Landing in a crater, Opportunity scored a "hole in one" by finding the mineral hematite, which typically forms in water. Water is key to life as we know it. Yet, acidic water soaked this area in Mars' ancient past, making conditions harder for life to thrive.
At a place called Comanche, Spirit found rocks ten times richer in key chemicals (magnesium and iron carbonates) than any other Martian rocks studied before. These rocks formed when Mars was warm and wet (had a thicker carbon-dioxide atmosphere and near-neutral-pH water). This warmer, watery environment could have supported life much better than the harshly acidic conditions the rover found elsewhere.
While dragging a wheel, Spirit churned up soil and found 90 percent pure silica at "Home Plate." On Earth, this kind of silica usually exists in hot springs or hot steam vents, where life as we know it often finds a hot, happy home. Perhaps ancient microbes on Mars did as well.
Spirit discovered that an ancient volcano erupted at "Home Plate," the rover's final resting place. Together, powerful steam eruptions from heated underground water produced some explosive volcanism. While violent, these extreme conditions can support microbial life on Earth. Once upon a time, maybe they did on Mars…
Score! Near the rim of Endeavor Crater, Opportunity found bright-colored veins of gypsum in the rocks. These rocks likely formed when water flowed through underground fractures in the rocks, leaving calcium behind. A slam-dunk sign that Mars was once more hospitable to life than it is today!
Opportunity found the most compelling signs of a watery past on Mars: clay minerals formed in neutral-pH water. Of all the places studied by the twin rovers, this environment at Endeavor Crater once had the friendliest conditions for ancient microbial life.
Opportunity is a crater explorer. The rover has visited and studied the geology well over 100 impact craters of all sizes in its 14 years on Mars. It has learned about the lives of craters: how they form and erode through time.
Cleaned Solar Arrays Gleam in Mars Rover's New Selfie
Long-Term Study of the Martian Environment
Opportunity has been continually monitoring Mars for more than 14 years! It has collected a wealth of scientific riches on the Martian environment by studying Mars' clouds and dust, the opacity (tau) of its atmosphere, and how it affects the solar panels (solar energy). This type of information will help inform future Mars missions.