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 and Meteor
5 January 2009
This meteor streaking toward the horizon through the early morning sky of January 4th is from the annual Quadrantid meteor shower. Aligned with the shower's radiant point high in the north (off the top of the view), the meteor trail passes to the right of bright bluish star Beta Scorpii. Remarkably, near the top of the trail is a small spot, the fuzzy greenish glow of a comet. Discovered in July of 2007, Comet Lulin (C/2007 N3), is too faint now to be easily seen by the unaided eye, but will likely brighten to become visible to skygazers by late February. The well-timed skyscape featuring both comet and meteor is particularly appropriate as cometary bodies are known to be the origins of planet Earth's annual meteor showers.