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. source
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.
Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles. source
Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles.
Comets have been observed and recorded since ancient times by many cultures. source
Comets have been observed and recorded since ancient times by many cultures.
Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. source
Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years.
Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. source
Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.
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. source
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.
Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. source
Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space.
The appearance of a comet is called an apparition. source
The appearance of a comet is called an apparition.
Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. source
Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus.
Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. source
Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System.
Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. source
Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide.
The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. source
The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets.
Particularly bright examples are called "Great Comets". source
Particularly bright examples are called "Great Comets".
As of November 2014 there are 5,253 known comets, a number that is steadily increasing as they are discovered. source
As of November 2014 there are 5,253 known comets, a number that is steadily increasing as they are discovered.
Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya–Seki. source
Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya–Seki.
A recent collision of a comet with a planet occurred in July 1994 when Comet Shoemaker–Levy 9 broke up into pieces and collided with Jupiter. source
A recent collision of a comet with a planet occurred in July 1994 when Comet Shoemaker–Levy 9 broke up into pieces and collided with Jupiter.
