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"
Leonids Over Indian Cove
18 November 2003
One year ago today an impressive meteor shower graced the skies of Earth. Pictured above from last year, at least six bright meteors are visible in only part of the sky above Indian Cove campground in California, USA, during a four-minute exposure. The 2002 Leonids packed a double punch with planet Earth plunging through two dense clouds of meteroids, dusty debris left by the passage of Comet Tempel-Tuttle. This year, unfortunately, the main peak of the Leonids Meteor Shower is not expected to be so impressive, with the Earth passing though parts of meteoroid clouds predicted to be much less dense. The main peak of the 2003 Leonids is predicted for tomorrow where some locations might see a bright meteor every minute.