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.
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APODs including "Comet"
Comet Hyakutake and a Solar Flare
17 May 1996
A rare coincidence was recently captured by the orbiting SOHO spacecraft. During the closest approach to the Sun of Comet Hyakutake on May 1, SOHO photographed the comet. By accident -- during the time this photograph was being taken -- a solar flare was being ejected from the Sun. Therefore, at the top of this false-color picture, Comet Hyakutake is visible, while emission to the left of the Sun is a solar flare. The Sun, at the center of the picture, was blocked by an artificial occulter in the LASCO telescope, allowing objects much dimmer than the Sun to be observed. SOHO was launched in December of 1995 and contains many instruments which study the Sun.