Extinct comet

Nature of extinct comets

Extinct comets are those that have expelled most of their volatile ice and have little left to form a tail or coma. Over time, most of the volatile material contained in a comet nucleus evaporates away, and the comet becomes a small, dark, inert lump of rock or rubble{{Cite web

|access-date=6 March 2014 Other related types of comet include transition comets, that are close to becoming extinct, such as were looked for in the Hubble search for transition comets. Comets such as C/2001 OG108 (LONEOS) may represent the transition between extinct comets and typical Halley-type comets (periods of 20–200 years) or long period comets (periods longer than 200 years).{{cite conference

Dormant comets

Dormant comets are those within which volatiles may be sealed, but which have inactive surfaces. For example, 14827 Hypnos may be the nucleus of an extinct comet that is covered by a crust several centimeters thick that prevents any remaining volatiles from outgassing.

The term dormant comet is also used to describe comets that may become active but are not actively outgassing. For example, 60558 Echeclus has previously displayed a cometary coma and thus also has been given the cometary designation 174P/Echeclus. After passing perihelion in early 2008, centaur 52872 Okyrhoe significantly brightened.{{cite web |access-date=2008-10-12}}

Distinction between comets and asteroids

When discovered, asteroids were seen as a class of objects distinct from comets, and there was no unified term for the two until "small Solar System body" was coined by the IAU in 2006. The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation of near-surface ices by solar radiation. A few objects have ended up being dual-listed because they were first classified as minor planets but later showed evidence of cometary activity. Conversely, some (perhaps all) comets are eventually depleted of their surface volatile ices and develop the appearance of asteroids. A further distinction is that comets typically have more eccentric orbits than most asteroids; most "asteroids" with notably eccentric orbits are probably dormant or extinct comets. Also, they are theorized to be common objects amongst the celestial bodies orbiting close to the Sun.

Roughly six percent of the near-Earth asteroids are thought to be extinct nuclei of comets which no longer experience outgassing.{{cite book |chapter-url = http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf |editor-first1 = W. F. |editor-last1=Bottke Jr. |editor-first2=A. |editor-last2=Cellino |editor-first3=P. |editor-last3=Paolicchi |editor-first4=Richard P. |editor-last4=Binzel

Extinct comets

Suspected or hypothesized extinct comets include:

• 14827 Hypnos
• 2101 Adonis
• 2015 TB145
• 3200 Phaethon{{cite journal
• 3552 Don Quixote{{cite journal
• P/2007 R5 (SOHO 1)
• 1996 PW possibly an extinct long-period comet

References

References

1. "Frequently asked questions - What is the difference between asteroids and comets?".
2. Space Telescope Science Institute. (10 September 1992). "Amateur Astronomers Will Use NASA's Hubble Space Telescope".
3. (25 September 2007). "SOHO's new catch: its first officially periodic comet". [[European Space Agency]].
4. (22 August 1996). "New Object Moves Like a Comet But Looks Like an Asteroid". [[NASA]].