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"
Meteor, Comet, and Seagull (Nebula)
21 October 2018
A meteor, a comet, and a photogenic nebula have all been captured in this single image. The closest and most fleeting is the streaking meteor on the upper right -- it was visible for less than a second. The meteor, which disintegrated in Earth's atmosphere, was likely a small bit of debris from the nucleus of Comet 21P/Giacobini-Zinner, coincidentally the comet captured in the same image. Comet 21P, pictured across the inner Solar System from Earth, is distinctive for its long dust tail spread horizontally across the image center. This comet has been visible with binoculars for the past few months but is now fading as it heads back out to the orbit of Jupiter. Farthest out at 3,500 light years distant is the IC 2177, the Seagull Nebula, visible on the left. The comparatively vast Seagull Nebula, with a wingspan on order 250 light-years, will likely remain visible for hundreds of thousands of years. Long exposures, taken about two weeks ago from Iwaki-City in Japan, were combined to capture the image's faintest elements. You, too, could see a meteor like this -- and perhaps sooner than you might think: tonight is the peak of the Orionids meteor shower.