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"
Comet R3 (PanSTARRS) Brightens
12 April 2026
Comet R3 is brightening rapidly -- will it survive? C/2025 R3 (PanSTARRS) has been slowly brightening and extending an ion tail since its discovery last year. This shedding mountain of dirty ice puts on its best sky show this month, though, because it passes its closest to both the Sun (April 19) and the Earth (April 25). The featured image, showing R3 already sporting a tail extending over 10 degrees, was taken two nights ago from Sion, Switzerland with the big mountain Bietschhorn on the left. Comet R3 will be visible during mid-April before sunrise. Although the future brightness of any comet is hard to predict, the brightness of R3 makes it already a good camera comet and it may become visible to the unaided eye in the next week. Comet R3's physical future is also unknown because, like Comet A1 (MAPS) earlier this month, it may disintegrate when it passes its closest to the Sun. Or it may live to leave the Solar System. Growing Gallery: Comet R3 in 2026