NASA Rover Finds That Water Flowed on Mars Surface Long Ago

NASA’s Mars Exploration Rover Opportunity, which landed on Mars nearly eight years ago, has discovered a thin, bright mineral vein along the rim of a huge crater called Endeavour. According to researchers this mineral is almost certainly gypsum that was deposited by liquid water billions of years ago. Analysis of the vein will help improve understanding of the history of wet environments on Mars. The vein examined most closely by Opportunity is about the width of a human thumb (0.4 to 0.8 inch, or 1 to 2 centimeters), 16 to 20 inches (40 to 50 centimeters) long, and protrudes slightly higher than the bedrock on either side of it. Observations   by   the   durable  rover reveal  this vein  and  others like it within an apron surrounding a segment of the rim of  Endeavour Crater. 

None like it were seen in the 20 miles (33 kilometers) of crater pocked plains that Opportunity explored for 90 months before it reached Endeavour, nor in the higher ground of the rim. The vein is informally named Homestake. The Homestake deposit, whether gypsum or another form of calcium sulfate, likely formed from water dissolving calcium out of volcanic rocks. The calcium combined with sulfur that was either leached from the rocks or introduced as volcanic gas, and it was deposited as calcium sulfate into an underground fracture that later became exposed at the surface.
source:www.nasa.gov