Extinct comet

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Comet nucleus of 9P/Tempel as imaged by the NASA Deep Impact space probe. This is not yet extinct but gives some idea of a cometary nucleus Tempel 1 (PIA02127).jpg
Comet nucleus of 9P/Tempel as imaged by the NASA Deep Impact space probe. This is not yet extinct but gives some idea of a cometary nucleus

An extinct comet is a comet that has expelled most of its volatile ice and has little left to form a tail and coma. In a dormant comet, rather than being depleted, any remaining volatile components have been sealed beneath an inactive surface layer.


Due to the near lack of a coma and tail, an extinct or dormant comet may resemble an asteroid rather than a comet and blur the distinction between these two classes of small Solar System bodies. When volatile materials such as nitrogen, water, carbon dioxide, ammonia, hydrogen and methane in the comet nucleus have evaporated away, all that remains is an inert rock or rubble pile. A comet may go through a transition phase as it comes close to extinction.

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 [1] that can resemble an asteroid. [2]

Disintegration of asteroid P/2013 R3 observed by the Hubble Space Telescope between late-October 2013 and early-January 2014. 14060-Asteroid-P2013R3-Disintegration-20140306.jpg
Disintegration of asteroid P/2013 R3 observed by the Hubble Space Telescope between late-October 2013 and early-January 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. [4] 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). [5] Minor planets of the group of damocloids have been studied as possible extinct cometary candidates due to the similarity of their orbital parameters with those of Halley-type comets. [5]

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. [6]

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. [7]

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. [8]

Roughly six percent of the near-Earth asteroids are thought to be extinct nuclei of comets which no longer experience outgassing. [6] [9] [10]

Extinct comets

Don Quixote (apmag 15) near perihelion in 2009. 3552Don2-LB4-mag15.jpg
Don Quixote (apmag 15) near perihelion in 2009.
The eccentric (e=0.66) comet-like orbit of Hypnos. Hypnos-orbit.gif
The eccentric (e=0.66) comet-like orbit of Hypnos.

Suspected or theorized extinct comets include:

See also

Related Research Articles

Comet Icy small Solar System body

A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.

Kuiper belt Area of the Solar System beyond the planets, comprising small bodies

The Kuiper belt is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger – 20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles, such as methane, ammonia and water. The Kuiper belt is home to three objects identified as dwarf planets by the IAU: Pluto, Haumea and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, may have originated in the region.

2060 Chiron Large 200km centaur/comet with 50-year orbit

2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orbiting between the asteroid belt and the Kuiper belt.

Centaur (small Solar System body)

A centaur, in planetary astronomy, is a small Solar System body with either a perihelion or a semi-major axis between those of the outer planets. Centaurs generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one known centaur, 514107 Kaʻepaokaʻawela, which may be in a stable orbit. Centaurs typically exhibit the characteristics of both asteroids and comets. They are named after the mythological centaurs that were a mixture of horse and human. Observational bias toward large objects makes determination of the total centaur population difficult. Estimates for the number of centaurs in the Solar System more than 1 km in diameter range from as low as 44,000 to more than 10,000,000.

Damocloids are a class of minor planets such as 5335 Damocles and 1996 PW that have Halley-type or long-period highly eccentric orbits typical of periodic comets such as Halley's Comet, but without showing a cometary coma or tail. David Jewitt defines a damocloid as an object with a Jupiter Tisserand invariant (TJ) of 2 or less, while Akimasa Nakamura defines this group with the following orbital elements:

596 Scheila

Scheila is a main-belt asteroid and main-belt comet orbiting the Sun. It was discovered on 21 February 1906 by August Kopff from Heidelberg. Kopff named the asteroid after a female English student with whom he was acquainted.

Hubble search for transition comets was a study involving amateur astronomers and the use of the Hubble Space Telescope, one of only six studies involving amateur astronomers approved by NASA.

Comet nucleus Central part of a comet

The nucleus is the solid, central part of a comet, once termed a dirty snowball or an icy dirtball. 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. 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. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust.

118401 LINEAR, provisional designation 1999 RE70, is an asteroid and main-belt comet (176P/LINEAR) that was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) 1-metre telescopes in Socorro, New Mexico on September 7, 1999. (118401) LINEAR was discovered to be cometary on November 26, 2005, by Henry H. Hsieh and David C. Jewitt as part of the Hawaii Trails project using the Gemini North 8-m telescope on Mauna Kea and was confirmed by the University of Hawaii's 2.2-m (88-in) telescope on December 24–27, 2005, and Gemini on December 29, 2005. Observations using the Spitzer Space Telescope have resulted in an estimate of 4.0±0.4 km for the diameter of (118401) LINEAR.

14827 Hypnos is a highly eccentric, sub-kilometer-sized carbonaceous asteroid that is thought to be an extinct comet. It is classified as near-Earth object and potentially hazardous asteroid of the Apollo group.

