A Clean Sweep
This image from Spirit's navigation camera atop its mast reveals another interplanetary "first" for the rock abrasion tool. The three dark circular areas on the rock "Humphrey" make up a rock abrasion tool mosaic, created by the tool's stainless steel brushes in about 15 minutes on Spirit's 56th sol on Mars. Even though a triple brushing was never conducted in a testbed, the rock abrasion tool's previous performance on the rock "Adirondack" convinced the science and engineering teams that it was fully capable of such an operation. The optimal situation for the miniature thermal emission spectrometer to analyze the difference between the rock's composition with dust and then without (after brushing) requires an area about three times that of one rock abrasion tool circumference. Scientists want to determine if the spectrometer is "reading" the dust or the harder coating underneath it. This mosaic provided the area that the spectrometer needed to conduct its assessment. The rock abrasion tool's two upper brushed imprints trail off and aren't completely round due to "Humphrey's" intricate slopes, which make it difficult to find a completely flat surface on which to place instruments.

From: NASA/JPL