PhysOrg looks at the sunny side of the Mars Rover Spirit getting stuck – in exactly the right place to make some major discoveries:
“Spirit had to get stuck to make its next discovery,” says [Ray Arvidson of the Washington University in St. Louis].
As the rover tried to break free, its wheels began to churn up the soil, uncovering sulfates underneath.
“Sulfates are minerals just beneath the surface that shout to us that they were formed in steam vents, since steam has sulfur in it. Steam is associated with hydrothermal activity – evidence of water-charged explosive volcanism. Such areas could have once supported life.”
“And most amazingly, the boundary between the sulfate-rich soil and the soil with just the generic concentration of sulfates runs right down the middle of the stranded rover. Spirit is lodged on the edge of a crater — sitting astride the boundary!”
“Also, the robot found that the top of the sulfate material is crusty. Ancient sulfates probably formed this crust as they were processed by variations in climate associated with changes in Mars’ orbit over millions of years.”
Here’s what the scientists think: When a Martian pole faces the sun in Martian summer, it gets warmer at that pole and the water ice shifts to the equator. It even snows there! Warm dark soil under the snow causes the bottom layer of snow to melt. The water trickles into the sulfates, dissolving the water-soluble iron sulfates and forming a crust with the calcium sulfates remaining.
It’s almost like they planned it.