Astronomy Picture of the Day . A Wheel on Mars . ... Credit Copyright: NASA / JPL-Caltech/Mars Science Laboratory Explanation: A wheel attached to NASA's Curiosity rover is firmly on the martian surface in this early picture from the Mars Science Laboratory mission , captured after a successful landing on August 5, 2012 at 10:32pm (PDT). Seen at the lower right of a Hazard Avoidance Camera fisheye wide-angle image, the rover's left rear wheel is 50 centimeters (about 20 inches) in diameter. ...