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"
Meteors and Milky Way over Mount Rainier
25 August 2015
Despite appearances, the sky is not falling. Two weeks ago, however, tiny bits of comet dust were. Featured here is the Perseids meteor shower as captured over Mt. Rainier, Washington, USA. The image was created from a two-hour time lapse video, snaring over 20 meteors, including one that brightened dramatically on the image left. Although each meteor train typically lasts less than a second, the camera was able to capture their color progressions as they disintegrated in the Earth's atmosphere. Here an initial green tint may be indicative of small amounts of glowing magnesium atoms that were knocked off the meteor by atoms in the Earth's atmosphere. To cap things off, the central band of our Milky Way Galaxy was simultaneously photographed rising straight up behind the snow-covered peak of Mt. Rainier. Another good meteor shower is expected in mid-November when debris from a different comet intersects Earth as the Leonids. Follow APOD on Facebook: in English or Spanish