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 Hale-Bopp Over New York City Credit and Copyright:
8 April 1997
What's that point of light above the World Trade Center? It's Comet Hale-Bopp! Both faster than a speeding bullet and able to "leap" tall buildings in its single orbit, Comet Hale-Bopp is also bright enough to be seen even over the glowing lights of one of the world's premier cities. In the foreground lies the East River, while much of New York City's Lower Manhattan can be seen between the river and the comet. Comet Hale-Bopp is now moving away from both the Sun and the Earth. It should, however, should remain visible even in northern cities for at least a month. To find Comet Hale-Bopp, look for the brightest object in the northwest sky just after sunset - or wait for its return in 2400 years.