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"
Late Night Vallentuna
15 August 2024
Bright Mars and even brighter Jupiter are in close conjunction just above the pine trees in this post-midnight skyscape from Vallentuna, Sweden. Taken on August 12 during a geomagnetic storm, the snapshot records the glow of aurora borealis or northern lights, beaming from the left side of the frame. Of course on that date Perseid meteors rained through planet Earth's skies, grains of dust from the shower's parent, periodic comet Swift-Tuttle. The meteor streak at the upper right is a Perseid plowing through the atmosphere at about 60 kilometers per second. Also well-known in Earth's night sky, the bright Pleiades star cluster shines below the Perseid meteor streak. In Greek myth, the Pleiades were seven daughters of the astronomical titan Atlas and sea-nymph Pleione. The Pleiades and their parents' names are given to the cluster's nine brightest stars. Gallery: Perseid Meteor Shower 2024 and Aurorae