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 Hale-Bopp is That Bright Credit and Copyright:
27 February 1997
What's that fuzzy star? It's not a star, it's Comet Hale-Bopp. Not only has Comet Hale-Bopp become easy to see in the morning sky, it has become hard not to see it. It's that bright. Any morning just before sunrise, look towards the east. Comet Hale-Bopp is one of the brightest objects up. Its dominating presence is shown dramatically by this photo taken just west of Williston, North Carolina, USA. Here Comet Hale-Bopp shines above the telephone poles lining Highway 70. Too tired to get up in the morning to see the comet? Don't worry, in less than a month it will also be visible in the evening sky, just before sunset. And it will have a longer tail. From the Space Shuttle, Dr. Steven Hawley says, "Hale-Bopp looks great."