Red Planet serves up blueberries

Martian pebbles point to water flow

By Lucy Sherriff, 16th June 2004

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Martian blueberries, marble-shaped pebbles known as haematite concretions, could be another indication that water once flowed on the surface of the red planet, according to researchers in the US.

In a study published tomorrow (17 June), geologists from the University of Utah describe how blueberries are formed in groundwater on Earth; they had expected the rocks would be present on the Martian surface.

Marjorie Chan, chair and professor of geology and geophysics at the university, said that she and her team had come up with a 'recipe' for the blueberries based on their research into haematite-rich areas in Utah, where the concretions probably formed about 25 million years ago. Based on this research, they theorised that there might be similar formations on Mars.

Haematite is iron oxide - a grey form of the mineral that has a larger crystalline structure than the more familiar red stuff, or rust. The concretions form when significant volumes of groundwater flowed through permeable rock, and chemical reactions trigger minerals to precipitate and start forming a layered, spherical ball. They all that is left once the soft sandstone is washed away, and are known as Moqui Marbles.

They get their name from an Hopi Indian legend that 'moqui,' or spirits of their ancestors, played marbles with the blueberries in the American Southwest.

The round rocks were spotted on Mars five days after Opportunity, one of the two Mars rovers, landed. On Earth the marbles vary in size from less than one 25th of an inch to over eight inches in diameter, but the Mars blueberries appear to be much more uniform.

Earth's marbles are composed of an aggregate of haematite and sandstone, with the iron oxide accounting for up to one third of the content, Mars blueberries are likely to be pure haematite. This is because Martian ground water was probably acidic.

The researchers say that aerial photographs of the marble covered areas of Utah closely resemble images beamed back from Martian satellites. Similar features - such as large landforms shaped like knobs, pipes and buttes, and bleached-looking sediment beds - show up in both sets of images. This suggests they were formed by similar processes. ®