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"
Meteors, Planes, and a Galaxy over Bryce Canyon
19 May 2014
Sometimes land and sky are both busy and beautiful. The landscape pictured in the foreground encompasses Bryce Canyon in Utah, USA, famous for its many interesting rock structures eroded over millions of years. The skyscape above, photogenic in its own right, encompasses the arching central disk of our Milky Way Galaxy, streaks that include three passing airplanes and at least four Eta Aquariid meteors, and bright stars that include the Summer Triangle. The above image is a digital panorama created from 12 smaller images earlier this month on the night May 6. If you missed the recent Eta Aquariids meteor shower though, don't fret -- you may get an unexpected reprieve. Sky enthusiasts are waiting to see if a new meteor shower develops in the early morning hours of Saturday, May 24, when the Earth moves through a possibly dense cloud of dust and debris ejected by Comet 209P/LINEAR. See for yourself: Bryce Canyon National Park Astronomy Festival June 25-28 Best space images: Free APOD Lecture in Paris on June 17