Sol 4166, October 13, 2015. Day by day, Opportunity is surveying the bare outcrops that line the Marathon Valley floor. On Sol 4166, it drove almost 19 meters (62 feet) to the southeast toward the southern wall of the valley. Above is a two-frame Navcam composite showing outcrops varying in tone, suggesting they also vary in composition, or at least degree of alteration, probably by water (click image to enlarge).
Opportunity raw images, its latest mission status, a location map. and atmospheric opacity, known as tau.