Ecstatic scientists used the Mars rover’s powerful camera Friday to take the first close-up images ever made of the Martian surface and immediately confronted a new mystery over what they saw. The images that Spirit sent down from its Martian parking spot, a few feet in front of its landing pad, was a flat patch of fine- and coarse-grained sand — much of it stuck together in clumpy patches that scientists conceded they did not yet understand.