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 Ikeya-Zhang Over Tenerife
26 March 2002
Comet Ikeya-Zhang has become bright enough to stand out in the night sky. Discovered February 1, the comet has now just rounded the Sun and has likely attained its peak brightness. The comet appears near the Sun and over the next week moves from the evening sky (just after sunset) to the morning sky (just before sunrise). Many observers report a current brightness approaching third magnitude. The comet is actually a giant snowball created during the early days of our Solar System and pushed out by the gravitational tugs by massive planets. Comet Ikeya-Zhang has been back to the inner Solar System at least once before in 1661. Above, the comet was photographed above Tenerife, one the Canary Islands, Spain.