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"
Messier Catalog at Uniform Scale
14 May 2026
What are some of the most interesting astronomical objects you can see in the night sky? Armed with a good pair of binoculars or a small telescope, if you live in the Northern Hemisphere, you can look for the very popular objects in the Messier Catalog. Most of them, but not all, are also visible from the southern half of the Earth. The featured image shows all 110 objects in the catalog at uniform scale -- the same magnification. Charles Messier created the catalog in the 18th century. He was interested in comets, and his catalog was a list of known comet-like "objects to avoid" in the sky when observing or hunting for comets. The deep sky objects in the catalog include a supernova remnant (the Crab Nebula, M1), other galaxies (such as Andromeda, M31), nebulae (e.g. the Orion Nebula, M42, a star-forming region) and stellar clusters (such as the Pleiades, M45, a bright young open cluster).