Currently, Mars has a thin atmosphere dominated by carbon dioxide, with pressures at most of the planet's surface so low that liquid water will immediately boil. But a variety of features we've discovered argue that the planet has once supported copious amounts of water, indicating that the planet's atmosphere must have differed considerably in the past. Using radar data from the Mars Reconnaissance Orbiter, scientists have now found a potential resting place for some material that was once in the Martian atmosphere: a huge deposit at the south pole that holds nearly as much CO2 as the planet's current atmosphere.
Mars' south pole has extensive ice deposits, but most of that material is thought to be water, with only a thin coating of carbon dioxide on top. However, the MRO's radar instrument identified several reflection-free zones, where most of the radar signal went entirely through the icy material to the planet's surface itself. Based on the authors' calculations, this can't be water ice, but it does have very similar reflective properties to dry ice, or frozen carbon dioxide. The area also has features that indicate that some of the dry ice has sublimated to a gaseous form, resulting in areas where the surface has collapsed.
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Robin Tunney Kate Groombridge Dania Ramirez Lucy Liu LeAnn Rimes
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