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What is in a comet's tail?

Comets actually have two tails: the dust tail and the gas or ion tail. The names should tell you what is in them. Both tails always point away from the Sun, independent of the comet's motion. The dust tail is formed of solid particles escaping from the cometary nucleus into their own solar orbits and may be slightly curved. It shines with reflected sunlight. The ion tail is pushed straight back from the coma by the solar wind and solar radiation pressure and glows from the fluorescence of the ionized molecules CO+, N2+, OH+, CO2+, and CH+. Some comets are also surrounded by huge (bigger than the Sun) clouds of hydrogen gas.


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