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 Breaks Up
16 April 2020
Cruising through the inner solar system, Comet ATLAS (C/2019 Y4) has apparently fragmented. Multiple separate condensations within its diffuse coma are visible in this telescopic close-up from April 12, composed of frames tracking the comet's motion against trailing background stars. Discovered at the end of December 2019, this comet ATLAS showed a remarkably rapid increase in brightness in late March. Northern hemisphere comet watchers held out hope that it would become a bright naked-eye comet as it came closer to Earth in late April and May. But fragmenting ATLAS is slowly fading in northern skies. The breakup of comets is not uncommon though. This comet ATLAS is in an orbit similar to the Great Comet of 1844 (C/1844 Y1) and both may be fragments of a single larger comet.