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"
Venus and Comet Pojmanski
3 March 2006
Shining brightly in the east at dawn, Venus dominates the sky in this view over a suburban landscape from Bursa, Turkey. An otherwise familiar scene for astronomer Tunc Tezel, his composite picture of the morning sky recorded on March 2nd also includes a surprise visitor to the inner solar system, Comet Pojmanski. Cataloged as C/2006 A1, the comet was discovered on January 2nd by Grzegorz Pojmanski of Warsaw University Astronomical Observatory in Poland. At the time very faint and tracking through southern skies, the comet has now moved north and grown just bright enough to be a good target for early-rising skygazers with binoculars. Enhanced and framed in this picture, the comet's tail has also grown to a length of several degrees. The comet will be at its closest approach to planet Earth, just over 100 million kilometers away, on March 5. For northern hemisphere observers in the next few days, the beginning of morning twilight really will be the best time to spot Comet Pojmanski.