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 Lovejoy in a Winter Sky
28 January 2015
Which of these night sky icons can you find in this beautiful and deep exposure of the northern winter sky? Skylights include the stars in Orion's belt, the Orion Nebula, the Pleiades star cluster, the bright stars Betelgeuse and Rigel, the California Nebula, Barnard's Loop, and Comet Lovejoy. The belt stars of Orion are nearly vertical in the central line between the horizon and the image center, with the lowest belt star obscured by the red glowing Flame Nebula. To the belt's left is the red arc of Barnard's Loop followed by the bright orange star Betelgeuse, while to the belt's right is the colorful Orion Nebula followed by the bright blue star Rigel. The blue cluster of bright stars near the top center is the Pleiades, and the red nebula to its left is the California nebula. The bright orange dot above the image center is the star Aldebaran, while the green object with the long tail to its right is Comet C/2014 Q2 (Lovejoy). The featured image was taken about two weeks ago near Palau village in Spain.