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"
Hyakutake, Big Dipper, and Observatory Dome
1 April 1996
In one of the more spectacular pictures yet taken, Comet Hyakutake is shown here on March 26 high in the dark Missouri sky. In the foreground is Elmcrest Observatory complete with a dim red light glowing inside the dome. The stars in the background moved slightly during the exposure causing them to appear as streaks instead of points of light. Nevertheless, the constellation of Ursa Major - including the Big Dipper - is visible. Can you spot it? (Hint: Hyakutake's tail flows through the Dipper's handle.) Photographs with both recognizable foreground and background objects visible can be quite striking as they add angular perspective and contrast to the outworldly and unfamiliar comet. Dare anyone try to compete with city lights and capture the Eiffel Tower or the New York skyline in front of the comet? Latest Comet Hyakutake images: APOD Hyakutake Archive, JPL, Fayetteville Observer-Times, NASA's Night of the Comet, ICSTARS, Jerry Lodriguss, ScienceWeb, Crni Vrh Obs., Cent. Mich U.