves from a nearby exploding star, its enormous gravity pulled in most of the surrounding material in an event so intense that hydrogen atoms fused into helium atoms.
