As Mars rover Curiosity looks to line up its fourth drilling target, it needed to give a rock a bit of a scrub.

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This photo beamed back from Mars on Aug. 17 (sol 722 of the mission) shows the circular scrub marks created by the rover’s robotic arm-mounted Dust Removal Tool — a metal brush used to remove surface dust from rocks in preparation for drilling and sampling. Cleaning a patch around 2.5 inches wide, mission scientists are deciding whether this rock — dubbed “Bonanza King” — should now be drilled into and sampled by Curiosity’s on-board chemistry lab.

As can be seen in the image snapped by Curiosity’s Mastcam, after the ruddy oxidized dust is removed from the rock (to avoid contaminating any drilled samples taken from the pristine rock’s interior), a dark grey surface is exposed. In this particular area, a couple of lighter veins of a mineral (possibly sulfate salts) can be seen intersecting the brushed area.

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In addition to the brush work, Curiosity also zapped Bonanza King with its ChemCam laser to take remote measurements of the minerals on the surface. Five tiny burn marks from the laser analysis is to the left of the brushed area.

Bonanza King is located on a ramp rising from the northeastern end of “Hidden Valley,” which is on the route to Curiosity’s ultimate destination, the slopes of Mount Sharp.

The pale rocks in the foreground of this fisheye image from NASA's Curiosity Mars rover's Hazcam include the "Bonanza King" target under consideration to become the fourth rock drilled by the Mars Science Laboratory mission.NASA/JPL-Caltrech