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"
SOHO Comet 367: Sungrazer
9 November 2001
The most prolific comet discovering instrument in history rides aboard the sun-staring SOHO spacecraft, 1.5 million kilometers sunward of planet Earth. Of course, most of these SOHO comets have been sungrazers - like the one illustrated in the dramatic montage above. Three frames taken hours apart on October 23rd, show bright SOHO comet number 367 plunging toward the fiery solar surface, its tail streaming away from the Sun located just beyond the left hand border. Each panel spans about one million kilometers at the distance of the Sun. From bottom to top, the comet's tail grows as the intensifying solar radiation heats the frozen comet material and increases the outflow of gas and dust. Because of their orbits, sungrazers are believed to belong to a family of comets produced by the breakup of a single much larger comet. Coincidentally, this sungrazer was discovered shortly after solar active regions blasted out clouds of energetic particles, like those that triggered the recent spectacular auroral storms. And like all SOHO sungrazers so far, comet number 367 was not seen to survive its close solar encounter.