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"
Schwassmann-Wachmann 3: Fragment B
4 May 2006
Periodic comet 73P/Schwassmann-Wachmann 3 has fallen apart before. A cosmic souffle of ice and dust left over from the early solar system, this comet was seen to split into several large pieces during the close-in part of its orbit in 1995. However, this time the comet seems to be rapidly disintegrating with over three dozen fragments, named alphabetically, now stretching several degrees across the sky. Since comets are relatively fragile, stresses from heat and gravity and outgassing, for example, could be responsible for their tendency to breakup in such a spectacular fashion. On April 18th, the Hubble Space Telescope recorded this sharp view of prolific Fragment B, itself trailing dozens of smaller pieces, each with its own cometary coma and tail. The picture spans over 3,000 kilometers at the comet's April 18 distance of 32 million kilometers from planet Earth. With its brightest fragment presently too faint to be seen with the naked eye, comet Schwassmann-Wachmann 3 will pass closest to Earth on May 13 at a distance of about 11 million kilometers.