Wet Down: Warm, Wet Conditions on Ancient Mars May Have Been Confined to Subsurface

When Mars orbiters decades ago spotted valleys and other fluvial landforms on the surface of the Red Planet, a tantalizing idea came to the fore. Perhaps, planetary scientists ventured, ancient Mars was blanketed by a thick atmosphere that kept the planet much warmer and wetter than it is now, with flowing water, lakes and maybe even an ocean covering at least part of its surface. And if Mars had water some three billion to four billion years ago, they wondered, why not life?

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Wet Down: Warm, Wet Conditions on Ancient Mars May Have Been Confined to Subsurface