In 1986, astronomers revealed the true nature of comets, comparing them to a "dirty snowball." This "dirty snowball" is actually an icy body composed of rocks, dust, methane, and ammonia, with a deep black exterior resembling a long potato. Its size is comparable to a small mountain on Earth, and it takes about half a day to orbit around it. However, when far from the Sun, the "dirty snowball" is nearly impossible for observers on Earth to detect. As it approaches the Sun, the heat causes the ice on its surface to sublimate, forming a cloud-like coma and nucleus, collectively known as the comet's head. The coma appears faint and nebula-like due to sunlight scattering, creating a long comet tail. At this point, the diameter of the comet's head can reach hundreds of thousands of kilometers, while the tail can extend for tens of millions of kilometers, yet its total mass is negligible, only about one billionth of Earth's mass.