Comet
A comet is a small Solar System body composed mainly of ice, dust, and organic compounds. As they approach the Sun, cometary ices sublimate, releasing gas and dust that form the glowing coma and distinctive tails—often extending millions of kilometers.
Comets originate from two primary reservoirs: the Kuiper Belt—home to short-period comets with orbits under ~200 years—and the distant Oort Cloud, which sends long-period comets with orbits spanning thousands of years. Occasionally, interstellar objects like ‘Oumuamua pass through our system, appearing comet-like.
They are “dirty snowballs” and among the most primitive remnants of the early Solar System, preserving original ices and organic material from 4.6 billion years ago.
Landmark missions include ESA’s Rosetta—with its lander Philae—which orbited and sampled Comet 67P/Churyumov–Gerasimenko (2014–2016). NASA’s Deep Impact struck Comet Tempel 1 in 2005 to analyze interior composition.
These missions discovered complex organic molecules, including amino-acid precursors, and supported the theory that comets may have delivered water and prebiotic compounds to early Earth.
Looking ahead, ESA–JAXA’s Comet Interceptor (launch planned for 2029) intends to perform a rapid flyby of a dynamically new or interstellar comet, using multiple spacecraft to sample both nucleus and coma environments.
Comets are studied across the electromagnetic spectrum—from radio to gamma rays—using telescopes and spacecraft to understand composition, internal structure, activity, and their roles in planetary formation, the evolution of the solar system, and the origin of life.
Sources
APODs including "Comet"
A Twisted Meteor Trail Over Tenerife
2 June 2010
Did this meteor take a twisting path? No one is sure. Considered opinions are solicited. Meteors, usually sand sized grains that originate in comets, will typically disintegrate as they enter the Earth's atmosphere. A fast moving meteor ionizes molecules in the Earth's atmosphere that subsequently glow when they reacquire electrons. Meteor paths that twist noticeably have been noted before, and even photographed, but attributing such behavior to the motion of the meteor itself and neither the wind-blown meteor train nor the observer remains somewhat controversial. The above meteor, imaged two weeks ago streaking over the Teide Observatory in Tenerife, Canary Islands, appears to swagger as much as several minutes of arc, which the experienced astrophotographer did not think could be attributed to drifting of the resulting train or motion of the camera mount. If truly an indication of a twisted meteor path, an underlying reason could be the pictured meteor was markedly non-spherical in shape, non-uniform in composition, or electrically charged. Non-uniform meteors, for example, may evaporate more on one side than another, causing a rotating meteor to wobble. Understanding meteors is important partly because meteors are candidates to have seeded Earth with prebiotic molecules that allowed for the development of life.