The rock abrasion tool used by the Spirit and Opportunity rovers was the Rock Abrasion Tool, abbreviated RAT. It was designed to grind away a thin patch of a Martian rock so the rovers’ instruments could examine a clean, freshly exposed surface.
Built by Honeybee Robotics, the RAT used a diamond-dusted wheel spinning at about 3,000 revolutions per minute. It could create a circular hole roughly 45 millimeters wide and several millimeters deep, then brush away the resulting dust. This gave Spirit and Opportunity access to a rock’s interior rather than only its weathered exterior.
Spirit first used the RAT on the rock Adirondack on February 6, 2004. The tool was not a conventional drill: its main job was abrasion and surface preparation. The rovers’ cameras and spectrometers could then study the exposed material for clues about Martian geology and past water activity.
A common mix-up is confusing the RAT with the rovers’ other instruments. RAT is the official acronym for Rock Abrasion Tool, not a nickname for the rover or a general-purpose drill.