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"
Lyrid Meteors from the Constellation Lyra
12 May 2020
Where are all of these meteors coming from? In terms of direction on the sky, the pointed answer is the constellation of Small Harp (Lyra). That is why the famous meteor shower that peaks every April is known as the Lyrids -- the meteors all appear to came from a radiant toward Lyra. In terms of parent body, though, the sand-sized debris that makes up the Lyrid meteors come from Comet Thatcher. The comet follows a well-defined orbit around our Sun, and the part of the orbit that approaches Earth is superposed in front of Lyra. Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Lyra. Featured here, a composite image containing over 33 meteors (can you find them all?) from last month's Lyrid meteor shower shows several bright meteors that streaked over a shore of Seč Lake in the Czech Republic. Also visible are the bright stars Vega and Altair, the planet Jupiter, and the central band of our Milky Way Galaxy. Notable APOD Submissions: Lyrid Meteor Shower 2020