Comet

cometslong-period cometJupiter-family cometshort-period cometJupiter-familyJupiter familyHalley-type cometJupiter family cometlong-periodcometary
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing.wikipedia
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Coma (cometary)

comacomaecometary activity
This produces a visible atmosphere or coma, and sometimes also a tail.
The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublime.

List of hyperbolic comets

hyperbolic cometC/1925 F1C/1959 O1
Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space.
This is a list of parabolic and hyperbolic comets in the Solar System.

Comet tail

tailcomet's tailtails
This produces a visible atmosphere or coma, and sometimes also a 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.

Great comet

brilliant cometclose approach to the earthcometary outburst
Particularly bright examples are called "great comets".
A great comet is a comet that becomes exceptionally bright.

Rosetta (spacecraft)

RosettaRosetta missionRosetta spacecraft
Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior. Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals.
Along with Philae, its lander module, Rosetta performed a detailed study of comet 67P/Churyumov–Gerasimenko (67P).

Deep Impact (spacecraft)

Deep ImpactDeep impact missionC/2009 P1
Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior.
It was designed to study the interior composition of the comet Tempel 1 (9P/Tempel), by releasing an impactor into the comet.

Solar wind

solar windslosessolar
These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet.
Other related phenomena include the aurora (northern and southern lights), the plasma tails of comets that always point away from the Sun, and geomagnetic storms that can change the direction of magnetic field lines.

Tempel 1

9P/TempelComet Tempel 19P/Tempel 1
Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior.
Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867.

Centaur (small Solar System body)

centaurcentaursCentaur (minor planet)
The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets.
Centaurs typically behave with characteristics of both asteroids and comets.

Naked eye

naked-eyeunaided eyenaked human eye
Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular.
In astronomy, the naked eye may be used to observe celestial events and objects visible without equipment, such as conjunctions, passing comets, meteor showers, and the brightest asteroids, including 4 Vesta.

Meteorite

meteoritesmeteoriticmeteoric
In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine, and related organic molecules) may have been formed on asteroids and comets.
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon.

Oort cloud

Oort cloud objectÖpik-Oort CloudÖpik–Oort cloud
Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.
These forces occasionally dislodge comets from their orbits within the cloud and send them toward the inner Solar System.

Stardust (spacecraft)

StardustStardust spacecraftStardust mission
In 2009, it was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission.
Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return these to Earth for analysis.

Kuiper belt

Kuiper belt objectKuiper belt objectsKuiper cliff
Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.
From this he concluded that "the outer region of the solar system, beyond the orbits of the planets, is occupied by a very large number of comparatively small bodies" and that, from time to time, one of their number "wanders from its own sphere and appears as an occasional visitor to the inner solar system", becoming a comet.

Halley's Comet

Comet Halley1P/HalleyHalley
The Giotto space probe found that the nucleus of Halley's Comet reflects about four percent of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly's surface reflects less than 3.0%; by comparison, asphalt reflects seven percent.
Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime.

Deep Space 1

Deep Space 1 (DS1)Deep Space OneDeep Space One Remote Agent Experiment
The Giotto space probe found that the nucleus of Halley's Comet reflects about four percent of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly's surface reflects less than 3.0%; by comparison, asphalt reflects seven percent.
Deep Space 1 (DS1) was a NASA technology demonstration spacecraft which flew by an asteroid and a comet.

Near-Earth object

near-Earth asteroidNEOnear-Earth
Roughly six percent of the near-Earth asteroids are thought to be extinct nuclei of comets that no longer experience outgassing, including 14827 Hypnos and 3552 Don Quixote.
Most known PHOs and NEOs are asteroids, but a small fraction are comets.

67P/Churyumov–Gerasimenko

67P/Churyumov-Gerasimenkocomet 67PChuryumov–Gerasimenko
Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals.
67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C-G) is a Jupiter-family comet, originally from the Kuiper belt, with a current orbital period of 6.45 years, a rotation period of approximately 12.4 hours and a maximum velocity of 135000 km/h.

Extinct comet

dormant cometextinct cometsdormant
Roughly six percent of the near-Earth asteroids are thought to be extinct nuclei of comets that no longer experience outgassing, including 14827 Hypnos and 3552 Don Quixote. However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids.
An extinct comet is a comet that has expelled most of its volatile ice and has little left to form a tail and coma.

Comet nucleus

nucleuscomet nucleicometary nucleus
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 nucleus is the solid, central part of a comet, popularly termed a dirty snowball or an icy dirtball.

Philae (spacecraft)

PhilaePhilae spacecraftPhilae lander
Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals.
Philae ( or ) is a robotic European Space Agency lander that accompanied the Rosetta spacecraft until it separated to land on comet 67P/Churyumov–Gerasimenko, ten years and eight months after departing Earth.

Formaldehyde

formalinH 2 COmethanal
In addition to the gases already mentioned, the nuclei contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane and perhaps more complex molecules such as long-chain hydrocarbons and amino acids.
HCN, HNC, H 2 CO, and dust have also been observed inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).

81P/Wild

Wild 2Comet Wild 2Wild-2
Comet 81P/Wild, also known as Wild 2 (pronounced "vilt two"), is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6, 1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland.

Great Comet of 1811

Great Comet1811 cometappearance in 1811 of a bright comet
The Great Comet of 1811 also had a coma roughly the diameter of the Sun.
The Great Comet of 1811, formally designated C/1811 F1, is a comet that was visible to the naked eye for around 260 days, a record it held until the appearance of Comet Hale–Bopp in 1997.

Outgassing

outgasoffgassingoutgassed
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing.
Natural outgassing is commonplace in comet s.