A Martian rock analysed by the NASA rover Opportunity contains clays formed in non-acidic water, an environment potentially suitable for the chemistry of ancient life to brew.
Opportunity landed on Mars in January 2004 for what was expected to be a 90-day mission to look for signs there was once water.
Opportunity and Spirit, another rover which succumbed to the Martian environment three years ago, both found rocks altered by highly acidic water.
