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.
25 November 2008
What if you're driving down the street and an object from space shoots across the sky right in front of you? Such was the case last week for many people in south central Canada. Specifically, an extremely bright fireball, presumably a desk-sized meteor from deep space, flashed across the sky just after sunset on 2008 November 20. The bright fireball was recorded on many images and movies, including the spectacular video shown above that was captured by a dashboard camera of a police cruiser in Edmonton, Alberta, Canada. Because at least two streaks appear to be visible, the falling object likely broke up into pieces as it fell deep into Earth's atmosphere. By triangulating fireball images from several simultaneously recorded sources, astronomers hope to find an approximate orbit from whence the object came, as well as the likely place(s) on Earth where large pieces would have impacted, were they to have survived entry. In the best case scenario, pieces would be recovered from a known deep space comet or asteroid, giving humanity an unprecedented look at an ancient object that likely holds clues to the early years of our Earth and the Solar System.