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Color image of comet against a background of stars.
This image of Comet C/2001 Q4 (NEAT) was taken at Kitt Peak National Observatory near Tucson, Ariz. in 2004.

Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the Sun for millions of kilometers.

Featured Mission: Rosetta
Europe's Rosetta mission is on a 10-year mission to explore comet 67P/Churyumov-Gerasimenko. The spacecraft will orbit the comet and study it as it approaches the Sun and deploy a lander to make the first landing on a comet.

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Last Updated: 8 Oct 2010