The Mars Exploration Rover Spirit acquired this navigation camera image on the 72nd martian day, or sol, of its mission (March 15, 2004), after digging its wheel into the drift dubbed "Serpent." Creating the commands that would generate this "scar" was not an easy task for rover controllers. Essentially, they had to choreograph an intricate dance for Spirit, maneuvering it up the side of the dune, shimmying its left front wheel a number of times to create the scuff, and then reversing to attain proper positioning for miniature thermal emission spectrometer observations. Before the task was finished, Spirit moved forward to put the scuff within proper reach of the rover's arm. This scar allows the rover's instruments to see below the drift surface, to determine the composition of the materials. Initial results indicate that the drift material is similar to the basaltic sands that have been seen throughout Spirit's journey to the large crater dubbed "Bonneville." The material does not seem to be the same as that inside the crater. Scientists are now looking to answer two questions: Why is the dark sand in the crater not the same as the dark sand in the drift? And why are there two different dark soil-type deposits in such a small place? 3/17/2004 3/17/2004 3/15/2004 3/15/2004 3/14/2004 3/14/2004 3/12/2004 3/11/2004 3/9/2004 3/9/2004 2/28/2004 2/27/2004 "Humphrey" at Gusev Crater, Mars, the Mars Exploration Rover Spirit's landing site. Spirit examined the lumpy rock with its suite of scientific instruments both before and after it drilled a hole into the rock surface on the 60th martian day, or sol, of its mission. "Humphrey" was one of several stops on the rover's way to the large crater dubbed "Bonneville." 2/27/2004 2/27/2004 The large, shadowed rock in the foreground is nicknamed "Sandia" for a mountain range in New Mexico. An imposing rock, "Sandia" is about 33 centimeters high and about 1.7 meters long. When lightened, this image reveals much about the pictured rocks, which the science team believes are ejected material, or ejecta, from the nearby crater called "Bonneville." Scientists believe "Sandia" is a basaltic rock that landed on its side after being ejected from the crater. The vertical lines on the side of the rock facing the camera are known by geologists as "flow banding" and typically run horizontally, indicating that "Sandia" is on its side. What look like small holes on the two visible sides of the rock are called vesicles; they were probably once gas bubbles within the lava. Many smaller rocks can be seen in the background of the image. Some rocks are completely exposed, while others are only peeking out of the surface. Scientists believe that two processes might be at work here: accretion, which occurs when winds deposit material that slowly buries many of the rocks; and deflation, which occurs when surface material is removed by wind, exposing more and more of the rocks. 2/26/2004 2/18/2004 2/18/2004