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 Southern Sky View
10 March 2002
On 1996 March 22, a Galaxy and a comet shared the southern sky. They were captured together, from horizon to horizon, in the night sky above Loomberah, New South Wales, Australia by astronomer Gordon Garradd. Garradd used a home made all-sky camera with a fisheye lens, resulting in a circular 200 degree field of view. This gorgeous sky view was dominated by the luminous band of our Milky Way Galaxy cut by dramatic, dark interstellar dust clouds. Along with the bright stars of our Galaxy, the Large Magellanic Cloud is visible at the lower left. That night sky was also graced by the long, lovely, bluish tail of Comet Hyakutake, which can be seen toward the top of the image, near the bright star Arcturus. Bright city lights from nearby Tamworth glow along the Northwestern horizon.