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"
Comet ATLAS and Orion's Belt
12 November 2020
With its closest approach to planet Earth scheduled for November 14, this Comet ATLAS (C/2020 M3) was discovered just this summer, another comet found by the NASA funded Asteroid Terrestrial-impact Last Alert System. It won't get as bright as Comet NEOWISE but it can still be spotted using binoculars, as it currently sweeps through the familiar constellation of Orion. This telephoto field from November 8, blends exposures registered on the comet with exposures registered on Orion's stars. It creates an effectively deep skyview that shows colors and details you can't quite see though, even in binoculars. The comet's telltale greenish coma is toward the upper left, above Orion's three belt stars lined-up across the frame below center. You'll also probably spot the Orion Nebula, and famous Horsehead Nebula in the stunning field of view. Of course one of Orion's belt stars is nearly 2,000 light-years away. On November 14, this comet ATLAS will fly a mere 2.9 light-minutes from Earth.