Comet

A comet is a small body in the solar system that orbits the sun and (at least occasionally)

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exhibits a coma (or atmosphere) and/or a tail -- both due primarily to the effects of solar radiation

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upon the comet's nucleus, which itself is a minor planet composed of rock, dust, and ices.

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Due to their origins in the outer solar system and their propensity to be highly affected by

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relatively close approaches to the major planets, comets' orbits are constantly evolving. Some

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are moved into sungrazing orbits that destroy the comets when they near the sun, while others are thrown out of the solar system forever. But a bright comet is one of the surest celestial events to capture the

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interest of the general public.

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Comets are believed to originate in a cloud (the Oort cloud) at large distances from the sun consisting of debris left over from the condensation of the solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state. Asteroids originate via a different process, but very old comets which have lost all their volatile materials may come to resemble asteroids.

Related Topics:
Oort cloud - Condensation - Solar nebula - Cool - Water - Solid - Gas - State - Asteroid - Volatile

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