The grey mineral on Mars that points to a watery world may be a mirage, say researchers. Grey hematite, the main reason the rover Opportunity was sent to Meridiani Planum on the Red Planet, may in fact be another form of hematite, scientists say, and therefore not such a strong clue to water after all. The debate hinges on how scientists have interpreted data from Opportunity's spectrometer, a device that analyses the rainbows or spectra of light reflected from the mineral's surface. U.S. researcher Dr Laurel Kirkland of the Lunar and Planetary Institute in Houston and team published their work...