The Space & Beyond Blog
Characteristics of comets
How comets are formed and where they originate from
What are comets made of?
Astronomer Fred Whipple created the term “dirty snowballs” as one of the many ways to describe the characteristics of comets. These bodies are made of dust, rocks, organic compounds, and ice, and have three parts: nucleus, coma, and tail. Ice, in the form of dry ice, water ice, and various frozen gases, makes up most of the celestial object.
How big are comets?
A comet nucleus can range in size from less than a mile (1 kilometer) to 15 miles (25 km) across. The longest comet tail, which measured over 354 million miles (570 million kilometers), belonged to Comet Hyakutake in May 1996.
Where do comets come from?
Thought to be leftovers of the early solar system, comets originate from the Oort Cloud — an area of cometary nuclei that surrounds the Sun at a distance of thousands of astronomical units. When a nucleus gets closer to the Sun, the ice melts and a tail is created. Astronomers believe there could be as many as one trillion comets in the Oort Cloud.
Orbit lengths vary among comets. Orbital periods can last from less than a century to over 100,000 years.
How are comets named?
Comets are more commonly named for their discoverers; up to three independent co-discoverers may share the credit. Increasinly, those discoverers are not individuals, but dedicated small-body discovery programs or solar-observing satellites. Numerous comets have been named for the Lincoln Near Earth Asteroid Research (LINEAR) project of the Massachusetts Institute of Technology in Boston, the Near Earth Asteroid Tracking (NEAT) program operated by the Jet Propulsion Laboratory in Pasadena, California, and the Lowell Observatory Near-Earth Object Search (LONEOS) run by Lowell Observatory in Flagstaff, Arizona.
Because the names of discoverers don’t allow for a unique identification, comets receive a more prosaic official name. This consists of a one-letter prefix, usually a C for “comet” or a P for “periodic,” followed by the year of discovery and an uppercase letter that indicates the half-month in which the discovery occured.