Cometary Nucleus

A cometary nucleus is the solid core of a comet, typically composed of ice, dust, and rocky material. It is a few kilometers wide and acts as the "heart" of the comet. When a comet approaches the Sun, the heat causes the ice to vaporize and release gas and dust, creating a glowing envelope called a coma and sometimes a tail. The nucleus remains mostly solid and unchanged during this process, serving as the primary source of the material that forms the coma and tail as the comet travels through space.