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"
Help Search for Interstellar Dust
25 October 2006
What caused that hole? The hole in question appears as a small dark circle on the far right. If the above image of aerogel seems dull and uninteresting, then welcome to one aspect of real world science. The interesting part is that something created that dark hole, and it might well be one of the first pieces of matter ever captured from outside our Solar System. Whatever created that hole was captured by the aerogel of the robotic Stardust spacecraft that flew across our Solar System for years and then returned a capsule to Earth. Scientists are now poring over the aerogel, looking to see what particles have become trapped. Many particles are surely from local Comet Wild 2, which Stardust flew past in 2004. Just a few particles, though, perhaps 10 or less, are expected to be from outside our Solar System. It is so difficult to find them that the Stardust team has created a downloadable interactive microscope program to allow anyone with a standard computer to help inspect aerogel slices and look for interstellar dust tracks. Good candidate tracks will later be inspected in great detail by members of the Stardust team.