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"
How Much is That Comet in the Window?
27 March 1996
The above true-color photo taken March 25th shows Comet Hyakutake passing below the stars of the Big Dipper. Many astronomy enthusiasts delight in helping people in their local community see the comet. Both Jerry Bonnell and I (RJN) from APOD have been so inclined - both now and when Comet Halley came by in 1986. During these sessions, many good questions are asked and occasionally a humorous situation will arise. One was with a little girl. She waited so patiently for her turn to look through the telescope, hardly able to contain her excitement. Finally her turn came. "Do you see the comet?" I asked. "Wow, wow, WOW!" She beamed. "You see it?" "No." One little boy seemed particularly bent on destruction. "This telescope looks like a big gun," he volunteered. "In some ways, it's even more powerful than a gun," I replied, hoping to challenge his imagination. "Really?" he countered. "Can we shoot down the comet?" "How expensive is the telescope?" is a fairly common question. But one time a real business-person showed up and, possibly feeling particularly affluent, asked "How much is the comet?" Latest Comet Hyakutake images: JPL, Crni Vrh Observatory, Slovenia, Fayetteville Observer-Times, NASA's Night of the Comet