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 Catalina Tails
1 January 2016
A new year's treat for binoculars, as 2016 begins Comet Catalina (C/2013 US10) now sweeps through planet Earth's predawn skies near bright Arcturus, alpha star of Bootes. But this telescopic mosaic from December 21 follows the pretty tails of the comet across a field of view as wide as 10 full moons. The smattering of distant galaxies and faint stars in the background are in the constellation Virgo. Trailing behind the comet's orbit, Catalina's dust tail fans out below and left in the frame. Its ion tail is angled toward the top right, away from the Sun and buffeted by the solar wind. On January 17, the outward bound visitor from the Oort Cloud will make its closest approach to Earth, a mere 110 million kilometers away, seen near bright stars along the handle of the Big Dipper.