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"
Leonids Over Joshua Tree National Park
5 November 2002
This year's Leonid Meteor Shower is predicted to have two peaks, like last year's. The first peak should come at about 04:00 hours Universal Time (UT) on November 19 and be primarily visible from Western Europe before sunrise. The second peak is predicted to occur at about 10:30 UT and be primarily visible from North America before local sunrise. During these times, the Leonid Meteor Shower might well develop into a true meteor storm, with rates possibly exceeding those measured during last year's storm. The meteors in these two peaks come from sand-sized particles ejected from Comet Tempel-Tuttle during trips to the inner Solar System in 1767 and 1866, respectively. If you're stuck without a view you can still catch the shower by looking for streaks caught by the web cameras of the Night Sky Live Project. Pictured above are several meteors from the 2001 Leonids streaking over Joshua Tree National Park in California, USA.