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"
Full Moon Perseids
18 August 2022
The annual Perseid meteor shower was near its peak on August 13. As planet Earth crossed through streams of debris left by periodic Comet Swift-Tuttle meteors rained in northern summer night skies. But even that night's nearly Full Moon shining near the top of this composited view couldn't hide all of the popular shower's meteor streaks. The image captures some of the brightest perseid meteors in many short exposures recorded over more than two hours before the dawn. It places the shower's radiant in the heroic constellation of Perseus just behind a well-lit medieval tower in the village of Sant Llorenc de la Muga, Girona, Spain. Observed in medieval times, the Perseid meteor shower is also known in Catholic tradition as the Tears of St. Lawrence, and festivities are celebrated close to the annual peak of the meteor shower. Joining the Full Moon opposite the Sun, bright planet Saturn also shines in the frame at the upper right.