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.
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Meteors, Comet, and Big Dipper over La Palma
23 April 2019
Meteor showers are caused by streams of solid particles, dust size and larger, moving as a group through space. In most cases, the orbits of these meteor streams can be identified with dust expelled from a comet. When the Earth passes through a stream, the particles leave brilliant trails through the night sky as they disintegrate in Earth's atmosphere. The meteor paths are all parallel to each other, but, like train tracks, the effect of perspective causes them to appear to originate from a radiant point in the distance. The featured image composite was taken during January's Quadrantid meteor shower from La Palma, one of Spain's Canary Islands, off the northwest coast of Africa. The Quadrantids radiant is visible just below the handle of the Big Dipper. A careful eye will also discern the faint green coma of Comet Wirtanen. Tonight is the peak of the modest Lyrid meteor shower, with several meteors per hour visible from dark locations with clear skies.