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"
A Leonid Meteor Over Sweden
21 November 2006
This past weekend, small remnant bits of a distant comet lit up the skies over much of planet Earth. Incoming reports, however, have this year's Leonid meteor shower as less active than Leonid meteor showers a few years ago. Nevertheless, some sky enthusiasts reported peak meteor bursts as high as one visual meteor per minute. The parent body of the Leonids meteor shower, Comet Tempel-Tuttle, leaves a trail of expelled sand-size particles every 33 years when it returns to the inner Solar System. When the Earth passes through a stream of these Sun-orbiting particles, a meteor shower results. Pictured above, a Leonid meteor was captured two days ago during the early morning hours of November 19 over Vallentuna, Sweden. Although activity levels in meteor showers are notoriously hard to predict, some astronomers speculate that Aurigids meteor shower next September might be unusually rich in bright meteors.