What idea is it that a comet is like a dirty snowball in science?

The idea that a comet is like a "dirty snowball" refers to its composition, which is primarily made up of ice, dust, and rocky material. This analogy highlights how comets contain frozen gases and water, similar to a snowball, along with various organic compounds and dust particles, hence the "dirty" aspect. When comets approach the Sun, the heat causes the ice to vaporize, creating a glowing coma and sometimes a tail, which further illustrates their dynamic nature as they travel through the solar system.