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"
Fairytale NEOWISE
23 July 2020
Comet dust falls through a twilight sky in this dream-like scene, but it's not part of a fairytale movie. Still, Castle Neuschwanstein, nestled in the Bavarian Alps, did inspire Disneyland's Sleeping Beauty Castle. Captured on July 20, the bright streak above the castle towers is likely a Perseid meteor. Though it peaks near mid-August, the annual summer meteor shower is active now. The meteor trail over the fairytale castle can be traced back to the shower's radiant in the heroic constellation Perseus off the top right of the frame. Perseid meteors are produced by dust from periodic Comet Swift-Tuttle. With its own broad dust tail now sweeping through northern skies the celestial apparition above the distant horizon is planet Earth's current darling, Comet NEOWISE. Comet NEOWISE Images: July 22 || 21 || 20 || 19 || 18 || 17 || 16 || 15 || 14 || 13 || 12 || 11 || 10 & earlier ||