NASA's rover Spirit has found a mineral that is the surest hint yet of water on Mars, scientists said on Monday.
Spirit discovered a so-called water-signature mineral called goethite in a section dubbed 'Columbia Hills', NASA scientists said.
"Goethite, like the jarosite that Opportunity found on the other side of Mars, is strong evidence for water activity," said Goestar Klingelhoefer of the University of Mainz, Germany. He is the lead scientist for the iron-mineral analyzer on each rover, the Moessbauer spectrometer.
NASA said Goethite forms only where there is water, which can be in liquid, ice or gaseous form.
Hematite, a mineral that had previously been found in Columbia Hills bedrock, usually, but not always, forms in the presence of water.
Opportunity has completed six months of inspecting the inside of 'Endurance Crater' and is ready to resume exploration of the broad plains of the Meridiani region.
The robots completed their mission in April, which was to find evidence of water on Mars.