Editing Comet (section)

=== Extinction ===
{{Main|Extinct comet}}

Jupiter-family comets and long-period comets appear to follow very different fading laws. The JFCs are active over a lifetime of about 10,000 years or ~1,000 orbits whereas long-period comets fade much faster. Only 10% of the long-period comets survive more than 50 passages to small perihelion and only 1% of them survive more than 2,000 passages.<ref name=dormant/> Eventually most of the volatile material contained in a comet nucleus evaporates, and the comet becomes a small, dark, inert lump of rock or rubble that can resemble an asteroid.<ref>{{cite web |last=Lyzenga |first=Greg |title=If comets melt, why do they seem to last for long periods of time |url=http://www.scientificamerican.com/article.cfm?id=if-comets-melt-why-do-the |work=[[Scientific American]] |date=16 November 1998 |access-date=13 August 2013}}</ref> Some asteroids in elliptical orbits are now identified as extinct comets.<ref>{{cite journal |url=http://www.boulder.swri.edu/~hal/PDF/asteroids3.pdf |archive-url=https://web.archive.org/web/20040202155133/http://www.boulder.swri.edu/~hal/PDF/asteroids3.pdf |archive-date=2004-02-02 |url-status=live |title=Evolution of Comets into Asteroids |journal=Asteroids III |last1=Bottke |first1=William F. Jr. |last2=Levison |first2=Harold F. |name-list-style=amp |page=669 |date=2002 |bibcode=2002aste.book..669W}}</ref><ref>{{cite journal |title=Are the IRAS-detected Apollo asteroids extinct comets? |journal=Monthly Notices of the Royal Astronomical Society |first=J. K. |last=Davies |volume=221 |pages=19P–23P |date=July 1986 |doi=10.1093/mnras/221.1.19P |bibcode=1986MNRAS.221P..19D|doi-access=free }}</ref><ref>{{cite book |chapter=The Comet-Asteroid Transition: Recent Telescopic Observations |title=Asteroids, Comets, Meteors 1993: Proceedings of the 160th Symposium of the International Astronomical Union, Held in Belgirate, Italy, June 14–18, 1993 |volume=160 |publisher=Springer |first=L. A. |last=McFadden |editor1-first=Andrea |editor1-last=Milani |editor2-first=Michel |editor2-last=Di Martino |editor3-first=A. |editor3-last=Cellino |page=95 |date=1994 |bibcode=1994IAUS..160...95M}}</ref><ref>{{cite journal |title=The enigmatic object 2201 Oljato: Is it an asteroid or an evolved comet? |journal=Journal of Geophysical Research |first1=L. A. |last1=McFadden |first2=A. L. |last2=Cochran |first3=E. S. |last3=Barker |first4=D. P. |last4=Cruikshank |first5=W. K. |last5=Hartmann |display-authors=1 |volume=98 |issue=E2 |pages=3031–3041 |date=February 1993 |doi=10.1029/92JE01895 |bibcode=1993JGR....98.3031M}}</ref> Roughly six percent of the near-Earth asteroids are thought to be extinct comet nuclei.<ref name=dormant/>