Comets are made up of the same stuff as the early Solar Nebula that collapsed to form the sun and planets. It is now known that comets contain significant amounts of water ice, dust, and carbon based compounds. They may have been an important source of water and organic molecules for Earth when many comets collided with our planet during a period of heavy bombardment over 4 billion years ago. Modern-day comets are like a time machine. They offer a window into the past when the Solar System was young and life on Earth was just beginning.
History is filled with famous comets.
Halley's comet, Hale-Bopp, Hyakutake and others have dazzled observers with their brilliant nuclei and dramatic tails. Recent comets like Hale-Bopp have been viewed by hundreds of millions of people, and Halley's comet has had a real impact on history, as in 1066 when it was so bright that it terrified millions of Europeans and was widely credited with the Norman victory at the Battle of Hastings. Unlike its famous cousins, comet Wild-2 is a relatively dim, new arrival to the inner solar system. Until recently it circled the sun in an orbit between Jupiter and Uranus, but everything changed in September 1974 when Wild-2 passed within 0.006 AU of Jupiter. This view, looking down on the sun shows the orbit of Wild-2 and its current location.