This image taken by the Mars Exploration Rover Opportunity shows a target dubbed "Campbell" on a rock called "MacKenzie" in "Endurance Crater." Opportunity dug a hole into the target with its rock abrasion tool, then captured this picture with its microscopic imager on sol 184 (July 30, 2004). The image mosaic is about 6 centimeters (2.4 inches) across.
NASA/JPL/Cornell/USGS
<a rel="nofollow" class="external free" href="http://photojournal.jpl.nasa.gov/catalog/PIA06787">http://photojournal.jpl.nasa.gov/catalog/PIA06787</a>