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"
Detailing Hale-Bopp Credit and Copyright:
8 May 1997
This enhanced composite image detailing structure in the coma and dust tail of Hale-Bopp was recorded May 5 - one day before the comet's passage from north to south across the plane of Earth's orbit. As the comet descends into murky twilight for northern hemisphere observers it will become increasingly easy to view from the south. Along with Southern Hemisphere observers, astronomers and a fleet of spacecraft of the International Solar-Terrestrial Physics program have been anxiously awaiting this north/south crossing. The comet's interaction with the changing equatorial solar wind and magnetic field during this crossing is expected to produce distortions and disconnections of Hale-Bopp's ion tail. Whisker-like structures, probably part of the ion tail, are visible above extending from the lower left of the bright coma.