mount of dust and other solids. The coma is a dense cloud of water, carbon dioxide, and other neutral gases which turn directly from solid to gas when leaving the nucleus. This happens because as a comet approaches the sun, the comet comes to a region of space where it is warm enough that the frozen solid materials inside the nucleus start to gain temperature. The black crust on the surface of the nucleus helps the comet to absorb heat, which causes some of the ices under the crust to turn to a gas. Press
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