A crop of "blueberries' found by Mars' Victoria Crater by a Nasa rover may indicate ground, not surface, water altered the area, US space officials said. Nasa officials said they thought the "blueberries' were formed by iron-rich minerals when groundwater percolated through sediment. The spheres were scattered across the surface almost everywhere the Opportunity rover trekked from its landing site to the crater. The crater's rim was "full of great big, juicy blueberries,' the rover's chief scientist Steven Squyres said.