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 and Lightning Beyond Bighorn Mountains
27 July 2020
Normally, Steamboat Point looks cool -- but not this cool. Every day, the iconic peak of the Bighorn Mountains is an interesting sight, in particular from US Highway 14 in Wyoming. On some rare days, the rocky vertical ridges look even more incredible when seen in front of a distant lightning storm. Earlier this month, though, something even more unusual happened -- the naked-eye Comet NEOWISE rose above it in the middle of the night. Just as a distant lightning storm was occurring in the background. Recognizing a rare opportunity, a determined astrophotographer spent a sleepless night capturing over 1400 images of this unusual triple conjunction. The featured image is among the best of them, with the foreground lit by the Moon off to the right. Comet C/2020 F3 (NEOWISE) is now headed back to the outer Solar System, destined to return only in about 6700 years. Comet NEOWISE Images: July 26 || 25 || 24 || 23 || 22 || 21 || 20 || 19 || 18 || 17 || 16 || 15 || 14 || 13 || 12 || 11 || 10 & earlier ||