Free Astronomy Magazine March-April 2021

21 MARCH-APRIL 2021 MARS ROVERS TOP DISCOVERIES BY SPIRIT • 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 environ- ment 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. To- gether, 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. TOP DISCOVERIES BY OPPORTUNITY • 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. • 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 under- ground 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 compelling signs of a watery past on Mars: clay minerals formed in neutral- pH water. Of all the places studied by Opportunity, this environment at Endeavor Crater once had the friendliest conditions for ancient microbial life. T he small spherules on the Martian surface in this close-up image are near Fram Crater, visited by Opportu- nity. The area shown is 1.2 inches (3 centimeters) across. These are exam- ples of the mineral concretions nick- named “blueberries.” Opportunity's investigation of the hematite-rich con- cretions during the rover's three-month prime mission in early 2004 provided evidence of a watery ancient environ- ment. [NASA/JPL-Caltech/Cornell/USGS]