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"
Another Comet LINEAR Breaks Up
21 May 2001
Last year, a different comet LINEAR (C/1999 S4) broke up. This year, a comet first imaged by the Lincoln Near Asteroid Research (LINEAR) telescope in New Mexico on 2001 January 3, is also breaking up. This new Comet LINEAR (C/2001 A2) unexpectedly brightened to the edge of naked-eye visiblilty a few weeks ago when its nucleus broke in two. Observations taken just last week now indicate that one of the two remaining nuclear fragments has again fragmented. The first piece to break off is visible on the upper left of the above false-color image by a Very Large Telescope, while additional fragmentation is inferred from the brightness and elongation of the spot on the lower right. When a comet nucleus splits, new surfaces are exposed and previously trapped ice and gas are released that evaporate and brighten in the energetic sunlight. Comet LINEAR may remain visible with little or no optical aid into early June. In contrast, at least two other much dimmer Comet LINEARs discovered recently appear stable.