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"
IRTF: Scanning the Infrared Skies
4 September 1996
Above, NASA's Infrared Telescope Facility (IRTF) poses in front of a starry background. Located on top of Hawaii's towering volcano Mauna Kea, the IRTF is the premier telescope for observing in near infrared light. This 3-meter telescope was established in 1979 and spends about half its time observing Solar System objects. In 1994, for example, the IRTF recorded pieces of the famous comet Shoemaker-Levy 9 plunge into Jupiter. Last year, the IRTF recorded an outburst of a volcano on Jupiter's moon Io. IRTF's observational successes outside our Solar System include understanding the infrared emission of dust and Pre-Main Sequence stars and even the identification of faint galaxies.