NASA boffins believe they have found evidence suggesting that Mars may not have been barren and lifeless for its entire history.

"We have found evidence that not all of Mars experienced an intense, acidic weathering environment 3.5 billion years ago, as has been proposed," said Bethany Ehlmann of Brown University. "We've found at least one region that was potentially more hospitable to life."

Ehlmann is one of the scientists analysing data from NASA's Mars Reconnaissance Orbiter (MRO) above the Red Planet. In this case, the information comes from an instrument on the orbiter called CRISM, the Compact Reconnaissance Imaging Spectrometer for Mars.

Some scientists had theorised that Mars has had a highly acidic environment for the last three billion years and more, meaning that life would have had a hard time coming into being. But now Ehlmann and her colleagues have used CRISM pictures to detect carbonate minerals in the neighbourhood of the Isidis crater.

If Mars had been acidic and lifeless for billions of years, as had been thought, these carbonates should have dissolved long ago. As the NASA boffins see it, their presence now means that there must have been watery environments present in the past, which would have been much more likely to sustain life. If there was any.

Truly massive amounts of carbonate would indicate that Mars once had a much thicker atmosphere, according to the scientists, but they don't think their finds are in that league.

"The carbonates that CRISM has observed are regional rather than global in nature," says Ehlmann.

"We have not found the types of carbonate deposits which might have trapped an ancient atmosphere."

According to NASA, the newly-mapped carbonate deposits could indicate places where future landers and rovers might profitably be sent to seek evidence of past life on Mars. ®