NASA's Mars Exploration Rover, Opportunity, recently began its 10th year on the surface of the red planet. The robotic geologist is exploring a hill on the western limb of the 14-mile-wide Endeavour crater.
Opportunity landed on Mars on Jan. 25, 2004, three weeks after its rover twin, Spirit. The robotic geologist almost immediately found evidence that water once flowed on the Martian surface in the backyard-size Eagle Crater. The rover met all its goals within the originally planned three-month mission. During the next four years, Opportunity successively explored larger and deeper craters, adding evidence about the planet's ancient wet environment.
In 2008, Opportunity's science team chose to send the rover toward an area of Endeavour crater's rim where the orbiting Mars Reconnaissance spacecraft detected traces of clay minerals. Clay minerals form under wet, non-acidic conditions that can be favorable for life. After a three-year journey across the treacherous Martian terrain, the rover reached the "Cape York" segment of Endeavour's rim in August 2011. This location has provided the rover access to geological deposits from an earlier period of Martian history than anything it has previously examined.
The rocks that Opportunity explored in the Cape York region appeared different from anything it had encountered in the past. They were a soft fine-grained, light-colored rock. However, the rover's analysis of the rocks revealed that they contained mostly volcanic basalt as well as the same mix of elements in the typical rocks that Opportunity had discovered before: sodium, potassium, chloride and magnesium.
Opportunity also discovered tiny spheres in an outcrop of rock it was examining. They were similar to the iron-rich spheres nicknamed "blueberries" the rover discovered years ago at its original landing site. These spheres, however, contain very little iron.
Mission scientists hope that Opportunity will solve these puzzles in the months ahead, in anticipation of discovering what early Mars was like.