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National Geographic Traveler has scoured the globe for the world's most beautiful, interesting, and off-beat road trips. Dive in to get drive directions, quizzes, photos, and more.
Wednesday, November 11, 2009 |
Photo: Mars, Like Earth, Has Cyclical Ice Ages, Study SaysAccording to the theory, Mars's permanent ice layer (left) recedes when the planet tilts away from the sun (second from left). When Mars tilts toward the sun, the ice layer expands beyond its original boundary (second from right). The impending arrival on Mars of the Phoenix lander, which will dig into Mars's underground (right), will help determine the theory's accuracy. Images courtesy Norbert Schörghofer, University of Hawaii
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ADVERTISEMENTNATIONAL GEOGRAPHIC'S PHOTO OF THE DAY50 Drives of a Lifetime
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