Comet nucleus

The solid, central part of a comet is known as the comet nucleus. The nucleus is a minor planet composed of rock, dust, and frozen gases. When heated by the sun, the gases sublimate or are ignited, and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the sun. Scientists believe the nucleus of some comets may be fragile because several comets have split apart for no apparent reason.^[1] Most comets are thought to have a nucleus that measures about 10 miles (16 kilometers) or less across.^[1] But we do know of comets that vary from 100 meters to 40km across. The potato-shaped nucleus of Halley's comet (16x8x8 km) contains equal amounts of ice and dust. About 80 percent of the ice is water ice, and frozen carbon monoxide makes up another 15 percent. Much of the remainder is frozen carbon dioxide, methane, and ammonia.^[1] Scientists believe that other comets are chemically similar to Halley's Comet. The nucleus of Halley's Comet is also extremely dark black. Scientists believe that the surface of the comet, and perhaps most other comets, is covered with a black crust of dust and rock that covers most of the ice. These comets release gas only when holes in this crust rotate toward the sun, exposing the interior ice to the warming sunlight. During a flyby in 2001, the Deep Space 1 spacecraft observed the nucleus of Comet Borrelly and found it to be about half the size (8×4 km) of the nucleus of Halley's Comet. Borrelly's nucleus was also potato-shaped and had a dark black surface.^[1] Like Halley's Comet, Comet Borrelly only released gas from small areas where holes in the crust exposed the ice to sunlight. The nucleus of comet Hale-Bopp was estimated to be about 30 to 40 kilometers across.^[1] Hale-Bopp appeared bright to the unaided eye because its unusually large nucleus gave off a great deal of dust and gas. The nucleus of Wild 2 is about 5km across.^[2] The nucleus of P/2007 R5 is probably only 100-200 meters in diameter.^[3]

References

1. ^ ^{a b c d e} Yeomans, Donald K. (2005). Comets (World Book Online Reference Center 125580). NASA. Retrieved on 2007-11-20.
2. ^ Comet 81P/Wild 2. The Planetary Society. Retrieved on 2007-11-20.
3. ^ SOHO's new catch: its first officially periodic comet. European Space Agency (25 September 2007). Retrieved on 2007-11-20.

External links

• Nucleus of Halley's Comet (16x8x8 km)
• Nucleus of Comet Wild 2 (5.5x4.0x3.3 km)