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.
3 October 2016
What would it be like to fly around a comet nucleus? To find out, just wait for your WebGL-compatible browser to load a detailed digital model of Comet 67P and then -- go exploring! With a standard mouse, the left button allows you to rotate the comet, the right button allows you to move the comet around, and the scroll wheel allows you to zoom in. ESA's robotic Rosetta spacecraft orbited Comet C67/P Churyumov-Gerasimenko from mid-2014 until last Friday, when, after a remarkable and successful mission, it was intentionally set down on the surface and powered down. Among many notable scientific achievements, Rosetta allowed humanity to better understand where comet jets form on comets as they near the Sun. Transparent Science: Browse 1,350+ codes in the Astrophysics Source Code Library