Leseprobe
Comets are considered among the most primitive bodies of our Solar System. Since they are rather small, and since they live the majority of their life in cold environments, far away from the Sun, they cannot have undergone much thermal evolution, and probably only the outer layers of the nucleus have been modified through bombardment by energetic charged particles, cosmic rays, or through surface erosion by interstellar grains or dust debris; moreover, the surface of cometary nuclei in the Oort cloud may have been heated by passing stars or supernova explosions. Despite the various processes that could have affected the surface of a nucleus during its history, its internal composition should have remained widely unchanged since the time of its formation, and it should reflect the composition of the proto-planetary disk, in the place where it formed.
