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 Lovejoy: Sungrazing Survivor
17 December 2011
Like most other sungrazing comets, Comet Lovejoy (C/2011 W3) was not expected to survive its close encounter with the Sun. But it did. This image from a coronograph onboard the sun-staring SOHO spacecraft identifies the still inbound remnants of the tail, with the brilliant head or coma emerging from the solar glare on December 16. The Sun's position, behind an occulting disk to block the overwhelming glare, is indicated by the white circle. Separated from its tail, Comet Lovejoy's coma is so bright it saturates the camera's pixels creating the horizontal streaks. Based on their orbits, sungrazer comets are thought to belong to the Kreutz family of comets, created by successive break ups from a single large parent comet that passed very near the Sun in the twelfth century. Most have been discovered with SOHO's cameras, but unlike many sungrazers, this one was first spotted by Australian astronomer Terry Lovejoy from an earth-based observatory. Comet Lovejoy is estimated to have come within 120,000 kilometers of the Sun's surface and likely had a large cometary nucleus to have survived its intense perihelion passage. Remarkable videos of the encounter from the Solar Dynamics Observatory can be found here.