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"
A Cool GIF of a 2025 Perseid
16 August 2025
The camera battery died about 2am local time on August 12, while shooting in the bright moonlit skies from a garden in Chastre, Brabant Wallon, Belgium, planet Earth. But not before it captured the frames used to compose this cool animated gif of a brilliant Perseid meteor and a lingering visible trail known as a persistent train. The Perseid meteor, a fast moving speck of dust from the tail of large periodic Comet Swift-Tuttle, was heated to incandescence by ram pressure and vaporized as it flashed through the upper atmosphere at 60 kilometers per second. Compared to the brief flash of the meteor, its wraith-like trail really is persistent. A characteristic of bright meteors, a smoke-like persistent train can often be followed for many minutes wafting in the winds at altitudes of 60 to 90 kilometers.