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"
Mediterranean Leonid 2001
7 December 2001
A road trip from Ankara to the Mediterranean coast southeast of Antalya, Turkey found clear skies and splendid scenery for astrophotographer Tunc Tezel's viewing of the 2001 Leonid meteor storm. There he captured this dream-like image of a fireball meteor near the horizon's twilight glow, reflected in calm ocean waters. Lights from coastal dwellings and nearby islands are seen in the foreground with brilliant Sirius shining as the brightest star in the heavens, visible in the constellation Canis Major at the upper right. Many enthusiasts who made special trips to view this November's Leonids were rewarded with similar spectacles of the fireball-rich storm. Airborne astronomers too had much to be thankful for as Leonid observations from a specially equiped aircraft flying at 40,000 feet produced bountiful data on the chemical composition of these dust grains from a comet's tail.