Long before spacecraft reached Mars, astronomers were debating about the white ice masses that cap the Martian poles. Were the permanent caps made of water, as on earth, or of frozen carbon dioxide? Last week scientists learned the answer when data radioed back by the Viking 2 orbiter erased any remaining doubt: The summer ice cap of Mars' North Pole is composed of frozen water. The discovery confirms that Mars has far more water than had previously been believed, and suggests that even more lies in a shell of permafrost below the planet's rocky surface. In fact, scientists said, the polar...
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