23 September 2004

Acid drops in the martian ocean

There is evidence from surface features on Mars that an ocean once existed there, but the 'missing carbonates' complicate the picture. It was thought that an ocean would create large carbonate deposits due to sedimentation of CO₂ from the atmosphere. So it was a surprise when the Mars Global Surveyor found no surface carbonates. Last year, data from Global Surveyor's thermal emission spectrometer did reveal carbonate in martian dust, but trace amounts only. This could mean that no water masses were stable long enough to catalyse carbonate formation. But an alternative explanation is presented this week. An atmosphere with partial CO₂ pressure of 1 bar, and a supply of iron, could produce acidic oceans unfavourable to carbonate formation. MER Opportunity recently found minerals rich in ferric iron and sulphate, consistent with this scenario.

Inhibition of carbonate synthesis in acidic oceans on early Mars
ALBERTO G. FAIR�N, DAVID FERN�NDEZ-REMOLAR, JAMES M. DOHM, VICTOR R. BAKER & RICARDO AMILS
Nature 431, 423–426 (2004); doi:10.1038/nature02911
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23 September 2004 table of contents