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 vs. The Moon
20 November 2002
Beautiful and bright, the 2002 Leonid meteors battled against glaring moonlight. This winning example, from Tuesday morning skies above Laughlin, Nevada, USA, finds an undaunted Leonid streaking between the familiar constellation of Orion (left) and an overexposed full Moon. As anticipated, the Leonid shower packed a double punch on November 19 with planet Earth plunging through two dense clouds of meteroids, dusty debris left by the passage of comet Tempel-Tuttle. Some European observers reported 10 or so meteors a minute during the first peak near 4:00 Universal Time while North American skygazers witnessed slightly lower rates near the second peak around 10:30 UT. Overall, observed rates were much lower than last year's Leonid meteor storm, but for many the sky was still filled with a rewarding spectacle of bright meteors. And that performance may be a fond farewell for years to come. The annual Leonid meteor shower will not likely approach even these rates again until the end of this century.