Extinct comet
Encyclopedia
Extinct comets are comet
s that have expelled most of their volatile ice and have little left to form a tail or coma
. The volatile material contained in the comet nucleus
evaporates away, and all that remains is inert rock or rubble that can resemble an asteroid
. Comets may go through a transition phase as they come close to extinction. A comet may be dormant rather than extinct, if its volatile component is sealed beneath an inactive surface layer.
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 that can resemble an asteroid.
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 typical Halley Family/long period comets and extinct comets. Damocloid asteroid
s have been studied as possible extinct cometary candidates due to the similarity of their orbital parameters with those of Halley Family 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 displayed a cometary coma and now also has the cometary designation 174P/Echeclus. After passing perihelion in early 2008, centaur 52872 Okyrhoe
significantly brightened.
" was coined in 2006 by the IAU
. 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 become 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.
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s that have expelled most of their volatile ice and have little left to form a tail or coma
Coma (cometary)
frame|right|The [[153P/Ikeya-Zhang|comet Ikeya-Zhang]] exhibiting a bright, condensed coma In astronomy, a coma is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate...
. The volatile material contained in the comet nucleus
Comet nucleus
The nucleus is the solid, central part of a comet, popularly termed a dirty snowball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma...
evaporates away, and all that remains is inert rock or rubble that can resemble an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
. Comets may go through a transition phase as they come close to extinction. A comet may be dormant rather than extinct, if its volatile component is sealed beneath an inactive surface layer.
Nature of extinct comets
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)
C/2001 OG108 (LONEOS)
C/2001 OG108 is a Halley-type comet with an orbital period of 48.51 years. It was discovered on 28 July 2001 by the LONEOS telescope at Lowell Observatory....
may represent the transition between typical Halley Family/long period comets and extinct comets. Damocloid asteroid
Damocloid asteroid
Damocloids are minor planets such as 5335 Damocles and 1996 PW that have Halley family or long-period highly eccentric orbits typical of periodic comets such as Comet Halley, but without showing a cometary coma or tail....
s have been studied as possible extinct cometary candidates due to the similarity of their orbital parameters with those of Halley Family comets.
Dormant comets are those within which volatiles may be sealed, but which have inactive surfaces. For example, 14827 Hypnos
14827 Hypnos
14827 Hypnos is an Apollo near-Earth asteroid discovered by Carolyn S. Shoemaker and Eugene Merle Shoemaker at Palomar Observatory on May 5, 1986...
may be the nucleus
Comet nucleus
The nucleus is the solid, central part of a comet, popularly termed a dirty snowball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma...
of an extinct comet that is covered by a crust several centimeters thick that prevents any remaining volatiles
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
from outgassing
Outgassing
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material. As an example, research has shown how the concentration of carbon dioxide in the Earth's atmosphere has sometimes been linked to ocean outgassing...
.
The term dormant comet is also used to describe comets that may become active but are not actively outgassing. For example 60558 Echeclus
60558 Echeclus
60558 Echeclus is a centaur in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as an asteroid with provisional designation . Research in 2001 by Rousselot and Petit at the Besançon observatory in France showed no evidence of cometary activity, but in late...
has displayed a cometary coma and now also has the cometary designation 174P/Echeclus. After passing perihelion in early 2008, centaur 52872 Okyrhoe
52872 Okyrhoe
52872 Okyrhoe is a centaur orbiting in the outer Solar System between Jupiter and Neptune. It was discovered on September 19, 1998, by Spacewatch.-Orbit:Centaurs have short dynamical lives due to strong interactions with the giant planets...
significantly brightened.
The 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 bodySmall Solar System body
A small Solar System body is an object in the Solar System that is neither a planet nor a dwarf planet, nor a satellite of a planet or dwarf planet:...
" was coined in 2006 by the IAU
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
. The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation
Outgassing
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material. As an example, research has shown how the concentration of carbon dioxide in the Earth's atmosphere has sometimes been linked to ocean outgassing...
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
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
and become 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.
Extinct comets
Suspected or theorized extinct comets include:- 2101 Adonis2101 Adonis2101 Adonis was one of the first near-Earth asteroids to be discovered. It was discovered by Eugene Delporte in 1936 and named after Adonis, the beautiful youth with whom the goddess Venus fell in love...
- 3200 Phaethon3200 Phaethon3200 Phaethon is an asteroid with an unusual orbit that brings it closer to the Sun than any other named asteroid . For this reason, it was named after the Greek myth of Phaëton, son of the sun god Helios...
- 3552 Don Quixote3552 Don Quixote3552 Don Quixote is a small main-belt, Amor, Mars crossing, potentially hazardous asteroid. It has a highly inclined comet-like orbit, and measures about 19 km in diameter. Its rotation period is 7.7 hours...
- P/2007 R5P/2007 R5Comet P/2007 R5 , also designated P/1999 R1 and P/2003 R5, is the first periodic comet to be discovered using the automated telescopes of the SOHO spacecraft....
(SOHO 1)
- 14827 Hypnos14827 Hypnos14827 Hypnos is an Apollo near-Earth asteroid discovered by Carolyn S. Shoemaker and Eugene Merle Shoemaker at Palomar Observatory on May 5, 1986...
External links
- "Low Albedos Among Extinct Comet Candidates", 2001
- Dark, dangerous asteroids found lurking near Earth (NewScientist 5 March 2010)