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 Meteor Over the Anza-Borrego Desert
11 August 1999
Meteors will be flashing across your skies over the next two nights. Specifically, the Perseid Meteor Shower should be at its best just before each morning's dawn. Observers at dark locations might see as much as a meteor a minute. Perseid meteors are bits of dirt that blew off Comet Swift-Tuttle and that burn up as they fall to Earth. Exciting expectations of a new filament in the Perseids might be tested this year. Pictured above is a meteor from the most active meteor shower of last year: the Leonids. Pictured above, a Leonid meteor was caught in November outshining even the brightest stars over the Anza-Borrego Desert in California. The Leonids will peak again this November and might provide an ever better show.