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"
Aurigids from 47,000 Feet
5 September 2007
On September 1, Aurigid meteors filled the sky, in keeping with an innovative prediction of an outburst from this historically tentative meteor shower. The prediction was made by Peter Jenniskens of the SETI Institute, in work with Esko Lyytinen of Finland and Jeremie Vaubaillon of Caltech. Astronomers flying at 47,000 feet on a dedicated mission to observe the outburst collected image data for this composite photo of the Aurigids' bright and colorful streaks. The source of the shower is understood to be Comet Kiess, a comet that would have swung through the inner solar system around 2,000 years ago, and again in 1911. Pushed outward by solar radiation pressure, dust from the tail of the comet has been drifting toward the Earth's orbit, creating the 2007 outburst as well as outbursts of the Aurigids recorded in 1935, 1986, and 1994. Of course, the shower's radiant point is in the eponymous constellation Auriga, the Charioteer.