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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