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"
Kenya Morning Moon, Planets, and Taurid
12 November 2015
On November 8, a waning crescent Moon joined the continuing parade of planets in Earth's early morning skies. Captured here from Amboseli National Park, Kenya, even the overexposed moonlight can't washout brilliant Venus though, lined up near the ecliptic plane with faint Mars and bright Jupiter above. As if Moon and planets aren't enough, a comparably bright Taurid meteor also streaks through the scene. In fact November's Taurid meteor showers have had a high proportion of bright fireballs. Apparently streaming from radiants in Taurus, the meteors are caused by our fair planet's annual passage through debris from Comet 2P/Encke. The comet's dust grains are catching up with Earth's atmosphere at a relatively low speed of about 27 kilometers per second.