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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APODs including "Comet"
The Red Planet Mars
30 July 2020
Mars looks pretty sharp in this backyard telescope image captured on July 23 from Hoegaarden, Belgium, planet Earth. The Red Planet's bright south polar cap is bathed in sunlight at the top of the inverted view, while the dark feature known as Syrtis Major extends toward the right (eastern) edge. Rising around midnight for now, the Red Planet is months away from its own opposition in early October. Telescopic views will improve even more as Earth, in its faster orbit, catches up to Mars, the ruddy disk growing larger and brighter still. The martian Jezero Crater is within the Syrtis Major region. That's the landing site for NASA's 2020 Mars Rover Perseverance, scheduled for launch today. Comet NEOWISE images from planet Earth: July 29, 28, 27, 26, 25, 24