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 Meteor Shower Next Week
8 November 1998
rly next week, a spectacular meteor storm is expected: the 1998 Leonids. It is widely thought that that the meteors from the Leonids meteor shower are just small pieces of Comet Temple-Tuttle falling to Earth. During each pass near the Sun, a comet will heat up and shed pieces of ice and rock from its nucleus. This debris continues to orbit the Sun until either evaporating or being swept up by some large solar-system body. A piece of comet debris striking the Moon creates a small crater, but a piece striking the Earth usually burns up in the atmosphere causing a brief, bright streak. The streak below center in the above picture of the northern sky actually depicts a meteor from the Perseid meteor shower, a usually impressive display that peaks every year in mid-August.