20898 Fountainhills, provisional designation 2000 WE147, is a dark asteroid in a cometary orbit (ACO) from the outermost regions of the asteroid belt, approximately 37 kilometers (23 miles) in diameter. It was discovered on 30 November 2000, by American amateur astronomer Charles W. Juels at the Fountain Hills Observatory in Arizona, United States. The D-type asteroid has a rotation period of 12.84 hours. It was named for the city of Fountain Hills, Arizona, in the United States.

Comet tail

A comet tail—and coma—are features visible in comets when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. Separate tails are formed of dust and gases, becoming visible through different phenomena; the dust reflects sunlight directly and the gases glow from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye.


354P/LINEAR is a small Solar System body that displayed characteristics of both an asteroid and a comet, and thus, was initially given a cometary designation. Because it has the orbit of a main-belt asteroid and showed the tail of a comet, it was listed as a main-belt comet. But within a month of discovery, an analysis of images by the Hubble telescope suggested that its tail was generated by dust and gravel resulting from a recent head-on collision between asteroids rather than from sublimation of cometary ice. This was the first time a small-body collision had been observed; since then, minor planet 596 Scheila has also been seen to undergo a collision, in late 2010. The position of the nucleus was remarkable for being offset from the axis of the tail and outside the dust halo, a situation never before seen in a comet. The tail is created by millimeter-sized particles being pushed back by solar radiation pressure.

C/2001 OG108 (LONEOS) 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. Of the short-period comets with known diameters and perihelion inside the orbit of Earth, C/2001 OG108 is the second largest after Comet Swift–Tuttle.

2000 DG8 is a dark centaur and damocloid on a retrograde and highly eccentric orbit from the outer region of the Solar System. It was first observed on 25 February 2000, by astronomers with the LINEAR program at the Lincoln Lab's ETS near Socorro, New Mexico, United States. It has not been observed since 2001. The unusual object measures approximately 16 kilometers (9.9 miles) in diameter.

<span class="nowrap">(127546) 2002 XU<sub>93</sub></span>

(127546) 2002 XU93, provisional designation 2002 XU93, is a trans-Neptunian object and centaur on highly inclined and eccentric orbit in the outer region of the Solar System. It measures approximately 170 kilometers (110 mi) in diameter and is one of few objects with such an unusual orbit. It was discovered on 4 December 2002, by American astronomer Marc Buie at the Kitt Peak National Observatory in Arizona, United States.

In planetary science, the term unusual minor planet, or unusual object, is used for a minor planet that possesses an unusual physical or orbital characteristic. For the Minor Planet Center (MPC), which operates under the auspices of the International Astronomical Union, any non-classical main-belt asteroid, which account for the vast majority of all minor planets, is an unusual minor planet. These include the near-Earth objects and Trojans as well as the distant minor planets such as centaurs and trans-Neptunian objects. In a narrower sense, the term is used for a group of bodies – including main-belt asteroids, Mars-crossers, centaurs and otherwise non-classifiable minor planets – that show a high orbital eccentricity, typically above 0.5 and/or a perihelion of less than 6 AU. Similarly, an unusual asteroid (UA) is an inner Solar System object with a high eccentricity and/or inclination but with a perihelion larger than 1.3 AU, which does exclude the near-Earth objects.

Chimera is a NASA mission concept to orbit and explore 29P/Schwassmann-Wachmann 1 (SW1), an active, outbursting small icy body in the outer solar system. The concept was developed in response to the 2019 NASA call for potential missions in the Discovery-class, and it would have been the first spacecraft encounter with a Centaur and the first orbital exploration of a small body in the outer solar system. The Chimera proposal was ranked in the first tier of submissions, but was not selected for further development for the programmatic reason of maintaining scientific balance.

<span class="nowrap">P/2019 LD<sub>2</sub></span> (ATLAS) Jupiter family comet

P/2019 LD2 (ATLAS) is a Jupiter-family comet discovered by the Asteroid Terrestrial-impact Last Alert System on 10 June 2019. It was initially reported as the first known Jupiter trojan asteroid to display cometary activity, but its classification as a Jupiter trojan was retracted after closer examination and a longer observation arc revealed its orbit to be unstable like a typical Jupiter family comet and implied that its position near the trojans is temporary.

(523676) 2013 UL10 (prov. designation:2013 UL10) is a reddish centaur with cometary activity orbiting the Sun between Jupiter and Uranus. It was discovered on 18 August 2010, by a team of astronomers with the Pan-STARRS survey at the Haleakalā Observatory, Hawaii. It is the first centaur known to have both comet-like activity and red surface colors. It is also one of the smallest centaurs, with a nucleus of no more than 10 kilometers (6.2 miles) in diameter. As of 2021, it has not been named.


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