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"
Tempel-Tuttle: The Leonid Comet
30 January 1998
Star trails streak this composite time exposure of Comet Tempel-Tuttle recorded by T. Puckett on January 26. Presently passing through the inner solar system on its 33 year orbit around the Sun, Tempel-Tuttle has brightened unexpectedly, but binoculars or small telescopes are still required to visually observe it. Tempel-Tuttle is also called "the Leonid Comet" as the yearly Leonid meteor shower results when the Earth crosses this comet's orbital plane and encounters cometary dust. So, while not currently rivaling the spectacle of a Hyakutake or Hale-Bopp, Tempel-Tuttle may still put on a show. When the Earth plunges through Tempel-Tuttle's debris tail in November of this year, many sky-watchers are anticipating an extremely active meteor shower to result, perhaps even a meteor storm!