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"
Most of Comet Tsuchinshan-ATLAS
18 October 2024
On October 14 it was hard to capture a full view of Comet C/2023 A3 Tsuchinshan-ATLAS. Taken after the comet's closest approach to our fair planet, this evening skyview almost does though. With two telephoto frames combined, the image stretches about 26 degrees across the sky from top to bottom, looking west from Gates Pass, Tucson, Arizona. Comet watchers that night could even identify globular star cluster M5 and the faint apparition of periodic comet 13P Olbers near the long the path of Tsuchinshan-ATLAS's whitish dust tail above the bright comet's coma. Due to perspective as the Earth is crossing the comet's orbital plane, Tsuchinshan-ATLAS also has a pronounced antitail. The antitail is composed of dust previously released and fanning out away from the Sun along the comet's orbit, visible as a needle-like extension below the bright coma toward the rugged western horizon. Growing Gallery: Comet Tsuchinshan-ATLAS in 2024