Boulders on Mars
This image was taken by the Mars rover Spirit as it explored the surface of Mars. It shows a series of dark boulders with an unusual texture. The largest boulder in the image is about 16 inches (40 centimeters) tall and is about 16 feet (5 meters) from the rover. These boulders are believed to be volcanic in origin and are covered with small holes known as vesicles.
NASA / JPL-Caltech / Cornell / NMMNH