The NASA rover Curiosity's measurements of the Martian air found it's mostly made of carbon dioxide with traces of other gases, according to two studies appearing in the Friday issue of the journal Science. (NASA / July 19, 2013)

NASA’s Curiosity rover has breathed in Martian air and sniffed out good news and bad news for alien life: The Red Planet’s atmosphere was likely several times thicker early in its history – but it’s probably been thin for billions of years, according to scientists on the Mars Science Laboratory mission.

Given Mars' current lack of hospitality, two papers published in the journal Science hint that the hunt for critters on Mars would have a better chance by looking for truly ancient signs of life rather than trying to find current – or even recent – biological activity.

"In current Mars, life has a lot to worry about," said Paul Mahaffy, lead scientist for the Sample Analysis at Mars suite that did the scientific heavy lifting for this work. "Not only is there a lot of ultraviolet radiation hitting the surface, there are these big thermal gradients between day and night [and] there’s very little water."

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-- Amina Khan, Los Angeles Times