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"
Fireworks and Shooting Stars
9 August 2002
erimenting with a new telescope and camera, photographer Jim Steele captured this surreal but festive image of fireworks in the night sky above Ashland, Oregon. The date was July 4th and the fiery streaks were part of the traditional annual celebration of independence day in the United States. Fiery streaks from another annual event will revisit dark skies this weekend, as shooting stars arc through the night during the much anticipated Perseid Meteor Shower. Perseid meteors are actually bits of dust from the periodic Comet Swift-Tuttle and once each year planet Earth orbits through Swift-Tuttle's cometary dust stream. As the comet dust enters Earth's atmosphere traveling at tens of kilometers per second, the particles are vaporized leaving bright and sometimes colorful trails. While Perseid meteors can be viewed over the next few nights, this year's shower is expected to peak on August 12 and 13 with a rate of dozens or more meteors per hour visible in moonless early morning skies.