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"
Beta Pictoris Revisited
28 November 1997
In the early 1980s, Beta Pictoris became one of the most important stars in the sky. Satellite and ground-based telescopic observations revealed the presence of a surrounding outer disk of material and an inner "clear" zone about the size of our solar system - strong evidence for the formation of planets. Beta Pictoris is 50 light years away and any orbiting planets are too small and faint to image at that distance. But evidence continues to mount that this star indeed has comet-like bodies in the disk and a Jupiter-sized planet orbiting within the central zone. Shown here in false color, this recent, highly detailed picture was obtained at the European Southern Observatory by blocking the overwhelming direct starlight and imaging the near-infrared light from the disk. The disk's warped bright inner region is indirect evidence for an orbiting planet.