Stephen site before and after ChemCam zapping, sols 610 and 627
The ChemCam instrument on Curiosity shoots a laser at a target to vaporize some of it, and "reads" the elemental makeup of the target from the wavelengths of light visible in the plasma. The vaporization causes an outward blast of air, which can very effectively dust off a Martian rock. The inset image was taken with Mastcam on sol 610 and shows the Windjana drill site and Stephen ChemCam target before any activity was performed there. The main image was taken with MAHLI on sol 627 and shows Stephen's surface blasted mostly clean except for the visible ChemCam shot points.