The extremely successful rover Opportunity has found a small bright strip of material on the surface of Mars that scientists believe could be calcium sulphate or gypsum. If confirmed it will provide strong evidence that billions of years ago water once flowed on and through cracks in the Martian landscape.

Scientist's presented the results on the 7th December 2011 at the American Geophysical Union's conference in San Francisco. The exposed sliver, named "Homestake" by the science team, is small at only about 40 to 50 centimetres (16 to 20 inches) in length and 1 to 2 centimetres (0.4 to 0.8 inches) wide but is a significant find.

Lead scientist Steve Squyres the Goldwin Smith Professor of Astronomy at Cornell University said, "To me, this is the single most powerful piece of evidence for liquid water at Mars that has been discovered by the Opportunity rover. We have found sulphates before. Those sulphates were formed somewhere - we don't know where. They've been moved around by the wind, they've been mixed in with other materials - it's a big, jumbled-up, fascinating mess."

He added, "This stuff formed right here. There was a fracture in the rock, water flowed through it, gypsum was precipitated from the water. End of story. There's no ambiguity."

Opportunity has been on Mars for almost eight years, covered 34 kilometres and is currently exploring an area located along the west rim of the large Endeavour Crater. The deposits were first identified photographically on the 7th November and then analysed by the Alpha Particle X-ray Spectrometer on the rover's arm, which indicated it was likely made of gypsum.