Composed mostly of water ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter. In addition to managing the detection and cataloging of Near-Earth objects, the NEO Program office will be responsible for facilitating communications between the astronomical community and the public should any potentially hazardous objects be discovered. 485 of these NEOs are asteroids with a diameter of approximately 1 kilometer or larger. Asteroids and comets are believed to be ancient remnants of the earliest years of the formation of our solar system more than four billion years ago.
Comets are bodies of ice, rock, and organic compounds that can be several miles in diameter.
Comets are thought to originate from a region beyond the orbits of the outermost planets. Some, called long-period comets, are in elliptical orbits of the Sun that take them far out beyond the planets and back. Others, called short-period comets, travel in shorter orbits nearer the Sun. When comets venture into the more intense sunlight of the inner solar system, the ices in the comet nucleus begin to vaporize and fall away. The evolved gas forms a tenuous atmosphere around the nucleus called a coma, while the dust previously in the nucleus forms a tail that can be thousands of miles long and sometimes can be seen from Earth.