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A Flip-Flopping Climate Could Explain Mars's Watery Past


In the 1970s, images of Mars taken by the Mariner and Viking spacecraft revealed enormous channels and valley networks—both of which are reminiscent of catastrophic floods and river drainage systems on Earth. The fluvial features were the first sign that 3.8 billion years ago, the planet was once a lush oasis, awash with oceans, lakes, and rivers.

But how was early Mars so wet? That question sparked a 40-year-long debate that has divided planetary astronomers into two camps: those that think Mars must have once contained a thicker and warmer atmosphere—which made the Red Planet hospitable to liquid water and potentially the evolution of life—and those that think Mars was mostly cold save for short bursts of warmth.

A new hypothesis might reconcile both camps, some scientists say. In a studyaccepted for publication in Earth and Planetary Science Letters, Natasha Batalha, a graduate student from Pennsylvania State University in University Park, and her colleagues suggest that Mars flip-flopped between a deep-freeze climate and a habitable one.  More


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