This animation shows the Mars Exploration Rover Opportunity digging a trench near the trough dubbed "Anatolia" with its left front wheel on sol 73. It was taken by the rover's hazard-avoidance camera.
The trench was dug so that Opportunity would be able to place its Mössbauer spectrometer on a soil target (the pile of material on the right side of the trench) during a four-day flight software update. The rover's alpha particle X-ray spectrometer was pointed at the sky at this time taking calibration measurements.
Spirit performed a similar operation during its flight software update, but its Mössbauer was placed on a rock dubbed "Route 66." Since there are no rocks at Opportunity's current location, rover team members chose a patch of soil.
The trench itself is 95 centimeters (38 inches) long by 16 centimeters (6 inches) wide by 11 centimeters (4 inches) deep. It is the deepest hole dug by either Spirit or Opportunity to date.
Image credit: NASA/JPL