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"
PanSTARRS and Planets
18 April 2026
Near the eastern horizon before sunrise, Comet C/2025 R3 PanSTARRS is getting brighter. Readily visible in binoculars and small telescopes, the comet may be just on the verge of naked-eye visibility from dark sky sites. Though it was not quite apparent to the eye, PanSTARRS is still easy to spot in this camera image taken on April 16. In the view from a volcanic peak overlooking France's Reunion Island, planet Earth, the comet shares eastern predawn skies with naked-eye planets Mars and Mercury and fainter Neptune. Saturn is hiding behind the low cloudbank that doesn't quite hide an old crescent Moon. This is a good weekend for northern hemisphere comet watchers to try to catch PanSTARRS an hour or so before sunrise, as the comet grows brighter approaching its perihelion on April 19. On April 26 the comet makes its closest approach to our fair planet but by then will be difficult to see in the solar glare. Good views of this comet PanSTARRS in late April and early May will be from the southern hemisphere.