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Asteroids are rocky worlds revolving around the sun that are to small to be called planets.
Despite their size, asteroids can be dangerous.
When a asteroid or a part of it crashes down to earth, it's called a meteorite.
Asteroids can reach as large as Ceres, which is 940km across.
meteors are bright streaks in the sky (shooting star)
Though meteorites just appear to be boring rocks, they're extremely important in that we can analyze them carefully in our labs.
That is called a meteorite, and a large one sometimes leaves a hole in the ground called a crater.
A rock that has not yet hit the atmosphere is called a "meteoroid"
A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail.
Comets are icy bodies in space that release gas or dust. They are often compared to dirty snowballs, though recent research has led some scientists to call them snowy dirtballs. Comets contain dust, ice, carbon dioxide, ammonia, methane and more.
After 500 or so passes near the Sun off most of a comet's ice and gas is lost leaving a rocky object very much like an asteroid in appearance. (Perhaps half of the near-Earth asteroids may be "dead" comets.) A comet whose orbit takes it near the Sun is also likely to either impact one of the planets or the Sun or to be ejected out of the solar system by a close encounter (esp. with Jupiter).