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"
The City Comet Credit and Copyright:
26 March 1997
Undaunted by the artificial glow from one of the most famous urban skylines on Earth, comet Hale-Bopp shines above the city of New York, USA. Photographed on March 23rd, this view from New Jersey shows the Hudson River in the foreground, the Empire State Building at the right, the George Washington Bridge at the left, and the comet with a visible tail above. The comet lies at a distance of about 120 million miles from New York. As bright as this comet has turned out to be, it might have been even brighter. On May 6, Hale-Bopp's orbit will take it within about 10 million miles of the point in the Earth's orbit which was occupied by planet Earth itself in early January. If the comet had also reached this point in January, it would have come almost as close to Earth as comet Hyakutake did last year. At that distance, Hale-Bopp might have been 100 times brighter than it is now, reaching -5th or -6th magnitude!