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"
An Extreme UltraViolet View of the Comet
30 March 1996
As the Sun floods Comet Hyakutake with ultraviolet light gases in the coma scatter the radiation and fluoresce making the comet a bright source in the ultraviolet sky. The above image made using data from NASA's Extreme UltraViolet Explorer (EUVE) satellite, represents the intensity of the comet in this invisible high energy band in false color. The image is about 3/4 of a degree high and 2 degress wide and offers insights to the composition of this visitor from the distant solar system that can be obtained from the highest energy bands of the ultraviolet spectrum. The International Ultraviolet Explorer (IUE) satellite has also examined ultraviolet light from the comet and now reports the detection of many bands of molecular emission particularly those due to molecular carbon (C2), carbon monoxide (CO) and caron dioxide (C02) ions as well as indications of a rapid increase in the production of water (H20). Latest Comet Hyakutake images: JPL, Fayetteville Observer-Times, NASA's Night of the Comet, ICSTARS, Crni Vrh Obs., Cent. Mich U.