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"
Atlantis Approaches Mir
2 April 1996
Imagine flying though space and approaching the Mir space station. The crew of the Space Shuttle Atlantis did just this in a mission that ended only two days ago. Mir, now 10 years old, is equipped for scientific experiments in astronomy, physics, materials, biology and chemistry. The top most module on Mir is an unmanned supply ship used to send food and supplies. The next module with the long boom carries telescopes and essential flight equipment and connects to the core module with living quarters and solar panels. To the left is the Spektr module carrying solar arrays and scientific equipment while on the right is a scientific module that also carries an airlock. The docking module seen at the bottom is the ultimate destination of Atlantis. The STS-76 mission left astronaut Shannon Lucid for a planned five month stay. Four more shuttle flights are currently planned to Mir, keeping a NASA astronaut continuously in space until late 1997. In late 1997, building on this jointly developed understanding and experience, the US and Russia will launch the first modules of the International Space Station. Latest Comet Hyakutake images: APOD Hyakutake Archive, JPL, Fayetteville Observer-Times, NASA's Night of the Comet, ICSTARS, Jerry Lodriguss, ScienceWeb, Crni Vrh Obs., Cent. Mich. U.