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asteroid
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a stony or metallic object orbiting the Sun that is smaller than a planet but that shows no evidence of an atmosphere or of other types of activity associated with comets
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asteroid belt
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the region of the solar system between the orbits of Mars and Jupiter in which most asteroids are located; the main belt, where the orbits are generally the most stable, extends from 2.2 to 3.3 AU from the Sun
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comet
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a small body of icy and dusty matter that revolves about the Sun; when a comet comes near the Sun, some of its material vaporizes, forming a large head of tenuous gas and often a tail
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Kuiper belt
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a region of space beyond Neptune that is dynamically stable (like the asteroid belt); the source region for most short-period comets
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near-Earth asteroid (NEA)
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an Earth-approaching asteroid, one whose orbit could bring it on a collision course with our planet
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near-Earth object (NEO)
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a comet or asteroid whose path intersects the orbit of Earth
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nucleus (of a comet)
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the solid chunk of ice and dust in the head of a comet
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Oort cloud
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the large spherical region around the Sun from which most “new” comets come; a reservoir of objects with aphelia at about 50,000 AU
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tail
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(of a comet) a tail consisting of two parts: the dust tail is made of dust loosened by the sublimation of ice in a comet that is then pushed by photons from the Sun into a curved stream; the ion tail is a stream of ionized particles evaporated from a comet and then swept away from the Sun by the solar wind