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"
Comet Hyakutake's Past and Future
23 March 1996
The above false-color picture of Comet Hyakutake taken just two days ago shows its rapidly developing tail. The comet now has a substantial coma with a bright center, lending it a dramatic eye-like appearance. This is not Comet Hyakutake's first visit to the inner Solar System. Recent orbital determinations clearly show Comet Hyakutake's was here before, although the previous approach is estimated to be about 8600 years ago - during the epoch of the first recorded human cities. Were this the comet's first trip to the inner Solar System, it probably would not appear as bright as it does now - first time comets typically do not shed as much luminous gas as veterans. Before making any approach to the inner Solar System, Comet Hyakutake was dormant in the Oort cloud of the outer Solar System for a few billion years, along with hundreds of thousands of similar comets. Comet Hyakutake is predicted to become the brightest comet since Comet West in 1976, which rivaled the brightest stars in the sky. Tonight, Comet Hyakutake can be seen best from about 10 pm near the Big Dipper's handle. Latest Comet Hyakutake images: Crni Vrh Observatory, Slovenia, Fayetteville Observer-Times