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	Frequently Asked Questions Send to a friend  Printable version  En Español Keywords Comets  Chemistry of the Universe  Interstellar Gas and Dust  Water and Water Ice  Resources FAQs about The Solar System Solar System Guide Astronomy Gift Shop 2009 Sky Almanac McDonald Observatory logo cap What are comets made of?  Comets are amalgamations of varying quantities of water and carbon dioxide ices, rock, dust, and various trace molecules -- including the sodium seen flaring out of Hale-Bopp in 1997. These "dirty snowballs" are interlopers from the farthest reaches of our solar system, and are believed to represent the last vestiges of the vast interstellar gas cloud from which our solar system formed. Other FAQs Select FAQ category Earth, Moon, and the Sun The Solar System Space Probes and Human Exploration Stars and Nebulae Astronomers and Observatories Galaxies and Cosmology Stargazing and Star Lore » FAQs about StarDate Online The Solar System Links Center for Mars Exploration Solar System Exploration NASA's Mars Exploration Program Cassini Mission to Saturn Voyager Mission to the Outer Planets ESA Mars Express Messenger Mission to Mercury New Horizons to Pluto
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