Carbonate minerals in Martian dust

The surprise was that the carbonates are in the dust, not in surface rocks, as many scientists had predicted.

TES discovered carbonate minerals that formed when water and the CO2 atmosphere react.

Goodbye ocean? Scientists have long searched Mars for carbonate minerals, a common by-product of weathering. But despite ample evidence for lots of water at the surface, massive carbonate deposits – relics of a possible ancient ocean – have proved elusive. Spectral data from the orbiting Thermal Emission Spectrometer (TES) came to the rescue – sort of. TES showed that Martian carbonate minerals do exist, but they are not primarily in the rocks. Instead, carbonate minerals dwell mainly in the dust that’s everywhere on Mars. These carbonates probably did not form in any large bodies of water, but rather as atmospheric moisture combined with airborne dust.