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"
Leonid Watching
16 November 2001
Will the Leonids storm this year? The annual Leonid meteor shower should peak this weekend and some predictions suggest that "storm" rates of a thousand or more meteors per hour are possible for observers located in eastern North and Central America during the early morning hours of Sunday, November 18. Similar high rates are also anticipated for the western Pacific region on the morning of November 19th. In any event, the 2001 Leonid shower should be dramatic and easy to watch, as were the Leonids of recent years. From top left to bottom right above are spectacular examples of bright fireball meteors from the 1998 Leonid shower as recorded by V. Winter and J. Dudley, Lorenzo Lovato, and Wally Pacholka. A 1998 image from the Puckett Observatory at lower left features the source of the debris stream which supplies the Leonid meteors, comet Tempel-Tuttle.