The "Mark" (full mosaic) - Sol 830

The grinding teeth have worn away on the rock abrasion tool of NASA's MER Spirit (after exposing interiors of five time more rock targets than its design goal of three rocks) but the tool still has useful wire bristles for brushing targets. In this image, a figure-eight-like imprint in the Martian soil marks the spot where Spirit has begun examining subsurface deposits layer by layer. The circular indentations resulted from brushing by the RAT, one of several instruments on the Rover's RA. As an effective brushing tool it is now fulfilling a soil profiling experiment on a target called "Progress". The experiment is a multi-step process of carefully brushing away fine layers of soil and then using the Moessbauer and Alpha particle X-ray Spectrometers, MI, and PanCam to examine the exposed surfaces during the long Martian Winter.
This view is a mosaic of exposures taken by Spirit's MI during the Rover's 830th Sol (such as (May 4, 2006). The total area shown here is about 6 cm (such as 2,4") square.