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"
Comet Pons-Brooks in Northern Spring
9 March 2024
As spring approaches for northern skygazers, Comet 12P/Pons-Brooks is growing brighter. Currently visible with small telescopes and binoculars, the Halley-type comet could reach naked eye visibility in the coming weeks. Seen despite a foggy atmosphere, the comet's green coma and long tail hover near the horizon in this well-composed deep night skyscape from Revuca, Slovakia recorded on March 5. M31, also known as the Andromeda galaxy, and bright yellowish star Mirach, beta star of the constellation Andromeda, hang in the sky above the comet. The Andromeda galaxy is some 2.5 million light-years beyond the Milky Way. Comet Pons-Brooks is a periodic visitor to the inner Solar System and less than 14 light-minutes away. Reaching its perihelion on April 21, this comet should be visible in the sky during the April 8 total solar eclipse.