The enigmatic ‘Meridiani Planum’ deposits on Mars ? found by the Opportunity rover ? could be remnants of a massive ancient ice-field, according to a study online in Nature Geoscience. Small pockets within the ice, where a thin film of water reacted with atmospheric dust, could have sustained an acidic environment capable of producing the unique chemical composition found in these deposits.

Paul Niles and Joseph Michalski analysed the chemistry, sedimentology and geology of the Meridiani Planum deposits using information obtained by the Mars rover Opportunity. They suggest that sulphate formation and chemical weathering occurring within an ancient ice-field ?? similar in size to the present polar ice caps on Mars ? is the best explanation for the observations. Once the ice sublimed away in a warmer climate, the remaining sediments kept their chemical signature.

The region of Meridiani Planum is near the equator and at present cannot sustain large ice-fields. The authors propose that the ice could have formed in ancient times, when the poles were in a different place or when the martian axis of rotation was at a different angle to its present-day orbit around the Sun.